Generation and reactions of carbenes derived from N-aziridinylimines

Abstract

Generation and reactions of carbenes derived from N-aziridinylimines have been studied. $\alpha$-Hydroxyalkylidene carbenes were generated from the corresponding $\alpha$,$\beta$-epoxy aziridinylimines by thermal decomposition. The alkylidene carbenes thus generated were found to form $\alpha$-hydroxy alkynes by 1,2-hydrogen migration in excellent yield. 2-Substituted alkylidene carbenes proceeded to various cyclopentenols, such as fused bicyclic, bridged bicyclic, and spiro compounds, by 1,5-C-H insertion reactions. $\alpha$-Hydroxyalkylidene carbenes containing silyloxy group led to furan derivatives by insertion into 5,6-related O-Si bond in good yield. The 1,6-O-Si and 1,7-O-Si insertion reactions were also observed. The order of reactivity in $\alpha$-hydroxyalkylidene carbenes is : 1,2-hydrogen shift $>>$ 1,5-O-Si insertion $>$ 1,5-C-H insertion $>$ 1,6-O-Si and 1,7-O-Si insertion $>$ 1,2-alkyl migration. The neighboring effect of heteroatoms on alkyl carbenes, also, has been studied. $\alpha$-Alkylthio and $\alpha$-alkylseleno alkylcarbenes generated from aziridinylimines proceeded more rapidly to the formation of the cyclized ylides than the formation of olefin products by 1,2-hydrogen migration. However, the 1,2-H shift of $\alpha$-alkoxy alkyl carbenes was much faster than the formation of the oxonium ylides. Using episulfonium ylides, a variety of structurally different sulfur-containing heterocyclic compounds including 1,4-dithiins, 1,4-oxathiins, 1,4-thiazines, and 1,4-dithiepines were obtained in high yields. Thermal reaction of aziridinylimines bearing oxetane at the $\alpha$-position afforded dihydrofuran derivatives by O-H insertion of alkylidene carbenes generated by aziridine and oxetane ring opening. In the case of aziridinylimines tethered to 5- or 6-membered cyclic ethers at the $\alpha$-position, 6- or 7-membered cyclic ethers were obtained by the direct ring expansion into C-C bond. However, the ring expansion products via the formation ...