Earth-abundant and water-tolerant manganese(i) catalyzed alkenylation of 2-arylindazole with alkyl and aryl alkynes through C-H bond activation is described with a unique level of -selectivity. The reaction proceeds through the control of C3 nucleophilicity of 2-aryl indazoles. This method is applied to the late-stage functionalization of complex molecules including ethinylestradiol, norethisterone, and N-protected amino acid derivatives. The kinetic isotope studies suggest that the C-H bond activation step may not be the rate-determining step.