The in situ reaction of dibromodifluoromethane, triphenylphosphine, and aldehydes in the presence of zinc dust affords good yields of gem-difiuoroolefins. Reduction of the difluoroolefins gives selectively the corresponding monofluoro-olefins in excellent yields. The scope and limitation of these procedures are described and compared with those of previous methods.

In recent years considerable attention has been focused on the generation of difluorocarbene for the synthesis of gem-difluorocyclopropanes and other difluoromethylene derivatives. A variety of difluorocarbene precursors have been examined,2 but these

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Scheme I ture) from 9, reacts with the sodium salt of methyl (dimethylphosphinyl)bromoacetate9 in 1,2-dimethoxy ethane to afford 11. Treatment of 11 with m-chloroperoxybenzoic acid gives rise to 12 as a 2:3 mixture of E and Z isomers.Reaction of silyl enol ether 13 (3.5 equiv) at -78 °C in 1,2-dimethoxyethane with methyllithium (2.5 equiv) generates, presumably, enolate 14, which reacts with the esters 12 (-78 °C (30 min) -*• room temperature (1 h)). Chromatography on silica gel afforded three products (Scheme