Formal insertion of selenoketenes into donor–acceptor cyclopropanes: mesomeric alkynylselenolates as key starting materials

Abstract

Donor–acceptor cyclopropanes (DACs) react with lithium alkynylselenolates in the presence of In(OTf)₃ to furnish tetrahydroselenophenes with exocyclic double bonds. The reaction can be regarded as a formal insertion of selenoketenes into the strained three-membered ring systems. Lithium alkynylselenolates are generated in situ from lithium acetylides and elemental selenium. The reactions afford tetrahydroselenophenes with a broad substrate scope and high yields (up to 95%).

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Introduction

Donor–acceptor cyclopropanes (DACs) are well-established as useful three-carbon synthons.¹ The high ring strain of 115 kJ mol⁻¹ and the polarization originating from the vicinally positioned donor and acceptor groups are the factors accounting for their versatile reactivity.² In addition to the intrinsic polarization, Lewis acids are able to polarize the C–C bond further by chelating to the corresponding acceptor moieties. The push–pull trigger caused by the electron-releasing donor moiety and the electron-withdrawing acceptor moiety enables the three-membered ring to behave as a masked 1,3-zwitterionic intermediate. Thus, these strained ring systems display various reactivities such as (3 + n)-cycloadditions,³ rearrangements⁴ and ring-opening reactions.⁵ Highly functionalized, saturated or partially saturated four-, five-, six- or seven-membered rings are furnished by various (3 + n)-cycloaddition reactions of D–A cyclopropanes with π-systems such as carbonyls,⁶ imines,⁷ nitrosoarenes,⁸ nitrones⁹ and polarized hetero-2π-components.¹⁰ However, cumulated π-systems have not been extensively explored as reaction partners with D–A cyclopropanes. In 2012, the Stolz group reported a (3 + 2)-cycloaddition of DACs with dipolarophiles such as isothiocyanates, carbodiimides and isocyanates to afford thioimidates, imidines and pyrrolidinones, respectively.¹¹ Shortly afterwards, in 2013, Wang and co-workers realized an intramolecular cycloaddition of DACs with an allene pendant on their aryl donor.¹² Werz et al. employed 3-thioxocyclobutanones as thioketene surrogates for the formal insertion of thioketenes, which are unstable under ambient conditions, into DACs (Scheme 1a).¹³ This reaction provided a broad scope of tetrahydrothiophenes in a formal (3 + 2)-cycloaddition followed by a (2 + 2)-cycloreversion. In 2019, Kerrigan and co-workers explored the reactivity of ketenes with DACs, and observed that the reaction outcome depended on the donor moiety and the employed reaction conditions. Palladium catalysis of vinyl cyclopropanes and ketenes furnished highly substituted tetrahydrofurans with an exocyclic double bond (Scheme 1b).¹⁴ However, when the catalytic system was changed to InBr₃-EtAlCl₂, a dual Lewis acid system, exclusive formation of cyclopentanones was observed.¹⁵ Recently, Mlostoń et al. successfully reacted sterically encumbered thioketenes with DACs to access the corresponding sulphur-containing heterocycles (Scheme 1c).¹⁶

Scheme 1 Previous work on the insertion of ketenes and thioketenes into DACs and our present work, with its basic idea of mesomerism between deprotonated selenoketene and deprotonated alkynylselenol.

In view of these prior reports, we were keen to test whether a formal insertion of selenoketenes into DACs, to access similar selenium analogues, would be possible. Selenoketenes are highly labile species, much less stable than their oxygen and sulphur analogues,¹⁷ but have been detected by flash-thermolysis and matrix-photolysis techniques.¹⁸ In 1980, a stable selenoketene was synthesised via selena-Cope rearrangement of silyl ethynyl selenide with a bulky allyl residue, which provided extra stabilization of the expected selenoketene.¹⁹ Such selenoketenes have been subjected to various addition and cycloaddition reactions.²⁰ Accordingly, we surmised that lithium alkynylselenolates, mesomeric forms of deprotonated selenoketenes, might be utilized for a formal insertion of selenoketenes into DACs to deliver tetrahydroselenophenes with an exocyclic double bond (Scheme 1, bottom).²¹

