Photocatalytic Strategy for Decyanative Transformations Enabled by Amine-Ligated Boryl RadicalClick to copy article linkArticle link copied!
- Yuto YoshidaYuto YoshidaDepartment of Life Science and Applied Chemistry, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa-ku, Nagoya 466-8555, JapanMore by Yuto Yoshida
- Waka OkadaWaka OkadaDepartment of Life Science and Applied Chemistry, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa-ku, Nagoya 466-8555, JapanMore by Waka Okada
- Kazutake TakadaKazutake TakadaDepartment of Life Science and Applied Chemistry, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa-ku, Nagoya 466-8555, JapanMore by Kazutake Takada
- Shuichi Nakamura*Shuichi Nakamura*E-mail: [email protected]Department of Life Science and Applied Chemistry, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa-ku, Nagoya 466-8555, JapanMore by Shuichi Nakamura
- Naoki Yasukawa*Naoki Yasukawa*E-mail: [email protected]Department of Life Science and Applied Chemistry, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa-ku, Nagoya 466-8555, JapanMore by Naoki Yasukawa
Abstract
Decyanation after α-functionalization by exploiting the inherent properties of cyano groups enables the strategic assembly of a carbon scaffold. Herein, we demonstrate an amine-ligated boryl radical-mediated cyano group transfer (CGT) strategy of malononitriles under photocatalytic conditions. This strategy allows for the cleavage of C(sp3)–CN and the formation of C(sp3)–D and C(sp3) to realize decyanative deuteration and cyclization via radical-polar crossover. Computational studies successfully demonstrated the reactivity of CGT promoters can be accurately assessed.
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The assembly of molecular complexities is a basic principle of organic chemistry. One goal of this study is to introduce, utilize, and remove functional group (FG) handles on demand. For example, streamlined access to molecular complexity can be achieved by combining FG-facilitated C–C bond construction with structural diversification involving FG-removal (Scheme 1-A). Among the various FGs, the cyano (CN) group is one of the most valuable and powerful activating groups for the functionalization of adjacent carbon atoms owing to its inherent electron-withdrawing properties and coordination ability. (1) Indeed, various protocols based on CN group-handles have been adopted for the total synthesis of (±)-isoretronecanol, (±)-xanthorrhizol, etc. (2) Nevertheless, the decyanation step is generally restricted the applicable substrates and diminishes the tolerance for other functional groups because the high C–CN bond dissociation energy (BDE) leads to the need for harsh conditions (transition metals and strong reductants). (3,4)
Scheme 1
Recently, photoredox catalysis has emerged as a powerful tool for the in situ formation of open-shell radical species under mild reaction conditions. (5) However, the use of organonitriles as radical precursors in (photo)redox chemistry is difficult due to their highly negative reduction potentials [e.g., Ered < −2 V vs saturated calomel electrode (SCE) for dimethylmalononitrile] (Scheme 1-B). To overcome the high negative reduction potential in the decyanation of organonitriles, stoichiometric samarium diiodide (SmI2) in hexamethylphosphoric triamide (HPMA) or organic superelectron donors is required. (6,7)
As an alternative strategy, an open-shell radical-mediated approach has proven to be highly reliable in accessing carbon-centered radicals from alkyl nitriles by homolytic C(sp3)–CN bond cleavage (Scheme 1-B). (8) Roberts discovered the phenomenon in which ammonia-ligated boryl radicals react with alkyl nitriles to form iminyl radicals, after which β-scission can proceed. (8a) However, synthetic applicability of this decyanative process was lacking.
Activated alkyl nitriles, which possess electron-withdrawing group at α-position, are ideal molecules for radical decyanation due to the dramatic improvement of their inherent nature such as BDEs of C–CN (acetonitrile vs malononitrile = 121.1 kcal mol−1 vs 78.9 kcal mol−1). (3) Curran pioneered the CGT process starting from malononitriles, involving a radical chain mechanism based on hydrogen atom transfer (HAT), which was first achieved with toxic tin hydride as a radical mediator. (8b) Thereafter, Curran, Kawamoto, and co-workers developed more environmentally friendly methods using N-heterocyclic borane (NHC-BH3), (8c,d) or tris(trimethylsilyl)silane, (8e) involving the formation of the corresponding radical species in the presence of radical initiators such as azonitriles and peroxides at elevated temperatures. Recently, similar reactions of mononitrile compounds have been achieved using sodium borohydride or NHC-BH3. (9) Very recently, Turlik, Schuppe, and co-workers introduced photoredox/HAT dual catalysis based on a de(iso)cyanation approach using NHC-ligated boryl radicals (Scheme 1-C). (10) Furthermore, from a structural point of view, a π-configuration with the unpaired electron in conjugation with the NHC ring feature in NHC-ligated boryl radicals, resulting in their low nucleophilicity. (11) Because the reactivity of CGT process stemmed from the reaction mechanism that nucleophilic addition of open-shell radicals to electrophilic CN group (Scheme 1-B), we reasoned that strongly nucleophilic boryl-radicals might benefit and exceed the reactivity of NHC-ligated boryl radicals. More importantly, all reported reactions rely on HAT events for preparation of the CGT promoters. Thus, the reaction mode is limited to hydrodecyanation because the in situ generated carbon-centered radicals abstract hydrogen atoms from the heteroatom-centered radical precursors.
We recently became interested in the synthetic potential of amine-ligated boryl radicals, which exhibit high nucleophilicity due to σ-conjugation on a tetrahedral B atom. (12−14) In our previous collaborative work with Leonori, the photocatalytic generation of these species from carboxylic acid-containing boron was exploited in the borylation of π-systems such as olefins and imines and halogen atom transfer (XAT) protocol, demonstrating the unique reactivity of amine-ligated boryl radicals. (14) The ability of amine-ligated boryl radicals to participate in decyanation has been overlooked by the synthetic community, although the possibility was suggested by Roberts. (8a) Thus, we questioned whether amine-ligated boryl radicals can be applied to decyanation and subsequent versatile functionalization based on the photocatalytic strategy, such as radical–polar crossover manifolds, for the assembly of molecular complexes. (15)
Herein, we demonstrate the cyano group transfer (CGT) concept of a mechanically distinct and decyanative transformation (Scheme 1-D). This method integrates an amine-ligated boryl radical-mediated decyanation process with photoredox catalysis and has enabled decyanative deuteration and cyclization by trapping carbanion intermediate.
Based on Roberts’s and Curran’s previous works, (8a,c) we hypothesized that the CGT step proceeds via in situ formation of the iminyl radical (B) by boryl radical addition to dimethylmalononitrile (2a) and subsequent β-fragmentation into the corresponding carbon-centered radical (C) and cyanoborane-amine complex (3). In fact, 3 was observed through 11B NMR monitoring of the reaction between 2a and the amine-ligated boryl radical (A), which was generated in situ in our previous study. (14) Therefore, computational studies were performed to evaluate CGT from 2a to A (Scheme 2-A). Density functional theory (DFT) calculations at the CPCM (DMF) UM06/6-311++G(3d,2p)//UM06/6-31+G(d,p) level of theory indicated that this CGT step is kinetically feasible (ΔG⧧ = +5.2 and +6.3 kcal mol−1 in each step). Notably, the boryl radical addition and β-fragmentation steps are both exothermic, with ΔG° values of −20.3 and −23.9 kcal mol–1, respectively.
Scheme 2
The proposed approach for the decyanative transformation is based on a photoredox catalytic cycle using the boryl radical (A)-mediated CGT process (Scheme 2-B). Initially, oxidative SET from a visible-light-excited photocatalyst (*PC) with the carboxylate formed upon deprotonation of boracarboxylic acid (1) generates a carboxyl radical, which, after subsequent decarboxylation, furnishes the boryl radical (A). This species undergoes CGT with malononitrile derivatives (2), followed by SET between the resulting carbon-centered radical (C) and the reduced photoredox catalyst (PC•–) to provide carbanion (D) while reinitiating the catalytic cycle. Finally, D reacts with the electrophiles to afford the product.
To demonstrate the above-mentioned strategy, we proposed a scenario in which carbanion (D), formed in situ, is trapped by deuterium oxide (D2O) as an electrophile to access α-deuterated nitriles. Due to their low acidity, the synthesis of α-deuterated nitriles, especially α,α-dialkyl-substituted nitriles, is still challenging. (16) The decyanative deuteration of 2 was implemented using boracarboxylic acid (1) as the CGT promoter, 4CzIPN as the photoredox catalyst, potassium carbonate (K2CO3) as the base, and D2O as the electrophile in DMF under irradiation by blue LEDs at room temperature (Scheme 2-C-top). Under these mild conditions, α,α-diphenethyl-substituted malononitrile (2b) was converted into 4b-d in 89% yield with 92% deuterium content (Table S1 in the SI). Based on the literature, (14a,17) the excited state 4CzIPN* (*Ered = +1.35 V vs SCE) would oxidize deprotonated boracarboxylic acid (1; Eox of Cs-salt = +0.38 V vs SCE) in the initiation point of the photoredox catalytic cycle. Furthermore, the reduced 4CzIPN•– (*E1/2 = −1.21 V vs SCE) would be able to smoothly reduce the in situ formed alkyl radical (C) to carbanion (D) (E1/2 of α-cyano radical ≈ −0.7 V vs SCE). (17c) Detailed mechanistic studies, such as light on/off experiments and radical trapping using DMF-d7 as a deuterating agent, imply the radical-polar crossover mechanism to form carbanion (D) (Figure S2 and Scheme S2 in the SI). More importantly, the previously reported decyanation reaction, which proceeds through a radical chain mechanism, using NHC-ligated boryl radical and D2O did not incorporate D atom to the decyanative product (Table S12 in the SI). Overall, these results demonstrate the photocatalytic strategy using 1 is a mechanically distinct concept and the potential for diversification of decyanative transformation.
Next, we evaluated the CGT promoters and their precursors (Scheme 2-C-top; Tables S11 and S12 in the SI). Borane-trimethylamine complex (Me3NBH3) is the simplest radical precursor for A, however, all our attempts to decyanative deuteration using photocatalysis and radical initiators failed. This is most likely due to the inherent properties of Me3NBH3, such as high BDEs of B–H (100.5 kcal mol−1) and redox potential (E1/2ox = +2.60 V vs SCE). (12a,c) Although the NHC-ligated boryl radical and silyl radical-mediated decyanation, which proceed in the presence of a radical initiator at elevated temperature, have been also previously reported, (8c,e) importantly, the use of these radicals instead of Me3N-ligated boryl radical was not successful under the photoredox catalytic conditions (18,19) at room temperature. To further demonstrate the reactivities of the Me3N-ligated boryl, NHC-ligated boryl, and silyl radicals, DFT calculations were performed at the same level as in Scheme 2-A (Scheme 2-C-bottom). The free-energy barriers of the addition step and β-fragmentation step for the Me3N-ligated boryl radical were much less among the evaluated radicals (NHC-ligated boryl radical and trimethylsilyl radical). This difference is attributed to the higher nucleophilicity, higher polarity, and less steric hindrance of the Me3N-ligated boryl radicals.
Control experiments using nondeuterated product (4b) as a starting material revealed that the deuteration of C–H via deprotonation and the HAT event with A is not involved in the reaction mechanism (Scheme 2-D). Computational studies to provide more detailed insight into the chemical properties of 4b also indicated that deprotonation is unfavorable under the standard reaction conditions owing to the low acidity of 4b (pKa = 34). Although HAT of the amine-ligated boryl radicals with the α-proton of nitriles was previously reported, (8a,12b,c) the radical addition of A to 2a is favored compared to the HAT of A with isobutylnitrile (ΔG⧧ = +5.2 kcal/mol vs +11.4 kcal/mol).
With the optimized reaction conditions in hand, the generality of the transformation was evaluated (Scheme 3). The 10-fold scale-up reaction of 2b (1 mmol) could also be successfully performed without loss of yield and D-contents. α,α-Dibenzyl- or α-phenyl-substituted malononitriles and cyclic malononitriles with 5–7 members, cyanoacetic esters, and cyanoacetic amides efficiently underwent the decyanative deuteration to afford the corresponding products (4c-d–4j-d) in good yields with high deuterium contents. Next, we tested the compatibility with useful functionalities using various α-aryl-substituted substrates and demonstrated that electron-rich methyl (4k-d) and methoxy (4l-d) groups, as well as electron-withdrawing fluoro (4m-d) and chloro (4n-d) atoms, at the para-position of each aromatic nucleus were applicable. Substrates with a methoxy group at the ortho or meta position were transformed into the desired deuterated products (4o-d and 4p-d). Furthermore, various types of α-(aryl-methyl)-substituted α-phenethylmalononitrile were screened, and these substrates provided the desired products containing halide (4q-d and 4r-d), trifluoromethyl (4s-d), and cyano (4t-d) functionalities, as well as heterocyclic (4u-d–4x-d) and naphthyl (4y-d) units, in moderate to high yields with high deuterium contents. The effects of the steric hindrance and functional groups on the alkyl motifs were evaluated. As the functional group on the α-carbon of the malononitriles became more sterically bulky, a stepwise decrease in the reactivity was observed (4z-d–4ac-d). Under the present reaction conditions, terminal olefin, alkyl chloride, ester, and cyano functionalities (4ad-d–4ag-d) were tolerated. However, considering the reactivity of boryl radical (A), the CGT strategy of substrates with α-proton and bromine failed because HAT and XAT processes are favored. Furthermore, mononitriles are not applicable for this decyanative deuteration.
Scheme 3
a1.2 equiv of 1 and 1.5 equiv of K2CO3 were used.
b1 mmol of 2 was used.
c100.0 equiv of D2O was used.
