136 Heterocycles with More than Two Heteroatoms: Higher Azoles (5-Membered) and Higher Azines (6-Membered)
Copper catalysis is often used, allowing a wider application under milder conditions.
4-Substituted 1,2,4-triazoles are accessible from the reaction between N,N'-diacylhydrazines and primary amines, but
this requires vigorous conditions so more reactive equivalents of the diacylhydrazines, such as N,N-dimethylformamide
azine, are usually preferred. 3-Substituted 1,2,4-triazoles result from the condensation of amidrazones (available from
reaction of hydrazine with a nitrile) with formic acid, esters or nitriles.
Tetrazoles are usually prepared by the reaction of azide anion, or an azide, with a nitrile or activated amide. Trimethylsilyl
azide is more convenient and safer; the silyl group is lost during the process.
Benzotriazole
Benzotriazole has signifi cant uses as an auxiliary for general organic synthesis. It has the properties of being an activat-
ing group for stabilisation of -carbocations and-carbanions and can also act as a leaving group.
The sequence below illustrates the stabilisation of a cation (Mannich reaction), the stabilisation of an anion to allow
lithiation and action as a leaving group for displacement with a Grignard nucleophile.