Cobalt-Catalyzed sp²-C−H Activation: Intermolecular Heterocyclization with Allenes at Room Temperature

The reactivity of allenes in transition-metal-catalyzed C−H activation chemistry is governed by the formation of either alkenyl–metal (M–alkenyl) or metal–π-allyl intermediates. Although either protonation or a β-hydride elimination is feasible with a M–alkenyl intermediate, cyclization has remained unexplored to date. Furthermore, due to the increased steric hindrance, the regioselectivity for the intramolecular cyclization of the metal–π-allyl intermediate was hampered towards the more substituted side. To address these issues, a unified approach to synthesize a diverse array of biologically and pharmaceutically relevant heterocyclic moieties by cobalt-catalyzed directed C−H functionalization was envisioned. Upon successful implementation, the present strategy led to the regioselective formation of dihydroisoquinolin-1(2H)-ones, isoquinolin-1(2H)-ones, dihydropyridones, and pyridones.