General procedure for the synthesis of 2-methoxy-3-trifluoromethyl-5-bromopyridine from 2-methoxy-3-trifluoromethylpyridine:
1. Trifluoroacetic acid (TFA, 80 mL) was added to a mixture of 2-methoxy-3-trifluoromethylpyridine (20.0 g, 113.0 mmol) and 1,3-dibromo-5,5-dimethylimidazolidine-2,4-dione (43.6 g, 152.0 mmol), and stirred for 18 hours at room temperature under argon protection.
2. Upon completion of the reaction, the TFA was removed by distillation under reduced pressure at 50 mbar and 45 °C. The residue was suspended in tert-butyl methyl ether (200 mL), filtered to remove the resulting colorless solid, and washed with tert-butyl methyl ether (50 mL).
3. The filtrate was concentrated under reduced pressure and suspended in ethyl acetate (EtOAc, 50 mL), filtered again to remove the insoluble colorless solid, and washed with ethyl acetate (50 mL).
4. The filtrate was concentrated under reduced pressure, diluted with heptane/tert-butyl methyl ether (5:1, 20 mL), and filtered to remove the insoluble colorless solid.
5. The filtrate was purified by silica gel column chromatography with heptane/ethyl acetate (100/0 to 90/10) as eluent.
6. The crude product was filtered through a plug of sodium bicarbonate (NaHCO3, 20 g) and the filtrate was evaporated under reduced pressure to give a golden yellow oil (27.9 g).
7. The oily substance was dissolved in heptane (20 mL), purified by filtration through a plug of silica gel (80 g), and eluted with heptane to afford 5-bromo-2-methoxy-3-trifluoromethylpyridine as a colorless oil (22.5 g, 74% yield).
1H-NMR (400MHz, DMSO-d6, 298K): δ 4.03 (s, 3H), 7.95 (d, 1H), 8.4 (d, 1H).
