Ethyl 4-cyclopropyl-3-oxobutyrate (1.20 g, 7.05 mmol, 1.2 eq.) obtained in Example 96a) and 4-azido-N-ethylbenzamide (1.20 g, 5.88 mmol) were dissolved in ethanol (25 ml), sodium ethoxide (556 mg, 7.35 mmol, 1.25 eq.) was added, and the mixture was stirred at room temperature for 30 min and at 80° C. for 2.5 hr. 2% Aqueous sodium carbonate solution (40 ml) was added to the reaction mixture, ethanol was evaporated, and the residue was diluted with water (20 ml) and washed twice with ethyl acetate-hexane (2:1, 50 ml). The organic layer was extracted with 1% aqueous sodium carbonate solution (20 ml). The aqueous layers were combined, acidified (pH<3) with 6N hydrochloric acid, and stood still at 5° C. The precipitate was collected by filtration, washed with cold water and dried to give the title compound as a pale-brown powder (1.88 g, 5.98 mmol, 101.7%).
