General procedure for the synthesis of 4-fluoropyridin-2-one from 4-aminopyridin-2-one: 4-amino-2-pyridinone (1.85 g, 16.8 mmol) was slowly added to a cooled solution of HF-pyridine complex (70%, 13.1 mL) at 0 °C. The mixture was cooled to -20 °C. Potassium tert-butoxide (3.0 mL, 25.2 mmol) was slowly added. The reaction mixture was stirred at -20 °C for 0.5 h and then slowly warmed to room temperature. The reaction was kept for 2 hours and then finally heated at 60 °C for 1 hour. The mixture was cooled to 0 °C and left to stand. Sodium carbonate (Na2CO3) was added to neutralize. The aqueous layer was extracted with ethyl acetate (5 times), the organic layers were combined, dried over anhydrous sodium sulfate (Na2SO4), filtered and concentrated under reduced pressure. Purification of the crude product by rapid chromatography on silica gel (dichloromethane/methanol: 95/5) afforded the target compound 4-fluoropyridin-2-one (1.14 g, 60% yield) as a colorless solid.
