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

Abstract

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‐1 H ‐pyrazole‐4‐carboxylic acids III in high yields. Esters III were hydrolyzed to the relative 5‐substituted 1‐phenyl‐1 H ‐pyrazole‐4‐carboxylic acids which were converted by heating to 5‐substituted 1‐phenyl‐1 H ‐pyrazoles in excellent yields. Reaction of II with methylhydrazine afforded in general a mixture of 3‐ and 5‐substituted ethyl 1‐methyl‐1 H ‐pyrazole‐4‐carboxylates with the exception of IIg , which gave in high yield methyl 5‐benzyl‐1‐methyl‐1 H ‐pyrazole‐4‐carboxylate, which was hydrolyzed to the relative pyrazolecarboxylic acid. This afforded by heating 5‐benzyl‐1‐methyl‐1 H ‐pyrazole in quantitative yield.