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. Book of ylide: Difluoromethylene phosphonium ylide, generated from Ph3P+CF2CO2−, was turned into an efficient difluorocarbene reagent, whereas the classical difluorocarbene reagents, HCF2Cl and FSO2CF2CO2TMS, generated the highly reactive difluoromethylene ylide. Interestingly, it was found that the ylides obtained from different carbene sources showed different reactivity in Wittig reactions (see scheme; TMS=trimethylsilyl).