[C:1]([C:5]1[S:9][C:8]([CH:10]2[CH2:15][CH:14]([C:16]([O:18]C)=[O:17])[CH2:13][CH2:12][N:11]2[C:20]([O:22][CH3:23])=[O:21])=[CH:7][CH:6]=1)([CH3:4])([CH3:3])[CH3:2].O.[Br-].[Li+].CC(OC)(C)C>C(#N)C>[C:1]([C:5]1[S:9][C:8]([CH:10]2[CH2:15][CH:14]([C:16]([OH:18])=[O:17])[CH2:13][CH2:12][N:11]2[C:20]([O:22][CH3:23])=[O:21])=[CH:7][CH:6]=1)([CH3:4])([CH3:2])[CH3:3]
Dimethyl 2-(5-tert-butylthiophen-2-yl)piperidine-1,4-dicarboxylate (2.49 g, 7.34 mmol) was dissolved in acetonitrile (20 mL). Water (0.400 mL) and lithium bromide (5.10 g, 58.68 mmol) were added. After 5 min, TEA (4.09 mL, 29.34 mmol) was added and the reaction heated at reflux for 1 h. MTBE (150 mL) and water (150 mL) were added, shaken and the phases separated. The organic phase was extracted with water (150 mL). The combined aqueous phases were acidified with 3 M HCl to pH 1 and extracted with MTBE (2×300 mL). The combined organic phases were dried with Na2SO4, filtered and evaporated in vacuo yielding 2-(5-tert-butylthiophen-2-yl)-1-(methoxycarbonyl)piperidine-4-carboxylic acid (1.125 g, 47.1%) as a white foam. MS m/z 326 (M+H)+
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