The modifier concentration dependence of rate and enantioselectivity (ee) was investigated of the diethyl-2-oxoglutarate (EOG) and pyruvaldehyde dimethyl acetal (PADA) hydrogenations catalyzed by cinchona alkaloid modified Pt-alumina catalysts. Using the E 4759 catalyst in acetic acid under mild experimental conditions (room temperature, hydrogen pressure I bar) an optical yield of 95-97% can be achieved. Recent studies on activated ketones of different structures (EtPy: ethyl pyruvate, EOG, EBF: ethyl benzoylformate, PADA) carried out under identical experimental conditions have called attention to the role of additional factors to be considered for the interpretation of the mechanism of Orito's reaction. (C) 2003 Elsevier Science B.V. All rights reserved.