Pyridine → 5-Chloro-3-iodo-1H-pyrrolo[2,3-b]pyridine

To a solution of 5-chloro-1H-pyrrolo[2,3-b]pyridine (1, 15.00 g, 98.31 mmol) in 300 mL of dichloromethane under an atmosphere or nitrogen, pyridine (7.951 mL, 98.31 mmol) and iodine monochloride (110 mL, 1.0 M in dichloromethane, 110 mmol) are added slowly over 20 minutes. The reaction is stirred at room temperature for 2 hours, then quenched with 100 mL of 1 M aqueous sodium thiosulfate pentahydrate. The layers are separated, solids collected from the aqueous layer by filtration and combined with the organic layer. The aqueous layer is extracted with ethyl acetate, and the organic layers are combined and washed with brine, then concentrated under vacuum. The resulting solid is washed with 20% ethyl acetate in hexane to provide the desired compound.