The catalytic system (-)-(diop)-Rh(I) (diop = 2,3-0-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane (7)) is described and is used for an extensive study of the hydrogenation of various precursors of alanine, phenylalanine, tyrosine, Dopa, and leucine. Optical yields in the range of 70-80 % are obtained in the reduction of ^-substituted -acetamidoacrylic acids. The presence of a carboxyl group is found not to be absolutely necessary for good optical yield. The favorable effect of the enamide function on the catalytic process is deduced from comparisons of the rates of hydrogenation of atropic and acetamidocinnamic acids, from the optical yields obtained in the reduction of different precursors of phenylalanine, and from the high optical yield (78 %) obtained in the hydrogenation of the enamide 12, a compound having no carboxyl groups.