Enantioselective conjugate addition of 1-bromonitroalkanes to α,β-unsaturated aldehydes catalyzed by chiral secondary amines

Abstract

Highly enantioselective conjugate addition of bromonitromethane to α,β-unsaturated aldehydes catalyzed by chiral secondary amines has been achieved. Diphenylprolinol triethylsilyl ether was found to be the best catalyst for the reaction under MeOH/AcONa system. Various β-aryl acroleins afforded nitrocyclopropanes with excellent enantioselectivities and in good yields; however, the reaction of β-alkyl acroleins did not provide the corresponding nitrocyclopropanes. Substituted 1-bromonitromethanes, such as 1-bromonitroethane and 1-phenyl-1-bromonitromethane, were also applied in the reaction with excellent enantioselectivities and improved diastereoselectivities. The new methodology is efficient for preparing highly substituted chiral nitrocyclopropanes.