Expanding Access to Previously Inaccessible 5-Membered N-Heteroarynes

We previously reported the synthesis of an inaccessible 7-aza-2,3-indolyne through the stabilization of interactions with nickel. This was achieved via intramolecular Suzuki coupling (i.e., oxidative addition and transmetalation) with ortho-borylaryl bromide derivatives of 7-azaindole. Many questions remained about the electronic structure of this complex, which herein we sought to answer through XPS studies. We also sought to expand the strategy to additional inaccessible five-membered heteroarynes and gain insights into factors that lead to successful aryne formation. Several new classes of heteroarynes derived from indole, pyrrolopyrimidine, and the remaining isomers of azaindole were accessed. Transmetalation studies show that aryne formation depends on the identity of the heteroarene. A borate complex of 4-azaindole was isolated and characterized via NMR spectroscopy and crystallographically. This complex could be promoted to undergo transmetalation through the installation of an electron-donating substituent, which was justified computationally. To demonstrate the utility of heteroarynes as a newly accessible functional group, a one-pot difunctionalization was achieved across these classes of heterocycles using newly accessible heteroaryne complexes.