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Single-Step Enantioselective Synthesis of Mechanically Planar Chiral [2]Rotaxanes Using a Chiral Leaving Group StrategyClick to copy article linkArticle link copied!
- Chong TianChong TianDepartment of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, United KingdomMore by Chong Tian
- Stephen D. P. FieldenStephen D. P. FieldenDepartment of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, United KingdomMore by Stephen D. P. Fielden
- Borja Pérez-SaavedraBorja Pérez-SaavedraDepartment of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, United KingdomMore by Borja Pérez-Saavedra
- Iñigo J. Vitorica-YrezabalIñigo J. Vitorica-YrezabalDepartment of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, United KingdomMore by Iñigo J. Vitorica-Yrezabal
- David A. Leigh*David A. Leigh*E-mail: [email protected]Department of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, United KingdomSchool of Chemistry and Molecular Engineering, East China Normal University, 200062 Shanghai, ChinaMore by David A. Leigh
Abstract
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We report a one-step enantioselective synthesis of mechanically planar chiral [2]rotaxanes. Previous studies of such molecules have generally involved the separation of enantiomers from racemic mixtures or the preparation and separation of diastereomeric intermediates followed by post-assembly modification to remove other sources of chirality. Here, we demonstrate a simple asymmetric metal-free active template rotaxane synthesis using a primary amine, an activated ester with a chiral leaving group, and an achiral crown ether lacking rotational symmetry. Mechanically planar chiral rotaxanes are obtained directly in up to 50% enantiomeric excess. The rotaxanes were characterized by NMR spectroscopy, high-resolution mass spectrometry, chiral HPLC, single crystal X-ray diffraction, and circular dichroism. Either rotaxane enantiomer could be prepared selectively by incorporating pseudoenantiomeric cinchona alkaloids into the chiral leaving group.
Copyright © 2020 American Chemical Society
Introduction
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Mechanical planar chirality arises in rotaxanes with achiral components when an unsymmetrical axle is threaded through a macrocycle lacking rotational symmetry (Figure 1). (1−4) Although lacking classical elements of chirality, studies on mechanically planar chiral rotaxanes suggest their asymmetry can be well expressed for applications. (5−7) However, despite mechanically planar chiral rotaxanes being known for nearly 50 years, their enantioselective synthesis remains challenging. (1d,8) Most studies on these systems rely on the separation of enantiomers from racemic mixtures by chiral stationary phase HPLC, limiting the scale of enantioenriched material that can readily be obtained. (9)
Figure 1
Figure 1. Enantioselective synthesis of mechanically planar chiral rotaxanes through metal-free active template N-acylation using a macrocycle lacking rotational symmetry and an electrophile with a point-chiral leaving group.
Goldup et al. have addressed this synthetic problem through a chiral auxiliary approach that forms intermediate diastereomeric rotaxanes having both point chirality and mechanically planar chirality. (10,11) Separation of these diastereomeric intermediates by flash chromatography, followed by removal of the point chirality by either substitution (10) or symmetrization, (11) afforded enantioenriched mechanically planar chiral rotaxanes. The only single-step synthesis of enantioenriched mechanically planar chiral rotaxanes to date used a chiral catalyst to resolve the interconverting enantiomers of a crown ether-ammonium pseudorotaxane by capping. (12) Despite attempts to optimize this method, it produced rotaxanes in just 4% enantiomeric excess (e.e.). Here we report a simple, single-step, enantioselective synthesis of mechanically planar chiral rotaxanes that produces either enantiomer in up to 50% e.e.
Metal-free active template reactions have recently been developed in which rotaxanes (13) are spontaneously assembled under kinetic control in a single step by combining a primary amine, electrophile, and crown ether (14) in apolar solvents. Crown ethers stabilize the transition states of various nucleophilic substitution reactions through the cavity by C–H hydrogen bonding, thereby favoring the formation of rotaxanes over the unthreaded axle. Different reactions, amines, and leaving groups result in different degrees of accelerated reaction through the ring, affording different rotaxane:thread selectivities. We chose crown ether-stabilized N-acylation for the present study (Scheme 1), as this active template reaction often results in a particularly high ratio of rotaxane:thread. (14) This suggested the reaction might be tolerant of the additional functionality necessary in the macrocycle (to break rotational symmetry) and axle building blocks (to provide a chiral leaving group).
Scheme 1
Scheme 1. : (a) Achiral Rotaxane Synthesis by Active Template N-Acylation Using Rotationally Symmetrical Crown Ethers; (b) Racemic and Unoptimized Enantioselective Synthesis of a Mechanically Planar Chiral Rotaxane
An example of an active template N-acylation is the reaction of 24-crown-8 1, primary amine 2, and electrophile 3 in toluene at room temperature, producing amide [2]rotaxane 4 in 84% yield (Scheme 1a). (14b) The rate-determining step of crown ether catalyzed N-acylation reactions is the collapse of the tetrahedral intermediate formed on addition of the amine to the activated ester. (15) The nitro-phenol ester used in the reaction of 1, 2, and 3 thus provides an opportunity for a chiral directing group to be incorporated into the leaving group that could interact with a rotationally unsymmetrical macrocycle in the transition state (Figure 1). (16)
Results and Discussion
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Development of an Enantioselective Rotaxane Synthesis
To establish that functionalized crown ethers could take part in the active template reaction, amine 2 and activated ester 3 were treated with commercially available dibenzo-24-crown-8 (5) in toluene, yielding the corresponding [2]rotaxane, 6, in 73% yield (Scheme 1a). However, although the rotaxane axle is unsymmetrical, dibenzo-24-crown-8 (5) is D2h symmetric and so rotaxane 6 is achiral. (1) Macrocycle 7, containing two different aromatic rings, lacks rotational symmetry (it has C1h symmetry, alternatively referred to as Cs). Reaction of 7 with 2 and 3 furnished racemic mechanically planar chiral rotaxane 8 in 78% yield (Scheme 1b). The enantiomers of 8 could be separated by chiral stationary phase HPLC (see Supporting Information).
Next, we investigated the structure and location for an effective chiral leaving group in the electrophile. Preliminary screening studies identified nitrophenol ester 9, in which the chiral information stems from an O-alkylated cinchonidine unit adjacent to the nitro-group (Scheme 1b). This electrophile was reactive under the rotaxane-forming conditions despite the introduction of the deactivating electron-donating ether linkage. Combining 2, 7, and 9 in a 1:1:1 stoichiometry in toluene at room temperature afforded rotaxane 8 in 43% yield (Scheme 1b). Under similar conditions, electrophiles based on alkyl (thio)esters or with the cinchonidine unit positioned at the ortho position of the nitrophenol ring were either unreactive or generated less rotaxane (see Supporting Information). HPLC analysis of rotaxane 8 (isolated by flash chromatography) obtained from electrophile 9 revealed that the (+)-enantiomer (determined by polarimetry) had been formed in 12% e.e., confirming that a point-chiral leaving group was able to induce enantioselectivity of a mechanically planar rotaxane product.
Increasing the electronic difference between the two aromatic substituents within the macrocycle improved the enantioselectivity of the active template reaction. Macrocycle 10, with a nitro group on the catechol unit (see Supporting Information for its synthesis), afforded rotaxane (+)-11 in 23% e.e. at room temperature, which increased to 40% e.e. (55% yield) when the rotaxane-forming reaction was performed at −40 °C (Figure 2a). Lowering the reaction temperature beyond −40 °C did not result in further improvements in enantioselectivity. (17)
Figure 2
Figure 2. (a) Enantioselective synthesis of mechanically planar chiral rotaxane 11. Reaction conditions: 2 equiv of amine 2, 1 equiv each of electrophile and crown ether 10, toluene, [0.14 M], –40 °C, 24 h. (b) Partial 1H NMR spectra (600 MHz, CDCl3, 295 K) of macrocycle 10 (top), rotaxane 11 (middle) and the corresponding unthreaded axle (bottom).
The opposite enantiomer of the rotaxane, (−)-11, could be selectively accessed using electrophile 12, derived from (+)-cinchonine, a pseudoenantiomer of cinchonidine (see Supporting Information for synthesis). (18) Combining 2, 10, and 12 at −40 °C gave rotaxane (−)-11 in 50% e.e. and 51% yield (Figure 2a). The difference in enantioenrichment is a consequence of electrophiles 9 and 12 being diastereomers rather than true enantiomers.
Characterization of Rotaxanes
Comparison of the 1H NMR spectra of macrocycle 10, rotaxane 11, and the unthreaded axle (see Supporting Information for synthesis) in CDCl3 at 298 K (Figure 2b) confirmed the interlocked structure of 11. The geminal protons of the crown ether display twice the number of environments in rotaxane 11 as in unthreaded 10 due to desymmetrization of the two macrocycle faces upon rotaxane formation, while H3 and H5 of the axle (hydrogen labeling shown in Figure 2a), which are situated either side of the amide group, display significant diastereotopic splitting (Δδ = 0.39 and 0.22 ppm respectively) within the chiral environment of rotaxane 11 which, as would be expected, is absent for the corresponding achiral noninterlocked axle. Upfield shifts of H6 and H7 (Δδ = −0.32 and −0.34 ppm) in the threaded axle and HA, HB, and HC (Δδ = −0.49, −0.21, and −0.37 ppm) of the nitrocatechol unit of the threaded macrocycle result from π–π interactions involving these moieties. These intercomponent interactions may play a role in rigidifying the transition state of the collapsing tetrahedral intermediate. The large downfield shift of the amide N–H proton H4 (Δδ = +1.74 ppm) in 11 is indicative of intercomponent hydrogen bonding between the amide and the glycol chain of the macrocycle. An upshield shift of HD (Δδ = −1.29 ppm) results from hydrogen bonding with the amide oxygen atom. (14b)
Enantioenriched samples of rotaxane 11 (40% e.e. for the (+) enantiomer and 50% e.e. for the (−) enantiomer) were compared by circular dichroism (Figure 3a). The CD spectra of the mechanically planar chiral rotaxane enantiomers are symmetrical in terms of curve shape and have exciton couplings of opposite sign with maxima at 243 nm. The difference in intensity (normalized for absorption) of the spectra in Figure 3a corresponds to the difference in enantioenrichment of the samples.
Figure 3
Figure 3. (a) Circular dichroism spectra (1.0 × 10–4 M, CH2Cl2, 298 K) of (+)-11 (red) and (−)-11 (blue), baseline corrected. (b) Chemical structure of racemic rotaxane 13. (c) X-ray crystal structure of racemic rotaxane 13, side-on view showing intercomponent hydrogen bonds (in green). Hydrogen bond lengths: N47H—O16, 2.20 Å; O49—HC6, 2.63 Å. Hydrogen bond angles: N47—H–O16, 158.4°; O49—H–C6, 161.8°. (d) X-ray crystal structure of 13 viewed along the axle showing π-stacking between the macrocycle 1,2-dihydroxynaphthalene and axle bis(trifluoromethyl)phenyl rings. Centroid–centroid distance, 3.67 Å. Angle described by C40 and centroids, 97.6°. Solvate molecules and other hydrogen atoms omitted for clarity.
Although we were unable to obtain high quality single crystals of 11, single crystals of a racemic sample of 13 suitable for analysis by X-ray diffraction were grown by slow evaporation of an isopropanol/hexane solution of 13 (Figure 3b). Rotaxane 13 contains the same macrocycle as 11 and an axle derived from amine 2 and a different acyl stopper. The X-ray crystal structure of 13 (Figure 3c), containing both rotaxane enantiomers in the unit cell, shows similar intercomponent interactions to those observed by 1H NMR for 11 in solution (Figure 2b). Hydrogen bonds are present between an oxygen of the macrocycle glycol chain and the amide hydrogen atom of the axle and between the amide oxygen and a macrocycle C–H hydrogen atom (analogous to HD in 11). (14) The di(alkoxyl)naphthalene ring of the macrocycle and bis(trifluoromethyl)benzene unit of the axle π-stack (Figure 3d, closest centroid-centroid distance = 3.67 Å), (19) with the nitro-catechol moiety positioned so as to cover one face of the amide group. A similar arrangement in the transition state of the active template reaction would orient the macrocycle with respect to the axle building blocks such that one mechanically planar chiral enantiomer would be favored over the other.
Origin of Enantioselectivity
A preliminary indication of the origin of chiral transduction in these systems comes from the relative energies of the tetrahedral intermediates preceding (+)- and (−)-11, calculated at the PM6 level (20) using the Gaussian 09 software package (21) (Supporting Information and Figure 4). The collapse of similar tetrahedral intermediates has previously been shown (15a) to be the rate-determining step for the glyme catalysis of ester aminolysis. Following the Hammond postulate, the differences between the diastereomeric tetrahedral intermediates to (+)- and (−)-11 from 9 and 12 may resemble those between the transition states. The lowest energy intermediate calculated for both pseudoenantiomeric leaving groups featured an (S) stereocenter adjacent to the ammonium unit, but with the macrocycle orientation inverted for the two pseudoenantiomers (Figure 4), meaning changing between the leaving groups of 9 and 12 favors the formation of a different enantiomer of 11, as observed experimentally. The somewhat surprising indication that the two chiral leaving groups both favor an (S)-tetrahedral intermediate may reflect why the pseudoenantiomers do not generate equal and opposite e.e.’s in the active template reaction. The noncovalent interactions in the intermediate (e.g., the stacking of the electron-rich naphthalene unit with the electron-poor aryl group of the nucleophile, and the hydrogen bonding of the glycol oxygens to the H–N atoms) are reminiscent of those present in the X-ray crystal structure of rotaxane 13.
Figure 4
Figure 4. Tentative rationale for the transfer of chirality from Euclidean point-chirality (of the leaving group) to mechanical planar chirality (of the rotaxane). The lowest energy tetrahedral intermediates were modeled (see Supporting Information) using (a) electrophile 9 or (b) electrophile 12. The di(alkoxyl)naphthalene ring of the macrocycle and bis(trifluoromethyl)benzene unit originating from the nucleophile π-stack, causing the nitro-catechol ring to be positioned so as to cover one face of the tetrahedral center of the intermediate. This thermodynamically favored arrangement of components ensures the different handedness of the pseudoenantiomeric leaving groups is well-expressed in the diastereomeric transition states, resulting in enantioselectivity in the mechanically planar chiral rotaxane product. Hydrogen bonds are indicated by black dotted lines.
Also consistent with the stacking of the electron-rich naphthalene unit with the electron-poor aryl group of the nucleophile providing the driving force for organization of the transition state is the experimental evidence that decreasing the electron density of the other aromatic ring of the macrocycle increases the enantioselectivity of rotaxane formation (i.e., 12% e.e. for (+)-8; 40% e.e. for (+)-11). The less electron-rich the catechol ring is, the less it competes with the naphthalene group for π-stacking with the bis(trifluoromethyl)benzylamine and so the greater the enantiodiscrimination in the transition state.
Conclusions
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The examples presented demonstrate that mechanically planar chiral rotaxanes can be directly accessed in up to 50% e.e. in a single synthetic step. The chirality of the point-chiral leaving group is transferred into mechanically planar chirality in the rotaxane through metal-free active template N-acylation. Pseudoenantiomeric cinchona alkaloids allow either rotaxane enantiomer to be accessed. X-ray crystallography and molecular modeling suggest that the origin of the enantioselectivity lies in π-stacking of an electron-rich aromatic ring on the macrocycle with an electron-poor aryl group originating from the nucleophilic axle building block. This positions the second aromatic ring of the macrocycle in an orientation that blocks one face of the electrophile. Simple methods for accessing enantioenriched mechanically planar chiral rotaxanes should improve their availability for investigation in applications such as asymmetric catalysis, (7) chiral (bio)molecule sensing, (1,6,22) and novel designs (23) of molecular machinery.
Supporting Information
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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jacs.0c03447.
Experimental procedures, synthesis and characterization data, including circular dichroism, chiral HPLC, NMR, MS, and X-ray crystallography data (PDF)
Crystallographic data for 13 (CIF)
Terms & Conditions
Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.
Author Information
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- David A. Leigh - Department of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom; School of Chemistry and Molecular Engineering, East China Normal University, 200062 Shanghai, China;
http://orcid.org/0000-0002-1202-4507;
- Chong Tian - Department of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom;http://orcid.org/0000-0001-7264-9042
Acknowledgments
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We thank the Engineering and Physical Sciences Research Council (EPSRC) (EP/P027067/1), the European Research Council (ERC) (Advanced Grant No. 786630), the China 1000 Talents Plan and East China Normal University for funding, the University of Manchester for a studentship (to S.D.P.F.), the Diamond Light Source (U.K.) for synchrotron beamtime on I19, the University of Manchester mass spectrometry service for high-resolution mass spectrometry, the Computational Shared Facility 3 (CSF3) at the University of Manchester for computational resources, and Jing Liu for preliminary studies. D.A.L. is a Royal Society Research Professor.
