New data in the enantioselective hydrogenation of ethyl pyruvate on Pt-cinchona chiral catalyst using continuous-flow fixed-bed reactor system: The origin of rate enhancement

Abstract

The origin of rate enhancement in the enantioselective heterogeneous catalytic hydrogenation of ethyl pyruvate on Pt modified with the parent cinchonas, as compared to the unmodified Pt, was studied in a solvent mixture toluene/AcOH 9/1. Hydrogenation experiments were carried out in a continuous-flow fixed-bed reactor and in several cases for comparison in batch reactors over E4759 catalyst. Our results obtained using a novel procedure, namely racemic hydrogenation followed by three changes of the chiral modifier (on the same catalyst) supported an intrinsic “ligand acceleration” character of the rate enhancement in ethyl pyruvate hydrogenation.