[F:1][C:2]([F:24])([F:23])[C:3]1[CH:8]=[CH:7][C:6]([CH:9]2[CH2:14][CH:13]([C:15]([O:17]C)=[O:16])[CH2:12][CH2:11][N:10]2[C:19]([O:21][CH3:22])=[O:20])=[CH:5][CH:4]=1.[Br-].[Li+].C(N(CC)CC)C.CC(OC)(C)C>C(#N)C.O>[CH3:22][O:21][C:19]([N:10]1[CH2:11][CH2:12][CH:13]([C:15]([OH:17])=[O:16])[CH2:14][CH:9]1[C:6]1[CH:5]=[CH:4][C:3]([C:2]([F:24])([F:1])[F:23])=[CH:8][CH:7]=1)=[O:20]
Dimethyl 2-(4-(trifluoromethyl)phenyl)piperidine-1,4-dicarboxylate (5.996 g, 17.36 mmol) was dissolved in acetonitrile (60 mL) and water (1.200 mL), then lithium bromide (12.06 g, 138.91 mmol) was added. Triethylamine (9.63 mL, 69.46 mmol) was added and the resulting brown suspension was heated under reflux for 1 h. Water and MTBE were added. The organic phase was extracted with water (×2). The combined aqueous layer was acidified to pH 1 with 3.8 M aq HCl and then extracted with MTBE (×2). The combined organic layer was washed with water and evaporated. Trace of water was azeotropically removed by MeCN. 1-(Methoxycarbonyl)-2-(4-(trifluoromethyl)phenyl)piperidine-4-carboxylic acid (5.71 g, 99%) was isolated as a brown oil. MS m/z 332 (M+H)+
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