Metal-Free–Catalyzed Oxidative Trimerization of Indoles Using NaNO₂ to Construct Quaternary Carbon Centers: Synthesis of 2-(1<i>H</i>-Indol-3-yl)-2,3′-biindolin-3-ones

<div><p></p><p>A simple, convenient, and efficient synthesis of 2-(1<i>H</i>-indol-3-yl)-2,3′-biindolin-3-one derivatives via a transition-metal-free-catalyzed oxidative trimeric reaction of indoles has been developed. This transformation may have occurred through a tandem oxidative homocoupling reaction by using NaNO₂ in pyridine as oxidant. This methodology provides an alternative approach for the direct generation of all-carbon quaternary centers at the C2 position of indoles.</p> </div