5-methyl-2-isoxazolamine (1.2 g, 12 mmol) was dissolved in dry pyridine (20 ml) and ethyl 2-acetyloxy-5-[(4-chlorosulfonylphenyl)ethynyl]-benzoate (4.1 g, 10 mmol) was added. The solution was kept at ambient temperature for 72 h. The solvent was evaporated and the residue dissolved in a small amount of tetrahydrofuran. The solution was added to a refluxing solution of potassium hydroxide (2.5 g, 38 mmol) in water (100 ml). After 5 min, ethanol (50 ml) was added and the solution acidified with formic acid to produce a precipitate. The solid was collected by filtration, washed with water and dried. It was recrystallize three times from ethanol. Yield 1.5 g, 35%.
