Step 4b: (2-chloropyridin-4-yl)methanol (1.1 g, 7.3 mmol) was dissolved in 20 mL of dichloromethane (DCM) and cooled to 0°C after displacing the air within the reaction system with argon. Phosphorus tribromide (PBr3, 0.76 mL, 8.1 mmol) was added slowly dropwise via syringe and the solution was observed to become turbid. The reaction mixture was stirred at room temperature for 3 hours. Upon completion of the reaction, the mixture was cooled to 0 °C again and the reaction was quenched with 5 mL of water. The pH was adjusted by adding 2 M potassium carbonate (K2CO3) solution to the reaction mixture. the aqueous and organic layers were separated, and the aqueous layer was extracted three times with ethyl acetate (EtOAc). The aqueous layer was extracted with ethyl acetate (EtOAc) three times. All organic layers were combined, dried with anhydrous sodium sulfate (Na2SO4), filtered and concentrated. The concentrate was purified by silica gel column chromatography (the silica gel column was pre-washed with an eluent containing 1% triethylamine (NEt3)) using a gradient elution from hexane to ethyl acetate (EtOAc) to afford the target product, 4-bromomethyl-2-chloropyridine, as pale pink crystals (700 mg, calculated as 50% yield based on the recovered starting material). The product was confirmed by NMR hydrogen spectroscopy (300 MHz, CDCl3): δ 8.37 (d, J=5.1 Hz, 1H), 7.35 (s, 1H), 7.27-7.20 (m, 1H), 4.35 (s, 2H).
