Phosphorus oxychloride → 4-Chloroimidazo(2,1-f)(1,2,4)triazine

Imidazo[1,2-f][1,2,4]triazin-4-ol (400 mg, 2.94 mmol, 1.0 eq) was dissolved in POCl3 (10 mL, 109.2 mmol, 37.1 eq) and the resulting mixture was stirred at reflux for 2 h. The mixture was concentrated in vacuo to remove POCl3. The residue was poured into ice water (30 mL) and neutralized with saturated aqueous NaHCO3 solution to adjust the pH to 6-7 while keeping the temperature below 5° C. The mixture was extracted with ethyl acetate (30 mL×4). The combined organic layer was washed with brine, dried over Na2SO4 and filtered. The filtrate was concentrated in vacuo and the residue was purified by flash column chromatography on silica gel (16% ethyl acetate in petro ether) to afford 4-chloroimidazo[1,2-f][1,2,4]triazine (300 mg, 66.0% yield).