Mesoionic Compounds An Unconventional Class of Aromatic Heterocycles

Mesoionic compounds are distinct types of heterocycles which belong to the class of non-benzenoid aromatics. Sydnone, the representative mesoionic compound has been extensively studied because of its unusual structure, chemical properties and synthetic utility. Sydnone is used as a versatile synthon in heterocyclic synthesis. This article gives a brief account of the comparative studies of the structural features of mesoionic compounds and other heteroaromatic systems. Some synthetically useful tandem reactions of sydnones are also discussed.