Visible-Light-Promoted Selenylative Radical Cyclization of 2‑Vinyl‑N‑Aryl Imines to 3H‑Indoles via Oxygen Photosensitization

A visible-light-promoted tandem selenylative radical cyclization of 2-vinyl-N-aryl imines to 3H-indoles was developed involving a series of selenyl radical addition, 5-endo-trig cyclization, and redox steps. The roles of triplet oxygen (3O2) and rhodamine-sensitized singlet oxygen (1O2) under visible light were investigated, revealing that the competing selenol-mediated hydrogen atom transfer process was effectively suppressed. The pivotal role of 1O2 in this tandem selenylative radical cyclization provides valuable insight into photocatalyst-controlled aerobic radical processes under visible light.