Triazole

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. ==Preparation==

There are several methods to prepare triazoles. 1,2,3-Triazoles 1,2,3-Triazoles, also known as vicinal triazoles, are usually prepared following (3+2) cycloaddition protocols. A common technique for unsubstituted triazoles is the 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. 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 or under neat reaction conditions. Conversely, ruthenium catalysts (RuAAC) select for 1,5-disubstituted 1,2,3-triazoles. 1,2,4-Triazoles Most techniques for producing 1,2,4-triazoles use the free energy of water, either by dehydrating a mixture of amides and hydrazides (the Pellizzari reaction) or imides and alkyl hydrazines (the Einhorn-Brunner reaction). Of those two, only the Einhorn-Brunner reaction is regioselective. Recent research has focused on grinding and microwave irradiation as greener substitutes. ==Applications==

Triazoles are compounds with a vast spectrum of applications, varying from materials (polymers), agricultural chemicals, pharmaceuticals, photoactive chemicals and dyes. Benzotriazole is used in various industrial processes. Cyclohexylethyltriazol (4-cyclohexyl-5-ethyl-2H-triazole) was briefly used as an alternative to Cardiazol (Metrazol) in the treatment of mental illnesses during the 1940s. Antifungals Many triazoles have antifungal effects: the triazole antifungal drugs include fluconazole, isavuconazole, itraconazole, voriconazole, pramiconazole, ravuconazole, and posaconazole and triazole plant-protection fungicides include epoxiconazole, , myclobutanil, propiconazole, prothioconazole, metconazole, cyproconazole, tebuconazole, flusilazole and paclobutrazol. Due to spreading resistance of plant pathogens towards fungicides of the strobilurin class, control of fungi such as Septoria tritici or Gibberella zeae relies heavily on triazoles. Food, like store bought potatoes, contain retardants such as triazole or tetcyclacis. In addition, paclobutrazol, uniconazole, , and triadimefon are used as plant growth retardants. Brassinazole inhibits brassinosteroid biosynthesis. Importance in chemical synthesis The azide alkyne Huisgen cycloaddition ==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==