Expanding Access to Previously Inaccessible 5-Membered N-Heteroarynes

We previously reported the synthesis of an inaccessible 7-aza-2,3-indolyne through stabilizing interactions with nickel. This was achieved via intramolecular Suzuki coupling (i.e. oxidative addition and transmetallation) with ortho-borylaryl bromide derivatives of 7-azaindole. However, in the development of this work, the same conditions were not successful for other het-eroarynes. Herein, we sought to expand the strategy to additional inaccessible five-membered heteroarynes and gain insights into that factors that lead to successful aryne formation. Five new classes of heteroarynes derived from indole, pyrrolopyrim-idine, and the remaining isomers of azaindole were accessed. Transmetallation studies show that aryne formation depends on the electronics 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 transmetallation through the installation of an electron-donating substituent. To demonstrate the utility of heteroarynes as a newly accessible functional group, a one-pot difunctionalization was achieved across these classes of heterocycles using the newly accessible heteroaryne complexes.