Synthesis of 1,3,4-oxadiazolium and 1,3,4-oxadiazolo[3,2-a]pyridinium salts

Protonation and alkylation of some simple 1,3,4-oxadiazoles has been studied, and a new synthesis of 1,3,4-oxadiazoles is described. Numerous 3-aryl-1,3,4-oxadiazolium salts, containing a novel type of heterocyclic cation, have been prepared by the action of carboxylic anhydrides on diacylarylhydrazines in the presence of perchloric or fluoroboric acid. 1,3,4-Oxadiazolo[3,2-a]pyridinium salts are similarly formed from 1 -acylamino-2-pyridones. The stability of the salts and their i.r. and n.m.r. spectra are discussed.