Visible-light-induced and copper-catalyzed oxidative cyclization of substituted o-aminophenylacetylene for the synthesis of quinoline and indole derivatives

Abstract

Herein, we report on the development of a mild and efficient intramolecular oxidative cyclization reaction of substituted aromatic enamines and the C(sp³)–H bond adjacent to nitrogen with alkynes or alkenes, leading to multi-substituted quinolines and indoles using dioxygen as a green oxidant. With visible light irradiation, a simple and cheap copper catalyst is able to functionalize the internal alkynes or alkenes via an intramolecular radical cyclization strategy without any extra photosensitizers. Preliminary mechanistic studies including radical capture reactions, isotope labeling experiments, and fluorescence quenching study are also conducted.