[CH:1](O)=[O:2].C(OC(=O)C)(=O)C.[NH2:11][C:12]1[C:17](=[O:18])[C:16]2[CH:19]=[C:20]([O:28][C:29]3[CH:34]=[CH:33][CH:32]=[CH:31][CH:30]=3)[C:21]([NH:23][S:24]([CH3:27])(=[O:26])=[O:25])=[CH:22][C:15]=2[O:14][CH:13]=1.C(OC(C)C)(C)C>C(Cl)Cl>[CH:1]([NH:11][C:12]1[C:17](=[O:18])[C:16]2[CH:19]=[C:20]([O:28][C:29]3[CH:30]=[CH:31][CH:32]=[CH:33][CH:34]=3)[C:21]([NH:23][S:24]([CH3:27])(=[O:25])=[O:26])=[CH:22][C:15]=2[O:14][CH:13]=1)=[O:2]27.6 g of formic acid was added to 30.6 g of acetic anhydride. The mixture was stirred for 1.5 hours at 40°-45° C. The reaction mixture was dropwise added to a solution of 34.6 g of 3-amino-7-methylsulfonylamino-6-phenoxy-4H-1-benzopyran-4-one dissolved in 400 ml of methylene chloride. The mixture was stirred for 1 hour at 20°-25° C. 400 ml of diisopropyl ether was added thereto. The resulting crystal was collected by filtration and recrystallized from acetonitrile to obtain 27.3 g (yield: 73%) of 3-formylamino-7-methylsulfonylamino-6-phenoxy-4H-1-benzopyran-4-one having a melting point of 236°-238° C.
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