Development of Novel Aryne Precursors: <i>o</i>-Triazenylarylboronic Acids

Arynes are important synthetic intermediates containing a formal triple bond in the aromatic ring. Although an aryne is conventionally generated under basic conditions from various precursors, unfortunately, limited methods exist for generating arynes under non-basic conditions. In this context, we have recently developed o-triazenylarylboronic acids as practical aryne precursors. These aryne precursors are obtained as stable solids storable in air at ambient temperature. On the other hand, they generate arynes under various non-basic conditions, including treatment with neutral silica gel, or 1,2-diol and p-nitrophenol, or sulfonic acid. These reaction conditions are applicable to a wide range of reactions of the precursors and arynophiles bearing various functional groups or pharmaceutical cores. In addition, we have developed a precursor of novel 3-triazenylaryne species for the efficient preparation of functionalized o-triazenylarylboronic acids. This 3-triazenylaryne precursor is regarded as a novel 1,2-benzdiyne equivalent that allows for iterative transformations involving arynes via o-triazenyl-arylboronic acids as key intermediates.