Heterogeneous asymmetric reactions Part 21.: Amino acid derived modifiers in the enantioselective hydrogenation of ethyl pyruvate over supported platinum catalyst

New modifiers were prepared from L-tryptophane and tested in the enantioselective hydrogenation of ethyl pyruvate over commercial alumina supported platinum catalyst. Most of these molecules induced only low enantiomeric excesses tee). (S)-3-(1-methyl-indol-3-yl)-2-methylamino-propan-1-ol was found to be the most effective. Using this modifier under mild reaction conditions (1 bar hydrogen pressure, 273 K), enantiomeric excess up to 43% was obtained. Due to the transformation of the modifier evidenced by ESI-MS, a slight increase in hydrogen pressure led to a dramatic drop of enantioselectivity. An interesting inversion of the sense of enantioselectivity was observed in the case of this modifier when the reaction was carried out in acetic acid instead of toluene. A possible explanation for this phenomenon is proposed. (C) 2001 Elsevier Science B.V. All rights reserved.