Pd/C(en)-Catalyzed Chemoselective Hydrogenation with Retention of the N-Cbz Protective Group and its Scope and Limitations

A chemoselective method for the hydrogenation of acetylene, olefin, azide, nitro and benzyl ester functionalities with retention of the aliphatic N-Cbz group was established. The chemoselectivity was accomplished by using a combination of 5% Pd/C–ethylenediamine [5% Pd/C(en)] and THF (or 1,4-dioxane) as a solvent, and the scope and limitations of this methodology were investigated. These results reinforce the utility of N-Cbz protective groups in synthetic chemistry, especially in peptide synthesis.