Iodine → 2-Chloro-5-fluoro-4-iodopyridine

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A tetrahydrofuran (5 ml) solution containing 2-chloro-5-fluoropyridine (500 mg) was added to a tetrahydrofuran (20 ml) solution containing lithium-N,N-diisopropylamide (2M tetrahydrofuran/ethylbenzene/heptane solution) (2.9 ml) at −75° C. in a nitrogen atmosphere, followed by stirring at −75° C. for 3 hours. Subsequently, a tetrahydrofuran (5 ml) solution containing iodine (1.16 g) was added, followed by stirring at −75° C. for 1 hour. Then, water/tetrahydrofuran (2 ml/8 ml), water (10 ml), and 3M aqueous sodium thiosulfate were slowly added at −75° C., −50° C., and −35° C., respectively, to the reaction solution. The reaction solution was adjusted to room temperature, followed by extraction with ethyl acetate. The resultant was washed with saturated saline and dried over anhydrous sodium sulfate. Thereafter, the solvent was distilled away under reduced pressure, the obtained residue was purified by silica gel chromatography (n-hexane:ethyl acetate=20:1 to 10:1), and a white solid of 2-chloro-5-fluoro-4-iodopyridine (457 mg) was thus obtained.

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