Facile Synthesis of 3‑Aryloxindoles via Brønsted Acid Catalyzed Friedel–Crafts Alkylation of Electron-Rich Arenes with 3‑Diazooxindoles

A simple metal-free method for the synthesis of 3-aryloxindoles via Brønsted acid catalyzed aromatic C–H functionalization of electron-rich arenes with 3-diazooxindoles is developed. In the presence of a catalytic amount of TfOH, a series of 3-aryloxindoles are synthesized as single regioisomers in good to excellent yields. This transformation is proposed to proceed through acid-catalyzed protonation of 3-diazooxindoles into diazonium ions followed by Friedel–Crafts-type alkylation of arenes.