R. Glaser, S. Geresh, Shlomo Luria
Aug 1, 1994
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Journal
Structural Chemistry
Abstract
Hydrogenation ofZ-(−)-(1′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, 1′R, 3′R, 4′S)- and (2S, 1′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 P212121, and at 213 K:a=5.054(1),b= 10.000(2),c=32.707(1) Å,V=1652.9(4) Å3,Z=4,R(F)=0.040, andRw(F)=0.037. The finding of the (2S)-configuration for the formamido-acid portion of the (+)-ester enabled the configurational assignment of the asymmetric hydrogenation products ofZ-methyl 2-formamido-4, 4,4-trifluoro-2-butenoate catalyzed by chiral diphosphine/rhodium(I) complexes.