| Abstract: | A facile and green synthesis of six‐membered cyclic carbonates, the potential monomers for isocyanate‐free polyurethanes and polycarbonates, was achieved by transesterification of diols with dimethyl carbonate catalyzed by immobilized Candida antarctica lipase B, Novozym®435, followed by thermal cyclization in a solvent‐free medium. The difference in the chemospecificity of the lipase for the primary, secondary and tertiary alcohols as acyl acceptors was utilized to obtain a highly chemoselective synthesis of the cyclic carbonate in high yield. In the lipase‐catalyzed reaction with diols, the product contained almost equal proportions of mono‐ and di‐carbonates with 1,3‐propanediol having two primary alcohols, a higher proportion of mono‐carbonate with 1,3‐butanediol having a primary and a secondary alcohol, and mainly mono‐carbonate with 3‐methyl‐1,3‐butanediol having a primary and a tertiary alcohol. The chemospecificity of cyclic carbonates formed by thermal treatment at 90 °C was closely related to the proportion of mono‐carbonate. The yield of cyclic carbonate was 99.3% with 3‐methyl‐1,3‐butanediol, 85.5% with 1,3‐butanediol, and 43.2% with 1,3‐propanediol. |