To demonstrate the utility of this CGT event, electrophiles were screened instead of D2O. Although trapping in situ generated carbanion (D) with a variety of electrophiles is feasible, in the case of intermolecular reactions, most efforts at intermolecular 1,2- or 1,4-addition did not succeed (up to 23% yield of acetylated adducts). We decided to adapt the CGT process to intramolecular transformations. Recently, a radical-polar crossover approach was applied to the synthesis of cyclopropanes via intramolecular alkylation. (15) These transformations are generally accomplished using two fragments via intermolecular radical addition and subsequent intramolecular alkylation. In contrast, the process developed herein represents a unimolecular fragment transformation, which is a potentially powerful strategy because the starting materials can be easily prepared by α-dialkylation of malononitriles. The reaction conditions were evaluated using α-(2-chloroethyl)-α-phenethyl-substituted malononitrile (2’a) as a starting material in the presence of boracarboxylic acid (1) and 4CzIPN under blue-light irradiation at room temperature (Scheme 4). Cesium fluoride (CsF) in DMA was chosen as the optimal reagent, affording the desired cyclopropane (5a) in 78% yield (Table S3 in the SI). No effect of the electron density on the aromatic ring (5a–5d) or carbon linker (5e–5f) was observed. Although a homolytic substitution between the radical intermediate and alkyl halide is also presumed, poor ability of chlorine as radical leaving group also supports the radical-polar crossover mechanism. (20)
Scheme 4
Inspired by the pioneering work on decarboxylative olefination by Ritter and Wu, (21) we decided to adapt this CGT process to retro-hydrocyanation by merging it with cobalt catalysis. Although retro-hydrocyanation can be achieved via oxidative addition to the C–CN bond and subsequent β-hydride elimination with the aid of nickel and aluminum dual catalysis, a high reaction temperature is typically required owing to the slow-rate of oxidative addition and endothermic nature of the reaction. (22) After the CGT process, the cobaloxime catalyst can trap in situ generated carbon-centered radicals and trigger a dehydrogenation reaction. However, none of the reactions using 1 as the boryl radical precursor afforded the desired unsaturated compounds. Considering the incompatibility of the redox potentials in the reaction system, the incorporation of a HAT catalyst into the catalytic system was explored, based on recent related studies on the Heck-type olefinations of Me3NBH3 using photoredox, cobalt, and HAT hybrid catalysis. (12d) This catalytic protocol was feasible, allowing the retro-hydrocyanation of malononitriles under mild reaction conditions (Table S5 and S6 in the SI; Scheme S5 in the SI for the assumed reaction mechanism); however, all efforts did not succeed in further improving the yield of olefins (6) (Scheme 5).
Scheme 5
In conclusion, a photocatalytic approach for the decyanative transformation of activated alkyl nitriles was developed in which photoredox catalysis was used to generate amine-ligated boryl radicals. This method reduces carbon-centered radical intermediates to carbanion intermediates, which trap the electrophiles (radical-polar crossover manifolds). Furthermore, DFT calculations accurately corroborated the experimentally proven unique reactivity of amine-ligated boryl radicals. Further studies of the CGT reactions are currently ongoing in our laboratory.
Data Availability
The data underlying this study are available in a published article and online Supporting Information.
Supporting Information
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.orglett.4c04701.
Experimental procedures, characterization data for all compounds, 1H, 11B, 13C, and 19F NMR spectra, and DFT calculations (PDF)
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Acknowledgments
This study was partially supported by JSPS KAKENHI (JSPS, numbers JP24K17678 and JP23K19242 to N.Y.) and Takahashi Industrial and Economic Research Foundation to N.Y. Computations were performed at the Research Center for Computational Science, Okazaki, Japan (Project: 24-IMS-C078).
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Photoredox catalysis provides access to reactive radical species under mild conditions from abundant, native functional groups, and, when combined with transition metal catalysis, this feature allows direct coupling of non-traditional nucleophile partners. In addn., photocatalysis can aid fundamental organometallic steps through modulation of the oxidn. state of transition metal complexes or through energy-transfer-mediated excitation of intermediate catalytic species. Metallaphotocatalysis provides access to distinct activation modes, which are complementary to those traditionally used in the field of transition metal catalysis, thereby enabling reaction development through entirely new mechanistic paradigms. This Review discusses key advances in the field of metallaphotocatalysis over the past decade and demonstrates how the unique mechanistic features permit challenging, or previously elusive, transformations to be accomplished.(b) Romero, N. A.; Nicewicz, D. A. Organic Photoredox Catalysis. Chem. Rev. 2016, 116 (17), 10075– 10166, DOI: 10.1021/acs.chemrev.6b00057Google Scholar5bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XpsVSnsrw%253D&md5=82228f21987c3d000c62cf672cdcea82Organic Photoredox CatalysisRomero, Nathan A.; Nicewicz, David A.Chemical Reviews (Washington, DC, United States) (2016), 116 (17), 10075-10166CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review. Use of org. photoredox catalysts in a myriad of synthetic transformations with a range of applications was reviewed. This overview was arranged by catalyst class where the photophysics and electrochem. characteristics of each was discussed to underscore the differences and advantages to each type of single electron redox agent. Net reductive and oxidative as well as redox neutral transformations that could be accomplished using purely org. photoredox-active catalysts was highlighted. An overview of the basic photophysics and electron transfer theory was presented in order to provide a comprehensive guide for employing this class of catalysts in photoredox manifolds.(c) Douglas, J. J.; Sevrin, M. J.; Stephenson, C. R. J. Visible Light Photocatalysis: Applications and New Disconnections in the Synthesis of Pharmaceutical Agents. Org. Process Res. Dev. 2016, 20 (7), 1134– 1147, DOI: 10.1021/acs.oprd.6b00125Google Scholar5chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XptVSht7k%253D&md5=02be4e42349d1175ff3f2b18612a3337Visible Light Photocatalysis: Applications and New Disconnections in the Synthesis of Pharmaceutical AgentsDouglas, James J.; Sevrin, Martin J.; Stephenson, Corey R. J.Organic Process Research & Development (2016), 20 (7), 1134-1147CODEN: OPRDFK; ISSN:1083-6160. (American Chemical Society)Photoredox catalysis has emerged as a powerful tool for the synthetic chemist to access challenging targets and to generate new structural complexity. This review focuses on the application of this mode of catalysis to arrive at known pharmaceutically active compds. Within this setting, the growing synergy with other modes of catalysis, such as nickel/photoredox dual catalysis, as well as pioneering examples utilizing continuous flow to transition photoredox catalysis to preparative scale will be highlighted.(d) Shaw, M. H.; Twilton, J.; MacMillan, D. W. C. Photoredox Catalysis in Organic Chemistry. J. Org. Chem. 2016, 81 (16), 6898– 6926, DOI: 10.1021/acs.joc.6b01449Google Scholar5dhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1Cqs77N&md5=b6ae8ae6e8fe632344b2f0409ad9698bPhotoredox Catalysis in Organic ChemistryShaw, Megan H.; Twilton, Jack; MacMillan, David W. C.Journal of Organic Chemistry (2016), 81 (16), 6898-6926CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)In recent years, photoredox catalysis has come to the forefront in org. chem. as a powerful strategy for the activation of small mols. In a general sense, these approaches rely on the ability of metal complexes and org. dyes to convert visible light into chem. energy by engaging in single-electron transfer with org. substrates, thereby generating reactive intermediates. In this Perspective, we highlight the unique ability of photoredox catalysis to expedite the development of completely new reaction mechanisms, with particular emphasis placed on multicatalytic strategies that enable the construction of challenging carbon-carbon and carbon-heteroatom bonds.(e) Sakakibara, Y.; Murakami, K. Switchable Divergent Synthesis Using Photocatalysis. ACS Catal. 2022, 12 (3), 1857– 1878, DOI: 10.1021/acscatal.1c05318Google Scholar5ehttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XhsFersrg%253D&md5=fc8b21c13c3a4b5625efea21ce04342fSwitchable Divergent Synthesis Using PhotocatalysisSakakibara, Yota; Murakami, KeiACS Catalysis (2022), 12 (3), 1857-1878CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)A review. Highly selective and divergent synthesis enables access to various mols. and has garnered broad interest not only from org. chemists, but also medicinal chemists and biologists who work with chem. libraries. Since the 20th century, such divergent transformations have been achieved using transition-metal-catalyzed reactions, in which the choice of catalyst or ligand crucially affects the selectivity. Over the past several decades, photocatalysts have attracted a considerable amt. of attention because they provide addnl. ways to control the reaction intermediates and product selectivity via electron or energy transfer. From this perspective, authors highlight the recent development of switchable and divergent syntheses using photocatalysts, which are difficult to achieve using classical catalytic transformations.(f) Leitch, J. A.; Rossolini, T.; Rogova, T.; Maitland, J. A. P.; Dixon, D. J. α-Amino Radicals via Photocatalytic Single-Electron Reduction ofImine Derivatives. ACS Catal. 2020, 10 (3), 2009– 2025, DOI: 10.1021/acscatal.9b05011Google ScholarThere is no corresponding record for this reference. - 6Kang, H.-Y.; Hong, W. S.; Cho, Y. S.; Koh, H. Y. Reductive decyanation of α-cyano and α-alkoxycarbonyl substituted nitriles promoted by samarium(II) iodide. Tetrahedron Lett. 1995, 36 (42), 7661– 7664, DOI: 10.1016/0040-4039(95)01606-IGoogle ScholarThere is no corresponding record for this reference.
- 7(a) Doni, E.; Murphy, J. A. Reductive decyanation of malononitriles and cyanoacetates using photoactivated neutral organic super-electron-donors. Org. Chem. Front. 2014, 1 (9), 1072– 1076, DOI: 10.1039/C4QO00202DGoogle ScholarThere is no corresponding record for this reference.(b) Hanson, S. S.; Doni, E.; Traboulsee, K. T.; Coulthard, G.; Murphy, J. A.; Dyker, C. A. Pushing the Limits of Neutral Organic Electron Donors: A Tetra(iminophosphorano)-Substituted Bispyridinylidene. Angew. Chem., Int. Ed. 2015, 54 (38), 11236– 11239, DOI: 10.1002/anie.201505378Google Scholar7bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXht1CiurbM&md5=ccf45f41685781621c941ac406da3fc0Pushing the Limits of Neutral Organic Electron Donors: A Tetra(iminophosphorano)-Substituted BispyridinylideneHanson, Samuel S.; Doni, Eswararao; Traboulsee, Kyle T.; Coulthard, Graeme; Murphy, John A.; Dyker, C. AdamAngewandte Chemie, International Edition (2015), 54 (38), 11236-11239CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)A new ground-state org. electron donor I has been prepd. that features four strongly π-donating iminophosphorano substituents on a bispyridinylidene skeleton. Cyclic voltammetry reveals a record redox potential of -1.70 V vs. SCE (SCE) for the couple involving the neutral org. donor and its dication. This highly reducing org. compd. can be isolated (44 %) or more conveniently generated in situ by a deprotonation reaction involving its readily prepd. pyridinium ion precursor. This donor is able to reduce a variety of aryl halides, and, owing to its redox potential, was found to be the first org. donor to be effective in the thermally induced reductive S-N bond cleavage of N,N-dialkylsulfonamides, and reductive hydrodecyanation of malonitriles.
- 8(a) Paul, V.; Roberts, B. P. Homolytic reactions of ligated boranes. Part 8. Electron spin resonance studies of radicals derived from ligated alkylboranes. J. Chem. Soc., Perkin Trans. 1988, 2 (7), 1183– 1193, DOI: 10.1039/p29880001183Google ScholarThere is no corresponding record for this reference.(b) Curran, D. P.; Seong, C. M. The Tin Hydride Reductive Decyanation of Geminal Dinitriles. Synlett 1991, 1991 (2), 107– 108, DOI: 10.1055/s-1991-20644Google ScholarThere is no corresponding record for this reference.(c) Kawamoto, T.; Geib, S. J.; Curran, D. P. Radical Reactions of N-Heterocyclic Carbene Boranes with Organic Nitriles: Cyanation of NHC-Boranes and Reductive Decyanation of Malononitriles. J. Am. Chem. Soc. 2015, 137 (26), 8617– 8622, DOI: 10.1021/jacs.5b04677Google ScholarThere is no corresponding record for this reference.(d) Bolt, D. A.; Curran, D. P. 1-Butyl-3-methylimidazol-2-ylidene Borane: A Readily Available, Liquid N-Heterocyclic Carbene Borane Reagent. J. Org. Chem. 2017, 82 (24), 13746– 13750, DOI: 10.1021/acs.joc.7b02730Google Scholar8dhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslyrs7jL&md5=c89a5079fadcf9e4e8fe53b3482f35321-Butyl-3-methylimidazol-2-ylidene Borane: A Readily Available, Liquid N-Heterocyclic Carbene Borane ReagentBolt, Daniel A.; Curran, Dennis P.Journal of Organic Chemistry (2017), 82 (24), 13746-13750CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)1-Butyl-3-methylimidazol-2-ylidene borane has been synthesized directly from two inexpensive com. reagents: 1-butyl-3-methylimidazolium bromide and sodium borohydride. This NHC-borane reagent is a stable, free-flowing liq. that shows promise for use in radical, ionic and metal-catalyzed reactions.(e) Kawamoto, T.; Shimaya, Y.; Curran, D. P.; Kamimura, A. Tris(trimethylsilyl)silane-mediated Reductive Decyanation and Cyano Transfer Reactions of Malononitriles. Chem. Lett. 2018, 47 (4), 573– 575, DOI: 10.1246/cl.171231Google ScholarThere is no corresponding record for this reference.
- 9(a) Kawamoto, T.; Oritani, K.; Curran, D. P.; Kamimura, A. Thiol-Catalyzed Radical Decyanation of Aliphatic Nitriles with Sodium Borohydride. Org. Lett. 2018, 20 (7), 2084– 2087, DOI: 10.1021/acs.orglett.8b00626Google ScholarThere is no corresponding record for this reference.(b) Kawamoto, T.; Oritani, K.; Kawabata, A.; Morioka, T.; Matsubara, H.; Kamimura, A. Hydrodecyanation of Secondary Alkyl Nitriles and Malononitriles to Alkanes using DiMeImd-BH3. J. Org. Chem. 2020, 85 (9), 6137– 6142, DOI: 10.1021/acs.joc.0c00105Google ScholarThere is no corresponding record for this reference.
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An example of deisocyanative deuteration using NHC-BD3. However, decyanative deuteration has not been reported.
