Asymmetric Synthesis of Pyranonaphthene‐Fused Spirooxindoles via Takemoto's Urea‐Catalyzed Cascade Three‐Component Reactions

Enantioselective construction of spiro[4H-pyranonaphthene-3,3'-oxindole] derivatives was realized through an organocatalytic cascade Michael/cyclization using Takemoto's urea. Under the optimized conditions, the reactions of isatins, malononitrile, and 1-naphthols yield the desired spirooxindoles in good yields (80%-93%) and moderate to high ee values (up to 99% ee). The absolute configurations of the spirooxindoles were assigned as S on the basis of an X-ray single-crystal analysis. This study has expanded the range of catalyst type and substrate scope for such asymmetric three-component reaction.