Enamine chemistry. Part 36. Alkylation of imines of medium–large ring ketones with electrophilic alkenes

Abstract

The alkylation of the benzylamine imines of cycloheptanone, cyclo-octanone, and cyclododecanone with acrylonitrile, methyl acrylate, methyl vinyl sulphone, phenyl vinyl ketone, and phenyl vinyl sulphone, has been studied. The course of the reaction is surprisingly sensitive to the size of the ring, the size of any substituent at C-2, and the relative reactivity of the electrophilic alkene. Only mono-2-substituted cycloalkanones were produced with all electrophilic alkenes except methyl acrylate, which reacted twice with cycloheptanone imine and, under forcing conditions, twice with, cyclo-octanone imine, to give 2,2-bis-β-methoxycarbonylethylcycloheptanone and 2,8-bis-β-methoxycarbonylethylcyclo-octanone, the latter in very low yield. Methylcycloheptanone imine gave the 2-alkylated-2-methyl ketone with acrylonitrile and methyl acrylate whereas 2-methylcyclododecanone imine gave a mixture of 2-alkylated-2-methyl- and 12-alkylated-2-methyl ketones.