Electrosynthesis of Dihydropyrano[4,3-b]indoles Based on a Double Oxidative [3+3] Cycloaddition

Abstract

Oxidative [3+3] cycloadditions offer an efficient route for six-membered-ring formation. This approach has been realized based on an electrochemical oxidative coupling of indoles/enamines with active methylene compounds followed by tandem 6π-electrocyclization leading to the synthesis of dihydropyrano[4,3-b]indoles and 2,3-dihydrofurans. The radical-radical cross-coupling of the radical species generated by anodic oxidation combined with the cathodic generation of the base from O₂ allows for mild reaction conditions for the synthesis of structurally complex heterocycles.

Keywords: [3+3] cycloaddition; electrochemistry; hydrogen atom transfer; indoles; radical chemistry.