This
study introduces a straightforward synthetic approach for
generating 7,8-dihydrobenzo[a]phenanthridine analogs
through visible-light-induced cyclization, showing promise as antitumor
agents. Unexpectedly, the incorporation of 1,1′-diarylethylene
as an additive significantly boosts yield. Through mechanistic investigations,
we uncover its crucial role as a trap for the methyl radical formed
after the N–O bond cleavage of O-acetyl oxime,
promoting intramolecular cyclization of a nitrogen-centered imine
radical. These insights into the mechanism pave the way for transformative
advancements in this synthesis strategy.