Results and discussion

We initiated the optimization of reaction conditions with the model cyclopropane 1a and trimethylsilylacetylene. Lithium 2-(trimethylsilyl)ethynyl-1-selenolate 2a was generated in situ from trimethylsilylacetylene, nBuLi and elemental selenium according to the literature procedure.²² The solution of 1a and various Lewis acids were added at 25 °C to the selenolate. Most of the commonly used Lewis acids such as Sc(OTf)₃, Yb(OTf)₃, AlCl₃, Cu(OTf)₂, Sn(OTf)₂, Ni(OTf)₂, Y(OTf)₃, NiBr₂ led to ring-opening of the DAC. Ring-closure to afford the desired five-membered ring containing selenium was observed only when In(OTf)₃, Bi(OTf)₃ or Eu(OTf)₃ were employed as Lewis acids (Table 1, entries 1–3), but at first only traces of the selenophene derivative were obtained. An increase in temperature to 50 °C showed an increase in yield of the product (entry 4). Increase in the catalyst loading to 50 mol% increased the product yield to 45% (entry 5). An increase in the temperature to 30 °C delivered 3a in 51% yield (entry 6). Although heating the reaction mixture up to 40 °C gave a better yield of 64%, further heating to 50 °C negatively influenced the yield of the product (entry 8). Screening the stoichiometry of the reagents showed that a 1 : 2 ratio of DAC to selenolate is the best choice. It was observed that the product 3a was formed in 87% yield when the catalyst loading was increased to 80 mol% (entry 9). The rationalization of high catalyst loading may be attributed to its dual role: activation of the DAC by chelation and π-complexation with the alkyne moiety.²³

Table 1 Optimization of the reaction conditions^a

Entry	Lewis acid	Catalyst loading (mol%)	T (°C)	Yield^b (%)
				3a
a Reaction conditions: 1a (100 μmol), 2 (in situ generated), Lewis acid, solvent (0.05 M) under Ar for 18 h. b Yields refer to purified and isolated products.
1	In(OTf)3	20	25	8
2	Bi(OTf)3	20	25	4
3	Eu(OTf)3	20	25	5
4	In(OTf)3	20	50	19
5	In(OTf)3	50	25	45
6	In(OTf)3	50	30	51
7	In(OTf)3	50	40	64
8	In(OTf)3	50	50	33
9	In(OTf)3	80	40	87

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With the optimized reaction conditions in hand, the scope of this method using in situ generated lithium alkynylselenolate 2a and variously substituted DACs was investigated (Scheme 2). Under the optimized reaction conditions, the reaction proceeded smoothly with halogen-bearing aryl cyclopropanes delivering the desired products 3b–3d in good to excellent yields. The electron-rich cyclopropane with a methoxy group on the aryl donor gave the product 3e in 48% yield. Notably, the cyclopropane with a biphenyl donor 1f reacted with the corresponding selenolate to furnish the corresponding product 3f in 76% yield. Aryl donors with ortho, meta and para methyl substituents 1g–1i afforded the corresponding products 3g–3i in yields up to 80%. Surprisingly, the electron-withdrawing cyano (–CN) substituent gave the product 3j in excellent yield (93%); however, the trifluoromethyl (–CF₃) group negatively influenced the reactivity and furnished products 3k in a moderate yield of 69%. The presence of an electron-withdrawing nitro (–NO₂) group at the meta and para position of the aryl donor yielded 3l and 3m in 92% and 72% yields, respectively. The naphthyl donor, an extended π-system, furnished the corresponding tetrahydroselenophene 3n in 77% yield. The thienyl donor was found to be tolerated under the reaction conditions and afforded product 3o in 45% yield. Ethyl esters as acceptor moieties delivered the corresponding product 3p in 73% yield. Vinyl and alkyl moieties as donors did not yield the desired products.

Scheme 2 Substrate scope with respect to DACs. ^a Reaction conditions: 1 (100 μmol), 2a (200 μmol), In(OTf)₃ (80 mol%), THF (2 mL), at 40 °C under Ar for 18 h. Yields refer to purified and isolated products. ^b Large scale refers to 1 mmol of DAC.

