A reliable synthesis of 1,1-dimethylpyrazolium 5-oxides

Reliable syntheses of compounds having the novel 1,1-dimethylpyrazolium 5-oxide ring system are reported. The method involves treating the dimethylhydrazone of a β-ketoester with a small amount of concentrated sulfuric acid or other catalyst and heating under reduced pressure for 1–24 hours. In this manner two new members of the series have been prepared and characterized.