1,1-Difluoroallenes are synthesized in good yield via zinc-promoted 1,2-elimination of 3,3-difluoro-2-iodoallylic acetates, which are prepared by the reaction of aldehydes or ketones with 1-iodo-2,2-difluorovinyllithium, generated from commercially available 1,1,1-trifluoro-2-iodoethane.

The article reports the preparation of 1,1‐difluoroallenes by difluorovinylidenation of carbonyl cmpounds. 1,1‐Difluoroallenes have been synthesized via either the formation of the second C–C double bond in fluorinated alkenes or the rearrangement of the C–C triple bonds in fluorinated alkynes.

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