3.46 g of 3-amino-7-methylsulfonylamino-6-phenoxy-4H-1-benzopyran-4-one was dissolved in 35 ml of N,N-dimethylformamide. Thereto were added 7 ml of bromobenzene, 1.66 g of potassium iodide, 1.38 g of potassium carbonate and 0.64 g of a copper powder. The mixture was refluxed for 6 hours. The reaction mixture was introduced into a mixture consisting of 300 ml of water and 200 ml of ethyl acetate. The insolubles were removed by filtration, and the filtrate was adjusted to pH 4 with 4N hydrochloric acid. The organic layer was separated, washed with water and a saturated aqueous sodium chloride solution in this order, and dried with anhydrous magnesium sulfate. The solvent was removed by distillation under reduced pressure. The residue was purified by a column chromatography (eluant: a 20:1 mixture of toluene and ethyl acetate) and then recrystallized from acetonitrile to obtain 430 mg (yield: 10.2%) of 7-methylsulfonylamino-3-phenylamino-6-phenoxy-4H-1-benzopyran-4-one having a melting point of 212°-213° C.
