1-Cyclopropyl-4-isothiocyanato naphthalene (13.3 mmol, 3.0 g) and aminoguanidine hydrochloride (26.6 mmol, 2.9 g) were mixed in 50 mL of N,N-dimethylformamide. N,N-diisopropylethylamine (39.9 mmol, 5.1 g) was slowly added under stirring conditions. The reaction mixture was stirred at room temperature for 50±12 hrs. After completion of the reaction, the solvent was removed to dryness by rotary evaporator. To the residue, 20 mL of 2 M sodium hydroxide solution was added and the reaction was continued for 50 ± 12 hours. After termination of the reaction, the reaction mixture was filtered and the filtrate was adjusted to pH=4 with dilute hydrochloric acid, at which time a large amount of white precipitate was observed to be generated. The precipitate was collected, washed with deionized water and subsequently dried under vacuum at 45-50 °C to afford the intermediate compound 5-amino-4-(4-cyclopropyl-1-naphthalene)-2,4-dihydro-3H-1,2,4-triazole-3-thiol (VI) in 2.85 g yield and 76% yield.
