Enantioselective hydrogenation of isophorone and kinetic resolution of 3,3,5-trimethylcyclohexanone over Pd catalysts in the presence of (S)-proline

Enantioselective hydrogenation of isophorone and kinetic resolution of 3,3,5-trimethylcyclohexanone (TMCH) over Pd catalysts in the presence of (S)-proline revealed that the enantioselectivity for hydrogenation of isophorone was mainly originated from the kinetic resolution of TMCH. The rapid hydrogenation of isophorone primarily yielded racemic TMCH, and the followed kinetic resolution consumed the (R)-TMCH enantiomer, leaving the (S)-TMCH enantiomer in excess. The kinetic resolution of racemic TMCH is closely related to the acidic/basic properties of the support, and the addition of K2CO3 to Al2O3 provided more enantio-differentiating environment through the enhanced adsorption of (S)-proline on the catalyst surface. As a result, the Pd/Al2O3-K2CO3 catalyst with finely dispersed Pd particles and enhanced adsorption of (S)-proline gave very high enantioselectivities (e.e. value up to 98%) for the enantioselective hydrogenation of isophorone.