Preparation of 2-Vinylcyclobutanones via m-Chloroperbenzoic Acid: Oxidation of Allylidenecyclopropanes.

The fused alkylidenecyclopropanes (I) react with MCPBA (II) to give the oxiranes (III) which are cleaved by m-chlorobenzoic acid (IV) also formed to produce the intermediate α-hydroxy carbocations (V).