Base-Controlled Rhodium(III)-Catalyzed Regioselective C-H Alkylation and Annulation of 2-Arylindoles with α-Cl Ketones.

A base-controlled rhodium(III)-catalyzed regioselective C-H alkylation and annulation of 2-arylindoles with α-Cl ketones in a single catalytic system is described, in which α-Cl ketones serve as C(sp3)-based electrophilic partners and oxidized alkyne equivalents. When using NaOAc as the base, the C-H functionalization selectively delivered 1-aryl-2-(2-aryl-1H-indol-3-yl)ethan-1-ones. In contrast, the same catalytic system with the base NaHCO3 predominately provided 5-aryl-11H-benzo[a]carbazoles. The developed reaction methodology features ideal functional group tolerance and a wide substrate scope and is operationally simple and scalable. Mechanistic studies, particularly deuterium labeling experiments and DFT calculations, suggest that reactive sites for C-H alkylation and C-H annulation are likely to occur.