Dynamic Kinetic Asymmetric Transformation of Racemic Diastereomers: Diastereo- and Enantioconvergent Michael-Henry Reactions to Afford Spirooxindoles Bearing Furan-Fused Rings.

Dynamic kinetic asymmetric transformation (DYKAT) reactions of racemic diastereomer mixtures that afford the products as essentially single diastereomers with high enantioselectivities are described. We demonstrated the DYKAT in the diastereo- and enantioselective synthesis of spirooxindoles bearing furan-fused rings. The starting materials of the DYKAT, dihydrobenzofuranone derivatives, were synthesized in racemic diastereomer mixtures, and these were transformed to the spirooxindole derivatives in high yields with high diastereo- and enantioselectivities through Michael-Henry cascade reactions with nitrostyrenes under organocatalytic conditions. In the reactions, regardless the stereochemistry of the starting materials, all the four isomers were transformed to single diastereomers with high enantioselectivities, and four new chiral centers were created.