Highly Enantioselective Synthesis of Chiral Pyranonaphthoquinone-Fused Spirooxindoles through Organocatalytic Three-Component Cascade Reactions

In the presence of cinchona-thiourea organocatalyst C1, the developed organocatalytic three-component cascade reaction of isatins, malononitrile, and 2-hydroxynaphthalene-1,4-diones readily proceeded to furnish chiral pyranonaphthoquinone-fused spirooxindoles in excellent chemical yields and high enantioselectivities (up to 99% yield and 97%ee). The absolute configurations of the spirooxindoles were assigned on the basis of an X-ray single crystal structure. Moreover, a reaction mechanism is proposed that accounts for the stereocontrolled formation of the chiral spirooxindoles,.