Thermal cyclisation of pyridazinylhydrazones to give s-triazolo[4,3-b]-pyridazines and pyridazino[2,3-a]benzimidazole

Abstract

Thermal (non-catalytic) cyclisation of 6-methylpyridazin-3-ylhydrazones (14) unexpectedly caused ring closure on to the 2-nitrogen atom of the ring, usually without elimination of ammonia but with elimination of the elements of a hydrocarbon, to give 3-substituted 6-methyl-s-triazolo[4,3-b]pyridazines [e.g.(21)]. Cyclohexanone 6-methylpyridazin-3-ylhydrazone (38) gave both 6-methyl-3-pentyl-s-triazolo[4,3-b]pyridazine (42) and 6,7,8,9-tetrahydro-2-methylpyridazino[2,3-a]benzimidazole (43).