Jiao, Z.; Jaunich, K. T.; Tao, T.; Gottschall, O.; Hughes, M. M.; Turlik, A.; Schuppe, A. W. Unified Approach to Deamination and Deoxygenation Through Isonitrile Hydrodecyanation: A Combined Experimental and Computational Investigation. Angew. Chem., Int. Ed. 2024, 63 (25), e202405779 DOI: 10.1002/anie.202405779Google ScholarThere is no corresponding record for this reference. - 11Walton, J. C.; Brahmi, M. M.; Fensterbank, L.; Lacôte, E.; Malacria, M.; Chu, Q.; Ueng, S.-H.; Solovyev, A.; Curran, D. P. EPR Studies of the Generation, Structure, and Reactivity of N-Heterocyclic Carbene Borane Radicals. J. Am. Chem. Soc. 2010, 132 (7), 2350– 2358, DOI: 10.1021/ja909502qGoogle Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXht1SgtLk%253D&md5=7424aa377a3479ba54d54c27b3ed1392EPR studies of the generation, structure, and reactivity of N-heterocyclic carbene borane radicalsWalton, John C.; Brahmi, Malika Makhlouf; Fensterbank, Louis; Lacote, Emmanuel; Malacria, Max; Chu, Qianli; Ueng, Shau-Hua; Solovyev, Andrey; Curran, Dennis P.Journal of the American Chemical Society (2010), 132 (7), 2350-2358CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Boryl radicals, stabilized by N-heterocyclic carbene Lewis bases, NHC-BH2· (NHC = 1,3-Ar2-2-imidazolylidene, 1,3-Ar2-2-imidazolidinylidene, 1,3-dimethyl-2-imidazolylidene, 1,3-dimethyl-2-benzimidazolylidene, 4,5,6,7-tetrahydro-1,3-Ar2-2-benzimidazolylidene, where Ar = 2,6-iPr2C6H3, 2,6-Me2-4-tBuC6H2, 2,4,6-Me3C6H2, 4-tBuC6H4, 3,5-Me2C6H3) were derived from the corresponding NHC-borane complexes NHC-BH3 by hydrogen abstraction and studied by EPR spectroscopy and DFT calcns. N-Heterocyclic carbene borane complexes (NHC-boranes) are a new "clean" class of reagents suitable for reductive radical chain transformations. Their structures are well suited for their reactivity to be tuned by inclusion of different NHC ring units and by appropriate placement of diverse substituents. EPR spectra were obtained for the boron-centered radicals generated on removal of one of the BH3 hydrogen atoms. This spectroscopic data, coupled with DFT computations, demonstrated that the NHC-BH2· radicals are planar π-delocalized species. Tert-Butoxyl radicals abstracted hydrogen atoms from NHC-boranes more than 3 orders of magnitude faster than did C-centered radicals, although the rate decreased markedly for sterically shielded NHC-BH3 centers. Combinations of two NHC-boryl radicals afforded 1,2-bis-NHC-diboranes at rates which also depended strongly on steric shielding. The termination rate increased to the diffusion-controlled limit for sterically unhindered NHC-boryls. Bromine atoms were rapidly transferred to imidazole-based NHC-boryl radicals from alkyl, allyl, and benzyl bromides. Chlorine-atom abstraction was, however, much less efficient and only obsd. for sterically unhindered NHC-boryls reacting with allylic and benzylic chlorides. For an NHC-borane contg. a bulky thexyl substituent at boron, the tertiary H atom of the thexyl group was selectively removed. The resulting β-boron-contg. alkyl radical rapidly underwent β scission of the B-C bond with prodn. of an NHC-boryl radical and an alkene.
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Representative recent reports on the reaction using amine-ligated boryl radicals:
(a) Kim, J. H.; Constantin, T.; Simonetti, M.; Llaveria, J.; Sheikh, N. S.; Leonori, D. A radical approach for the selective C–H borylation of azines. Nature 2021, 595, 677– 683, DOI: 10.1038/s41586-021-03637-6Google Scholar12ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhs1Skt7%252FI&md5=c59f9b42b0e161c22289549f23e62645A radical approach for the selective C-H borylation of azinesKim, Ji Hye; Constantin, Timothee; Simonetti, Marco; Llaveria, Josep; Sheikh, Nadeem S.; Leonori, DanieleNature (London, United Kingdom) (2021), 595 (7869), 677-683CODEN: NATUAS; ISSN:0028-0836. (Nature Portfolio)B functional groups are often introduced in place of arom. C-H bonds to expedite small-mol. diversification through coupling of mol. fragments1-3. Current approaches based on transition-metal-catalyzed activation of C-H bonds are effective for the borylation of many (hetero)arom. derivs.4,5 but show narrow applicability to azines (N-contg. arom. heterocycles), which are key components of many pharmaceutical and agrochem. products6. Here the authors report an azine borylation strategy using stable and inexpensive amine-borane7 reagents. Photocatalysis converts these low-mol.-wt. materials into highly reactive boryl radicals8 that undergo efficient addn. to azine building blocks. This reactivity provides a mechanistically alternative tactic for sp2 C-B bond assembly, where the elementary steps of transition-metal-mediated C-H bond activation and reductive elimination from azine-organometallic intermediates are replaced by a direct, Minisci9-style, radical addn. The strongly nucleophilic character of the amine-boryl radicals enables predictable and site-selective C-B bond formation by targeting the azine's most activated position, including the challenging sites adjacent to the basic N atom. This approach enables access to arom. sites that elude current strategies based on C-H bond activation, and led to borylated materials that would otherwise be difficult to prep. The authors have applied this process to the introduction of amine-borane functionalities to complex and industrially relevant products. The diversification of the borylated azine products by mainstream cross-coupling technologies establishes arom. amino-boranes as a powerful class of building blocks for chem. synthesis.(b) Lei, G.; Xu, M.; Chang, R.; Funes-Ardoiz, I.; Ye, J. Hydroalkylation of Unactivated Olefins via Visible-Light-Driven Dual Hydrogen Atom Transfer Catalysis. J. Am. Chem. Soc. 2021, 143 (29), 11251– 11261, DOI: 10.1021/jacs.1c05852Google Scholar12bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhs1Wmtb3L&md5=55cd74e33c55b98ec04c2a810d55c32dHydroalkylation of Unactivated Olefins via Visible-Light-Driven Dual Hydrogen Atom Transfer CatalysisLei, Guangyue; Xu, Meichen; Chang, Rui; Funes-Ardoiz, Ignacio; Ye, JuntaoJournal of the American Chemical Society (2021), 143 (29), 11251-11261CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Radical hydroalkylation of olefins enabled by hydrogen atom transfer (HAT) catalysis represents a straightforward means to access C(sp3)-rich mols. from abundant feedstock chems. without the need for prefunctionalization. While Giese-type hydroalkylation of activated olefins initiated by HAT of hydridic carbon-hydrogen bonds is well-precedented, hydroalkylation of unactivated olefins in a similar fashion remains elusive, primarily owing to a lack of general methods to overcome the inherent polarity-mismatch in this scenario. Here, the use of visible-light-driven dual HAT catalysis to achieve this goal, where catalytic amts. of an amine-borane and an in situ generated thiol were utilized as the hydrogen atom abstractor and donor, resp. is reported. The reaction is completely atom-economical and exhibits a broad scope. Exptl. and computational studies support the proposed mechanism and suggest that hydrogen-bonding between the amine-borane and substrates is beneficial to improving the reaction efficiency.(c) Zhang, Z.-Q.; Sang, Y.-Q.; Wang, C.-Q.; Dai, P.; Xue, X.-S.; Piper, J. L.; Peng, Z.-H.; Ma, J.-A.; Zhang, F.-G.; Wu, J. Difluoromethylation of Unactivated Alkenes Using Freon-22 through Tertiary Amine-Borane-Triggered Halogen Atom Transfer. J. Am. Chem. Soc. 2022, 144 (31), 14288– 14296, DOI: 10.1021/jacs.2c05356Google Scholar12chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XhvFelsbvN&md5=02b51df1073859ed1d110aa520542978Difluoromethylation of Unactivated Alkenes Using Freon-22 through Tertiary Amine-Borane-Triggered Halogen Atom TransferZhang, Zhi-Qi; Sang, Yue-Qian; Wang, Cheng-Qiang; Dai, Peng; Xue, Xiao-Song; Piper, Jared L.; Peng, Zhi-Hui; Ma, Jun-An; Zhang, Fa-Guang; Wu, JieJournal of the American Chemical Society (2022), 144 (31), 14288-14296CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The application of abundant and inexpensive fluorine feedstock sources to synthesize fluorinated compds. is an appealing yet underexplored strategy. Here, authors report a photocatalytic radical hydrodifluoromethylation of unactivated alkenes with an inexpensive industrial chem., chlorodifluoromethane (ClCF2H, Freon-22). This protocol is realized by merging tertiary amine-ligated boryl radical-induced halogen atom transfer (XAT) with organophotoredox catalysis under blue light irradn. A broad scope of readily accessible alkenes featuring a variety of functional groups and drug and natural product moieties could be selectively difluoromethylated with good efficiency in a metal-free manner. Combined exptl. and computational studies suggest that the key XAT process of ClCF2H is both thermodynamically and kinetically favored over the hydrogen atom transfer pathway owing to the formation of a strong boron-chlorine (B-Cl) bond and the low-lying antibonding orbital of the carbon-chlorine (C-Cl) bond.(d) Jiang, H.-W.; Yu, W.-L.; Wang, D.; Xu, P.-F. Photocatalyzed H2-Acceptorless Dehydrogenative Borylation by Using Amine Borane. ACS Catal. 2024, 14 (11), 8666– 8675, DOI: 10.1021/acscatal.4c00401Google ScholarThere is no corresponding record for this reference.(e) Zhang, Z.; Tilby, M. J.; Leonori, D. Boryl radical-mediated halogen-atom transfer enables arylation of alkyl halides with electrophilic and nucleophilic coupling partners. Nat. Synth. 2024, 3, 1221– 1230, DOI: 10.1038/s44160-024-00587-5Google ScholarThere is no corresponding record for this reference.(f) Zhang, Z.; Poletti, L.; Leonori, D. A Radical Strategy for the Alkylation of Amides with Alkyl Halides by Merging Boryl Radical-Mediated Halogen-Atom Transfer and Copper Catalysis. J. Am. Chem. Soc. 2024, 146 (32), 22424– 22430, DOI: 10.1021/jacs.4c05487Google ScholarThere is no corresponding record for this reference.(g) Park, C.; Gi, S.; Yoon, S.; Kwon, S. J.; Lee, S. ChemRxiv 2024. DOI: 10.26434/chemrxiv-2024-4fj46 .Google ScholarThere is no corresponding record for this reference.(h) Jiang, H.-W.; Qin, H.-N.; Wang, A.-L.; Zhang, R.; Xu, P.-F. Photocatalytic Borylation of Imines and Alkenes via Decarboxylation of Trimethylamine Carboxyborane: A New Approach for Generating Boryl Radicals. Org. Lett. 2024, 26 (43), 9282– 9287, DOI: 10.1021/acs.orglett.4c03443Google ScholarThere is no corresponding record for this reference.(i) Corpas, J.; Alonso, M.; Leonori, D. Boryl Radical-Mediated Halogen-Atom Transfer (XAT) Enables the Sonogashira-Like Alkynylation of Alkyl Halides. Chem. Sci. 2024, 15 (45), 19113– 19118, DOI: 10.1039/D4SC06516FGoogle ScholarThere is no corresponding record for this reference. - 13(a) Garwood, J. J. A.; Chen, A. D.; Nagib, D. A. Radical Polarity. J. Am. Chem. Soc. 2024, 146 (41), 28034– 28059, DOI: 10.1021/jacs.4c06774Google ScholarThere is no corresponding record for this reference.(b) Wu, C.; Hou, X.; Zheng, Y.; Li, P.; Lu, D. Electrophilicity and Nucleophilicity of Boryl Radicals. J. Org. Chem. 2017, 82 (6), 2898– 2905, DOI: 10.1021/acs.joc.6b02849Google ScholarThere is no corresponding record for this reference.
- 14(a) Buettner, C. S.; Stavagna, C.; Tilby, M. J.; Górski, B.; Douglas, J. J.; Yasukawa, N.; Leonori, D. Synthesis and Suzuki-Miyaura Cross-Coupling of Alkyl Amine-Boranes. A Boryl Radical-Enabled Strategy. J. Am. Chem. Soc. 2024, 146 (34), 24042– 24052, DOI: 10.1021/jacs.4c07767Google ScholarThere is no corresponding record for this reference.(b) Yasukawa, N.; Naito, S.; Obata, K.; Nakamura, S. Amine-Ligated Boryl Radical-Enabled Hydrofunctionalization of Styrenes via Halogen-Atom Transfer of Alkyl and Aryl Bromides. Synthesis 2024, DOI: 10.1055/a-2427-9313Google ScholarThere is no corresponding record for this reference.
