[Cl:1][C:2]1[C:10]2[C:6](=[N:7][O:8][N:9]=2)[CH:5]=[CH:4][CH:3]=1.[Br:11]Br.[O-]S([O-])=O.[Na+].[Na+]>ClCCl.C(OCC)(=O)C.[Fe]>[Br:11][C:5]1[C:6]2[C:10](=[N:9][O:8][N:7]=2)[C:2]([Cl:1])=[CH:3][CH:4]=1
4-Chlorobenzo[c][1,2,5]oxadiazole (1.0 g, 6.5 mmol) was treated with iron powder (14 mg, 0.2 mmol), stirred and heated to 50° C. and then treated in portions with bromine (1.1 g, 7.1 mmol) to produce a homogeneous red melt solution. The flask was fitted with a reflux condenser and the temperature was raised to 85° C. and stirred for 60 min. An additional 450 mg of bromine were added, heating was continued for 1 h more and then the mixture was allowed to stand for 18 h at 20° C. The solid contents of the flask were dissolved in 15 mL dichloromethane and stirred for 30 min with 15 mL saturated Na2SO3 solution. The mixture was diluted with 30 mL ethyl acetate and the organic phase was washed with 15 mL saturated NaCl, dried (Na2SO4) and concentrated under vacuum. The material was chromatographed on silica with a 0-7% ethyl acetate-hexane gradient to give the title compound as a white solid (1.4 g; 93%): mp 81-83° C.; 1H NMR (400 MHz, CDCl3) δ 7.58 (d, J=7.5 Hz, 1H), 7.33 (d, J=7.5 Hz, 1H); EIMS m/z 232.
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