Ru(II)-Catalyzed Sustainable C-H Methylation of Indolines with Organoboranes in Ethanol.

A sustainable protocol for Ru(II)-catalyzed regioselective C(sp 2 )-H methylation of indolines in the presence of ethanol has been explored. A wide array of substituted indolines were successfully methylated via the developed protocol with good to excellent yields. Deuterium labeling experiments suggested the reversible nature of the C-H activation step. Kinetic isotope effect studies revealed that C-H activation might be the rate-determining step. Gram scale reaction and post-transformation reactions of the methylated product demonstrated the potential of the developed protocol.