tert-Butylhydrazine monohydrochloride → 1-tert-butyl-5-(5-chloro-isoxazol-3-yl)-1H-pyrazole-4-carboxylic acid ethyl ester

Participants

Reaction Conditions

Reaction Steps

A solution of 2-(5-chloro-isoxazole-3-carbonyl)-3-dimethylamino-acrylic acid ethyl ester (294.8 mg, 1.08 mmol) in absolute ethanol (1.4 mL, 0.77M) was treated with tert-butylhydrazine hydrochloride (137.3 mg, 1.10 mmol) and sodium acetate (108.6 mg, 1.32 mmol). The resulting mixture was heated to 90° C. overnight. At this time, the reaction was cooled to 25° C. and was concentrated in vacuo. The reaction was partitioned between water (200 mL) and dichloromethane (2×50 mL). The combined organics were washed with a saturated aqueous sodium chloride solution, dried over magnesium sulfate, filtered and concentrated in vacuo. Biotage chromatography (40S column 60% ethyl acetate/hexanes) followed by ISCO CombiFlash (4 g column 0-20% ethyl acetate/hexanes) afforded 1-tert-butyl-5-(5-chloro-isoxazol-3-yl)-1H-pyrazole-4-carboxylic acid ethyl ester (67.4 g, 21%) as a yellow oil.

Provenance & Evidence