A chiral functionalized salt-catalyzed asymmetric Michael addition of ketones to nitroolefins

The chiral functionalized salt catalysis, which differs from the known enzyme- and transition metal-based methods, has been successfully developed to carry out the Michael addition of ketones to nitroolefins. Chiral anion salt (type I), chiral cation salt (type II), or chiral anion-chiral cation salt (type III) could be expected to be remarkably effective catalysts and afford the corresponding chemically and optically pure Michael addition adducts. A primary amine group activating the ketone during salt catalysis was their obvious and common property. Based on preliminary experimental investigations and previous reports on primary amine catalysis, a reaction pathway via imine, enamine, iminium ion to imine was proposed.