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

The Mallory reaction is of significant synthetic importance, involving the photocyclization of stilbenes/diarylethenes and their analogues into polycyclic aromatics. However, the application of the Mallory reaction 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 intermiate decreased the HOMO-LUMO energy gap, thereby enhancing visible light absorption. This study provides a rapid and practical approach for preparation of phenanthridinone skeleton and also provides a new idea for design new visible light photoswitches.