Pyrazole-3,5-dicarboxylic acid, reaction with

Diazopropyne reacts similarly with a monosubstituted acetylene to form 3(5)-alkynylpyrazoles (68LA113). Thus, the reaction of diazopropyne with acetylene-carboxylic acid methyl ether results in 5-ethynyl-l//-pyrazole-3-carboxylic acid methyl ether in 48 h in 62% yield. 5-Ethynyl-l//-pyrazole-3,4-dicarboxylic acid dimethyl ester was prepared by reaction of diazopropyne with acetylenedicar-boxylic acid methyl ether (Scheme 10). 

Reaction of ethyl 5-amino-3-methylthio-l//-pyrazol-4-carboxylate 267 with sodium nitrite in the presence of hydrochloric acid gives the diazo intermediate 268, which on treatment with active methylenic compounds such as ethyl a-chloroacetate or a-chloroacetylacetone affords the hydrazonyl chlorides 269 and 270, respectively, whose reaction with triethylamine in refluxing ethanol convert them into ethyl 4-hydro-2-methylthiopyrazolo[5,l-c]-[l,2,4]triazole-3,6-dicarboxylate 271 and ethyl 6-acetyl-4-hydro-2-methylthiopyrazolo[5,l-c][l,2,4]triazole-3-carboxy-late 272 (Scheme 23) <2001MI1>. 

Af-Unsubstituted pyrazoles and indazoles add to compounds containing activated double and triple bonds (67HC 22)1,B-76MI40402>. Amongst C—C double and triple bonds, maleic anhydride, acrylic acid esters and nitriles, acetylene-carboxylic and -dicarboxylic esters (78AHC(23)263), quinones, and some a,/3-unsaturated ketones have been used with success. Phenylacetylene reacts with pyrazole in the presence of Na/HMPT as catalyst to yield the Z isomer of 1-styrylpyrazole in a highly stereoselective reaction (78JHC1543). 

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