New data on the Orito reaction:: Effect of substrate structure on nonlinear phenomenon

The nonlinear phenomenon (NLP) was studied for the first time in the enantioselective hydrogenation of ethyl pyruvate (EP) and ketopantolactone (KPL) under identical conditions, on Pt catalyst modified by quinine and cinchonine, and for comparison with cinchonidine-cinchonine pair. The data obtained using the three methods allowed recognition of a new observation, namely that the NLP depends not only on the chiral modifier but also on the substrate to be hydrogenated. This observation can presumably be interpreted on the basis of differences in the structure of the substrate-modifier complexes formed and in the adsorption-desorption processes of the complexes, thus the NLP is not solely dependent on the adsorption of cinchona alkaloids, as suggested by earlier experimental data.