Preparation and Regioselective SN2‘ Reaction of Novel gem-Difluorinated Vinyloxiranes with RLi

Abstract

A series of hitherto unknown 3,4-epoxy-1,1-difluorobutenes were prepared from the readily accessible α,β-epoxy ketones and these compounds were found to undergo regioselective S_N2‘ reactions with hard RLi nucleophiles occurring at the highly positively charged terminal fluorine-possessing sp² carbon atom in quite sharp contrast to the cases of the corresponding nonfluorinated vinyloxiranes which only attained a low level of regioselectivity. Addition of HMPA substantially improved the products' olefinic stereoselectivity. Theoretical calculations were used to qualitatively explore the nature of selectivity in these reactions.