[C:1]([N:4]1[C:9]2[CH:10]=[C:11]([NH2:17])[C:12]([N+:14]([O-:16])=[O:15])=[CH:13][C:8]=2[O:7][C:6]([CH3:19])([CH3:18])[CH2:5]1)(=[O:3])[CH3:2].N([O-])=O.[Na+].[N-]=[N+]=[N-].[Na+].O>Cl>[C:1]([N:4]1[C:9]2=[CH:10][C:11]3[C:12](=[N+:14]([O-:16])[O:15][N:17]=3)[CH:13]=[C:8]2[O:7][C:6]([CH3:19])([CH3:18])[CH2:5]1)(=[O:3])[CH3:2]
To a suspension of 530 mg 4-acetyl 6-amino-3,4-dihydro-2,2-dimethyl-7-nitro-2H-1,4-benzoxazine in 3 ml 5N HCl, was added dropwise 3 ml aqueous solution containing 156 mg sodium nitrite under ice cooling, the mixture was stirred for one hour under ice cooling, 1 ml aqueous solution containing 73 mg sodium nitrite was further added dropwise, and the resulting mixture was stirred for ten minutes. To the reaction mixture thus obtained, was added dropwise 3 ml aqueous solution containing 137 mg sodium azide under ice cooling, and the mixture was stirred for 90 minutes. After addition of 10 ml water, the precipitate which separated out was collected by filtration, and its solution in 5 ml toluene was heated under reflux for eight hours. The reaction mixture was diluted with ethyl acetate, the diluted solution was dried over anhydrous magnesium sulfate, and the solvents were distilled off from the dried solution. The residue was subjected to column chromatography on silica gel, the crystals obtained by elution with a 50:1 mixture of chloroform and ethyl acetate were recrystallized from 14 ml ethanol, giving 267 mg of 8-acetyl-7,8-dihydro-6,6-dimethyl-6H-[1,2,5]oxadiazolo[3,4-g][1,4]benzoxazine 3-oxide.
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