Direct C2-Functionalization of Indoles Triggered by the Generation of Iminium Species from Indole and Sulfonium Salt.

An indole core bearing a functional group on the C2 position is often found as a key structure in biologically active natural products and pharmaceuticals. Here, we report direct C2-functionalization of indoles triggered by the formation of an iminium species generated from indole and a sulfonium reagent. The reaction proceeded under very mild conditions to give the corresponding C2-substituted indole derivatives in good to high yields.