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Recent reviews on the radical–polar crossover approach:
(a) Pitzer, L.; Schwarz, J. L.; Glorius, F. Reductive radical-polar crossover: traditional electrophiles in modern radical reactions. Chem. Sci. 2019, 10 (36), 8285– 8291, DOI: 10.1039/C9SC03359AGoogle Scholar15ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhsFyksbfP&md5=70a31c58fb41d171e85452607442f1dbReductive radical-polar crossover: traditional electrophiles in modern radical reactionsPitzer, Lena; Schwarz, J. Luca; Glorius, FrankChemical Science (2019), 10 (36), 8285-8291CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)A review. The concept of reductive radical-polar crossover (RRPCO) reactions has recently emerged as a valuable and powerful tool to overcome limitations of both radical and traditional polar chem. Esp. in case of addns. to carbonyl compds., the synergy of radical and polar pathways is of great advantage since it enables the use of traditional carbonyl electrophiles in radical reactions. The most recent and synthetically important transformations following this line are summarized in the first part of this review. The second part deals with transformations, in which the concept of RRPCO promotes the usage of alkyl halides as electrophiles in radical reactions.(b) Sharma, S.; Singh, J.; Sharma, A. Visible Light Assisted Radical-Polar/Polar-Radical Crossover Reactions in Organic Synthesis. Adv. Synth. Catal. 2021, 363 (13), 3146– 3169, DOI: 10.1002/adsc.202100205Google Scholar15bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXpsVOitr0%253D&md5=421ea498c6f56872d2f376dd49da7477Visible Light Assisted Radical-Polar/Polar-Radical Crossover Reactions in Organic SynthesisSharma, Shivani; Singh, Jitender; Sharma, AnujAdvanced Synthesis & Catalysis (2021), 363 (13), 3146-3169CODEN: ASCAF7; ISSN:1615-4150. (Wiley-VCH Verlag GmbH & Co. KGaA)A review. Chemists are generally familiar with polar reactions and radical reactions, in comparison are underdeveloped. This methodol. tends to bridge the gap between the radical-polar crossover (RPCO) and polar-radical crossover (PRCO) reactions as well as overcomes limitations of both radical and traditional polar chem. By bringing together the unorthodox chem. of radicals with orthodox carbocations and carbanions, the green quotient of such reactions was significantly improved. The development and shaping up of this area in the last few years in the form of synthetically important transformations was summarised in this review.(c) Liu, M.; Ouyang, X.; Xuan, C.; Shu, C. Advances in photoinduced radical–polar crossover cyclization (RPCC) of bifunctional alkenes. Org. Chem. Front. 2024, 11 (3), 895– 915, DOI: 10.1039/D3QO01929BGoogle ScholarThere is no corresponding record for this reference. - 16(a) Makosza, M.; Judka, M. New Reactions of γ-Halocarbanions: Simple Synthesis of Substituted Tetrahydrofurans. Chem. Eur. J. 2002, 8 (18), 4234– 4240, DOI: 10.1002/1521-3765(20020916)8:18<4234::AID-CHEM4234>3.0.CO;2-GGoogle ScholarThere is no corresponding record for this reference.(b) Krishnakumar, V.; Gunanathan, C. Ruthenium-catalyzed selective a-deuteration of aliphatic nitriles using D2O. Chem. Commun. 2018, 54 (63), 8705– 8708, DOI: 10.1039/C8CC03971BGoogle ScholarThere is no corresponding record for this reference.(c) Zhou, Q.-Q.; Zou, Y.-Q.; Kar, S.; Diskin-Posner, Y.; Ben-David, Y.; Milstein, D. Manganese Pincer Catalyzed Nitrile Hydration, α-Deuteration, and α-Deuterated Amide Formation via Metal Ligand Cooperation. ACS Catal. 2021, 11 (16), 10239– 10245, DOI: 10.1021/acscatal.1c01748Google Scholar16chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhslWltr%252FO&md5=c1bee6703400dc96e3e2ed8687f0fbb5Manganese-Pincer-Catalyzed Nitrile Hydration, α-Deuteration and α-Deuterated Amide Formation via Metal Ligand CooperationZhou, Quan-Quan; Zou, You-Quan; Kar, Sayan; Diskin-Posner, Yael; Ben-David, Yehoshoa; Milstein, DavidACS Catalysis (2021), 11 (16), 10239-10245CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)A simple and efficient system for the hydration and α-deuteration of nitriles to form amides RC(O)NH2 [R = Me, Bn, 4-FC6H4, etc.] and α-deuterated nitriles R1CD2CN [R1 = PhCH2CH2, 3-MeC6H4, 3-pyridyl, etc.] catalyzed by a single pincer complex of the earth-abundant manganese capable of metal-ligand cooperation is reported. The deuteration reaction is selective and tolerates a wide range of functional groups, giving the corresponding amides in moderate to good yields. Changing the solvent from tert-butanol to toluene and using D2O results in formation of α-deuterated nitriles in high selectivity. Moreover, α-deuterated amides can be obtained in one step directly from nitriles and D2O in THF. Preliminary mechanistic studies suggest the transformations contributing toward activation of the nitriles via a metal-ligand cooperative pathway, generating the manganese ketimido and enamido pincer complexes as the key intermediates for further transformations.(d) Gao, Y.; Pink, M.; Carta, V.; Smith, J. M. Ene Reactivity of an Fe = NR Bond Enables the Catalytic α-Deuteration of Nitriles and Alkynes. J. Am. Chem. Soc. 2022, 144 (37), 17165– 17172, DOI: 10.1021/jacs.2c07462Google ScholarThere is no corresponding record for this reference.
- 17(a) Luo, J.; Zhang, J. Donor–Acceptor Fluorophores for Visible-Light-Promoted Organic Synthesis: Photoredox/Ni DualCatalytic C(sp3)–C(sp2) Cross-Coupling. ACS Catal. 2016, 6 (2), 873– 877, DOI: 10.1021/acscatal.5b02204Google Scholar17ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtVGks7w%253D&md5=5a0a4b4dea7900247422ec669f5013eaDonor-Acceptor Fluorophores for Visible-Light-Promoted Organic Synthesis: Photoredox/Ni Dual Catalytic C(sp3)-C(sp2) Cross-CouplingLuo, Jian; Zhang, JianACS Catalysis (2016), 6 (2), 873-877CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)We describe carbazolyl dicyanobenzene (CDCB)-based donor-acceptor (D-A) fluorophores as a class of cheap, easily accessible, and efficient metal-free photoredox catalysts for org. synthesis. By changing the no. and position of carbazolyl and cyano groups on the center benzene ring, CDCBs with a wide range of photoredox potentials are obtained to effectively drive the energetically demanding C(sp3)-C(sp2) cross-coupling of carboxylic acids and alkyltrifluoroborates with aryl halides via a photoredox/Ni dual catalysis mechanism. This work validates the utility of D-A fluorophores in guiding the rational design of metal-free photoredox catalysts for visible-light-promoted org. synthesis.(b) Speckmeier, E.; Fischer, T. G.; Zeitler, K. A Toolbox Approach To Construct Broadly Applicable Metal-Free Catalysts for Photoredox Chemistry: Deliberate Tuning of Redox Potentials and Importance of Halogens in Donor–Acceptor Cyanoarenes. J. Am. Chem. Soc. 2018, 140 (45), 15353– 15365, DOI: 10.1021/jacs.8b08933Google Scholar17bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhvVaqt7bK&md5=96e90165e53cd04bba476e6a28e50d54A Toolbox Approach To Construct Broadly Applicable Metal-Free Catalysts for Photoredox Chemistry: Deliberate Tuning of Redox Potentials and Importance of Halogens in Donor-Acceptor CyanoarenesSpeckmeier, Elisabeth; Fischer, Tillmann G.; Zeitler, KirstenJournal of the American Chemical Society (2018), 140 (45), 15353-15365CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The targeted choice of specific photocatalysts has been shown to play a crit. role for the successful realization of challenging photoredox catalytic transformations. Herein, we demonstrate the successful implementation of a rational design strategy for a series of deliberate structural manipulations of cyanoarene-based, purely org. donor-acceptor photocatalysts, using 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) as a starting point. Systematic modifications of both the donor substituents as well as the acceptors' mol. core allowed us to identify strongly oxidizing as well as strongly reducing catalysts (e.g., for an unprecedented detriflation of unactivated naphthol triflate), which addnl. offer remarkably balanced redox potentials with predictable trends. Esp. halogen arene core substitutions are instrumental for our targeted alterations of the catalysts' redox properties. Based on their preeminent electrochem. and photophys. characteristics, all novel, purely org. photoredox catalysts were evaluated in three challenging, mechanistically distinct classes of benchmark reactions (either requiring balanced, highly oxidizing or strongly reducing properties) to demonstrate their enormous potential as customizable photocatalysts, that outperform and complement prevailing typical best photocatalysts.(c) Bortolamei, N.; Isse, A. A.; Gennaro, A. Estimation of standard reduction potentials of alkyl radicals involved in atom transfer radical polymerization. Electrochim. Acta 2010, 55 (27), 8312– 8318, DOI: 10.1016/j.electacta.2010.02.099Google Scholar17chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtlahsr%252FL&md5=a2656fc0430e4d3553dd37eeb4caa062Estimation of standard reduction potentials of alkyl radicals involved in atom transfer radical polymerizationBortolamei, Nicola; Isse, Abdirisak A.; Gennaro, ArmandoElectrochimica Acta (2010), 55 (27), 8312-8318CODEN: ELCAAV; ISSN:0013-4686. (Elsevier B.V.)The redox properties of some alkyl radicals, which are important in atom transfer radical polymn. both as initiators and mimics of the propagating radical chains, have been investigated in CH3CN by an indirect electrochem. method based on homogeneous redox catalysis involving alkyl halides (RX) and electrogenerated arom. or heteroarom. radical anions (D·-). Dissociative electron transfer between RX and D·- yields an intermediate radical (R·), which further reacts with D·- either by radical coupling or by electron transfer. Examn. of the competition between these reactions, which depends on ED°D/D·-/D·-, allows detn. of the std. redn. potential of R· as well as the self-exchange reorganization energy λR·/R-·. The std. redn. potentials obtained for the radicals ·CH2CN, ·CH2CO2Et and ·CH(CH3)CO2Me are -0.72 ± 0.06, -0.63 ± 0.07 and -0.66 ± 0.07 V vs. SCE, resp. Quite high values of λR·/R- (from 122 to 164 kJ mol-1) were found for all radicals, indicating that a significant change of structure accompanies electron transfer to R·.
- 18(a) Xia, P.-J.; Song, D.; Ye, Z.-P.; Hu, Y.-Z.; Xiao, J.-A.; Xiang, H.-Y.; Chen, X.-Q.; Yang, H. Photoinduced Single-Electron Transfer as an Enabling Principle in the Radical Borylation of Alkenes with NHC-Borane. Angew. Chem., Int. Ed. 2020, 59 (17), 6706– 6710, DOI: 10.1002/anie.201913398Google ScholarThere is no corresponding record for this reference.(b) Xia, P.-J.; Ye, Z.-P.; Hu, Y.-Z.; Xiao, J.-A.; Chen, K.; Xiang, H.-Y.; Chen, X.-Q.; Yang, H. Photocatalytic C–F Bond Borylation of Polyfluoroarenes with NHC-boranes. Org. Lett. 2020, 22 (5), 1742– 1747, DOI: 10.1021/acs.orglett.0c00020Google Scholar18bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXivVart7k%253D&md5=59a866fee0f69fcba8a026448306c90aPhotocatalytic C-F Bond Borylation of Polyfluoroarenes with NHC-boranesXia, Peng-Ju; Ye, Zhi-Peng; Hu, Yuan-Zhuo; Xiao, Jun-An; Chen, Kai; Xiang, Hao-Yue; Chen, Xiao-Qing; Yang, HuaOrganic Letters (2020), 22 (5), 1742-1747CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)The first photoredox-catalyzed defluoroborylation of polyfluoroarenes with NHC-BH3 has been facilely achieved at room temp. via a single-electron-transfer (SET)/radical addn. pathway. This new strategy makes full use of the advantage of photoredox catalysis to generate the key boryl radical via direct activation of a B-H bond. Good functional group tolerance and high regioselectivity offer this protocol incomparable advantages in prepg. a wide array of valuable polyfluoroarylboron compds. Moreover, both computational and exptl. studies were performed to illustrate the reaction mechanism.
- 19(a) Xu, N.-X.; Li, B.-X.; Wang, C.; Uchiyama, M. Sila- and Germacarboxylic Acids: Precursors for the Corresponding Silyl and Germyl Radicals. Angew. Chem., Int. Ed. 2020, 59 (26), 10639– 10644, DOI: 10.1002/anie.202003070Google Scholar19ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXntFGiurc%253D&md5=40a4e320732fb029c7392e0402393576Sila- and Germacarboxylic Acids: Precursors for the Corresponding Silyl and Germyl RadicalsXu, Ning-Xin; Li, Bi-Xiao; Wang, Chao; Uchiyama, MasanobuAngewandte Chemie, International Edition (2020), 59 (26), 10639-10644CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Silicon-contg. compds. are widely used as synthetic building blocks, functional materials, and bioactive reagents. In particular, silyl radicals are important intermediates for the synthesis and transformation of organosilicon compds. Herein, we describe the first protocol for the generation of silyl radicals by photoinduced decarboxylation of silacarboxylic acids, which can be easily prepd. in high yield on a gram scale and are very stable to air and moisture. Irradn. of silacarboxylic acids with blue LEDs (455 nm) in the presence of a com. available photocatalyst releases silyl radicals, which can further react with various alkenes to give the corresponding silylated products in good-to-high yields with broad functional-group compatibility. This reaction proceeds in the presence of water, enabling efficient deuterosilylation of alkenes with D2O as the deuterium source. Germyl radicals were similarly obtained.(b) Zhang, G.; Wang, K.; Zhang, D.; Zhang, C.; Tan, W.; Chen, Z.; Chen, F. Decarboxylative Allylation of Silanecarboxylic Acids Enabled by Organophotocatalysis. Org. Lett. 2023, 25 (40), 7406– 7411, DOI: 10.1021/acs.orglett.3c02907Google Scholar19bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3sXitVGrt73E&md5=55e9ba69a54089473b0831cc3810ec3fDecarboxylative Allylation of Silanecarboxylic Acids Enabled by OrganophotocatalysisZhang, Guodong; Wang, Kaiping; Zhang, Duo; Zhang, Chengyu; Tan, Wei; Chen, Zhanzhan; Chen, FengOrganic Letters (2023), 25 (40), 7406-7411CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)Herein the authors present a visible-light-facilitated transition-metal-free allylic silylation reaction under mild conditions. This protocol is enabled by an inexpensive organophotocatalyst and provides efficient and concise synthetic routes to substituted allylsilanes, particularly from readily available allyl sulfones and stable silanecarboxylic acids as silyl radical precursors. Further studies reveal that this strategy is also generally compatible with vinyl sulfones to access vinylsilanes. The Ag catalytic system opens up an alternative entry to realize the decarboxylative allylation of silanecarboxylic acids.
- 20(a) Phelan, J. P.; Lang, S. B.; Compton, J. S.; Kelly, C. B.; Dykstra, R.; Gutierrez, O.; Molander, G. A. Redox-Neutral Photocatalytic Cyclopropanation via Radical/PolarCrossover. J. Am. Chem. Soc. 2018, 140 (25), 8037– 8047, DOI: 10.1021/jacs.8b05243Google ScholarThere is no corresponding record for this reference.(b) Wu, Y.-W.; Tseng, M.-C.; Li, C.-Y.; Chou, H.-H.; Tseng, Y.-F.; Hsieh, H.-J. The Leaving Group Effect in Free Radical SH2’ Reactions. J. Chin. Chem. Soc. 1999, 46 (6), 861– 863, DOI: 10.1002/jccs.199900116Google ScholarThere is no corresponding record for this reference.
