Conversion between Difluorocarbene and Difluoromethylene Ylide

Abstract The interconversion between difluoromethylene ylide and difluorocarbene is described. The difluoromethylene ylide precursor, Ph 3 P + CF 2 CO 2 − , could be turned into an efficient difluorocarbene reagent, whereas the classical difluorocarbene reagents, HCF 2 Cl and FSO 2 CF 2 CO 2 TMS, 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.