gem-Difluorocyclopropenes by [1+2] cycloaddition reactions between difluorocarbene and acetylenes having terminal or internal triple bonds

Difluorocarbene, generated by the Burton method, i.e. by the dissociation of (triphenylphosphonio)difluoromethanide, was found to add to terminal or internal acetylenes with astonishing ease. Actually, it reacts roughly 10 times faster with 4-octyne than with cis-4-octene. The gem-difluorocyclopropenes resulting from the [1+2] cycloaddition process can be isolated with good to excellent yields. They are perfectly stable under anhydrous conditions while in aqueous media they are quantitatively converted to cyclopropenones. - Unsubstituted olefinic ring positions rapidly undergo a base catalyzed hydrogen/deuterium exchange. The acidity of such 2-alkyl- or 2-aryl-1,1-difluorocyclopropenes is estimated to be higher than that of terminal acetylenes.