The general procedure for the synthesis of 2-bromo-4,5-dimethylpyridine and 2-bromo-3,4-dimethylpyridine using 3,4-dimethylpyridine as starting material was as follows: first, 71.3 g (0.8 mol) of 2-(dimethylamino)ethanol was dissolved in 500 mL of n-hexane and the mixture was cooled to 0 °C. Subsequently, 1.0 liter (1.6 moles) of n-butyllithium solution (1.6 M in hexane) was slowly added and stirred at 0°C for 15 minutes. Next, 17.9 g (166.7 mmol) of 3,4-dimethylpyridine dissolved in 500 mL of hexane was added dropwise and stirring was continued at 0 °C for 1 hour. The reaction mixture was further cooled to -78 °C and a solution of 331.7 g (1.0 mol) of carbon tetrabromide dissolved in 1.0 liter of tetrahydrofuran was added. After stirring at -78°C for 1 hour, the mixture was slowly warmed to room temperature. Cool again to 0°C and slowly add 1.5 liters of water dropwise. The organic and aqueous phases were separated, the organic phase was washed with water, dried with magnesium sulfate and concentrated under reduced pressure. The crude product was first pre-purified by passing through a ~1 kg silica gel column (eluent: cyclohexane/ethyl acetate, 9:1, subsequently adjusted to 7:3). The fractions containing the target product were combined and concentrated under reduced pressure. Further purification by silica gel column (eluent: cyclohexane/ethyl acetate, 9:1) resulted in a final product containing approximately 10% of the regional isomer 2-bromo-3,4-dimethylpyridine.
