GENERAL STEPS: Example 42 Synthesis of 6,6'-dibromo-2,2'-bipyridine 52b. In a dry three-necked round-bottomed flask, 2,6-dibromopyridine (42) (2.32 g, 10 mmol) was dissolved in 250 mL of anhydrous diethyl ether and cooled to -78°C. The solution was prepared in a dry, three-necked round-bottomed flask. The apparatus was equipped with a solid charging funnel for pre-dried copper(II) chloride (2 g, 14.9 mmol). Butyllithium (2.4 M hexane solution, 4.6 mL, 11 mmol) was slowly added dropwise at -78 °C and the reaction mixture was stirred for 2 h at this temperature. Subsequently, copper (II) chloride was added slowly over 30 minutes and stirring was continued at -78 °C for 30 minutes. The reaction system was bubbled through dry oxygen at -78 °C for 1 h, then raised to room temperature and continued to bubble for 1 h. The reaction system was then purged with 200 mL of dry oxygen. Upon completion of the reaction, the reaction was quenched with 200 mL of water and 50 mL of 1 M HCl solution and a precipitate was observed to form. The reaction mixture was filtered and the solid product was collected and recrystallized with THF. The brown solid obtained was dissolved in THF and filtered through Millipore filter. The filtrate was concentrated in vacuum to afford the target product 6,6'-dibromo-2,2'-bipyridine as a white powder in 79% yield. The product characterization data were as follows: 1H NMR (CDCl3) δ (ppm): 7.50 (dd, J = 0.6, 8.1 Hz, 2H, Hpyridine), 7.66 (t, J = 7.8 Hz, 2H, Hpyridine), 8.37 (dd, J = 0.6, 8.4 Hz, 2H, Hpyridine). 13C NMR (CDCl3) δ (ppm): 119.71, 128.15, 138.86, 141.15, 155.16. mass spectrum (MS), m/z (relative abundance): 314 (M++2, 100%), 312 (M+, 45%), 233 (M+-Br, 54%), 153 (M+-2Br, 32%).