The generality of the proposed methodology was then evaluated using different selenolate precursors 2 (Scheme 3). These were generated from the corresponding terminal alkynes and elemental selenium and reacted with cyclopropane 1a. Under the optimized conditions, alkynes with a more sterically encumbered terminus such as the triisopropylsilyl (TIPS) group underwent smooth transformation and furnished the product 4a in 49% yield. The lithium alkynylselenolate generated from phenylacetylene afforded the corresponding product 4b in 60% yield. The presence of a meta-methyl group on the phenylacetylene lowered the yield of corresponding product 4c to 43% yield. Changing to the aliphatic pentyne as the selenolate precursor delivered the corresponding tetrahydroselenophene 4d in 58% yield. Utilising cyclopropyl acetylene as precursor furnished the product 4e in 45% yield. tert-Butylacetylene was found to be tolerated under the reaction conditions and afforded the product 4f in 51% yield.

Scheme 3 Substrate scope with respect to various alkynes. Reaction conditions: 1a (100 μmol), 2 (200 μmol), In(OTf)₃ (80 mol%), THF (2 mL), at 40 °C under Ar for 18 h. Yields refer to purified and isolated products.

To shine a light on the reaction mechanism, the stereochemical course of the reaction using enantioenriched cyclopropane (S)-1a (98% ee) was explored. It was found that the product 4b was formed in 79% yield with 95% ee (Scheme 4). The reaction was observed to proceed with high stereospecificity, with only a slight erosion of enantiopurity. This clearly rules out the likelihood of an S_N1 pathway, in which a racemic mixture would have been observed. This prompted us to conclude that the initial attack is an S_N2-like ring-opening of the highly strained ring system by in situ generated alkynylselenolate 2b, followed by a ring-closure to obtain (R)-4b with an inverted stereochemistry.

Scheme 4 Stereospecificity experiment.

A plausible mechanism for the transformation of DACs to tetrahydroselenophenes is proposed in Scheme 5. In(OTf)₃ activates the strained three-membered ring (S)-1a by coordinating to the acceptor moieties. This depletes the electron density from the C–C bond between the donor-substituted and the acceptor-substituted carbon atoms of the cyclopropane, thereby weakening it. The nucleophilic selenolate 2b undergoes an S_N2-like ring-opening of the highly strained system, leading to open-chain intermediate 5b. The emerging malonate attacks the electrophilic carbon next to selenium in a 5-exo-dig fashion to obtain 6b. Protonation furnishes product (R)-4b. Because of the bulky dicarboxylate moiety, the final step takes place in a highly selective manner; only one of the two possible double bond isomers is formed.

Scheme 5 Proposed mechanism.

Finally, we demonstrated the utility of the proposed methodology by subjecting tetrahydroselenophene 3c to several further transformations (Scheme 6). Notably, oxidation of 3c using 3.0 equivalents of mCPBA delivered selenoxide 7c in 98% yield as a single diastereoisomer; the double bond was not effected by oxidation. Desilylation of 3c under acidic conditions using pTsOH delivered the corresponding product 8c in 68% yield. The structure of 8c was unambiguously confirmed by single crystal X-ray analysis. Decarboxylation and concomitant desilylation of 3c using NaOH furnished dihydroselenophene 9c in 88% yield.

Scheme 6 Follow-up reactions.

Conclusions

In summary, we have demonstrated a simple and efficient strategy for the construction of tetrahydroselenophenes starting from D–A cyclopropanes and alkynylselenolates. Alkynylselenolates can be regarded as mesomeric forms of deprotonated selenoketenes. This transformation thus represents the formal insertion of a selenoketene into the three-membered ring. The method was found to be general, and an extensive substrate scope with high functional group tolerance was realized. Various tetrahydroselenophene derivatives were obtained in good to excellent yields. The concept of exploiting such masked (and previously neglected) mesomerism might pave the way to other types of formal cycloaddition reactions with unusual or unstable cumulated π-systems.

Experiments

General procedure for the synthesis of tetrahydroselenophene 3

A flame-dried, argon-filled microwave tube was charged with alkyne (2.2 equiv.) in THF (0.1 M) at 0 °C. The solution was cooled to −78 °C. To this solution was added nBuLi (2.0 equiv.). The reaction was stirred for 1 h and slowly warmed to 25 °C. Elemental grey selenium (2.2 equiv.) was then added in one portion. Further stirring led to dissolution of the selenium, whereby the solution changed colour from black to pale yellow, furnishing 2.

