1,1′-Diarylethylene\nas a Key Additive for the\nVisible Light Synthesis of Bioactive Dihydrobenzo[<i>a</i>]phenanthridine Compounds

This\nstudy introduces a straightforward synthetic approach for\ngenerating 7,8-dihydrobenzo[<i>a</i>]phenanthridine analogs\nthrough visible-light-induced cyclization, showing promise as antitumor\nagents. Unexpectedly, the incorporation of 1,1′-diarylethylene\nas an additive significantly boosts yield. Through mechanistic investigations,\nwe uncover its crucial role as a trap for the methyl radical formed\nafter the N–O bond cleavage of <i>O-</i>acetyl oxime,\npromoting intramolecular cyclization of a nitrogen-centered imine\nradical. These insights into the mechanism pave the way for transformative\nadvancements in this synthesis strategy.