[CH3:1][O:2][C:3]1[C:7]([Br:8])=[CH:6][S:5][N:4]=1.[N+](C1C=C([N+]([O-])=O)C=C(C(OO)=O)C=1)([O-])=[O:10]>C(Cl)Cl>[CH3:1][O:2][C:3]1[C:7]([Br:8])=[CH:6][S:5](=[O:10])[N:4]=1To a solution of 3-methoxy-4-bromoisothiazole (2.9 g, 15 mmol) in methylene chloride (15 ml) there can be was added, in portions, 3,5-dinitroperbenzoic acid (3.4 g, 15 mmol) with ice bath cooling. After about one hour, the precipitated 3,5-dinitrobenzoic acid can be filtered off and the solvent evaporated in vacuo. By triturating the residue with diethyl ether, a crystalline product, 3-methoxy-4-bromoisothiazole-1-oxide, can be obtained. Additional material can be obtained by chromatographing the mother liquors on silica gel, eluting with chloroform.
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