Hydrogenation of Z-(-)-(I'R, 3'R, 4'S)-menthyl 2-formamido-4,4,4-trifluoro-2-butenoate catalyzed by Pd/C was performed at atmospheric pressure to yield a mixture of (2R, I'R, 3'R, 4'S)-and (2S, I'R, 3'R, 4'S)-menthyl 2-formamido-4,4,4-trifluorobutanoate diastereomers in a 55:45 ratio, respectively. Repeated fractional crystallization from ethyl acetate and vapor diffusion of petroleum ether afforded (+)-(2S, 1 'R, 3'R, 4'S)-menthyl 2-formamido-4,4,4-trifluorobutanoate as clear colorless, crystalline prisms which were subjected to single-crystal X-ray diffraction analysis. The crystals belong to the orthorhombic system P21212 I, and at 213 K: a = 5.054 (1) The finding of the (2S)-configuration for the formamido-acid portion of the (+)-ester enabled the configurational assignment of the asymmetric hydrogenation products of Z-methyl 2-formamido-4,4,4-trifluoro-2-butenoate catalyzed by chiral diphosphine/rhodium(I) complexes.