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.