Lithium Hydroxide → 1-tert-butyl-5-(5-chloro-isoxazol-3-yl)-1H-pyrazole-4-carboxylic acid

A solution of 1-tert-butyl-5-(5-chloro-isoxazol-3-yl)-1H-pyrazole-4-carboxylic acid ethyl ester (55.3 mg, 0.18 mmol) in absolute ethanol (0.93 mL, 0.2M) was treated with a 2M aqueous lithium hydroxide solution (0.18 mL, 0.37 mmol). The reaction was stirred at 25° C. for 1.5 h and then was heated to 100° C. for 1 h. At this time, the reaction was allowed to cool to 25° C. and was stirred at 25° C. overnight. At this time, the reaction was concentrated in vacuo. The residue was treated with water followed by acidification to pH=1 with a 1N aqueous hydrochloric acid solution. The resulting precipitate that formed was collected by filtration, washed with water and hexanes and dried in vacuo to afford 1-tert-butyl-5-(5-chloro-isoxazol-3-yl)-1H-pyrazole-4-carboxylic acid (38.7 mg, 77%) as an off-white solid.