Synthesis of Triazoles (III): Azidation of Dialkoxyacetylenes-Intramolecular [2+3] Cycloaddition

Significance

A tandem azidation/cyclization reaction to form fused triazoles is reported. ω,ω-Dialkoxyacetylenes are selectively converted into corresponding mono azides which undergo intramolecular [2+3] cycloaddition to afford triazoles in moderate to good yields. Indium(III) triflate was shown to be the most powerful Lewis acid to promote the selective azide/alkoxide exchange. Interestingly, in contrast to the aliphatic acetals, acetals derived from aromatic aldehydes gave gem-diazides as major products under the same reaction conditions, which, however, were not subjected to the cycloaddition conditions.