2-Cobaloxime−(E)-1,3-pentadienyl complexes (cobaloxime = pyridine(dimethylglyoxime)2cobalt(III)) react with a variety of cyclohexenones in [4 + 2] cycloaddition reactions. These cycloaddition reactions produce octalones with cis ring junctions through exo transition states. The octalones are removed from the cobalt via demetalation reactions that replace the cobalt with a hydrogen and provide pyr(dmg)2CoMe, which can be recycled into the synthesis of the starting dienyl complex.