References
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This article references 23 other publications.
- 1(a) Bruns, C. J.; Stoddart, J. F. The Nature of the Mechanical Bond: From Molecules to Machines; John Wiley & Sons: Hoboken, NJ, 2017.Google ScholarThere is no corresponding record for this reference.(b) Jamieson, E. M. G.; Modicom, F.; Goldup, S. M. Chirality in rotaxanes and catenanes. Chem. Soc. Rev. 2018, 47, 5266– 5311, DOI: 10.1039/C8CS00097BGoogle Scholar1bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtVSgtLbL&md5=cd9e0683f4dad9b913c00554a76fd67dChirality in rotaxanes and catenanesJamieson, E. M. G.; Modicom, F.; Goldup, S. M.Chemical Society Reviews (2018), 47 (14), 5266-5311CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)A review. Although chiral mech. interlocked mols. (MIMs) have been synthesized and studied, enantiopure examples are relatively under-represented in the pantheon of reported catenanes and rotaxanes and the underlying chirality of the system is often even overlooked. This is changing with the advent of new applications of MIMs in catalysis, sensing and materials and the appearance of new methods to access unusual stereogenic units unique to the mech. bond. Here we discuss the different stereogenic units that have been investigated in catenanes and rotaxanes, examples of their application, methods for assigning abs. stereochem. and provide a perspective on future developments.(c) Evans, N. H. Chiral catenanes and rotaxanes: Fundamentals and emerging applications. Chem. - Eur. J. 2018, 24, 3101– 3112, DOI: 10.1002/chem.201704149Google Scholar1chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvV2lsL3K&md5=607f6e2649003bc3be5e25959095e696Chiral Catenanes and Rotaxanes: Fundamentals and Emerging ApplicationsEvans, Nicholas H.Chemistry - A European Journal (2018), 24 (13), 3101-3112CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)A review. Mol. chirality provides a key challenge in host-guest recognition and other related chem. applications such as asym. catalysis. For a mol. to act as an efficient enantioselective receptor, it requires multi-point interactions between host and chiral guest, which may be achieved by an appropriate chiral 3D scaffold. As a consequence of their interlocked structure, catenanes and rotaxanes may present such a 3D scaffold, and can be chiral by inclusion of a classical chiral element and/or as a consequence of the mech. bond. This Minireview presents illustrative examples of chiral [2]catenanes and [2]rotaxanes, and discusses where these mols. have been used in chem. applications such as chiral host-guest recognition and asym. catalysis.(d) Nakazono, K.; Takata, T. Mechanical chirality of rotaxanes: Synthesis and function. Symmetry 2020, 12, 144, DOI: 10.3390/sym12010144Google ScholarThere is no corresponding record for this reference.https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=&md5=9874b665cc7a056b8e2f928dd3112440
- 2
If a prochiral or meso thread is incorporated into a rotaxane, then chirality can arise from the position of the ring on the axle. See:
(a) Alvarez-Pérez, M.; Goldup, S. M.; Leigh, D. A.; Slawin, A. M. Z. A chemically-driven molecular information ratchet. J. Am. Chem. Soc. 2008, 130, 1836– 1838, DOI: 10.1021/ja7102394Google Scholar2ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXntVektg%253D%253D&md5=76aab0e6c0e12a2435cab00b1e24f8e8A Chemically-Driven Molecular Information RatchetAlvarez-Perez, Monica; Goldup, Stephen M.; Leigh, David A.; Slawin, Alexandra M. Z.Journal of the American Chemical Society (2008), 130 (6), 1836-1838CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)A chem. driven mol. information ratchet is described. The equil. macrocycle distribution in a [2]rotaxane is driven away from its 50:50 population of thread binding sites to a 33:67 ratio by benzoylation under the influence of a chiral catalyst. The reaction corresponds to a dynamic kinetic resoln. of rotaxane co-conformers that interconvert through shuttling.(b) Cakmak, Y.; Erbas-Cakmak, S.; Leigh, D. A. Asymmetric catalysis with a mechanically point-chiral rotaxane. J. Am. Chem. Soc. 2016, 138, 1749– 1751, DOI: 10.1021/jacs.6b00303Google Scholar2bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvFOmtbs%253D&md5=2947cbc3f81dbd3a1045eee79d0b88acAsymmetric Catalysis with a Mechanically Point-Chiral RotaxaneCakmak, Yusuf; Erbas-Cakmak, Sundus; Leigh, David A.Journal of the American Chemical Society (2016), 138 (6), 1749-1751CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Mech. point-chirality in a [2]rotaxane is utilized for asym. catalysis. Stable enantiomers of the rotaxane result from a bulky group in the middle of the thread preventing a benzylic amide macrocycle shuttling between different sides of a prochiral center, creating point chirality in the vicinity of a secondary amine group. The resulting mechanochirogenesis delivers enantioselective organocatalysis via both enamine (up to 71:29 er) and iminium (up to 68:32 er) activation modes.(c) Dommaschk, M.; Echavarren, J.; Leigh, D. A.; Marcos, V.; Singleton, T. A. Dynamic control of chiral space through local symmetry breaking in a rotaxane organocatalyst. Angew. Chem., Int. Ed. 2019, 58, 14955– 14958, DOI: 10.1002/anie.201908330Google Scholar2chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhslGnt7%252FL&md5=aadf621b679f534ef0bb3a548d8a13e6Dynamic Control of Chiral Space Through Local Symmetry Breaking in a Rotaxane OrganocatalystDommaschk, Marcel; Echavarren, Javier; Leigh, David A.; Marcos, Vanesa; Singleton, Thomas A.Angewandte Chemie, International Edition (2019), 58 (42), 14955-14958CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)We report on a switchable rotaxane mol. shuttle that features a pseudo-meso 2,5-disubstituted pyrrolidine catalytic unit on the axle whose local symmetry is broken according to the position of a threaded benzylic amide macrocycle. The macrocycle can be selectively switched (with light in one direction; with catalytic acid in the other) with high fidelity between binding sites located to either side of the pyrrolidine unit. The position of the macrocycle dictates the facial bias of the rotaxane-catalyzed conjugate addn. of aldehydes to vinyl sulfones. The pseudo-meso non-interlocked thread does not afford significant selectivity as a catalyst (2-14 % ee), whereas the rotaxane affords selectivities of up to 40 % ee with switching of the position of the macrocycle changing the handedness of the product formed (up to 60 % Δee). - 3
Mechanical planar chirality can also result from confinement of an unsymmetrical macrocycle to one side of a nonprochiral axle possessing Dnh symmetry. See:
(a) Mochizuki, Y.; Ikeyatsu, K.; Mutoh, Y.; Hosoya, S.; Saito, S. Synthesis of mechanically planar chiral rac-[2]rotaxanes by partitioning of an achiral [2]rotaxane: Stereoinversion induced by shuttling. Org. Lett. 2017, 19, 4347– 4350, DOI: 10.1021/acs.orglett.7b02043Google Scholar3ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht1Orsb3K&md5=eaca9095b5144363977bfa45406ed000Synthesis of Mechanically Planar Chiral rac-[2]Rotaxanes by Partitioning of an Achiral [2]Rotaxane: Stereoinversion Induced by ShuttlingMochizuki, Yuta; Ikeyatsu, Katsuhiko; Mutoh, Yuichiro; Hosoya, Shoichi; Saito, ShinichiOrganic Letters (2017), 19 (16), 4347-4350CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)Mech. planar chiral [2]rotaxanes were synthesized by the introduction of bulky pyrrole moieties into the axle component of an achiral [2]rotaxane. The enantiomers were sepd. by chiral HPLC. The shuttling of the ring component between the two compartments at high temp. induced the stereoinversion of the mech. planar chiral [2]rotaxane. The rate of the stereoinversion was studied quant., and the kinetic parameters were detd.(b) Corra, S.; de Vet, C.; Groppi, J.; La Rosa, M.; Silvi, S.; Baroncini, M.; Credi, A. Chemical on/off switching of mechanically planar chirality and chiral anion recognition in a [2]rotaxane molecular shuttle. J. Am. Chem. Soc. 2019, 141, 9129– 9133, DOI: 10.1021/jacs.9b00941Google Scholar3bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtVKgsbnJ&md5=2a44d8764ac0143d193ca738b273e557Chemical On/Off Switching of Mechanically Planar Chirality and Chiral Anion Recognition in a [2]Rotaxane Molecular ShuttleCorra, Stefano; de Vet, Christiaan; Groppi, Jessica; La Rosa, Marcello; Silvi, Serena; Baroncini, Massimo; Credi, AlbertoJournal of the American Chemical Society (2019), 141 (23), 9129-9133CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)We exploit a reversible acid-base triggered mol. shuttling process to switch an appropriately designed rotaxane between prochiral and mech. planar chiral forms. The mech. planar enantiomers and their interconversion, arising from ring shuttling, have been characterized by NMR spectroscopy. We also show that the supramol. interaction of the pos. charged rotaxane with optically active anions causes an imbalance in the population of the two enantiomeric coconformations. This result represents an unprecedented example of chiral mol. recognition and can disclose innovative approaches to enantioselective sensing and catalysis. - 4
For examples of other stereochemical consequences of threading, see:
(a) Fuller, A.-M. L.; Leigh, D. A.; Lusby, P. J. Sequence isomerism in [3]rotaxanes. J. Am. Chem. Soc. 2010, 132, 4954– 4959, DOI: 10.1021/ja1006838Google Scholar4ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXjt1enur4%253D&md5=1336c39e1e0ab5bfa07b655e6dff81aeSequence Isomerism in [3]RotaxanesFuller, Anne-Marie L.; Leigh, David A.; Lusby, Paul J.Journal of the American Chemical Society (2010), 132 (13), 4954-4959CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)We describe a strategy for assembling different macrocycles onto a nonsym. rotaxane thread in a precise sequence. If the macrocycles are small and rigid enough so that they cannot pass each other then the sequence is maintained mech., affording stereoisomerism in a manner reminiscent of atropisomerism. The method is exemplified through the synthesis of a pair of [3]rotaxane diastereomers that are constitutionally identical other than for the sequence of the different macrocycles on the thread. The synthesis features the iterative binding of different palladium(II) pyridine-2,6-dicarboxamide complexes to a pyridine ligand on the thread followed by their macrocyclization by ring-closing olefin metathesis. Removal of the palladium(II) from the first rotaxane formed frees the pyridine site to coordinate to a second, different, palladium(II) pyridine-2,6-dicarboxamide unit which, following macrocyclization, provides a multiring rotaxane of predetd. macrocycle sequence.(b) Talotta, C.; Gaeta, C.; Qi, Z.; Schalley, C. A.; Neri, P. Pseudorotaxanes with self-sorted sequence and stereochemical orientation. Angew. Chem., Int. Ed. 2013, 52, 7437– 7441, DOI: 10.1002/anie.201301570Google Scholar4bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXptVams7w%253D&md5=c14fb6b298fdad413e2dfe089fa1d5e2Pseudorotaxanes with Self-Sorted Sequence and Stereochemical OrientationTalotta, Carmen; Gaeta, Carmine; Qi, Zhenhui; Schalley, Christoph A.; Neri, PlacidoAngewandte Chemie, International Edition (2013), 52 (29), 7437-7441CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)We have successfully demonstrated that calix[6]arene-based pseudo[3]rotaxanes with bisammonium axles have intriguing self-sorting capabilities, even when structural differences are small and located remote from the binding sites. This is the first reported integrative self-sorting system that is able to discriminate simultaneously at the sequence and stereochem. level. All these aspects can be considered a further significant step toward mimicking the efficiency and complexity of natural systems.(c) La Manna, P.; Talotta, C.; Gaeta, C.; Soriente, A.; De Rosa, M.; Neri, P. Threading of an inherently directional calixarene wheel with oriented ammonium axles. J. Org. Chem. 2017, 82, 8973– 8983, DOI: 10.1021/acs.joc.7b01388Google Scholar4chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtlSmt7jF&md5=92dcb7947abcffa21351abcdb8da9b3dThreading of an Inherently Directional Calixarene Wheel with Oriented Ammonium AxlesLa Manna, Pellegrino; Talotta, Carmen; Gaeta, Carmine; Soriente, Annunziata; De Rosa, Margherita; Neri, PlacidoJournal of Organic Chemistry (2017), 82 (17), 8973-8983CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)The threading of monostoppered alkylbenzylammonium axles 7+ and 8+ with the calix[6]-wheel 3 can occur by both routes of entering the macrocycle 3 in the cone conformation: passage through the upper rim and the through the lower rim. Thus, under thermodn. conditions, with both the axles 7+ and 8+, the two possible orientations of calix[2]pseudorotaxane, namely, endo-benzyl and endo-alkyl, are formed by a stereoselectivity controlled by the endo-alkyl rule. Interestingly, by 1H NMR monitoring of the threading process between 8+ and 3, we revealed two calix[2]pseudorotaxane isomers in which the calix-wheel adopts 1,2,3-alternate and cone conformations, which represent the kinetic and thermodn. species, resp. Finally, the synthesis of ammonium-based oriented calix[2]rotaxane is here described.(d) Cui, J.-S.; Ba, Q.-K.; Ke, H.; Valkonen, A.; Rissanen, K.; Jiang, W. Directional shuttling of a stimuli-responsive cone-like macrocycle on a single-state symmetric dumbbell axle. Angew. Chem., Int. Ed. 2018, 57, 7809– 7814, DOI: 10.1002/anie.201803349Google Scholar4dhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtVSgsrrF&md5=72a3ebcbf3e5506baf70dbc06102aed7Directional Shuttling of a Stimuli-Responsive Cone-Like Macrocycle on a Single-State Symmetric Dumbbell AxleCui, Jie-Shun; Ba, Qian-Kai; Ke, Hua; Valkonen, Arto; Rissanen, Kari; Jiang, WeiAngewandte Chemie, International Edition (2018), 57 (26), 7809-7814CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Rotaxane-based mol. shuttles are often operated using low-symmetry axles and changing the states of the binding stations. A mol. shuttle capable of directional shuttling of an acid-responsive cone-like macrocycle on a single-state sym. dumbbell axle is now presented. The axle contains three binding stations: one sym. di(quaternary ammonium) station and two nonsym. phenyltriazole stations arranged in opposite orientations. Upon addn. of an acid, the protonated macrocycle shuttles from the di(quaternary ammonium) station to the phenyltriazole binding station closer to its Bu groups. This directional shuttling presumably originates from charge repulsion and an orientational binding preference between the cone-like cavity and the nonsym. phenyltriazole station. This mechanism for achieving directional shuttling by manipulating only the wheels instead of the tracks is new for artificial mol. machines.(e) Zheng, L.-S.; Cui, J.-S.; Jiang, W. Biomimetic synchronized motion of two interacting macrocycles in [3]rotaxane-based molecular shuttles. Angew. Chem., Int. Ed. 2019, 58, 15136– 15141, DOI: 10.1002/anie.201910318Google Scholar4ehttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhslChur3M&md5=089367e0700c88df98a807badb9fa824Biomimetic Synchronized Motion of Two Interacting Macrocycles in [3]Rotaxane-Based Molecular ShuttlesZheng, Li-Shuo; Cui, Jie-Shun; Jiang, WeiAngewandte Chemie, International Edition (2019), 58 (42), 15136-15141CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Noncovalent interactions between all the neighboring components in biomol. machines are responsible for their synchronized motion and thus complex functions. This strategy has rarely been used in multicomponent mol. machines. Here, we report four [3]rotaxane-based mol. shuttles. Noncovalent interactions among the three components (two interacting macrocycles and one axle) not only cause a "systems-level" effect on the relative positions of the two macrocycles along the axle, but also result in a synchronized motion of the two macrocycles when adding partial amt. of stimuli. Moreover, the intermediate state with one shuttled macrocycle even exist predominantly in the soln. during the titrn. of stimuli, which is theor. unexpected for the [3]rotaxane with two non-interacting rings. This biomimetic strategy may provide a method for constructing highly complex mol. machines.(f) Ng, A. W. H.; Yee, C.-C.; Au-Yeung, H. Y. Radial hetero[5]catenanes: peripheral isomer sequences of the interlocked macrocycles. Angew. Chem., Int. Ed. 2019, 58, 17375– 17382, DOI: 10.1002/anie.201908576Google Scholar4fhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhvF2gsL3P&md5=3958fdfab392146b25f7cc50c442f720Radial Hetero[5]catenanes: Peripheral Isomer Sequences of the Interlocked MacrocyclesNg, Antony Wing Hung; Yee, Chi-Chung; Au-Yeung, Ho YuAngewandte Chemie, International Edition (2019), 58 (48), 17375-17382CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)A pair of radial [5]catenanes, with either an isomeric cyclic -AABB- or -ABAB- type sequence of the interlocked β-cyclodextrin (β-CD) and cucurbit[6]uril (CB[6]) units, has been efficiently synthesized. Because of a marked difference in the binding strength and interlocking sequence of the peripheral macrocycles, interesting sequence-dependent properties, characteristic of mech. bonded macrocycles, were realized. Variable-temp. 1H NMR studies showed that the -ABAB- isomer has a more independent β-CD dynamic, whereas the β-CD motions in the -AABB- isomer are coupled. Dynamics of the pH-insensitive β-CD can also be further modulated upon base-triggered mobilization of the CB[6]. These unique properties of the mech. bond expressed in a sequence-specific fashion and the transmission of the control on the macrocycle dynamics from one interlocked component to another, highlight the potential of similar complex hetero[n]catenanes in the design of advanced, multicomponent mol. machines. - 5Ishiwari, F.; Nakazono, K.; Koyama, Y.; Takata, T. Induction of single handed helicity of polyacetylenes using mechanically chiral rotaxanes as chiral sources. Angew. Chem., Int. Ed. 2017, 56, 14858– 14862, DOI: 10.1002/anie.201707926Google Scholar5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1KgtLfF&md5=5d805b25736ceb243e94f1c60e272e16Induction of Single-Handed Helicity of Polyacetylenes Using Mechanically Chiral Rotaxanes as Chiral SourcesIshiwari, Fumitaka; Nakazono, Kazuko; Koyama, Yasuhito; Takata, ToshikazuAngewandte Chemie, International Edition (2017), 56 (47), 14858-14862CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Effective induction of preferred-handed helicity of polyacetylenes by pendant mech. chiral rotaxanes is discussed. Polyacetylenes possessing optically active mech. chiral rotaxanes in the side chains were synthesized by the polymn. of the corresponding enantiopure [2]rotaxane-type ethynyl monomers prepd. by the chiral-phase HPLC sepns. The CD Cotton effects revealed that the polyacetylenes took preferred-handed helical conformations depending on the rotaxane chirality. The preferred-handed helix was not disturbed by an addnl. chiral substituent on the rotaxane side chain. These results demonstrate the significance and utility of mech. chiral rotaxanes for the effective construction of asym. fields.
