Cp*Rh(III)-Catalyzed Regioselective C(sp3)-H Methylation of 8-Methylquinolines with Organoborons.

Rh(III)-catalyzed highly regioselective methylation of the unactivated C(sp3)-H bond of 8-methylquinolines with bench stable organoboron reagents is described. A variety of substituted 8-methylquinolines provided the highly regioselective monomethylated products with potassium methyltrifluoroborates/methylboronic acid through primary C(sp3)-H bond activation. Complete chemoselectivity and regioselectivity were observed in all cases as methylation at the C2 position or dimethylation of the C(sp3)-H bond of 8-methylquinoline was not detected. The mechanistic study uncovered the fact that the reaction may proceed through the five-membered rhodacycle intermediate.