Phosphine-Catalyzed Activation of Vinylcyclopropanes: Rearrangement of Vinylcyclopropylketones to Cycloheptenones.

We report a phosphine-catalyzed activation of electron-deficient vinylcyclopropanes (VCPs) to generate an ambident C5 synthon that is poised to undergo consecutive reactions. The utility of the activation is demonstrated in a phosphine-catalyzed rearrangement of vinylcyclopropylketones to cycloheptenones in good yields with a broad substrate scope. Mechanistic investigations support a stepwise process comprising homoconjugate addition, water-assisted proton transfer, and 7-endo-trig SN 2' ring closure.