Photoinduced and <i>N</i>‑Bromosuccinimide-Mediated Cyclization of 2‑Azido‑<i>N</i>‑phenylacetamides

An efficient synthesis of quinoxalin-2(1H)-ones or spiro[cyclohexene-1,2′-imidazol]-4′-ones has been achieved in moderate to high yields by the visible light-induced and N-bromosuccinimide-mediated cyclization reaction of 2-azido-N-phenylacetamides at ambient temperature. Both the regioselectivity and the speed of cyclization are affected by the substituents attached to the phenyl ring. For example, quinoxalin-2-ones are produced as the main products when the substrates bear electron-withdrawing groups at the para-position of the phenyl ring; in contrast, spiro[cyclohexene-1,2′-imidazol]-4′-ones are obtained as the main products when the substrates bear electron-donating groups at the para-position.