1,4-Diaryl-
and 1-aryl-4-alkyl-substituted 1,2,4-triazolium salts
are convenient air-stable precursors to carbenes used both as organocatalysts
or as ligands for transition metal complexes. Traditionally, they
are prepared via a multistep synthetic pathway with the low-yielding
formation of the triazolium ring occurring in the last step. We have
developed an alternative two-step synthesis involving the conversion
of a primary amine or aniline derivative to the corresponding 4-substituted
triazole followed by a copper-catalyzed arylation with diaryliodonium
salts. This transition metal-catalyzed arylation can be carried out
under mild conditions in acetonitrile and is tolerant toward both
water and oxygen. Additionally, the high functional group tolerance
of the protocol described here gives easy access to triazolium salts
containing heterocyclic substituents or sulfides.
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