O2-promoted photocyclization of arylimines: A mild strategy of generating phenanthridines

Abstract

A visible light-induced cyclization of arylimines using trifluoromethanesulfonic acid (TfOH) as the catalyst is reported. The transformation, conducted under air and mild conditions utilizes O2 as the oxidant, eliminating the need for leaving groups or excess acid. Optimization studies reveal the pivotal role of TfOH and visible light in the reaction. The methodology allows a broad substrate scope, accommodating various electron-donating and electron-withdrawing groups. The reaction conditions enable gram-scale synthesis and show inhibitory effects on cancer cell lines and low toxicity towards normal cells. Mechanistic insights indicate a visible light-induced 6π-electrocyclization. This method provides a practical and efficient approach for the synthesis of phenanthridine derivatives.