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

Abstract

A simple, convenient, and efficient synthesis of 2-(1H-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.

GRAPHICAL ABSTRACT

Keywords:

• Indole
• quaternary carbon
• trimerization

Notes

^a Reaction conditions: indole (0.5 mmol), NaNO₂ (0.5 mmol), and solvent (0.6 mL) at rt for overnight.

^b Isolated yield.

^a Reaction conditions: indole (0.5 mmol), NaNO₂ (0.5 mmol), CH₃SO₃H (1.0 mmol), pyridine (0.6 mL), rt.

^b Isolated yield.