In recent years, transformation of carbon dioxide into valuable chemicals is of great importance in terms of greenhouse gas, abundant and cheaper feedstocks. One of the most successful example is the synthesis of cyclic carbonates from CO2 and epoxides. The cyclic carbonates are widely used as organic syntheses and pharmaceutical intermediates, aprotic solvents, and raw materials for plastics etc.In our works, we mainly concentrated on the asymmetric synthesis of chiral cyclic carbonate, which could be converted to chiral drugs and other materials. Opitical pure cyclic carbonates are precursors of chiral alcohols. Herein we discuss the reaction of carbon dioxide with epoxides catalyzed by the two catalytic systems as follows.1) The chiral catalyst of SalenCo(OAc)/chiral ionic liquid was developed to catalyze the asymmetric cycloaddition reaction of CO2 and epoxides yielding the chiral cyclic carbonates in high yield and excellent enatioselectivity under very mild condition. The synergistic effects between chiral catalyst and cocatalyst were discussed.2) Some cinchona-derived quaternary ammonium salts were synthesized from cinchona alkaloids, which were used as cocatalyst combined SalenCo(OAc) to catalyze the coupling reaction of epoxide and carbon dioxide. Using N-benzyl-cinchoninium chloride (1a) as cocatalyst, the highest 73%ee value of PC was achieved at room temperature.
|