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Copper(I) Iodide Catalyzed [3 + 3] Annulation of Iodonium Ylides with Pyridinium 1,4-Zwitterionic Thiolates for the Synthesis of 1,4-Oxathiin Scaffolds
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Copper(I) Iodide Catalyzed [3 + 3] Annulation of Iodonium Ylides with Pyridinium 1,4-Zwitterionic Thiolates for the Synthesis of 1,4-Oxathiin Scaffolds
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Organic Letters

Cite this: Org. Lett. 2023, 25, 26, 4830–4834
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https://doi.org/10.1021/acs.orglett.3c01538
Published June 26, 2023

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Abstract

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The selective assembly of the 1,4-oxathiin nucleus has been treated as a powerful strategy to access this scaffold present in molecules with very interesting properties. In this study, the chameleon-like reactivity of pyridinium 1,4-zwitterionic thiolates is exploited to assemble the 1,4-oxathiin core through a [3 + 3] annulation. The optimal annulation partner has been found to be the iodonium ylide of the cyclic 1,3-diketones. The developed protocol allows the synthesis of a variety of bicyclic 1,4-oxathiin derivatives under very mild conditions under copper(I) iodide catalysis. Access to benzoannulated 1,4-oxathiins has been achieved through iodine-mediated aromatization of the initially obtained bicyclic compounds.

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The development of novel methodologies for the preparation of sulfur-containing heterocyclic compounds has become a key objective for the synthetic community as these sulfur-based molecules are present in pharmaceutically active molecules, (1a) natural products, (1b) and various functional materials. (1c) Specifically, 1,4-oxathiin containing molecules have drawn great attention as they have a wide array of potential applications, such as fungicides or pesticides, (2a) antiviral, (2b) bioimaging, (2c) anticancer drugs, (2d) and even artificial sweetening agents. (2e)

While several methodologies for the preparation of the benzoannulated derivatives of 1,4-oxathiins have been reported, (3) examples regarding the synthesis of simple 1,4-oxathiins are scarce. A couple of examples report their preparation from ring expansions of 1,3-oxathiolanes, (4) and more recently Khan et al. (2d) utilized copper catalysis to forge this core by the reaction of 4-hydroxydithiocoumarins, arylacetylenes, and DMSO. The synthesis of the 5,6-dihydrogenated-1,4-oxathiin core is a bit more developed and can be for instance accomplished by [4 + 2] annulation as reported by Nishino et al. (5) and Ye et al. (6) or ring expansion of thiiranes with copper carbenes as reported by Xu et al. (7) Nonetheless, given the low quantity of methodologies reported so far, the development of novel transformations for the preparation of these heterocycle derivatives is highly desirable.

Pyridinium 1,4-zwitterionic thiolates (PZTs) (8) can be regarded as air-stable, odorless and easy-to-handle sulfur containing synthons. Depending on the reaction partner, PZTs can engage as 1,3-dipoles in [3+m] annulations if the pyridine moiety acts as a leaving group or as 1,5-dipoles in [5+m] annulations if the pyridine unit remains in the final product. This versatility has accounted for the preparation of a myriad of different sulfur or sulfur and nitrogen containing scaffolds. (9) In this context, we have recently reported the use of predictive catalysis as a tool for designing a novel reaction in which a copper carbene can be trapped with PZTs, furnishing dihydropyridothiazines through a [5 + 1] annulation, which upon oxidation with DDQ and sulfur extrusion, afford indolizine derivatives with high yields (Scheme 1a). (10) Xu et al. also recently reported that diazo(aryl)methyl(diaryl)phosphine oxides react with PZTs to give a [5 + 1] annulation product under blue light irradiation, (11a) but interestingly, benzo[c]thiopyran scaffolds were obtained via [3 + 3] annulation when the reaction was carried out under microwave irradiation (Scheme 1b). (11b) The authors postulate that the [3 + 3] annulation reaction capitalizes from an intramolecular Michael addition of an electron-rich phenyl group in the zwitterionic intermediate formed upon nucleophilic attack of the PZT to the carbene.

Scheme 1

Scheme 1. Different Reaction Modes of PZTs and Carbene or Metallacarbene Species (E = Ester Group)
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The in-depth mechanistic information gained from our previous study prompted us to further explore the reactivity of PZTs in carbene chemistry. Inspired by the low abundance of methodologies available for the preparation of 1,4-oxathiins we envisioned that by modifying the α-oxo metal carbene and the reaction conditions, we could switch the chemoselectivity of the reaction and promote an oxa-Michael addition from the α-oxo carbene that triggers a [3 + 3] annulation toward a 1,4-oxathiin scaffold (Scheme 1c). We thus present here our efforts to achieve a copper catalyzed [3 + 3] annulation between pyridinium 1,4-zwitterionic thiolates and metal carbenes generated in situ from iodonium ylides.

Our study commenced with the reaction of PZT 1a and 2-diazo-5,5-dimethylcyclohexane-1,3-dione (Scheme 2, Z = N2). This cyclic diazo dicarbonyl compound derived from dimedone (12) was chosen because it had been previously described to efficiently engage as a 3-atom reagent in annulation reactions (13) including [3 + 3] annulations. (14) However, when the two compounds were mixed in dichloromethane (DCM) in the presence of 20 mol% of CuI and stirred at 40 °C for 24 h, only starting materials were recovered. Increasing the temperature to 80 °C in dichloroethane (DCE) resulted in the formation of a 36% yield of 1,4-oxathiin derivative 3aa. With the aim to work at milder reaction conditions, we decided to test iodonium ylides as carbene precursors, which are bench-stable, nontoxic, and easy to prepare from the corresponding 1,3-dicarbonyl compounds. (15) 2-(Phenyl-λ3-iodanylidene)cyclohexane-1,3-dione derivatives have also been tested as 3-atom synthons in [3 + 3] annulation reactions, especially in rhodium catalyzed cascades encompassing C–H activation with a directing group, carbene migratory insertion, and annulation. (16) After some optimization with the iodonium ylide derived from 1,3-cyclohexandione (Scheme 2, Z = PhI) we were able to isolate a 56% yield of 1,4-oxathiin 3aa at 40 °C (see the SI for details). It should be noted that a blank reaction without copper showed that the presence of the catalyst is crucial for the reaction to take place.

Scheme 2

Scheme 2. Optimization of the Carbene Precursor Substrate
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After obtaining optimized conditions, we moved to investigate the scope of the reaction (Scheme 3). First, by varying the type of ester in the PZT starting material 1 we were able to synthesize a variety of products (3aa–3ga) with good tolerance of the differing ester groups (Scheme 3). Changing the esters from methyl to ethyl resulted in an increase in the yield (3ba). Further elongating the ester or adding branching reduced the yield to around 40% (3ca–3ea) most likely due to the increased steric interactions. The benzyl ester was also similarly tolerated with a comparable yield (3fa). Finally, the use of a PZT containing a methyl ester next to the pyridinium and a phenyl ketone next to the sulfur (1g), furnished product 3ga in a 25% yield. Considering the added complexity and benefit of being able to obtain an unsymmetric ketone/ester instead of a diester this is a considerable achievement.

Scheme 3

Scheme 3. Scope of the Reactiona,b
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aReaction conditions: 1 (0.1 mmol), 2 (0.3 mmol), CuI (0.02 mmol) in 3.2 mL of dichloromethane at 40 °C for 24 h.

bIsolated yields.

cYield for the reaction at 1 mmol scale.

dORTEP drawing at 50% ellipsoid probability.

After examining the effect of different PZT starting materials, we then moved to the complementary reagent: the iodonium carbene precursor. We examined a range of compounds prepared from cyclic 1,3-diketone analogues. We investigated the effect of the substitution on the ring and the size of the ring (Scheme 3). Using the iodonium prepared from unsubstituted 1,3-cyclohexanedione (2b) resulted in a moderate drop in the yield, highlighting the important role of the substitution in the 5 position. Using 2-(phenyl-λ3-iodanylidene)cyclopentane-1,3-dione 2c the product 3ac was formed in a 70% yield. Reaction of this iodonium ylide with PZT functionalized with different ester groups, such as ethyl and tert-butyl was also evaluated. The reaction with ethyl decorated PZT 1b, gave an excellent 81% yield of the corresponding 1,4-oxathiin, whereas the reaction with bulkier tert-butyl ester substituted 1d furnished 3dc in a 67% yield. Iodonium ylides substituted with aromatic groups in the 5 position were then evaluated. Phenyl substituted substrate 2d gave the product 3ad in a similar yield to that of the dimethyl product 3aa. Further substitution on the aromatic ring itself gave comparable yields (3ae–3ah) with tolerance for different substituents, both electron donating (Me, MeO) and electron withdrawing (Cl, Br), suggesting the ease of the preparation of a large variety of products by the simple variation of the aromatic group. The structure of 3ah could be confirmed by single-crystal X-ray diffraction analysis (CCDC-2260600). For the 4-bromo substituted derivative 2g, we again studied the effect of variation of the ester groups, resulting in similar yields for methyl and ethyl esters and a moderate decrease for the annulation with tert-butyl PZT. Finally, we scaled up the reaction to a 1 mmol scale for the synthesis of 1,4-oxathiin derivatives 3ac and 3ag which gave almost identical yields of 73% and 61%, respectively, proving the scalability of the reaction.

We then examined the possibility of using linear iodonium compounds (Scheme 4). The reaction of PZT 1a with 3-(phenyl-λ3-iodanylidene)pentane-2,4-dione (2i) provided furan 3′ai via formal [3 + 3] annulation followed by a spontaneous and unexpected ring-contraction/sulfur extrusion. (17) It should be noted that a 24% yield of an indolizine was also isolated in this reaction, formed by [5 + 1] annulation followed by formal acetaldehyde elimination and sulfur extrusion, in contrast to all other reactions evaluated where this annulation, reported in our previous study, (10) was never observed. Next, the reaction of the iodonium ylide derived from 1,3-diphenylpropane-1,3-dione (2j) was carried out to give an analogous furan 3′aj in 52% yield together with unidentified products. On the other hand, the reaction with the linear iodonium ylide derived from diethyl malonate (2k) only led to decomposition products, hinting that ester derivatives are not suitable for the reaction.

Scheme 4

Scheme 4. Reaction with Linear Iodonium Ylides
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To show the practical application of the newly developed synthesis, we looked at functionalizing the products further (Scheme 5). We first performed ester hydrolysis, which under basic conditions provided the diacid 5ag in a good yield. This acid was slightly unstable and degraded slowly under standard conditions. We then performed an aromatization reaction, using iodine and potassium carbonate as a base following a procedure previously described for the aromatization of isocoumarine scaffolds. (18) Benzoannulated 1,4-oxathiin scaffold 4ag was obtained in a good 65% yield. We then attempted an iodination reaction of the α-carbonyl position using NIS; (18) however, we observed the subsequent aromatization leading to the same aromatic product 4ag in a slightly lower yield.

Scheme 5

Scheme 5. Further Functionalization of the 1,4-Oxathiin Derivatives
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Based on our previous work and our experimental observations, we propose the mechanism shown in Scheme 6. First, extrusion of iodobenzene in the presence of the copper catalyst yields the copper carbene I. Then the pyridinium 1,4-thiolate 1 nucleophilically attacks carbene I to form the metal bound intermediate II or upon copper release metal unbound intermediate III. The O-enolate nucleophilically attacks, in a conjugate addition, the carbon attached to the pyridinium moiety, effectively displacing pyridine and closing the 1,4-oxathiin ring of 3.

Scheme 6

Scheme 6. Proposed Mechanism for the Reaction of PZTs with Iodonium Ylides
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One possible explanation for the change in selectivity seen using PZTs in copper catalyzed annulations, [3 + 3] in the present study vs [5 + 1] in our previous one (Scheme 1a), (10) is the restricted geometry in intermediate III due to the large cyclic moiety causing an approach of the negatively charged oxygen to the sp2 carbon attached to the pyridinium ring providing easier access to the conjugate addition. This explanation is in line with the previous study by Xu et al. (11b) reporting that an increase of the steric hindrance of the pyridinium ring of the PZT, favored the [3 + 3] annulation over the [5 + 1] annulation with phosphoryl carbenes. Furthermore, we also observe that the two annulations compete when 2j, a more flexible (open-chain) and less sterically congested iodonium ylide, is reacted. However, the higher prevalence of an oxygen centered negative charge in intermediate III (Scheme 6) in comparison to the analogous intermediate in the reaction with acyl carbenes (Scheme 1a), could also explain a more favored conjugated attack of the harder negative oxygen that finally displaces the pyridine group.

In conclusion, we have successfully described a novel synthesis of bicyclic 5,6-dihydrogenated-1,4-oxathiin derivatives through a copper-catalyzed [3 + 3] annulation of PZT and iodonium ylides of cyclic 1,3-dicarbonyl compounds. Linear iodonium ylides afford furan derivatives through complementary ring contraction and sulfur extrusion. The method uses a simple, inexpensive, and stable copper catalyst and runs under mild conditions. The obtained compounds can be transformed to benzoannulated 1,4-oxathiin derivatives through an iodine mediated aromatization. The selectivity in the cyclization of the intermediate formed upon S attack to the carbene has been rationalized based on steric factors.

Data Availability

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The data underlying this study are available in the published article and its Supporting Information.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.orglett.3c01538.

  • Experimental details and spectral data for all unknown compounds and crystallographic data (PDF)

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CCDC 2260600 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: + 44 1223 336033.

