Asymmetric Relay Catalysis Reaction Consisting of Metal Complex and Chiral Phosphoric Acids

Metal complex and organo combined catalysis is a new and exciting research area and has attracted close atten- tion. Relay catalysis (or sequential catalysis), in which both the organocatalyst and the metal catalyst perform two distinct catalytic cycles for the consecutive reactions, enables the assembling readily available starting materials into structurally complex molecules. Besides, relay catalysis can also accomplish unprecedented reactions, which are not accessible through the use of either of the catalytic systems alone. More essentially, it avoids the purification of unstable intermediate and im- proves process economy and atom economy. Chiral phosphoric acids become the hottest kind of organocatalysts in recent decades. Chiral phosphoric acid has been applied to asymmetric transfer hydrogenation of imines, enantioselective Friedel-Crafts reaction, Mannich reaction, hydrophosphonylation reaction, Strecker reaction, aza-Diels-Alder reaction, alky- lation of diazoester reaction and so on. Chiral phosphoric acid can act as both proton donor and proton acceptor simultane- ously, and the system of which combining with metal has attracted intensive study. Transition metal catalysis was dominated in catalytic organic synthesis. Owing to the explosive development of organocatalysis in recent years, the combination of transition metal catalysts and organocatalysts has displayed as a new and powerful strategy for developing new and useful reactions, and has attracted increasing attention. In this review, we summarize recent progress in the field of metal com- plex/phosphoric acids relay catalysis. And in our opinion, the study of new catalysis systems will continue to be an exciting research area, the inquiry of the applications in the total synthesis of natural products is worthy of further investigation and the exploration of appropriate catalysis systems applied in industrial production represents the future research direction.