General procedure for the synthesis of 1-tert-butyl-1H-pyrazole-4-carboxylic acid from ethyl 1-tert-butyl-1H-pyrazole-3-carboxylate:
1. In 8 mL of THF-MeOH-H2O (3:1:1, v/v) mixed solvent, ethyl 1-tert-butyl-1H-pyrazole-3-carboxylate (327 mg, 1.66 mmol) and LiOH (120 mg, 5.0 mmol) were added.
2. The reaction mixture was stirred at 25 °C for 12 hours.
3. After completion of the reaction, H2O and EtOAc were added to the mixture and acidified with 10% HCl solution.
4. The organic layer was separated, dried with Na2SO4 and concentrated under reduced pressure to afford the target product 1-tert-butyl-1H-pyrazole-4-carboxylic acid (217 mg, 78% yield).
Mass spectral data: m/z 168.
