Treatment of 5, bdisubstituted N-nitrosooxazolidones with alkoxides initiates a series of reactions which are best explained by postulating the formation of unsaturated carbenes,: C= C&. The latter react with olefins, such as cyclohexene or alkyl vinyl ethers, to yield disubstituted methylenecyclopropanes, and with alcohols, ROH, by insertion into the 0-H bond to yield vinyl ethers, R&= CHOR '(see Table I). Treatment of 3-nitroso-l-oxa-3- ...