Transition state analogues - a guide for the rational design of enantioselective heterogeneous hydrogenation catalysts

The present level of understanding the mechanism of the enantioselective hydrogenation of alpha -ketoeaters over platinum, chirally modified by natural cinchona alkaloids is reviewed with special emphasis on the enantioselective hydrogenations of ethyl and methylpyruvate to the corresponding lactates. This knowledge is used in a combined experimental and theoretical approach to reveal the approximate structure of the crucial enantio-differentiating transition complexes formed by interaction of the reactant alpha -ketoester and the chiral modifier. The use of the concept of transition state analogues is shown to be a valuable guide for designing new efficient synthetic modifiers for this complex catalytic system. (C) 2000 Elsevier Science B.V. All rights reserved.