Asymmetric Synthesis of Nitrocyclopropanes Catalyzed by Chiral Primary Amines

Asymmetric conjugate addition of bromonitromethane to α,β-unsaturated ketones was studied using a series of chiral primary amines as the catalysts. The cascade intramolecular cyclopropanation provided nitrocyclopropanes efficiently. Excellent enantioselctivities and good yields were obtained for several cyclic enones catalyzed by a bifunctional thiourea-primary amine. Both acid and base additives were found to be necessary for the transformation.