Reaction of 2‐dimethylaminomethylene‐1,3‐diones with dinucleophiles. VI. Synthesis of ethyl or methyl 1,5‐disubstituted 1H‐pyrazole‐4‐carboxylates

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Abstract
Reaction of ethyl or methyl 3‐oxoalkanoates with N,N‐dimethylformamide dimethyl acetal gave, generally in excellent yields, a series of ethyl or methyl 2‐dimethylaminomethylene‐3‐oxoalkanoates II which reacted with phenylhydrazine to afford the esters of 5‐substituted 1‐phenyl‐1H‐pyrazole‐4‐carboxylic acids III in high yields. Esters III were hydrolyzed to the relative 5‐substituted 1‐phenyl‐1H‐pyrazole‐4‐carboxylic acids which were converted by heating to 5‐substituted 1‐phenyl‐1H‐pyrazoles in excellent yields. Reaction of II with methylhydrazine afforded in general a mixture of 3‐ and 5‐substituted ethyl 1‐methyl‐1H‐pyrazole‐4‐carboxylates with the exception of IIg, which gave in high yield methyl 5‐benzyl‐1‐methyl‐1H‐pyrazole‐4‐carboxylate, which was hydrolyzed to the relative pyrazolecarboxylic acid. This afforded by heating 5‐benzyl‐1‐methyl‐1H‐pyrazole in quantitative yield.

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