Conversion between Difluorocarbene and Difluoromethylene Ylide

The interconversion between difluoromethylene ylide and difluorocarbene is described. The difluoromethylene ylide precursor, Ph₃P⁺CF₂CO₂^?, could be turned into an efficient difluorocarbene reagent, whereas the classical difluorocarbene reagents, HCF₂Cl and FSO₂CF₂CO₂TMS, could generate highly reactive difluoromethylene ylide. Thus the Wittig difluoro‐olefination and difluorocyclopropanation could be selectively realized by using the same reagent. In addition, the ylides obtained from different carbene sources showed different reactivity in Wittig reactions.