C(OCC)(=O)C.C(O)C.[C:10]([O:14][C:15]([NH:17][C@@H:18]([CH2:23][C:24]1[CH:29]=[CH:28][CH:27]=[CH:26][CH:25]=1)[C:19](=[O:22])[CH2:20][Cl:21])=[O:16])([CH3:13])([CH3:12])[CH3:11].[BH4-].[Na+]>C(O)(=O)C>[C:10]([O:14][C:15]([NH:17][C@@H:18]([CH2:23][C:24]1[CH:25]=[CH:26][CH:27]=[CH:28][CH:29]=1)[C@H:19]([OH:22])[CH2:20][Cl:21])=[O:16])([CH3:13])([CH3:11])[CH3:12]Ethyl acetate (4.2 ml) and ethanol (16.7 ml) were added to (3S)-3-tert-butoxycarbonylamino-1-chloro-4-phenyl-2-butanone (2.08 g). Sodium borohydride (133 mg) was added in portions to the obtained mixture at −10° C., and they were stirred for 1 hour 40 minutes. Acetic acid (0.40 ml) was added to the reaction mixture to terminate the reaction. The reaction mixture was slowly heated to 60° C. for the duration of 1 hour and then stirred at 60° C. for 30 minutes. The reaction mixture was slowly cooled to −10° C. for the duration of 1 hour 50 minutes and then stirred at −10° C. for 6 hours. The crystals thus formed were taken by the filtration, washed with 0° C. water and dried under reduced pressure to obtain intended (2S,3S)-3-tert-butoxycarbonylamino-1-chloro-2-hydroxy-4-phenylbutane (1.52 g).
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