[O:1]=[C:2]1[CH2:7][CH2:6][N:5]([C:8]([O:10][C:11]([CH3:14])([CH3:13])[CH3:12])=[O:9])[CH2:4][CH:3]1[C:15]([O:17][CH3:18])=[O:16].[BH4-].[Na+]>CO>[OH:1][CH:2]1[CH2:7][CH2:6][N:5]([C:8]([O:10][C:11]([CH3:12])([CH3:13])[CH3:14])=[O:9])[CH2:4][CH:3]1[C:15]([O:17][CH3:18])=[O:16]To a cold (0° C.) solution of 1-tert-butyl 3-methyl 4-oxo-1,3-piperidinedicarboxylate (134.0 g, 520.8 mmol) in methanol (800 mL) was added NaBH4 (9.85 g, 260.4 mmol) portionwise. The resulting mixture was stirred overnight to be allowed to warm to room temperature. The solvent was removed under reduced pressure, the residue was dissolved into ethyl acetate, washed with brine, dried over MgSO4, filterd, and concentrated under reduced pressure to give 1-tert-butyl 3-methyl 4-hydroxy-1,3-piperidinedicarboxylate, which was used for the next reaction without further purification. (120.8 g, yield 90%)
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