Pergamon Tetrahedron: Asymmetry 10 (1999) 61–76 TETRAHEDRON: ASYMMETRY Enantioselective hydrogenation of pyrrolidine-2,3,5-triones over the Pt–cinchonidine system A. Szabo, N. Künzle, T. Mallat and A. Baiker * Laboratory of Technical Chemistry, Swiss Federal Institute of Technology, ETH-Zentrum, CH-8092 Zürich, Switzerland Received 15 October 1998; accepted 9 December 1998 Abstract 1- and 4-Substituted pyrrolidine-2,3,5-triones 5, 6 and 9 have been synthesized and hydrogenated to 3-hydroxy derivatives 10–12 with 17–91% ee using a 5 wt% Pt/Al 2 O 3 catalyst in the presence of small amounts of cinchonidine. The influence of substituents on the enantioselectivity is discussed. © 1999 Elsevier Science Ltd. All rights reserved. 1. Introduction Enantioselective hydrogenation of carbonyl compounds is one of the most intensively studied areas of asymmetric catalysis. 1 An efficient strategy to achieve reasonable enantioselectivity over solid catalysts is the modification of an active metal by a preadsorbed homochiral compound. 2 Since the first application of cinchona-modified Pt, 3 considerable effort has been made to broaden the application range of this catalyst system. Good to high ees were obtained in the hydrogenation of α-ketoesters (97.5%), 4 α- ketoacids (85%) 5 and ketopantolactone (91.6%). 6 The hydrogenation of other types of activated carbonyl compounds such as α-diketones, trifluoroacetophenone and pyruvamides was less successful, affording only 60% ee or less. 7 We have reported recently 8 that a cyclic imidoketone could be hydrogenated to the corresponding alcohol with 91% ee, using the Pt–cinchonidine system. The aim of the present work is to reveal the influence of the structure of cyclic ketoimides on the enantiodifferentiation. A series of 1- and 4-substituted pyrrolidine-2,3,5-triones was prepared and hydrogenated with a cinchonidine-modified Pt/Al 2 O 3 catalyst. The simple and economical procedure, starting from easily available racemic com- pounds, seems to be a promising method for the preparation of chiral alcohols. It has been reported that enantiomerically pure alcohols such as (S)-N-methyl-2-hydroxysuccinimide are excellent chiral auxiliaries for Lewis acid catalyzed enantioselective Diels–Alder reactions of enolates. 9 * Corresponding author. E-mail: baiker@tech.chem.ethz.ch 0957-4166/99/$ - see front matter © 1999 Elsevier Science Ltd. All rights reserved. PII: S0957-4166(98)00499-6