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Author Information

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  • Corresponding Author
  • Authors
    • Àlex Díaz-Jiménez - Institut de Química Computacional i Catàlisi and Departament de Química, Universitat de Girona, C/Maria Aurèlia Capmany, 69, 17003 Girona, Catalunya Spain;  Orcidhttps://orcid.org/0000-0003-1241-8263
    • Stuart C. D. Kennington - Institut de Química Computacional i Catàlisi and Departament de Química, Universitat de Girona, C/Maria Aurèlia Capmany, 69, 17003 Girona, Catalunya Spain;  Orcidhttps://orcid.org/0000-0001-6804-7794
    • Anna Roglans - Institut de Química Computacional i Catàlisi and Departament de Química, Universitat de Girona, C/Maria Aurèlia Capmany, 69, 17003 Girona, Catalunya Spain;  Orcidhttps://orcid.org/0000-0002-7943-5706
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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We are grateful for financial support from the Ministerio de Ciencia e Innovación (PID2020-113711GB-I00 MCIN/AEI/10.13039/501100011033), the Generalitat de Catalunya (Departament de Recerca i Universitats, 2021SGR00623), the Spanish government for the predoctoral FPU grant to À.D.-J., and Margarita Salas grant (NextGenerationEU) to the University of Barcelona (S.C.D.K.). We also thank X. Fontrodona from the University of Girona for the X-ray structural determinations.

