Step 1: Dissolve 3-bromo-5-fluoropyridine (5.0 g, 28.4 mmol) in anhydrous THF (23 mL) at -78 °C and slowly dropwise add LDA (2M solution of cyclohexane/ethylphenol THF, 21.3 mL, 42.6 mmol) to the solution of anhydrous THF (23 mL), with the dropwise addition time being controlled to be within 10 minutes. After dropwise addition, stirring was continued at -78 °C for 30 min. Subsequently, a solution of anhydrous THF (23 mL) in iodomethane (2.6 mL, 42.6 mmol) was slowly added dropwise, and after completion of dropwise addition, stirring was continued at -78 °C for 30 min. The reaction mixture was warmed to room temperature and stirred for 2 h. Upon completion of the reaction, the reaction was quenched with saturated NaHCO3 solution. NH4Cl solution was added and after stirring for 30 minutes at room temperature, the reaction mixture was extracted with EtOAc. The organic layers were combined, dried and concentrated under reduced pressure, and the residue was purified by column chromatography (SiO2, EtOAc/cyclohexane) to afford the target product 3-bromo-4-methyl-5-fluoropyridine (3.6 g, 66% yield).
