[Br:1][C:2]1[CH:3]=[N:4][CH:5]=[C:6]([Br:8])[CH:7]=1.ClC1C=CC=C(C(OO)=[O:17])C=1>C(Cl)Cl>[Br:1][C:2]1[CH:3]=[N+:4]([O-:17])[CH:5]=[C:6]([Br:8])[CH:7]=13,5-Dibromopyridine 2.37 g is dissolved in methylene chloride 25 ml and thereto is added m-chloroperbenzoic acid 2.96 g at room temperature under stirring. After stirring for 5 hours at room temperature, additional m-chloroperbenzoic acid 246 mg is added thereto and the mixture is stirred. After 15 hours the solvent is removed in vacuo and the residue is purified by silica gel chromatography (solvent; n-hexane:ethyl acetate=1:1) to give 3,5-dibromopyridine N-oxide as colorless crystals, 2.26 g. mp 140–142° C.
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