Difluoroketenimine: Generation from Difluorocarbene and Isocyanide, and Its [3+2] Cycloadditions with Alkenes or Alkynes.

Ketenimines have been explored as useful building blocks for the synthesis of heteroatom containing cyclic compounds through the cycloaddition with polar multiple bonds. Herein we report the cycloaddition of difluoroketenimine with non-polar multiple bonds, namely the cycloaddition with alkenes or alkynes. The difluoroketenimine is generated from the coupling of tert-butylisocyanide and difluorocarbene, which is formed in situ from (bromodifluoromethyl)trimethylsilane. The difluoroketenimine then reacts in situ with alkenes or alkynes to afford fluorinated pyrrolidines or pyrroles. DFT study suggests that a fluorinated cyclic (alkyl)(amino)carbene is involved as the key intermediate in these reactions.