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-pi-allyl intermediates. Although either protonation or a beta-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-pi-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.