Heterogeneous asymmetric reactions, 14. Epicinchona alkaloids in the enantioselective hydrogenation of ethyl, pyruvate over Pt/alumina. What determines the sense of enantioselection?

The enantioselective hydrogenation of ethyl pyruvate to (R)- and (S)-ethyl lactate over Pt/Al2O3, catalyst was investigated using epiquinine (42% ee) and epiquinidine (22% ee) as modifiers and the results were compared with t hose found for quinine (85% ee) and quinidine (81% ee). The experimental re sults show that the sense of enantioselection is determined by the conforma tion of the entire alkaloid, and the structure of the intermediate is a 1:1 complex of the pyruvate and the 'anti open' conformer of the cinchona alka loid.