- 21(a) Sun, X.; Chen, J.; Ritter, T. Catalytic dehydrogenative decarboxyolefination of carboxylic acids. Nat. Chem. 2018, 10, 1229– 1233, DOI: 10.1038/s41557-018-0142-4Google Scholar21ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhvV2rurnF&md5=dadc15c403fc928c694f2e3cd3ccf88cCatalytic dehydrogenative decarboxyolefination of carboxylic acidsSun, Xiang; Chen, Junting; Ritter, TobiasNature Chemistry (2018), 10 (12), 1229-1233CODEN: NCAHBB; ISSN:1755-4330. (Nature Research)Alkenes are among the most versatile building blocks and are widely used for the prodn. of polymers, detergents and synthetic lubricants. Currently, alkenes are sourced from petroleum feedstocks such as naphtha. In light of the necessity to invent sustainable prodn. methods, multiple approaches to making alkenes from abundant fatty acids have been evaluated. However, all attempts so far have required at least one stoichiometric additive, which is an obstruction for applications at larger scales. Here, we report an approach to making olefins from carboxylic acids, in which every addnl. reaction constituent can be used as a catalyst. We show how abundant fatty acids can be converted to alpha-olefins, and expand the method to include structurally complex carboxylic acids, giving access to synthetically versatile intermediates. Our approach is enabled by the cooperative interplay between a cobalt catalyst, which functions as a proton redn. catalyst, and a photoredox catalyst, which mediates oxidative decarboxylation; coupling both processes enables catalytic conversion of carboxylic acids to olefins.(b) Cao, H.; Jiang, H.; Feng, H.; Kwan, J. M. C.; Liu, X.; Wu, J. Photo-induced Decarboxylative Heck-Type Coupling of Unactivated Aliphatic Acids and Terminal Alkenes in the Absence of Sacrificial Hydrogen Acceptors. J. Am. Chem. Soc. 2018, 140 (47), 16360– 16367, DOI: 10.1021/jacs.8b11218Google Scholar21bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXitFGgsb7P&md5=e8940e5ff0554e8467569ec21389a684Photo-induced Decarboxylative Heck-Type Coupling of Unactivated Aliphatic Acids and Terminal Alkenes in the Absence of Sacrificial Hydrogen AcceptorsCao, Hui; Jiang, Heming; Feng, Hongyu; Kwan, Jeric Mun Chung; Liu, Xiaogang; Wu, JieJournal of the American Chemical Society (2018), 140 (47), 16360-16367CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)1,2-Disubstituted alkenes such as vinyl arenes, vinyl silanes, and vinyl boronates are among the most versatile building blocks that can be found in every sector of chem. science. We herein report a noble-metal-free method of accessing such olefins through a photo-induced decarboxylative Heck-type coupling using alkyl carboxylic acids, one of the most ubiquitous building blocks, as the feedstocks. This transformation was achieved in the absence of external oxidants through the synergistic combination of an organo photo-redox catalyst and a cobaloxime catalyst, with H2 and CO2 as the only byproducts. Both control expts. and DFT calcns. supported a radical-based mechanism, which eventually led to the development of a selective three-component coupling of aliph. carboxylic acids, acrylates, and vinyl arenes. More than 90 olefins across a wide range of functionalities were effectively synthesized with this simple protocol.(c) Dam, P.; Zuo, K.; Azofra, L. M.; El-Sepelgy, O. Biomimetic Photoexcited Cobaloxime Catalysis in Organic Synthesis. Angew. Chem., Int. Ed. 2024, 63 (33), e202405775 DOI: 10.1002/anie.202405775Google ScholarThere is no corresponding record for this reference.
- 22(a) Fang, X.; Yu, P.; Morandi, B. Catalytic reversible alkene-nitrile interconversion through controllable transfer hydrocyanation. Science 2016, 351 (6275), 832– 836, DOI: 10.1126/science.aae0427Google Scholar22ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XisFOjs7c%253D&md5=dd3431972c160fdcf176b245b2d2c695Catalytic reversible alkene-nitrile interconversion through controllable transfer hydrocyanationFang, Xianjie; Yu, Peng; Morandi, BillScience (Washington, DC, United States) (2016), 351 (6275), 832-836CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)A review. Nitriles and alkenes are important synthetic intermediates with complementary reactivity that play a central role in the prepn. of materials, pharmaceuticals, cosmetics, and agrochems. Here, we report a nickel-catalyzed transfer hydrocyanation reaction between a wide range (60 examples) of alkyl nitriles and alkenes. This strategy not only overcomes the toxicity challenge posed by the use of HCN in traditional approaches, but also encompasses distinct chem. advances, including retro-hydrocyanation and anti-Markovnikov regioselectivity. In a broader context, this work highlights an approach to the reversible hydrofunctionalization of alkenes through thermodynamically controlled transfer reactions to circumvent the use of volatile and hazardous reagents in the lab.(b) Yu, P.; Morandi, B. Nickel-Catalyzed Cyanation of Aryl Chlorides and Triflates Using Butyronitrile: Merging Retro-hydrocyanation with Cross-Coupling. Angew. Chem., Int. Ed. 2017, 56 (49), 15693– 15697, DOI: 10.1002/anie.201707517Google ScholarThere is no corresponding record for this reference.(c) Bhawal, B. N.; Morandi, B. Catalytic Transfer Functionalization through Shuttle Catalysis. ACS Catal. 2016, 6 (11), 7528– 7535, DOI: 10.1021/acscatal.6b02333Google Scholar22chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsFKms7zJ&md5=37ef5aa9ad0a29b009b16194d58a7bdbCatalytic Transfer Functionalization through Shuttle CatalysisBhawal, Benjamin N.; Morandi, BillACS Catalysis (2016), 6 (11), 7528-7535CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)In this review, we describe an emerging type of catalysis that enables the catalytic reversible transfer of chem. entities beyond the well-established transfer hydrogenation reactions. Shuttle catalysis facilitates the transfer of small mols. (e.g., CO, HCN) or reactive intermediates between two substrates in an isodesmic process. In many cases, these often safer processes provide unprecedented synthetic flexibility and complement other catalytic bond-forming and bond-breaking reactions.(d) Bhawal, B. N.; Morandi, B. Shuttle Catalysis─New Strategies in Organic Synthesis. Chem. Eur. J. 2017, 23 (50), 12004– 12013, DOI: 10.1002/chem.201605325Google ScholarThere is no corresponding record for this reference.
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Abstract
Scheme 1
Scheme 1. Introduction of Cyano Group Transfer (CGT) and Synthetic ScenarioScheme 2
Scheme 2. Theoretical and Experimental Evaluations of CGT Process and Application to Decyanative DeuterationScheme 3
Scheme 3. Substrate Scopea1.2 equiv of 1 and 1.5 equiv of K2CO3 were used.
b1 mmol of 2 was used.
c100.0 equiv of D2O was used.
Scheme 4
Scheme 4. CGT Strategy for Intramolecular CyclizationScheme 5
Scheme 5. CGT Strategy for Decyanative OlefinationReferences
This article references 22 other publications.
- 1
Selected reviews on the functionalization of nitriles:
(a) Wang, S. Y.; Chu, X.-Q.; Fang, Y.; Ji, S.-J. Chapter 8 Acetonitrile as Reagents in Organic Synthesis: Reactions and Applications. In Solvents as Reagents in Organic Synthesis: Reactions and Applications , 2017; pp 355– 375.There is no corresponding record for this reference.(b) López, R.; Palomo, C. Cyanoalkylation: Alkylnitriles in Catalytic C–C Bond-Forming Reactions. Angew. Chem., Int. Ed. 2015, 54 (45), 13170– 13184, DOI: 10.1002/anie.2015024931bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsFaqs7zK&md5=e750efddbc245ff5a2a6d2a4bad4c837Cyanoalkylation: Alkylnitriles in Catalytic C-C Bond-Forming ReactionsLopez, Rosa; Palomo, ClaudioAngewandte Chemie, International Edition (2015), 54 (45), 13170-13184CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)A review. Alkyl nitriles are one of the most ubiquitous nitrogen-contg. chems. and are widely employed in reactions which result in nitrile-group conversion into other functionalities. Nevertheless, their use as carbon pronucleophiles in carbon-carbon bond-forming reactions has been hampered by difficulties assocd. mainly with the catalytic generation of active species, i.e., α-cyano carbanions or metalated nitriles. Recent investigations have addressed this challenge and have resulted in different modes of alkylnitrile activation. This review illustrates these findings, which have set the foundation for the development of practical and conceptually new catalytic, direct cyanoalkylation methodologies.(c) Chu, X.-Q.; Ge, D.; Shen, Z.-L.; Loh, T.-P. Recent Advances in Radical-Initiated C(sp3)–H Bond Oxidative Functionalization of Alkyl Nitriles. ACS Catal. 2018, 8 (1), 258– 271, DOI: 10.1021/acscatal.7b03334There is no corresponding record for this reference.(d) Zhong, P.; Zhang, L.; Luo, N.; Liu, J. Advances in the Application of Acetonitrile in Organic Synthesis since 2018. Catalysts 2023, 13 (4), 761, DOI: 10.3390/catal13040761There is no corresponding record for this reference. - 2(a) Li, J.; Zhao, H.; Jiang, X.; Wang, X.; Hu, H.; Yu, L.; Zhang, Y. The Cyano Group as a Traceless Activation Group for the Intermolecular [3 + 2] Cycloaddition of Azomethine Ylides: A Five-Step Synthesis of (±)-Isoretronecanol. Angew. Chem., Int. Ed. 2015, 54 (21), 6306– 6310, DOI: 10.1002/anie.201500961There is no corresponding record for this reference.(b) Lujan-Montelongo, J. A.; Covarrubias-Zuniga, A.; Romero-Ortega, M.; Avila-Zarraga, J. G. An Efficient Synthesis of (±)-Xanthorrhizol: One Pot Decyanation and Demethylation. Lett. Org. Chem. 2008, 5 (6), 470– 472, DOI: 10.2174/157017808785740525There is no corresponding record for this reference.
- 3(a) Zavitsas, A. A. The Relation between Bond Lengths and Dissociation Energies of Carbon-Carbon Bonds. J. Phys. Chem. A 2003, 107 (6), 897– 898, DOI: 10.1021/jp02693673ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXjsFKktQ%253D%253D&md5=88bc72045beef047ddd29bc1e468d1b2The Relation between Bond Lengths and Dissociation Energies of Carbon-Carbon BondsZavitsas, Andreas A.Journal of Physical Chemistry A (2003), 107 (6), 897-898CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)Bond lengths (r, Å) of typical carbon-carbon bonds correlate linearly with bond dissocn. energies (BDEs) in the full range of single, double, triple, and highly strained bonds, with BDEs ranging from 16 to 230 kcal mol-1. The equation is r = 1.748-0.002371(BDE), tested with 41 typical carbon-carbon bonds, ranging in length from 1.20 to 1.71 Å. This sets a max. bond length limit of 1.75 Å for carbon-carbon bonds.(b) Lee, J. C.; Koh, H. Y.; Lee, Y. S.; Kang, H.-Y. Geminal substituent Effects on Decyanation Reactions. Bull. Korean Chem. Soc. 1997, 18 (7), 783– 785There is no corresponding record for this reference.
- 4(a) Mattalia, J.-M.; Marchi-Delapierre, C.; Hazimeh, H.; Chanon, M. The reductive decyanation reaction: chemical methods and synthetic applications. Arkivoc 2006, 2006, 90– 118, DOI: 10.3998/ark.5550190.0007.408There is no corresponding record for this reference.(b) Mattalia, J.-M. R. The reductive decyanation reaction: an overview and recent developments. Beilstein J. Org. Chem. 2017, 13, 267– 284, DOI: 10.3762/bjoc.13.304bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXpsFansrw%253D&md5=5bbc1e7fcd8b964eb3e009a0eff2ec2eThe reductive decyanation reaction: an overview and recent developmentsMattalia, Jean-Marc R.Beilstein Journal of Organic Chemistry (2017), 13 (), 267-284CODEN: BJOCBH; ISSN:1860-5397. (Beilstein-Institut zur Foerderung der Chemischen Wissenschaften)A review. This review presents an overview of the reductive decyanation reaction with a special interest for recent developments. This transformation allows synthetic chemists to take advantages of the nitrile functional group before its removal. Mechanistic details and applications to org. synthesis are provided.(c) Paul, N.; Patra, T.; Maiti, D. Recent Developments in Hydrodecyanation and Decyanative Functionalization Reactions. Asian J. Org. Chem. 2022, 11 (1), e202100591 DOI: 10.1002/ajoc.202100591There is no corresponding record for this reference.(d) Nakao, Y. Metal-mediated C–CN Bond Activation in Organic Synthesis. Chem. Rev. 2021, 121 (1), 327– 344, DOI: 10.1021/acs.chemrev.0c00301There is no corresponding record for this reference.