- 6Kameta, N.; Nagawa, Y.; Karikomi, M.; Hiratani, K. Chiral sensing for amino acid derivative based on a [2]rotaxane composed of an asymmetric rotor and an asymmetric axle. Chem. Commun. 2006, 3714– 3716, DOI: 10.1039/b607251hGoogle Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XoslGkt7g%253D&md5=902399c1175d7ae28d3d0fd1fd7a2307Chiral sensing for amino acid derivative based on a [2]rotaxane composed of an asymmetric rotor and an asymmetric axleKameta, Naohiro; Nagawa, Yoshinobu; Karikomi, Michinori; Hiratani, KazuhisaChemical Communications (Cambridge, United Kingdom) (2006), (35), 3714-3716CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)A chiral racemic [2]rotaxane contg. both an asym. rotor and an asym. axle is prepd.; the rotaxane forms diastereomeric complexes with D- and L-phenylalaninols as obsd. by both 1H NMR and by fluorescence spectra. The [2]rotaxane is prepd. in 11 steps (longest linear sequence); selective cleavage of a macrobicyclic dilactone with two different amines is used to establish the rotaxane structure. Alaninol, prolinol, and tryptophanol do not form observable diastereomeric complexes with the [2]rotaxane.
- 7Heard, A.; Goldup, S. M. Synthesis of a mechanically planar chiral rotaxane ligand for enantioselective catalysis. Chem. 2020, 6, 994– 1006, DOI: 10.1016/j.chempr.2020.02.006Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXntVKqtr8%253D&md5=5aa1d4f1c6ec02663e1c8ded58788b21Synthesis of a Mechanically Planar Chiral Rotaxane Ligand for Enantioselective CatalysisHeard, Andrew W.; Goldup, Stephen M.Chem (2020), 6 (4), 994-1006CODEN: CHEMVE; ISSN:2451-9294. (Cell Press)A mech. planar chiral rotaxane-based Au complex that mediates a cyclopropanation reaction with stereoselectivities that are comparable with the best conventional covalent catalyst has been described.
- 8Glen, P. E.; O’Neill, J. A. T.; Lee, A.-L. Synthesis of a C1-symmetric Box macrocycle and studies towards active-template synthesis of mechanically planar chiral rotaxanes. Tetrahedron 2013, 69, 57– 68, DOI: 10.1016/j.tet.2012.10.069Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xhs1Gqu7jM&md5=e18243cbce1e53103e196019450bebd6Synthesis of a C1-symmetric Box macrocycle and studies towards active-template synthesis of mechanically planar chiral rotaxanesGlen, Pauline E.; O'Neill, James A. T.; Lee, Ai-LanTetrahedron (2013), 69 (1), 57-68CODEN: TETRAB; ISSN:0040-4020. (Elsevier Ltd.)A C1-sym. Box macrocycle has been synthesized for the first time. The Box macrocycle along with other C1 and C2-sym. Box ligands were evaluated and compared as ligands in the Cadiot-Chodkiewicz, oxidative Heck and CuAAC "click" reactions as part of our studies towards achieving active-metal template synthesis of mech. planar chiral rotaxanes. This study constitutes the first report of Cadiot-Chodkiewicz and CuAAC "click" reactions using Box ligands, as well as the first dedicated study of oxidative Heck reactions using Box ligands.
- 9(a) Yamamoto, C.; Okamoto, Y.; Schmidt, T.; Jäger, R.; Vögtle, F. Enantiomeric resolution of cycloenantiomeric rotaxane, topologically chiral catenane, and pretzel-shaped molecules: Observation of pronounced circular dichroism. J. Am. Chem. Soc. 1997, 119, 10547– 10548, DOI: 10.1021/ja971764qGoogle Scholar9ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXms1Ogtbo%253D&md5=c8ebdf71b077d8f911a4aeca9af600c3Enantiomeric Resolution of Cycloenantiomeric Rotaxane, Topologically Chiral Catenane, and Pretzel-Shaped Molecules: Observation of Pronounced Circular DichroismYamamoto, Chiyo; Okamoto, Yoshio; Schmidt, Thomas; Jaeger, Ralf; Voegtle, FritzJournal of the American Chemical Society (1997), 119 (43), 10547-10548CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Cycloenantiomerism has been obsd. in rotaxanes for the first time. The object and its mirror image of these mech. bonded mols. result from different sequences of the sulfonamide group and the three amide groups on the wheel in rotaxanes I (I = ring1 threaded by dumbbell1) and II, bearing an unsym. dumbbell. The corresponding racemates of II could be base-line sepd. by HPLC on Chiralcel OD. Under similar conditions the topol. chiral sulfonamide catenane III (= ring1 threaded through ring1) and the species IV (= ring1 threaded through ring1 and further intramolecularly bridged by an ethyleneoxy chain) possessing the topol. of a pretzel could be base-line sepd. The sepn. factor α was found to be very large for compds. III and IV (6.95, 5.20 resp.), the optical rotations [α]D range from 20° to 168°. The pronounced CD curves of I-IV are reported.(b) Schalley, C. A.; Beizai, K.; Vögtle, F. On the way to rotaxane-based molecular motors: Studies in molecular mobility and topological chirality. Acc. Chem. Res. 2001, 34, 465– 476, DOI: 10.1021/ar000179iGoogle Scholar9bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXit1Slu7s%253D&md5=ea34c2315bbca974bc1da16ebad978aeOn the Way to Rotaxane-Based Molecular Motors: Studies in Molecular Mobility and Topological ChiralitySchalley, Christoph A.; Beizai, Kaweh; Voegtle, FritzAccounts of Chemical Research (2001), 34 (6), 465-476CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)A review, with many refs. ATP synthase represents a machine at the mol. level which couples the rotation of an axle in a wheel with the endergonic prodn. of ATP, the general source of chem. energy in the cell. The natural system prototypically bears all features of a macroscopic motor: a rotor within a stator held by a membrane and fueled by a difference in chem. potential in the form of a proton gradient combined with a machine for ATP prodn. The assembly of axle and wheel to a rotor device reminds one very much of a rotaxane. In this Account, we discuss some important features of motors and their (potential) realization in simpler artificial model systems, i.e., the mol. mobility of mech. bound mols., the importance of chirality for unidirectional motion, the sources of energy for driving the rotation, and the potential of using membranes and surfaces for ordering a large no. of devices to achieve macroscopic effects.(c) Kameta, N.; Hiratani, K.; Nagawa, Y. A novel synthesis of chiral rotaxanes via covalent bond formation. Chem. Commun. 2004, 466– 467, DOI: 10.1039/b314744dGoogle Scholar9chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXhtVaqsLs%253D&md5=5194842cb82d9206734e17b7b47b560cA novel synthesis of chiral rotaxanes via covalent bond formationKameta, Naohiro; Hiratani, Kazuhisa; Nagawa, YoshinobuChemical Communications (Cambridge, United Kingdom) (2004), (4), 466-467CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)Chiral rotaxanes composed of the asym. crownophane incorporating two hydroxy groups as a rotor moiety and the asym. axis were effectively synthesized via covalent bond formation, i.e. tandem Claisen rearrangement, esterification, and aminolysis.(d) Hirose, K.; Ukimi, M.; Ueda, S.; Onoda, C.; Kano, R.; Tsuda, K.; Hinohara, Y.; Tobe, Y. The asymmetry is derived from mechanical interlocking of achiral axle and achiral ring components – Syntheses and properties of optically pure [2]rotaxanes. Symmetry 2018, 10, 20, DOI: 10.3390/sym10010020Google Scholar9dhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXms12ksrk%253D&md5=8f8874418a7381fb8c829ccf9e415454The asymmetry is derived from mechanical interlocking of achiral axle and achiral ring components -syntheses and properties of optically pure [2]rotaxanes-Hirose, Keiji; Ukimi, Masaya; Ueda, Shota; Onoda, Chie; Kano, Ryohei; Tsuda, Kyosuke; Hinohara, Yuko; Tobe, YoshitoSymmetry (2018), 10 (1), 20/1-20/17CODEN: SYMMAM; ISSN:2073-8994. (MDPI AG)Rotaxanes consisting of achiral axle and achiral ring components can possess supramol. chirality due to their unique geometrical architectures. To synthesize such chiral rotaxanes, we adapted a prerotaxane method based on aminolysis of a metacyclophane type prerotaxane that had planar chirality, which is composed of an achiral stopper unit and a crown ether type ring component. The prerotaxanes were well resolved using chiral HPLC into a pair of enantiomerically pure prerotaxanes, which were transferred into corresponding chiral rotaxanes, resp. Obtained chiral rotaxanes were revealed to have considerable enantioselectivity.(e) Gell, C. E.; McArdle-Ismaguilov, T. A.; Evans, N. H. Modulating the expression of chirality in a mechanically chiral rotaxane. Chem. Commun. 2019, 55, 1576– 1579, DOI: 10.1039/C8CC10044FGoogle Scholar9ehttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtFSgtro%253D&md5=f8da15dc4c54a9d1e48c9b94639bc631Modulating the expression of chirality in a mechanically chiral rotaxaneGell, Charles E.; McArdle-Ismaguilov, Timur A.; Evans, Nicholas H.Chemical Communications (Cambridge, United Kingdom) (2019), 55 (11), 1576-1579CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)The expression of mech. chirality by a hydrogen bond templated rotaxane, as detected by 1H NMR spectroscopy, may be modulated by affecting the co-conformational behavior of the rotaxane through varying solvent or by addn. of acid and base.(f) Gaedke, M.; Witte, F.; Anhäuser, J.; Hupatz, H.; Schröder, H. V.; Valkonen, A.; Rissanen, K.; Lützen, A.; Paulus, B.; Schalley, C. A. Chiroptical inversion of a planar chiral redox-switchable rotaxane. Chem. Sci. 2019, 10, 10003– 10009, DOI: 10.1039/C9SC03694FGoogle Scholar9fhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhs12qsr3F&md5=f41698d0b46acbb2dd1d0ede427f0c3dChiroptical inversion of a planar chiral redox-switchable rotaxaneGaedke, Marius; Witte, Felix; Anhaeuser, Jana; Hupatz, Henrik; Schroeder, Hendrik V.; Valkonen, Arto; Rissanen, Kari; Luetzen, Arne; Paulus, Beate; Schalley, Christoph A.Chemical Science (2019), 10 (43), 10003-10009CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)A tetrathiafulvalene (TTF)-contg. crown ether macrocycle with Cs symmetry was designed to implement planar chirality into a redox-active [2]rotaxane. The directionality of the macrocycle atom sequence together with the non-sym. axle renders the corresponding [2]rotaxane mech. planar chiral. Enantiomeric sepn. of the [2]rotaxane was achieved by chiral HPLC. The electrochem. properties - caused by the reversible oxidn. of the TTF - are similar to a non-chiral control. Reversible inversion of the main band in the ECD spectra for the individual enantiomers was obsd. after oxidn. Exptl. evidence, conformational anal. and DFT calcns. of the neutral and doubly oxidized species indicate that mainly electronic effects of the oxidn. are responsible for the chiroptical switching. This is the first electrochem. switchable rotaxane with a reversible inversion of the main ECD band.
- 10Bordoli, R.; Goldup, S. M. An efficient approach to mechanically planar chiral rotaxanes. J. Am. Chem. Soc. 2014, 136, 4817– 4820, DOI: 10.1021/ja412715mGoogle Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXivFOgsb8%253D&md5=26241c538a08e27cdea71d888a604dbbAn Efficient Approach to Mechanically Planar Chiral RotaxanesBordoli, Robert J.; Goldup, Stephen M.Journal of the American Chemical Society (2014), 136 (13), 4817-4820CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)We describe the first method for prodn. of mech. planar chiral rotaxanes in excellent enantiopurity without the use of chiral sepn. techniques and, for the first time, unambiguously assign the abs. stereochem. of the products. This proof-of-concept study, which employs a chiral pool sugar as the source of asymmetry and a high-yielding active template reaction for mech. bond formation, finally opens the door to detailed investigation of these challenging targets.
- 11Jinks, M. A.; de Juan, A.; Denis, M.; Fletcher, C. J.; Galli, M.; Jamieson, E. M. G.; Modicom, F.; Zhang, Z.; Goldup, S. M. Stereoselective synthesis of mechanically planar chiral rotaxanes. Angew. Chem., Int. Ed. 2018, 57, 14806– 14810, DOI: 10.1002/anie.201808990Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhvFCktbnN&md5=463a427f8e848aba26919cf18965b0b1Stereoselective Synthesis of Mechanically Planar Chiral RotaxanesJinks, Michael A.; de Juan, Alberto; Denis, Mathieu; Fletcher, Catherine J.; Galli, Marzia; Jamieson, Ellen M. G.; Modicom, Florian; Zhang, Zhihui; Goldup, Stephen M.Angewandte Chemie, International Edition (2018), 57 (45), 14806-14810CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Chiral interlocked mols. in which the mech. bond provides the sole stereogenic unit are typically produced with no control over the mech. stereochem. Here we report a stereoselective approach to mech. planar chiral rotaxanes in up to 98:2 d.r. using a readily available α-amino acid-derived azide. Symmetrization of the covalent stereocenter yields a rotaxane in which the mech. bond provides the only stereogenic element.
- 12Makita, Y.; Kihara, N.; Nakakoji, N.; Takata, T.; Inagaki, S.; Yamamoto, C.; Okamoto, Y. Catalytic asymmetric synthesis and optical resolution of planar chiral rotaxane. Chem. Lett. 2007, 36, 162– 163, DOI: 10.1246/cl.2007.162Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXpt1GlsQ%253D%253D&md5=a6f7ae113ee30d97a0b38fc0900b8d1bCatalytic asymmetric synthesis and optical resolution of planar chiral rotaxaneMakita, Yoshimasa; Kihara, Nobuhiro; Nakakoji, Naohisa; Takata, Toshikazu; Inagaki, Shinji; Yamamoto, Chiyo; Okamoto, YoshioChemistry Letters (2007), 36 (1), 162-163CODEN: CMLTAG; ISSN:0366-7022. (Chemical Society of Japan)Planar chiral rotaxanes were synthesized from crown ether and secondary ammonium salt via trialkylphosphine-catalyzed acylative end-capping. Their optical resoln. was achieved by chiral HPLC after acylative neutralization of the ammonium group. When optically active phosphine (Me3CPMeCH2)2 was used as the chiral acylation catalyst, optically active rotaxane (4.4% ee) was obtained.
