[C:1]([N:5]1[C:9]([CH3:10])=[C:8]([C:11]([O:13]CC)=[O:12])[CH:7]=[N:6]1)([CH3:4])([CH3:3])[CH3:2].O.[OH-].[Li+].Cl>C(O)C.O.O1CCOCC1.O.CCOCC>[C:1]([N:5]1[C:9]([CH3:10])=[C:8]([C:11]([OH:13])=[O:12])[CH:7]=[N:6]1)([CH3:4])([CH3:2])[CH3:3]
In a mixture of ethanol:water:dioxane (1:1:1, 21 mL) was placed ethyl 1-tert-butyl-5-methyl-1H-pyrazole-4-carboxylate (1.48 g, 7.04 mmol) and lithium hydroxide hydrate (886 mg, 21.12 mmol). The reaction was stirred at 40° C. for 3 hrs and then at RT overnight. The reaction was diluted with water (25 mL) and ether (25 mL). The ether layer was discarded and the aqueous phase made acidic (pH˜=4) with 1N HCl. The acidic phase was then extracted with ethyl acetate (2×25 mL) and the combined ethyl acetate layers were washed with brine, dried (Na2SO4), and evaporated at reduced pressure to give 1-tert-butyl-5-methyl-1H-pyrazole-4-carboxylic acid as a white solid (1.12 g, 87% yield). 1H NMR (300 MHz, DMSO-d6): δ 1.56 (s, 9 H), 2.67 (s, 3 H), 7.65 (s, 1 H), 12.13 (s, 1 H); MS (ESI) m/z: 183.0 (M++).
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