[C:1]([NH:4]/[C:5](=[CH:10]\[C:11]1[CH:16]=[CH:15][CH:14]=[CH:13][CH:12]=1)/[C:6]([O:8]C)=[O:7])(=[O:3])[CH3:2].[H][H].[CH3:19]O>[Rh]>[CH3:19][N:4]([C:1](=[O:3])[CH3:2])[C@@H:5]([C:6]([OH:8])=[O:7])[CH2:10][C:11]1[CH:16]=[CH:15][CH:14]=[CH:13][CH:12]=1A 100 mL Fisher-Porter tube was charged with methyl (Z)-α-acetamidocinnamate (300 mg, 1.36 mmol), rhodium catalyst [(COD)Rh(1,2-Bis((2R,5R)-2,5-diethylphospholano)benzene)]+CF3SO3- prepared as in Example 15 (1.0 mg, 0.00136 mmol), MeOH (6.0 mL), and a stir bar. After sealing, the pressure head was then connected to a hydrogen tank (Matheson, 99.998%) and the lines were purged of air by four vacuum/H2 cycles. After two vacuum/H2 cycles on the reaction mixture, the tube was pressurized to an initial pressure of 30 psig H2. The reaction was allowed to stir at 20° C. for 2 h after which no further H2 uptake was observed. Complete conversion to product was indicated by capillary GC (methyl silicone column). The reaction was concentrated on a rotovap and the residue was chromatographed on a short SiO2 column (ca. 6×0.5 cm) using 80% ethyl acetate/hexane as eluent. The fractions containing product were concentrated on a rotovap to give methyl (R)-N-acetylphenylalanine as a colorless crystalline solid (270 mg, 90%). Enantiomeric excess analysis by HPLC using Daicel Chiralcel OJ column as described above indicated 99% enantiomeric purity. Other substrates were hydrogenated using the above procedure and the resulting data is summarized in Tables 1 and 2.
Loading…
