Synthesis Of ß-Lactones By Epoxide Carbonylations

Although the insertion of CO into epoxides was reported last year (J Org Chem, 2001, 66, 5424), the conditions were quite harsh. A new catalyst allows carbonylation of propylene oxide to 95% conversion in 1 hr at 50^oC. The reaction works with asymmetric epoxides generated by the Jacobsen HKR process to give lactones in 95% yield with > 98% retention of configuration and the reaction can be run neat.