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 nonpolar multiple bonds, namely, the cycloaddition
with alkenes or alkynes. The difluoroketenimine is generated from
the coupling of tert-butyl isocyanide 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.