Ethyl 4-cyclopentyl-3-oxobutyrate (0.781 g, 3.94 mmol, 1.25 eq.) obtained in Example 103a) and 4-azido-N-ethylbenzamide (0.60 g, 3.15 mmol) were dissolved in ethanol (20 ml), sodium ethoxide (298 mg, 3.94 mmol, 1.25 eq.) was added, and the mixture was stirred at room temperature for 30 min, and then at 50° C. for 12 hr. Water (20 ml) was added to the reaction mixture, ethanol was evaporated, and the residue was diluted with 2% aqueous sodium carbonate solution (20 ml) and washed with ethyl acetate-hexane (2:1, 50 ml). The organic layer was extracted with 2% aqueous sodium carbonate solution (20 ml). The aqueous layers were combined, acidified (pH<3) with 6N hydrochloric acid, and extracted with ethyl acetate (35 ml and 30 ml). The organic layers were combined, washed with saturated brine, dried over anhydrous sodium sulfate, and concentrated, and diethyl ether and ethyl acetate were added. The precipitate was collected by filtration, washed with diethyl ether and dried to give the title compound as a pale-yellow powder (971 mg, 2.84 mmol, 90.0%).
