Sydnone

Sydnones are mesoionic heterocyclic chemical compounds possessing a 1,2,3-oxadiazole core with a keto group in the 5 position. Like other mesoionic compounds they are di-polar, possessing both positive and negative charges which are delocalized across the ring. Recent computational studies have indicated that sydnones and other similar mesoionic compounds are nonaromatic, "though well-stabilized in two separate regions by electron and charge delocalization." Sydnones are heterocyclic compounds named after the city of Sydney, Australia.

A sydnone imine in which the keto group of sydnone (=O) has been replaced with an imino (=NH) group can be found as a substructure in the stimulant drugs feprosidnine and mesocarb.

Discovery
Sydnone was first prepared in 1935 by Earl & Mackney by cyclodehydration of N-Nitroso-N-phenylglycine with acetic anhydride. Later work showed that this could be applied fairly generally to the nitrosamines of N-substituted amino acids.

Examples

 * Cefanone (Cephanone)
 * Ipramidil
 * 3-Thiomorpholino-sydnonimine
 * The reaction between methyl 3-benzyl-sydnone-4-acetate and diphenylacetylene is described in Ex1 of gives an analog of Bufezolac.
 * Synthesis and Biological Evaluation of Coumarinyl Sydnone Derivatives.