Oxiranones (a-lactones) are low-temperature species that can be generated by photodecarboxylation of malonyl peroxides'8 or by epoxidation of ketenes?" Two derivatives have been reported to be stable at ambient temperature (one of them in solution, only). 4+ A matrix isolation study of the reaction of methylene with carbon dioxide has been described by Milligan and Jac0x. G Recently we reported on the carboxylation of diphenylcarbene la ...