Cyclic selenonium exo-ylides (3,4-dihydro-1H-2-benzoselenin-2-io)methanides; syntheses and reactions

Abstract

Stable cyclic selenonium exo-ylides (3,4-dihydro-1H-2-benzoselenin-2-io)methanides; (5a–e) have been synthesized by reactions of 3,4-dihydro-1H-2-benzoselenin2,2-dichloride (4) or N-(3,4-dihydro-1H-2-benzoselenin-2-io)toluene-P-sulphonamidate (6) and active methylene compounds. The ylidic nature and the stable configuration of (5a–e) were established on the basis of their spectral data. The reactions of ylides having acetyl group(s)(5a,b) with dimethyl acetylenedi-carboxylate afforded the furan derivatives (8a,b) and (9a) and the dihydrobenzoselenin (3), while reactions of the ylides having no acetyl group, (5c–e), afforded the benzoselenonines (14c–e). The diacetylmethanide (5a) when heated gave the benzoselenepine (15), while (5c) when heated afforded the styrene derivative (18) and a tetrasubstituted ethylene (19). When heated, (5d) gave the [1,2] rearranged product (22). 3,4-Dihydro-1H-2-benzoselenin-2-io)phenacylide (31) was generated by the reaction of the selenonium salt (24) with sodium hydride but was too unstable to be isolated. Thermal decomposition of (31) yielded (3), its counterparts (26–28), a styrene derivative (25), and a novel rearrangement product (29).