Preparation of b-lactones by carbonyl insertion into expoxides

An improved method for the synthesis of -lactones by the atom-efficient carbon monoxide insertion into epoxides has been published (Lee J T et al, J Org Chem, 2001, 66, 5424). When the researchers at University of Ottawa and Dow Chemical tried to repeat a 1993 patent describing carbonyl insertion, they obtained mostly polyester, not lactone when the reported CO2(CO)8/3-hydroxypyridine catalyst was used - this catalyst usually works well for the carbomethoxylation of epoxides. After a number of failures, they eventually came up with bis(triphenylphosphine) iminium Co(CO)4 in conjunction with a Lewis acid (BF3·Et20 or SnCl4) in DME or THF which gave lactones in excellent yields.