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Example 1: Synthesis of 4-chloro-6-ethyl-5-fluoropyrimidine <1-1> Preparation of 4-chloro-6-ethyl-5-fluoropyrimidine 80 g of 6-ethyl-5-fluoropyrimidin-4(3H)-one was dissolved in a solvent mixture of 240 mL of dichloromethane and 57.4 mL of N,N-dimethylformamide. Subsequently, 78.24 mL of triethylamine was added to the solution as a base. Phosphoryl chloride (POCl3) was slowly added dropwise to the reaction system over a period of 30 minutes. The reaction mixture was stirred under reflux conditions for 5 hours to ensure complete reaction, after which it was cooled to room temperature. 352 mL of 3N hydrochloric acid solution was carefully added to the reaction mixture at a controlled temperature not exceeding 20°C. The aqueous phase was extracted with 100 mL of dichloromethane and the organic layers were combined and washed with 100 mL of water. The organic layer was dried over anhydrous magnesium sulfate and concentrated under reduced pressure to afford the oily target product 4-chloro-6-ethyl-5-fluoropyrimidine (85.9 g, 95% yield). 1H-NMR (300 MHz, CDCl3) δ (ppm): 8.70 (1H, s), 2.90 (2H, q), 1.34 (3H, t).