Bifunctional phase-transfer catalysts for fixation of CO2 with epoxides under ambient pressure
A series of bifunctional phase-transfer catalysts with a quaternary onium center and a hydrogen-bonding donor group were prepared for the fixation of CO2 with commercially available epoxides under mild conditions by using a CO2 balloon (1 atm). In the presence of 2.5 mol% of achiral bifunctional phase-transfer catalysts, cyclic carbonates were obtained in good to excellent yields (up to 95%). Additionally, optical carbonates and epoxides were obtained through the kinetic resolution of rac-epoxides by 1 mol% of chiral bifunctional phase-transfer catalysts with low enantioselectivities. These catalysts featured a simple synthetic route, good modularity and high efficiency.