Cooperative N-Heterocyclic Carbene/Palladium-Catalyzed Umpolung 1,4-Addition of Vinyl Bromides to Enals.

A highly stereoselective umpolung 1,4-addition of vinyl bromides to enals is enabled by NHC/palladium cooperative catalysis, generating various valuable γ,δ-unsaturated carbonyl derivatives in excellent yields (up to 90%). A detailed mechanism investigation indicates the NHC act as both organocatalyst and ligand for palladium during this system.