Carbene reactions of N-aziridinylimines

Abstract

Carbene reactions of N-aziridinylimines have been studied. -Hydroxy alkylidene carbenes were generated from the corresponding -oxetanyl-N-aziridinylimines by thermal decomposition of aziridine ring and oxetane ring opening. The alkylidene carbenes thus generated were found to form substituted dihydrofuran derivatives via intramolecular 1,5-O-H insertion. In the case of N-aziridinylimines tethered to 5- and 6- membered cyclic ethers at -position, 6- and 7- membered cyclic ethers were obtained by the direct ring expansion of alkyl carbene into C-C bond. However, thermal reactions of N-aziridinylimines bearing cyclic acetal at -position afforded ring expansion products via the oxonium ylide intermediates. The ammonium ylide formation of alkyl carbene has been studied. -Nitrogen substituted alkyl carbenes generated from N-aziridinylimines underwent the ring expansion via the formation of cyclized ammonium ylide and 1,2-hydrogen migration. The ratio of two products were affected by the nature of the functional group attached to nitrogen atom and by the ring strain of cyclic compound. The order of the functional group, in which more ring expansion product via ammonium ylide intermediate was obtained, was as follows : Benzyl ＞ Benzoyl ＞ Benzyloxycarbonyl ＞ Tosyl ＞ Trifluoroacetyl. More ring expansion products were obtained in 5- membered ring pyrrolidine derivatives than in 6- membered ring piperidine derivatives. This ring expansion reaction was also applicable to lactam derivatives.