The Enantioface-differentiating (Asymmetric) Hydrogenation of the C=O Double Bond with Modified Raney Nickel. XXX. The Temperature Dependency of the Optical Yield

Abstract

The effect of the reaction temperature upon the optical yield was studied in the liquid-phase enantioface-differentiating hydrogenation of methyl acetoacetate with various modified Raney nickel catalysts (MRNi) under an atmospheric pressure of hydrogen. The results obtained are as follows: 1) the enantiomer produced in excess in the reactions with (S)-alanine-, (S)-2-aminobutyric acid-, and (S)-valine-MRNi, changed from (S)-(+) to (R)-(−) with the elevation in the reaction temperature (The temperature, T₀, at which the direction of the differentiation changed decreased in the order of alanine-, 2-aminobutyric acid-, and valine-MRNi. The origin of T₀ is expected to be steric and polar effects that act in opposite directions for the differentiation of the enantioface.), and 2) the temperature dependence of the optical yield with (R,R)-tartaric acid- and (S) -lactic acid-MRNi differed from that with other catalysts. The OH group of the modifying reagent is expected to play an important role in enantioface-differentiation by making a hydrogen bond with the substrate.