General procedure for the synthesis of 4-amino-3,5-dichloropyridazine from 3,4,5-trichloropyridazine: 3,4,5-trichloropyridazine (3,500 mg, 2.73 mmol) was dissolved in a mixture of ethanol (5.5 mL) and ammonium hydroxide (5.5 mL) in a microwave reactor and heated at 120 °C for 25 min. After completion of the reaction, the reaction solution was concentrated under reduced pressure to remove the solvent. The crude product was purified by silica gel column chromatography, and the eluent was a mixed solution of acetone and dichloromethane (acetone volume fraction 0-15%). 4-Amino-3,5-dichloropyridazine was finally obtained in 36% yield (163 mg). The structure of the product was confirmed by 1H NMR (400 MHz, CDCl3): δ 5.11 (broad peak, 2H), 8.74 (single peak, 1H).LC-MS analysis showed a retention time of Rt = 0.27 min and a mass spectrum m/z 164 [M + H]+.
