5-Cyano-2-benzofurancarboxylic acid (300 mg, 1.60 mmol) and t-butyl 4-aminophenoxyacetate (395 mg, 1.76 mmol) were dissolved in N,N-dimethylformamide (40 ml), and 1-hydroxy-1H-benzotriazole (238 mg, 1.76 mmol) and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (342 mg, 1.76 mmol) were added. The mixture was stirred at room temperature for 18 hours. Water (100 ml) was added to the reaction mixture, and the mixture was extracted with ethyl acetate. The extract was washed with water and saturated brine, and dried over anhydrous magnesium sulfate. After filtration, low boiling matters were distilled away from the filtrate under reduced pressure and the residue was purified by silica gel column chromatography (n-hexane/ethyl acetate=1/1) to give 512 mg of t-butyl 4-[(5-cyano-2-benzofuranyl)carbonylamino]phenoxyacetate as a pale-yellow solid (82%).
