Hydrochloric Acid → Ethyl cis(+/-)-2-{3-(benzyloxy)-4-[(1H-imidazol-2-ylcarbonyl)amino]piperidin-1-yl}-1,3-thiazole-5-carboxylate

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A 4 N hydrochloric acid/ethyl acetate solution (10 mL, 40 mmol) was added to tert-butyl cis(±)-3-(benzyloxy)-4-[(1H-imidazol-2-ylcarbonyl)amino]piperidine-1-carboxylate obtained in Example (90e) (0.3 g, 0.75 mmol), and the mixture was stirred at room temperature for 20 minutes. Following concentration under reduced pressure, the residue was dissolved in DMF (8 mL). Diisopropylethylamine (0.45 g, 3.5 mmol) and ethyl 2-bromo-1,3-thiazole-5-carboxylate (0.21 g, 0.9 mmol) were added, and the mixture was stirred at 70° C. for 1.5 hours. Dilute hydrochloric acid was added to the reaction solution, followed by extraction with ethyl acetate. The organic layer was washed with water, saturated aqueous sodium bicarbonate solution and brine, and dried over anhydrous sodium magnesium sulfate. Following concentration under reduced pressure, the residue was purified by silica gel column chromatography (elution solvent: hexane/ethyl acetate=5/1, ethyl acetate) to obtain 0.26 g of the title compound as a light brown solid (76%).

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