A solution of cyclopropane diester 1 (100 μmol, 1.0 equiv.) and In(OTf)₃ (80 μmol, 0.8 equiv.) dissolved in THF (0.1 M) were added to the in situ generated 2 under an argon atmosphere. The solution was stirred at 40 °C (oil bath) until TLC analysis showed full conversion of cyclopropane 1. The reaction tube was allowed to cool to the room temperature. EtOAc (10 mL) was added, and the reaction mixture was then washed with saturated NaHCO₃ solution and extracted with EtOAc (3 × 20 mL). The organic layers were combined and dried over Na₂SO₄. The solvent was evaporated under reduced pressure. The crude product 3 was purified by silica gel column chromatography.

Author contributions

A. J. conducted the experiments, analysed the data and wrote the draft. P. G. J. determined the crystal structure of compound 8c and assisted with manuscript preparation. D. B. W. supervised the work and finalised the manuscript.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

A DAAD scholarship to A. J. is gratefully acknowledged.

References

1. (a) H.-U. Reissig and R. Zimmer, Donor-Acceptor-Substituted Cyclopropane Derivatives and Their Application in Organic Synthesis, Chem. Rev., 2003, 103, 1151–1196; (b) S. J. Gharpure and L. N. Nanda, Application of Oxygen/Nitrogen Substituted Donor-Acceptor Cyclopropanes on the Total Synthesis of Natural Products, Tetrahedron Lett., 2017, 58, 711–720; (c) C. A. Carson and M. A. Kerr, Heterocycles from Cyclopropanes: Applications in Natural Product Synthesis, Chem. Soc. Rev., 2009, 38, 3051–3060; (d) O. A. Ivanova and I. V. Trushkov, Donor-Acceptor Cyclopropanes in the Synthesis of Carbocycles, Chem. Rec., 2019, 19, 2189–2208.
2. (a) M. S. Gordon, Ring Strain in Cyclopropane, Cyclopropene, Silacyclopropane, and Silacyclopropene, J. Am. Chem. Soc., 1980, 102, 7419–7422; (b) T. F. Schneider, J. Kaschel and D. B. Werz, A New Golden Age for Donor-Acceptor Cyclopropanes, Angew. Chem., Int. Ed., 2014, 53, 5504–5523; (c) D. B. Werz and A. T. Biju, Uncovering the Neglected Similarities of Arynes and Donor-Acceptor Cyclopropanes, Angew. Chem., Int. Ed., 2020, 59, 3385–3398; (d) J. Turkowska, J. Durka, M. Ociepa and D. Gryko, Reversal of Regioselectivity in Reactions of Donor-Acceptor Cyclopropanes with Electrophilic Olefins, Chem. Commun., 2022, 58, 509–512; (e) D. A. McLeod, M. K. Thøgersen, C. L. Barløse, M. L. Skipper, E. B. Obregón and K. A. Jørgensen, Enantioselective (8+3)-Cycloadditions by Activation of Donor-Acceptor Cyclopropanes Employing Chiral Brønsted Base Catalysis, Angew. Chem., Int. Ed., 2022, 61, e202206096; (f) M. A. Belaya, D. A. Knyazev, D. D. Borisov, R. A. Novikov and Y. V. Tomilov, GaCl₃-Mediated Cascade (2+4)-Cycloaddition/(4+2)-Annulation of Donor-Acceptor Cyclopropanes with Conjugated Dienes: Strategy for the Construction of Benzobicyclo3.3.1nonane Skeleton, J. Org. Chem., 2021, 86, 8089–8100; (g) G. Nie, X. Huang, Z. Wang, D. Pan, J. Zhang and Y. R. Chi, Umpolung of Donor–Acceptor Cyclopropanes via N-Heterocyclic Carbene Organic Catalysis, Org. Chem. Front., 2021, 8, 5105–5111; (h) A. Kreft, A. Lücht, J. Grunenberg, P. G. Jones and D. B. Werz, Kinetic Studies of Donor-Acceptor Cyclopropanes: The Influence of Structural and Electronic Properties on the Reactivity, Angew. Chem., Int. Ed., 2019, 58, 1955–1959.