- 13De Bo, G.; Dolphijn, G.; McTernan, C. T.; Leigh, D. A. [2]Rotaxane formation by transition state stabilization. J. Am. Chem. Soc. 2017, 139, 8455– 8457, DOI: 10.1021/jacs.7b05640Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVSqur%252FO&md5=7123a1ffc8d0440ad6ad0691e596b0fb[2]Rotaxane Formation by Transition State StabilizationDe Bo, Guillaume; Dolphijn, Guillaume; McTernan, Charlie T.; Leigh, David A.Journal of the American Chemical Society (2017), 139 (25), 8455-8457CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)We report on the synthesis of [2]rotaxanes driven by stabilization of the axle-forming transition state. A bifunctional macrocycle, with hydrogen bond donors at one end and acceptors at the other, is used to stabilize the charges that develop during the addn. of a primary amine to a cyclic sulfate.
- 14(a) Fielden, S. D. P.; Leigh, D. A.; McTernan, C. T.; Pérez-Saavedra, B.; Vitorica-Yrezabal, I. J. Spontaneous assembly of rotaxanes from a primary amine, crown ether and electrophile. J. Am. Chem. Soc. 2018, 140, 6049– 6052, DOI: 10.1021/jacs.8b03394Google Scholar14ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXoslygur4%253D&md5=143f336521cd2b5083c42df69971e9c8Spontaneous Assembly of Rotaxanes from a Primary Amine, Crown Ether and ElectrophileFielden, Stephen D. P.; Leigh, David A.; McTernan, Charlie T.; Perez-Saavedra, Borja; Vitorica-Yrezabal, Inigo J.Journal of the American Chemical Society (2018), 140 (19), 6049-6052CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)We report the synthesis of crown ether-ammonium, amide and amine [2]rotaxanes via transition state stabilization of axle-forming reactions. In contrast to the two-step "clipping" and "capping" strategies generally used for rotaxane synthesis, here the components assemble into the interlocked mol. in a single, reagent-less, step under kinetic control. The crown ether accelerates the reaction of the axle-forming components through the cavity to give the threaded product in a form of metal-free active template synthesis. Rotaxane formation can proceed through the stabilization of different transition states featuring 5-coordinate (e.g., SN2) or 4-coordinate (e.g., acylation, Michael addn.) carbon. Examples prepd. using the approach include crown-ether-peptide rotaxanes and switchable mol. shuttles.(b) Tian, C.; Fielden, S. D. P.; Whitehead, G. F. S.; Vitorica-Yrezabal, I. J.; Leigh, D. A. Weak functional group interactions revealed through metal-free active template rotaxane synthesis. Nat. Commun. 2020, 11, 744, DOI: 10.1038/s41467-020-14576-7Google Scholar14bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXjs1Oht78%253D&md5=b8e0b875979c58fb67f32c4e332a0387Weak functional group interactions revealed through metal-free active template rotaxane synthesisTian, Chong; Fielden, Stephen D. P.; Whitehead, George F. S.; Vitorica-Yrezabal, Inigo J.; Leigh, David A.Nature Communications (2020), 11 (1), 744CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)Abstr.: Modest functional group interactions can play important roles in mol. recognition, catalysis and self-assembly. However, weakly assocd. binding motifs are often difficult to characterize. Here, we report on the metal-free active template synthesis of [2]rotaxanes in one step, up to 95% yield and >100:1 rotaxane:axle selectivity, from primary amines, crown ethers and a range of C=O, C=S, S(=O)2 and P=O electrophiles. In addn. to being a simple and effective route to a broad range of rotaxanes, the strategy enables 1:1 interactions of crown ethers with various functional groups to be characterized in soln. and the solid state, several of which are too weak - or are disfavored compared to other binding modes - to be obsd. in typical host-guest complexes. The approach may be broadly applicable to the kinetic stabilization and characterization of other weak functional group interactions.
- 15(a) Hogan, J. C.; Gandour, R. D. Structural requirements for glyme catalysis in butylaminolysis of aryl acetates in chlorobenzene. Identification of -OCH2CH2OCH2CH2OCH2CH2O- as the optimal subunit for catalysis. J. Org. Chem. 1991, 56, 2821– 2826, DOI: 10.1021/jo00008a044Google Scholar15ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXhs1egsrg%253D&md5=e8ea46e5508a4c411f6b730e50144047Structural requirements for glyme catalysis in butylaminolysis of aryl acetates in chlorobenzene. Identification of -OCH2CH2OCH2CH2OCH2CH2O- as the optimal subunit for catalysisHogan, John C.; Gandour, Richard D.Journal of Organic Chemistry (1991), 56 (8), 2821-6CODEN: JOCEAH; ISSN:0022-3263.The catalytic behavior of linear (open-chain) polyethers (glymes) in butylaminolysis of 4-nitrophenyl acetate in PhCl was reexamd. A plot of the catalytic rate const. vs. chain length of catalyst indicated that four oxygens in a OCH2CH2OCH2CH2OCH2CH2O subunit are necessary for optimal catalysis. This was confirmed by a Hammett anal., which employed four addnl. aryl acetates. Previous studies were incorrect because of impurities in the glymes. The Hammett study supported the conclusions of others that breakdown of the zwitterionic tetrahedral intermediate is rate-limiting. A specific structure for a glyme-zwitterionic tetrahedral intermediate complex, which contains an ammonium ion that hydrogen bonds to the ether oxygens, was implied.(b) Basilio, N.; García-Río, L.; Mejuto, J. C.; Pérez-Lorenzo, M. A. New reaction pathway in the ester aminolysis catalyzed by glymes and crown ethers. J. Org. Chem. 2006, 71, 4280– 4285, DOI: 10.1021/jo060389uGoogle Scholar15bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XjslKntrg%253D&md5=bf529e9b807b9896c32784b1bc9f3eadA New Reaction Pathway in the Ester Aminolysis Catalyzed by Glymes and Crown EthersBasilio, Nuno; Garcia-Rio, Luis; Mejuto, Juan C.; Perez-Lorenzo, MoisesJournal of Organic Chemistry (2006), 71 (11), 4280-4285CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)Butylaminolysis of p-nitrophenyl acetate in chlorobenzene in the presence of different kinds of phase-transfer catalysts (crown ethers and glymes) supports the existence of a reaction pathway exhibiting a first-order dependence on the concn. of the phase transfer catalyst and a second-order dependence on the concn. of butylamine. This novel reaction pathway must be included in the mechanism traditionally accepted for the catalysis by phase-transfer agents of aminolysis reactions in aprotic solvents.
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Chiral leaving groups have previously been employed in asymmetric substitution reactions. See:
Lepore, S. D.; Mondal, D. Recent advances in heterolytic nucleofugal leaving groups. Tetrahedron 2007, 63, 5103– 5122, DOI: 10.1016/j.tet.2007.03.049Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXlt1Gqtb0%253D&md5=c14fc2154ae71160104290742c427ebdRecent advances in heterolytic nucleofugal leaving groupsLepore, Salvatore D.; Mondal, DeboprosadTetrahedron (2007), 63 (24), 5103-5122CODEN: TETRAB; ISSN:0040-4020. (Elsevier Ltd.)A review. This review begins with a discussion of advances in sulfonate and carboxylate-based leaving groups. Also included are organometallic leaving groups, heterocyclic leaving groups, activation-deactivation leaving groups, and nucleophile assisting leaving groups. - 17Heller, D.; Buschmann, H.; Scharf, H.-D. Nonlinear temperature behavior of product ratios in selection processes. Angew. Chem., Int. Ed. Engl. 1996, 35, 1852– 1854, DOI: 10.1002/anie.199618521Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28Xls1Gqurs%253D&md5=1c478757fcc2cd908334343a7229163aNonlinear temperature behavior of product ratios in selection processesHeller, Detlef; Buschmann, Helmut; Scharf, Hans-DeiterAngewandte Chemie, International Edition in English (1996), 35 (16), 1852-1854CODEN: ACIEAY; ISSN:0570-0833. (VCH)The homogeneous asym. hydrogenation of an amino acid precursor using a rhodium complex catalyst contg. chiral ligands (in which the oxidative addn. of hydrogen is rate detg.) shows a nonlinear temp. dependence of product selectivity due to a change in the concn. ratio of the diastereomeric substrate complex intermediates (formed prior to the rate detg. step) with temp. Other causes for this type of nonlinearity and the applications of the isoinversion principle are discussed.
- 18Cinchona alkaloids in synthesis and catalysis: Ligands, immobilization and organocatalysis; Eui Song, C., Ed.; Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, 2009.Google ScholarThere is no corresponding record for this reference.
- 19(a) Hunter, C. A.; Sanders, J. K. M. The nature of π–π interactions. J. Am. Chem. Soc. 1990, 112, 5525– 5534, DOI: 10.1021/ja00170a016Google Scholar19ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3cXksVShur8%253D&md5=ec2815e7f5f04a985e6594a1aad84b6cThe nature of π-π interactionsHunter, Christopher A.; Sanders, Jeremy K. M.Journal of the American Chemical Society (1990), 112 (14), 5525-34CODEN: JACSAT; ISSN:0002-7863.A simple model of the charge distribution in a π-system is used to explain the strong geometrical requirements for interactions between arom. mols. The key feature of the model is that it considers the σ-framework and the π-electrons sep. and demonstrates that net favorable π-π interactions are actually the result of π-σ attractions that overcome π-π repulsions. The calcns. correlate with observations made on porphyrin π-π interactions both in soln. and in the cryst. state. By using an idealized π-atom, some general rules for predicting the geometry of favorable π-π interactions are derived. In particular a favorable offset or slipped geometry is predicted. These rules successfully predict the geometry of intermol. interactions in the crystal structures of arom. mols. and rationalize a range of host-guest phenomena. The theory demonstrates that the electron donor-acceptor concept can be misleading: it is the properties of the atoms at the points of intermol. contact rather than the overall mol. properties which are important.(b) Riwar, L.-J.; Trapp, N.; Kuhn, B.; Diederich, F. Substituent effects in parallel displaced π–π stacking interactions: Distance matters. Angew. Chem., Int. Ed. 2017, 56, 11252– 11257, DOI: 10.1002/anie.201703744Google Scholar19bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXnsV2qsrg%253D&md5=a9b0d6d22c13b54915292feb77c35bbfSubstituent Effects in Parallel-Displaced π-π Stacking Interactions: Distance MattersRiwar, Leslie-Joana; Trapp, Nils; Kuhn, Bernd; Diederich, FrancoisAngewandte Chemie, International Edition (2017), 56 (37), 11252-11257CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Host-guest systems with Rebek imide type receptors and a 2,6-di(isobutyramido)pyridine ligand were employed to investigate substituent effects in parallel-displaced π-π stacking interactions. Changing the intermol. distance between the para substituent on the arom. platform of the receptor and the pyridine ring of the guest results in a strongly different substituent effect. With a short ethyne-1,2-diyl spacer between the Rebek imide and the arom. platform, partial overlap of substituent and guest stabilizes the π-π stacking interactions independent of the electronic nature of the substituent (Wheeler-Houk model). When the substituent is shifted further away by using a buta-1,3-diyne-1,4-diyl spacer, direct, through-space interactions between substituent and guest are prevented. A linear correlation between logKa (Ka = assocn. const.) and the Hammett substituent const. σpara is obsd., confirming predictions by the Hunter-Sanders model exptl.
- 20Stewart, J. J. P. Optimization of parameters for semiempirical methods V. Modification of NDDO approximations and application to 70 elements. J. Mol. Model. 2007, 13, 1173– 1213, DOI: 10.1007/s00894-007-0233-4Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXhtlequr7N&md5=7d22928c8e3423f3ca8f2e7c77e6e6c9Optimization of parameters for semiempirical methods V: modification of NDDO approximations and application to 70 elementsStewart, James J. P.Journal of Molecular Modeling (2007), 13 (12), 1173-1213CODEN: JMMOFK; ISSN:0948-5023. (Springer GmbH)Several modifications that have been made to the NDDO core-core interaction term and to the method of parameter optimization are described. These changes have resulted in a more complete parameter optimization, called PM6, which has, in turn, allowed 70 elements to be parameterized. The av. unsigned error (AUE) between calcd. and ref. heats of formation for 4,492 species was 8.0 kcal mol-1. For the subset of 1,373 compds. involving only the elements H, C, N, O, F, P, S, Cl, and Br, the PM6 AUE was 4.4 kcal mol-1. The equivalent AUE for other methods were: RM1: 5.0, B3LYP 6-31G*: 5.2, PM5: 5.7, PM3: 6.3, HF 6-31G*: 7.4, and AM1: 10.0 kcal mol-1. Several long-standing faults in AM1 and PM3 have been cor. and significant improvements have been made in the prediction of geometries.
- 21Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, Ö.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, revision D.01; Gaussian, Inc.; Wallingford, CT, 2013.Google ScholarThere is no corresponding record for this reference.
- 22(a) Lim, J. Y. C.; Marques, I.; Félix, V.; Beer, P. D. A chiral halogen-bonding [3]rotaxane for the recognition and sensing of biologically relevant dicarboxylate anions. Angew. Chem., Int. Ed. 2018, 57, 584– 588, DOI: 10.1002/anie.201711176Google Scholar22ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvFensbnM&md5=4e268891b96ba85ed20cc8b0ae3f5065A Chiral Halogen-Bonding [3]Rotaxane for the Recognition and Sensing of Biologically Relevant Dicarboxylate AnionsLim, Jason Y. C.; Marques, Igor; Felix, Vitor; Beer, Paul D.Angewandte Chemie, International Edition (2018), 57 (2), 584-588CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)The unprecedented application of a chiral halogen-bonding [3]rotaxane host system for the discrimination of stereo- and E/Z geometric isomers of a dicarboxylate anion guest is described. Synthesized by a chloride anion templation strategy, the [3]rotaxane host recognizes dicarboxylates through the formation of 1:1 stoichiometric sandwich complexes. This process was analyzed by mol. dynamics simulations, which revealed the crit. synergy of halogen and hydrogen bonding interactions in anion discrimination. In addn., the centrally located chiral (S)-BINOL motif of the [3]rotaxane axle component facilitates the complexed dicarboxylate species to be sensed via a fluorescence response.(b) Ba̧k, K. M.; Porfyrakis, K.; Davis, J. J.; Beer, P. D. Exploiting the mechanical bond for molecular recognition and sensing of charged species. Mater. Chem. Front. 2020, 4, 1052– 1073, DOI: 10.1039/C9QM00698BGoogle Scholar22bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXisVKns7fI&md5=4bc0f8a347f0cf280885149aa598c7fbExploiting the mechanical bond for molecular recognition and sensing of charged speciesBak, Krzysztof M.; Porfyrakis, Kyriakos; Davis, Jason J.; Beer, Paul D.Materials Chemistry Frontiers (2020), 4 (4), 1052-1073CODEN: MCFAC5; ISSN:2052-1537. (Royal Society of Chemistry)A review. The unique properties of the mech. bond have been increasingly used for the purpose of mol. recognition. The recent progress in the development of cation and anion template strategies for the construction of mech. interlocked mols. (MIMs) have resulted in a variety of ion binding catenane and rotaxane host structures. The appropriate integration of reporting redox- and photo-active centers into their structural frameworks can result in prototype mol. sensors for targeting charged species and mol. switches for potential nanotechnol. applications. This review presents progress in the field of MIM hosts for ion recognition and sensing since 2014, focusing on the synthetic approaches employed and mechanisms of host-guest binding and detection.
