[NH:1]1[CH2:6][CH2:5][CH:4]([C:7]([OH:9])=[O:8])[CH2:3][CH2:2]1.[OH-].[Na+].[C:12](Cl)([O:14][CH2:15][C:16]1[CH:21]=[CH:20][CH:19]=[CH:18][CH:17]=1)=[O:13]>O>[CH2:15]([O:14][C:12]([N:1]1[CH2:6][CH2:5][CH:4]([C:7]([OH:9])=[O:8])[CH2:3][CH2:2]1)=[O:13])[C:16]1[CH:21]=[CH:20][CH:19]=[CH:18][CH:17]=1Piperidine-4-carboxylic acid (64.8 g, 0.5 mol) in H2O (50 mL) was treated with NaOH (44.0 g, 1.1 mol). The reaction mixture was cooled to 0° C. and treated with CbzCl (93.8 g, 0.55 mol). The reaction mixture was stirred at ambient temperature for 4 hours and the mixture was extracted with Et2O (3 150 mL). The aqueous phase was acidified with 6 N HCl (140 mL) and extracted with EtOAc (3 200 mL). The solution was dried over MgSO4, filtered, and concentrated to afford crude piperidine-1,4-dicarboxylic acid monobenzyl ester (120 g), which was used without further purification: MS (ESI) m/z 262 [M−H]+.
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