Benzofurazan N-Oxides as Mild Reagents for the Generation of α-Imino Gold Carbenes: Synthesis of Functionalized 7-Nitroindoles.

An efficient gold-catalyzed [3 + 2] annulation of benzofurazan N-oxides with ynamides has been developed, which provides a concise and regioselective access to highly functionalized 7-nitroindoles. Although N-oxides are often considered as oxygen transfer reagents in gold catalysis, benzofurazan N-oxide was found to act as a facile precursor for an α-imino gold carbene intermediate. Benzofurazan can also react with ynamides to afford quinoxaline N-oxides via a [4 + 2] annulation process.