Highly Enantioselective Organocatalyzed Construction of Quaternary Carbon Centers via Cross-Aldol Reaction of Ketones in Water

The asymmetric construction of quaternary carbon centers via cross-aldol reactions of ketones with beta,gamma-unsaturated keto esters catalyzed by 4-(tert-butyldiphenylsilyloxy)-pyrrolidine-2-carbox-ylic acid in water is described. The adducts bearing two adjacent chiral centers were obtained in high yields, mostly up to 99% ee, and with high diastereoselectivities. The corresponding polyfunctional products could also be easily transformed to useful lactones with three chiral centers.