Abstract The Pd/C-catalyzed efficient and regioselective hydrogen–deuterium (HD) exchange reaction on the benzylic site proceeded in D 2 O in the presence of a small amount of H 2 gas. The use of the Pd/C–ethylenediamine complex [Pd/C (en)] as a catalyst instead of Pd/C led to the efficient deuterium incorporation into the benzylic site of O-benzyl protective groups without hydrogenolysis. These HD exchange reactions provide a post ...