Molecular-Sieves Controlled Diastereo- and Enantioselectivity: Unexpected Effect in the Organocatalyzed Direct Aldol Reaction

An efficient asymmetric organocatalyst was developed for the direct aldol reaction between ketones and aldehydes to afford β-hydroxy ketones in high stereoselectivity ( ANTI/ SYN up to 92:8, ee up to <99%). The key of the success was the use of activated molecular sieves (4 A MS), which acted as a water scavenger. The influence of additives such as water or different types of molecular sieves on the reactivity and stereoselectivity of the reaction was also studied.