Azirines are three-membered heterocyclic unsaturated (i.e. they contain a double bond) compounds containing a nitrogen atom and related to the saturated analogue aziridine.[1] They are highly reactive yet have been reported in a few natural products such as Dysidazirine. There are two isomers of azirine: 1H-Azirines with a carbon-carbon double bond are not stable and rearrange to the tautomeric 2H-azirine, a compound with a carbon-nitrogen double bond. 2H-Azirines can be considered strained imines and are isolable.
2H-Azirine is most often obtained by the thermolysis of vinyl azides.[2] 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.[3] Due to the weak N-O bond, the isoxazole ring tends to collapse under UV irradiation, rearranging to azirine. [4]
Substituted azirines can be produced via the Neber rearrangement.
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.