Synthesis of Bisfurazanobenzo-2, 1, 3-thiadiazole and Related Compounds

Nitration of 4, 7-dibromobenzo-2, 1, 3-thiadiazole (I) with fuming nitric acid afforded 4, 7-dibromo-5, 6-dinitrobenzo-2, 1, 3-thiadiazole (II) and, unexpectedly, the tribromo derivative : C6Br3N3O2S (III). Compound II was readily converted by treatment with sodium azide into bisfuroxanobenzo-2, 1, 3-thiadiazole (IV), which was reduced with triethylphosphite to give bisfurazanobenzo-2, 1, 3-thiadiazole (VII). Compound VII was also synthesized starting from 4-bromo-6, 7-(2', 1', 3'-oxadiazole) benzo-2, 1, 3-thiadiazole (VIII). Reduction of VII with sodium hydrosulfite gave 4, 5-diamino-6, 7-(2', 1', 3'-oxadiazole)-benzo-2, 1, 3-thiadiazole (XI), which was cyclized to 4, 5-(2', 1', 3'-oxadiazole) benzo [1, 2-c : 3, 4-c'] bis [1, 2, 5] thiadiazole (XII) by treatment with N-sulfinylaniline. The transformation of XII to benzo [1, 2-c : 3, 4-c' : 5, 6-c"] tris [1, 2, 5] thiadiazole (XIV), via 4, 5-diaminobenzo-[1, 2-c : 3, 4-c'] bis [1, 2, 5] thiadiazole (XIII), is also described.