Imine induced metal-free C-H arylation of indoles

We report a metal-free and mild protocol for the direct arylation of indole at the C2 position using an imine transient directing group. Aryltriazenes are used as the aryl source with controllable activity, releasing the aryl radical and amine in a sustained manner under the action of a promoter. The transient imine directing groups were generated in situ by condensation of indole-3-carbaldehydes and the released amine to facilitate the direct C2 arylation of indoles via aryl radical addition with the assistance of transient unsaturated imine. This strategy is characterized by the absence of additional auxiliary groups, simple operation, and metal-free and mild reaction conditions, and provides insight into the metal-free direct arylation of indoles induced by in situ generated transient directing groups. A simple, mild, and metal- and extra-auxiliary group-free method for the direct arylation of indole-3-carbaldehydes induced by an in situ generated transient directing group was developed.