The 1H-pyrazole-3-carboxylic acid 2, obtained from the furan-2,3-dione 1 and N-Benzylidene-N'-(3-nitrophenyl) hydrazine, was converted via reactions of its acid chloride 3 with various alcohols or N-nucleophiles into the corresponding ester or amide derivatives 4 or 5, respectively. Nitrile 6 and anilino-pyrazole acid 7 derivatives of 2 were also obtained by dehydration of 5a in a mixture of SOCl2 with DMF and reduction of 2 with sodium polysulphide, respectively. While cyclocondensation reactions of 2 or 7 with phenyl hydrazine or hydrazine hydrate and 6 with only anhydrous hydrazine lead to derivatives of pyrazolo[3,4-d]pyridazinone 8 and pyrazolo[3,4-d]pyridazine amine 9, respectivel. The reaction of 2 with 2-hydrazino-pyridine provided hydrazono-pyrazole acid derivative 10, which was decarboxylated to give hydrazono-pyrazole derivative 11. Pyrazolo[4,3-d]oxazinone 12 and 2-quinolyl pyrazolo[3,4-d]pyridazine 13 derivatives were also prepared by cyclocondensation reactions of 2 with hydroxylamine hydrochloride and 7 with acetaldehyde, respectively.