A mixture of 460 mg of ethyl 4-(t-butoxycarbonylamino)-2-hydroxybenzoate, 300 mg of cyclopentanol, 1.5 g of diethyl azodicarboxylate (40% solution in toluene), 900 mg of triphenylphosphine and 10 ml of tetrahydrofuran was stirred at room temperature for 3 days. The solvent was evaporated and the residue was purified by the silica gel chromatography (ethyl acetate/hexane) to obtain crude ethyl 4-(t-butoxycarbonylamino)-2-cyclopentyloxybenzoate. A mixture of this crude product, 20 ml of ethanol and 5 ml of 1 M aqueous sodium hydroxide solution was stirred at room temperature overnight. After the treatment with ethyl acetate as the extracting solvent in an ordinary manner, the title compound was obtained.
