Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XXI. The Effect of Water on the Asymmetric Activity of the Catalyst

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The effect of water added to the hydrogenation system of methyl acetoacetate was investigated on catalysts modified with L-amino acids, their derivatives, and D- or L-hydroxy acids. In the absence of water, catalysts modified with all L-amino acids except L-serine and L-proline gave methyl Ds(−)-3-hydroxybutyrate, and in the presence of water all the catalysts modified with L-amino acids gave methyl Ls(+)-3-hydroxybutyrate. On the other hand, the catalysts modified with L- or D-hydroxy acids were not affected by the addition of water and gave an Ls(+) or Ds(−) hydrogenation product respectively. In the presence of water, the catalyst modified with the L-valine methyl ester gave an Ls(+) product, while the catalysts modified with N-acetyl L-amino acids were not affected by water. As a whole, it was concluded that water added to the hydrogenation system affected the amino group of the modifying reagent on the catalyst surface, which might play an important role in the asymmetric control of the substrate approaching the catalyst surface. The water in the hydrogenation system also promoted the hydrogenation rate, regardless of the modifying reagents.
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