MODE OF ENANTIOFACE-DIFFERENTIATION IN THE HYDROGENATION OF 2-ALKANONE OVER AN ASYMMETRICALLY MODIFIED NICKEL-CATALYST

The enantioface-differentiating hydrogenation of 2-alkanone over tartaric acid-NaBr-modified Raney nickel (TA-NaBr-MRNi) gave an excellent optical yield when an appreciable amount of pivalic acid coexisted with the substrate. The function of tartaric acid and pivalic acid in the reaction process is as follows. (1) Tartrate adsorbed on the catalyst makes an associative complex with pivalic acid and 2-alkanone through hydrogen bonding by sharing its two hydroxyl groups with the C=O group of pivalic acid and that of the 2-alkanone. (2) The repulsion between the alkyl group of pivalic acid and that of 2-alkanone in the associative complex fixes the adsorption mode of 2-alkanone on the catalyst in such a way that one enantioface of the substrate faces the nickel surface. The experimental results, which included stereochemistry and optics yield of the reaction, were in good agreement with the prediction from the proposed reaction model.