Structural Requirements in Chiral Diphosphine‐Rhodium Complexes. V. Asymmetric Homogeneous Hydrogenation of Z‐α‐acetamidocinnamate Esters of Chiral Alcohols with DIOP‐Rhodium(I) Complexes and Symmetrical Diphosphine‐Rhodium(I) Complexes

Z‐(−)‐(1R, 3R, 4S)‐menthyl‐α‐acetamidocinnamate was hydrogenated with neutral diphosphine‐rhodium(I) complexes containing (+)‐(2S, 3S) or (−)‐(2R, 3R)‐2,3‐isopropylidene‐2,3‐dihydroxy‐1,4‐bis(diphenylphosphino)butane(DIOP) to give a diastereomeric mixture of N‐acetylphenylalanine (1R, 3R, 4S)‐menthyl ester (76.8% diastereomeric excess [d.e.] (S, 3R) and 52.5% d.e. (R, 3R), respectively). The behavior of the unsaturated (−)‐menthyl ester substrate was also investigated with neutral diphosphine‐rhodium(I) complexes containing symmetrical α, ω‐bis(diphenylphosphino)alkanes {Ph₂P(CH₂)_nPPh₂} 6.6% d.e. (S, 3R) [n = 3]; 12.0% d.e. (R, 3R) [n = 4]; 7.2% d.e. (R, 3R) [n = 5]; and 7.4% d.e. (R, 3R) [n = 6]. Z‐(−)‐(1S, 2R, 4S)‐bornyl‐α‐acetamidocinnamate was similarly studied: 49.8% (S, 2R)[(+)‐(2S, 3S)‐DIOP]; 64.1% d.e. (R, 2R) [(−)‐(2R, 3R)‐DIOP]; 4.9% d.e. (S, 2R) [n = 3]; 9.1% d.e. (R, 2R) [n = 4]; 13.6% d.e. (R, 2R) [n = 5]; and 12.0% d.e. (R, 2R) [n = 6].