THERMOLYSIS OF 2-(3-BUTYN-1-OXY)-2-METHOXY-5,5-DIMETHYL-DELTA(3)-1,3,4-OXADIAZOLINE IN SOLUTION - A REMARKABLE CASCADE OF CARBENE AND OTHER REACTIONS

Thermolysis of 2-(3-butyn-1-oxy)-2-methoxy-5,5-dimethyl-Delta(3)-1,3,4-oxadiazoline in benzene or in toluene affords (1 alpha,1a alpha,3a alpha,6a alpha,6b alpha)-methyl 1a-ethenyloctahydro-6a-methoxy-2,2-dimethyl-3,6- dioxacyclobut[cd]indene-1-carboxylate in up to 74% yield. A reasonable mechanism involves about ten sequential steps and some novel intermediates including a dioxycarbene, a cyclopropenone ketal, and a vinylogous dioxycarbene. Various steps in the proposed mechanism were inferred from the results of deuterium-labeling experiments and from the incorporation of key intermediates from solution into the final product.