The general procedure for the synthesis of 3-chloro-6-(methylthio)pyridazine from 3-chloro-6-(methylsulfonyl)pyrazine was as follows: 3-chloro-6-(methylthio)pyridazine (90 mg, 0.50 mmol) was dissolved in dichloromethane (10 mL), and isochloroperbenzoic acid (220 mg, 1.00 mmol) was added. The reaction mixture was stirred at 0 °C for 30 min under nitrogen protection. After completion of the reaction, water (20 mL) was added to the reaction solution and extracted twice with dichloromethane (10 mL). The organic layers were combined, washed with saturated brine and dried over anhydrous magnesium sulfate. The solvent was removed by concentration under reduced pressure and the resulting residue was purified by silica gel column chromatography (eluent: ethyl acetate/hexane, gradient elution, 10%-100%) to afford the target compound 3-chloro-6-(methylsulfonyl)pyrazine (77 mg, 71% yield) as a white solid.1H-NMR (CDCl3, 400 MHz) data were as follows:δ 3.45 (3H, s) 7.81 (1H, d, J = 8.2Hz), 8.16 (1H, d, J = 8.4Hz).
