L-Proline Diamides with an Axially Chiral Binaphthylene Backbone as Efficient­ Organocatalysts for Direct Asymmetric Aldol Reactions: The Effect of Acetic Acid

Abstract

A series of L-proline diamides derived from optically active 1,1'-binaphthyl-2,2'-diamines have been synthesized in good yields and their catalytic abilities as organocatalysts in direct asymmetric aldol reactions have been evaluated. Among these organocatalysts, bis(prolinamides) exhibit higher catalytic abilities. The aldol reaction of arylaldehydes with acetone or cyclohexanone proceeds smoothly using the organocatalyst (10 mol%) in the presence of acetic acid (10 mol%) as an additive in toluene at -40 °C for 48-72 hours to give the corresponding aldol products in high yields (<90%) and with good to high enantioselectivities (<98%) and high anti-diastereoselectivities (<98:2).