Synthesis of 5-Iodo-1,4-disubstituted-1,2,3-triazoles Mediated by in Situ Generated Copper(I) Catalyst and Electrophilic Triiodide Ion

Mixing copper­(II) perchlorate and sodium iodide solutions
results in copper­(I) species and the electrophilic triiodide ions,
which collectively mediate the cycloaddition reaction of organic azide
and terminal alkyne to afford 5-iodo-1,4-disubstituted-1,2,3-triazoles.
One molar equivalent of an amine additive is required for achieving
a full conversion. Excessive addition of the amine compromises the
selectivity for 5-iodo-1,2,3-triazole by promoting the formation of
5-proto-1,2,3-triazole. Based on preliminary kinetic and structural
evidence, a mechanistic model is formulated in which a 5-iodo-1,2,3-triazole
is formed via iodination of a copper­(I) triazolide intermediate by
the electrophilic triiodide ions (and possibly triethyliodoammonium
ions). The experimental evidence explains the higher reactivity of
the in situ generated copper­(I) species and triiodide ion in the formation
of 5-iodo-1,2,3-triazoles than that of the pure forms of copper­(I)
iodide and iodine.