Under nitrogen protection, 4-bromo-[2,2'-bipyridine] 1-oxide (786 mg, 3.13 mmol) was dissolved in dry chloroform (10 mL) and the solution was cooled to 0 °C. Subsequently, phosphorus tribromide (PBr3, 1.0 mL, 10 mmol) was slowly added to the solution. The reaction mixture was heated to reflux for 5 hours. After completion of the reaction, the mixture was poured into ice water, the pH was adjusted to alkaline with 6N aqueous sodium hydroxide and extracted with chloroform (CHCl3). The organic layers were combined, dried with anhydrous sodium sulfate (Na2SO4) and concentrated under reduced pressure to give the white solid product 4-bromo-2,2'-bipyridine (728 mg, 3.09 mmol, 98.7% yield). The structure of the product was confirmed by 1H NMR, IR spectroscopy, melting point and ESI-MS.1H NMR (CDCl3): δ = 8.69 (d, J = 5.0 Hz, 1H), 8.63 (d, J = 1.8 Hz, 1H), 8.49 (d, J = 5.1 Hz, 1H), 8.39 (d, J = 8.0 Hz, 1H), 7.83 ( dt, J1 = 8.0 Hz, J2 = 1.6 Hz, 1H), 7.48 (dd, J1 = 5.1 Hz, J2 = 1.8 Hz, 1H), 7.34 (ddd, J1 = 7.5 Hz, J2 = 4.8 Hz, J3 = 1.6 Hz, 1H). ir (kbr): ν = 1565, 1545, 1452, 1386, 1280, 1066, 994, 833 1066, 994, 833, 787, 687 cm-1. Melting point: 51.5-53 °C. ESI-MS: m/z = 256.9, 258.9 [M + Na]+ (calculated values C10H7N2Br + Na = 256.9, 258.9).
