Stable Difluoromethylene Olefination Solutions

Abstract

The reaction of terminal difluoromethylene olefins with fluoride ion provides a facile method for the generation of fluorinated carbanions.² Since the initial report of the preparation of terminal 1,1-difluoromethylene olefins via the reaction of aldehydes with difluoromethylene ylids,³ considerable interest has been focused on this type of reaction as a general route to these interesting carbanion precursors. An improved method of ylid generation from triphenylphosphine and dibromodifluoromethane circumvented several of the problems encountered in the sodium chloro-difluoroacetate method - namely, isomerization of the initially formed terminal olefin and hydrogen fluoride addition.⁴ Two major unsolved problems in this improved method,⁴ as well as the acetate salt method,⁵ prevented this type of olefination reaction from attaining generality. First, non-activated ketones did not react, thereby limiting the reaction to aldehydes and ketones activated by a perhaloalkyl group. Secondly, the olefinating solution (via either method) showed no stability, 3, 4 limiting the