Benzo[c][1,2,5]oxadiazole (2.5 g, 21 mmol) was added as raw material, iron powder (0.23 g, 4.2 mmol) was added and heated to 90°C to melt. Subsequently, bromine (3.2 ml, 62 mmol) was slowly added dropwise to the molten liquid and the reaction mixture was refluxed for 2 hours. Upon completion of the reaction, the resulting solution was poured into ice water and a precipitate was precipitated and collected by filtration. The precipitate was mixed with aqueous NaHCO3 solution, stirred for 15 min and filtered again. Purification by fast chromatography (hexane/EtOAc 9:1) afforded 4,7-dibromobenzofurazan as an orange solid (1.5 g, 25% yield). The product was characterized as follows: melting point 88-92 °C; IR spectra (thin film method, cm-1 ) 1514, 1344, 1201, 1026, 954, 871, 841; 1H NMR (500MHz, CDCl3) δ 7.51 (2H, s, Ar-H); 13C NMR (126MHz, CDCl3) δ 149.6 (C=N), 134.4 (C=N), 134.4 (C=N), 134.4 (C=N). ), 134.4 (Ar-C), 108.9 (ipso-Ar-C); mass spectra (EI) m/z 280 ([81Br,81Br] M+, 6%), 278 ([81Br,79Br] M+, 8%), 276 ([79Br,79Br] M+, 6%), 250 (5%), 248 (10%), 246 (7%) , 197 (5%). All data are in agreement with literature reports.