References

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    The hitherto unreported 2-aryl-10H-thiochromeno[3,2-b][1,4]oxathiin-10-one derivs. I (R = H, Cl, CF3; R1 = H, Cl; R2 = H, 4-F, 3-Me, 3-(CCH), etc.; R3 = H, Cl, F) are obtained in a single pot from 4-hydroxydithiocoumarins II, R2 = H, 4-F, 3-Me, 4-C(CH3)3 instead of R2 = H, 4-F, 3-Me, 3-(CCH), etc. arylacetylenes R2-C6H4CCH and DMSO in the presence of 10 mol% CuI and K2CO3 in an oil bath at 70°C. The novelties of the present protocol are (i) selective C-H functionalization at the C-3 position of 4-hydroxydithiocoumarin, (ii) regioselective hydrothiolation with arylacetylenes and (iii) concomitant cyclization. The major advantages are mild reaction conditions, broad substrate scope and good yield. Among the synthesized compds. I the following five compds. I (R = R1 = R2 = R3 = H; R = H, R1 = Cl, R2 = 4-F, R3 = H; R = CF3, R1 = H, R2 = 4-Me, R3 = H; R = R1 = R2 = H, R3 = F; R = R1 = H, R2 = 4-F, R3 = F) showed anticancer activity against a hu-man breast cancer cell line (MCF-7) and a cervical cancer cell line (HeLa).
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    (e) Bassoli, A.; Merlini, L.; Morini, G.; Vedani, A. A three-dimensional receptor model for isovanillic sweet derivatives. J. Chem. Soc., Perkin Trans. 2 1998, 1449– 1454,  DOI: 10.1039/a709167b
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    2e
    A three-dimensional receptor model for isovanillic sweet derivatives
    Bassoli, Angela; Merlini, Lucio; Morini, Gabriella; Vedani, Angelo
    Journal of the Chemical Society, Perkin Transactions 2: Physical Organic Chemistry (1998), (6), 1449-1454CODEN: JCPKBH; ISSN:0300-9580. (Royal Society of Chemistry)
    Using pseudoreceptor modeling, we have derived a three-dimensional binding-site model for the structurally uncharacterized sweet-taste receptor. The receptor model was derived based on 17 sweet compds. of the isovanillyl class (4-methoxy-3-hydroxybenzyl) as the training set and consists of nine key amino-acid residues embedded in a hydrophobic receptor cavity. The underlying technol. (software PrGen) allows for a dynamical treatment of the ligand-receptor complex (ligand equilibration and Monte-Carlo scanning of receptor space) as well as for receptor-mediated ligand alignment. Free energies of ligand binding are estd. based on ligand-receptor interactions, ligand desolvation energy, change of ligand internal energy and change of ligand entropy upon receptor binding. The validity of the receptor model has been assessed by using a test set of eight isovanillyl sweet compds. different from the training set. For these ligands, the obtained binding-site surrogate is capable of predicting free energies of ligand binding, ΔG°, to within 0.99 kcal mol-1 (rms) of their exptl. value, corresponding to an uncertainty in the sweetness of a factor of 5.5. Maximal individual errors of predicted sweetness do not exceed a factor of 18.
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  3. 3
    Tikad, A.; El Kazzouli, S.; Guillaumet, G. 1,4-Dioxins, oxathiins, dithiins and their benzo derivatives. Comprehensive Heterocyclic Chemistry IV 2022, 8, 863– 908,  DOI: 10.1016/B978-0-12-818655-8.00015-9
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    (a) Mattay, J.; Dittmer, C. Synthesis of 1,4-oxathiins and 5,6-dihydro-1,4-oxathiins. J. Org. Chem. 1986, 51, 1894– 1897,  DOI: 10.1021/jo00360a045
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    Synthesis of 1,4-oxathiins and 5,6-dihydro-1,4-oxathiins
    Mattay, Jochen; Dittmer, Christel
    Journal of Organic Chemistry (1986), 51 (10), 1894-7CODEN: JOCEAH; ISSN:0022-3263.
    1,4-Oxathiins I [R = R1 = Me, Ph; RR1 = (CH2)3, (CH2)4] were synthesized by an eliminative ring expansion from easily accessible 1,3-oxathiolanes II (R2 = Cl, Br, F3CCO2). This synthesis can be also applied to the prepn. of 5,6-dihydro-1,4-oxathiins.
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    (b) Klásek, A.; Rudolf, O.; Rouchal, M.; Lycka, A.; Ruzicka, A. Reaction of 4-hydroxy-2-quinolones with thionyl chloride – preparation of new spiro-benzo[1,3]oxathioles and their transformations. Tetrahedron 2013, 69, 492– 499,  DOI: 10.1016/j.tet.2012.11.034
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    Reaction of 4-hydroxy-2-quinolones with thionyl chloride - preparation of new spiro-benzo[1,3]oxathioles and their transformations
    Klasek, Antonin; Rudolf, Ondrej; Rouchal, Michal; Lycka, Antonin; Ruzicka, Ales
    Tetrahedron (2013), 69 (2), 492-499CODEN: TETRAB; ISSN:0040-4020. (Elsevier Ltd.)
    4-Hydroxy-2-quinolones [1; R = H (a), Me (b), Ph (c)] react with thionyl chloride to give new spiro-benzo[1,3]oxathioles (3) and bis(4-hydroxy-2-quinolon-3-yl)sulfides (2) and small quantities of 3-chloro-4-hydroxyquinolin-2-ones (4) (1-4 = I - IV, resp.). Compds. 3 afford sulfides 2 by heating in different solvents and [1,4]oxathiino[3,2-c:5,6-c']diquinoline-6,8(5H,9H)-diones (VI) by reaction with triphenylphosphine. The reconversion of compds. 2 to 3 was achieved using bromine. The reaction mechanisms are discussed for all transformations. All compds. were characterized by IR, 1H, and 13C NMR (in some cases also 15N NMR) spectroscopy, and EI and/or ESI mass spectrometry. The x-ray structure was detd. for compd. 3b.
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  5. 5
    Nguyen, V.-H.; Nishino, H.; Kajikawa, S.; Kurosawa, K. Mn(III)-based reactions of alkenes and alkynes with thiols. An approach toward substituted 2,3-dihydro-1,4-oxathiins and simple route to (E)-vinyl sulfides. Tetrahedron 1998, 54, 11445– 11460,  DOI: 10.1016/S0040-4020(98)00707-8
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    Mn(III)-based reactions of alkenes and alkynes with thiols. An approach toward substituted 2,3-dihydro-1,4-oxathiins and simple route to (E)-vinyl sulfides
    Nguyen, Van-Ha; Nishino, Hiroshi; Kajikawa, Shougo; Kurosawa, Kazu
    Tetrahedron (1998), 54 (38), 11445-11460CODEN: TETRAB; ISSN:0040-4020. (Elsevier Science Ltd.)
    The 1st example using Mn(III) acetate in the reaction of 1,1-diarylethenes with α-mercaptoketones was examd. A mixt. of the ethenes and α-mercaptoketones was treated with Mn(III) acetate in HOAc, affording cycloaddn. products in moderate yields, together with substituted products. The reaction may involve the formation of a carbocation and subsequent cyclization to give the substituted 2,3-dihydro-1,4-oxathiin. A similar reaction with thioglycolic acid gave 1,4-oxathiolan-2-one. While thiyl radicals easily formed by Mn(III) oxidn. with ethanethiol or benzenethiol reacted with alkynes to give preferentially (E)-vinyl sulfides in quant. yields.
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  6. 6
    Wang, T.; Gao, Z.-H.; Ye, S. [4 + 2] and [3 + 2] Annulations of α-chloroaldehydes and dithio- esters: synthesis of 1,4-oxathiin-2(3H)-ones and 1,3-oxathioles. Adv. Synth. Catal. 2017, 359, 3479– 3483,  DOI: 10.1002/adsc.201700601
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    6
    [4+2] and [3+2] Annulations of α-Chloroaldehydes and Dithioesters: Synthesis of 1,4-Oxathiin-2(3H)-ones and 1,3-Oxathioles
    Wang, Tong; Gao, Zhong-Hua; Ye, Song
    Advanced Synthesis & Catalysis (2017), 359 (20), 3479-3483CODEN: ASCAF7; ISSN:1615-4150. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The [4+2] and [3+2] annulations of α-chloroaldehydes with dithioesters were reported. In the presence of an N-heterocyclic carbene (NHC) catalyst, the [4+2] annulation went smoothly to afford highly substituted 1,4-oxathiin-2(3H)-ones, while the [3+2] annulation was obsd. to give 1,3-oxathioles in the absence of an NHC.
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  7. 7
    Chen, X.; Xu, J. Synthesis of 3-acyl-5,6-dihydro-1,4-oxathiines through ring expansion of thiiranes. Tetrahedron Lett. 2017, 58, 1651– 1654,  DOI: 10.1016/j.tetlet.2017.03.039
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    7
    Synthesis of 3-acyl-5,6-dihydro-1,4-oxathiines through ring expansion of thiiranes
    Chen, Xingpeng; Xu, Jiaxi
    Tetrahedron Letters (2017), 58 (16), 1651-1654CODEN: TELEAY; ISSN:0040-4039. (Elsevier Ltd.)
    Synthesis of 3-acyl-5,6-dihydro-1,4-oxathiines was achieved via reactions of thiiranes and α-diazo-β-1,3-dicarbonyl compds. under microwave and copper sulfate-assisted conditions. The current method provided a direct and simple strategy in efficient prepn. of 3-acyl-1,4-oxathiines from readily available thiiranes and trans-3-acyl-5,6-dihydro-1,4-oxathiines as stereospecific products for 1,2-disubstituted cis-thiiranes. The reaction mechanism was also proposed.
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  8. 8
    (a) Moafi, L.; Ahadi, S.; Khavasi, H.-R.; Bazgir, A. Three-component diastereoselective synthesis of stable 1,4-diionic organosulfurs. Synthesis 2011, 9, 1399– 1402
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    (b) Huang, J.; Zhang, L.; Meng, X. Recent advances in the cyclization reactions of pyridinium 1,n-zwitterions (n = 4 and 5): scope and mechanism. Org. Chem. Front. 2023, 10, 2813– 2829,  DOI: 10.1039/D3QO00228D
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    8b
    Recent advances in the cyclization reactions of pyridinium 1,n-zwitterions (n = 4 and 5): scope and mechanism
    Huang, Jiali; Zhang, Lei; Meng, Xiangtai
    Organic Chemistry Frontiers (2023), 10 (11), 2813-2829CODEN: OCFRA8; ISSN:2052-4129. (Royal Society of Chemistry)
    Nitrogen- and sulfur-contg. heterocyclic compds. widely exist in bioactive natural products and drug mols. with unique bioactivity. In the past few decades, great efforts have been devoted to developing convenient and efficient strategies for the synthesis of these compds. Pyridinium zwitterions with unique reactivity play a significant role in the construction of nitrogen- and sulfur-contg. heterocycles. In recent years, pyridinium zwitterions have been extensively used in cyclization reactions for the synthesis of novel heterocyclic compds. This review summarizes the recent advances in cyclization reactions involving pyridinium 1,n-zwitterions (n = 4 and 5) and highlights the applications of these zwitterions in the efficient construction of heterocycles.
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  9. 9
    (a) Cheng, B.; Li, Y.; Wang, T.; Zhang, X.; Li, H.; Li, Y.; Zhai, H. Pyridinium 1,4-zwitterionic thiolates as a useful class of sulfur-containing synthons: application to the synthesis of 2,5-dihydro-1,4,5-thiadiazepines. Chem. Commun. 2019, 55, 14606– 14608,  DOI: 10.1039/C9CC08326J
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    9a
    Pyridinium 1,4-zwitterionic thiolates as a useful class of sulfur-containing synthons: application to the synthesis of 2,5-dihydro-1,4,5-thiadiazepines
    Cheng, Bin; Li, Yuntong; Wang, Taimin; Zhang, Xinping; Li, Hui; Li, Yun; Zhai, Hongbin
    Chemical Communications (Cambridge, United Kingdom) (2019), 55 (97), 14606-14608CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    A novel [4+3] cascade cyclization reaction of pyridinium 1,4-zwitterionic thiolates with azoalkenes derived from α-halo hydrazones in situ has been developed. This reaction was found to allow expedient access to an array of 2,5-dihydro-1,4,5-thiadiazepines. Libraries of highly functionalized sulfoxide and sulfone analogs of 2,5-dihydro-1,4,5-thiadiazepines were also obtained via selective oxidn. with m-CPBA.
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    (b) Zhai, S.; Zhang, X.; Cheng, B.; Li, H.; Li, Y.; He, Y.; Li, Y.; Wang, T.; Zhai, H. Synthesis of tetrasubstituted thiophenes via a [3 + 2] cascade cyclization reaction of pyridinium 1,4-zwitterionic thiolates and activated allenes. Chem. Commun. 2020, 56, 3085– 3088,  DOI: 10.1039/D0CC00262C
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    9b
    Synthesis of tetrasubstituted thiophenes via a [3+2] cascade cyclization reaction of pyridinium 1,4-zwitterionic thiolates and activated allenes
    Zhai, Shengxian; Zhang, Xinping; Cheng, Bin; Li, Hui; Li, Yuntong; He, Yixuan; Li, Yun; Wang, Taimin; Zhai, Hongbin
    Chemical Communications (Cambridge, United Kingdom) (2020), 56 (20), 3085-3088CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    A [3+2] cascade cyclization reaction of pyridinium 1,4-zwitterionic thiolates I (X = H, OMe; R = OMe, OEt, Ph; R1 = OMe, OEt, Ph) and activated allenes R2(R3)C=C=CHR4 [R2 = H, Me, Et, CH2OH; R3 = H, Me, hydroxy(phenyl)methyl, 4-fluorophenyl, etc.; R2R3 = -(CH2)5-; R4 = benzenesulfonyl, benzoyl, (benzyloxy)carbonyl, etc.] has been developed, which allows facile access to a library of tetrasubstituted thiophenes II with great variety under thermal conditions.
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    (c) Cheng, B.; Duan, X.; Li, Y.; Zhang, X.; Li, H.; Wu, F.; Li, Y.; Wang, T.; Zhai, H. Development and application of pyridinium 1,4-zwitterionic thiolates: synthesis of polysubstituted thiophenes. Eur. J. Org. Chem. 2020, 2020, 1896– 1906,  DOI: 10.1002/ejoc.202000165
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    9c
    Development and Application of Pyridinium 1,4-Zwitterionic Thiolates: Synthesis of Polysubstituted Thiophenes
    Cheng, Bin; Duan, Xiaoguang; Li, Yuntong; Zhang, Xinping; Li, Hui; Wu, Fufang; Li, Yun; Wang, Taimin; Zhai, Hongbin
    European Journal of Organic Chemistry (2020), 2020 (12), 1896-1906CODEN: EJOCFK; ISSN:1099-0690. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Pyridinium 1,4-zwitterionic thiolates as a class of sulfur-contg. synthons were applied to a [3+2] cascade cyclization reaction with activated alkynes, affording a library of polysubstituted thiophenes with excellent regioselectivities, esp. those bearing various fluorine-contg. groups (I + II → III, R's are electron-withdrawing groups). The freshly disclosed pyridinium 1,4-zwitterionic thiolates decorated with acyl or trifluoromethyl groups exhibited powerful potential in the synthesis of polysubstituted thiophenes. Of particular note is that pyridinium I (R1 = CF3) could introduce sulfur and CF3 groups to target products simultaneously.
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    (d) Cheng, B.; Bao, B.; Xu, W.; Li, Y.; Li, H.; Zhang, X.; Li, Y.; Wang, T.; Zhai, H. Synthesis of fully substituted pyrazoles from pyridinium 1,4-zwitterionic thiolates and hydrazonoyl chlorides via a [[3 + 3]-1] pathway. Org. Biomol. Chem. 2020, 18, 2949– 2955,  DOI: 10.1039/D0OB00224K
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    9d
    Synthesis of fully substituted pyrazoles from pyridinium 1,4-zwitterionic thiolates and hydrazonoyl chlorides via a [[3 + 3] - 1] pathway
    Cheng, Bin; Bao, Bian; Xu, Wei; Li, Yuntong; Li, Hui; Zhang, Xinping; Li, Yun; Wang, Taimin; Zhai, Hongbin
    Organic & Biomolecular Chemistry (2020), 18 (15), 2949-2955CODEN: OBCRAK; ISSN:1477-0520. (Royal Society of Chemistry)
    A novel and practical protocol for the synthesis of fully substituted pyrazoles I [R1 = t-Bu, Ph, 2-furyl, etc.; R2 = CF3, CO2Me, C(O)Ph, etc.; R3 = CO2Me, CO2Et, C(O)Ph] from pyridinium 1,4-zwitterionic thiolates and hydrazonoyl chlorides in excellent yields under mild conditions was described. The transformation proceeded via an unusual [[3 + 3] - 1] pathway, which involved a formal [3 + 3] cascade cyclization followed by a spontaneous ring-contraction/sulfur extrusion reaction from 4H-1,3,4-thiadiazine intermediates.
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    (e) Cheng, B.; Li, Y.; Wang, T.; Zhang, X.; Li, H.; He, Y.; Li, Y.; Zhai, H. Application of pyridinium 1,4-zwitterionic thiolates: synthesis of benzopyridothiazepines and benzothiophenes. J. Org. Chem. 2020, 85, 6794– 6802,  DOI: 10.1021/acs.joc.0c00374
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    9e
    Application of Pyridinium 1,4-Zwitterionic Thiolates: Synthesis of Benzopyridothiazepines and Benzothiophenes
    Cheng, Bin; Li, Yuntong; Wang, Taimin; Zhang, Xinping; Li, Hui; He, Yixuan; Li, Yun; Zhai, Hongbin
    Journal of Organic Chemistry (2020), 85 (10), 6794-6802CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
