Interrupting the [Au]-Catalyzed Nitroalkyne Cycloisomerization: Trapping the Putative α-Oxo Gold Carbene with Benzo[]isoxazole.

The [Au]-catalyzed nitroalkyne cycloisomerization of 2-alkynylnitrobenzenes leading to anthranils has been interrupted by possible trapping of the postulated intermediate α-oxo gold carbene with an external nucleophile such as benzo[]isoxazole (anthranil). At the outset, this provides a simple synthesis of highly functionalized 3-acyl-(2-formylphenyl)-2-indazoles with the sequential C-O, C-N, and N-N bond formations. This provides indirect support for the existence of α-oxo gold carbenes in the [Au]-catalyzed internal redox processes of nitroalkynes.