Efficient Catalysts of Acyclic Guanidinium Iodide for the Synthesis of Cyclic Carbonates from Carbon Dioxide and Epoxides under Mild Conditions

We have studied the synthesis of five-membered cyclic carbonates through the cycloaddition of CO2 to epoxides by using acyclic guanidinium salts. We have found that the cycloaddition reactions proceed smoothly at ordinary temperatures and pressures and result in good yields when acyclic guanidinium iodides are employed as catalysts. Both cation moiety and anion moiety of the guanidinium salts play important roles in their catalytic activity. It is essential to have active hydrogens on the cation moiety as well as an iodide ion as the anion moiety so as to achieve good catalytic activity. Guanidinium iodides with three or more active hydrogens give cyclic carbonates in high yields in polar solvents such as 1-methylpyrrolidin-2-one, whereas the guanidinium iodides with one or two active hydrogens show good catalytic activity in less polar solvents such as 2-methyltetrahydrofuran.