Structural requirements in chiral diphosphine-rhodium complexes—XII: Asymmetric homogeneous hydrogenation of Z-α-N-methylacetamidocinnamic acid and methyl ester catalyzed by rhodium(I) complexes of DIOP and its carbocyclic analogues

Z-α-N-methylacetamidocinnamic acid and its methyl ester were hydrogenated with rhodhim(I) complexes containing (2R, 3R)-O-2,3-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane (DIOP) or its carbocyclic analogues: (1R,2R)-trans-1,2-bis(diphenylphosphinomethyl)cyclobutane or (1S,2S)-trans-1,2-bis(diphenylphosphinomethyl) cyclohexane. The N-acetyl-N-methylphenylalanine methyl ester reaction product was formed with an optical purity of 73% ee-(R) (2R, 3R)-DIOP]; 43% ee-(R) (1R, 2R)-cyclobutane analogue]; and 26% ee-(R) (1S,2S])-cyclohexane analogue]. Similarly, N-acetyl-N-methylphenylalanine was formed with an optical purity of 87% ee-R (2R, 3R)-DIOP] and 68% ee-(R) (1R, 2R)-cyclobutane analogue].