Azirine
Organic ring compounds with the formula C2H3N
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 1H-azirine, containing a carbon-carbon double bond, is not stable and rearranges to the tautomeric 2H-azirine, containing a carbon-nitrogen double bond, which is at least 30 kcal·mol−1 lower in energy. 2H-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.
01Preparation
2H-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. Azirine can be generated during photolysis of isoxazole. Due to the weak N-O bond, the isoxazole ring tends to collapse under UV irradiation, rearranging to azirine.
Substituted azirines can be produced via the Neber rearrangement.
02Reactions
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.
Sources and credits
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