[C:1]([O:5][C:6]([N:8]1[CH2:13][CH2:12][CH2:11][CH2:10][CH:9]1[C:14](=[O:18])[CH:15]=[N+]=[N-])=[O:7])([CH3:4])([CH3:3])[CH3:2].[BrH:19]>C(OCC)(=O)C.C(O)(=O)C.COC(C)(C)C>[C:1]([O:5][C:6]([N:8]1[CH2:13][CH2:12][CH2:11][CH2:10][CH:9]1[C:14](=[O:18])[CH2:15][Br:19])=[O:7])([CH3:4])([CH3:3])[CH3:2]A solution of 2-(2-diazo-acetyl)-piperidine-1-carboxylic acid tert-butyl ester (0.51 g, 2.0 mmol) in dry ethyl acetate (11 mL) was cooled to −45° C. and treated with a 33% solution of hydrobromic acid in acetic acid (0.24 mL), which was added dropwise over 45 min. The cold reaction mixture was diluted with tert-butyl methyl ether (34 mL) and left to warm to room temperature. The mixture was washed twice with saturated sodium hydrogenocarbonate (2*11 mL) and with saturated sodium chloride. The organic phase was dried over sodium sulphate and evaporated. The residue was purified by flash chromatography (heptane/ethyl acetate gradient) to yield 2-(2-bromo-acetyl)-piperidine-1-carboxylic acid tert-butyl ester (0.28 g, 45%) as a light yellow oil, MS (ISP): 306.1, 308.1 (M+H)+.
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