Asymmetric Hydrogenation with Modified Raney Nickel. IX

Abstract

Abstract The asymmetric hydrogenation catalysts were prepared from the Raney nickel catalyst by modifying it with ls-3,3-dimethyl-2-hydroxybutyric acid and the corresponding amino acid, l-t-leucine, which have most methyl groups at the β-position. The asymmetric activities of the catalysts were measured by the hydrogenation of the methyl acetoacetate to methyl 3-hydroxybutyrate. The asymmetric activity of the catalyst modified with an aqueous solution of ls-3,3-dimethyl-2-hydroxybutyric acid was very low, and the direction of asymmetric activity at pH 5.0 was inverted by the temperature of the modifying solution. However, there was a high asymmetric activity in the catalyst modified with l-t-leucine, and this activity was not so influenced by the temperature of the modifying solution. The aysmmetric activities of catalysts modified with α-hydroxy acids and the corresponding amino acids reported in this paper and the previous papers are compared, and the effect of the bulk of the α-alkyl substituent of the modifying reagent upon the asymmetric activity of the catalyst is discussed.