Azirines are three membered heterocyclic unsaturated (i.e. they contain a double bond

Double bond

A double bond in chemistry is a chemical bond between two chemical elements involving four bonding electrons instead of the usual two. The most common double bond, that between two carbon atoms, can be found in alkenes. Many types of double bonds between two different elements exist, for example in...

) compounds containing a nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

 atom and related to the saturated analogue aziridine

Aziridine

Aziridines are organic compounds containing the aziridine functional group, a three-membered heterocycle with one amine group and two methylene groups...

. They are highly reactive yet are found in a number of natural products

Biomolecule

A biomolecule is any molecule that is produced by a living organism, including large polymeric molecules such as proteins, polysaccharides, lipids, and nucleic acids as well as small molecules such as primary metabolites, secondary metabolites, and natural products...

 such as the antibiotic

Antibiotic

An antibacterial is a compound or substance that kills or slows down the growth of bacteria.The term is often used synonymously with the term antibiotic; today, however, with increased knowledge of the causative agents of various infectious diseases, antibiotic has come to denote a broader range of...

 azirinomycin, isolated from Streptomyces auras. There are two isomer

Isomer

In chemistry, isomers are compounds with the same molecular formula but different structural formulas. Isomers do not necessarily share similar properties, unless they also have the same functional groups. There are many different classes of isomers, like stereoisomers, enantiomers, geometrical...

s of azirine: 1H-azirines with a carbon-carbon double bond are not stable and rearrange to the tautomer

Tautomer

Tautomers are isomers of organic compounds that readily interconvert by a chemical reaction called tautomerization. This reaction commonly results in the formal migration of a hydrogen atom or proton, accompanied by a switch of a single bond and adjacent double bond...

ic 2H-azirine, a compound with a carbon-nitrogen double bond. 2H-Azirines can be considered strained imine

Imine

An imine is a functional group or chemical compound containing a carbon–nitrogen double bond, with the nitrogen attached to a hydrogen atom or an organic group. If this group is not a hydrogen atom, then the compound is known as a Schiff base...

s and are isolable.

Preparation

2H-Azirines are most often obtained by the thermolysis of vinyl azide

Azide

Azide is the anion with the formula N3−. It is the conjugate base of hydrazoic acid. N3− is a linear anion that is isoelectronic with CO2 and N2O. Per valence bond theory, azide can be described by several resonance structures, an important one being N−=N+=N−...

s. During this reaction, a nitrene

Nitrene

In chemistry, a nitrene is the nitrogen analogue of a carbene. The nitrogen atom has only 6 valence electrons and is therefore considered an electrophile...

 is formed as an intermediate. Alternatively, they can be obtained by oxidation of the corresponding aziridine

Aziridine

Aziridines are organic compounds containing the aziridine functional group, a three-membered heterocycle with one amine group and two methylene groups...

.

Reactions

Photolysis of azirines (under 300 nm) is a very efficient way to generate nitrile ylide

Nitrile ylide

Nitrile ylides also known as nitrilium ylides, or nitrilium methylides are generally reactive intermediates. Usually, they cannot be isolated. However, a structure has been determined on a by X-ray crystallography. As ylides, they possess a negative charge and a positive charge on adjacent atoms....

s. These nitrile ylides are dipolar compounds

1,3-dipole

In organic chemistry, a 1,3-dipolar compound or 1,3-dipole is a dipolar compound with delocalized electrons and a separation of charge over three atoms...

 and can be trapped by a variety of dipolarophiles to yield heterocyclic compounds, e.g. pyrroline

Pyrroline

Pyrrolines, also known under the name dihydropyrroles, are three different heterocyclic organic chemical compounds that differ in the position of the double bond. Pyrrolines are formally derived from the aromate pyrrole by hydrogenation...

s.

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

Nucleophile

A nucleophile is a species that donates an electron-pair to an electrophile to form a chemical bond in a reaction. All molecules or ions with a free pair of electrons can act as nucleophiles. Because nucleophiles donate electrons, they are by definition Lewis bases.Nucleophilic describes the...

 or an electrophile

Electrophile

In general electrophiles are positively charged species that are attracted to an electron rich centre. In chemistry, an electrophile is a reagent attracted to electrons that participates in a chemical reaction by accepting an electron pair in order to bond to a nucleophile...

.

An azirine is an intermediate in the Neber rearrangement

Neber rearrangement

The Neber rearrangement is an organic reaction in which an oxime is converted into an alpha-aminoketone in a rearrangement reaction.The oxime is first converted to a ketoxime tosylate by reaction with tosyl chloride...

.