Facile Synthesis of Substituted 1,1-Difluoroallenes via Carbonyl Difluorovinylidenation

Abstract

Abstract:Two methods for difluorovinylidenation of carbonyl compounds have been developed to synthesize 1,1-difluoroallenes bearing various substituents. The Reaction of 1-bromo-2,2-difluorovinyllithium, generated from 1,1-dibromo-2,2-difluoroethylene and butyllithium, with aldehydes or ketones and subsequent acetylation with acetic anhydride gave 2-bromo-3,3-difluoroallylic acetates. Elimination of these acetates with butyllithium afforded 1,1-difluoroallenes in high yield (method A). 3,3-Difluoro-2-iodoallylic acetates were similarly prepared from aldehydes or ketones on treatment with 2,2-difluoro-1-iodovinyllithium, generated from 1,1,1-trifluoro-2-iodoethane and LDA, followed by acetylation. These acetates readily underwent elimination with zinc metal to afford 1,1-difluoroallenes in high yield (method B).Scheme 1 Synthesis of 1,1-difluoroallenes by difluorovinylidenation of aldehydes or ketones