Enantioselective synthesis of quaternary α-amino acids via l -tert-leucine-derived squaramide-catalyzed conjugate addition of α-nitrocarboxylates to enones

Article abstract of DOI:10.1021/acs.joc.6b00543

Enantioselective Michael addition of tertiary α-nitroesters to β-unsubstituted vinyl ketones has been carried out in the presence of an l-tert-leucine-derived squaramide as organocatalyst. The products, quaternary α-nitroesters, were formed in excellent yield and moderate to good ee's in most cases. Scale-up of the reaction and synthetic applications of the products, including transformation to representative quaternary α-amino acids, have also been demonstrated.