- 23(a) Fu, X.; Zhang, Q.; Rao, S.-J.; Qu, D.-H.; Tian, H. One-pot synthesis of a [c2]daisy-chain-containing hetero[4]rotaxane via a self-sorting strategy. Chem. Sci. 2016, 7, 1696– 1701, DOI: 10.1039/C5SC04844CGoogle Scholar23ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XlvFSnug%253D%253D&md5=1311bf6985bf30388fbb8363db8b1d43One-pot synthesis of a [c2]daisy-chain-containing hetero[4]rotaxane via a self-sorting strategyFu, Xin; Zhang, Qi; Rao, Si-Jia; Qu, Da-Hui; Tian, HeChemical Science (2016), 7 (3), 1696-1701CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)Construction and efficient synthesis of hetero[n]rotaxanes with high structural complexity were always attractive challenges. Herein, we demonstrate a facile one-pot prepn. of a hetero[4]rotaxane, by employing a self-sorting strategy, which contains an interpenetrated dibenzo-24-crown-8 (DB24C8) based [c2]daisy chain structure and was ended with a benzo-21-crown-7 (B21C7) based rotaxane at each side. Key to the design involved encoding the selective threading using a steric hindrance-related "language", where highly selective self-assemblies occurred in a three-component self-sorting process, which included the threading of a benzylalkylammonium into a B21C7 and interpenetrated dimerized formation of a DB24C8 based [c2]daisy chain simultaneously; the precise pre-assembled system resulted in the efficient synthesis of hetero[4]rotaxane with a high-level of structural complexity under the "CuAAC" reaction.(b) Rao, S.-J.; Zhang, Q.; Mei, J.; Ye, X.-H.; Gao, C.; Wang, Q.-C.; Qu, D.-H.; Tian, H. One-pot synthesis of hetero[6]rotaxane bearing three different kinds of macrocycle through a self-sorting process. Chem. Sci. 2017, 8, 6777– 6783, DOI: 10.1039/C7SC03232CGoogle Scholar23bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht1OlsrbK&md5=77896875347a042e516027a6c186c3c6One-pot synthesis of hetero[6]rotaxane bearing three different kinds of macrocycle through a self-sorting processRao, Si-Jia; Zhang, Qi; Mei, Ju; Ye, Xu-Hao; Gao, Chuan; Wang, Qiao-Chun; Qu, Da-Hui; Tian, HeChemical Science (2017), 8 (10), 6777-6783CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)A six-component self-sorting process that involves three types of crown ether macrocycles namely bis(p-phenylene-34-crown-10) (BPP34C10), dibenzo-24-crown-8 (DB24C8) and benzo-21-crown-7 (B21C7) and three types of cation guest mols. namely a 4,4'-bipyridine dication (BPY2+), dibenzylammonium (DBA) and benzylalkylammonium (BAA) ions was carefully and thoroughly investigated. Based on this well-established highly selective six-component self-sorting process, a hetero[6]rotaxane bearing three different kinds of crown ether macrocycle I was designed and successfully synthesized through a facile and efficient one-pot ''click'' stoppering strategy. Such work is proposed to be a significant advance in the construction of mech. interlocked mols. with high structural complexity, as well as a good supplement in the areas of multi-component self-sorting and noncovalent self-assembly.(c) Chen, S.; Wang, Y.; Nie, T.; Bao, C.; Wang, C.; Xu, T.; Lin, Q.; Qu, D.-H.; Gong, X.; Yang, Y.; Zhu, L.; Tian, H. An artificial molecular shuttle operates in lipid bilayers for ion transport. J. Am. Chem. Soc. 2018, 140, 17992– 17998, DOI: 10.1021/jacs.8b09580Google Scholar23chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXit1Cit7bM&md5=aa1dc80fe9cfcddf8cfd9d3c8e98e7a9An Artificial Molecular Shuttle Operates in Lipid Bilayers for Ion TransportChen, Sujun; Wang, Yichuan; Nie, Ting; Bao, Chunyan; Wang, Chenxi; Xu, Tianyi; Lin, Qiuning; Qu, Da-Hui; Gong, Xueqing; Yang, Yi; Zhu, Linyong; Tian, HeJournal of the American Chemical Society (2018), 140 (51), 17992-17998CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Inspired by natural biomol. machines, synthetic mol.-level machines have been proven to perform well-defined mech. tasks and measurable work. To mimic the function of channel proteins, we herein report the development of a synthetic mol. shuttle, [2]rotaxane 3, as a unimol. vehicle that can be inserted into lipid bilayers to perform passive ion transport through its stochastic shuttling motion. The [2]rotaxane mol. shuttle is composed of an amphiphilic mol. thread with three binding stations, which is interlocked in a macrocycle wheel component that tethers a K+ carrier. The structural characteristics enable the rotaxane to transport ions across the lipid bilayers, similar to a cable car, transporting K+ with an EC50 value of 1.0 μM (3.0 mol % relative to lipid). We expect that this simple mol. machine will provide new opportunities for developing more effective and selective ion transporters.(d) Zheng, X.; Zhang, Y.; Cao, N.; Li, X.; Zhang, S.; Du, R.; Wang, H.; Ye, Z.; Wang, Y.; Cao, F.; Li, H.; Hong, X.; Sue, A. C.-H.; Yang, C.; Liu, W.-G.; Li, H. Coulombic-enhanced hetero radical pairing interactions. Nat. Commun. 2018, 9, 1961, DOI: 10.1038/s41467-018-04335-0Google Scholar23dhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC1MfksV2rtQ%253D%253D&md5=ad05f0a95e2b5bc61894f64baec97facCoulombic-enhanced hetero radical pairing interactionsZheng Xujun; Zhang Yang; Cao Ning; Li Xin; Zhang Shuoqing; Du Renfeng; Ye Zhenni; Wang Yan; Cao Fahe; Li Haoran; Hong Xin; Li Hao; Zheng Xujun; Yang Chuluo; Wang Haiying; Sue Andrew C-H; Liu Wei-GuangNature communications (2018), 9 (1), 1961 ISSN:.Spin-spin interactions between two identical aromatic radicals have been studied extensively and utilized to establish supramolecular recognition. Here we report that spin-pairing interactions could also take place between two different π-electron radicals, namely a bipyridinium radical cation (BPY(+•)) and a naphthalene-1,8:4,5-bis(dicarboximide) radical anion (NDI((box drawings horizontal)•)). The occurrence of this type of previously unreported hetero radical-pairing interactions is attributed to enhancement effect of Coulombic attraction between these two radicals bearing opposite charges. The Coulombic-enhanced hetero radical pairing interactions are employed to drive host-guest recognition, as well as the reversible switching of a bistable [2]rotaxane.(e) Li, W.-J.; Wang, W.; Wang, X.-Q.; Li, M.; Ke, Y.; Yao, R.; Wen, J.; Yin, G.-Q.; Jiang, B.; Li, X.; Yin, P.; Yang, H. B. Daisy chain dendrimers: Integrated mechanically interlocked molecules with stimuli-induced dimension modulation feature. J. Am. Chem. Soc. 2020, 142, 8473– 8482, DOI: 10.1021/jacs.0c02475Google Scholar23ehttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXnsVyktLk%253D&md5=3584ff44f451edbaf4bf8c436d775c91Daisy Chain Dendrimers: Integrated Mechanically Interlocked Molecules with Stimuli-Induced Dimension Modulation FeatureLi, Wei-Jian; Wang, Wei; Wang, Xu-Qing; Li, Mu; Ke, Yubin; Yao, Rui; Wen, Jin; Yin, Guang-Qiang; Jiang, Bo; Li, Xiaopeng; Yin, Panchao; Yang, Hai-BoJournal of the American Chemical Society (2020), 142 (18), 8473-8482CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The precise construction of the high-order mech. interlocked mols. (MIMs) with well-defined topol. arrangements of multiple mech. interlocked units has been a great challenge. Herein, we present the first successful prepn. of a new family of daisy chain dendrimers, in which the individual [c2]daisy chain rotaxane units serve as the branches of dendrimer skeleton. In particular, the third-generation daisy chain dendrimer with 21 [c2]daisy chain rotaxane moieties was realized, which might be among the most complicated discrete high-order MIMs comprised of multiple [c2]daisy chain rotaxane units. Interestingly, such unique topol. arrangements of multiple stimuli-responsive [c2]daisy chain rotaxanes endowed the resultant daisy chain dendrimers controllable and reversible nanoscale dimension modulation through the collective and amplified extension/contraction of each [c2]daisy chain rotaxane branch upon the addn. of acetate anions or DMSO mols. as external stimulus. Furthermore, on the basis of such an intriguing size switching feature of daisy chain dendrimers, dynamic composite polymer films were constructed through the incorporation of daisy chain dendrimers into polymer films, which could undergo fast, reversible, and controllable shape transformations when DMSO mols. were employed as stimulus. The successful merging of [c2]daisy chain rotaxanes and dendrimers described herein provides not only a brand-new type of high-order mech. interlocked systems with well-defined topol. arrangements of [c2]daisy chain rotaxanes, but also a successful and practical approach toward the construction of supramol. dynamic materials.
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Abstract
Figure 1
Figure 1. Enantioselective synthesis of mechanically planar chiral rotaxanes through metal-free active template N-acylation using a macrocycle lacking rotational symmetry and an electrophile with a point-chiral leaving group.
Scheme 1
Scheme 1. : (a) Achiral Rotaxane Synthesis by Active Template N-Acylation Using Rotationally Symmetrical Crown Ethers; (b) Racemic and Unoptimized Enantioselective Synthesis of a Mechanically Planar Chiral RotaxaneFigure 2
Figure 2. (a) Enantioselective synthesis of mechanically planar chiral rotaxane 11. Reaction conditions: 2 equiv of amine 2, 1 equiv each of electrophile and crown ether 10, toluene, [0.14 M], –40 °C, 24 h. (b) Partial 1H NMR spectra (600 MHz, CDCl3, 295 K) of macrocycle 10 (top), rotaxane 11 (middle) and the corresponding unthreaded axle (bottom).
Figure 3
Figure 3. (a) Circular dichroism spectra (1.0 × 10–4 M, CH2Cl2, 298 K) of (+)-11 (red) and (−)-11 (blue), baseline corrected. (b) Chemical structure of racemic rotaxane 13. (c) X-ray crystal structure of racemic rotaxane 13, side-on view showing intercomponent hydrogen bonds (in green). Hydrogen bond lengths: N47H—O16, 2.20 Å; O49—HC6, 2.63 Å. Hydrogen bond angles: N47—H–O16, 158.4°; O49—H–C6, 161.8°. (d) X-ray crystal structure of 13 viewed along the axle showing π-stacking between the macrocycle 1,2-dihydroxynaphthalene and axle bis(trifluoromethyl)phenyl rings. Centroid–centroid distance, 3.67 Å. Angle described by C40 and centroids, 97.6°. Solvate molecules and other hydrogen atoms omitted for clarity.
Figure 4
Figure 4. Tentative rationale for the transfer of chirality from Euclidean point-chirality (of the leaving group) to mechanical planar chirality (of the rotaxane). The lowest energy tetrahedral intermediates were modeled (see Supporting Information) using (a) electrophile 9 or (b) electrophile 12. The di(alkoxyl)naphthalene ring of the macrocycle and bis(trifluoromethyl)benzene unit originating from the nucleophile π-stack, causing the nitro-catechol ring to be positioned so as to cover one face of the tetrahedral center of the intermediate. This thermodynamically favored arrangement of components ensures the different handedness of the pseudoenantiomeric leaving groups is well-expressed in the diastereomeric transition states, resulting in enantioselectivity in the mechanically planar chiral rotaxane product. Hydrogen bonds are indicated by black dotted lines.
References
This article references 23 other publications.
- 1(a) Bruns, C. J.; Stoddart, J. F. The Nature of the Mechanical Bond: From Molecules to Machines; John Wiley & Sons: Hoboken, NJ, 2017.There is no corresponding record for this reference.(b) Jamieson, E. M. G.; Modicom, F.; Goldup, S. M. Chirality in rotaxanes and catenanes. Chem. Soc. Rev. 2018, 47, 5266– 5311, DOI: 10.1039/C8CS00097B1bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtVSgtLbL&md5=cd9e0683f4dad9b913c00554a76fd67dChirality in rotaxanes and catenanesJamieson, E. M. G.; Modicom, F.; Goldup, S. M.Chemical Society Reviews (2018), 47 (14), 5266-5311CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)A review. Although chiral mech. interlocked mols. (MIMs) have been synthesized and studied, enantiopure examples are relatively under-represented in the pantheon of reported catenanes and rotaxanes and the underlying chirality of the system is often even overlooked. This is changing with the advent of new applications of MIMs in catalysis, sensing and materials and the appearance of new methods to access unusual stereogenic units unique to the mech. bond. Here we discuss the different stereogenic units that have been investigated in catenanes and rotaxanes, examples of their application, methods for assigning abs. stereochem. and provide a perspective on future developments.(c) Evans, N. H. Chiral catenanes and rotaxanes: Fundamentals and emerging applications. Chem. - Eur. J. 2018, 24, 3101– 3112, DOI: 10.1002/chem.2017041491chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvV2lsL3K&md5=607f6e2649003bc3be5e25959095e696Chiral Catenanes and Rotaxanes: Fundamentals and Emerging ApplicationsEvans, Nicholas H.Chemistry - A European Journal (2018), 24 (13), 3101-3112CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)A review. Mol. chirality provides a key challenge in host-guest recognition and other related chem. applications such as asym. catalysis. For a mol. to act as an efficient enantioselective receptor, it requires multi-point interactions between host and chiral guest, which may be achieved by an appropriate chiral 3D scaffold. As a consequence of their interlocked structure, catenanes and rotaxanes may present such a 3D scaffold, and can be chiral by inclusion of a classical chiral element and/or as a consequence of the mech. bond. This Minireview presents illustrative examples of chiral [2]catenanes and [2]rotaxanes, and discusses where these mols. have been used in chem. applications such as chiral host-guest recognition and asym. catalysis.(d) Nakazono, K.; Takata, T. Mechanical chirality of rotaxanes: Synthesis and function. Symmetry 2020, 12, 144, DOI: 10.3390/sym12010144There is no corresponding record for this reference.https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=&md5=9874b665cc7a056b8e2f928dd3112440
- 2
If a prochiral or meso thread is incorporated into a rotaxane, then chirality can arise from the position of the ring on the axle. See:
(a) Alvarez-Pérez, M.; Goldup, S. M.; Leigh, D. A.; Slawin, A. M. Z. A chemically-driven molecular information ratchet. J. Am. Chem. Soc. 2008, 130, 1836– 1838, DOI: 10.1021/ja71023942ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXntVektg%253D%253D&md5=76aab0e6c0e12a2435cab00b1e24f8e8A Chemically-Driven Molecular Information RatchetAlvarez-Perez, Monica; Goldup, Stephen M.; Leigh, David A.; Slawin, Alexandra M. Z.Journal of the American Chemical Society (2008), 130 (6), 1836-1838CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)A chem. driven mol. information ratchet is described. The equil. macrocycle distribution in a [2]rotaxane is driven away from its 50:50 population of thread binding sites to a 33:67 ratio by benzoylation under the influence of a chiral catalyst. The reaction corresponds to a dynamic kinetic resoln. of rotaxane co-conformers that interconvert through shuttling.(b) Cakmak, Y.; Erbas-Cakmak, S.; Leigh, D. A. Asymmetric catalysis with a mechanically point-chiral rotaxane. J. Am. Chem. Soc. 2016, 138, 1749– 1751, DOI: 10.1021/jacs.6b003032bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvFOmtbs%253D&md5=2947cbc3f81dbd3a1045eee79d0b88acAsymmetric Catalysis with a Mechanically Point-Chiral RotaxaneCakmak, Yusuf; Erbas-Cakmak, Sundus; Leigh, David A.Journal of the American Chemical Society (2016), 138 (6), 1749-1751CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Mech. point-chirality in a [2]rotaxane is utilized for asym. catalysis. Stable enantiomers of the rotaxane result from a bulky group in the middle of the thread preventing a benzylic amide macrocycle shuttling between different sides of a prochiral center, creating point chirality in the vicinity of a secondary amine group. The resulting mechanochirogenesis delivers enantioselective organocatalysis via both enamine (up to 71:29 er) and iminium (up to 68:32 er) activation modes.(c) Dommaschk, M.; Echavarren, J.; Leigh, D. A.; Marcos, V.; Singleton, T. A. Dynamic control of chiral space through local symmetry breaking in a rotaxane organocatalyst. Angew. Chem., Int. Ed. 2019, 58, 14955– 14958, DOI: 10.1002/anie.2019083302chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhslGnt7%252FL&md5=aadf621b679f534ef0bb3a548d8a13e6Dynamic Control of Chiral Space Through Local Symmetry Breaking in a Rotaxane OrganocatalystDommaschk, Marcel; Echavarren, Javier; Leigh, David A.; Marcos, Vanesa; Singleton, Thomas A.Angewandte Chemie, International Edition (2019), 58 (42), 14955-14958CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)We report on a switchable rotaxane mol. shuttle that features a pseudo-meso 2,5-disubstituted pyrrolidine catalytic unit on the axle whose local symmetry is broken according to the position of a threaded benzylic amide macrocycle. The macrocycle can be selectively switched (with light in one direction; with catalytic acid in the other) with high fidelity between binding sites located to either side of the pyrrolidine unit. The position of the macrocycle dictates the facial bias of the rotaxane-catalyzed conjugate addn. of aldehydes to vinyl sulfones. The pseudo-meso non-interlocked thread does not afford significant selectivity as a catalyst (2-14 % ee), whereas the rotaxane affords selectivities of up to 40 % ee with switching of the position of the macrocycle changing the handedness of the product formed (up to 60 % Δee). - 3
