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

Org Lett. 2021 Apr 2;23(7):2632-2637. doi: 10.1021/acs.orglett.1c00539. Epub 2021 Mar 19.

Abstract

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[c]isoxazole (anthranil). At the outset, this provides a simple synthesis of highly functionalized 3-acyl-(2-formylphenyl)-2H-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.