[F:1][C:2]1[CH:7]=[C:6]([C:8]([F:11])([F:10])[F:9])[CH:5]=[CH:4][C:3]=1[CH:12]1[CH2:17][CH:16]([C:18]([O:20]C)=[O:19])[CH2:15][CH2:14][N:13]1[C:22]([O:24][CH3:25])=[O:23].[Br-].[Li+].CCN(CC)CC.CC(OC)(C)C>C(#N)C.O>[F:1][C:2]1[CH:7]=[C:6]([C:8]([F:10])([F:9])[F:11])[CH:5]=[CH:4][C:3]=1[CH:12]1[CH2:17][CH:16]([C:18]([OH:20])=[O:19])[CH2:15][CH2:14][N:13]1[C:22]([O:24][CH3:25])=[O:23]
Dimethyl 2-(2-fluoro-4-(trifluoromethyl)phenyl)piperidine-1,4-dicarboxylate (5.33 g, 14.67 mmol) was dissolved in acetonitrile (35 mL) and water (0.700 mL), then lithium bromide (10.19 g, 117.37 mmol) was added. Et3N (8.18 mL, 58.68 mmol) was added and the resulting yellow suspension was heated under reflux for 1 h. Water (50 mL) and MTBE (150 mL) were added. The phases were separated and the organic layer was extracted with water (2 times). The pooled water layers were acidified to pH 1 with 3.8 M HCl and extracted with MTBE (2 times). The combined organic layer was dried over Na2SO4, filtered and evaporated yielding 2-(2-fluoro-4-(trifluoromethyl)phenyl)-1-(methoxycarbonyl)piperidine-4-carboxylic acid (4.82 g, 94%) as a slightly yellow solid. MS m/z 348 (M−H)−
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