To a solution prepared by dissolving 43.91 g (215.03 mM) of 3-carbethoxy-5-methylimidazo[1,2-a]pyridine in 200 ml of ethyl acetate was added 31.58 g (236.53 mM) of N-chlorosuccinimide. Then, 1.66 ml (21.50 mM) of trifluoroacetic acid was added dropwise at room temperature. This mixture was stirred under argon gas at room temperature for 14 hours. After completion of the reaction, the reaction mixture was poured in 300 ml of saturated aqueous NaHCO3 solution with ice-cooling and extracted with 200 ml of ethyl acetate. The organic layer was washed with 300 ml of saturated aqueous NaCl solution and dried over MgSO4 and the solvent was distilled off under reduced pressure to recover 22.15 g of crude 3-carbethoxy-5-chloromethylimidazo[1,2-a]pyridine as tan-colored liquid. To a solution prepared by dissolving 22.15 g of this crude 3-carbethoxy-5-chloromethylimidazo[1,2-a]pyridine in 200 ml of acetonitrile was added 4.95 ml (92.80 mM) of sulfuric acid with ice-cooling and the mixture was stirred. The purified precipitate was recovered by filtration, rinsed with a small amount of acetonitrile, and dried in vacuo to provide 16.20 g (yield 22.4%) of the title compound as orchre powders.