    Pyridinium 1,4-zwitterionic thiolates, a novel kind of sulfur-contg. synthons, were applied to the synthesis of 12aH-benzo[f]pyrido[1,2-d][1,4]thiazepines and benzo[b]thiophenes. Benzopyridothiazepines, e.g., I (R1, R2 = MeO2C, EtO2C, PhCO, 2-furylcarbonyl, etc.; R3 = H, Me), were produced through a 1,5-dipolar cycloaddn. reaction from pyridinium 1,4-zwitterionic thiolates, e.g., II, with arynes, whereas benzothiophenes, e.g. III, as side products were generated via a [3+2] cascade cyclization. The [5+2] reaction mode of pyridinium 1,4-zwitterionic thiolates is disclosed for the first time.
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    (f) Cheng, B.; Li, Y.; Zhang, X.; Duan, S.; Li, H.; He, Y.; Li, Y.; Wang, T.; Zhai, H. Two reaction modes of pyridinium 1,4-zwitterionic thiolates with sulfenes: synthesis of 3H-1,2-dithiole 2,2-dioxides, 1,9a-dihydropyrido[2,1-c][1,4]thiazines, and indolizines. Org. Lett. 2020, 22, 5817– 5821,  DOI: 10.1021/acs.orglett.0c01888
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    9f
    Two Reaction Modes of Pyridinium 1,4-Zwitterionic Thiolates with Sulfenes: Synthesis of 3H-1,2-Dithiole 2,2-Dioxides, 1,9a-Dihydropyrido[2,1-c][1,4]thiazines, and Indolizines
    Cheng, Bin; Li, Yuntong; Zhang, Xinping; Duan, Shengguo; Li, Hui; He, Yixuan; Li, Yun; Wang, Taimin; Zhai, Hongbin
    Organic Letters (2020), 22 (15), 5817-5821CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
    Two reaction modes of pyridinium 1,4-zwitterionic thiolates with sulfenes generated in-situ from alkanesulfonyl chlorides were described with DIPEA as the base. 3H-1,2-Dithiole 2,2-dioxides were obtained via a formal [3+2] pathway from alkylmethanesulfonyl chlorides, while 1,9a-dihydropyrido[2,1-c][1,4]thiazines were obtained via a stepwise [(5 + 2) - 1] pathway from phenylmethanesulfonylchlorides. Moreover, as an application, indolizines were accessed via a stepwise {[(5+2)- 1]- 1} pathway, with 1,9a-dihydropyrido[2,1-c][1,4]thiazines as the transient intermediates.
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    (g) Cheng, B.; Li, H.; Duan, S.; Zhang, X.; He, Y.; Li, Y.; Li, Y.; Wang, T.; Zhai, H. Synthesis of indolizines from pyridinium 1,4-zwitterionic thiolates and propiolic acid derivatives via a formal [4 + 1] pathway. Org. Biomol. Chem. 2020, 18, 6253– 6257,  DOI: 10.1039/D0OB01398F
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    9g
    Synthesis of indolizines from pyridinium 1,4-zwitterionic thiolates and propiolic acid derivatives via a formal [4 + 1] pathway
    Cheng, Bin; Li, Hui; Duan, Shengguo; Zhang, Xinping; He, Yixuan; Li, Yuntong; Li, Yun; Wang, Taimin; Zhai, Hongbin
    Organic & Biomolecular Chemistry (2020), 18 (32), 6253-6257CODEN: OBCRAK; ISSN:1477-0520. (Royal Society of Chemistry)
    A novel cyclization reaction of pyridinium 1,4-zwitterionic thiolates I (R = Me, Et, t-Bu, i-Pr; R1 = H, OMe, dimethoxymethyl, 1,3-dioxolan-2-yl, 2-methyl-1,3-dioxolan-2-yl) and propiolic acid derivs. HCCC(O)R2 [R2 = OMe, methyl(phenyl)aminyl, (thiophen-2-ylmethyl)oxidanyl, etc.] mediated by triethylamine was described, which allows the facile synthesis of indolizines II under mild reaction conditions. The net transformation involves an acetylide-driven formal [5 + 1] annulation reaction followed by a spontaneous ring-contraction/sulfur extrusion process of transient pyridothiazine intermediates.
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    (h) Cheng, B.; Zhang, X.; Li, H.; He, Y.; Li, Y.; Sun, H.; Wang, T.; Zhai, H. Synthesis of pyridothiazepines via a 1,5-dipolar cycloaddition reaction between pyridinium 1,4-zwitterionic thiolates and activated allenes. Adv. Synth. Catal. 2020, 362, 4668– 4672,  DOI: 10.1002/adsc.202000655
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    9h
    Synthesis of Pyridothiazepines via a 1,5-Dipolar Cycloaddition Reaction between Pyridinium 1,4-Zwitterionic Thiolates and Activated Allenes
    Cheng, Bin; Zhang, Xinping; Li, Hui; He, Yixuan; Li, Yun; Sun, Haiyan; Wang, Taimin; Zhai, Hongbin
    Advanced Synthesis & Catalysis (2020), 362 (21), 4668-4672CODEN: ASCAF7; ISSN:1615-4150. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The synthesis of pyridothiazepines I [R1 = H, Me, CH(OMe)2, etc.; R2 = allyl, Ph, Bn, etc.; R3 = CF3, CO2Me, CO2Et, etc.; R4 = CO2Me, CO2Et, C(O)C6H5, etc.] was achieved via a dipolar cycloaddn. reaction between pyridinium 1,4-zwitterionic thiolates and activated allenes conducted under thermal conditions. Meanwhile, a ring-contraction reaction of the resulting pyridothiazepine derivs. via the extrusion of 3-thioxoacrylates was also described.
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    (i) He, Y.; Wu, P.; Zhang, X.; Wang, T.; Tao, Q.; Zhou, K.; Ouyang, Z.; Zhai, H.; Cheng, D. J.; Cheng, B. Synthesis of aryl-fused 1,4-oxathiepines from pyridinium 1,4-zwitterionic thiolates and vinylidene ortho-quinone methides. Org. Chem. Front. 2022, 9, 4612– 4618,  DOI: 10.1039/D2QO00735E
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    9i
    Synthesis of aryl-fused 1,4-oxathiepines from pyridinium 1,4-zwitterionic thiolates and vinylidene ortho-quinone methides
    He, Yixuan; Wu, Ping; Zhang, Xiang; Wang, Taimin; Tao, Qingqing; Zhou, Kang; Ouyang, Zijun; Zhai, Hongbin; Cheng, Dao-Juan; Cheng, Bin
    Organic Chemistry Frontiers (2022), 9 (17), 4612-4618CODEN: OCFRA8; ISSN:2052-4129. (Royal Society of Chemistry)
    The synthesis of aryl-fused 1,4-oxathiepines from pyridinium 1,4-zwitterionic thiolates with ortho-alkynyl arom. phenols was achieved in good to excellent yields under mild conditions. The key reactive intermediates (i.e., vinylidene ortho-quinone methides) were readily generated in-situ from α-alkynylnaphthalen-2-ols and they can also be generated from 2-alkynylphenols successfully by rationally varying the substituent of the Ph ring according to computational results. Replacing vinylidene ortho-quinone methides (VQMs) with common ortho-quinone methides (QMs) was also investigated, and benzooxathiepine was obtained in a moderate yield with (2-(bromomethyl)phenoxy)(tert-butyl)dimethylsilane as the QM precursor. Moreover, a preliminary study of the catalytic asym. version of this novel (3 + 4) reaction was attempted, affording a unique axially chiral arene-acyclic alkene scaffold with moderate enantioselectivity.
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    (j) Wang, C.; Liu, X. H.; Wang, X. L.; Ma, Z. W.; Ding, D.; Liu, J. T.; Meng, L.; Cui, H. P.; Chen, Y. J. Synthesis of functionalized 4,1-benzothiazepines via a [4 + 3] annulation between aza-o-quinone methides and pyridinium 1,4-zwitterionic thiolates. Adv. Synth. Catal. 2022, 364, 296– 301,  DOI: 10.1002/adsc.202101034
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    9j
    Synthesis of Functionalized 4,1-Benzothiazepines via a [4+3] Annulation between Aza-o-Quinone Methides and Pyridinium 1,4-Zwitterionic Thiolates
    Wang, Chuan-Chuan; Liu, Xue-Hua; Wang, Xin-Lu; Cui, Hua-Peng; Ma, Zhi-Wei; Ding, Degang; Liu, Jun-Tao; Meng, Lei; Chen, Ya-Jing
    Advanced Synthesis & Catalysis (2022), 364 (2), 296-301CODEN: ASCAF7; ISSN:1615-4150. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The [4+3] annulation of aza-o-quinone methides and pyridinium 1,4-zwitterionic thiolates has been developed for the one-step synthesis of functionalized 2,3-unsatd. 4,1-benzothiazepines I (R1 = H, 9-Me, 8-Br, etc.; R2 = Ac, Ts, Bz, etc.; R3 = H, OMe, Cl, etc.; EWG1 = COOMe, COOEt, COOiPr, COOiBu; EWG2 = COOMe, COOEt, COPh, etc.) under mild and metal-free conditions. The produced 4,1-benzothiazepines can easily be converted into biol. interesting sulfoxides and sulfones via selective oxidization with m-CPBA.
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    (k) Schifferer, L.; Hoppmann, L.; Groeters, R.; Mück-Lichtenfeld, C.; Daniliuc, C. G.; García Mancheño, O. Divergent access to fused N-heterocycle-thiazolines by solvent-dependent reaction of isoquinolinium thiolates with silylketene acetals. Chem. Commun. 2023, 59, 6032– 6035,  DOI: 10.1039/D3CC00781B
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    9k
    Divergent access to fused N-heterocycle-thiazolines by solvent-dependent reaction of isoquinolinium thiolates with silylketene acetals
    Schifferer, Lukas; Hoppmann, Leon; Groeters, Robin; Mueck-Lichtenfeld, Christian; Daniliuc, Constantin G.; Garcia Mancheno, Olga
    Chemical Communications (Cambridge, United Kingdom) (2023), 59 (40), 6032-6035CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    A solvent-dependent, divergent synthesis of highly functionalized N,S-heterocycles presenting a thiazoline and an isoquinuclidine (DCE as solvent) or tetrahydroisoquinoline (DMF as solvent) scaffolds by cyclization reactions of isoquinolinium 1,4-zwitterionic thiolates was reported. The robustness and applicability of the method were also demonstrated by an efficient 6-times upscaling of the reaction and derivatization of the thiazoline-isoquinuclidine derivs.
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    (l) Sun, S.; Wei, Y.; Xu, J. Difluorocarbene-triggered [1 + 5] annulation: access to functionalized 1,1-difluoro-1,9a-dihydropyrido[2,1-c][1,4]thiazine derivatives. Org. Lett. 2023, 25, 2868– 2872,  DOI: 10.1021/acs.orglett.3c00842
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    9l
    Difluorocarbene-triggered [1+5] annulation: access to functionalized 1,1-difluoro-1,9a-dihydropyrido[2,1-c][1,4]thiazine derivatives
    Sun, Simin; Wei, Yuliang; Xu, Jiaxi
    Organic Letters (2023), 25 (16), 2868-2872CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
    Difluorocarbene-triggered [1+5] annulation is developed to access 1,1-difluoro-1,9a-dihydropyrido[2,1-c][1,4]thiazine-3,4-dicarboxylate derivs. in satisfactory to good yields via the direct reaction of potassium bromodifluoroacetate and pyridinium 1,4-zwitterionic thiolates under heating., e.g., I. Pyridinium 1,4-zwitterionic thiolates first nucleophilically attack difluorocarbene generated from potassium bromodifluoroacetate followed by an intramol. nucleophilic addn. to pyridiniums. This method provides an expeditious route to introduce the difluoromethyl group into the 1,9a-dihydropyrido[2,1-c][1,4]thiazine ring, even to modify drug mols.
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    (m) Wei, Y.; Sun, S.; Xu, J. Direct and safe one-pot synthesis of functionalized dimethyl 1-aryl-1,9a-dihydropyrido[2,1-c][1,4]thiazine-1-phosphonates. Tetrahedron Lett. 2023, 120, 154444,  DOI: 10.1016/j.tetlet.2023.154444
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    9m
    Direct and safe one-pot synthesis of functionalized dimethyl 1-aryl-1,9a-dihydropyrido[2,1-c][1,4]thiazine-1-phosphonates
    Wei, Yuliang; Sun, Simin; Xu, Jiaxi
    Tetrahedron Letters (2023), 120 (), 154444CODEN: TELEAY; ISSN:0040-4039. (Elsevier Ltd.)
    A visible-light-induced direct and safe synthesis of functionalized di-Me 1-aryl-1,9a-dihydropyrido[2,1-c][1,4]thiazine-1-phosphonates trans/cis-I (R1 = 4-Me, 3-Cl, 4-I, etc.; R2 = H, 8-Me, 7-Me, 7-Br; R3 = Me, Et; R4 = OMe, OEt, Ph) is realized from di-Me (aryl(2-tosylhydrazono)methyl)phosphonates (E/Z)-R1C6H4C(=NNHTs)P(O)(OMe)2 and pyridinium 1,4-zwitterionic thiolates II (R5 = H, 4-Me, 3-Me, 3-Br) with cesium carbonate as base in dichloromethane. The reaction involves the carbene generation from di-Me (aryl(2-tosylhydrazono)methyl)phosphonates in the presence of cesium carbonate as base and the [1+5] annulation of the carbenes with pyridinium 1,4-zwitterionic thiolates II to synthesize functionalized 1,9a-dihydropyrido[2,1-c][1,4]thiazine derivs. I. The method avoids prepg., storing, and using potentially dangerous phosphoryl diazo compds. and features simple, convenient, catalyst-free, and mild reaction conditions.
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  10. 10
    Monreal-Corona, R.; Diaz-Jimenez, A.; Roglans, A.; Poater, A.; Pla-Quintana, A. Indolizine synthesis through annulation of pyridinium 1,4-thiolates and copper carbenes: a predictive catalysis approach. Adv. Synth. Catal. 2023, 365, 760– 766,  DOI: 10.1002/adsc.202201277
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    10
    Indolizine Synthesis through Annulation of Pyridinium 1,4-Thiolates and Copper Carbenes: A Predictive Catalysis Approach
    Monreal-Corona, Roger; Diaz-Jimenez, Alex; Roglans, Anna; Poater, Albert; Pla-Quintana, Anna
    Advanced Synthesis & Catalysis (2023), 365 (5), 760-766CODEN: ASCAF7; ISSN:1615-4150. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Predictive catalysis was applied to the reaction of pyridinium 1,4-zwitterionic thiolates with a copper carbene. Theor. calcns. were first performed to det. the suitability of their annulation reaction and to make predictions about the performance of different copper salts, diazo species, and pyridinium derivs. With calcns. in hand, the exptl. conditions were optimized, the scope of the reaction was assessed, and the precision of the predictions was evaluated. Yields up to 90% were obtained for the synthesis of indolizine scaffolds in the reactivity of pyridinium 1,4-zwitterionic thiolates with a metal carbene.
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  11. 11
    (a) Sun, S.; Wei, Y.; Xu, J. Visible-light-induced [1 + 5] annulation of phosphoryl diazomethylarenes and pyridinium 1,4-zwitterionic thiolates. Org. Lett. 2022, 24, 6024– 5030,  DOI: 10.1021/acs.orglett.2c02321
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    11a
    Visible-Light-Induced [1+5] Annulation of Phosphoryl Diazomethylarenes and Pyridinium 1,4-Zwitterionic Thiolates
    Sun, Simin; Wei, Yuliang; Xu, Jiaxi
    Organic Letters (2022), 24 (32), 6024-6030CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
    Visible-light-induced [1+5] annulation of phosphoryl diazomethylarenes and pyridinium 1,4-zwitterionic thiolates generates various trifunctionalized dialkyl 1-phosphoryl-1,9a-dihydropyrido[2,1-c][1,4]thiazine-3,4-dicarboxylates in good to excellent yields and diastereoselectivities. The annulation involves the nucleophilic attack of thiolates on diazomethylarene-generated carbenes followed by an intramol. cyclization, is free of catalysts, is atom-economical, and has mild reaction conditions.
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    (b) Sun, S.; Wei, Y.; Xu, J. Microwave-mediated stereocontrolled annulations of diazo(aryl)methyl(diaryl)phosphine oxides with pyridinium 1,4-zwitterionic thiolates. Chem. Commun. 2022, 59, 239– 242,  DOI: 10.1039/D2CC05483C
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    Microwave-mediated stereocontrolled annulations of diazo(aryl)methyl(diaryl)phosphine oxides with pyridinium 1,4-zwitterionic thiolates
    Sun Simin; Wei Yuliang; Xu Jiaxi
    Chemical communications (Cambridge, England) (2022), 59 (2), 239-242 ISSN:.
    Chemoselective annulations of phosphoryl carbenes generated from diazo(aryl)methyl(diaryl)phosphine oxides with pyridinium 1,4-zwitterionic thiolates were performed under microwave irradiation, affording 1-diarylphosphoryl-1H-benzo[c]thiopyran derivatives via [3+3] annulation and indolizine derivatives via ([1+5]-1) annulation with P-Cope elimination as the key step. The annuloselectivity was controlled by the steric hindrance of pyridiniums in pyridinium 1,4-zwitterionic thiolates.
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    El Ashry, E. S. H.; Awad, L. F.; El Kilany, Y.; Ibrahim, E. I. A versatile precursor for annulated heterocycles. Adv. Heterocycl. Chem. 2009, 98, 1– 141,  DOI: 10.1016/S0065-2725(09)09801-8
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    Dimedone: a versatile precursor for annulated heterocycles
    El Ashry, El Sayed H.; Awad, Laila F.; El Kilany, Yeldez; Ibrahim, Elsayed I.
    Advances in Heterocyclic Chemistry (2009), 98 (), 1-141CODEN: AHTCAG; ISSN:0065-2725. (Elsevier Inc.)
    A review. Topics thus discussed included dimedone-annulated three-membered and four-membered heterocyclic compds., dimedone-annulated five-membered heterocyclic compds. with one heteroatom, two heteroatoms, three heteroatoms, dimedone-annulated five-membered and six-membered heterocyclic compds., etc.
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  13. 13

