General procedure for the synthesis of 2,4-difluoro-5-nitropyridine from 2,4-dichloro-5-nitropyridine: In a 250 mL round-bottomed flask, 2,4-dichloro-5-nitropyridine (0.73 g, 3.8 mmol), potassium fluoride (0.659 g, 11.3 mmol) and 18-crown-6 (0.160 g, 0.605 mmol) were added to an N-methyl pyrrolidone (3 mL) solution to form a brown suspension. The reaction mixture was heated to reflux at 100 °C under nitrogen atmosphere for 3 hours. Upon completion of the reaction, the mixture was partitioned between water and a mixed ether/hexane solvent. The organic layer was separated, washed sequentially with water and brine, dried over anhydrous sodium sulfate and concentrated under reduced pressure to give the brown solid product 2,4-difluoro-5-nitropyridine (0.515 g, 85% yield). The structure of the product was confirmed by 1H NMR (400 MHz, CDCl3) δ 9.07 (d, J = 9.7 Hz, 1H), 6.96 (dd, J = 9.5, 2.5 Hz, 1H) and 19F NMR (376 MHz, CDCl3) δ -52.20 (d, J = 29.3 Hz), -98.13 (d, J = 28.9 Hz).
