Synthesis and some reactions of 4‐(ethoxycarbonyl)‐1,5‐diphenyl‐1 H ‐pyrazole‐3‐carboxylic acid

1,5‐Diphenyl‐1 H ‐pyrazole‐3,4‐dicarboxylic acid‐4‐ethyl ester 2 , obtained from the 4‐ethoxycarbonyl‐5‐phenyl‐2,3‐furandione 1 and N ‐benzylidene‐ N ′‐phenyl hydrazine, was converted via reactions of its acid chloride 3 with various alcohols or N‐nucleophiles into the corresponding ester 5 or amide derivatives 6 , respectively. In addition, 2 was decarboxylated to give ethyl 1,5‐diphenylpyrazole‐4‐carboxylate 4 . Nitrile 7 derivative of 2 was also obtained by dehydration of 6a in a mixture of SOCl 2 and DMF. While cyclocondensation reaction of 2 with hydrazine hydrate leads to the formation of pyrazolo[3,4‐ d ]pyridazine‐4,7‐dione 8 , the reaction of 3 with anhydrous hydrazine provided a new bis pyrazole derivative 9 .