Phosphorus oxychloride → Ethyl 4-[2,4-dichloro-7-(1-ethylpropyl)-1H-benzimidazol-1-yl]butanoate

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The solution of ethyl 4-[4-chloro-7-(1-ethylpropyl)-2-oxo-2,3-dihydro-1H-benzimidazol-1-yl]butanoate (6.8 g, 19.32 mmol) in phosphorus oxychloride (70 mL) was stirred at 100-110° C. for 2 days. After cooled to room temperature, the excess phosphorus oxychloride was removed by distillation and the residue was poured into water. The aqueous phase was extracted with ethyl acetate (100 mL×3) and the combined extracts were washed with saturated aqueous sodium bicarbonate (100 mL×2) and water (100 mL), dried over sodium sulfate and concentrated in vacuo. The residue was purified by silica gel column (petroleum ether/ethyl acetate, 50/1) to afford the title compound (2.4 g, 34%) as light yellow oil.

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