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

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.