Sydnone
Sydnones are mesoionic heterocyclic chemical compounds possessing a C5-oxygenated 1,2,3-oxadiazole core, named after the city of Sydney, Australia. Like other mesoionic compounds they are dipolar, possessing both positive and negative charges which are delocalized across the ring.
Discovery
N-phenylsydnone was first prepared in 1935 by and 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.The parent compound sydnone is not synthetically accessible and may not exist.
Chemical structure
Sydnones have the following resonance structures. The exocyclic oxygen atom has a significant negative charge.Image:Sydnone Resonance Structures.svg
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."
Examples
- Cefanone
- 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.