[Cl:1][C:2]1[CH:10]=[C:9]2[C:5]([C:6](=[O:12])[C:7](=[O:11])[NH:8]2)=[CH:4][C:3]=1[O:13][CH3:14].C(O)(=[O:17])C>C(OC(=O)C)(=O)C.O.[O-2].[O-2].[O-2].[Cr+6]>[Cl:1][C:2]1[C:3]([O:13][CH3:14])=[CH:4][C:5]2[C:6](=[O:12])[O:11][C:7](=[O:17])[NH:8][C:9]=2[CH:10]=1Chromium trioxide (4.7 g) was added in small portions to a stirred suspension of 6-chloro-5-methoxyisatin (5.9 g) in glacial acetic acid (22 ml) and acetic anhydride (22 ml) at 80°. Some spontaneous ignition of the chromium trioxide was observed where this reagent became exposed to the air in the stirring vortex. The mixture was cooled and diluted with water (100 ml). The solid product was recrystallised from industrial methylated spirit to give the novel compound 7-chloro-6-methoxy-1H-3,1-benzoxazine-2,4-dione containing some unreacted starting material.
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