Enantioselective hydrogenation of exocyclic α,β-unsaturated ketones Part II.: Hydrogenation in the presence of (S)-proline

In the asymmetric synthesis of chiral compounds, the reduction of prochiral unsaturated reactants has a great importance. (S)-proline as a chiral auxiliary is used in the hydrogenations of exocyclic alpha,beta-unsaturated ketones with palladium on carbon Z catalysts, producing the corresponding saturated ketones with an optical purity up to 20%. The influence of the parameters (solvents, additives) on the optical yield is also investigated. The highest enantioselectivity was obtained in ethyl acetate and acetonitrile (ee 20%), at atmospheric pressure and room temperature. (C) 2002 Elsevier Science B.V. All rights reserved.