A formal enantioselective acetate Mannich reaction: the nitro functional group as a traceless agent for activation and enantiocontrol in the synthesis of beta-amino acids

A two-step procedure involving the enantioselective addition of alpha-nitro esters to imines, followed by reductive denitration, provides a convenient new enantioselective synthesis of beta-amino acids. Specifically, beta-phenyl alanine derivatives with up to 98% ee are formed in good yield (64-88%) over two steps. The utility of the approach is demonstrated through the first enantioselective synthesis of the key beta-amino acid of (+)-chaenorhine.