General procedure for the synthesis of 5-tert-butyl-2-p-tolyl-2H-pyrazol-3-amine from 4,4-dimethyl-3-oxopentanenitrile and 4-methylphenylhydrazine hydrochloride: 4-methylphenylhydrazine hydrochloride (5.20 g, 33 mmol) and 4,4-dimethyl-3-oxopentanenitrile (3.75 g, 30 mmol) were dissolved in an ethanol solution of 0.4 M HCl (100 mL) and heated at reflux for 48 hours. Upon completion of the reaction, the mixture was cooled to room temperature and the pH was adjusted to 10-11 by slow addition of 1 M NaOH solution.Subsequently, the reaction mixture was partitioned between water and ethyl acetate. The aqueous phase was extracted twice with dichloromethane. All organic phases were combined, washed sequentially with water and saturated brine and dried over anhydrous sodium sulfate. The solvent was removed by concentration under reduced pressure to give the crude product. The crude product was recrystallized from a solvent mixture of ethyl acetate and petroleum ether to give 5-tert-butyl-2-p-tolyl-2H-pyrazol-3-amine (compound 25a) as a white solid (5.88 g, 86% yield).
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