N-Heterocyclic Carbene Catalyzed γ-Dihalomethylenation of Enals by Single-Electron Transfer.

An N-heterocyclic carbene (NHC) catalyzed dihalomethylenation of enals is described. It is a rare example of merging NHC catalysis with single-electron chemistry, a challenging topic with limited previous success. The versatile carbon-centered trihalomethyl radicals have been demonstrated, for the first time, to be compatible with an NHC-bound intermediate, thus leading to efficient and regioselective intermolecular C-C bond formation. The mild process provides straightforward access to unsaturated δ,δ-dihalo esters.