To a solution of ethyl (1E)-N-{[(2,4,6-trimethylphenyl)sulfonyl]oxy}ethanimidate (11 g, 37 mmol) in 1,2-dimethoxyethane (15 mL) was slowly added dropwise perchloric acid (5 mL) under ice-cooling. The mixture was stirred for 0.5 hr under ice-cooling, and water (20 mL) was added. Water (10 mL) was further added, and the mixture was stirred. The resulting precipitate was collected by filtration and washed with water. The obtained white solid was dissolved in ethyl acetate. The aqueous layer was separated and dried over anhydrous magnesium sulfate. The insoluble material was filtered off, and the obtained solution was added dropwise to a solution of 4-(benzyloxy)pyridine (5.6 g, 30 mmol) produced in the above in ethyl acetate (30 mL) under ice-cooling. After stirring at room temperature for 1 day, the reaction mixture was concentrated under reduced pressure. Ethyl acetate and diethyl ether were added to the obtained residue. The separated oil was washed with ethyl acetate/diethyl ether and diethyl ether, and concentrated under reduced pressure. To a solution of the obtained residue in N,N-dimethylformamide (50 mL) were added potassium carbonate (5.0 g, 36 mmol) and ethyl 2-butynoate (3.4 g, 30 mmol), and the mixture was stirred at room temperature for 1 day. The reaction mixture was concentrated under reduced pressure, water was added to the obtained residue, and the mixture was extracted with ethyl acetate. The collected organic layer was washed with saturated brine and dried over anhydrous magnesium sulfate, and the insoluble material was filtered off. The filtrate was concentrated under reduced pressure, the obtained residue was purified by silica gel column chromatography (ethyl acetate/hexane=10/90→50/50), and the obtained solution was concentrated under reduced pressure. The obtained residue was washed with diisopropyl ether to give the title compound (1.5 g, 16%) as a colorless solid.
