Chiral Spirooxindole-Butenolide Synthesis through Asymmetric N-Heterocyclic Carbene-Catalyzed Formal (3+2) Annulation of 3-Bromoenals and Isatins

By using an N-heterocyclic carbene catalyst bearing a hydroxyl moiety, the asymmetric formal (3 + 2) cyclization of aryl 3-bromoenals and isatins was achieved to produce a series of chiral spirooxindolebutenolides including an alkenyl-substituted compound, which underwent benzannulations with benzynes to form intriguing spirocyclic scaffolds.