N-Heterocyclic Carbene-Catalyzed β-Addition of Enals to 3-Alkylenyloxindoles: Synthesis of Oxindoles with All-Carbon Quaternary Stereocenters

The N-heterocyclic carbene-catalyzed β-addition of enals to 3-alkylenyloxindoles was developed. All of β-aryl, β-alkenyl and β-alkyl enals worked well for the reaction to give the corresponding 3,3-disubstituted oxindoles bearing contiguous all-carbon quaternary and tertiary stereocenters in good yields with moderate to high diastereoselectivities and excellent enantioselectivities.