{{more footnotes needed|date=August 2013}} {{Chembox |ImageFile=Sydnone circle structure.png |ImageSize = 120px |IUPACName=2''H''-Oxadiazol-5-one |OtherNames=1,2,3-Oxadiazol-5(2''H'')-one |Section1={{Chembox Identifiers | CASNo = 534-24-7 | PubChem=12443168 | ChemSpiderID = 65792731 | StdInChI=1S/C2H2N2O2/c5-2-1-3-4-6-2/h1,4H | StdInChIKey = BIGWXAGEQONZGD-UHFFFAOYSA-N | SMILES = C1=NNOC1=O }} |Section2={{Chembox Properties |C=2|H=2|N=2|O=2 }} }}
'''Sydnones''' are mesoionic heterocyclic chemical compounds possessing a C5-oxygenated 1,2,3-oxadiazole core,<ref>{{GoldBookRef|title=sydnones|file=S06207}}</ref><ref name=Stewart>{{cite journal|last1=Stewart|first1=F. H. C.|title=The Chemistry of the Sydnones|journal=Chemical Reviews|date=1 April 1964|volume=64|issue=2|pages=129–147|doi=10.1021/cr60228a004}}</ref><ref name=Browne>{{cite journal|last1=Browne|first1=Duncan L.|last2=Harrity|first2=Joseph P.A.|title=Recent developments in the chemistry of sydnones|journal=Tetrahedron|date=January 2010|volume=66|issue=3|pages=553–568|doi=10.1016/j.tet.2009.10.085}}</ref> 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 {{ill|Alan W. Mackney|qid=Q112249660}} by cyclodehydration of N-Nitroso-N-phenylglycine with acetic anhydride.<ref>{{cite journal|last1=Earl|first1=J. Campbell|last2=Mackney|first2=Alan W.|title=204. The action of acetic anhydride on N-nitrosophenylglycine and some of its derivatives|journal=Journal of the Chemical Society (Resumed)|date=1935|pages=899|doi=10.1039/jr9350000899}}</ref> Later work showed that this could be applied fairly generally to the nitrosamines of N-substituted amino acids.<ref name=Stewart/>
The parent compound '''sydnone''' is not synthetically accessible and may not exist.<ref name=Stewart/>{{rp|p=130}}<ref name=Browne/>{{rp|p=554}}
== Chemical structure == Sydnones have the following resonance structures.{{citation needed|date=December 2024}}<!--Browne and Harrity (2010) instead list 5 resonance structures--> The exocyclic oxygen atom (O6) has a significant negative charge.<ref name=Browne/> 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."<ref>{{cite journal|last1=Simas|first1=Alfredo|title=Are mesoionic compounds aromatic?|journal=Canadian Journal of Chemistry|date=1998|volume=76|issue=6 |pages=869–872|doi=10.1139/v98-065}}</ref>
==Examples== * Cefanone (Cephanone) * Ipramidil * 3-Thiomorpholino-sydnonimine {{US patent|4332801}} * The reaction between methyl 3-benzyl-sydnone-4-acetate and diphenylacetylene is described in Ex1 of {{Cite patent|country=GB|number=1387306}} gives an analog of Bufezolac. * Synthesis and Biological Evaluation of Coumarinyl Sydnone Derivatives.<ref name="PatelPatel2011">{{cite journal|last1=Patel|first1=Keshav C.|last2=Patel|first2=Himanshu D.|title=Synthesis and Biological Evaluation of Coumarinyl Sydnone Derivatives|journal=e-Journal of Chemistry|volume=8|issue=1|year=2011|pages=113–118|issn=0973-4945|doi=10.1155/2011/705856|doi-access=free}}</ref>
==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== {{reflist}} * {{cite journal | title = Sydnone anions and abnormal N-heterocyclic carbenes of O-ethylsydnones. Characterizations, calculations and catalyses. |author1=S. Wiechmann |author2=T. Freese |author3=M. H. H. Drafz |author4=E. G. Hübner |author5=J. C. Namyslo |author6=M. Nieger |author7=A. Schmidt | journal = Chem. Commun. | volume = 50 | pages = 11822–11824 | year = 2014 |issue=80 | doi = 10.1039/C4CC05461J |pmid=25156208 | doi-access =free|hdl=10138/224668 |hdl-access=free }} * {{cite journal | title = Synthesis of Sydnones and Sydnone Imines |author1=Claude V. Greco |author2=Wayne H. Nyberg |author3=C. C. Cheng | journal = Journal of Medicinal Chemistry | volume = 5 | issue = 4 | pages = 861–865 | year = 1962 | doi = 10.1021/jm01239a022 |pmid=14056419 }} * {{cite journal | title = Meso-ionic compounds |author1=Wilson Baker |author2=W. D. Ollis | journal = Quarterly Reviews, Chemical Society | volume = 11 | pages = 15–30 | year = 1957 | doi = 10.1039/QR9571100015 |s2cid=96888271 }} * {{cite journal | title = The Preparation of Substituted Hydrazines. I. Alkylhydrazines via Alkylsydnones |author1=Joseph Fugger |author2=Jack M. Tien |author3=I. Moyer Hunsberger | journal = J. Am. Chem. Soc. | volume = 77 | issue = 7 | pages = 1843–1848 | year = 1955 | doi = 10.1021/ja01612a039 }} * {{cite journal | title = The Preparation of Substituted Hydrazines. II.1 3-Pyridylhydrazine via the Phototropic N-(3-Pyridyl)-sydnone |author1=Jack M. Tien |author2=I. Moyer Hunsberger | journal = J. Am. Chem. Soc. | volume = 77 | issue = 24 | pages = 6604–6607 | year = 1955 | doi = 10.1021/ja01629a052 }} 88, 178 (1961); * {{cite journal | title = Sydnones. III. Preparation and Interconversion of Mercurated Derivatives of N-(3-Pyridyl)-sydnone1-3a |author1=Jack M. Tien |author2=I. Moyer Hunsberger | journal = J. Am. Chem. Soc. | volume = 83 | issue = 1 | pages = 178–182 | year = 1961 | doi = 10.1021/ja01462a035 }} * {{cite journal | author = Alan R. Katritzky | journal = Chem. Ind. | pages = 521 | year = 1955 }}, (); * {{cite journal | title = Some new mesoionic compounds |author1=Alexander Lawson |author2=D. H. Miles | journal = J. Chem. Soc. | pages = 2865–2871 | year = 1959 | doi = 10.1039/JR9590002865 }} * {{cite journal | title = A Kinetic Study of the Reaction of a "Meso-ionic" Compound (Dehydrodithizone) with Haloacetates |author1=J. Ogilvie |author2=V. K. Miyamoto |author3=Thomas C. Bruice | journal = J. Am. Chem. Soc. | volume = 83 | issue = 11 | pages = 2493–2495 | year = 1961 | doi = 10.1021/ja01472a017 }} * {{cite journal | title = A New Class of Central Nervous System Stimulants | author = LEMONT B. KIER, LAURETTA E. FOX, D. DHAWAN & I. W. WATERS | journal = Nature | volume = 195 | issue = 4843 | pages = 817–818 | year = 1962 | doi = 10.1038/195817a0 | pmid = 14455827 |bibcode = 1962Natur.195..817K | s2cid = 1683698 }}
== External links == * [https://goldbook.iupac.org/terms/view/S06207 IUPAC Goldbook entry] * [https://books.google.com/books?id=OQrIk2rlduAC&dq=mesoionic+sydnone&pg=PA86 Dictionary of Organic Compounds]
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Category:Oxadiazoles Category:Simple aromatic rings Category:Lactones