Developing efficient strategies for the synthesis of biologically active compounds is indisputably the most important topic in organic chemistry. This thesis describes experimental and computational studies on the site-selective catalytic reactions to enable efficient synthesis of functionalized quinolones, phosphorus-containing amino acid derivatives, and valuable cyclic compounds. Divergent C–C bond formation reactions of quinolones have been achieved by site-selective C–H activation using directing groups. Regiodivergent ring-opening cross-coupling of vinyl aziridines with phosphorus nucleophiles has been developed for the facile and efficient synthesis of enantioenriched phosphorus-containing amino acid derivatives. Moreover, synthetic methodologies involving C–H activation have been developed for construction of privileged ring systems including benzazepines, carbazoles, and lactones. Mechanistic investigations using density functional theory were also conducted to elucidate the reaction mechanism.