Efficient Palladium‐Catalyzed Aerobic Oxidative Carbocyclization to Seven‐Membered Heterocycles

The use of molecular oxygen in palladium‐catalyzed oxidation reactions is highly widespread in organic chemistry. However, the direct reoxidation of palladium by O(2) is often kinetically unfavored, thus leading the deactivation of the palladium catalyst during the catalytic cycle. In the present work, we report a highly selective palladium‐catalyzed carbocyclization of bisallenes to seven‐membered heterocycles under atmospheric pressure of O(2). The use of a homogenous hybrid catalyst (Co(salophen)‐HQ, HQ=hydroquinone) significantly promotes efficient electron transfer between the palladium catalyst and O(2) through a low‐energy pathway. This aerobic oxidative transformation shows broad substrate scope and functional group compatibility and allowed the preparation of O‐containing seven‐membered rings in good yields in most cases.