Facile Synthesis of Chiral Spirooxindole-Based Isotetronic Acids and 5-1H-Pyrrol-2-ones through Cascade Reactions with Bifunctional Organocatalysts

Unprecedented organocatalyzed asymmetric cascade reactions have been developed for the facile synthesis of chiral spirooxindole-based isotetronic acids and 5-1h-pyrrol-2-ones. the asymmetric 1,2-addition reactions of alpha-ketoesters to isatins and imines by using an acid-base bifunctional 6'-oh cinchona alkaloid catalyst, followed by cyclization and enolization of the resulting adducts, gave chiral spiroisotetronic acids and 5-1h-pyrrol-2-ones, respectively, in excellent optical purities (up to 98% ee). ft-ir analysis supported the existence of hydrogen-bonding interaction between the 6'-oh group of the cinchona catalyst and an isatin carbonyl group, an interaction that might be crucial for catalyst activity and stereocontrol.