Copper-catalyzed oxidative trimerization of indoles by using TEMPO to construct quaternary carbon centers: the synthesis of 2-(1H-indol-3-yl)-2,3′-biindolin-3-ones

A simple, convenient, and efficient synthesis of 2-(1H-indol-3-yl)-2,3'-biindolin-3-one derivatives has been developed by the oxidative trimeric reaction of indoles using the TEMPO/CuCl2 catalyst system under ambient air. This methodology provides an alternative approach for the direct generation of all-carbon quaternary centers at the C-2 position of indoles.