3. (a) Y. Xia, X. Liu and X. Feng, Asymmetric Catalytic Reactions of Donor-Acceptor Cyclopropanes, Angew. Chem., Int. Ed., 2021, 60, 9192–9204; (b) V. Pirenne, E. G. L. Robert and J. Waser, Catalytic (3+2)-Annulation of Donor-Acceptor Aminocyclopropane Monoesters and Indoles, Chem. Sci., 2021, 12, 8706–8712; (c) H. K. Grover, M. R. Emmett and M. A. Kerr, Carbocycles from Donor-Acceptor Cyclopropanes, Org. Biomol. Chem., 2015, 13, 655–671; (d) H. Xu, J.-L. Hu, L. Wang, S. Liao and Y. Tang, Asymmetric Annulation of Donor-Acceptor Cyclopropanes with Dienes, J. Am. Chem. Soc., 2015, 137, 8006–8009; (e) T. Kaicharla, T. Roy, M. Thangaraj, R. G. Gonnade and A. T. Biju, Lewis Acid Catalyzed Selective Reactions of Donor-Acceptor Cyclopropanes with 2-Naphthols, Angew. Chem., Int. Ed., 2016, 55, 10061–10064; (f) M. Petzold, P. G. Jones and D. B. Werz, (3+3)-Annulation of Carbonyl Ylides with Donor-Acceptor Cyclopropanes: Synergistic Dirhodium(II) and Lewis Acid Catalysis, Angew. Chem., Int. Ed., 2019, 58, 6225–6229; (g) A. U. Augustin, J. L. Merz, P. G. Jones, G. Mlostoń and D. B. Werz, (4+3)-Cycloaddition of Donor-Acceptor Cyclopropanes with Thiochalcones: A Diastereoselective Access to Tetrahydrothiepines, Org. Lett., 2019, 21, 9405–9409; (h) G. A. Oliver, M. N. Loch, A. U. Augustin, P. Steinbach, M. Sharique, U. K. Tambar, P. G. Jones, C. Bannwarth and D. B. Werz, Cycloadditions of Donor-Acceptor Cyclopropanes and -butanes using S=N-Containing Reagents: Access to Cyclic Sulfinamides, Sulfonamides, and Sulfinamidines, Angew. Chem., Int. Ed., 2021, 60, 25825–25831; (i) A. Jacob, P. Barkawitz, P. G. Jones and D. B. Werz, Insertion of S₂ into Donor-Acceptor Cyclopropanes: Access to Dithiolanes and Their Conversion to Thietane Dioxides, Org. Lett., 2022, 24, 3028–3032; (j) P. G. Sergeev, R. A. Novikov and Y. V. Tomilov, Lewis Acid–Catalyzed Formal (4+2)– and (2+2+2)–Cycloaddition Between 1−Azadienes and Styrylmalonates as Analogues of Donor–Acceptor Cyclopropanes, Adv. Synth. Catal., 2021, 363, 5292–5299.
4. (a) T. F. Schneider, J. Kaschel, S. I. Awan, B. Dittrich and D. B. Werz, From Furan to Molecular Stairs: Syntheses, Structural Properties, and Theoretical Investigations of Oligocyclic Oligoacetals, Chem. – Eur. J., 2010, 16, 11276–11288; (b) S. Y. Shim, Y. Choi and D. H. Ryu, Asymmetric Synthesis of Cyclobutanone via Lewis Acid Catalyzed Tandem Cyclopropanation/Semipinacol Rearrangement, J. Am. Chem. Soc., 2018, 140, 11184–11188; (c) A. Ortega, R. Manzano, U. Uria, L. Carrillo, E. Reyes, T. Tejero, P. Merino and J. L. Vicario, Catalytic Enantioselective Cloke-Wilson Rearrangement, Angew. Chem., Int. Ed., 2018, 57, 8225–8229; (d) R. K. Varshnaya, P. Singh, N. Kaur and P. Banerjee, Cascade intramolecular rearrangement/cycloaddition of nitrocyclopropane carboxylates with alkynes/alkenes: access to uncommon bi(hetero)cyclic systems, Org. Chem. Front., 2021, 8, 1267–1274; (e) S. Thangamalar, M. Thangamani and K. Srinivasan, The Cloke-Wilson rearrangement of aroyl-substituted donor-acceptor cylopropanes containing arylethyl donors, Org. Biomol. Chem., 2022, 20, 3145–3153.