Mechanical planar chirality can also result from confinement of an unsymmetrical macrocycle to one side of a nonprochiral axle possessing Dnh symmetry. See:
(a) Mochizuki, Y.; Ikeyatsu, K.; Mutoh, Y.; Hosoya, S.; Saito, S. Synthesis of mechanically planar chiral rac-[2]rotaxanes by partitioning of an achiral [2]rotaxane: Stereoinversion induced by shuttling. Org. Lett. 2017, 19, 4347– 4350, DOI: 10.1021/acs.orglett.7b020433ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht1Orsb3K&md5=eaca9095b5144363977bfa45406ed000Synthesis of Mechanically Planar Chiral rac-[2]Rotaxanes by Partitioning of an Achiral [2]Rotaxane: Stereoinversion Induced by ShuttlingMochizuki, Yuta; Ikeyatsu, Katsuhiko; Mutoh, Yuichiro; Hosoya, Shoichi; Saito, ShinichiOrganic Letters (2017), 19 (16), 4347-4350CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)Mech. planar chiral [2]rotaxanes were synthesized by the introduction of bulky pyrrole moieties into the axle component of an achiral [2]rotaxane. The enantiomers were sepd. by chiral HPLC. The shuttling of the ring component between the two compartments at high temp. induced the stereoinversion of the mech. planar chiral [2]rotaxane. The rate of the stereoinversion was studied quant., and the kinetic parameters were detd.(b) Corra, S.; de Vet, C.; Groppi, J.; La Rosa, M.; Silvi, S.; Baroncini, M.; Credi, A. Chemical on/off switching of mechanically planar chirality and chiral anion recognition in a [2]rotaxane molecular shuttle. J. Am. Chem. Soc. 2019, 141, 9129– 9133, DOI: 10.1021/jacs.9b009413bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtVKgsbnJ&md5=2a44d8764ac0143d193ca738b273e557Chemical On/Off Switching of Mechanically Planar Chirality and Chiral Anion Recognition in a [2]Rotaxane Molecular ShuttleCorra, Stefano; de Vet, Christiaan; Groppi, Jessica; La Rosa, Marcello; Silvi, Serena; Baroncini, Massimo; Credi, AlbertoJournal of the American Chemical Society (2019), 141 (23), 9129-9133CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)We exploit a reversible acid-base triggered mol. shuttling process to switch an appropriately designed rotaxane between prochiral and mech. planar chiral forms. The mech. planar enantiomers and their interconversion, arising from ring shuttling, have been characterized by NMR spectroscopy. We also show that the supramol. interaction of the pos. charged rotaxane with optically active anions causes an imbalance in the population of the two enantiomeric coconformations. This result represents an unprecedented example of chiral mol. recognition and can disclose innovative approaches to enantioselective sensing and catalysis. - 4
For examples of other stereochemical consequences of threading, see:
(a) Fuller, A.-M. L.; Leigh, D. A.; Lusby, P. J. Sequence isomerism in [3]rotaxanes. J. Am. Chem. Soc. 2010, 132, 4954– 4959, DOI: 10.1021/ja10068384ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXjt1enur4%253D&md5=1336c39e1e0ab5bfa07b655e6dff81aeSequence Isomerism in [3]RotaxanesFuller, Anne-Marie L.; Leigh, David A.; Lusby, Paul J.Journal of the American Chemical Society (2010), 132 (13), 4954-4959CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)We describe a strategy for assembling different macrocycles onto a nonsym. rotaxane thread in a precise sequence. If the macrocycles are small and rigid enough so that they cannot pass each other then the sequence is maintained mech., affording stereoisomerism in a manner reminiscent of atropisomerism. The method is exemplified through the synthesis of a pair of [3]rotaxane diastereomers that are constitutionally identical other than for the sequence of the different macrocycles on the thread. The synthesis features the iterative binding of different palladium(II) pyridine-2,6-dicarboxamide complexes to a pyridine ligand on the thread followed by their macrocyclization by ring-closing olefin metathesis. Removal of the palladium(II) from the first rotaxane formed frees the pyridine site to coordinate to a second, different, palladium(II) pyridine-2,6-dicarboxamide unit which, following macrocyclization, provides a multiring rotaxane of predetd. macrocycle sequence.(b) Talotta, C.; Gaeta, C.; Qi, Z.; Schalley, C. A.; Neri, P. Pseudorotaxanes with self-sorted sequence and stereochemical orientation. Angew. Chem., Int. Ed. 2013, 52, 7437– 7441, DOI: 10.1002/anie.2013015704bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXptVams7w%253D&md5=c14fb6b298fdad413e2dfe089fa1d5e2Pseudorotaxanes with Self-Sorted Sequence and Stereochemical OrientationTalotta, Carmen; Gaeta, Carmine; Qi, Zhenhui; Schalley, Christoph A.; Neri, PlacidoAngewandte Chemie, International Edition (2013), 52 (29), 7437-7441CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)We have successfully demonstrated that calix[6]arene-based pseudo[3]rotaxanes with bisammonium axles have intriguing self-sorting capabilities, even when structural differences are small and located remote from the binding sites. This is the first reported integrative self-sorting system that is able to discriminate simultaneously at the sequence and stereochem. level. All these aspects can be considered a further significant step toward mimicking the efficiency and complexity of natural systems.(c) La Manna, P.; Talotta, C.; Gaeta, C.; Soriente, A.; De Rosa, M.; Neri, P. Threading of an inherently directional calixarene wheel with oriented ammonium axles. J. Org. Chem. 2017, 82, 8973– 8983, DOI: 10.1021/acs.joc.7b013884chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtlSmt7jF&md5=92dcb7947abcffa21351abcdb8da9b3dThreading of an Inherently Directional Calixarene Wheel with Oriented Ammonium AxlesLa Manna, Pellegrino; Talotta, Carmen; Gaeta, Carmine; Soriente, Annunziata; De Rosa, Margherita; Neri, PlacidoJournal of Organic Chemistry (2017), 82 (17), 8973-8983CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)The threading of monostoppered alkylbenzylammonium axles 7+ and 8+ with the calix[6]-wheel 3 can occur by both routes of entering the macrocycle 3 in the cone conformation: passage through the upper rim and the through the lower rim. Thus, under thermodn. conditions, with both the axles 7+ and 8+, the two possible orientations of calix[2]pseudorotaxane, namely, endo-benzyl and endo-alkyl, are formed by a stereoselectivity controlled by the endo-alkyl rule. Interestingly, by 1H NMR monitoring of the threading process between 8+ and 3, we revealed two calix[2]pseudorotaxane isomers in which the calix-wheel adopts 1,2,3-alternate and cone conformations, which represent the kinetic and thermodn. species, resp. Finally, the synthesis of ammonium-based oriented calix[2]rotaxane is here described.(d) Cui, J.-S.; Ba, Q.-K.; Ke, H.; Valkonen, A.; Rissanen, K.; Jiang, W. Directional shuttling of a stimuli-responsive cone-like macrocycle on a single-state symmetric dumbbell axle. Angew. Chem., Int. Ed. 2018, 57, 7809– 7814, DOI: 10.1002/anie.2018033494dhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtVSgsrrF&md5=72a3ebcbf3e5506baf70dbc06102aed7Directional Shuttling of a Stimuli-Responsive Cone-Like Macrocycle on a Single-State Symmetric Dumbbell AxleCui, Jie-Shun; Ba, Qian-Kai; Ke, Hua; Valkonen, Arto; Rissanen, Kari; Jiang, WeiAngewandte Chemie, International Edition (2018), 57 (26), 7809-7814CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Rotaxane-based mol. shuttles are often operated using low-symmetry axles and changing the states of the binding stations. A mol. shuttle capable of directional shuttling of an acid-responsive cone-like macrocycle on a single-state sym. dumbbell axle is now presented. The axle contains three binding stations: one sym. di(quaternary ammonium) station and two nonsym. phenyltriazole stations arranged in opposite orientations. Upon addn. of an acid, the protonated macrocycle shuttles from the di(quaternary ammonium) station to the phenyltriazole binding station closer to its Bu groups. This directional shuttling presumably originates from charge repulsion and an orientational binding preference between the cone-like cavity and the nonsym. phenyltriazole station. This mechanism for achieving directional shuttling by manipulating only the wheels instead of the tracks is new for artificial mol. machines.(e) Zheng, L.-S.; Cui, J.-S.; Jiang, W. Biomimetic synchronized motion of two interacting macrocycles in [3]rotaxane-based molecular shuttles. Angew. Chem., Int. Ed. 2019, 58, 15136– 15141, DOI: 10.1002/anie.2019103184ehttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhslChur3M&md5=089367e0700c88df98a807badb9fa824Biomimetic Synchronized Motion of Two Interacting Macrocycles in [3]Rotaxane-Based Molecular ShuttlesZheng, Li-Shuo; Cui, Jie-Shun; Jiang, WeiAngewandte Chemie, International Edition (2019), 58 (42), 15136-15141CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Noncovalent interactions between all the neighboring components in biomol. machines are responsible for their synchronized motion and thus complex functions. This strategy has rarely been used in multicomponent mol. machines. Here, we report four [3]rotaxane-based mol. shuttles. Noncovalent interactions among the three components (two interacting macrocycles and one axle) not only cause a "systems-level" effect on the relative positions of the two macrocycles along the axle, but also result in a synchronized motion of the two macrocycles when adding partial amt. of stimuli. Moreover, the intermediate state with one shuttled macrocycle even exist predominantly in the soln. during the titrn. of stimuli, which is theor. unexpected for the [3]rotaxane with two non-interacting rings. This biomimetic strategy may provide a method for constructing highly complex mol. machines.(f) Ng, A. W. H.; Yee, C.-C.; Au-Yeung, H. Y. Radial hetero[5]catenanes: peripheral isomer sequences of the interlocked macrocycles. Angew. Chem., Int. Ed. 2019, 58, 17375– 17382, DOI: 10.1002/anie.2019085764fhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhvF2gsL3P&md5=3958fdfab392146b25f7cc50c442f720Radial Hetero[5]catenanes: Peripheral Isomer Sequences of the Interlocked MacrocyclesNg, Antony Wing Hung; Yee, Chi-Chung; Au-Yeung, Ho YuAngewandte Chemie, International Edition (2019), 58 (48), 17375-17382CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)A pair of radial [5]catenanes, with either an isomeric cyclic -AABB- or -ABAB- type sequence of the interlocked β-cyclodextrin (β-CD) and cucurbit[6]uril (CB[6]) units, has been efficiently synthesized. Because of a marked difference in the binding strength and interlocking sequence of the peripheral macrocycles, interesting sequence-dependent properties, characteristic of mech. bonded macrocycles, were realized. Variable-temp. 1H NMR studies showed that the -ABAB- isomer has a more independent β-CD dynamic, whereas the β-CD motions in the -AABB- isomer are coupled. Dynamics of the pH-insensitive β-CD can also be further modulated upon base-triggered mobilization of the CB[6]. These unique properties of the mech. bond expressed in a sequence-specific fashion and the transmission of the control on the macrocycle dynamics from one interlocked component to another, highlight the potential of similar complex hetero[n]catenanes in the design of advanced, multicomponent mol. machines. - 5Ishiwari, F.; Nakazono, K.; Koyama, Y.; Takata, T. Induction of single handed helicity of polyacetylenes using mechanically chiral rotaxanes as chiral sources. Angew. Chem., Int. Ed. 2017, 56, 14858– 14862, DOI: 10.1002/anie.2017079265https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1KgtLfF&md5=5d805b25736ceb243e94f1c60e272e16Induction of Single-Handed Helicity of Polyacetylenes Using Mechanically Chiral Rotaxanes as Chiral SourcesIshiwari, Fumitaka; Nakazono, Kazuko; Koyama, Yasuhito; Takata, ToshikazuAngewandte Chemie, International Edition (2017), 56 (47), 14858-14862CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Effective induction of preferred-handed helicity of polyacetylenes by pendant mech. chiral rotaxanes is discussed. Polyacetylenes possessing optically active mech. chiral rotaxanes in the side chains were synthesized by the polymn. of the corresponding enantiopure [2]rotaxane-type ethynyl monomers prepd. by the chiral-phase HPLC sepns. The CD Cotton effects revealed that the polyacetylenes took preferred-handed helical conformations depending on the rotaxane chirality. The preferred-handed helix was not disturbed by an addnl. chiral substituent on the rotaxane side chain. These results demonstrate the significance and utility of mech. chiral rotaxanes for the effective construction of asym. fields.
- 6Kameta, N.; Nagawa, Y.; Karikomi, M.; Hiratani, K. Chiral sensing for amino acid derivative based on a [2]rotaxane composed of an asymmetric rotor and an asymmetric axle. Chem. Commun. 2006, 3714– 3716, DOI: 10.1039/b607251h6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XoslGkt7g%253D&md5=902399c1175d7ae28d3d0fd1fd7a2307Chiral sensing for amino acid derivative based on a [2]rotaxane composed of an asymmetric rotor and an asymmetric axleKameta, Naohiro; Nagawa, Yoshinobu; Karikomi, Michinori; Hiratani, KazuhisaChemical Communications (Cambridge, United Kingdom) (2006), (35), 3714-3716CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)A chiral racemic [2]rotaxane contg. both an asym. rotor and an asym. axle is prepd.; the rotaxane forms diastereomeric complexes with D- and L-phenylalaninols as obsd. by both 1H NMR and by fluorescence spectra. The [2]rotaxane is prepd. in 11 steps (longest linear sequence); selective cleavage of a macrobicyclic dilactone with two different amines is used to establish the rotaxane structure. Alaninol, prolinol, and tryptophanol do not form observable diastereomeric complexes with the [2]rotaxane.
- 7Heard, A.; Goldup, S. M. Synthesis of a mechanically planar chiral rotaxane ligand for enantioselective catalysis. Chem. 2020, 6, 994– 1006, DOI: 10.1016/j.chempr.2020.02.0067https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXntVKqtr8%253D&md5=5aa1d4f1c6ec02663e1c8ded58788b21Synthesis of a Mechanically Planar Chiral Rotaxane Ligand for Enantioselective CatalysisHeard, Andrew W.; Goldup, Stephen M.Chem (2020), 6 (4), 994-1006CODEN: CHEMVE; ISSN:2451-9294. (Cell Press)A mech. planar chiral rotaxane-based Au complex that mediates a cyclopropanation reaction with stereoselectivities that are comparable with the best conventional covalent catalyst has been described.
- 8Glen, P. E.; O’Neill, J. A. T.; Lee, A.-L. Synthesis of a C1-symmetric Box macrocycle and studies towards active-template synthesis of mechanically planar chiral rotaxanes. Tetrahedron 2013, 69, 57– 68, DOI: 10.1016/j.tet.2012.10.0698https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xhs1Gqu7jM&md5=e18243cbce1e53103e196019450bebd6Synthesis of a C1-symmetric Box macrocycle and studies towards active-template synthesis of mechanically planar chiral rotaxanesGlen, Pauline E.; O'Neill, James A. T.; Lee, Ai-LanTetrahedron (2013), 69 (1), 57-68CODEN: TETRAB; ISSN:0040-4020. (Elsevier Ltd.)A C1-sym. Box macrocycle has been synthesized for the first time. The Box macrocycle along with other C1 and C2-sym. Box ligands were evaluated and compared as ligands in the Cadiot-Chodkiewicz, oxidative Heck and CuAAC "click" reactions as part of our studies towards achieving active-metal template synthesis of mech. planar chiral rotaxanes. This study constitutes the first report of Cadiot-Chodkiewicz and CuAAC "click" reactions using Box ligands, as well as the first dedicated study of oxidative Heck reactions using Box ligands.
