Visible light-induced Mallory reaction of tertiary benzanilides via iminium intermediates†

The Mallory reaction, which involves the photocyclization of stilbenes/diarylethenes and their analogues into polycyclic aromatics, is of significant synthetic importance. However, its application to tertiary benzanilides has not been explored to date. Besides, most of the reported Mallory reactions require ultraviolet irradiation. In this study, we show the first Mallory reaction of tertiary benzanilides promoted by visible light via iminium intermediates formed in situ from tertiary benzanilide, Tf₂O (triflic anhydride) and pyridine. UV/vis absorption spectroscopy combined with density functional theory (DFT) calculations revealed that the formation of the iminium intermediate decreased the HOMO–LUMO energy gap, thereby enhancing visible light absorption. This study provides a rapid and practical approach for the preparation of the phenanthridinone skeleton and provides a new idea for the design of new visible light photoswitches.