Dimethyl Sulfide → L-(-)-Tryptophanol

Temperatur

70 °C

To a stirred solution of (S)-tryptophan (4.0 g, 20.0 mmol) in THF (100 mL) at 0° C. was slowly added BH3.Me2S complex (5.9 mL, 10M solution in THF, 59.0 mmol). The reaction mixture was heated to 70° C. for 16 h and, after cooling, the excess borane was quenched by the addition of MeOH (10 mL) at 0° C. The reaction mixture was then concentrated in vacuo and the resultant white solid was dissolved in EtOAc (100 mL) and washed with aqueous 20% NaOH solution (2×70 mL). The organic layer was then extracted into aqueous 2M HCl (2×100 mL). The combined acidic aqueous layers were then basified to pH 14 (addition of solid NaOH) and were re-extracted with EtOAc (2×150 mL). The combined organic fractions were washed with brine (70 mL), dried over MgSO4, filtered and concentrated in vacuo to give the title compound (3.5 g, 92%) as a white solid that required no further purification. δH (CD3OD) 7.46 (1H, d, J 7.9 Hz), 7.21 (1H, d, J 8.0 Hz), 6.96 (3H, m), 3.79 (1H, dd, J 11.3 and 3.6 Hz), 3.54 (1H, dd, J 11.2 and 6.2 Hz), 3.05 (1H, m), 2.80 (1H, m), 2.61 (1H, m). Exchangeable protons were not observed.