- 9(a) Yamamoto, C.; Okamoto, Y.; Schmidt, T.; Jäger, R.; Vögtle, F. Enantiomeric resolution of cycloenantiomeric rotaxane, topologically chiral catenane, and pretzel-shaped molecules: Observation of pronounced circular dichroism. J. Am. Chem. Soc. 1997, 119, 10547– 10548, DOI: 10.1021/ja971764q9ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXms1Ogtbo%253D&md5=c8ebdf71b077d8f911a4aeca9af600c3Enantiomeric Resolution of Cycloenantiomeric Rotaxane, Topologically Chiral Catenane, and Pretzel-Shaped Molecules: Observation of Pronounced Circular DichroismYamamoto, Chiyo; Okamoto, Yoshio; Schmidt, Thomas; Jaeger, Ralf; Voegtle, FritzJournal of the American Chemical Society (1997), 119 (43), 10547-10548CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Cycloenantiomerism has been obsd. in rotaxanes for the first time. The object and its mirror image of these mech. bonded mols. result from different sequences of the sulfonamide group and the three amide groups on the wheel in rotaxanes I (I = ring1 threaded by dumbbell1) and II, bearing an unsym. dumbbell. The corresponding racemates of II could be base-line sepd. by HPLC on Chiralcel OD. Under similar conditions the topol. chiral sulfonamide catenane III (= ring1 threaded through ring1) and the species IV (= ring1 threaded through ring1 and further intramolecularly bridged by an ethyleneoxy chain) possessing the topol. of a pretzel could be base-line sepd. The sepn. factor α was found to be very large for compds. III and IV (6.95, 5.20 resp.), the optical rotations [α]D range from 20° to 168°. The pronounced CD curves of I-IV are reported.(b) Schalley, C. A.; Beizai, K.; Vögtle, F. On the way to rotaxane-based molecular motors: Studies in molecular mobility and topological chirality. Acc. Chem. Res. 2001, 34, 465– 476, DOI: 10.1021/ar000179i9bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXit1Slu7s%253D&md5=ea34c2315bbca974bc1da16ebad978aeOn the Way to Rotaxane-Based Molecular Motors: Studies in Molecular Mobility and Topological ChiralitySchalley, Christoph A.; Beizai, Kaweh; Voegtle, FritzAccounts of Chemical Research (2001), 34 (6), 465-476CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)A review, with many refs. ATP synthase represents a machine at the mol. level which couples the rotation of an axle in a wheel with the endergonic prodn. of ATP, the general source of chem. energy in the cell. The natural system prototypically bears all features of a macroscopic motor: a rotor within a stator held by a membrane and fueled by a difference in chem. potential in the form of a proton gradient combined with a machine for ATP prodn. The assembly of axle and wheel to a rotor device reminds one very much of a rotaxane. In this Account, we discuss some important features of motors and their (potential) realization in simpler artificial model systems, i.e., the mol. mobility of mech. bound mols., the importance of chirality for unidirectional motion, the sources of energy for driving the rotation, and the potential of using membranes and surfaces for ordering a large no. of devices to achieve macroscopic effects.(c) Kameta, N.; Hiratani, K.; Nagawa, Y. A novel synthesis of chiral rotaxanes via covalent bond formation. Chem. Commun. 2004, 466– 467, DOI: 10.1039/b314744d9chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXhtVaqsLs%253D&md5=5194842cb82d9206734e17b7b47b560cA novel synthesis of chiral rotaxanes via covalent bond formationKameta, Naohiro; Hiratani, Kazuhisa; Nagawa, YoshinobuChemical Communications (Cambridge, United Kingdom) (2004), (4), 466-467CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)Chiral rotaxanes composed of the asym. crownophane incorporating two hydroxy groups as a rotor moiety and the asym. axis were effectively synthesized via covalent bond formation, i.e. tandem Claisen rearrangement, esterification, and aminolysis.(d) Hirose, K.; Ukimi, M.; Ueda, S.; Onoda, C.; Kano, R.; Tsuda, K.; Hinohara, Y.; Tobe, Y. The asymmetry is derived from mechanical interlocking of achiral axle and achiral ring components – Syntheses and properties of optically pure [2]rotaxanes. Symmetry 2018, 10, 20, DOI: 10.3390/sym100100209dhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXms12ksrk%253D&md5=8f8874418a7381fb8c829ccf9e415454The asymmetry is derived from mechanical interlocking of achiral axle and achiral ring components -syntheses and properties of optically pure [2]rotaxanes-Hirose, Keiji; Ukimi, Masaya; Ueda, Shota; Onoda, Chie; Kano, Ryohei; Tsuda, Kyosuke; Hinohara, Yuko; Tobe, YoshitoSymmetry (2018), 10 (1), 20/1-20/17CODEN: SYMMAM; ISSN:2073-8994. (MDPI AG)Rotaxanes consisting of achiral axle and achiral ring components can possess supramol. chirality due to their unique geometrical architectures. To synthesize such chiral rotaxanes, we adapted a prerotaxane method based on aminolysis of a metacyclophane type prerotaxane that had planar chirality, which is composed of an achiral stopper unit and a crown ether type ring component. The prerotaxanes were well resolved using chiral HPLC into a pair of enantiomerically pure prerotaxanes, which were transferred into corresponding chiral rotaxanes, resp. Obtained chiral rotaxanes were revealed to have considerable enantioselectivity.(e) Gell, C. E.; McArdle-Ismaguilov, T. A.; Evans, N. H. Modulating the expression of chirality in a mechanically chiral rotaxane. Chem. Commun. 2019, 55, 1576– 1579, DOI: 10.1039/C8CC10044F9ehttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtFSgtro%253D&md5=f8da15dc4c54a9d1e48c9b94639bc631Modulating the expression of chirality in a mechanically chiral rotaxaneGell, Charles E.; McArdle-Ismaguilov, Timur A.; Evans, Nicholas H.Chemical Communications (Cambridge, United Kingdom) (2019), 55 (11), 1576-1579CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)The expression of mech. chirality by a hydrogen bond templated rotaxane, as detected by 1H NMR spectroscopy, may be modulated by affecting the co-conformational behavior of the rotaxane through varying solvent or by addn. of acid and base.(f) Gaedke, M.; Witte, F.; Anhäuser, J.; Hupatz, H.; Schröder, H. V.; Valkonen, A.; Rissanen, K.; Lützen, A.; Paulus, B.; Schalley, C. A. Chiroptical inversion of a planar chiral redox-switchable rotaxane. Chem. Sci. 2019, 10, 10003– 10009, DOI: 10.1039/C9SC03694F9fhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhs12qsr3F&md5=f41698d0b46acbb2dd1d0ede427f0c3dChiroptical inversion of a planar chiral redox-switchable rotaxaneGaedke, Marius; Witte, Felix; Anhaeuser, Jana; Hupatz, Henrik; Schroeder, Hendrik V.; Valkonen, Arto; Rissanen, Kari; Luetzen, Arne; Paulus, Beate; Schalley, Christoph A.Chemical Science (2019), 10 (43), 10003-10009CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)A tetrathiafulvalene (TTF)-contg. crown ether macrocycle with Cs symmetry was designed to implement planar chirality into a redox-active [2]rotaxane. The directionality of the macrocycle atom sequence together with the non-sym. axle renders the corresponding [2]rotaxane mech. planar chiral. Enantiomeric sepn. of the [2]rotaxane was achieved by chiral HPLC. The electrochem. properties - caused by the reversible oxidn. of the TTF - are similar to a non-chiral control. Reversible inversion of the main band in the ECD spectra for the individual enantiomers was obsd. after oxidn. Exptl. evidence, conformational anal. and DFT calcns. of the neutral and doubly oxidized species indicate that mainly electronic effects of the oxidn. are responsible for the chiroptical switching. This is the first electrochem. switchable rotaxane with a reversible inversion of the main ECD band.
- 10Bordoli, R.; Goldup, S. M. An efficient approach to mechanically planar chiral rotaxanes. J. Am. Chem. Soc. 2014, 136, 4817– 4820, DOI: 10.1021/ja412715m10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXivFOgsb8%253D&md5=26241c538a08e27cdea71d888a604dbbAn Efficient Approach to Mechanically Planar Chiral RotaxanesBordoli, Robert J.; Goldup, Stephen M.Journal of the American Chemical Society (2014), 136 (13), 4817-4820CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)We describe the first method for prodn. of mech. planar chiral rotaxanes in excellent enantiopurity without the use of chiral sepn. techniques and, for the first time, unambiguously assign the abs. stereochem. of the products. This proof-of-concept study, which employs a chiral pool sugar as the source of asymmetry and a high-yielding active template reaction for mech. bond formation, finally opens the door to detailed investigation of these challenging targets.
- 11Jinks, M. A.; de Juan, A.; Denis, M.; Fletcher, C. J.; Galli, M.; Jamieson, E. M. G.; Modicom, F.; Zhang, Z.; Goldup, S. M. Stereoselective synthesis of mechanically planar chiral rotaxanes. Angew. Chem., Int. Ed. 2018, 57, 14806– 14810, DOI: 10.1002/anie.20180899011https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhvFCktbnN&md5=463a427f8e848aba26919cf18965b0b1Stereoselective Synthesis of Mechanically Planar Chiral RotaxanesJinks, Michael A.; de Juan, Alberto; Denis, Mathieu; Fletcher, Catherine J.; Galli, Marzia; Jamieson, Ellen M. G.; Modicom, Florian; Zhang, Zhihui; Goldup, Stephen M.Angewandte Chemie, International Edition (2018), 57 (45), 14806-14810CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Chiral interlocked mols. in which the mech. bond provides the sole stereogenic unit are typically produced with no control over the mech. stereochem. Here we report a stereoselective approach to mech. planar chiral rotaxanes in up to 98:2 d.r. using a readily available α-amino acid-derived azide. Symmetrization of the covalent stereocenter yields a rotaxane in which the mech. bond provides the only stereogenic element.
- 12Makita, Y.; Kihara, N.; Nakakoji, N.; Takata, T.; Inagaki, S.; Yamamoto, C.; Okamoto, Y. Catalytic asymmetric synthesis and optical resolution of planar chiral rotaxane. Chem. Lett. 2007, 36, 162– 163, DOI: 10.1246/cl.2007.16212https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXpt1GlsQ%253D%253D&md5=a6f7ae113ee30d97a0b38fc0900b8d1bCatalytic asymmetric synthesis and optical resolution of planar chiral rotaxaneMakita, Yoshimasa; Kihara, Nobuhiro; Nakakoji, Naohisa; Takata, Toshikazu; Inagaki, Shinji; Yamamoto, Chiyo; Okamoto, YoshioChemistry Letters (2007), 36 (1), 162-163CODEN: CMLTAG; ISSN:0366-7022. (Chemical Society of Japan)Planar chiral rotaxanes were synthesized from crown ether and secondary ammonium salt via trialkylphosphine-catalyzed acylative end-capping. Their optical resoln. was achieved by chiral HPLC after acylative neutralization of the ammonium group. When optically active phosphine (Me3CPMeCH2)2 was used as the chiral acylation catalyst, optically active rotaxane (4.4% ee) was obtained.
- 13De Bo, G.; Dolphijn, G.; McTernan, C. T.; Leigh, D. A. [2]Rotaxane formation by transition state stabilization. J. Am. Chem. Soc. 2017, 139, 8455– 8457, DOI: 10.1021/jacs.7b0564013https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVSqur%252FO&md5=7123a1ffc8d0440ad6ad0691e596b0fb[2]Rotaxane Formation by Transition State StabilizationDe Bo, Guillaume; Dolphijn, Guillaume; McTernan, Charlie T.; Leigh, David A.Journal of the American Chemical Society (2017), 139 (25), 8455-8457CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)We report on the synthesis of [2]rotaxanes driven by stabilization of the axle-forming transition state. A bifunctional macrocycle, with hydrogen bond donors at one end and acceptors at the other, is used to stabilize the charges that develop during the addn. of a primary amine to a cyclic sulfate.
- 14(a) Fielden, S. D. P.; Leigh, D. A.; McTernan, C. T.; Pérez-Saavedra, B.; Vitorica-Yrezabal, I. J. Spontaneous assembly of rotaxanes from a primary amine, crown ether and electrophile. J. Am. Chem. Soc. 2018, 140, 6049– 6052, DOI: 10.1021/jacs.8b0339414ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXoslygur4%253D&md5=143f336521cd2b5083c42df69971e9c8Spontaneous Assembly of Rotaxanes from a Primary Amine, Crown Ether and ElectrophileFielden, Stephen D. P.; Leigh, David A.; McTernan, Charlie T.; Perez-Saavedra, Borja; Vitorica-Yrezabal, Inigo J.Journal of the American Chemical Society (2018), 140 (19), 6049-6052CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)We report the synthesis of crown ether-ammonium, amide and amine [2]rotaxanes via transition state stabilization of axle-forming reactions. In contrast to the two-step "clipping" and "capping" strategies generally used for rotaxane synthesis, here the components assemble into the interlocked mol. in a single, reagent-less, step under kinetic control. The crown ether accelerates the reaction of the axle-forming components through the cavity to give the threaded product in a form of metal-free active template synthesis. Rotaxane formation can proceed through the stabilization of different transition states featuring 5-coordinate (e.g., SN2) or 4-coordinate (e.g., acylation, Michael addn.) carbon. Examples prepd. using the approach include crown-ether-peptide rotaxanes and switchable mol. shuttles.(b) Tian, C.; Fielden, S. D. P.; Whitehead, G. F. S.; Vitorica-Yrezabal, I. J.; Leigh, D. A. Weak functional group interactions revealed through metal-free active template rotaxane synthesis. Nat. Commun. 2020, 11, 744, DOI: 10.1038/s41467-020-14576-714bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXjs1Oht78%253D&md5=b8e0b875979c58fb67f32c4e332a0387Weak functional group interactions revealed through metal-free active template rotaxane synthesisTian, Chong; Fielden, Stephen D. P.; Whitehead, George F. S.; Vitorica-Yrezabal, Inigo J.; Leigh, David A.Nature Communications (2020), 11 (1), 744CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)Abstr.: Modest functional group interactions can play important roles in mol. recognition, catalysis and self-assembly. However, weakly assocd. binding motifs are often difficult to characterize. Here, we report on the metal-free active template synthesis of [2]rotaxanes in one step, up to 95% yield and >100:1 rotaxane:axle selectivity, from primary amines, crown ethers and a range of C=O, C=S, S(=O)2 and P=O electrophiles. In addn. to being a simple and effective route to a broad range of rotaxanes, the strategy enables 1:1 interactions of crown ethers with various functional groups to be characterized in soln. and the solid state, several of which are too weak - or are disfavored compared to other binding modes - to be obsd. in typical host-guest complexes. The approach may be broadly applicable to the kinetic stabilization and characterization of other weak functional group interactions.
- 15(a) Hogan, J. C.; Gandour, R. D. Structural requirements for glyme catalysis in butylaminolysis of aryl acetates in chlorobenzene. Identification of -OCH2CH2OCH2CH2OCH2CH2O- as the optimal subunit for catalysis. J. Org. Chem. 1991, 56, 2821– 2826, DOI: 10.1021/jo00008a04415ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXhs1egsrg%253D&md5=e8ea46e5508a4c411f6b730e50144047Structural requirements for glyme catalysis in butylaminolysis of aryl acetates in chlorobenzene. Identification of -OCH2CH2OCH2CH2OCH2CH2O- as the optimal subunit for catalysisHogan, John C.; Gandour, Richard D.Journal of Organic Chemistry (1991), 56 (8), 2821-6CODEN: JOCEAH; ISSN:0022-3263.The catalytic behavior of linear (open-chain) polyethers (glymes) in butylaminolysis of 4-nitrophenyl acetate in PhCl was reexamd. A plot of the catalytic rate const. vs. chain length of catalyst indicated that four oxygens in a OCH2CH2OCH2CH2OCH2CH2O subunit are necessary for optimal catalysis. This was confirmed by a Hammett anal., which employed four addnl. aryl acetates. Previous studies were incorrect because of impurities in the glymes. The Hammett study supported the conclusions of others that breakdown of the zwitterionic tetrahedral intermediate is rate-limiting. A specific structure for a glyme-zwitterionic tetrahedral intermediate complex, which contains an ammonium ion that hydrogen bonds to the ether oxygens, was implied.(b) Basilio, N.; García-Río, L.; Mejuto, J. C.; Pérez-Lorenzo, M. A. New reaction pathway in the ester aminolysis catalyzed by glymes and crown ethers. J. Org. Chem. 2006, 71, 4280– 4285, DOI: 10.1021/jo060389u15bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XjslKntrg%253D&md5=bf529e9b807b9896c32784b1bc9f3eadA New Reaction Pathway in the Ester Aminolysis Catalyzed by Glymes and Crown EthersBasilio, Nuno; Garcia-Rio, Luis; Mejuto, Juan C.; Perez-Lorenzo, MoisesJournal of Organic Chemistry (2006), 71 (11), 4280-4285CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)Butylaminolysis of p-nitrophenyl acetate in chlorobenzene in the presence of different kinds of phase-transfer catalysts (crown ethers and glymes) supports the existence of a reaction pathway exhibiting a first-order dependence on the concn. of the phase transfer catalyst and a second-order dependence on the concn. of butylamine. This novel reaction pathway must be included in the mechanism traditionally accepted for the catalysis by phase-transfer agents of aminolysis reactions in aprotic solvents.
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Chiral leaving groups have previously been employed in asymmetric substitution reactions. See:
Lepore, S. D.; Mondal, D. Recent advances in heterolytic nucleofugal leaving groups. Tetrahedron 2007, 63, 5103– 5122, DOI: 10.1016/j.tet.2007.03.04916https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXlt1Gqtb0%253D&md5=c14fc2154ae71160104290742c427ebdRecent advances in heterolytic nucleofugal leaving groupsLepore, Salvatore D.; Mondal, DeboprosadTetrahedron (2007), 63 (24), 5103-5122CODEN: TETRAB; ISSN:0040-4020. (Elsevier Ltd.)A review. This review begins with a discussion of advances in sulfonate and carboxylate-based leaving groups. Also included are organometallic leaving groups, heterocyclic leaving groups, activation-deactivation leaving groups, and nucleophile assisting leaving groups. - 17Heller, D.; Buschmann, H.; Scharf, H.-D. Nonlinear temperature behavior of product ratios in selection processes. Angew. Chem., Int. Ed. Engl. 1996, 35, 1852– 1854, DOI: 10.1002/anie.19961852117https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28Xls1Gqurs%253D&md5=1c478757fcc2cd908334343a7229163aNonlinear temperature behavior of product ratios in selection processesHeller, Detlef; Buschmann, Helmut; Scharf, Hans-DeiterAngewandte Chemie, International Edition in English (1996), 35 (16), 1852-1854CODEN: ACIEAY; ISSN:0570-0833. (VCH)The homogeneous asym. hydrogenation of an amino acid precursor using a rhodium complex catalyst contg. chiral ligands (in which the oxidative addn. of hydrogen is rate detg.) shows a nonlinear temp. dependence of product selectivity due to a change in the concn. ratio of the diastereomeric substrate complex intermediates (formed prior to the rate detg. step) with temp. Other causes for this type of nonlinearity and the applications of the isoinversion principle are discussed.
