Attempts to Synthesize a Thiirane, Selenirane, and Thiirene by Dealkylation of Chalcogeniranium and Thiirenium Salts

Abstract

Thiiranium salts [Ad2SR]+X− (5, 8, 9, 11, 12; X−=Tf2N− (Tf=CF3SO2), SbCl6−) and seleniranium salts [Ad2SeR]+X− (14, 16, 17, 23–25; X−=Tf2N−, BF4−, CHB11Cl11−, SbCl6−) are synthesized from strained alkene bis(adamantylidene) (1). The disulfides and the diselenides (Me3SiCH2CH2E)2 (4, 13), (tBuMe2SiCH2CH2E)2 (7, 22), and (NCCH2CH2E)2 (10, 15; E=S, Se) have been used. The thiirenium salts [tBu2C2SR]+X− (34) and [Ad2C2SR]+X− (35, 36) are prepared from the bis‐tert‐butylacetylene (2) and bis‐adamantyl‐acetylene (3) with R=Me3SiCH2CH2 and tBuMe2SiCH2CH2. Attempts to cleave off the groups Me3SiCH2CH2, tBuMe2SiCH2CH2, and NCCH2CH2 resulted in thiiranes 27, 30. No selenirane Ad2Se (33) is formed from seleniranium salts, instead cleavage to the alkene (1) and diselenide (13, 15) occurs. The thiirenium salt [Ad2C2SCH2CH2SiMe3]+Tf2N− (35) does not yield the thiirene Ad2C2S (37), the three‐membered ring is cleaved, forming the alkyne (3) and disulfide (4). All compounds are characterized by ESI mass spectra, NMR spectra, and by quantum chemical calculations. Crystal structures of the salts 8, 12, 25, 17, 26, 36 and the thiiranes 27, 30 are presented.

Aromaticity and antiaromaticity in monoheterocyclic three‐membered rings: Application of natural bond orbital theory

“…The strong antiaromaticity calculated here for thiirene may explain the recent failure by Poleschner and Seppelt to synthesize this molecule by dealkylation from a thiirenium ion. [ 54 ] In addition, though there are crystal structures of the saturated analogs (e.g., thiirane or chloriranium ion), [ 54,55 ] there are no reports in the Cambridge Structural Database (CSD) of these unsaturated species likely due to their moderate to very strong antiaromatic nature. [ 56 ]…”

“…The strong antiaromaticity calculated here for thiirene may explain the recent failure by Poleschner and Seppelt to synthesize this molecule by dealkylation from a thiirenium ion. [54] In addition, though there are crystal structures of the saturated analogs (e.g., thiirane or chloriranium ion), [54,55] there are no reports in the Cambridge Structural Database (CSD) of these unsaturated species likely due to their moderate to very strong antiaromatic nature. [56] Hyperconjugative aromaticity refers to molecules in which the filled π C=C orbital interacts with the σ* orbital(s) of exo-cyclic substituents on the heteroatom via hyperconjugation to create a pseudo 2π electron aromatic system (Figure 2).…”