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.