Studies on Mesoionic Compounds. III. Synthesis of Ψ-3-Aryl-5-imino-3, 5-dihydro-1-oxa-2, 3, 4-triazole Hydrochlorides and Their Derivatives

Several hitherto unknown mesoionic compounds, Ψ-3-aryl-5-imino-3, 5-dihydro-1-oxa-2, 3, 4-triazole hydrochlorides (III) were synthesized starting from monoarylhydrazines (IV) via cyanohydrazines (V) and nitrosocyanohydrazines (VI). The mesoionic compounds (III) were converted into their N-acyl derivatives (VIII) by treatment with various acylating agents. The free base (VII) was isolated in crystalline from the 3-phenyl homolog of III by treatment with aqueous bicarbonate ; although the corresponding sydnonimine hydrochloride has been known to result in the ring opening under similar conditions.