    For selected recent examples, see:

    (a) He, X.; Zhou, Y.; Shang, Y.; Yang, C.; Zuo, Y. Synthesis of 2-arylimino-6,7-dihydrobenzo[d[[1,3]oxathiole-4(5H)-ones via Rh2(OAc)4-catalyzed reactions of cyclic 2-diazo-1,3-diketones with aryl isothiocyanates. ACS Omega 2016, 1, 1277– 1283,  DOI: 10.1021/acsomega.6b00295
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    13a
    Synthesis of 2-Arylimino-6,7-dihydrobenzo[d][1,3]oxathiol-4(5H)-ones via Rh2(OAc)4-Catalyzed Reactions of Cyclic 2-Diazo-1,3-diketones with Aryl Isothiocyanates
    He, Xinwei; Zhou, Yao; Shang, Yongjia; Yang, Cheng; Zuo, Youpeng
    ACS Omega (2016), 1 (6), 1277-1283CODEN: ACSODF; ISSN:2470-1343. (American Chemical Society)
    A convenient and efficient synthesis of 2-arylimino-6,7-dihydrobenzo[d][1,3]oxathiol-4(5H)-ones was developed via a Rh2(OAc)4 catalyzed reaction of cyclic 2-diazo-1,3-diketones and aryl isothiocyanates in acetone at 60° C. This reaction uses readily available stable cyclic 2-diazo-1,3-diketone as starting material and generates the desired products in good to excellent yields (78-93%). The reaction proceeds under mild reaction conditions, produces only N2 as the byproduct, and features a broad substrate scope. A plausible mechanism for this reaction is also discussed.
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    (b) Thombal, R. S.; Kim, S.-T.; Baik, M.-H.; Lee, Y. R. Ruthenium catalyzes the synthesis of γ-butenolides fused with cyclohexanones. Chem. Commun. 2019, 55, 2940– 2943,  DOI: 10.1039/C9CC00101H
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    13b
    Ruthenium catalyzes the synthesis of γ-butenolides fused with cyclohexanones
    Thombal, Raju S.; Kim, Seoung-Tae; Baik, Mu-Hyun; Lee, Yong Rok
    Chemical Communications (Cambridge, United Kingdom) (2019), 55 (20), 2940-2943CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    Ruthenium(II)-catalyzed reactions of cyclic diazodicarbonyl compds. with β-ketoamides for chemo- and stereoselective construction of cyclohexanone-fused γ-butenolides were described. This study represented the first example of the addn. of an enol substrate which was formed by the tautomerization of the β-ketoamides to the electrophilic carbene center for unusual cyclization through amide cleavage. The combined exptl. and computational studies shed light on the mechanistic pathway favoring the unusual ring formation reaction instead of the involvement of the general carbonyl ylide intermediates for the product generation.
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    (c) Wu, Y.; He, X.; Xie, M.; Li, R.; Ning, Y.; Duan, J.; Zhang, E.; Shang, Y. Rh(III)-catalyzed cascade nucleophilic addition/annulation of 2-diazo-1,3-diketones with 1,3-dicarbonyl compounds to access 6,7-dihydrobenzofuran-4(5H)-ones. J. Org. Chem. 2021, 86, 7370– 7380,  DOI: 10.1021/acs.joc.1c00259
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    Rh(III)-Catalyzed Cascade Nucleophilic Addition/Annulation of 2-Diazo-1,3-diketones with 1,3-Dicarbonyl Compounds To Access 6,7-Dihydrobenzofuran-4(5H)-ones
    Wu, Yinsong; He, Xinwei; Xie, Mengqing; Li, Ruxue; Ning, Yi; Duan, Jiahui; Zhang, Enshen; Shang, Yongjia
    Journal of Organic Chemistry (2021), 86 (11), 7370-7380CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
    A Rh(III)-catalyzed cascade nucleophilic addn./intramol. annulation of 2-diazo-1,3-diketones I (R1 = H, Me; R2 = H, Me, Ph, 4-chlorophenyl, etc.) with 1,3-dicarbonyl compds. (e.g., 1,3-diketones and β-keto esters) R3C(O)CH2C(O)R4 (R3 = Me, OEt, Ph, 4-chlorophenyl, etc.; R4 = Me, i-Pr, Ph, CF3, etc.) is achieved to afford 6,7-dihydrobenzofuran-4(5H)-ones II in up to 91% yields. Notably, a wide range of substrates and functional groups were well-tolerated under the optimized reaction conditions to give desired products II in moderate to excellent yields with release of N2 and H2O as byproducts. Moreover, the method described is scalable and adaptable to late-stage functionalization.
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  14. 14
    Wu, W.; Wu, X.; Fan, X.; Zhu, J. Rh(III)-Catalyzed enaminone-directed C-H coupling with diazadicarbonyls for skeleton-divergent synthesis of isocoumarins and naphthalenes. Org. Lett. 2022, 24, 7850– 7855,  DOI: 10.1021/acs.orglett.2c03288
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    14
    Rh(III)-Catalyzed Enaminone-Directed C-H Coupling with Diazodicarbonyls for Skeleton-Divergent Synthesis of Isocoumarins and Naphthalenes
    Wu, Weiping; Wu, Xuan; Fan, Shuaixin; Zhu, Jin
    Organic Letters (2022), 24 (42), 7850-7855CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
    Diversity-oriented synthesis is tremendously useful for expanding the explorable chem. space but restricted by the limited available toolbox of skeleton-diversification chem. Authors report herein Rh(III)-catalyzed coupling of enaminones and diazodicarbonyls for skeleton-divergent synthesis of isocoumarins and naphthalenes. The diazodicarbonyl ring size and pH dependence of the skeleton-forming process demonstrates the achievement of both substrate- and reagent-controlled skeletal diversity generation in a single type of system. An intriguing C-C bond cleavage reactivity is crit. for enabling facile synthetic access to isocoumarins.
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  15. 15

