CHIRAL SULFONATED PHOSPHINES .9. ROLE OF WATER IN THE HYDROGENATION OF DEHYDRO AMINO-ACIDS

Homogeneous reduction of (Z)-alpha-acetamido- and (Z)-alpha-benzamidodocinnamic acid methyl ester and alpha-acetamidoacrylic acid methyl ester in an organic-water medium in the presence of a soluble catalyst obtained by mixing [Rh(COD)Cl]2 and a phosphine occurred with regiospecific incorporation of a deuterium atom at the position alpha to the acetamido and the ester group. When the reduction was performed under a deuterium atmosphere in the presence of water, hydrogen incorporation occurred at the same position and the overall reaction was a cis addition of HD. The amount of incorporation of deuterium depends on the nature of the phosphine, the solvent, and the amount of water. A mechanism involving a hydrogen-deuterium exchange on a sigma-rhodium monohydride intermediate is proposed.