Visible Light-Mediated Energy Transfer Enables Intramolecular Cyclization of O‑Acetyl Oximes to Phenanthridines

O‑Acetyl oximes undergo N–O bond cleavage/intramolecular cyclization for the synthesis of phenanthridines under visible-light-mediated energy transfer are described. In contrast to the well-established approaches, neither external oxidant/reductant nor additive is required for this reaction.