A Selective Direct Aldol Reaction in Aqueous Media Catalyzed byZinc–Proline

Abstract

AbstractThe Zn–proline complex is shown to catalyze the aldol reaction of acetone and a wide range of arenecarbaldehydes in aqueous media, accepting even deactivated arenecarbaldehydes such as methoxybenzaldehydes in good yields. Enantiomeric excesses of up to 56 % could be obtained with 5 mol‐% of the catalyst at room temperature, and up to 66 % at –15 °C. The aldol reaction is regio‐ and stereoselective with hydroxyacetone (moderate yields) and dihydroxyacetone (excellent donor, 80–90 % yields with 5 mmol‐equiv.). Plausible mechanisms for the reaction are discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)