Mild and selective hydrogen–deuterium exchange for aromatic hydrogen of amines

The direct electrophilic deuteration of the aromatic moiety in aromatic and aralkyl amines is reported. The acid‐catalyzed deuteration is facilitated by deuterated trifluoromethanesulfonic acid, [D]triflic acid, CF 3 SO 3 D, TfOD, which acts as both the reaction solvent and the source of the deuterium label. The mild conditions enable room temperature hydrogen/deuterium exchange for most of the para ‐substituted aromatic amine derivatives studied. In addition, short reaction times and a high degree of aromatic deuteration are achieved and isolation of the product is simple. The optical activity of the chiral aralkyl amines studied was preserved.