A 4-hydroxyproline/trimethyl borate system for asymmetric synthesis of triple aldols from double aldol cyclic hemiacetals

Abstract We developed a 4-hydroxyproline-catalyzed asymmetric cross-aldol reaction between aldehydes and cyclic hemiacetals derived from copper-catalyzed asymmetric double aldol reaction reported previously by our group. The addition of trimethyl borate, which acted as a ring-opening reagent for hemiacetals, was critical for producing triple aldol compounds with excellent diastereoselectivity.