抄録
Readily obtainable primary α- and β-amino acid lithium salts were found to be efficient catalysts for iminium-enamine-type asymmetric organocatalyses. By using L-phenylalanine lithium salt as a catalyst, asymmetric Michael addition of α-branched aldehydes to nitroalkenes was achieved via the formation of enamines to obtain synthetically useful γ-nitroaldehydes possessing a quaternary carbon stereogenic center in high yields with high enantioselectivity. On the other hand, highly enantioselective Michael addition of malonates to enones was successfully carried out by the iminium catalysis using a mixed catalyst consisting of a primary β-amino acid, O-tert-butyldiphenylsilyl (S)-β-homoserine, and its lithium salt. Details of the studies regarding to the organocatalyses using primary α- and β-amino acid lithium salt-catalysts including substrate scopes and mechanistic studies are described.
