Periselective, Lewis acid-induced intramolecular Diels–Alder reaction of conjugated carbodiimides: efficient synthesis of nitrogen heterocycles, indolo[2,3-b]quinolines and pyrido[2,3-b]indole

A suitable Lewis acid has been found that accelerates the intramolecular Diels–Alder reaction of conjugated carbodiimides with high periselectivity control, thus providing an efficient and straightforward procedure for constructing indolo[2,3-b]quinoline and pyrido[2,3-b]indole frameworks.