[F:1][C:2]1[CH:23]=[CH:22][C:5]([CH2:6][CH2:7][CH:8]2[CH2:13][CH:12]([C:14]([O:16]C)=[O:15])[CH2:11][CH2:10][N:9]2[C:18]([O:20][CH3:21])=[O:19])=[CH:4][CH:3]=1.[Br-].[Li+].C(N(CC)CC)C>C(#N)C.O.CC(OC)(C)C>[F:1][C:2]1[CH:3]=[CH:4][C:5]([CH2:6][CH2:7][CH:8]2[CH2:13][CH:12]([C:14]([OH:16])=[O:15])[CH2:11][CH2:10][N:9]2[C:18]([O:20][CH3:21])=[O:19])=[CH:22][CH:23]=1
Dimethyl 2-(4-fluorophenethyl)piperidine-1,4-dicarboxylate (3.18 g, 9.83 mmol) was dissolved in acetonitrile (35 mL) and water (0.7 mL) and lithium bromide (6.83 g, 78.67 mmol) was added. Triethylamine (5.45 mL, 39.34 mmol) was added and the resulting suspension was heated under reflux for 5 h. MTBE and water were added, the phases separated and the organic layer was extracted with water. The combined aqueous layers were acidified to pH 1 with 3.8 M HCl and extracted with MTBE. The combined organic layers were washed with water, dried with Na2SO4 and evaporated. Crude 2-(4-fluorophenethyl)-1-(methoxycarbonyl)piperidine-4-carboxylic acid (4.37 g) was isolated. MS m/z 310 (M+H)+
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