Triazole

Source: Wikipedia, the free encyclopedia.
Not to be confused with Thiazole.

A triazole is a

molecular formula C2H3N3. Triazoles exhibit substantial isomerism
, depending on the positioning of the nitrogen atoms within the ring.

Many triazoles are versatile, biologically active compounds commonly used as fungicides and plant retardants. However, triazoles are also useful in

haptic ligands
.

Isomerism

There are four triazole isomers, which are conventionally divided into two pairs of tautomers. In the 1,2,3-triazoles, the three nitrogen atoms are adjacent; in the 1,2,4-triazoles, an interstitial carbon separates out one nitrogen atom. Each category has two tautomers that differ by which nitrogen has a hydrogen bonded to it.

-HN-N=N-CH=CH- interconverts with =N-HN-N=CH-CH= (1,2,3-triazole) and -HN-N=CH-N=CH- interconverts with =N-N=CH-NH-CH= (1,2,4-triazole)

Preparation

There are several methods to prepare triazoles.

1,2,3-Triazoles

Main article: 1,2,3-Triazole

1,2,3-Triazoles, also known as vicinal triazoles, are usually prepared following (3+2)

Huisgen azide-alkyne 1,3-dipolar cycloaddition: a azide and an alkyne react at high temperature to form a ring. However, the Huisgen strategy produces a mixture of isomers (typically 1,4- and 1,5-disubstituted) when used to produce substituted triazoles.

Thermal addition gives a mixture of 1,4 and 1,5 isomers
Thermal addition gives a mixture of 1,4 and 1,5 isomers

In order to selectively prepare a desired isomer, metal catalysts are employed. In the copper-catalysed azide-alkyne cycloaddition (CuAAC), copper(I) salts select for the formation of 1,4-disubstituted 1,2,3-triazoles. One such catalyst is CuBr(PPh3)3, which is relatively stable towards oxidation even at elevated temperatures and can produce triazoles with a broad range of substituents either in solvent[1][2] or under neat[3] reaction conditions.

1,4 isomer from a CuI catalyst
1,4 isomer from a CuI catalyst

Conversely, ruthenium catalysts (RuAAC) select for 1,5-disubstituted 1,2,3-triazoles.[4][5]

1,5 isomer from a Ru catalyst
1,5 isomer from a Ru catalyst

1,2,4-Triazoles

Main article: 1,2,4-Triazole

Most techniques for producing 1,2,4-triazoles use the free energy of water, either by dehydrating a mixture of

Einhorn-Brunner reaction). Of those two, only the Einhorn-Brunner reaction is regioselective.[6] Recent research has focused on grinding and microwave irradiation as greener substitutes.[7]

Applications

Triazoles are compounds with a vast spectrum of applications, varying from materials (polymers), agricultural chemicals, pharmaceuticals, photoactive chemicals and dyes.[8][9]

Benzotriazole is used in chemical photography as a restrainer and fog suppressant.

Cyclohexylethyltriazol was briefly used as an alternative to Cardiazol (Metrazol) in convulsive shock therapy treatment of mental illnesses during the 1940s.

Importance in agriculture

Many triazoles have antifungal effects: the triazole

plant-protection fungicides include epoxiconazole, triadimenol [de], myclobutanil, propiconazole, prothioconazole, metconazole, cyproconazole, tebuconazole, flusilazole and paclobutrazol
.

Due to spreading resistance of plant pathogens towards fungicides of the strobilurin class,

Septoria tritici or Gibberella zeae[11] relies heavily on triazoles. Food, like store bought potatoes, contain retardants such as triazole or tetcyclacis.[12][13]

In addition,

plant growth retardants.[14] Brassinazole inhibits brassinosteroid
biosynthesis.

Importance in chemical synthesis

The

azide alkyne Huisgen cycloaddition[5] is a mild and selective reaction that gives 1,2,3-triazoles as products. The reaction has been widely used in bioorthogonal chemistry and in organic synthesis. Triazoles are relatively stable functional groups and triazole linkages can be used in a variety of applications, e.g. replacing the phosphate backbone of DNA.[15]

Related heterocycles

  • Imidazole, an analog with two nonadjacent nitrogen atoms
  • Pyrazole, an analog with two adjacent nitrogen atoms
  • Tetrazole, an analog with four nitrogen atoms
  • Triazolium salts, substituted analogues that can be used as NHC precursors

External links

References

  1. PMID 31553192
    .
  2. ^ Virant, Miha (2019). Development of homogeneous palladium catalytic systems for selected transformations of terminal acetylenes (PhD). University of Ljubljana.
  3. doi:10.1002/ejoc.201403100
    .
  4. S2CID 199490788
    .
  5. ^
    doi:10.1002/anie.196305651
    .
  6. ^ Temple, Carroll (2009). 1,2,4-Triazoles. Chemistry of Heterocyclic Compounds. Vol. 39. Wiley-Blackwell.
  7. ISBN 978-0-12-817113-4
    .
  8. doi:10.1021/cr60210a001
    .
  9. PMID 21954075
    .
  10. PMID 12233175
    .
  11. doi:10.1016/j.cropro.2006.06.006
    .
  12. doi:10.4067/S0718-16202009000200013
    .
  13. doi:10.1002/ps.2780210402
    .
  14. ^ Latimer, Joyce G. (2022). "Growth Regulators for Containerized Herbaceous Perennial Plants" (PDF). GrowerTalks. Ball Publishing. pp. 14–60. Retrieved 2022-04-06.
  15. PMID 18656947
    .
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