4- Acetylenyl-l-methylpyrazole-5-carboxylic

For this reason, the heterocyclization of acetylenic derivatives of pyrazolecar-boxylic acids with different arrangements in the ring of the interacting groups was studied (Table XXVI). The reaction is carried out in boiling pyridine in the presence of catalytic amounts of PhC=CCu (81IZV1342). 4-Acetylenyl-l-methylpyrazole-5-carboxylic acids (Scheme 121) are fully isomerized into the pyranopyrazoles in 20 min in 62-84% yields. 

In the heterocyclization reactions of 4-acetylenyl-l-methylpyrazole-3-carbox-ylic acids and 4-acetylenyl-l-methylpyrazole-5-carboxylic acids the behavior is the same. Isomeric l-methyl-4-phenylethynylpyrazole-3-carboxylic acid forms... 

In the heterocyclization reactions of 4-acetylenyl-l-methylpyrazole-3-carbox-ylic acids and 4-acetylenyl-l-methylpyrazole-5-carboxylic acids the behavior is the same. Isomeric I-methyI-4-phenyIethynyIpyrazole-3-carboxylic acid forms 3 -lactones, 2-methyl-7-oxo-5-phenylpyrano[3,4-c]pyrazole, in 71 % yield (20 min) (Scheme 122). The same ester is obtained by acetylenic condensation (3 h) of 4-iodo-l-methylpyrazole-3-carboxylic acid with copper phenylacetylide. 

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