2,3-Furandiones in general are considered convenient and versatile synthons in heterocyclic synthesis 1 . A convenient method for their synthesis, the mechanism of reactions and semi-empirical (AM1 and PM3) and ab initio (DFT) calculations on the interaction of 4-benzoyl-5-phenyl-2,3-dihydro-2,3-furandione (1) with several semicarbazones, ureas, thioureas and anilides have been reported recently 2-7 . The reactions of 2,3-furandione (1) and various hydrazines or hydrazones result in new pyrazole-3-carboxylic acids, pyrazolo-pyridazinones and some of their derivatives. The pyrazole carboxylic acids can be easily transformed into the corresponding acid chloride, ester, or amide derivatives by general chemical procedures 8-12 . Pyrazole derivatives in general are well-known nitrogen-containing heterocyclic compounds and various procedures have been developed for their syntheses [13][14][15] .The chemistry of pyrazole derivatives has been the subject of much research due to their importance in various applications and their widespread potential biological and pharmacological activities, such as antiinflammatory, antipyretic, analgesic, antimicrobial, antiviral, antitumor, antifungal, pesticidal, anticonvulsant, CNS regulant, antihistaminic, antibiotic and antidepressant activities [16][17][18][19][20][21][22][23][24][25] . The possible biological properties of the pyrazol, pyridazinone, pyrazolopyridazinone 26 and oxazin derivatives make it attractive to study these compounds.In view of these important properties, we decided both to provide the reproducibility of the reactions of 1H-pyrazole-3carboxylic acid chlorides (3a-b) with urea-nucleophiles and to extend our investigations related to preparing new hetrocycles which include the pyrazole ring in their structure.The 1H-pyrazole-3-carboxylic acids 2 or their remarkably stable acid chlorides 3 can easily be converted into the corresponding 1Hpyrazole-3-carbonyl-N'-urea derivatives (5a-k) from reaction with urea nucleophiles. It has been demonstrated that with the variation in reaction conditions, the reaction changes thus leading to different products. All newly synthesized compounds were characterized by elemental analysis, FT-IR, 1 H and 13 C NMR spectral data. All compounds were compared with their previous analogues.
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