5. (a) E. Budynina, K. Ivanov, I. Sorokin and M. Melnikov, Ring Opening of Donor–Acceptor Cyclopropanes with N-Nucleophiles, Synthesis, 2017, 3035–3068; (b) B. Mondal, D. Das and J. Saha, Multicomponent, Tandem 1,3- and 1,4-Bisarylation of Donor-Acceptor Cyclopropanes and Cyclobutanes with Electron-Rich Arenes and Hypervalent Arylbismuth Reagents, Org. Lett., 2020, 22, 5115–5120; (c) A. Guin, T. Rathod, R. N. Gaykar, T. Roy and A. T. Biju, Lewis Acid Catalyzed Ring-Opening 1,3-Aminothiolation of Donor-Acceptor Cyclopropanes Using Sulfenamides, Org. Lett., 2020, 22, 2276–2280; (d) Z. Zuo, C. G. Daniliuc and A. Studer, Cooperative NHC/Photoredox Catalyzed Ring-Opening of Aryl Cyclopropanes to 1-Aroyloxylated-3-Acylated Alkanes, Angew. Chem., Int. Ed., 2021, 60, 25252–25257; (e) J. Wallbaum, L. K. B. Garve, P. G. Jones and D. B. Werz, Ring-Opening Regio-, Diastereo-, and Enantioselective 1,3-Chlorochalcogenation of Cyclopropyl Carbaldehydes, Chem. – Eur. J., 2016, 22, 18756–18759; (f) S. Kolb, M. Petzold, F. Brandt, P. G. Jones, C. R. Jacob and D. B. Werz, Electrocatalytic Activation of Donor-Acceptor Cyclopropanes and Cyclobutanes: An Alternative C(sp³)-C(sp³) Cleavage Mode, Angew. Chem., Int. Ed., 2021, 60, 15928–15934; (g) Z. Zuo and A. Studer, 1,3-Oxyalkynylation of Aryl Cyclopropanes with Ethylnylbenziodoxolones Using Photoredox Catalysis, Org. Lett., 2022, 24, 949–954; (h) N. L. Ahlburg, T. Freese, S. Kolb, S. Mummel, A. Schmidt and D. B. Werz, Functionalization of Sydnones with Donor–Acceptor Cyclopropanes, Cyclobutanes, and Michael Acceptors, Eur. J. Org. Chem., 2021, 1603–1606.
6. (a) P. D. Pohlhaus, S. D. Sanders, A. T. Parsons, W. Li and J. S. Johnson, Scope and Mechanism for Lewis Acid-Catalyzed Cycloadditions of Aldehydes and Donor-Acceptor Cyclopropanes: Evidence for A Stereospecific Intimate Ion Pair Pathway, J. Am. Chem. Soc., 2008, 130, 8642–8650; (b) J. Sabbatani and N. Maulide, Temporary Generation of a Cyclopropyl Oxocarbenium Ion Enables Highly Diastereoselective Donor-Acceptor Cyclopropane Cycloaddition, Angew. Chem., Int. Ed., 2016, 55, 6780–6783; (c) A. Kreft, P. G. Jones and D. B. Werz, The Cyclopropyl Group as a Neglected Donor in Donor-Acceptor Cyclopropane Chemistry, Org. Lett., 2018, 20, 2059–2062; (d) M. Faltracco, K. N. A. van de Vrande, M. Dijkstra, J. M. Saya, T. A. Hamlin and E. Ruijter, Palladium-Catalyzed Cascade to Benzoxepins by Using Vinyl-Substituted Donor-Acceptor Cyclopropanes, Angew. Chem., Int. Ed., 2021, 60, 14410–14414.
7. (a) A. T. Parsons, A. G. Smith, A. J. Neel and J. S. Johnson, Dynamic Kinetic Asymmetric Synthesis of Substituted Pyrrolidines from Racemic Cyclopropanes and Aldimines: Reaction Development and Mechanistic Insights, J. Am. Chem. Soc., 2010, 132, 9688–9692; (b) J. Preindl, S. Chakrabarty and J. Waser, Dearomatization of Electron Poor Six-Membered N-Heterocycles Through (3+2) Annulation with Aminocyclopropanes, Chem. Sci., 2017, 8, 7112–7118; (c) K. Verma and P. Banerjee, Synthesis of Indenopyridine Derivatives via MgI₂ -Promoted (2+4)-Cycloaddition Reaction of In-situ Generated 2-Styrylmalonate from Donor-Acceptor Cyclopropanes and Chalconimines, Adv. Synth. Catal., 2018, 360, 3687–3692.
