A Systematic Study of Chiral Homoprolinols and Their Derivatives in the Catalysis of Enantioselective Addition of Diethylzinc to Aldehydes

Homoprolinol analogs, a class of optically active gamma-amino alcohols, were examined systematically in the enantioselective addition reactions of diethylzinc to aldehydes. By comparison of the results catalyzed by these gamma-amino alcohols with those by the beta-amino alcohols based on pyrrolidine architecture reported in the literature references, we have observed that the gamma-amino alcohols are superior to the corresponding beta-amino alcohols when the nitrogen and the oxygen are unsubstituted. Among the homoprolinols we tested, 2b gave the best results (45-88% yields, 44-81% ee) in the addition reactions. To the best of our knowledge, 2b has been noticed as one of the most efficient gamma-amino alcohol catalysts based on pyrrolidine framework. Chirality 23:921-928, 2011. (C) 2011 Wiley-Liss, Inc.