[C:1]([O:5][C:6]([N:8]1[CH2:13][CH2:12][CH:11]([C:14](O)=[O:15])[CH2:10][CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2].B#B.[H][H].Cl.[OH-].[Na+]>C1COCC1>[C:1]([O:5][C:6]([N:8]1[CH2:13][CH2:12][CH:11]([CH2:14][OH:15])[CH2:10][CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2]To a solution of piperidine-1,4-dicarboxylic acid mono-tert-butyl ester (19.3 g, 84.0 mmol) in THF (100 mL) was added diborane (185 mL, 1.0 M solution in THF) over a period of 10 min at 0° C. Hydrogen gas was rapidly evolved and after gas evolution had ceased the reaction was stirred at room temperature for 1 h. The reaction mixture was again cooled to 0° C., and 1 M aqueous HCl was added dropwise to the reaction mixture with further evolution of hydrogen. Addition of HCl was continued until the evolution of hydrogen had almost ceased. The mixture was then stirred for 10 min and made basic (pH 13-14) by the addition of 1 M NaOH solution. The aqueous solution was extracted with ethyl acetate, the organic phase washed with brine, dried and concentrated under reduced pressure to yield 4-Hydroxymethyl-piperidine-1-carboxylic acid tert-butyl ester (18.12 g, 100%).
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