[CH2:1]([N:8]1[CH2:13][CH2:12][C:11]([NH:17][C:18]2[CH:23]=[CH:22][CH:21]=[CH:20][CH:19]=2)([C:14]([OH:16])=[O:15])[CH2:10][CH2:9]1)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.[OH-].[Na+].Br[CH2:27][CH3:28]>CO>[CH2:1]([N:8]1[CH2:9][CH2:10][C:11]([NH:17][C:18]2[CH:23]=[CH:22][CH:21]=[CH:20][CH:19]=2)([C:14]([O:16][CH2:27][CH3:28])=[O:15])[CH2:12][CH2:13]1)[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1Benzyl-4-phenylamino-piperidine-4-carboxylic acid (40.1 g, 0.13 mol) and NaOH (5.12 g, 0.13 mol) was dissolved in methanol (1000 mL). The mixture was heated to reflux for 0.5 h. Then the solvent was removed under reduced pressure. The residue was dissolved in HMPT (300 mL). Bromo-ethane (17.44, 0.16 mol) was added at 20° C. The mixture was stirred overnight at 20° C. The reaction mixture was poured into ice-water and extracted with EtOAc (3×400 mL). The combined organics were washed with brine, dried over Na2SO4 and evaporated under vacuum. The residue was purified by silicagel column chromatography (Petroleum ether./EtOAc 2:1) to give ethyl 1-benzyl-4-(phenylamino)piperidine-4-carboxylate.
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