[C:1]([C:5]1[CH:9]=[C:8]([C:10]([O:12]CC)=[O:11])[N:7]([CH2:15][CH3:16])[N:6]=1)([CH3:4])([CH3:3])[CH3:2].[OH-].[Li+]>C(O)C.O1CCOCC1.O.CCOC(C)=O.C(O)(=O)CC(CC(O)=O)(C(O)=O)O>[C:1]([C:5]1[CH:9]=[C:8]([C:10]([OH:12])=[O:11])[N:7]([CH2:15][CH3:16])[N:6]=1)([CH3:4])([CH3:2])[CH3:3]
To a solution of ethyl 3-tert-butyl-1-ethyl-1H-pyrazole-5-carboxylate (0.35 g, 1.6 mmol) in a mixture of ethanol:dioxane:water (1:1:1, 6 mL) was added lithium hydroxide (0.15 g, 6.2 mmol). The reaction mixture was stirred overnight at RT. The solution diluted with EtOAc (50 mL) and 5% citric acid (50 mL). The organic phase separated, washed with brine (20 mL), dried (Na2SO4) and evaporated under reduced pressure to afford 3-tert-butyl-1-ethyl-1H-pyrazole-5-carboxylic acid (0.30 g, 98% yield) as a yellow solid. 1H NMR (400 MHz, DMSO-d6): δ 6.64 (s, 1H), 4.40 (q, J=7.2 Hz, 2H), 1.27 (t, J=7.2 Hz, 3H), 1.22 (s, 9H); MS (ESI) m/z: 197.3 (M+H+).
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