Synthesis
The general procedure for the synthesis of 5-bromo-2-iodopyridine from 2,5-dibromopyridine was as follows: an aqueous solution of 57% hydriodic acid (HI) was added to a reaction system containing 2,5-dibromopyridine (12.60 g, 53.2 mmol) and sodium iodide (NaI, 11.40 g, 76 mmol). The reaction mixture was heated to reflux for 24 h, subsequently cooled to room temperature and diluted with 100 mL of water. The pH of the mixture was adjusted to alkaline with sodium bicarbonate (NaHCO3), and then treated with the addition of sodium dithionite (Na2S2O4) until the solution became colorless. The reaction mixture was extracted with dichloromethane (DCM, 5 x 60 mL), the organic phases were combined and dried over anhydrous sodium sulfate (Na2SO4). The solvent was removed by concentration under reduced pressure and the obtained residue was collected by filtration, washed with ether (Et2O, 60 mL) and dried over air to give 5-bromo-2-iodopyridine (8.28 g, 55% yield) as a light gray powder.
References
[1] Bioorganic and Medicinal Chemistry Letters, 2006, vol. 16, # 17, p. 4528 - 4532
[2] Chemical Communications, 2012, vol. 48, # 8, p. 1120 - 1122
[3] European Journal of Organic Chemistry, 2003, # 8, p. 1559 - 1568
[4] Journal of Organic Chemistry, 2001, vol. 66, # 2, p. 605 - 608
[5] Organic Letters, 2004, vol. 6, # 26, p. 4905 - 4907