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Recent reviews on the photoredox catalysis:
(a) Twilton, J.; Le, C.; Zhang, P.; Shaw, M. H.; Evans, R. W.; MacMillan, D. W. C. The merger of transition metal and photocatalysis. Nat. Rev. Chem. 2017, 1, 0052, DOI: 10.1038/s41570-017-00525ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtVyksbzJ&md5=6f3cdda2c704c2bdaa298d31604ec0e7The merger of transition metal and photocatalysisTwilton, Jack; Le, Chi; Zhang, Patricia; Shaw, Megan H.; Evans, Ryan W.; MacMillan, David W. C.Nature Reviews Chemistry (2017), 1 (7), 0052CODEN: NRCAF7; ISSN:2397-3358. (Nature Research)A review. The merger of transition metal catalysis and photocatalysis, termed metallaphotocatalysis, has recently emerged as a versatile platform for the development of new, highly enabling synthetic methodologies. Photoredox catalysis provides access to reactive radical species under mild conditions from abundant, native functional groups, and, when combined with transition metal catalysis, this feature allows direct coupling of non-traditional nucleophile partners. In addn., photocatalysis can aid fundamental organometallic steps through modulation of the oxidn. state of transition metal complexes or through energy-transfer-mediated excitation of intermediate catalytic species. Metallaphotocatalysis provides access to distinct activation modes, which are complementary to those traditionally used in the field of transition metal catalysis, thereby enabling reaction development through entirely new mechanistic paradigms. This Review discusses key advances in the field of metallaphotocatalysis over the past decade and demonstrates how the unique mechanistic features permit challenging, or previously elusive, transformations to be accomplished.(b) Romero, N. A.; Nicewicz, D. A. Organic Photoredox Catalysis. Chem. Rev. 2016, 116 (17), 10075– 10166, DOI: 10.1021/acs.chemrev.6b000575bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XpsVSnsrw%253D&md5=82228f21987c3d000c62cf672cdcea82Organic Photoredox CatalysisRomero, Nathan A.; Nicewicz, David A.Chemical Reviews (Washington, DC, United States) (2016), 116 (17), 10075-10166CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review. Use of org. photoredox catalysts in a myriad of synthetic transformations with a range of applications was reviewed. This overview was arranged by catalyst class where the photophysics and electrochem. characteristics of each was discussed to underscore the differences and advantages to each type of single electron redox agent. Net reductive and oxidative as well as redox neutral transformations that could be accomplished using purely org. photoredox-active catalysts was highlighted. An overview of the basic photophysics and electron transfer theory was presented in order to provide a comprehensive guide for employing this class of catalysts in photoredox manifolds.(c) Douglas, J. J.; Sevrin, M. J.; Stephenson, C. R. J. Visible Light Photocatalysis: Applications and New Disconnections in the Synthesis of Pharmaceutical Agents. Org. Process Res. Dev. 2016, 20 (7), 1134– 1147, DOI: 10.1021/acs.oprd.6b001255chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XptVSht7k%253D&md5=02be4e42349d1175ff3f2b18612a3337Visible Light Photocatalysis: Applications and New Disconnections in the Synthesis of Pharmaceutical AgentsDouglas, James J.; Sevrin, Martin J.; Stephenson, Corey R. J.Organic Process Research & Development (2016), 20 (7), 1134-1147CODEN: OPRDFK; ISSN:1083-6160. (American Chemical Society)Photoredox catalysis has emerged as a powerful tool for the synthetic chemist to access challenging targets and to generate new structural complexity. This review focuses on the application of this mode of catalysis to arrive at known pharmaceutically active compds. Within this setting, the growing synergy with other modes of catalysis, such as nickel/photoredox dual catalysis, as well as pioneering examples utilizing continuous flow to transition photoredox catalysis to preparative scale will be highlighted.(d) Shaw, M. H.; Twilton, J.; MacMillan, D. W. C. Photoredox Catalysis in Organic Chemistry. J. Org. Chem. 2016, 81 (16), 6898– 6926, DOI: 10.1021/acs.joc.6b014495dhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht1Cqs77N&md5=b6ae8ae6e8fe632344b2f0409ad9698bPhotoredox Catalysis in Organic ChemistryShaw, Megan H.; Twilton, Jack; MacMillan, David W. C.Journal of Organic Chemistry (2016), 81 (16), 6898-6926CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)In recent years, photoredox catalysis has come to the forefront in org. chem. as a powerful strategy for the activation of small mols. In a general sense, these approaches rely on the ability of metal complexes and org. dyes to convert visible light into chem. energy by engaging in single-electron transfer with org. substrates, thereby generating reactive intermediates. In this Perspective, we highlight the unique ability of photoredox catalysis to expedite the development of completely new reaction mechanisms, with particular emphasis placed on multicatalytic strategies that enable the construction of challenging carbon-carbon and carbon-heteroatom bonds.(e) Sakakibara, Y.; Murakami, K. Switchable Divergent Synthesis Using Photocatalysis. ACS Catal. 2022, 12 (3), 1857– 1878, DOI: 10.1021/acscatal.1c053185ehttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XhsFersrg%253D&md5=fc8b21c13c3a4b5625efea21ce04342fSwitchable Divergent Synthesis Using PhotocatalysisSakakibara, Yota; Murakami, KeiACS Catalysis (2022), 12 (3), 1857-1878CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)A review. Highly selective and divergent synthesis enables access to various mols. and has garnered broad interest not only from org. chemists, but also medicinal chemists and biologists who work with chem. libraries. Since the 20th century, such divergent transformations have been achieved using transition-metal-catalyzed reactions, in which the choice of catalyst or ligand crucially affects the selectivity. Over the past several decades, photocatalysts have attracted a considerable amt. of attention because they provide addnl. ways to control the reaction intermediates and product selectivity via electron or energy transfer. From this perspective, authors highlight the recent development of switchable and divergent syntheses using photocatalysts, which are difficult to achieve using classical catalytic transformations.(f) Leitch, J. A.; Rossolini, T.; Rogova, T.; Maitland, J. A. P.; Dixon, D. J. α-Amino Radicals via Photocatalytic Single-Electron Reduction ofImine Derivatives. ACS Catal. 2020, 10 (3), 2009– 2025, DOI: 10.1021/acscatal.9b05011There is no corresponding record for this reference. - 6Kang, H.-Y.; Hong, W. S.; Cho, Y. S.; Koh, H. Y. Reductive decyanation of α-cyano and α-alkoxycarbonyl substituted nitriles promoted by samarium(II) iodide. Tetrahedron Lett. 1995, 36 (42), 7661– 7664, DOI: 10.1016/0040-4039(95)01606-IThere is no corresponding record for this reference.
- 7(a) Doni, E.; Murphy, J. A. Reductive decyanation of malononitriles and cyanoacetates using photoactivated neutral organic super-electron-donors. Org. Chem. Front. 2014, 1 (9), 1072– 1076, DOI: 10.1039/C4QO00202DThere is no corresponding record for this reference.(b) Hanson, S. S.; Doni, E.; Traboulsee, K. T.; Coulthard, G.; Murphy, J. A.; Dyker, C. A. Pushing the Limits of Neutral Organic Electron Donors: A Tetra(iminophosphorano)-Substituted Bispyridinylidene. Angew. Chem., Int. Ed. 2015, 54 (38), 11236– 11239, DOI: 10.1002/anie.2015053787bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXht1CiurbM&md5=ccf45f41685781621c941ac406da3fc0Pushing the Limits of Neutral Organic Electron Donors: A Tetra(iminophosphorano)-Substituted BispyridinylideneHanson, Samuel S.; Doni, Eswararao; Traboulsee, Kyle T.; Coulthard, Graeme; Murphy, John A.; Dyker, C. AdamAngewandte Chemie, International Edition (2015), 54 (38), 11236-11239CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)A new ground-state org. electron donor I has been prepd. that features four strongly π-donating iminophosphorano substituents on a bispyridinylidene skeleton. Cyclic voltammetry reveals a record redox potential of -1.70 V vs. SCE (SCE) for the couple involving the neutral org. donor and its dication. This highly reducing org. compd. can be isolated (44 %) or more conveniently generated in situ by a deprotonation reaction involving its readily prepd. pyridinium ion precursor. This donor is able to reduce a variety of aryl halides, and, owing to its redox potential, was found to be the first org. donor to be effective in the thermally induced reductive S-N bond cleavage of N,N-dialkylsulfonamides, and reductive hydrodecyanation of malonitriles.
- 8(a) Paul, V.; Roberts, B. P. Homolytic reactions of ligated boranes. Part 8. Electron spin resonance studies of radicals derived from ligated alkylboranes. J. Chem. Soc., Perkin Trans. 1988, 2 (7), 1183– 1193, DOI: 10.1039/p29880001183There is no corresponding record for this reference.(b) Curran, D. P.; Seong, C. M. The Tin Hydride Reductive Decyanation of Geminal Dinitriles. Synlett 1991, 1991 (2), 107– 108, DOI: 10.1055/s-1991-20644There is no corresponding record for this reference.(c) Kawamoto, T.; Geib, S. J.; Curran, D. P. Radical Reactions of N-Heterocyclic Carbene Boranes with Organic Nitriles: Cyanation of NHC-Boranes and Reductive Decyanation of Malononitriles. J. Am. Chem. Soc. 2015, 137 (26), 8617– 8622, DOI: 10.1021/jacs.5b04677There is no corresponding record for this reference.(d) Bolt, D. A.; Curran, D. P. 1-Butyl-3-methylimidazol-2-ylidene Borane: A Readily Available, Liquid N-Heterocyclic Carbene Borane Reagent. J. Org. Chem. 2017, 82 (24), 13746– 13750, DOI: 10.1021/acs.joc.7b027308dhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslyrs7jL&md5=c89a5079fadcf9e4e8fe53b3482f35321-Butyl-3-methylimidazol-2-ylidene Borane: A Readily Available, Liquid N-Heterocyclic Carbene Borane ReagentBolt, Daniel A.; Curran, Dennis P.Journal of Organic Chemistry (2017), 82 (24), 13746-13750CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)1-Butyl-3-methylimidazol-2-ylidene borane has been synthesized directly from two inexpensive com. reagents: 1-butyl-3-methylimidazolium bromide and sodium borohydride. This NHC-borane reagent is a stable, free-flowing liq. that shows promise for use in radical, ionic and metal-catalyzed reactions.(e) Kawamoto, T.; Shimaya, Y.; Curran, D. P.; Kamimura, A. Tris(trimethylsilyl)silane-mediated Reductive Decyanation and Cyano Transfer Reactions of Malononitriles. Chem. Lett. 2018, 47 (4), 573– 575, DOI: 10.1246/cl.171231There is no corresponding record for this reference.
- 9(a) Kawamoto, T.; Oritani, K.; Curran, D. P.; Kamimura, A. Thiol-Catalyzed Radical Decyanation of Aliphatic Nitriles with Sodium Borohydride. Org. Lett. 2018, 20 (7), 2084– 2087, DOI: 10.1021/acs.orglett.8b00626There is no corresponding record for this reference.(b) Kawamoto, T.; Oritani, K.; Kawabata, A.; Morioka, T.; Matsubara, H.; Kamimura, A. Hydrodecyanation of Secondary Alkyl Nitriles and Malononitriles to Alkanes using DiMeImd-BH3. J. Org. Chem. 2020, 85 (9), 6137– 6142, DOI: 10.1021/acs.joc.0c00105There is no corresponding record for this reference.
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An example of deisocyanative deuteration using NHC-BD3. However, decyanative deuteration has not been reported.
Jiao, Z.; Jaunich, K. T.; Tao, T.; Gottschall, O.; Hughes, M. M.; Turlik, A.; Schuppe, A. W. Unified Approach to Deamination and Deoxygenation Through Isonitrile Hydrodecyanation: A Combined Experimental and Computational Investigation. Angew. Chem., Int. Ed. 2024, 63 (25), e202405779 DOI: 10.1002/anie.202405779There is no corresponding record for this reference. - 11Walton, J. C.; Brahmi, M. M.; Fensterbank, L.; Lacôte, E.; Malacria, M.; Chu, Q.; Ueng, S.-H.; Solovyev, A.; Curran, D. P. EPR Studies of the Generation, Structure, and Reactivity of N-Heterocyclic Carbene Borane Radicals. J. Am. Chem. Soc. 2010, 132 (7), 2350– 2358, DOI: 10.1021/ja909502q11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXht1SgtLk%253D&md5=7424aa377a3479ba54d54c27b3ed1392EPR studies of the generation, structure, and reactivity of N-heterocyclic carbene borane radicalsWalton, John C.; Brahmi, Malika Makhlouf; Fensterbank, Louis; Lacote, Emmanuel; Malacria, Max; Chu, Qianli; Ueng, Shau-Hua; Solovyev, Andrey; Curran, Dennis P.Journal of the American Chemical Society (2010), 132 (7), 2350-2358CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Boryl radicals, stabilized by N-heterocyclic carbene Lewis bases, NHC-BH2· (NHC = 1,3-Ar2-2-imidazolylidene, 1,3-Ar2-2-imidazolidinylidene, 1,3-dimethyl-2-imidazolylidene, 1,3-dimethyl-2-benzimidazolylidene, 4,5,6,7-tetrahydro-1,3-Ar2-2-benzimidazolylidene, where Ar = 2,6-iPr2C6H3, 2,6-Me2-4-tBuC6H2, 2,4,6-Me3C6H2, 4-tBuC6H4, 3,5-Me2C6H3) were derived from the corresponding NHC-borane complexes NHC-BH3 by hydrogen abstraction and studied by EPR spectroscopy and DFT calcns. N-Heterocyclic carbene borane complexes (NHC-boranes) are a new "clean" class of reagents suitable for reductive radical chain transformations. Their structures are well suited for their reactivity to be tuned by inclusion of different NHC ring units and by appropriate placement of diverse substituents. EPR spectra were obtained for the boron-centered radicals generated on removal of one of the BH3 hydrogen atoms. This spectroscopic data, coupled with DFT computations, demonstrated that the NHC-BH2· radicals are planar π-delocalized species. Tert-Butoxyl radicals abstracted hydrogen atoms from NHC-boranes more than 3 orders of magnitude faster than did C-centered radicals, although the rate decreased markedly for sterically shielded NHC-BH3 centers. Combinations of two NHC-boryl radicals afforded 1,2-bis-NHC-diboranes at rates which also depended strongly on steric shielding. The termination rate increased to the diffusion-controlled limit for sterically unhindered NHC-boryls. Bromine atoms were rapidly transferred to imidazole-based NHC-boryl radicals from alkyl, allyl, and benzyl bromides. Chlorine-atom abstraction was, however, much less efficient and only obsd. for sterically unhindered NHC-boryls reacting with allylic and benzylic chlorides. For an NHC-borane contg. a bulky thexyl substituent at boron, the tertiary H atom of the thexyl group was selectively removed. The resulting β-boron-contg. alkyl radical rapidly underwent β scission of the B-C bond with prodn. of an NHC-boryl radical and an alkene.
