Mechanistic insights into the base-mediated deuteration of pyridyl phosphonium and ammonium salts

Pyridines can be deuterated at the remote sites by treatment with KOtBu in DMSO-d6, although without discrimination between the meta- and para-position. Herein, base-catalyzed deuterations have been studied, computationally and experimentally, using a series of pyridyl phosphonium salts with a temporary electron-withdrawing group to block the para-position while increasing the acidity in the other positions.