The synthesis of 11 H ‐1,2,4‐triazolo[4,3‐ b ]pyridazino[4,5‐ b ]indoles,11 H ‐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

This paper describes the synthesis of the previously unknown 11 H ‐1,2,4‐triazolo[4,3‐ b ]pyridazino[4,5‐ b ]indoles (2) and 11 H ‐tetrazolo[4,5‐ b ]pyridazino[4,5‐ b ]indoles (3) from 4‐hydrazino‐5 H ‐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 1 H‐nmr spectra.