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Representative recent reports on the reaction using amine-ligated boryl radicals:
(a) Kim, J. H.; Constantin, T.; Simonetti, M.; Llaveria, J.; Sheikh, N. S.; Leonori, D. A radical approach for the selective C–H borylation of azines. Nature 2021, 595, 677– 683, DOI: 10.1038/s41586-021-03637-612ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhs1Skt7%252FI&md5=c59f9b42b0e161c22289549f23e62645A radical approach for the selective C-H borylation of azinesKim, Ji Hye; Constantin, Timothee; Simonetti, Marco; Llaveria, Josep; Sheikh, Nadeem S.; Leonori, DanieleNature (London, United Kingdom) (2021), 595 (7869), 677-683CODEN: NATUAS; ISSN:0028-0836. (Nature Portfolio)B functional groups are often introduced in place of arom. C-H bonds to expedite small-mol. diversification through coupling of mol. fragments1-3. Current approaches based on transition-metal-catalyzed activation of C-H bonds are effective for the borylation of many (hetero)arom. derivs.4,5 but show narrow applicability to azines (N-contg. arom. heterocycles), which are key components of many pharmaceutical and agrochem. products6. Here the authors report an azine borylation strategy using stable and inexpensive amine-borane7 reagents. Photocatalysis converts these low-mol.-wt. materials into highly reactive boryl radicals8 that undergo efficient addn. to azine building blocks. This reactivity provides a mechanistically alternative tactic for sp2 C-B bond assembly, where the elementary steps of transition-metal-mediated C-H bond activation and reductive elimination from azine-organometallic intermediates are replaced by a direct, Minisci9-style, radical addn. The strongly nucleophilic character of the amine-boryl radicals enables predictable and site-selective C-B bond formation by targeting the azine's most activated position, including the challenging sites adjacent to the basic N atom. This approach enables access to arom. sites that elude current strategies based on C-H bond activation, and led to borylated materials that would otherwise be difficult to prep. The authors have applied this process to the introduction of amine-borane functionalities to complex and industrially relevant products. The diversification of the borylated azine products by mainstream cross-coupling technologies establishes arom. amino-boranes as a powerful class of building blocks for chem. synthesis.(b) Lei, G.; Xu, M.; Chang, R.; Funes-Ardoiz, I.; Ye, J. Hydroalkylation of Unactivated Olefins via Visible-Light-Driven Dual Hydrogen Atom Transfer Catalysis. J. Am. Chem. Soc. 2021, 143 (29), 11251– 11261, DOI: 10.1021/jacs.1c0585212bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhs1Wmtb3L&md5=55cd74e33c55b98ec04c2a810d55c32dHydroalkylation of Unactivated Olefins via Visible-Light-Driven Dual Hydrogen Atom Transfer CatalysisLei, Guangyue; Xu, Meichen; Chang, Rui; Funes-Ardoiz, Ignacio; Ye, JuntaoJournal of the American Chemical Society (2021), 143 (29), 11251-11261CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Radical hydroalkylation of olefins enabled by hydrogen atom transfer (HAT) catalysis represents a straightforward means to access C(sp3)-rich mols. from abundant feedstock chems. without the need for prefunctionalization. While Giese-type hydroalkylation of activated olefins initiated by HAT of hydridic carbon-hydrogen bonds is well-precedented, hydroalkylation of unactivated olefins in a similar fashion remains elusive, primarily owing to a lack of general methods to overcome the inherent polarity-mismatch in this scenario. Here, the use of visible-light-driven dual HAT catalysis to achieve this goal, where catalytic amts. of an amine-borane and an in situ generated thiol were utilized as the hydrogen atom abstractor and donor, resp. is reported. The reaction is completely atom-economical and exhibits a broad scope. Exptl. and computational studies support the proposed mechanism and suggest that hydrogen-bonding between the amine-borane and substrates is beneficial to improving the reaction efficiency.(c) Zhang, Z.-Q.; Sang, Y.-Q.; Wang, C.-Q.; Dai, P.; Xue, X.-S.; Piper, J. L.; Peng, Z.-H.; Ma, J.-A.; Zhang, F.-G.; Wu, J. Difluoromethylation of Unactivated Alkenes Using Freon-22 through Tertiary Amine-Borane-Triggered Halogen Atom Transfer. J. Am. Chem. Soc. 2022, 144 (31), 14288– 14296, DOI: 10.1021/jacs.2c0535612chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XhvFelsbvN&md5=02b51df1073859ed1d110aa520542978Difluoromethylation of Unactivated Alkenes Using Freon-22 through Tertiary Amine-Borane-Triggered Halogen Atom TransferZhang, Zhi-Qi; Sang, Yue-Qian; Wang, Cheng-Qiang; Dai, Peng; Xue, Xiao-Song; Piper, Jared L.; Peng, Zhi-Hui; Ma, Jun-An; Zhang, Fa-Guang; Wu, JieJournal of the American Chemical Society (2022), 144 (31), 14288-14296CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The application of abundant and inexpensive fluorine feedstock sources to synthesize fluorinated compds. is an appealing yet underexplored strategy. Here, authors report a photocatalytic radical hydrodifluoromethylation of unactivated alkenes with an inexpensive industrial chem., chlorodifluoromethane (ClCF2H, Freon-22). This protocol is realized by merging tertiary amine-ligated boryl radical-induced halogen atom transfer (XAT) with organophotoredox catalysis under blue light irradn. A broad scope of readily accessible alkenes featuring a variety of functional groups and drug and natural product moieties could be selectively difluoromethylated with good efficiency in a metal-free manner. Combined exptl. and computational studies suggest that the key XAT process of ClCF2H is both thermodynamically and kinetically favored over the hydrogen atom transfer pathway owing to the formation of a strong boron-chlorine (B-Cl) bond and the low-lying antibonding orbital of the carbon-chlorine (C-Cl) bond.(d) Jiang, H.-W.; Yu, W.-L.; Wang, D.; Xu, P.-F. Photocatalyzed H2-Acceptorless Dehydrogenative Borylation by Using Amine Borane. ACS Catal. 2024, 14 (11), 8666– 8675, DOI: 10.1021/acscatal.4c00401There is no corresponding record for this reference.(e) Zhang, Z.; Tilby, M. J.; Leonori, D. Boryl radical-mediated halogen-atom transfer enables arylation of alkyl halides with electrophilic and nucleophilic coupling partners. Nat. Synth. 2024, 3, 1221– 1230, DOI: 10.1038/s44160-024-00587-5There is no corresponding record for this reference.(f) Zhang, Z.; Poletti, L.; Leonori, D. A Radical Strategy for the Alkylation of Amides with Alkyl Halides by Merging Boryl Radical-Mediated Halogen-Atom Transfer and Copper Catalysis. J. Am. Chem. Soc. 2024, 146 (32), 22424– 22430, DOI: 10.1021/jacs.4c05487There is no corresponding record for this reference.(g) Park, C.; Gi, S.; Yoon, S.; Kwon, S. J.; Lee, S. ChemRxiv 2024. DOI: 10.26434/chemrxiv-2024-4fj46 .There is no corresponding record for this reference.(h) Jiang, H.-W.; Qin, H.-N.; Wang, A.-L.; Zhang, R.; Xu, P.-F. Photocatalytic Borylation of Imines and Alkenes via Decarboxylation of Trimethylamine Carboxyborane: A New Approach for Generating Boryl Radicals. Org. Lett. 2024, 26 (43), 9282– 9287, DOI: 10.1021/acs.orglett.4c03443There is no corresponding record for this reference.(i) Corpas, J.; Alonso, M.; Leonori, D. Boryl Radical-Mediated Halogen-Atom Transfer (XAT) Enables the Sonogashira-Like Alkynylation of Alkyl Halides. Chem. Sci. 2024, 15 (45), 19113– 19118, DOI: 10.1039/D4SC06516FThere is no corresponding record for this reference. - 13(a) Garwood, J. J. A.; Chen, A. D.; Nagib, D. A. Radical Polarity. J. Am. Chem. Soc. 2024, 146 (41), 28034– 28059, DOI: 10.1021/jacs.4c06774There is no corresponding record for this reference.(b) Wu, C.; Hou, X.; Zheng, Y.; Li, P.; Lu, D. Electrophilicity and Nucleophilicity of Boryl Radicals. J. Org. Chem. 2017, 82 (6), 2898– 2905, DOI: 10.1021/acs.joc.6b02849There is no corresponding record for this reference.
- 14(a) Buettner, C. S.; Stavagna, C.; Tilby, M. J.; Górski, B.; Douglas, J. J.; Yasukawa, N.; Leonori, D. Synthesis and Suzuki-Miyaura Cross-Coupling of Alkyl Amine-Boranes. A Boryl Radical-Enabled Strategy. J. Am. Chem. Soc. 2024, 146 (34), 24042– 24052, DOI: 10.1021/jacs.4c07767There is no corresponding record for this reference.(b) Yasukawa, N.; Naito, S.; Obata, K.; Nakamura, S. Amine-Ligated Boryl Radical-Enabled Hydrofunctionalization of Styrenes via Halogen-Atom Transfer of Alkyl and Aryl Bromides. Synthesis 2024, DOI: 10.1055/a-2427-9313There is no corresponding record for this reference.
- 15
Recent reviews on the radical–polar crossover approach:
(a) Pitzer, L.; Schwarz, J. L.; Glorius, F. Reductive radical-polar crossover: traditional electrophiles in modern radical reactions. Chem. Sci. 2019, 10 (36), 8285– 8291, DOI: 10.1039/C9SC03359A15ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhsFyksbfP&md5=70a31c58fb41d171e85452607442f1dbReductive radical-polar crossover: traditional electrophiles in modern radical reactionsPitzer, Lena; Schwarz, J. Luca; Glorius, FrankChemical Science (2019), 10 (36), 8285-8291CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)A review. The concept of reductive radical-polar crossover (RRPCO) reactions has recently emerged as a valuable and powerful tool to overcome limitations of both radical and traditional polar chem. Esp. in case of addns. to carbonyl compds., the synergy of radical and polar pathways is of great advantage since it enables the use of traditional carbonyl electrophiles in radical reactions. The most recent and synthetically important transformations following this line are summarized in the first part of this review. The second part deals with transformations, in which the concept of RRPCO promotes the usage of alkyl halides as electrophiles in radical reactions.(b) Sharma, S.; Singh, J.; Sharma, A. Visible Light Assisted Radical-Polar/Polar-Radical Crossover Reactions in Organic Synthesis. Adv. Synth. Catal. 2021, 363 (13), 3146– 3169, DOI: 10.1002/adsc.20210020515bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXpsVOitr0%253D&md5=421ea498c6f56872d2f376dd49da7477Visible Light Assisted Radical-Polar/Polar-Radical Crossover Reactions in Organic SynthesisSharma, Shivani; Singh, Jitender; Sharma, AnujAdvanced Synthesis & Catalysis (2021), 363 (13), 3146-3169CODEN: ASCAF7; ISSN:1615-4150. (Wiley-VCH Verlag GmbH & Co. KGaA)A review. Chemists are generally familiar with polar reactions and radical reactions, in comparison are underdeveloped. This methodol. tends to bridge the gap between the radical-polar crossover (RPCO) and polar-radical crossover (PRCO) reactions as well as overcomes limitations of both radical and traditional polar chem. By bringing together the unorthodox chem. of radicals with orthodox carbocations and carbanions, the green quotient of such reactions was significantly improved. The development and shaping up of this area in the last few years in the form of synthetically important transformations was summarised in this review.(c) Liu, M.; Ouyang, X.; Xuan, C.; Shu, C. Advances in photoinduced radical–polar crossover cyclization (RPCC) of bifunctional alkenes. Org. Chem. Front. 2024, 11 (3), 895– 915, DOI: 10.1039/D3QO01929BThere is no corresponding record for this reference. - 16(a) Makosza, M.; Judka, M. New Reactions of γ-Halocarbanions: Simple Synthesis of Substituted Tetrahydrofurans. Chem. Eur. J. 2002, 8 (18), 4234– 4240, DOI: 10.1002/1521-3765(20020916)8:18<4234::AID-CHEM4234>3.0.CO;2-GThere is no corresponding record for this reference.(b) Krishnakumar, V.; Gunanathan, C. Ruthenium-catalyzed selective a-deuteration of aliphatic nitriles using D2O. Chem. Commun. 2018, 54 (63), 8705– 8708, DOI: 10.1039/C8CC03971BThere is no corresponding record for this reference.(c) Zhou, Q.-Q.; Zou, Y.-Q.; Kar, S.; Diskin-Posner, Y.; Ben-David, Y.; Milstein, D. Manganese Pincer Catalyzed Nitrile Hydration, α-Deuteration, and α-Deuterated Amide Formation via Metal Ligand Cooperation. ACS Catal. 2021, 11 (16), 10239– 10245, DOI: 10.1021/acscatal.1c0174816chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhslWltr%252FO&md5=c1bee6703400dc96e3e2ed8687f0fbb5Manganese-Pincer-Catalyzed Nitrile Hydration, α-Deuteration and α-Deuterated Amide Formation via Metal Ligand CooperationZhou, Quan-Quan; Zou, You-Quan; Kar, Sayan; Diskin-Posner, Yael; Ben-David, Yehoshoa; Milstein, DavidACS Catalysis (2021), 11 (16), 10239-10245CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)A simple and efficient system for the hydration and α-deuteration of nitriles to form amides RC(O)NH2 [R = Me, Bn, 4-FC6H4, etc.] and α-deuterated nitriles R1CD2CN [R1 = PhCH2CH2, 3-MeC6H4, 3-pyridyl, etc.] catalyzed by a single pincer complex of the earth-abundant manganese capable of metal-ligand cooperation is reported. The deuteration reaction is selective and tolerates a wide range of functional groups, giving the corresponding amides in moderate to good yields. Changing the solvent from tert-butanol to toluene and using D2O results in formation of α-deuterated nitriles in high selectivity. Moreover, α-deuterated amides can be obtained in one step directly from nitriles and D2O in THF. Preliminary mechanistic studies suggest the transformations contributing toward activation of the nitriles via a metal-ligand cooperative pathway, generating the manganese ketimido and enamido pincer complexes as the key intermediates for further transformations.(d) Gao, Y.; Pink, M.; Carta, V.; Smith, J. M. Ene Reactivity of an Fe = NR Bond Enables the Catalytic α-Deuteration of Nitriles and Alkynes. J. Am. Chem. Soc. 2022, 144 (37), 17165– 17172, DOI: 10.1021/jacs.2c07462There is no corresponding record for this reference.
