Cobalt-Catalyzed Oxidase C−H/N−H Alkyne Annulation: Mechanistic Insights and Access to Anticancer Agents

Cp*‐free cobalt‐catalyzed alkyne annulations by C−H/N−H functionalizations were accomplished with molecular O2 as the sole oxidant. The user‐friendly oxidase strategy proved viable with various internal and terminal alkynes through kinetically relevant C−H cobaltation, providing among others step‐economical access to the anticancer topoisomerase‐I inhibitor 21,22‐dimethoxyrosettacin. DFT calculations suggest that electronic effects control the regioselectivity of the alkyne insertion step. Mit O2: Co(OAc)2 enabled the aerobic C−H/N−H functionalization with O2 as the sole oxidant under Cp*‐free conditions, which enabled step‐economical access to anticancer isoquinolones by highly selective C−H activation (see scheme, Cp*=pentamethylcyclopentadienyl).