Catalytic Enantioselective Aza-Henry Reactions

Asymmetric aza-Henry reactions provide excellent routes for the synthesis of optically active organic compounds bearing two vicinal different nitrogenated functionalities that can be further transformed into a variety of interesting compounds such as 1,2-diamines or alpha-amino acids. The catalytic asymmetric version of the reaction (also called the nitro-Mannich reaction) provides highly efficient access to enantiomerically pure compounds. Both metal-based and organic catalysts can be used to promote these reactions in a enantioselective way; in particular, a great variety of different organocatalysts - including thioureas, N-oxides, quaternary ammonium salts and chiral Bronsted acids - have demonstrated their efficiency, as has recently been reported by several research groups. In addition, considerable effort is being made in controlling the syn/anti diastereoselectivities of these reactions when substituted nitroalkanes are used as substrates. In this microreview recent advances, including scope and limitations, are discussed and applications of different catalytic systems for catalytic asymmetric aza-Henry reactions are presented. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)