Pyridazines are an important class of heterocyclic compounds, particularly in a wide range of biological activities,[1] highly selective turn on fluorescent sensor for zinc ion,[2] human rhinovirus (HRV-3) inhibitors [3], and non-competitive reversible inhibitors of protein Tyrosine phosphatase 1B (PTP1B) [4]. Initially, the aminopyridazine moiety (1) was reacted with triethylorthoformate and hydrazine hydrate, respectively, to give compound (2). The treatment of compound (2) with various aromatic aldehydes in boiling ethanol and then oxidative heterocyclization of the corresponding imines in an appropriate solvent yielded the corresponding novelheterocyclic system of [1,2,4] triazolo[4,3:1,6]pyrimido[4,5:3,4]pyridazino[1,6d][1,2,4]triazine derivatives 3(a-g) in good yields (Scheme 1).

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