Stable Difluoromethylene Olefination Solutions

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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