A new class of heterocyclic betaines: 1,1‐dimethyl‐3‐phenylpyrazolium‐5‐oxide

1,1‐Dimethyl‐3‐phenylpyrazolium‐5‐oxide (1) was isolated as a minor product (3%) in the reaction of ethyl benzoylacetate with 1,1‐dimethylhydrazine and also was obtained as the major product (58%) from the reaction of methyl p ‐toluenesulfonate with ethyl benzoylacetate dimethylhydrazone. The structural assignment was made on the basis of chemical reactions and spectral data and the formula is represented by a resonance structure for which there are two principal canonical forms. Reaction of 1 with methanol at room temperature afforded methyl benzoylacetate dimethylhydrazone. Ethyl benzoylacetate dimethylhydrazone was shown to exist as a tautomeric mixture containing 65% of the imine form at room temperature.