Mechanistic aspects of formal [3 + 4] cycloadditions between vinylcarbenoids and furans

Rhodium(II) acetate catalyzed decomposition of diethyl 4-diazo-2-pentenedioate resulted in the fomation of a vinylcarbenoid, which underwent formal [3 + 4] cycloaddition reactions with a series of furans. The most likely mechanism for these reactions involves cyclopropanation followed by a Cope rearrangement of the divinylcyclopropane intermediate.