Facile Synthesis of New [1,2,4]Triazolo[4,3-b]pyridazine

A number of new [1,2,4]triazolo[4,3-b]pyridazines were prepared by either cyclocondesation of substituted hydrazinopyridazines with orthoesters or oxidative cyclization of their hydrazone analogs in nitrobenzene as an oxidizing agent. A host of other new [1,2,4]triazolo[4,3-b]pyridazine derivatives were synthesized by sequential treatment of the latter compounds with carbon disulfide and alkyl halides.