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 SOCl 2 to give N-substituted furopyridazinone derivatives.

We hereby report the first preparation of the 5,6-dihydro-4H-furo[2,3-c]pyrrol-4-one (3) and its derivatives starting from methyl 3-(methoxycarbonyl)furan-2-acetate (8). The ester functionality connected to the methylene group was regiospecifically converted to the desired monohydrazide 9. Conversion of 9 into the acyl azide 10 followed by Curtius rearrangement gave the corresponding isocyanate derivative 11 (Scheme 2). Reaction of 11 with different nucleophiles produced urethane and urea derivatives (Scheme 3). Intramolecular cyclization reactions provided the target compounds (Scheme 5). Removal of the amine-protecting group formed the title compound 3.Introduction. -Isoindolinone (¼ 2,3-dihydro-1H-isoindol-1-one; 1) derivatives show a wide range of important biological activities. A series of isoindolinone derivatives have recently been synthesized and screened. Some substituted isoindolinone derivatives have quite potent metabotropic glutamate receptor 1 antagonist activity [1]. Moreover, it has been demonstrated that some derivatives show an antipsychotic-like effect in an animal model.

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Synthesis of Furo[2,3-d]pyridazin-4(5H)-one and Its N(5)-SubstitutedDerivatives. -A new and efficient method for the synthesis of furopyridazinone derivatives via intramolecular cyclization reactions of 2-hydrazonomethylfuran-3-carboxylate derivatives is developed. -(KARAHAN, E.; KOZA, G.; BALCI*, M.; Helv. Chim. Acta 97 (2014) 11, 1487-1496, http://dx.doi.org/10.1002/hlca.201400042 ; Dep. Chem., Middle East Tech. Univ., TR-06800 Ankara, Turk.; Eng.) -C. Cyrus