Synthesis and in vitro Cytotoxicity Studies of Novel Triazolo[4,3-b]pyridazinones

New triazolo[4,3-b]pyridazinones were synthesized and evaluated for their potential in vitro cytotoxic antitumor properties. The compounds were prepared by 1,3-dipolar cycloaddition of pyridazin-3-ones with N-aryl-C-ethoxycarbonylnitrile imines, generated in situ from ethylhydrazono-α-bromoglyoxylates. The peri- and regioselectivity of the reaction were ascertained by 1H and 13C NMR spectroscopy of the cycloadducts