Azirine  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. They are highly reactive yet have been reported in a few natural products such as Dysidazirine. There are two isomers of azirine: 1"H"-azirine with a carbon-carbon double bond are not stable and rearrange to the tautomeric 2"H"-azirine, a compound with a carbon-nitrogen double bond. 2"H"-Azirines can be considered strained imines and are isolable.  2"H"-Azirine is most often obtained by the thermolysis of vinyl azides. During this reaction, a nitrene is formed as an intermediate. Alternatively, they can be obtained by oxidation of the corresponding aziridine. 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. An azirine is an intermediate in the Neber rearrangement.