Inversion of enantioselectivity in the hydrogenation of ketopantolactone on platinum modified by ether derivatives of cinchonidine

Asymmetric hydrogenation of ketopantolactone was studied on a 5 wt% Pt/Al2O3 catalyst in the presence of cinchonidine and its O-methyl. -ethyl. -phenyl and -trimethylsilyl derivatives. Inversion of enantioselectivity with the latter two bulky substituents proved that in the enantiodifferentiating step cinchonidine adsorbs via the quinoline ring lying approximately parallel to the Pt surface. The striking nonlinear effect observed with cinchonidine-O-phenyl-cinchonidine mixtures is attributed to differences in the adsorption strength and geometry of the modifiers. (C) 2003 Elsevier Ltd. All rights reserved.