2- Methyl-7-oxo-5-phenylpyrano

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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