Cycloaddition of Epoxide and CO₂ with PEG-Supported Guanidinium Catalyst

Significance

Hexaalkylguanidinium (HAG) salts have been found to promote the reaction of epoxides and carbon dioxide (CO₂) to afford the corresponding cyclic carbonates. This paper described the development of a polymer-supported HAG as a catalyst for the cyclic carbonate formation reaction. A polymer-supported hexaalkyl­guanidinium bromide 3 was readily prepared by mixing brominated poly(ethylene glycol) (PEG₆₀₀₀) and N-alkylated guanidine 2, where the PEG was chosen as a CO₂-philic polymer support. The cycloaddition of CO₂ with isopropyloxymethyloxirane (4) was carried out at 110 °C under 4 MPa CO₂ pressure without any co-solvents to give 99% yield of cyclic carbonate 5. The reactions of various epoxides bearing methyl, phenyl, chloro­methyl, and phenoxymethyl groups gave 93-99% yield of the corresponding cyclic carbonates under similar conditions to show the good substrate tolerance.