Catalytic [5 + 1]-Cycloadditions of Vinylcyclopropanes and Vinylidenes

Polysubstituted cyclohexenes
bearing 1,3 (meta) substitution patterns are challenging
to access using the Diels–Alder
reaction (the ortho–para rule).
Here, we report a cobalt-catalyzed reductive [5 + 1]-cycloaddition
between a vinylcyclopropane and a vinylidene to provide methylenecyclohexenes
bearing all-meta relationships. Vinylidene equivalents
are generated from 1,1-dichloroalkenes using Zn as a stoichiometric
reductant. Experimental observations are consistent with a mechanism
involving a cobaltacyclobutane formed from a [2 + 2]-cycloaddition
between a cobalt vinylidene and a vinylcyclopropane.