Azirines are three-membered

heterocyclic A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). Heterocyclic chemistry is the branch of organic chemistry dealing with the synthesis, properties, and ...

unsaturated (i.e. they contain a

double bond In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betw ...

) compounds containing a

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

atom and related to the saturated analogue

aziridine Aziridine is an organic compound consisting of the three-membered heterocycle . It is a colorless, toxic, volatile liquid that is of significant practical interest. Aziridine was discovered in 1888 by the chemist Siegmund Gabriel. Its derivati ...

. They are highly reactive yet have been reported in a few natural products such as

Dysidazirine Dysidazirine is a organic compound with formula C19H33NO2. It was discovered as a natural product in 1988 in the marine sponge '' Dysidea fragilis''. Chemically, it is a 2''H''-azirine derivative. Dysidazirine synthesis was reported for the ...

. There are two

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. Iso ...

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

tautomer Tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert. The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the relocation of a hydr ...

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

imine In organic chemistry, an imine ( or ) is a functional group or organic compound containing a carbon–nitrogen double bond (). The nitrogen atom can be attached to a hydrogen or an organic group (R). The carbon atom has two additional single bo ...

s and are isolable.

Preparation

2''H''-Azirine is most often obtained by the

thermolysis Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic as heat is req ...

of vinyl

azide In chemistry, azide is a linear, polyatomic anion with the formula and structure . It is the conjugate base of hydrazoic acid . Organic azides are organic compounds with the formula , containing the azide functional group. The dominant applic ...

s. During this reaction, a

nitrene In chemistry, a nitrene or imene () is the nitrogen analogue of a carbene. The nitrogen atom is uncharged and univalent, so it has only 6 electrons in its valence level—two covalent bonded and four non-bonded electrons. It is therefore consid ...

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

. 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. : Synth-Azirin

Reactions

Photolysis Photodissociation, photolysis, photodecomposition, or photofragmentation is a chemical reaction in which molecules of a chemical compound are broken down by photons. It is defined as the interaction of one or more photons with one target molecule. ...

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

nitrile ylide Nitrile ylides also known as ''nitrilium ylides'', or ''nitrilium methylides'' are generally reactive intermediates. With a few exceptions, they cannot be isolated. However, a structure has been determined on particularly stable nitrile ylideby X-r ...

s. These nitrile ylides are dipolar compounds and can be trapped by a variety of dipolarophiles to yield heterocyclic compounds, e.g.

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. 1-Pyrrolin ...

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

nucleophile In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are ...

or an

electrophile In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively charged, have an atom that carries ...

. An azirine is an intermediate in the

Neber rearrangement The Neber rearrangement is an organic reaction in which a ketoxime is converted into an alpha- aminoketone via a rearrangement reaction. : The oxime is first converted to an O-sulfonate, for example a tosylate by reaction with tosyl chloride. ...

References

{{Reflist Nitrogen heterocycles Imines Three-membered rings

Preparation

Reactions

See also

References