Studies on mesoionic compounds. Part 6. Synthesis of three new mesoionic heterocyclic systems; sulphur-containing analogues of sydnone

The synthesis of three new classes of mesoionic heterocycle, 1,2,3-oxadiazolium-5-thiolate (3), 1,2,3-thiadiazolium-5-olate (4), and 1,2,3-thiadiazolium-5-thiolate (6), from the Meerwein alkylation product of sydnone is described.