Enantioselective hydrogenation of α,β-unsaturated carboxylic acids over cinchonidine-modified Pd catalysts: effect of substrate structure on the adsorption mode

Systematic variation of the substrate structure in the enantioselective hydrogenation of α,β-unsaturated carboxylic acids over cinchonidine-modified Pd catalysts indicated that aryl substituents in β position changed the adsorption mode of the substrates on the metal surface and eventually the configuration of the products formed in excess as compared to aliphatic substrates. The configuration of the products formed in excess by hydrogenation of eight α,β-unsaturated carboxylic acids, of which two have not been described yet, indicated that the substrates bearing aromatic ring in β position were adsorbed on the opposite face of the CC group compared to acids having aliphatic group in β position.