Synthesis of Furo[2,3-d]pyridazin-4(5H)-one and Its N(5)-Substituted Derivatives

We report the efficient preparation of furo[2,3-d] pyridazin-4(5H)-one and its N-substituted derivatives starting from methyl 2-methylfuran-3-carboxylate. The Me group was converted to the aldehyde group, which was then condensed with hydrazine derivatives. Then, the ester functionalities were hydrolyzed to the corresponding acids, followed by treatment with SOCl2 to give N-substituted furopyridazinone derivatives.