Iodine → phenylalaninol, (S)-
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[BH4-].[Na+].[NH2:3][C@H:4]([C:12](O)=[O:13])[CH2:5][C:6]1[CH:11]=[CH:10][CH:9]=[CH:8][CH:7]=1.II.[OH-].[K+]>O1CCCC1.ClCCl>[NH2:3][C@H:4]([CH2:12][OH:13])[CH2:5][C:6]1[CH:7]=[CH:8][CH:9]=[CH:10][CH:11]=1[BH4-].[Na+].[NH2:3][C@H:4]([C:12](O)=[O:13])[CH2:5][C:6]1[CH:11]=[CH:10][CH:9]=[CH:8][CH:7]=1.II.[OH-].[K+]>O1CCCC1.ClCCl>[NH2:3][C@H:4]([CH2:12][OH:13])[CH2:5][C:6]1[CH:7]=[CH:8][CH:9]=[CH:10][CH:11]=1
To a suspension of sodium borohydride (16.5 g) in dry tetrahydrofuran (600 mL), (L)-phenylalanine (30 g) was added at one portion. The flask was cooled to 0° C. under nitrogen atmosphere. Iodine (46.18 g) solution in tetrahydrofuran (150 mL) was added slowly in drop-wise manner over 40 minutes, resulting in vigorous evolution of H2. After the complete addition of iodine, the reaction mixture was heated to reflux for 18 hours and cooled to room temperature. The reaction mixture was quenched with methanol until the reaction mixture became clear. Further, the solution was stirred for 30 minutes at room temperature. The solvents were removed by rotary evaporation to obtain a white paste which was dissolved by 20% aqueous potassium hydroxide (450 mL). The solution was stirred for 4 hours and then dichloromethane was added. The organic layers were separated and the aqueous layer was extracted with dichloromethane. The combined organic layers were washed with brine and dried over anhydrous sodium sulfate. The solvents were evaporated under reduced pressure to afford 32.5 g of (L)-phenylalaninol as a viscous liquid. The crude product was used as such for the next step.
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