Metal-free Catalyzed Oxidative Trimerization of Indoles by Using TEMPO in Air: An Entry into 3-(1H-indol-3-yl)-3,3'-biindolin-2-ones

A simple, convenient and highly efficient aerobic oxidative trimerization of indoles has been developed using TEMPO in air, and the corresponding 3-(1H-indol-3-yl)-3,3'-biindolin-2- one derivatives were obtained in moderate to excellent yields. This methodology provides an alternative approach for the direct generation of all-carbon quaternary centers at the C3 position of indoles.