New methodology for the deoxygenative difluoromethylenation of aldehydes and ketones; unexpected formation of tetrafluorocyclopropanes.

Generation of difluoromethylene phosphorus ylides in the presence of aldehydes and ketones results in Wittig-type reactions to give gem-difluoroalkenes. Subsequent in situ addition of difluorocarbene (carbenoid) can occur (increased with triphenylphosphine and decreased with tributylphosphine) to give tetrafluorocyclopropanes. [Reaction: see text]