Azirine

{{Short description|Organic ring compounds with the formula C2H3N}} {{Chembox  | ImageFile = Azirin.svg | ImageSize = 100px  | IUPACName = 2''H''-Azirine | OtherNames =  | Section1 = {{Chembox Identifiers | CASNo = 157-16-4 | Beilstein = 1633516 | ChEBI = 30971 | ChEMBL = | ChemSpiderID = 119750 | DrugBank = | EC_number = | KEGG = | MeSHName = | PubChem = 135972 | InChI = 1S/C2H3N/c1-2-3-1/h1H,2H2 | InChIKey = NTJMGOWFGQXUDY-UHFFFAOYSA-N | SMILES = C1C=N1 }} | Section2 = {{Chembox Properties | C=2 | H=3 | N=1 | Appearance = | Density = | MeltingPt = | BoilingPt = | Solubility = }} | Section3 = {{Chembox Hazards | MainHazards = | FlashPt = | AutoignitionPt = }} }} '''Azirines''' are heterocyclic organic compounds containing a three-membered ring with two carbon atoms and one nitrogen atom, the unsaturated analogs of aziridines. Azirine, the parent compound, has two isomers: the antiaromatic 1''H''-azirine, containing a carbon–carbon double bond, is not stable and rearranges to the tautomeric 2''H''-azirine, containing a carbon–nitrogen double bond, which is at least 30 kcal·mol−1 lower in energy.<ref>{{cite journal |last1=Januar |first1=Lawrence A. |last2=Molinski |first2=Tadeusz F. |title=Acremolin from Acremonium strictum is N2,3-Etheno-2'-isopropyl-1-methylguanine, not a 1H-Azirine. Synthesis and Structural Revision |journal=Organic Letters |date=17 May 2013 |volume=15 |issue=10 |pages=2370–2373 |doi=10.1021/ol400752s |pmc=3957326}}</ref> 2''H''-Azirines can be considered strained imines and are isolable. They are highly reactive yet have been reported in a few natural products such as dysidazirine.<ref>{{cite journal |last1=Pinho e Melo |first1=Teresa M. V. D. |last2=d'A. Rocha Gonsalves |first2=António M. |title=Exploiting 2-Halo-2H-Azirine Chemistry |journal=Current Organic Synthesis |volume=1 |issue=3 |pages=275–292 |doi=10.2174/1570179043366729 |url=https://www.researchgate.net/profile/Teresa-Melo-3/publication/233640215_Exploiting_2-Halo-2H-Azirine_Chemistry/links/0fcfd50d1ffdc2d0e0000000/Exploiting-2-Halo-2H-Azirine-Chemistry.pdf |archive-url=https://web.archive.org/web/20260422032250/https://www.researchgate.net/profile/Teresa-Melo-3/publication/233640215_Exploiting_2-Halo-2H-Azirine_Chemistry/links/0fcfd50d1ffdc2d0e0000000/Exploiting-2-Halo-2H-Azirine-Chemistry.pdf |archive-date=2026-04-22}}</ref>

== Preparation== 2''H''-Azirine is most often obtained by the thermolysis of vinyl azides.<ref>{{cite journal|title=2''H''-Azirines as synthetic tools in organic chemistry|vauthors=Palacios F, Ochoa de Retana AM, Martinez de Marigorta E, de los Santos JM|journal=Eur. J. Org. Chem.|year=2001|pages=2401–2414|doi=10.1002/1099-0690(200107)2001:13<2401::AID-EJOC2401>3.0.CO;2-U|volume=2001|issue=13}}</ref> During this reaction, a nitrene is formed as an intermediate. Alternatively, they can be obtained by oxidation of the corresponding aziridine. Azirine can be generated during photolysis of isoxazole.<ref>{{cite journal |last1=Ullman |first1=Edwin F. |last2=Singh |first2=Balwant |title=Photochemical Transposition of Ring Atoms in Five-Membered Heterocycles. The Photorearrangement of 3,5-Diphenylisoxazole |journal=J. Am. Chem. Soc. |date=April 1966 |volume=88 |issue=8 |pages=1844–1845 |doi=10.1021/ja00960a066 |bibcode=1966JAChS..88.1844U}}</ref> Due to the weak N–O bond, the isoxazole ring tends to collapse under UV irradiation, rearranging to azirine.<ref>{{cite journal | author1 = Cheng, K. |author2=Qi, J. |author3=Ren, X. |author4=Zhang, J. |author5=Li, H. |author6=Xiao, H. |author7=Wang, R. |author8=Liu, Z. |author9=Meng, L |author10=Ma, N. |author11=Sun, H.| title = Developing Isoxazole as a Native Photo-Cross-Linker for Photoaffinity Labeling and Chemoproteomics. | journal = Angew. Chem. Int. Ed. |volume=61 |issue= 47 | article-number = e202209947 | date = 2022| doi = 10.1002/anie.202209947 |pmid=36151600 |hdl=2031/8f64b6a6-b7a5-44e1-919c-e000ffe424f0 |hdl-access=free }}</ref> :350px|Azirine synthesis{{Clear|left}}

Substituted azirines can be produced via the Neber rearrangement.

== Reactions == Photolysis of azirines (under 300 nm) is a very efficient way to generate nitrile ylides. These nitrile ylides are dipolar compounds and can be trapped by a variety of dipolarophiles to yield heterocyclic compounds, e.g. pyrrolines.

The strained ring system also undergoes reactions that favor ring opening and can act as a nucleophile or an electrophile.

Azirines readily hydrolyse to give aminoketones which are themselves susceptible to self-condensation.

==See also== * Dysidazirine, one of only a few naturally occurring azirines

==References==

Category:Azirines