Enantioselective Assembly of Spirocyclic Oxindole-dihydropyranones through NHC-Catalyzed Cascade Reaction of Isatins with N‑Hydroxybenzotriazole Esters of α,β-Unsaturated Carboxylic Acid

An NHC-catalyzed formal [4 + 2] reaction of isatins with N-hydroxybenzotriazole ester of α,β-unsaturated carboxylic acids bearing γ-H to construct spirocyclic oxindole-dihydropyranones featuring a chiral tetrasubstituted carbon stereogenic center was developed. The high enantioselectivity, the ready availability of the raw materials, the facile assembly, and the potential biological significance of the final products make this protocol an attractive alternative for the synthesis of spirocyclic heterocycles.