Synthesis
The general procedure for the synthesis of 3-bromo-5-methylpyridine from 3,5-dibromopyridine and trimethylcyclotriboroxane was as follows: under nitrogen protection, cesium carbonate (1.38 g, 4.22 mmol), trimethylcyclotriboroxane (0.2 mL, 1.47 mmol), and tetrakis(triphenylphosphine)palladium(0) (0.488 g, 0.42 mmol ). Subsequently, a solution of 3,5-dibromopyridine (1.0 g, 4.22 mmol) dissolved in a 9:1 solvent mixture of dioxane and water (10 mL) was added. The reaction mixture was stirred at 110 °C for 16 hours. Upon completion of the reaction, trimethylcyclotriboroxane (0.2 mL, 1.47 mmol) was added again and the reaction temperature was lowered to 100 °C and the reaction continued to be stirred for 16 hours. At the end of the reaction, the reaction mixture was cooled to room temperature, filtered through diatomaceous earth and the filter cake was washed with ethyl acetate. The filtrate was concentrated and the resulting residue was purified by silica gel column chromatography with the eluent being a 80:20 solvent mixture of hexane and ethyl acetate, resulting in 3-bromo-5-methylpyridine as a colorless oil (0.654 g, 90% yield). The product was identified by 1H NMR (300 MHz, CDCl3): δ 2.34 (s, 3H), 7.66 (s, 1H), 8.36 (s, 1H), 8.49 (s, 1H).GC-MS (EI) analysis showed: m/z = 171.0, 173.0 [M].
