Example 2 Preparation of 2-chloro-4-methoxy-5-nitropyridine: 2-hydroxy-4-methoxy-5-nitropyridine (100 g) was mixed with dimethylaniline (92 mL) at 10 °C to 20 °C. Subsequently, phosphorus trichloride (300 mL) was slowly added in the same temperature range. The reaction mixture was heated to reflux for 2.0 hours. After the reaction was completed, it was cooled to room temperature and the mixture was slowly poured into ice water. After adjusting the pH to 10-12 with an alkali solution, extraction was carried out with ethyl acetate. The organic layer was washed sequentially with brine and dried with anhydrous sodium sulfate. The solvent was removed by distillation under reduced pressure to give the crude product. Finally, purification by crystallization with diisopropyl ether gave 2-chloro-4-methoxy-5-nitropyridine (70.0 g).
