Efficient and Convenient Heterogeneous Palladium‐Catalyzed Regioselective Deuteration at the Benzylic Position

The Pd/C‐catalyzed efficient and regioselective hydrogen–deuterium (H‐D) 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 H‐D exchange reactions provide a post synthetic and D 2 ‐gas‐free deuterium‐labeling method on a wide variety of benzylic sites using D 2 O as the deuterium source and heterogeneous Pd/C or Pd/C(en) as a reusable heterogeneous palladium catalyst under mild and neutral conditions.