4-Iodopyrazole-3 -carboxylic acid

The interaction between a 4-iodopyrazole-3-carboxylic acid and copper ace-tylides having both donor and acceptor substituents at the triple bond generated six- rather than five-membered lactones, as in the aromatic series (Scheme 117). 

The isomeric 4-iodopyrazole-5-carboxylic acid is cyclocondensed in a similar way. Introduction of the additional methyl group into the ring has no effect on the direction of cycloaddition 4-iodo-l,3-dimethylpyrazole-5-carboxylic acid forms only 5-lactones (Scheme 118). 

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