General procedure for the synthesis of 1-chloro-2-methoxy-5-methyl-4-nitrobenzene (S4) from 2-methoxy-5-methyl-4-nitroaniline (S3, 0.5 g, 2.75 mmol): S3 was dissolved in 5 mL of water, and 5 mL of concentrated hydrochloric acid that had been pre-cooled to 5 °C was added and stirred well. Subsequently, a solution (200 μL) prepared from 1 mg of sodium nitrite (NaNO2) dissolved in 3 mL of water was added slowly and dropwise. The reaction mixture was kept stirred at 5 °C for 1 h to complete the diazotization reaction. The resulting diazonium salt solution was slowly poured into 5 mL of concentrated hydrochloric acid solution containing 0.35 g of cuprous chloride (CuCl), and stirring was continued until nitrogen release ceased. Upon completion of the reaction, the resulting precipitate was collected by filtration, washed three times with cold water, and dried to give 0.45 g (81% yield) of the target product S4 as a gray-yellow solid.
