Cl.[CH3:2][O:3][C:4]([CH:6]1[C:11](=O)[CH2:10][CH2:9][N:8]([CH2:13][C:14]2[CH:19]=[CH:18][CH:17]=[CH:16][CH:15]=2)[CH2:7]1)=[O:5].C(=O)([O-])[O-].C([O-])(=O)C.[NH4+].C([BH3-])#[N:30].[Na+]>CO.O>[CH3:2][O:3][C:4]([CH:6]1[CH:11]([NH2:30])[CH2:10][CH2:9][N:8]([CH2:13][C:14]2[CH:19]=[CH:18][CH:17]=[CH:16][CH:15]=2)[CH2:7]1)=[O:5]To a 25° C. solution of 1-benzyl-4-oxo-piperidine-3-carboxylic acid methyl ester hydrochloride (2.97 g, 10 mmol) in MeOH (10 mL) was added MP-Carbonate (12 g, 30 mmol, 2.54 mmol/g). After shaking at 25° C. for 1 h, the solution was filtered. To the resultant solution was added ammonium acetate (7.71 g, 100 mmol). After stirring at 65° C. overnight, sodium cyanoborohydride (610 mg, 10 mmol) was added into the resultant mixture and the mixture further stirred for 2 h at 50° C. The solution was then concentrated in vacuo to give a solid. The resultant solid was dissolved in water (100 mL) and the aqueous layer was extracted with CH2Cl2. The organic extracts were combined, washed with brine and dried over MgSO4. The solution was filtered and concentrated in vacuo to give the crude product 4-amino-1-benzyl-piperidine-3-carboxylic acid methyl ester (6) as a mixture of diastereomers. LCMS showed m/z: 249 (M+H)+. This material was used without further purification.
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