Cyclization of ethyl 4-benzoyl-5-methylisoxazole-3-carboxylate (I) with hydrazine hydrate affords the isoxazolopyridazinone (II). Regioselective alkylation of (II) with ethyl bromide gives the 6-ethyl derivative (III). This is then subjected to oxidative isoxazole ring cleavage with cerium ammonium nitrate to furnish the nitro ketone (IV). Finally, cyclization of (IV) with ethanolic hydrazine leads to the target pyrazolopyridazinone.