The general procedure for the synthesis of 2,6-difluoro-3-nitropyridine from 2,6-dichloro-3-nitropyridine was as follows: 3-bromo-2,6-dichloropyridine (4.70 g, 20.7 mmol) was dissolved in DMSO (103 mL) at room temperature, followed by the addition of cesium fluoride (12.6 g, 82.9 mmol). The reaction mixture was stirred at 80°C for 8 hours in air. After completion of the reaction, the mixture was poured into water and extracted with ether (Et2O). The organic layer was separated, washed sequentially with water and brine, dried over anhydrous sodium sulfate (Na2SO4) and subsequently concentrated under reduced pressure (400 Torr, 40°C). The residue was purified by silica gel column chromatography using ethyl acetate (EtOAc) solution in hexane as eluent to afford 3-bromo-2,6-difluoropyridine (3B) as a colorless oil (2.58 g, 64% yield). Its nuclear magnetic resonance hydrogen spectrum (1H NMR, CDCl3) data were as follows: δ 6.79 (1H, dd, J = 8.3, 3.0 Hz), 8.03 (1H, ddd, J = 8.4, 8.4, 7.0 Hz). Nuclear Magnetic Resonance Fluorine Spectroscopy (19F NMR, CDCl3) data: δ -69.3 Hz, -63.8 Hz. compounds 4B to 8B were prepared similarly as described for 3B.
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