Enantioselective Hydrogenation of N‐Acetyldehydroamino Acids over Supported Palladium Catalysts

Abstract The enantioselective hydrogenation of two N ‐acetyldehydroamino acids over Cinchona alkaloid‐modified, supported palladium catalysts has been studied. Moderate enantioselectivities, up to 36 %, were obtained in the hydrogenation of 2‐acetamidocinnamic acid over cinchonidine‐modified Pd/TiO 2 under low hydrogen pressure. Increase in the pressure or use of benzylamine as additive led to a gradual decrease in the enantiomeric excess and eventually inversion of the sense of the enantioselectivity. On the contrary, the optical purity of the product resulting from the hydrogenation of 2‐acetamidoacrylic acid was significantly increased by addition of benzylamine to the reaction mixture. Enantiomeric excess values up to 58 % and 60 % were obtained over Pd/Al 2 O 3 modified by cinchonidine and cinchonine, respectively. These optical purities are the best obtained in the hydrogenation of dehydroamino acid derivatives over chirally modified heterogeneous metal catalysts.