Geometric constraints regulated regioselectivity: Pd-catalyzed α-deuteration of pyridines with secondary phosphine oxide.

A Pd-catalyzed regioselective H/D exchange at the α-position of pyridines was achieved by employing secondary phosphine oxide as an internal base. The proposed five-membered structure enabled the reaction to overcome its conventional -directing feature, allowing the efficient deuteration of pyridines and quinolines at adjacent sites of N-atoms.