General procedure for the synthesis of 5-fluoro-2-iodopyridine from 2-bromo-5-fluoropyridine: under nitrogen protection, Cu2O (7.2 mg, 10 mol%), L-proline (11.5 mg, 20 mol%), 2-bromo-5-fluoropyridine (0.50 mmol), potassium iodide (KI, 249 mg, 0.75 mmol) and ethanol (EtOH, 1.5 mL). After sealing the Schlenk tube with a PTFE valve, the reaction mixture was stirred at 110 °C. The reaction process was monitored by gas chromatography (GC) analysis. Upon completion of the reaction, the yield was determined by GC using an appropriate internal standard (e.g., chlorobenzene or 1-chloro-4-methylbenzene) for highly volatile products; or the solvent was removed by distillation under reduced pressure. The resulting crude product was purified by silica gel column chromatography (eluent ratio of petroleum ether/ethyl acetate = 10/1) to give the target product 5-fluoro-2-iodopyridine.
