Magnesium–Ligand Cooperation Enables Regioselective Transfer Hydrogenation of Quinolines to 1,2-Dihydroquinolines

We report the first magnesium-catalyzed regioselective reduction of quinolines to 1,2-dihydroquinolines, utilizing H3N·BH3. This protocol operates under mild conditions and tolerates a broad range of functional groups. Comprehensive mechanistic investigations, including kinetic analysis, deuterium labeling, and density functional theory calculations, elucidate a concerted hydride transfer pathway. This work serves as a blueprint for employing s-block metals with high-precision reactivity, which are traditionally reserved for transition metals.