8. (a) S. Chakrabarty, I. Chatterjee, B. Wibbeling, C. G. Daniliuc and A. Studer, Stereospecific Formal (3+2)-Dipolar Cycloaddition of Cyclopropanes with Nitrosoarenes: An Approach to Isoxazolidines, Angew. Chem., Int. Ed., 2014, 53, 5964–5968; (b) S. Das, C. G. Daniliuc and A. Studer, Multicomponent 1,3-Bifunctionalization of Donor-Acceptor Cyclopropanes with Arenes and Nitrosoarenes, Org. Lett., 2016, 18, 5576–5579.
9. (a) I. S. Young and M. A. Kerr, A Homo (3+2)-Dipolar Cycloaddition: The Reaction of Nitrones with Cyclopropanes, Angew. Chem., Int. Ed., 2003, 42, 3023–3026; (b) Y.-B. Kang, X.-L. Sun and Y. Tang, Highly Enantioselective and Diastereoselective Cycloaddition of Cyclopropanes with Nitrones and Its Application in The Kinetic Resolution of 2-Substituted Cyclopropane-1,1-Dicarboxylates, Angew. Chem., Int. Ed., 2007, 46, 3918–3921.
10. (a) F. de Nanteuil and J. Waser, Catalytic (3+2)- Annulation of Aminocyclopropanes for The Enantiospecific Synthesis of Cyclopentylamines, Angew. Chem., Int. Ed., 2011, 50, 12075–12079; (b) N. L. Ahlburg, P. G. Jones and D. B. Werz, cis-Selective, Enantiospecific Addition of Donor-Acceptor Cyclopropanes to Activated Alkenes: An Iodination/Michael-Cyclization Cascade, Org. Lett., 2020, 22, 6404–6408; (c) S. Nicolai and J. Waser, (4+3)-Annulation of Donor-Acceptor Cyclopropanes and Azadienes: Highly Stereoselective Synthesis of Azepanones, Angew. Chem., Int. Ed., 2022, 61, e202209006; (d) A. U. Augustin and D. B. Werz, Exploiting Heavier Organochalcogen Compounds in Donor-Acceptor Cyclopropane Chemistry, Acc. Chem. Res., 2021, 54, 1528–1541.
11. A. F. G. Goldberg, N. R. O'Connor, R. A. Craig and B. M. Stoltz, Lewis Acid Mediated (3+2)-Cycloadditions of Donor-Acceptor Cyclopropanes with Heterocumulenes, Org. Lett., 2012, 14, 5314–5317.
12. Z. Wang, J. Ren and Z. Wang, Lewis Acids Promoted Formal Intramolecular (3+2)-Parallel and Cross-Cycloadditions of Cyclopropane 1,1-Diesters with Allenes, Org. Lett., 2013, 15, 5682–5685.
13. A. U. Augustin, M. Busse, P. G. Jones and D. B. Werz, Formal Insertion of Thioketenes into Donor-Acceptor Cyclopropanes by Lewis Acid Catalysis, Org. Lett., 2018, 20, 820–823.
14. M. Mondal, M. Panda, V. McKee and N. J. Kerrigan, Asymmetric Synthesis of Tetrahydrofurans through Palladium(0) Catalyzed (3+2)-Cycloaddition of vinyl-cyclopropanes with Ketenes, J. Org. Chem., 2019, 84, 11983–11991.
15. M. Mondal, M. Panda, N. W. Davis, V. McKee and N. J. Kerrigan, Asymmetric Synthesis of Cyclopentanones Through Dual Lewis Acid Catalysed (3+2)-Cycloaddition of Donor-Acceptor Cyclopropanes with Ketenes, Chem. Commun., 2019, 55, 13558–13561.
16. G. Mlostoń, M. Kowalczyk, A. U. Augustin, P. G. Jones and D. B. Werz, Lewis-Acid Catalyzed (3+2)-Cycloadditions of Donor-Acceptor Cyclopropanes with Thioketenes, Eur. J. Org. Chem., 2021, 6250–6253.
