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