    For recent reviews, see:

    (a) Yusubov, M. S.; Yoshimura, A.; Zhdankin, V. V. Iodonium ylides in organic synthesis. Arkivoc 2017, 1, 342– 374,  DOI: 10.3998/ark.5550190.p009.732
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    (b) Tong, M.; Zhang, X.; Wang, Y.; Wang, Z. Advances in reactions of iodonium ylides. Chin. J. Org. Chem. 2021, 41, 126– 143,  DOI: 10.6023/cjoc202006021
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    (c) Mi, X.; Pi, C.; Feng, W.; Cui, X. Recent progress in the application of iodonium ylides in organic synthesis. Org. Chem. Front. 2022, 9, 6999– 7015,  DOI: 10.1039/D2QO01332K
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    15c
    Recent progress in the application of iodonium ylides in organic synthesis
    Mi, Xia; Pi, Chao; Feng, Weisheng; Cui, Xiuling
    Organic Chemistry Frontiers (2022), 9 (24), 6999-7015CODEN: OCFRA8; ISSN:2052-4129. (Royal Society of Chemistry)
    A review. In this review, the most important breakthrough of iodonium ylides in org. reactions such as cyclization, C-H transformation, difunctionalization of alkenes and radiofluorination in recent five years was presented. The relative mechanisms are also mentioned.
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  16. 16

    For selected recent examples, see:

    (a) Jiang, Y.; Li, P.; Zhao, J.; Liu, B.; Li, X. Iodonium ylides as carbene precursors in Rh(III)-catalyzed C-H activation. Org. Lett. 2020, 22, 7475– 7479,  DOI: 10.1021/acs.orglett.0c02618
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    Iodonium Ylides as Carbene Precursors in Rh(III)-Catalyzed C-H Activation
    Jiang, Yuqin; Li, Pengfei; Zhao, Jie; Liu, Bingxian; Li, Xingwei
    Organic Letters (2020), 22 (19), 7475-7479CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
    The rhodium(III)-catalyzed coupling of C-H substrates with iodonium ylides has been realized for the efficient synthesis of diverse cyclic skeletons, where the iodonium ylides have been identified as efficient and outstanding carbene precursors. The reaction systems are applicable to both sp2 and sp3 C-H substrates under mild and redox-neutral conditions. The catalyst loading can be as low as 0.5 mol % in a gram-scale reaction. Representative products exhibit cytotoxicity toward human cancer cells at nanomolar levels.
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    (b) Nunewar, S.; Kumar, S.; Pandhare, H.; Nanduri, S.; Kanchupalli, V. Rh(III)-catalyzed chemodivergent annulations between indoles and iodonium carbenes: a rapid access to tricyclic and tetracyclic N-heterocycles. Org. Lett. 2021, 23, 4233– 42398,  DOI: 10.1021/acs.orglett.1c01167
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    16b
    Rh(III)-Catalyzed Chemodivergent Annulations between Indoles and Iodonium Carbenes: A Rapid Access to Tricyclic and Tetracyclic N-Heterocylces
    Nunewar, Saiprasad; Kumar, Sanjeev; Pandhare, Harishchandra; Nanduri, Srinivas; Kanchupalli, Vinaykumar
    Organic Letters (2021), 23 (11), 4233-4238CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
    Herein, an acid-controlled highly tunable selectivity of Rh(III)-catalyzed [4 + 2] and [3 + 3] annulations of N-carboxamide indoles with iodonium ylides lead to form synthetically important tricyclic and tetracyclic N-heterocycles is reported. Here, iodonium ylide serves as a carbene precursor. The protocol proceeds under operationally simple conditions and provides novel tricyclic and tetracyclic scaffolds such as 3,4-dihydroindolo[1,2-c]quinazoline-1,6(2H,5H)-dione and 1H-[1,3]oxazino[3,4-a]indol-1-one derivs. with a broad range of functional group tolerance and moderate to excellent yields. Furthermore, the protocol synthetic utility was extended for various chem. transformations and was easily scaled up to a large-scale level.
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    (c) Yin, C.; Li, L.; Yu, C. Rh(III)-catalyzed C-H Annulation of sulfoxonium ylides with iodonium ylides towards isocoumarins. Org. Biomol. Chem. 2022, 20, 1112– 1116,  DOI: 10.1039/D1OB02273C
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  1. Akira Yoshimura, Viktor V. Zhdankin. Recent Progress in Synthetic Applications of Hypervalent Iodine(III) Reagents. Chemical Reviews 2024, 124 (19) , 11108-11186. https://doi.org/10.1021/acs.chemrev.4c00303
  2. Xueqing Liu, Sijia Shi, Wenqian Ding, Zhiyue He, Yu Shen, Yong Nian, Xiaowei Wu. Accessing 7,8-Dihydroquinoline-2,5-diones via Rh-Catalyzed Olefinic C–H Activation/[4+2] Cyclization. Organic Letters 2024, 26 (24) , 5136-5140. https://doi.org/10.1021/acs.orglett.4c01536
  3. Jingnan Xu, Ren-Yin Yang, Bo Xu. Chameleonic Reactivity of Imidoyl Sulfoxonium Ylides: Access to Functionalized Pyrroles and Dihydro-pyridines. Organic Letters 2024, 26 (1) , 62-67. https://doi.org/10.1021/acs.orglett.3c03625
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  • Abstract

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    Scheme 1

    Scheme 1. Different Reaction Modes of PZTs and Carbene or Metallacarbene Species (E = Ester Group)
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    Scheme 2

    Scheme 2. Optimization of the Carbene Precursor Substrate
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    Scheme 3

    Scheme 3. Scope of the Reactiona,b
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    aReaction conditions: 1 (0.1 mmol), 2 (0.3 mmol), CuI (0.02 mmol) in 3.2 mL of dichloromethane at 40 °C for 24 h.

    bIsolated yields.

    cYield for the reaction at 1 mmol scale.

    dORTEP drawing at 50% ellipsoid probability.

    Scheme 4

    Scheme 4. Reaction with Linear Iodonium Ylides
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    Scheme 5

    Scheme 5. Further Functionalization of the 1,4-Oxathiin Derivatives
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    Scheme 6

    Scheme 6. Proposed Mechanism for the Reaction of PZTs with Iodonium Ylides
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  • References

    This article references 18 other publications.

