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. ^[1] They are highly reactive yet have 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.

Preparation

2H-Azirines are 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.

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.

An azirine is an intermediate in the Neber rearrangement.

References

1. Teresa M. V. D. Pinho e Melo and Antonio M. d’A. Rocha Gonsalves (2004). "Exploiting 2-Halo-2H-Azirine Chemistry". Current Organic Synthesis 1 (3): 275–292. doi:10.2174/1570179043366729.
2. F. Palacios, A. M. Ochoa de Retana, E. Martinez de Marigorta, J. M. de los Santos (2001). "2H-Azirines as synthetic tools in organic chemistry". Eur. J. Org. Chem 2001 (13): 2401–2414. doi:10.1002/1099-0690(200107)2001:13<2401::AID-EJOC2401>3.0.CO;2-U.