[Li+].[BH4-].[C:3]([O:7][C:8]([NH:10][C@H:11]1[CH2:17][CH2:16][S:15][C@H:14]2[CH2:18][CH2:19][CH2:20][C@@H:21]([C:22](OC)=[O:23])[N:13]2[C:12]1=[O:26])=[O:9])([CH3:6])([CH3:5])[CH3:4]>C1COCC1>[OH:23][CH2:22][C@H:21]1[N:13]2[C@@H:14]([S:15][CH2:16][CH2:17][C@H:11]([NH:10][C:8](=[O:9])[O:7][C:3]([CH3:5])([CH3:4])[CH3:6])[C:12]2=[O:26])[CH2:18][CH2:19][CH2:20]1LiBH4 (2 M in THF, 1.57 mL, 3.14 mmol) was added dropwise to a 0° C. solution of (4S,7S,10aS)-methyl 4-(tert-butoxycarbonylamino)-5-oxooctahydro-2H-pyrido[2,1-b][1,3]thiazepine-7-carboxylate (750 mg, 2.09 mL) in THF (8 mL). The reaction mixture was then stirred at rt overnight. The reaction mixture was cooled to 0° C. and carefully quenched by slow addition of saturated aqueous NH4Cl. After 10 min of stirring, the mixture was partitioned between EtOAc and water. The organic phase was isolated, washed with saturated aqueous NaCl, dried over MgSO4, filtered and concentrated to give tert-butyl (4S,7S,10aS)-7-(hydroxymethyl)-5-oxooctahydro-2H-pyrido[2,1-b][1,3]thiazepin-4-ylcarbamate (513 mg, 1.55 mmol, 74.2% yield) as a white solid. Anal. Calcd. for C15H26N2O4S m/z 330.4. found: 330.9 (M+H)+.
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