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      Klasek, Antonin; Rudolf, Ondrej; Rouchal, Michal; Lycka, Antonin; Ruzicka, Ales
      Tetrahedron (2013), 69 (2), 492-499CODEN: TETRAB; ISSN:0040-4020. (Elsevier Ltd.)
      4-Hydroxy-2-quinolones [1; R = H (a), Me (b), Ph (c)] react with thionyl chloride to give new spiro-benzo[1,3]oxathioles (3) and bis(4-hydroxy-2-quinolon-3-yl)sulfides (2) and small quantities of 3-chloro-4-hydroxyquinolin-2-ones (4) (1-4 = I - IV, resp.). Compds. 3 afford sulfides 2 by heating in different solvents and [1,4]oxathiino[3,2-c:5,6-c']diquinoline-6,8(5H,9H)-diones (VI) by reaction with triphenylphosphine. The reconversion of compds. 2 to 3 was achieved using bromine. The reaction mechanisms are discussed for all transformations. All compds. were characterized by IR, 1H, and 13C NMR (in some cases also 15N NMR) spectroscopy, and EI and/or ESI mass spectrometry. The x-ray structure was detd. for compd. 3b.
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    5. 5
      Nguyen, V.-H.; Nishino, H.; Kajikawa, S.; Kurosawa, K. Mn(III)-based reactions of alkenes and alkynes with thiols. An approach toward substituted 2,3-dihydro-1,4-oxathiins and simple route to (E)-vinyl sulfides. Tetrahedron 1998, 54, 11445– 11460,  DOI: 10.1016/S0040-4020(98)00707-8
      5
      Mn(III)-based reactions of alkenes and alkynes with thiols. An approach toward substituted 2,3-dihydro-1,4-oxathiins and simple route to (E)-vinyl sulfides
      Nguyen, Van-Ha; Nishino, Hiroshi; Kajikawa, Shougo; Kurosawa, Kazu
      Tetrahedron (1998), 54 (38), 11445-11460CODEN: TETRAB; ISSN:0040-4020. (Elsevier Science Ltd.)
      The 1st example using Mn(III) acetate in the reaction of 1,1-diarylethenes with α-mercaptoketones was examd. A mixt. of the ethenes and α-mercaptoketones was treated with Mn(III) acetate in HOAc, affording cycloaddn. products in moderate yields, together with substituted products. The reaction may involve the formation of a carbocation and subsequent cyclization to give the substituted 2,3-dihydro-1,4-oxathiin. A similar reaction with thioglycolic acid gave 1,4-oxathiolan-2-one. While thiyl radicals easily formed by Mn(III) oxidn. with ethanethiol or benzenethiol reacted with alkynes to give preferentially (E)-vinyl sulfides in quant. yields.
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    6. 6
      Wang, T.; Gao, Z.-H.; Ye, S. [4 + 2] and [3 + 2] Annulations of α-chloroaldehydes and dithio- esters: synthesis of 1,4-oxathiin-2(3H)-ones and 1,3-oxathioles. Adv. Synth. Catal. 2017, 359, 3479– 3483,  DOI: 10.1002/adsc.201700601
      6
      [4+2] and [3+2] Annulations of α-Chloroaldehydes and Dithioesters: Synthesis of 1,4-Oxathiin-2(3H)-ones and 1,3-Oxathioles
      Wang, Tong; Gao, Zhong-Hua; Ye, Song
      Advanced Synthesis & Catalysis (2017), 359 (20), 3479-3483CODEN: ASCAF7; ISSN:1615-4150. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The [4+2] and [3+2] annulations of α-chloroaldehydes with dithioesters were reported. In the presence of an N-heterocyclic carbene (NHC) catalyst, the [4+2] annulation went smoothly to afford highly substituted 1,4-oxathiin-2(3H)-ones, while the [3+2] annulation was obsd. to give 1,3-oxathioles in the absence of an NHC.
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    7. 7
      Chen, X.; Xu, J. Synthesis of 3-acyl-5,6-dihydro-1,4-oxathiines through ring expansion of thiiranes. Tetrahedron Lett. 2017, 58, 1651– 1654,  DOI: 10.1016/j.tetlet.2017.03.039
      7
      Synthesis of 3-acyl-5,6-dihydro-1,4-oxathiines through ring expansion of thiiranes
      Chen, Xingpeng; Xu, Jiaxi
      Tetrahedron Letters (2017), 58 (16), 1651-1654CODEN: TELEAY; ISSN:0040-4039. (Elsevier Ltd.)
      Synthesis of 3-acyl-5,6-dihydro-1,4-oxathiines was achieved via reactions of thiiranes and α-diazo-β-1,3-dicarbonyl compds. under microwave and copper sulfate-assisted conditions. The current method provided a direct and simple strategy in efficient prepn. of 3-acyl-1,4-oxathiines from readily available thiiranes and trans-3-acyl-5,6-dihydro-1,4-oxathiines as stereospecific products for 1,2-disubstituted cis-thiiranes. The reaction mechanism was also proposed.
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    8. 8
      (a) Moafi, L.; Ahadi, S.; Khavasi, H.-R.; Bazgir, A. Three-component diastereoselective synthesis of stable 1,4-diionic organosulfurs. Synthesis 2011, 9, 1399– 1402
      There is no corresponding record for this reference.
      (b) Huang, J.; Zhang, L.; Meng, X. Recent advances in the cyclization reactions of pyridinium 1,n-zwitterions (n = 4 and 5): scope and mechanism. Org. Chem. Front. 2023, 10, 2813– 2829,  DOI: 10.1039/D3QO00228D
      8b
      Recent advances in the cyclization reactions of pyridinium 1,n-zwitterions (n = 4 and 5): scope and mechanism
      Huang, Jiali; Zhang, Lei; Meng, Xiangtai
      Organic Chemistry Frontiers (2023), 10 (11), 2813-2829CODEN: OCFRA8; ISSN:2052-4129. (Royal Society of Chemistry)
      Nitrogen- and sulfur-contg. heterocyclic compds. widely exist in bioactive natural products and drug mols. with unique bioactivity. In the past few decades, great efforts have been devoted to developing convenient and efficient strategies for the synthesis of these compds. Pyridinium zwitterions with unique reactivity play a significant role in the construction of nitrogen- and sulfur-contg. heterocycles. In recent years, pyridinium zwitterions have been extensively used in cyclization reactions for the synthesis of novel heterocyclic compds. This review summarizes the recent advances in cyclization reactions involving pyridinium 1,n-zwitterions (n = 4 and 5) and highlights the applications of these zwitterions in the efficient construction of heterocycles.
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    9. 9
      (a) Cheng, B.; Li, Y.; Wang, T.; Zhang, X.; Li, H.; Li, Y.; Zhai, H. Pyridinium 1,4-zwitterionic thiolates as a useful class of sulfur-containing synthons: application to the synthesis of 2,5-dihydro-1,4,5-thiadiazepines. Chem. Commun. 2019, 55, 14606– 14608,  DOI: 10.1039/C9CC08326J
      9a
      Pyridinium 1,4-zwitterionic thiolates as a useful class of sulfur-containing synthons: application to the synthesis of 2,5-dihydro-1,4,5-thiadiazepines
      Cheng, Bin; Li, Yuntong; Wang, Taimin; Zhang, Xinping; Li, Hui; Li, Yun; Zhai, Hongbin
      Chemical Communications (Cambridge, United Kingdom) (2019), 55 (97), 14606-14608CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      A novel [4+3] cascade cyclization reaction of pyridinium 1,4-zwitterionic thiolates with azoalkenes derived from α-halo hydrazones in situ has been developed. This reaction was found to allow expedient access to an array of 2,5-dihydro-1,4,5-thiadiazepines. Libraries of highly functionalized sulfoxide and sulfone analogs of 2,5-dihydro-1,4,5-thiadiazepines were also obtained via selective oxidn. with m-CPBA.
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      (b) Zhai, S.; Zhang, X.; Cheng, B.; Li, H.; Li, Y.; He, Y.; Li, Y.; Wang, T.; Zhai, H. Synthesis of tetrasubstituted thiophenes via a [3 + 2] cascade cyclization reaction of pyridinium 1,4-zwitterionic thiolates and activated allenes. Chem. Commun. 2020, 56, 3085– 3088,  DOI: 10.1039/D0CC00262C
      9b
      Synthesis of tetrasubstituted thiophenes via a [3+2] cascade cyclization reaction of pyridinium 1,4-zwitterionic thiolates and activated allenes
      Zhai, Shengxian; Zhang, Xinping; Cheng, Bin; Li, Hui; Li, Yuntong; He, Yixuan; Li, Yun; Wang, Taimin; Zhai, Hongbin
      Chemical Communications (Cambridge, United Kingdom) (2020), 56 (20), 3085-3088CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      A [3+2] cascade cyclization reaction of pyridinium 1,4-zwitterionic thiolates I (X = H, OMe; R = OMe, OEt, Ph; R1 = OMe, OEt, Ph) and activated allenes R2(R3)C=C=CHR4 [R2 = H, Me, Et, CH2OH; R3 = H, Me, hydroxy(phenyl)methyl, 4-fluorophenyl, etc.; R2R3 = -(CH2)5-; R4 = benzenesulfonyl, benzoyl, (benzyloxy)carbonyl, etc.] has been developed, which allows facile access to a library of tetrasubstituted thiophenes II with great variety under thermal conditions.
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      (c) Cheng, B.; Duan, X.; Li, Y.; Zhang, X.; Li, H.; Wu, F.; Li, Y.; Wang, T.; Zhai, H. Development and application of pyridinium 1,4-zwitterionic thiolates: synthesis of polysubstituted thiophenes. Eur. J. Org. Chem. 2020, 2020, 1896– 1906,  DOI: 10.1002/ejoc.202000165
      9c
      Development and Application of Pyridinium 1,4-Zwitterionic Thiolates: Synthesis of Polysubstituted Thiophenes
      Cheng, Bin; Duan, Xiaoguang; Li, Yuntong; Zhang, Xinping; Li, Hui; Wu, Fufang; Li, Yun; Wang, Taimin; Zhai, Hongbin
      European Journal of Organic Chemistry (2020), 2020 (12), 1896-1906CODEN: EJOCFK; ISSN:1099-0690. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Pyridinium 1,4-zwitterionic thiolates as a class of sulfur-contg. synthons were applied to a [3+2] cascade cyclization reaction with activated alkynes, affording a library of polysubstituted thiophenes with excellent regioselectivities, esp. those bearing various fluorine-contg. groups (I + II → III, R's are electron-withdrawing groups). The freshly disclosed pyridinium 1,4-zwitterionic thiolates decorated with acyl or trifluoromethyl groups exhibited powerful potential in the synthesis of polysubstituted thiophenes. Of particular note is that pyridinium I (R1 = CF3) could introduce sulfur and CF3 groups to target products simultaneously.
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      (d) Cheng, B.; Bao, B.; Xu, W.; Li, Y.; Li, H.; Zhang, X.; Li, Y.; Wang, T.; Zhai, H. Synthesis of fully substituted pyrazoles from pyridinium 1,4-zwitterionic thiolates and hydrazonoyl chlorides via a [[3 + 3]-1] pathway. Org. Biomol. Chem. 2020, 18, 2949– 2955,  DOI: 10.1039/D0OB00224K
      9d
      Synthesis of fully substituted pyrazoles from pyridinium 1,4-zwitterionic thiolates and hydrazonoyl chlorides via a [[3 + 3] - 1] pathway
      Cheng, Bin; Bao, Bian; Xu, Wei; Li, Yuntong; Li, Hui; Zhang, Xinping; Li, Yun; Wang, Taimin; Zhai, Hongbin
      Organic & Biomolecular Chemistry (2020), 18 (15), 2949-2955CODEN: OBCRAK; ISSN:1477-0520. (Royal Society of Chemistry)
      A novel and practical protocol for the synthesis of fully substituted pyrazoles I [R1 = t-Bu, Ph, 2-furyl, etc.; R2 = CF3, CO2Me, C(O)Ph, etc.; R3 = CO2Me, CO2Et, C(O)Ph] from pyridinium 1,4-zwitterionic thiolates and hydrazonoyl chlorides in excellent yields under mild conditions was described. The transformation proceeded via an unusual [[3 + 3] - 1] pathway, which involved a formal [3 + 3] cascade cyclization followed by a spontaneous ring-contraction/sulfur extrusion reaction from 4H-1,3,4-thiadiazine intermediates.
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      (e) Cheng, B.; Li, Y.; Wang, T.; Zhang, X.; Li, H.; He, Y.; Li, Y.; Zhai, H. Application of pyridinium 1,4-zwitterionic thiolates: synthesis of benzopyridothiazepines and benzothiophenes. J. Org. Chem. 2020, 85, 6794– 6802,  DOI: 10.1021/acs.joc.0c00374
      9e
      Application of Pyridinium 1,4-Zwitterionic Thiolates: Synthesis of Benzopyridothiazepines and Benzothiophenes
      Cheng, Bin; Li, Yuntong; Wang, Taimin; Zhang, Xinping; Li, Hui; He, Yixuan; Li, Yun; Zhai, Hongbin
      Journal of Organic Chemistry (2020), 85 (10), 6794-6802CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
      Pyridinium 1,4-zwitterionic thiolates, a novel kind of sulfur-contg. synthons, were applied to the synthesis of 12aH-benzo[f]pyrido[1,2-d][1,4]thiazepines and benzo[b]thiophenes. Benzopyridothiazepines, e.g., I (R1, R2 = MeO2C, EtO2C, PhCO, 2-furylcarbonyl, etc.; R3 = H, Me), were produced through a 1,5-dipolar cycloaddn. reaction from pyridinium 1,4-zwitterionic thiolates, e.g., II, with arynes, whereas benzothiophenes, e.g. III, as side products were generated via a [3+2] cascade cyclization. The [5+2] reaction mode of pyridinium 1,4-zwitterionic thiolates is disclosed for the first time.
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      (f) Cheng, B.; Li, Y.; Zhang, X.; Duan, S.; Li, H.; He, Y.; Li, Y.; Wang, T.; Zhai, H. Two reaction modes of pyridinium 1,4-zwitterionic thiolates with sulfenes: synthesis of 3H-1,2-dithiole 2,2-dioxides, 1,9a-dihydropyrido[2,1-c][1,4]thiazines, and indolizines. Org. Lett. 2020, 22, 5817– 5821,  DOI: 10.1021/acs.orglett.0c01888
      9f
      Two Reaction Modes of Pyridinium 1,4-Zwitterionic Thiolates with Sulfenes: Synthesis of 3H-1,2-Dithiole 2,2-Dioxides, 1,9a-Dihydropyrido[2,1-c][1,4]thiazines, and Indolizines
      Cheng, Bin; Li, Yuntong; Zhang, Xinping; Duan, Shengguo; Li, Hui; He, Yixuan; Li, Yun; Wang, Taimin; Zhai, Hongbin
      Organic Letters (2020), 22 (15), 5817-5821CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
      Two reaction modes of pyridinium 1,4-zwitterionic thiolates with sulfenes generated in-situ from alkanesulfonyl chlorides were described with DIPEA as the base. 3H-1,2-Dithiole 2,2-dioxides were obtained via a formal [3+2] pathway from alkylmethanesulfonyl chlorides, while 1,9a-dihydropyrido[2,1-c][1,4]thiazines were obtained via a stepwise [(5 + 2) - 1] pathway from phenylmethanesulfonylchlorides. Moreover, as an application, indolizines were accessed via a stepwise {[(5+2)- 1]- 1} pathway, with 1,9a-dihydropyrido[2,1-c][1,4]thiazines as the transient intermediates.
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      (g) Cheng, B.; Li, H.; Duan, S.; Zhang, X.; He, Y.; Li, Y.; Li, Y.; Wang, T.; Zhai, H. Synthesis of indolizines from pyridinium 1,4-zwitterionic thiolates and propiolic acid derivatives via a formal [4 + 1] pathway. Org. Biomol. Chem. 2020, 18, 6253– 6257,  DOI: 10.1039/D0OB01398F
      9g
      Synthesis of indolizines from pyridinium 1,4-zwitterionic thiolates and propiolic acid derivatives via a formal [4 + 1] pathway
      Cheng, Bin; Li, Hui; Duan, Shengguo; Zhang, Xinping; He, Yixuan; Li, Yuntong; Li, Yun; Wang, Taimin; Zhai, Hongbin
      Organic & Biomolecular Chemistry (2020), 18 (32), 6253-6257CODEN: OBCRAK; ISSN:1477-0520. (Royal Society of Chemistry)
      A novel cyclization reaction of pyridinium 1,4-zwitterionic thiolates I (R = Me, Et, t-Bu, i-Pr; R1 = H, OMe, dimethoxymethyl, 1,3-dioxolan-2-yl, 2-methyl-1,3-dioxolan-2-yl) and propiolic acid derivs. HCCC(O)R2 [R2 = OMe, methyl(phenyl)aminyl, (thiophen-2-ylmethyl)oxidanyl, etc.] mediated by triethylamine was described, which allows the facile synthesis of indolizines II under mild reaction conditions. The net transformation involves an acetylide-driven formal [5 + 1] annulation reaction followed by a spontaneous ring-contraction/sulfur extrusion process of transient pyridothiazine intermediates.
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      (h) Cheng, B.; Zhang, X.; Li, H.; He, Y.; Li, Y.; Sun, H.; Wang, T.; Zhai, H. Synthesis of pyridothiazepines via a 1,5-dipolar cycloaddition reaction between pyridinium 1,4-zwitterionic thiolates and activated allenes. Adv. Synth. Catal. 2020, 362, 4668– 4672,  DOI: 10.1002/adsc.202000655
      9h
      Synthesis of Pyridothiazepines via a 1,5-Dipolar Cycloaddition Reaction between Pyridinium 1,4-Zwitterionic Thiolates and Activated Allenes
      Cheng, Bin; Zhang, Xinping; Li, Hui; He, Yixuan; Li, Yun; Sun, Haiyan; Wang, Taimin; Zhai, Hongbin
      Advanced Synthesis & Catalysis (2020), 362 (21), 4668-4672CODEN: ASCAF7; ISSN:1615-4150. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The synthesis of pyridothiazepines I [R1 = H, Me, CH(OMe)2, etc.; R2 = allyl, Ph, Bn, etc.; R3 = CF3, CO2Me, CO2Et, etc.; R4 = CO2Me, CO2Et, C(O)C6H5, etc.] was achieved via a dipolar cycloaddn. reaction between pyridinium 1,4-zwitterionic thiolates and activated allenes conducted under thermal conditions. Meanwhile, a ring-contraction reaction of the resulting pyridothiazepine derivs. via the extrusion of 3-thioxoacrylates was also described.
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      (i) He, Y.; Wu, P.; Zhang, X.; Wang, T.; Tao, Q.; Zhou, K.; Ouyang, Z.; Zhai, H.; Cheng, D. J.; Cheng, B. Synthesis of aryl-fused 1,4-oxathiepines from pyridinium 1,4-zwitterionic thiolates and vinylidene ortho-quinone methides. Org. Chem. Front. 2022, 9, 4612– 4618,  DOI: 10.1039/D2QO00735E
      9i
      Synthesis of aryl-fused 1,4-oxathiepines from pyridinium 1,4-zwitterionic thiolates and vinylidene ortho-quinone methides
      He, Yixuan; Wu, Ping; Zhang, Xiang; Wang, Taimin; Tao, Qingqing; Zhou, Kang; Ouyang, Zijun; Zhai, Hongbin; Cheng, Dao-Juan; Cheng, Bin
      Organic Chemistry Frontiers (2022), 9 (17), 4612-4618CODEN: OCFRA8; ISSN:2052-4129. (Royal Society of Chemistry)
      The synthesis of aryl-fused 1,4-oxathiepines from pyridinium 1,4-zwitterionic thiolates with ortho-alkynyl arom. phenols was achieved in good to excellent yields under mild conditions. The key reactive intermediates (i.e., vinylidene ortho-quinone methides) were readily generated in-situ from α-alkynylnaphthalen-2-ols and they can also be generated from 2-alkynylphenols successfully by rationally varying the substituent of the Ph ring according to computational results. Replacing vinylidene ortho-quinone methides (VQMs) with common ortho-quinone methides (QMs) was also investigated, and benzooxathiepine was obtained in a moderate yield with (2-(bromomethyl)phenoxy)(tert-butyl)dimethylsilane as the QM precursor. Moreover, a preliminary study of the catalytic asym. version of this novel (3 + 4) reaction was attempted, affording a unique axially chiral arene-acyclic alkene scaffold with moderate enantioselectivity.
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      (j) Wang, C.; Liu, X. H.; Wang, X. L.; Ma, Z. W.; Ding, D.; Liu, J. T.; Meng, L.; Cui, H. P.; Chen, Y. J. Synthesis of functionalized 4,1-benzothiazepines via a [4 + 3] annulation between aza-o-quinone methides and pyridinium 1,4-zwitterionic thiolates. Adv. Synth. Catal. 2022, 364, 296– 301,  DOI: 10.1002/adsc.202101034
      9j
      Synthesis of Functionalized 4,1-Benzothiazepines via a [4+3] Annulation between Aza-o-Quinone Methides and Pyridinium 1,4-Zwitterionic Thiolates
      Wang, Chuan-Chuan; Liu, Xue-Hua; Wang, Xin-Lu; Cui, Hua-Peng; Ma, Zhi-Wei; Ding, Degang; Liu, Jun-Tao; Meng, Lei; Chen, Ya-Jing
      Advanced Synthesis & Catalysis (2022), 364 (2), 296-301CODEN: ASCAF7; ISSN:1615-4150. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The [4+3] annulation of aza-o-quinone methides and pyridinium 1,4-zwitterionic thiolates has been developed for the one-step synthesis of functionalized 2,3-unsatd. 4,1-benzothiazepines I (R1 = H, 9-Me, 8-Br, etc.; R2 = Ac, Ts, Bz, etc.; R3 = H, OMe, Cl, etc.; EWG1 = COOMe, COOEt, COOiPr, COOiBu; EWG2 = COOMe, COOEt, COPh, etc.) under mild and metal-free conditions. The produced 4,1-benzothiazepines can easily be converted into biol. interesting sulfoxides and sulfones via selective oxidization with m-CPBA.
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      (k) Schifferer, L.; Hoppmann, L.; Groeters, R.; Mück-Lichtenfeld, C.; Daniliuc, C. G.; García Mancheño, O. Divergent access to fused N-heterocycle-thiazolines by solvent-dependent reaction of isoquinolinium thiolates with silylketene acetals. Chem. Commun. 2023, 59, 6032– 6035,  DOI: 10.1039/D3CC00781B
      9k
      Divergent access to fused N-heterocycle-thiazolines by solvent-dependent reaction of isoquinolinium thiolates with silylketene acetals
      Schifferer, Lukas; Hoppmann, Leon; Groeters, Robin; Mueck-Lichtenfeld, Christian; Daniliuc, Constantin G.; Garcia Mancheno, Olga
      Chemical Communications (Cambridge, United Kingdom) (2023), 59 (40), 6032-6035CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      A solvent-dependent, divergent synthesis of highly functionalized N,S-heterocycles presenting a thiazoline and an isoquinuclidine (DCE as solvent) or tetrahydroisoquinoline (DMF as solvent) scaffolds by cyclization reactions of isoquinolinium 1,4-zwitterionic thiolates was reported. The robustness and applicability of the method were also demonstrated by an efficient 6-times upscaling of the reaction and derivatization of the thiazoline-isoquinuclidine derivs.
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      (l) Sun, S.; Wei, Y.; Xu, J. Difluorocarbene-triggered [1 + 5] annulation: access to functionalized 1,1-difluoro-1,9a-dihydropyrido[2,1-c][1,4]thiazine derivatives. Org. Lett. 2023, 25, 2868– 2872,  DOI: 10.1021/acs.orglett.3c00842
      9l
      Difluorocarbene-triggered [1+5] annulation: access to functionalized 1,1-difluoro-1,9a-dihydropyrido[2,1-c][1,4]thiazine derivatives
      Sun, Simin; Wei, Yuliang; Xu, Jiaxi
      Organic Letters (2023), 25 (16), 2868-2872CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
      Difluorocarbene-triggered [1+5] annulation is developed to access 1,1-difluoro-1,9a-dihydropyrido[2,1-c][1,4]thiazine-3,4-dicarboxylate derivs. in satisfactory to good yields via the direct reaction of potassium bromodifluoroacetate and pyridinium 1,4-zwitterionic thiolates under heating., e.g., I. Pyridinium 1,4-zwitterionic thiolates first nucleophilically attack difluorocarbene generated from potassium bromodifluoroacetate followed by an intramol. nucleophilic addn. to pyridiniums. This method provides an expeditious route to introduce the difluoromethyl group into the 1,9a-dihydropyrido[2,1-c][1,4]thiazine ring, even to modify drug mols.
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      (m) Wei, Y.; Sun, S.; Xu, J. Direct and safe one-pot synthesis of functionalized dimethyl 1-aryl-1,9a-dihydropyrido[2,1-c][1,4]thiazine-1-phosphonates. Tetrahedron Lett. 2023, 120, 154444,  DOI: 10.1016/j.tetlet.2023.154444
      9m
      Direct and safe one-pot synthesis of functionalized dimethyl 1-aryl-1,9a-dihydropyrido[2,1-c][1,4]thiazine-1-phosphonates
      Wei, Yuliang; Sun, Simin; Xu, Jiaxi
      Tetrahedron Letters (2023), 120 (), 154444CODEN: TELEAY; ISSN:0040-4039. (Elsevier Ltd.)
      A visible-light-induced direct and safe synthesis of functionalized di-Me 1-aryl-1,9a-dihydropyrido[2,1-c][1,4]thiazine-1-phosphonates trans/cis-I (R1 = 4-Me, 3-Cl, 4-I, etc.; R2 = H, 8-Me, 7-Me, 7-Br; R3 = Me, Et; R4 = OMe, OEt, Ph) is realized from di-Me (aryl(2-tosylhydrazono)methyl)phosphonates (E/Z)-R1C6H4C(=NNHTs)P(O)(OMe)2 and pyridinium 1,4-zwitterionic thiolates II (R5 = H, 4-Me, 3-Me, 3-Br) with cesium carbonate as base in dichloromethane. The reaction involves the carbene generation from di-Me (aryl(2-tosylhydrazono)methyl)phosphonates in the presence of cesium carbonate as base and the [1+5] annulation of the carbenes with pyridinium 1,4-zwitterionic thiolates II to synthesize functionalized 1,9a-dihydropyrido[2,1-c][1,4]thiazine derivs. I. The method avoids prepg., storing, and using potentially dangerous phosphoryl diazo compds. and features simple, convenient, catalyst-free, and mild reaction conditions.
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    10. 10
      Monreal-Corona, R.; Diaz-Jimenez, A.; Roglans, A.; Poater, A.; Pla-Quintana, A. Indolizine synthesis through annulation of pyridinium 1,4-thiolates and copper carbenes: a predictive catalysis approach. Adv. Synth. Catal. 2023, 365, 760– 766,  DOI: 10.1002/adsc.202201277
      10
      Indolizine Synthesis through Annulation of Pyridinium 1,4-Thiolates and Copper Carbenes: A Predictive Catalysis Approach
      Monreal-Corona, Roger; Diaz-Jimenez, Alex; Roglans, Anna; Poater, Albert; Pla-Quintana, Anna
      Advanced Synthesis & Catalysis (2023), 365 (5), 760-766CODEN: ASCAF7; ISSN:1615-4150. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Predictive catalysis was applied to the reaction of pyridinium 1,4-zwitterionic thiolates with a copper carbene. Theor. calcns. were first performed to det. the suitability of their annulation reaction and to make predictions about the performance of different copper salts, diazo species, and pyridinium derivs. With calcns. in hand, the exptl. conditions were optimized, the scope of the reaction was assessed, and the precision of the predictions was evaluated. Yields up to 90% were obtained for the synthesis of indolizine scaffolds in the reactivity of pyridinium 1,4-zwitterionic thiolates with a metal carbene.
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    11. 11
      (a) Sun, S.; Wei, Y.; Xu, J. Visible-light-induced [1 + 5] annulation of phosphoryl diazomethylarenes and pyridinium 1,4-zwitterionic thiolates. Org. Lett. 2022, 24, 6024– 5030,  DOI: 10.1021/acs.orglett.2c02321
      11a
      Visible-Light-Induced [1+5] Annulation of Phosphoryl Diazomethylarenes and Pyridinium 1,4-Zwitterionic Thiolates
      Sun, Simin; Wei, Yuliang; Xu, Jiaxi
      Organic Letters (2022), 24 (32), 6024-6030CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
      Visible-light-induced [1+5] annulation of phosphoryl diazomethylarenes and pyridinium 1,4-zwitterionic thiolates generates various trifunctionalized dialkyl 1-phosphoryl-1,9a-dihydropyrido[2,1-c][1,4]thiazine-3,4-dicarboxylates in good to excellent yields and diastereoselectivities. The annulation involves the nucleophilic attack of thiolates on diazomethylarene-generated carbenes followed by an intramol. cyclization, is free of catalysts, is atom-economical, and has mild reaction conditions.
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      (b) Sun, S.; Wei, Y.; Xu, J. Microwave-mediated stereocontrolled annulations of diazo(aryl)methyl(diaryl)phosphine oxides with pyridinium 1,4-zwitterionic thiolates. Chem. Commun. 2022, 59, 239– 242,  DOI: 10.1039/D2CC05483C
      11b
      Microwave-mediated stereocontrolled annulations of diazo(aryl)methyl(diaryl)phosphine oxides with pyridinium 1,4-zwitterionic thiolates
      Sun Simin; Wei Yuliang; Xu Jiaxi
      Chemical communications (Cambridge, England) (2022), 59 (2), 239-242 ISSN:.
      Chemoselective annulations of phosphoryl carbenes generated from diazo(aryl)methyl(diaryl)phosphine oxides with pyridinium 1,4-zwitterionic thiolates were performed under microwave irradiation, affording 1-diarylphosphoryl-1H-benzo[c]thiopyran derivatives via [3+3] annulation and indolizine derivatives via ([1+5]-1) annulation with P-Cope elimination as the key step. The annuloselectivity was controlled by the steric hindrance of pyridiniums in pyridinium 1,4-zwitterionic thiolates.
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    12. 12
      El Ashry, E. S. H.; Awad, L. F.; El Kilany, Y.; Ibrahim, E. I. A versatile precursor for annulated heterocycles. Adv. Heterocycl. Chem. 2009, 98, 1– 141,  DOI: 10.1016/S0065-2725(09)09801-8
      12
      Dimedone: a versatile precursor for annulated heterocycles
      El Ashry, El Sayed H.; Awad, Laila F.; El Kilany, Yeldez; Ibrahim, Elsayed I.
      Advances in Heterocyclic Chemistry (2009), 98 (), 1-141CODEN: AHTCAG; ISSN:0065-2725. (Elsevier Inc.)
      A review. Topics thus discussed included dimedone-annulated three-membered and four-membered heterocyclic compds., dimedone-annulated five-membered heterocyclic compds. with one heteroatom, two heteroatoms, three heteroatoms, dimedone-annulated five-membered and six-membered heterocyclic compds., etc.
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    13. 13

