Sydnone Compounds. XX. The Synthesis and the Schmidt Reaction of 4‐Formyl‐3‐Arylsydnone

A convenient method to prepare 4‐formyl‐3‐arylsydone (I) from 3‐arylsydnone by the Vilsmeier reaction in moderate yields (30%‐76%) was carefully investigated. According to the Schmidt reaction, I reacts with sodium azide in concentrated sulfuric acid to produce 3‐arylsydnone‐4‐carboxamide (II). But 3‐arylsydnone‐4‐carhonitrile (III) is obtained, if dilute sulfuric acid was used instead. When III treates with concentrated sulfuric acid, II is obtained in good yield. The all possible reaction mechanisms are suggested.