Specific Synthesis of 1,2- and 1,3-Dialkylidenecycloheptanes by [3+2+2] Cyclization of Alkenyl Fischer Carbene Complexes and Allenes

The 1,2- and 1,3-dialkylidenecycloheptane rings are specifically assembled from chromium alkenyl Fischer carbene complexes and allenes via [3+2+2] cyclization reactions. The former cycloadducts are obtained when the cyclization is performed in the presence of 1 equiv of [Ni(cod)2], while the [Rh(cod)Cl]2-catalyzed cyclization leads to the latter cycloadducts.