Heterogeneous enantioselective hydrogenation of isophorone over proline modified Pd catalysts

Enantioselective hydrogenation of isophorone (3,5,5-trimethyl-2-cyclohexenone) over (S)-proline modified Pd catalysts has been studied. Both the Pd particle size and the acid-base properties of the support influenced the hydrogenation reaction of isophorone and the subsequent kinetic resolution of 3,3,5-trimethylcyclohexanone (TMCH). This was explained by assuming the reaction pathway as a consequential process. The rapid hydrogenation of isophorone initially yielded racemic TMCH, and then the slow kinetic resolution consumed the (R)-TMCH, leaving (S)-TMCH in excess. Most promisingly, the Pd/MgO catalyst with enhanced adsorption of proline and moderate Pd particle sizes resulted in high enantioselectivity (ee of 95%) and 43% yield of TMCH. (c) 2006 Elsevier B.V. All rights reserved.