Enantioselective hydrogenation of (E)-α-phenylcinnamic acid with cinchonidine-modified Pd/TiO2:: influence of solvents and additives

Both the enantioselectivity and activity of the hydrogenation of (E)-alpha-phenylcinnamic acid with cinchonidine-modified Pd catalysts are strongly solvent dependent; polar solvents with higher solubility for the substrate are preferable. The simultaneous increases in the enantioselectivity and activity, also induced by the addition of either a small amount of water to aprotic solvents or an amine such as benzylamine, indicate that preferential acceleration of the selective reaction has occurred, thus strongly suggesting the importance of the product desorption step on the modified sites.