      For selected recent examples, see:

      (a) He, X.; Zhou, Y.; Shang, Y.; Yang, C.; Zuo, Y. Synthesis of 2-arylimino-6,7-dihydrobenzo[d[[1,3]oxathiole-4(5H)-ones via Rh2(OAc)4-catalyzed reactions of cyclic 2-diazo-1,3-diketones with aryl isothiocyanates. ACS Omega 2016, 1, 1277– 1283,  DOI: 10.1021/acsomega.6b00295
      13a
      Synthesis of 2-Arylimino-6,7-dihydrobenzo[d][1,3]oxathiol-4(5H)-ones via Rh2(OAc)4-Catalyzed Reactions of Cyclic 2-Diazo-1,3-diketones with Aryl Isothiocyanates
      He, Xinwei; Zhou, Yao; Shang, Yongjia; Yang, Cheng; Zuo, Youpeng
      ACS Omega (2016), 1 (6), 1277-1283CODEN: ACSODF; ISSN:2470-1343. (American Chemical Society)
      A convenient and efficient synthesis of 2-arylimino-6,7-dihydrobenzo[d][1,3]oxathiol-4(5H)-ones was developed via a Rh2(OAc)4 catalyzed reaction of cyclic 2-diazo-1,3-diketones and aryl isothiocyanates in acetone at 60° C. This reaction uses readily available stable cyclic 2-diazo-1,3-diketone as starting material and generates the desired products in good to excellent yields (78-93%). The reaction proceeds under mild reaction conditions, produces only N2 as the byproduct, and features a broad substrate scope. A plausible mechanism for this reaction is also discussed.
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      (b) Thombal, R. S.; Kim, S.-T.; Baik, M.-H.; Lee, Y. R. Ruthenium catalyzes the synthesis of γ-butenolides fused with cyclohexanones. Chem. Commun. 2019, 55, 2940– 2943,  DOI: 10.1039/C9CC00101H
      13b
      Ruthenium catalyzes the synthesis of γ-butenolides fused with cyclohexanones
      Thombal, Raju S.; Kim, Seoung-Tae; Baik, Mu-Hyun; Lee, Yong Rok
      Chemical Communications (Cambridge, United Kingdom) (2019), 55 (20), 2940-2943CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      Ruthenium(II)-catalyzed reactions of cyclic diazodicarbonyl compds. with β-ketoamides for chemo- and stereoselective construction of cyclohexanone-fused γ-butenolides were described. This study represented the first example of the addn. of an enol substrate which was formed by the tautomerization of the β-ketoamides to the electrophilic carbene center for unusual cyclization through amide cleavage. The combined exptl. and computational studies shed light on the mechanistic pathway favoring the unusual ring formation reaction instead of the involvement of the general carbonyl ylide intermediates for the product generation.
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      (c) Wu, Y.; He, X.; Xie, M.; Li, R.; Ning, Y.; Duan, J.; Zhang, E.; Shang, Y. Rh(III)-catalyzed cascade nucleophilic addition/annulation of 2-diazo-1,3-diketones with 1,3-dicarbonyl compounds to access 6,7-dihydrobenzofuran-4(5H)-ones. J. Org. Chem. 2021, 86, 7370– 7380,  DOI: 10.1021/acs.joc.1c00259
      13c
      Rh(III)-Catalyzed Cascade Nucleophilic Addition/Annulation of 2-Diazo-1,3-diketones with 1,3-Dicarbonyl Compounds To Access 6,7-Dihydrobenzofuran-4(5H)-ones
      Wu, Yinsong; He, Xinwei; Xie, Mengqing; Li, Ruxue; Ning, Yi; Duan, Jiahui; Zhang, Enshen; Shang, Yongjia
      Journal of Organic Chemistry (2021), 86 (11), 7370-7380CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
      A Rh(III)-catalyzed cascade nucleophilic addn./intramol. annulation of 2-diazo-1,3-diketones I (R1 = H, Me; R2 = H, Me, Ph, 4-chlorophenyl, etc.) with 1,3-dicarbonyl compds. (e.g., 1,3-diketones and β-keto esters) R3C(O)CH2C(O)R4 (R3 = Me, OEt, Ph, 4-chlorophenyl, etc.; R4 = Me, i-Pr, Ph, CF3, etc.) is achieved to afford 6,7-dihydrobenzofuran-4(5H)-ones II in up to 91% yields. Notably, a wide range of substrates and functional groups were well-tolerated under the optimized reaction conditions to give desired products II in moderate to excellent yields with release of N2 and H2O as byproducts. Moreover, the method described is scalable and adaptable to late-stage functionalization.
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    14. 14
      Wu, W.; Wu, X.; Fan, X.; Zhu, J. Rh(III)-Catalyzed enaminone-directed C-H coupling with diazadicarbonyls for skeleton-divergent synthesis of isocoumarins and naphthalenes. Org. Lett. 2022, 24, 7850– 7855,  DOI: 10.1021/acs.orglett.2c03288
      14
      Rh(III)-Catalyzed Enaminone-Directed C-H Coupling with Diazodicarbonyls for Skeleton-Divergent Synthesis of Isocoumarins and Naphthalenes
      Wu, Weiping; Wu, Xuan; Fan, Shuaixin; Zhu, Jin
      Organic Letters (2022), 24 (42), 7850-7855CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
      Diversity-oriented synthesis is tremendously useful for expanding the explorable chem. space but restricted by the limited available toolbox of skeleton-diversification chem. Authors report herein Rh(III)-catalyzed coupling of enaminones and diazodicarbonyls for skeleton-divergent synthesis of isocoumarins and naphthalenes. The diazodicarbonyl ring size and pH dependence of the skeleton-forming process demonstrates the achievement of both substrate- and reagent-controlled skeletal diversity generation in a single type of system. An intriguing C-C bond cleavage reactivity is crit. for enabling facile synthetic access to isocoumarins.
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    15. 15

      For recent reviews, see:

      (a) Yusubov, M. S.; Yoshimura, A.; Zhdankin, V. V. Iodonium ylides in organic synthesis. Arkivoc 2017, 1, 342– 374,  DOI: 10.3998/ark.5550190.p009.732
      There is no corresponding record for this reference.
      (b) Tong, M.; Zhang, X.; Wang, Y.; Wang, Z. Advances in reactions of iodonium ylides. Chin. J. Org. Chem. 2021, 41, 126– 143,  DOI: 10.6023/cjoc202006021
      There is no corresponding record for this reference.
      (c) Mi, X.; Pi, C.; Feng, W.; Cui, X. Recent progress in the application of iodonium ylides in organic synthesis. Org. Chem. Front. 2022, 9, 6999– 7015,  DOI: 10.1039/D2QO01332K
      15c
      Recent progress in the application of iodonium ylides in organic synthesis
      Mi, Xia; Pi, Chao; Feng, Weisheng; Cui, Xiuling
      Organic Chemistry Frontiers (2022), 9 (24), 6999-7015CODEN: OCFRA8; ISSN:2052-4129. (Royal Society of Chemistry)
      A review. In this review, the most important breakthrough of iodonium ylides in org. reactions such as cyclization, C-H transformation, difunctionalization of alkenes and radiofluorination in recent five years was presented. The relative mechanisms are also mentioned.
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    16. 16

      For selected recent examples, see:

      (a) Jiang, Y.; Li, P.; Zhao, J.; Liu, B.; Li, X. Iodonium ylides as carbene precursors in Rh(III)-catalyzed C-H activation. Org. Lett. 2020, 22, 7475– 7479,  DOI: 10.1021/acs.orglett.0c02618
      16a
      Iodonium Ylides as Carbene Precursors in Rh(III)-Catalyzed C-H Activation
      Jiang, Yuqin; Li, Pengfei; Zhao, Jie; Liu, Bingxian; Li, Xingwei
      Organic Letters (2020), 22 (19), 7475-7479CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
      The rhodium(III)-catalyzed coupling of C-H substrates with iodonium ylides has been realized for the efficient synthesis of diverse cyclic skeletons, where the iodonium ylides have been identified as efficient and outstanding carbene precursors. The reaction systems are applicable to both sp2 and sp3 C-H substrates under mild and redox-neutral conditions. The catalyst loading can be as low as 0.5 mol % in a gram-scale reaction. Representative products exhibit cytotoxicity toward human cancer cells at nanomolar levels.
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      (b) Nunewar, S.; Kumar, S.; Pandhare, H.; Nanduri, S.; Kanchupalli, V. Rh(III)-catalyzed chemodivergent annulations between indoles and iodonium carbenes: a rapid access to tricyclic and tetracyclic N-heterocycles. Org. Lett. 2021, 23, 4233– 42398,  DOI: 10.1021/acs.orglett.1c01167
      16b
      Rh(III)-Catalyzed Chemodivergent Annulations between Indoles and Iodonium Carbenes: A Rapid Access to Tricyclic and Tetracyclic N-Heterocylces
      Nunewar, Saiprasad; Kumar, Sanjeev; Pandhare, Harishchandra; Nanduri, Srinivas; Kanchupalli, Vinaykumar
      Organic Letters (2021), 23 (11), 4233-4238CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
      Herein, an acid-controlled highly tunable selectivity of Rh(III)-catalyzed [4 + 2] and [3 + 3] annulations of N-carboxamide indoles with iodonium ylides lead to form synthetically important tricyclic and tetracyclic N-heterocycles is reported. Here, iodonium ylide serves as a carbene precursor. The protocol proceeds under operationally simple conditions and provides novel tricyclic and tetracyclic scaffolds such as 3,4-dihydroindolo[1,2-c]quinazoline-1,6(2H,5H)-dione and 1H-[1,3]oxazino[3,4-a]indol-1-one derivs. with a broad range of functional group tolerance and moderate to excellent yields. Furthermore, the protocol synthetic utility was extended for various chem. transformations and was easily scaled up to a large-scale level.
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      (c) Yin, C.; Li, L.; Yu, C. Rh(III)-catalyzed C-H Annulation of sulfoxonium ylides with iodonium ylides towards isocoumarins. Org. Biomol. Chem. 2022, 20, 1112– 1116,  DOI: 10.1039/D1OB02273C
      16c
      Rh(III)-catalyzed C-H annulation of sulfoxonium ylides with iodonium ylides towards isocoumarins
      Yin, Chuanliu; Li, Lianghao; Yu, Chuanming
      Organic & Biomolecular Chemistry (2022), 20 (5), 1112-1116CODEN: OBCRAK; ISSN:1477-0520. (Royal Society of Chemistry)
      The direct synthesis of isocoumarin skeletons e.g., 3,3-dimethyl-3,4-dihydro-1H-benzo[c]chromene-1,6(2H)-dione has been realized through the Rh(III)-catalyzed [3 + 3] annulation of sulfoxonium ylides RC(O)CH=S(O)(CH3)2 (R = Ph, furan-2-yl, naphthalen-2-yl, cyclohexyl, etc.) with iodonium carbenes e.g., 5,5-dimethyl-2-(phenyl- λ3-iodanylidene)cyclohexane-1,3-dione. The synthetic protocol was constructed efficiently with broad functional group tolerance and mild reaction conditions. This reaction can be formally viewed as the result of C-H activation, carbene insertion and nucleophilic addn. processes. Furthermore, the further conversions of the product and gram-scale reactions also demonstrate to support the effectiveness of the synthesis protocol. The direct synthesis of isocoumarin skeletons e.g., 3,3-dimethyl-3,4-dihydro-1H-benzo[c]chromene-1,6(2H)-dione has been realized through the Rh(III)-catalyzed [3 + 3] annulation of sulfoxonium ylides RC(O)CH=S(O)(CH3)2 (R = Ph, furan-2-yl, naphthalen-2-yl, cyclohexyl, etc.) with iodonium carbenes e.g., 5,5-dimethyl-2-(phenyl-3-iodanylidene)cyclohexane-1,3-dione.
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      (d) Yang, Z.; Liu, C.; Lei, J.; Zhou, Y.; Gao, X.; Li, Y. Rh(III)-catalyzed C-H/C-C bond annulation of enaminones with iodonium ylides to form isocoumarins. Chem. Commun. 2022, 58, 13483– 13486,  DOI: 10.1039/D2CC05899E
      16d
      Rh(III)-catalyzed C-H/C-C bond annulation of enaminones with iodonium ylides to form isocoumarins
      Yang, Zi; Liu, Chaoshui; Lei, Jieni; Zhou, Yi; Gao, Xiaohui; Li, Yaqian
      Chemical Communications (Cambridge, United Kingdom) (2022), 58 (97), 13483-13486CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      A straightforward approach to synthesize isocoumarins via Rh(III)-catalyzed C-H/C-C bond activation/annulation cascade of enaminones and iodonium ylides has been explored. The established protocol is characterized by an exceedingly simple reaction system, high regioselectivity and good functional group tolerance. Moreover, this strategy may provide a new route to cleavage of the C(sp2)-C(O) bond of unstrained ketones.
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      (e) John, S. E.; Bora, D.; Dastari, S.; Valapila, D. G.; Shankaraiah, N. Synthesis of alpha-pyrones and chromen-2-ones by transition-metal catalyzed annulations of sulfoxonium and iodonium ylides with cis-stilbene acids. New J. Chem. 2022, 46, 19722– 19730,  DOI: 10.1039/D2NJ03454A
      16e
      Synthesis of alpha-pyrones and chromen-2-ones by transition-metal catalyzed annulations of sulfoxonium and iodonium ylides with cis-stilbene acids
      John, Stephy Elza; Bora, Darshana; Dastari, Sowmya; Valapil, Durgesh Gurukkala; Shankaraiah, Nagula
      New Journal of Chemistry (2022), 46 (41), 19722-19730CODEN: NJCHE5; ISSN:1144-0546. (Royal Society of Chemistry)
      A transition metal-catalyzed carbene insertion strategy has been developed to activate the inactivated sp2 C-H bond of medicinally important cis-stilbene acids. This approach enables the facile construction of α-pyrone and chromene-2-one skeletons on the olefinic bond of cis-stilbene acid with high atom economy, good yield, broad functional group tolerance and gram-scale synthetic feasibility. The strategy unveils the efficiency of acid functionalities as directing groups along with sulfoxonium and hypervalent iodonium ylides as carbene precursors. The constructed architectures were explored for their photophys. properties showing emission ranging from 500 to 600 nm, and the biol. potential was examd. through mol. docking anal. and percentage inhibition studies. Addnl., ESI-MS studies were also performed to identify the key intermediates, helping to sketch a probable mechanism.
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    17. 17
      Cheng, B.; Bao, B.; Xu, W.; Li, Y.; Li, H.; Zhang, X.; Li, Y.; Wang, T.; Zhai, H. Synthesis of fully substituted pyrazoles from pyridinium 1,4-zwitterionic thiolates and hydrazonoyl chlorides via a [[3 + 3]-1] pathway. Org. Biomol. Chem. 2020, 18, 2949– 2955,  DOI: 10.1039/D0OB00224K
      17
      Synthesis of fully substituted pyrazoles from pyridinium 1,4-zwitterionic thiolates and hydrazonoyl chlorides via a [[3 + 3] - 1] pathway
      Cheng, Bin; Bao, Bian; Xu, Wei; Li, Yuntong; Li, Hui; Zhang, Xinping; Li, Yun; Wang, Taimin; Zhai, Hongbin
      Organic & Biomolecular Chemistry (2020), 18 (15), 2949-2955CODEN: OBCRAK; ISSN:1477-0520. (Royal Society of Chemistry)
      A novel and practical protocol for the synthesis of fully substituted pyrazoles I [R1 = t-Bu, Ph, 2-furyl, etc.; R2 = CF3, CO2Me, C(O)Ph, etc.; R3 = CO2Me, CO2Et, C(O)Ph] from pyridinium 1,4-zwitterionic thiolates and hydrazonoyl chlorides in excellent yields under mild conditions was described. The transformation proceeded via an unusual [[3 + 3] - 1] pathway, which involved a formal [3 + 3] cascade cyclization followed by a spontaneous ring-contraction/sulfur extrusion reaction from 4H-1,3,4-thiadiazine intermediates.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXlsVWhurY%253D&md5=8e3ba5938299035f1a3ce3b694640328
    18. 18
      Wu, W.; Wu, X.; Fan, S.; Zhu, J. Rh(III)-catalyzed enaminone-directed C–H coupling with diazodicarbonyls for skeleton-divergent synthesis of isocoumarins and naphthalenes. Org. Lett. 2012, 24, 7850– 7855,  DOI: 10.1021/acs.orglett.2c03288
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