The synthesis of 11H‐1,2,4‐triazolo[4,3‐b]pyridazino[4,5‐b]indoles,11H‐tetrazolo[4,5‐b]pyridazino[4,5‐b]indoles and 1,2,4‐triazolo[3,4‐f]‐1,2,4‐triazino[4,5‐a]indoles

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Abstract
This paper describes the synthesis of the previously unknown 11H‐1,2,4‐triazolo[4,3‐b]pyridazino[4,5‐b]indoles (2) and 11H‐tetrazolo[4,5‐b]pyridazino[4,5‐b]indoles (3) from 4‐hydrazino‐5H‐pyridazino[4,5‐b]indoles (1), as well as the synthesis of 1,2,4‐triazolo[3,4‐f]‐1,2,4‐triazino‐[4,5‐a]indoles (10) from 2‐indolecarbohydrazide (4). Compounds 2 were obtained by acylation of compounds 1, followed of thermal cyclization and compounds 3 by treating compounds 1 with nitrous acid. The reactions of compound 4 with formic acid or ethyl orthoformiate gave 1,2‐dihydro‐1‐oxo‐1,2,4‐triazino[4,5‐a]indole (6). Treating this last compound with phosphorus oxychloride or phosphorus pentasulfide, followed by hydrazine, gave 1‐hydrazino‐1,2,4‐triazino‐[4,5‐a]indole (9). Acylation of this last compound, followed of cyclization gave compounds 10. All the compounds were characterized by elemental analysis and ir and 1H‐nmr spectra.