ClC1C=CC=C(C(OO)=[O:9])C=1.[CH3:12][C:13]1[C:21]2[C:16](=[N:17][CH:18]=[CH:19][CH:20]=2)[S:15][N:14]=1.[OH-].[Na+]>C(O)(=O)C.ClCCl.O>[CH3:12][C:13]1[C:21]2[C:16](=[N:17][CH:18]=[CH:19][CH:20]=2)[S:15][N+:14]=1[O-:9]A solution of m-chloroperbenzoic acid (160 mmol) in acetic acid (200 mL) was added dropwise to a solution of 3-methylisothiazolo[5,4-b]pyridine (107 mmol) in dichloromethane (200 mL). The reaction mixture was maintained for 6 h at 25° C. The reaction mixture was diluted with water (100 mL), the pH was adjusted to 8 with 10% sodium hydroxide, and the layers were separated. The aqueous layer was extracted with ethyl acetate (10×100 mL) and the combined organic layers were dried (magnesium sulfate) and concentrated to provide 3-methylisothiazolo[5,4-b]pyridine-N-oxide in 62% yield as a yellow solid.
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