Regioselectivity in ring-expansion of 1-substituted Bicyclo[2.1.l]hexan-2-ones: preferential migration of methylene over bridgehead carbon

Abstract

Ring expansion of several 1-substituted bicyclo[2.1.1]hexan-2-ones has been investigated in order to compare the effect of substitution on the migratory aptitude of the bridgehead carbon in relation to the methylene carbon. In the cases examined it was observed that there is a marked preference for migration of the methylene carbon, with the substituted substrates displaying higher regioselectivity than the parent ketone. In the rearrangement of both 1-fluoro- and 1-chloro-bicyclo[2.1.1]- hexan-2-one, migration of the methylene carbon occurs exclusively.