17. M. H. Ghandehari, D. Davalian, M. Yalpani and M. H. Partovi, Base-Catalyzed Decomposition of 1,2,3-Selenadiazoles and Acid-Catalyzed Formation of Diselenafulvenes, J. Org. Chem., 1974, 39, 3906–3912.
18. (a) R. Schulz and A. Schweig, 6-Fulveneselone, Angew. Chem., Int. Ed. Engl., 1980, 19, 69–70; (b) R. S. Sukhai, R. de Jong and L. Brandsma, A Convenient Method for the Preparation of Substituted Selenoamides and Thioamides, Synthesis, 1977, 888–889; (c) A. Holm, C. Berg, C. Bjerre, B. Bak and H. Svanholt, Isolation and Characterization of Selenoketens, J. Chem. Soc., Chem. Commun., 1979, 99.
19. E. Schaumann and F.-F. Grabley, Stable Selenoketenes via Selena-Cope Rearrangement, Tetrahedron Lett., 1980, 21, 4251–4254.
20. (a) M. Koketsu, M. Kanoh, E. Itoh and H. Ishihara, Reaction of Allenyl Selenoketene, Generated by 3,3-Sigmatropic Rearrangement with Amines, J. Org. Chem., 2001, 66, 4099–4101; (b) M. Koketsu, K. Mizutani, T. Ogawa, A. Takahashi and H. Ishihara, Synthesis of 3-Acyl-1-alkyl-2-alkylseleno-1-cyclobutene using Alkyneselenolate, J. Org. Chem., 2004, 69, 8938–8941.
21. (a) M. Kaname and H. Sashida, Tandem Addition–Cyclization of O-Ethynylphenyllithiums and Isoselenocyanates: A Convenient Preparation of Functionalized Benzo[C]Selenophenes, Tetrahedron Lett., 2011, 52, 3279–3282; (b) M. Buerger, S. H. Roettger, M. N. Loch, P. G. Jones and D. B. Werz, Pd-Catalyzed Cyanoselenylation of Internal Alkynes: Access to Tetrasubstituted Selenoenol Ethers, Org. Lett., 2020, 22, 5025–5029; (c) R. M. Gai, R. F. Schumacher, D. F. Back and G. Zeni, Regioselective Formation of Tetrahydroselenophenes via 5-exo-dig-Cyclization of 1-Butylseleno-4-alkynes, Org. Lett., 2012, 14, 6072–6075; (d) V. A. D′yakonov, A. G. Ibragimov, L. M. Khalilov, A. A. Makarov, R. K. Timerkhanov, R. A. Tuktarova, O. A. Trapeznikova and L. F. Galimova, Dzhemilev Reaction in the Synthesis of Five-Membered Sulfur and Selenium Heterocycles, Chem. Heterocycl. Compd., 2009, 45, 317–326; (e) M. Segi, T. Takahashi, H. Ichinose, G. M. Li and T. Nakajima, An Efficient Construction of a Selenocarbonyl Unit by the Reaction of Acetal Derivatives with Bis(Dimethylaluminum) Selenide, Tetrahedron Lett., 1992, 33, 7865–7868.
22. (a) D. B. Werz and R. Gleiter, Polyalkynes Capped by Sulfur and Selenium, J. Org. Chem., 2003, 68, 9400–9405; (b) R. Gleiter and D. B. Werz, Alkynes Between Main Group Elements: From Dumbbells via Rods to Squares and Tubes, Chem. Rev., 2010, 110, 4447–4488; (c) R. Pietschnig, K. Merz and S. Schäfer, Synthesis, Charge Distribution, and Dimerization Behavior of Lithium Alkynylselenolates, Heteroat. Chem., 2005, 16, 169–174.
23. S. Pathipati, A. van der Werf and N. Selander, Indium(III)-Catalyzed Transformations of Alkynes: Recent Advances in Carbo- and Heterocyclization Reactions, Synthesis, 2017, 4931–4941.

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Footnote

† Electronic supplementary information (ESI) available. CCDC 2210773. For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d2qo01568d

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