[C:1]([C:5]1[CH:6]=[C:7]([CH:11]2[CH2:16][CH:15]([C:17]([O:19]C)=[O:18])[CH2:14][CH2:13][N:12]2[C:21]([O:23][CH3:24])=[O:22])[CH:8]=[CH:9][CH:10]=1)([CH3:4])([CH3:3])[CH3:2].[Br-].[Li+].C(N(CC)CC)C.CC(OC)(C)C>C(#N)C.O>[C:1]([C:5]1[CH:6]=[C:7]([CH:11]2[CH2:16][CH:15]([C:17]([OH:19])=[O:18])[CH2:14][CH2:13][N:12]2[C:21]([O:23][CH3:24])=[O:22])[CH:8]=[CH:9][CH:10]=1)([CH3:4])([CH3:2])[CH3:3]Dimethyl 2-(3-tert-butylphenyl)piperidine-1,4-dicarboxylate (3.17 g, 9.51 mmol) was dissolved in acetonitrile (60 mL) and water (1.200 mL), then lithium bromide (6.61 g, 76.06 mmol) was added in one portion. Triethylamine (5.27 mL, 38.03 mmol) was added and the resulting brown suspension was heated under reflux for 1.5 h. Water (120 mL) and MTBE (120 mL) were added. The organic phase was extracted with water (2×25 mL). The pooled aqueous layer was acidified to pH 1 with 0.5 M HCl (30 mL) and extracted with MTBE (2×150 mL). The combined organic layer was washed with water (25 mL), dried over Na2SO4 and evaporated. 2-(3-tert-Butylphenyl)-1-(methoxycarbonyl)piperidine-4-carboxylic acid (2.73 g, 90%) was isolated as a foam.
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