- 17(a) Luo, J.; Zhang, J. Donor–Acceptor Fluorophores for Visible-Light-Promoted Organic Synthesis: Photoredox/Ni DualCatalytic C(sp3)–C(sp2) Cross-Coupling. ACS Catal. 2016, 6 (2), 873– 877, DOI: 10.1021/acscatal.5b0220417ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtVGks7w%253D&md5=5a0a4b4dea7900247422ec669f5013eaDonor-Acceptor Fluorophores for Visible-Light-Promoted Organic Synthesis: Photoredox/Ni Dual Catalytic C(sp3)-C(sp2) Cross-CouplingLuo, Jian; Zhang, JianACS Catalysis (2016), 6 (2), 873-877CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)We describe carbazolyl dicyanobenzene (CDCB)-based donor-acceptor (D-A) fluorophores as a class of cheap, easily accessible, and efficient metal-free photoredox catalysts for org. synthesis. By changing the no. and position of carbazolyl and cyano groups on the center benzene ring, CDCBs with a wide range of photoredox potentials are obtained to effectively drive the energetically demanding C(sp3)-C(sp2) cross-coupling of carboxylic acids and alkyltrifluoroborates with aryl halides via a photoredox/Ni dual catalysis mechanism. This work validates the utility of D-A fluorophores in guiding the rational design of metal-free photoredox catalysts for visible-light-promoted org. synthesis.(b) Speckmeier, E.; Fischer, T. G.; Zeitler, K. A Toolbox Approach To Construct Broadly Applicable Metal-Free Catalysts for Photoredox Chemistry: Deliberate Tuning of Redox Potentials and Importance of Halogens in Donor–Acceptor Cyanoarenes. J. Am. Chem. Soc. 2018, 140 (45), 15353– 15365, DOI: 10.1021/jacs.8b0893317bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhvVaqt7bK&md5=96e90165e53cd04bba476e6a28e50d54A Toolbox Approach To Construct Broadly Applicable Metal-Free Catalysts for Photoredox Chemistry: Deliberate Tuning of Redox Potentials and Importance of Halogens in Donor-Acceptor CyanoarenesSpeckmeier, Elisabeth; Fischer, Tillmann G.; Zeitler, KirstenJournal of the American Chemical Society (2018), 140 (45), 15353-15365CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The targeted choice of specific photocatalysts has been shown to play a crit. role for the successful realization of challenging photoredox catalytic transformations. Herein, we demonstrate the successful implementation of a rational design strategy for a series of deliberate structural manipulations of cyanoarene-based, purely org. donor-acceptor photocatalysts, using 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) as a starting point. Systematic modifications of both the donor substituents as well as the acceptors' mol. core allowed us to identify strongly oxidizing as well as strongly reducing catalysts (e.g., for an unprecedented detriflation of unactivated naphthol triflate), which addnl. offer remarkably balanced redox potentials with predictable trends. Esp. halogen arene core substitutions are instrumental for our targeted alterations of the catalysts' redox properties. Based on their preeminent electrochem. and photophys. characteristics, all novel, purely org. photoredox catalysts were evaluated in three challenging, mechanistically distinct classes of benchmark reactions (either requiring balanced, highly oxidizing or strongly reducing properties) to demonstrate their enormous potential as customizable photocatalysts, that outperform and complement prevailing typical best photocatalysts.(c) Bortolamei, N.; Isse, A. A.; Gennaro, A. Estimation of standard reduction potentials of alkyl radicals involved in atom transfer radical polymerization. Electrochim. Acta 2010, 55 (27), 8312– 8318, DOI: 10.1016/j.electacta.2010.02.09917chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtlahsr%252FL&md5=a2656fc0430e4d3553dd37eeb4caa062Estimation of standard reduction potentials of alkyl radicals involved in atom transfer radical polymerizationBortolamei, Nicola; Isse, Abdirisak A.; Gennaro, ArmandoElectrochimica Acta (2010), 55 (27), 8312-8318CODEN: ELCAAV; ISSN:0013-4686. (Elsevier B.V.)The redox properties of some alkyl radicals, which are important in atom transfer radical polymn. both as initiators and mimics of the propagating radical chains, have been investigated in CH3CN by an indirect electrochem. method based on homogeneous redox catalysis involving alkyl halides (RX) and electrogenerated arom. or heteroarom. radical anions (D·-). Dissociative electron transfer between RX and D·- yields an intermediate radical (R·), which further reacts with D·- either by radical coupling or by electron transfer. Examn. of the competition between these reactions, which depends on ED°D/D·-/D·-, allows detn. of the std. redn. potential of R· as well as the self-exchange reorganization energy λR·/R-·. The std. redn. potentials obtained for the radicals ·CH2CN, ·CH2CO2Et and ·CH(CH3)CO2Me are -0.72 ± 0.06, -0.63 ± 0.07 and -0.66 ± 0.07 V vs. SCE, resp. Quite high values of λR·/R- (from 122 to 164 kJ mol-1) were found for all radicals, indicating that a significant change of structure accompanies electron transfer to R·.
- 18(a) Xia, P.-J.; Song, D.; Ye, Z.-P.; Hu, Y.-Z.; Xiao, J.-A.; Xiang, H.-Y.; Chen, X.-Q.; Yang, H. Photoinduced Single-Electron Transfer as an Enabling Principle in the Radical Borylation of Alkenes with NHC-Borane. Angew. Chem., Int. Ed. 2020, 59 (17), 6706– 6710, DOI: 10.1002/anie.201913398There is no corresponding record for this reference.(b) Xia, P.-J.; Ye, Z.-P.; Hu, Y.-Z.; Xiao, J.-A.; Chen, K.; Xiang, H.-Y.; Chen, X.-Q.; Yang, H. Photocatalytic C–F Bond Borylation of Polyfluoroarenes with NHC-boranes. Org. Lett. 2020, 22 (5), 1742– 1747, DOI: 10.1021/acs.orglett.0c0002018bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXivVart7k%253D&md5=59a866fee0f69fcba8a026448306c90aPhotocatalytic C-F Bond Borylation of Polyfluoroarenes with NHC-boranesXia, Peng-Ju; Ye, Zhi-Peng; Hu, Yuan-Zhuo; Xiao, Jun-An; Chen, Kai; Xiang, Hao-Yue; Chen, Xiao-Qing; Yang, HuaOrganic Letters (2020), 22 (5), 1742-1747CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)The first photoredox-catalyzed defluoroborylation of polyfluoroarenes with NHC-BH3 has been facilely achieved at room temp. via a single-electron-transfer (SET)/radical addn. pathway. This new strategy makes full use of the advantage of photoredox catalysis to generate the key boryl radical via direct activation of a B-H bond. Good functional group tolerance and high regioselectivity offer this protocol incomparable advantages in prepg. a wide array of valuable polyfluoroarylboron compds. Moreover, both computational and exptl. studies were performed to illustrate the reaction mechanism.
- 19(a) Xu, N.-X.; Li, B.-X.; Wang, C.; Uchiyama, M. Sila- and Germacarboxylic Acids: Precursors for the Corresponding Silyl and Germyl Radicals. Angew. Chem., Int. Ed. 2020, 59 (26), 10639– 10644, DOI: 10.1002/anie.20200307019ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXntFGiurc%253D&md5=40a4e320732fb029c7392e0402393576Sila- and Germacarboxylic Acids: Precursors for the Corresponding Silyl and Germyl RadicalsXu, Ning-Xin; Li, Bi-Xiao; Wang, Chao; Uchiyama, MasanobuAngewandte Chemie, International Edition (2020), 59 (26), 10639-10644CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Silicon-contg. compds. are widely used as synthetic building blocks, functional materials, and bioactive reagents. In particular, silyl radicals are important intermediates for the synthesis and transformation of organosilicon compds. Herein, we describe the first protocol for the generation of silyl radicals by photoinduced decarboxylation of silacarboxylic acids, which can be easily prepd. in high yield on a gram scale and are very stable to air and moisture. Irradn. of silacarboxylic acids with blue LEDs (455 nm) in the presence of a com. available photocatalyst releases silyl radicals, which can further react with various alkenes to give the corresponding silylated products in good-to-high yields with broad functional-group compatibility. This reaction proceeds in the presence of water, enabling efficient deuterosilylation of alkenes with D2O as the deuterium source. Germyl radicals were similarly obtained.(b) Zhang, G.; Wang, K.; Zhang, D.; Zhang, C.; Tan, W.; Chen, Z.; Chen, F. Decarboxylative Allylation of Silanecarboxylic Acids Enabled by Organophotocatalysis. Org. Lett. 2023, 25 (40), 7406– 7411, DOI: 10.1021/acs.orglett.3c0290719bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3sXitVGrt73E&md5=55e9ba69a54089473b0831cc3810ec3fDecarboxylative Allylation of Silanecarboxylic Acids Enabled by OrganophotocatalysisZhang, Guodong; Wang, Kaiping; Zhang, Duo; Zhang, Chengyu; Tan, Wei; Chen, Zhanzhan; Chen, FengOrganic Letters (2023), 25 (40), 7406-7411CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)Herein the authors present a visible-light-facilitated transition-metal-free allylic silylation reaction under mild conditions. This protocol is enabled by an inexpensive organophotocatalyst and provides efficient and concise synthetic routes to substituted allylsilanes, particularly from readily available allyl sulfones and stable silanecarboxylic acids as silyl radical precursors. Further studies reveal that this strategy is also generally compatible with vinyl sulfones to access vinylsilanes. The Ag catalytic system opens up an alternative entry to realize the decarboxylative allylation of silanecarboxylic acids.
- 20(a) Phelan, J. P.; Lang, S. B.; Compton, J. S.; Kelly, C. B.; Dykstra, R.; Gutierrez, O.; Molander, G. A. Redox-Neutral Photocatalytic Cyclopropanation via Radical/PolarCrossover. J. Am. Chem. Soc. 2018, 140 (25), 8037– 8047, DOI: 10.1021/jacs.8b05243There is no corresponding record for this reference.(b) Wu, Y.-W.; Tseng, M.-C.; Li, C.-Y.; Chou, H.-H.; Tseng, Y.-F.; Hsieh, H.-J. The Leaving Group Effect in Free Radical SH2’ Reactions. J. Chin. Chem. Soc. 1999, 46 (6), 861– 863, DOI: 10.1002/jccs.199900116There is no corresponding record for this reference.
- 21(a) Sun, X.; Chen, J.; Ritter, T. Catalytic dehydrogenative decarboxyolefination of carboxylic acids. Nat. Chem. 2018, 10, 1229– 1233, DOI: 10.1038/s41557-018-0142-421ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhvV2rurnF&md5=dadc15c403fc928c694f2e3cd3ccf88cCatalytic dehydrogenative decarboxyolefination of carboxylic acidsSun, Xiang; Chen, Junting; Ritter, TobiasNature Chemistry (2018), 10 (12), 1229-1233CODEN: NCAHBB; ISSN:1755-4330. (Nature Research)Alkenes are among the most versatile building blocks and are widely used for the prodn. of polymers, detergents and synthetic lubricants. Currently, alkenes are sourced from petroleum feedstocks such as naphtha. In light of the necessity to invent sustainable prodn. methods, multiple approaches to making alkenes from abundant fatty acids have been evaluated. However, all attempts so far have required at least one stoichiometric additive, which is an obstruction for applications at larger scales. Here, we report an approach to making olefins from carboxylic acids, in which every addnl. reaction constituent can be used as a catalyst. We show how abundant fatty acids can be converted to alpha-olefins, and expand the method to include structurally complex carboxylic acids, giving access to synthetically versatile intermediates. Our approach is enabled by the cooperative interplay between a cobalt catalyst, which functions as a proton redn. catalyst, and a photoredox catalyst, which mediates oxidative decarboxylation; coupling both processes enables catalytic conversion of carboxylic acids to olefins.(b) Cao, H.; Jiang, H.; Feng, H.; Kwan, J. M. C.; Liu, X.; Wu, J. Photo-induced Decarboxylative Heck-Type Coupling of Unactivated Aliphatic Acids and Terminal Alkenes in the Absence of Sacrificial Hydrogen Acceptors. J. Am. Chem. Soc. 2018, 140 (47), 16360– 16367, DOI: 10.1021/jacs.8b1121821bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXitFGgsb7P&md5=e8940e5ff0554e8467569ec21389a684Photo-induced Decarboxylative Heck-Type Coupling of Unactivated Aliphatic Acids and Terminal Alkenes in the Absence of Sacrificial Hydrogen AcceptorsCao, Hui; Jiang, Heming; Feng, Hongyu; Kwan, Jeric Mun Chung; Liu, Xiaogang; Wu, JieJournal of the American Chemical Society (2018), 140 (47), 16360-16367CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)1,2-Disubstituted alkenes such as vinyl arenes, vinyl silanes, and vinyl boronates are among the most versatile building blocks that can be found in every sector of chem. science. We herein report a noble-metal-free method of accessing such olefins through a photo-induced decarboxylative Heck-type coupling using alkyl carboxylic acids, one of the most ubiquitous building blocks, as the feedstocks. This transformation was achieved in the absence of external oxidants through the synergistic combination of an organo photo-redox catalyst and a cobaloxime catalyst, with H2 and CO2 as the only byproducts. Both control expts. and DFT calcns. supported a radical-based mechanism, which eventually led to the development of a selective three-component coupling of aliph. carboxylic acids, acrylates, and vinyl arenes. More than 90 olefins across a wide range of functionalities were effectively synthesized with this simple protocol.(c) Dam, P.; Zuo, K.; Azofra, L. M.; El-Sepelgy, O. Biomimetic Photoexcited Cobaloxime Catalysis in Organic Synthesis. Angew. Chem., Int. Ed. 2024, 63 (33), e202405775 DOI: 10.1002/anie.202405775There is no corresponding record for this reference.
- 22(a) Fang, X.; Yu, P.; Morandi, B. Catalytic reversible alkene-nitrile interconversion through controllable transfer hydrocyanation. Science 2016, 351 (6275), 832– 836, DOI: 10.1126/science.aae042722ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XisFOjs7c%253D&md5=dd3431972c160fdcf176b245b2d2c695Catalytic reversible alkene-nitrile interconversion through controllable transfer hydrocyanationFang, Xianjie; Yu, Peng; Morandi, BillScience (Washington, DC, United States) (2016), 351 (6275), 832-836CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)A review. Nitriles and alkenes are important synthetic intermediates with complementary reactivity that play a central role in the prepn. of materials, pharmaceuticals, cosmetics, and agrochems. Here, we report a nickel-catalyzed transfer hydrocyanation reaction between a wide range (60 examples) of alkyl nitriles and alkenes. This strategy not only overcomes the toxicity challenge posed by the use of HCN in traditional approaches, but also encompasses distinct chem. advances, including retro-hydrocyanation and anti-Markovnikov regioselectivity. In a broader context, this work highlights an approach to the reversible hydrofunctionalization of alkenes through thermodynamically controlled transfer reactions to circumvent the use of volatile and hazardous reagents in the lab.(b) Yu, P.; Morandi, B. Nickel-Catalyzed Cyanation of Aryl Chlorides and Triflates Using Butyronitrile: Merging Retro-hydrocyanation with Cross-Coupling. Angew. Chem., Int. Ed. 2017, 56 (49), 15693– 15697, DOI: 10.1002/anie.201707517There is no corresponding record for this reference.(c) Bhawal, B. N.; Morandi, B. Catalytic Transfer Functionalization through Shuttle Catalysis. ACS Catal. 2016, 6 (11), 7528– 7535, DOI: 10.1021/acscatal.6b0233322chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsFKms7zJ&md5=37ef5aa9ad0a29b009b16194d58a7bdbCatalytic Transfer Functionalization through Shuttle CatalysisBhawal, Benjamin N.; Morandi, BillACS Catalysis (2016), 6 (11), 7528-7535CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)In this review, we describe an emerging type of catalysis that enables the catalytic reversible transfer of chem. entities beyond the well-established transfer hydrogenation reactions. Shuttle catalysis facilitates the transfer of small mols. (e.g., CO, HCN) or reactive intermediates between two substrates in an isodesmic process. In many cases, these often safer processes provide unprecedented synthetic flexibility and complement other catalytic bond-forming and bond-breaking reactions.(d) Bhawal, B. N.; Morandi, B. Shuttle Catalysis─New Strategies in Organic Synthesis. Chem. Eur. J. 2017, 23 (50), 12004– 12013, DOI: 10.1002/chem.201605325There is no corresponding record for this reference.
Supporting Information
Supporting Information
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.orglett.4c04701.
Experimental procedures, characterization data for all compounds, 1H, 11B, 13C, and 19F NMR spectra, and DFT calculations (PDF)
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