- 18Cinchona alkaloids in synthesis and catalysis: Ligands, immobilization and organocatalysis; Eui Song, C., Ed.; Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, 2009.There is no corresponding record for this reference.
- 19(a) Hunter, C. A.; Sanders, J. K. M. The nature of π–π interactions. J. Am. Chem. Soc. 1990, 112, 5525– 5534, DOI: 10.1021/ja00170a01619ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3cXksVShur8%253D&md5=ec2815e7f5f04a985e6594a1aad84b6cThe nature of π-π interactionsHunter, Christopher A.; Sanders, Jeremy K. M.Journal of the American Chemical Society (1990), 112 (14), 5525-34CODEN: JACSAT; ISSN:0002-7863.A simple model of the charge distribution in a π-system is used to explain the strong geometrical requirements for interactions between arom. mols. The key feature of the model is that it considers the σ-framework and the π-electrons sep. and demonstrates that net favorable π-π interactions are actually the result of π-σ attractions that overcome π-π repulsions. The calcns. correlate with observations made on porphyrin π-π interactions both in soln. and in the cryst. state. By using an idealized π-atom, some general rules for predicting the geometry of favorable π-π interactions are derived. In particular a favorable offset or slipped geometry is predicted. These rules successfully predict the geometry of intermol. interactions in the crystal structures of arom. mols. and rationalize a range of host-guest phenomena. The theory demonstrates that the electron donor-acceptor concept can be misleading: it is the properties of the atoms at the points of intermol. contact rather than the overall mol. properties which are important.(b) Riwar, L.-J.; Trapp, N.; Kuhn, B.; Diederich, F. Substituent effects in parallel displaced π–π stacking interactions: Distance matters. Angew. Chem., Int. Ed. 2017, 56, 11252– 11257, DOI: 10.1002/anie.20170374419bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXnsV2qsrg%253D&md5=a9b0d6d22c13b54915292feb77c35bbfSubstituent Effects in Parallel-Displaced π-π Stacking Interactions: Distance MattersRiwar, Leslie-Joana; Trapp, Nils; Kuhn, Bernd; Diederich, FrancoisAngewandte Chemie, International Edition (2017), 56 (37), 11252-11257CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Host-guest systems with Rebek imide type receptors and a 2,6-di(isobutyramido)pyridine ligand were employed to investigate substituent effects in parallel-displaced π-π stacking interactions. Changing the intermol. distance between the para substituent on the arom. platform of the receptor and the pyridine ring of the guest results in a strongly different substituent effect. With a short ethyne-1,2-diyl spacer between the Rebek imide and the arom. platform, partial overlap of substituent and guest stabilizes the π-π stacking interactions independent of the electronic nature of the substituent (Wheeler-Houk model). When the substituent is shifted further away by using a buta-1,3-diyne-1,4-diyl spacer, direct, through-space interactions between substituent and guest are prevented. A linear correlation between logKa (Ka = assocn. const.) and the Hammett substituent const. σpara is obsd., confirming predictions by the Hunter-Sanders model exptl.
- 20Stewart, J. J. P. Optimization of parameters for semiempirical methods V. Modification of NDDO approximations and application to 70 elements. J. Mol. Model. 2007, 13, 1173– 1213, DOI: 10.1007/s00894-007-0233-420https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXhtlequr7N&md5=7d22928c8e3423f3ca8f2e7c77e6e6c9Optimization of parameters for semiempirical methods V: modification of NDDO approximations and application to 70 elementsStewart, James J. P.Journal of Molecular Modeling (2007), 13 (12), 1173-1213CODEN: JMMOFK; ISSN:0948-5023. (Springer GmbH)Several modifications that have been made to the NDDO core-core interaction term and to the method of parameter optimization are described. These changes have resulted in a more complete parameter optimization, called PM6, which has, in turn, allowed 70 elements to be parameterized. The av. unsigned error (AUE) between calcd. and ref. heats of formation for 4,492 species was 8.0 kcal mol-1. For the subset of 1,373 compds. involving only the elements H, C, N, O, F, P, S, Cl, and Br, the PM6 AUE was 4.4 kcal mol-1. The equivalent AUE for other methods were: RM1: 5.0, B3LYP 6-31G*: 5.2, PM5: 5.7, PM3: 6.3, HF 6-31G*: 7.4, and AM1: 10.0 kcal mol-1. Several long-standing faults in AM1 and PM3 have been cor. and significant improvements have been made in the prediction of geometries.
- 21Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, Ö.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, revision D.01; Gaussian, Inc.; Wallingford, CT, 2013.There is no corresponding record for this reference.
- 22(a) Lim, J. Y. C.; Marques, I.; Félix, V.; Beer, P. D. A chiral halogen-bonding [3]rotaxane for the recognition and sensing of biologically relevant dicarboxylate anions. Angew. Chem., Int. Ed. 2018, 57, 584– 588, DOI: 10.1002/anie.20171117622ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvFensbnM&md5=4e268891b96ba85ed20cc8b0ae3f5065A Chiral Halogen-Bonding [3]Rotaxane for the Recognition and Sensing of Biologically Relevant Dicarboxylate AnionsLim, Jason Y. C.; Marques, Igor; Felix, Vitor; Beer, Paul D.Angewandte Chemie, International Edition (2018), 57 (2), 584-588CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)The unprecedented application of a chiral halogen-bonding [3]rotaxane host system for the discrimination of stereo- and E/Z geometric isomers of a dicarboxylate anion guest is described. Synthesized by a chloride anion templation strategy, the [3]rotaxane host recognizes dicarboxylates through the formation of 1:1 stoichiometric sandwich complexes. This process was analyzed by mol. dynamics simulations, which revealed the crit. synergy of halogen and hydrogen bonding interactions in anion discrimination. In addn., the centrally located chiral (S)-BINOL motif of the [3]rotaxane axle component facilitates the complexed dicarboxylate species to be sensed via a fluorescence response.(b) Ba̧k, K. M.; Porfyrakis, K.; Davis, J. J.; Beer, P. D. Exploiting the mechanical bond for molecular recognition and sensing of charged species. Mater. Chem. Front. 2020, 4, 1052– 1073, DOI: 10.1039/C9QM00698B22bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXisVKns7fI&md5=4bc0f8a347f0cf280885149aa598c7fbExploiting the mechanical bond for molecular recognition and sensing of charged speciesBak, Krzysztof M.; Porfyrakis, Kyriakos; Davis, Jason J.; Beer, Paul D.Materials Chemistry Frontiers (2020), 4 (4), 1052-1073CODEN: MCFAC5; ISSN:2052-1537. (Royal Society of Chemistry)A review. The unique properties of the mech. bond have been increasingly used for the purpose of mol. recognition. The recent progress in the development of cation and anion template strategies for the construction of mech. interlocked mols. (MIMs) have resulted in a variety of ion binding catenane and rotaxane host structures. The appropriate integration of reporting redox- and photo-active centers into their structural frameworks can result in prototype mol. sensors for targeting charged species and mol. switches for potential nanotechnol. applications. This review presents progress in the field of MIM hosts for ion recognition and sensing since 2014, focusing on the synthetic approaches employed and mechanisms of host-guest binding and detection.
- 23(a) Fu, X.; Zhang, Q.; Rao, S.-J.; Qu, D.-H.; Tian, H. One-pot synthesis of a [c2]daisy-chain-containing hetero[4]rotaxane via a self-sorting strategy. Chem. Sci. 2016, 7, 1696– 1701, DOI: 10.1039/C5SC04844C23ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XlvFSnug%253D%253D&md5=1311bf6985bf30388fbb8363db8b1d43One-pot synthesis of a [c2]daisy-chain-containing hetero[4]rotaxane via a self-sorting strategyFu, Xin; Zhang, Qi; Rao, Si-Jia; Qu, Da-Hui; Tian, HeChemical Science (2016), 7 (3), 1696-1701CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)Construction and efficient synthesis of hetero[n]rotaxanes with high structural complexity were always attractive challenges. Herein, we demonstrate a facile one-pot prepn. of a hetero[4]rotaxane, by employing a self-sorting strategy, which contains an interpenetrated dibenzo-24-crown-8 (DB24C8) based [c2]daisy chain structure and was ended with a benzo-21-crown-7 (B21C7) based rotaxane at each side. Key to the design involved encoding the selective threading using a steric hindrance-related "language", where highly selective self-assemblies occurred in a three-component self-sorting process, which included the threading of a benzylalkylammonium into a B21C7 and interpenetrated dimerized formation of a DB24C8 based [c2]daisy chain simultaneously; the precise pre-assembled system resulted in the efficient synthesis of hetero[4]rotaxane with a high-level of structural complexity under the "CuAAC" reaction.(b) Rao, S.-J.; Zhang, Q.; Mei, J.; Ye, X.-H.; Gao, C.; Wang, Q.-C.; Qu, D.-H.; Tian, H. One-pot synthesis of hetero[6]rotaxane bearing three different kinds of macrocycle through a self-sorting process. Chem. Sci. 2017, 8, 6777– 6783, DOI: 10.1039/C7SC03232C23bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht1OlsrbK&md5=77896875347a042e516027a6c186c3c6One-pot synthesis of hetero[6]rotaxane bearing three different kinds of macrocycle through a self-sorting processRao, Si-Jia; Zhang, Qi; Mei, Ju; Ye, Xu-Hao; Gao, Chuan; Wang, Qiao-Chun; Qu, Da-Hui; Tian, HeChemical Science (2017), 8 (10), 6777-6783CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)A six-component self-sorting process that involves three types of crown ether macrocycles namely bis(p-phenylene-34-crown-10) (BPP34C10), dibenzo-24-crown-8 (DB24C8) and benzo-21-crown-7 (B21C7) and three types of cation guest mols. namely a 4,4'-bipyridine dication (BPY2+), dibenzylammonium (DBA) and benzylalkylammonium (BAA) ions was carefully and thoroughly investigated. Based on this well-established highly selective six-component self-sorting process, a hetero[6]rotaxane bearing three different kinds of crown ether macrocycle I was designed and successfully synthesized through a facile and efficient one-pot ''click'' stoppering strategy. Such work is proposed to be a significant advance in the construction of mech. interlocked mols. with high structural complexity, as well as a good supplement in the areas of multi-component self-sorting and noncovalent self-assembly.(c) Chen, S.; Wang, Y.; Nie, T.; Bao, C.; Wang, C.; Xu, T.; Lin, Q.; Qu, D.-H.; Gong, X.; Yang, Y.; Zhu, L.; Tian, H. An artificial molecular shuttle operates in lipid bilayers for ion transport. J. Am. Chem. Soc. 2018, 140, 17992– 17998, DOI: 10.1021/jacs.8b0958023chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXit1Cit7bM&md5=aa1dc80fe9cfcddf8cfd9d3c8e98e7a9An Artificial Molecular Shuttle Operates in Lipid Bilayers for Ion TransportChen, Sujun; Wang, Yichuan; Nie, Ting; Bao, Chunyan; Wang, Chenxi; Xu, Tianyi; Lin, Qiuning; Qu, Da-Hui; Gong, Xueqing; Yang, Yi; Zhu, Linyong; Tian, HeJournal of the American Chemical Society (2018), 140 (51), 17992-17998CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Inspired by natural biomol. machines, synthetic mol.-level machines have been proven to perform well-defined mech. tasks and measurable work. To mimic the function of channel proteins, we herein report the development of a synthetic mol. shuttle, [2]rotaxane 3, as a unimol. vehicle that can be inserted into lipid bilayers to perform passive ion transport through its stochastic shuttling motion. The [2]rotaxane mol. shuttle is composed of an amphiphilic mol. thread with three binding stations, which is interlocked in a macrocycle wheel component that tethers a K+ carrier. The structural characteristics enable the rotaxane to transport ions across the lipid bilayers, similar to a cable car, transporting K+ with an EC50 value of 1.0 μM (3.0 mol % relative to lipid). We expect that this simple mol. machine will provide new opportunities for developing more effective and selective ion transporters.(d) Zheng, X.; Zhang, Y.; Cao, N.; Li, X.; Zhang, S.; Du, R.; Wang, H.; Ye, Z.; Wang, Y.; Cao, F.; Li, H.; Hong, X.; Sue, A. C.-H.; Yang, C.; Liu, W.-G.; Li, H. Coulombic-enhanced hetero radical pairing interactions. Nat. Commun. 2018, 9, 1961, DOI: 10.1038/s41467-018-04335-023dhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC1MfksV2rtQ%253D%253D&md5=ad05f0a95e2b5bc61894f64baec97facCoulombic-enhanced hetero radical pairing interactionsZheng Xujun; Zhang Yang; Cao Ning; Li Xin; Zhang Shuoqing; Du Renfeng; Ye Zhenni; Wang Yan; Cao Fahe; Li Haoran; Hong Xin; Li Hao; Zheng Xujun; Yang Chuluo; Wang Haiying; Sue Andrew C-H; Liu Wei-GuangNature communications (2018), 9 (1), 1961 ISSN:.Spin-spin interactions between two identical aromatic radicals have been studied extensively and utilized to establish supramolecular recognition. Here we report that spin-pairing interactions could also take place between two different π-electron radicals, namely a bipyridinium radical cation (BPY(+•)) and a naphthalene-1,8:4,5-bis(dicarboximide) radical anion (NDI((box drawings horizontal)•)). The occurrence of this type of previously unreported hetero radical-pairing interactions is attributed to enhancement effect of Coulombic attraction between these two radicals bearing opposite charges. The Coulombic-enhanced hetero radical pairing interactions are employed to drive host-guest recognition, as well as the reversible switching of a bistable [2]rotaxane.(e) Li, W.-J.; Wang, W.; Wang, X.-Q.; Li, M.; Ke, Y.; Yao, R.; Wen, J.; Yin, G.-Q.; Jiang, B.; Li, X.; Yin, P.; Yang, H. B. Daisy chain dendrimers: Integrated mechanically interlocked molecules with stimuli-induced dimension modulation feature. J. Am. Chem. Soc. 2020, 142, 8473– 8482, DOI: 10.1021/jacs.0c0247523ehttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXnsVyktLk%253D&md5=3584ff44f451edbaf4bf8c436d775c91Daisy Chain Dendrimers: Integrated Mechanically Interlocked Molecules with Stimuli-Induced Dimension Modulation FeatureLi, Wei-Jian; Wang, Wei; Wang, Xu-Qing; Li, Mu; Ke, Yubin; Yao, Rui; Wen, Jin; Yin, Guang-Qiang; Jiang, Bo; Li, Xiaopeng; Yin, Panchao; Yang, Hai-BoJournal of the American Chemical Society (2020), 142 (18), 8473-8482CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The precise construction of the high-order mech. interlocked mols. (MIMs) with well-defined topol. arrangements of multiple mech. interlocked units has been a great challenge. Herein, we present the first successful prepn. of a new family of daisy chain dendrimers, in which the individual [c2]daisy chain rotaxane units serve as the branches of dendrimer skeleton. In particular, the third-generation daisy chain dendrimer with 21 [c2]daisy chain rotaxane moieties was realized, which might be among the most complicated discrete high-order MIMs comprised of multiple [c2]daisy chain rotaxane units. Interestingly, such unique topol. arrangements of multiple stimuli-responsive [c2]daisy chain rotaxanes endowed the resultant daisy chain dendrimers controllable and reversible nanoscale dimension modulation through the collective and amplified extension/contraction of each [c2]daisy chain rotaxane branch upon the addn. of acetate anions or DMSO mols. as external stimulus. Furthermore, on the basis of such an intriguing size switching feature of daisy chain dendrimers, dynamic composite polymer films were constructed through the incorporation of daisy chain dendrimers into polymer films, which could undergo fast, reversible, and controllable shape transformations when DMSO mols. were employed as stimulus. The successful merging of [c2]daisy chain rotaxanes and dendrimers described herein provides not only a brand-new type of high-order mech. interlocked systems with well-defined topol. arrangements of [c2]daisy chain rotaxanes, but also a successful and practical approach toward the construction of supramol. dynamic materials.
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Experimental procedures, synthesis and characterization data, including circular dichroism, chiral HPLC, NMR, MS, and X-ray crystallography data (PDF)
Crystallographic data for 13 (CIF)
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