Divergent Annulative C-C Coupling of Indoles Initiated by Manganese-Catalyzed C-H Activation

Manganese(I)-catalyzed C–H activation of indoles and divergent annulative coupling with alkyne-tethered cyclohexadienones has been realized under operationally simple conditions. These annulation systems are under condition control. The coupling in the presence of BPh3 additive followed a C–H activation-alkyne insertion-Michael addition pathway, affording an exocyclic olefin attached to a tetrahydrofuran ring. In contrast, when Zn(OAc)2/PivOH additives were introduced, initial olefination en route to intramolecular Diels–Alder reaction and subsequent elimination of an alcohol was followed to deliver a fused six-membered ring. The selectivity stands in contrast to those reported using rhodium(III) and cobalt(III) catalysts, highlighting the unique reactivity and selectivity of manganese catalysts.