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 John Campbell Earl 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 (O6) has a significant negative charge.
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 (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.
Related compounds 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.
See also Chemical compounds with unusual names Montréalone Münchnone Sydnone imine
References
88, 178 (1961);
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External links IUPAC Goldbook entry Dictionary of Organic Compounds