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

A sustainable protocol for Ru(II)-catalyzed regioselective C(sp²)–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.