Influence of achiral amine additives on the Orito's reaction

In enantioselective hydrogenation of ethyl pyruvate and methylbenzoyl formate over Pt/Al2O3 catalyst achiral tertiary and secondary amine additives increased both the reaction rate and the enantiomeric excess using low cinchonidine concentration and toluene as a solvent. However, no beneficial effect of primary amine was observed. Results of circular dichroism spectroscopic measurements proved that in the presence of both secondary and tertiary amines the virtual concentration of chiral modifier increased in accordance with the shift of dimer–monomer equilibrium of cinchonidine. The effect of achiral amines was more pronounced at ethyl pyruvate than at methylbenzoyl formate substrate.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (104 K)Download as PowerPoint slideHighlights► Achiral amine additives increase both the reaction rate and the enantiomeric excess in the Orito's reaction. ► Achiral amine effect is strongly substrate, solvent and concentration dependent phenomenon. ► Shifting the dimer/monomer ratio of cinchonidine is a probable reason of the achiral amine effect.