Photoinduced Copper-Catalyzed Carbocyclization of 1,7-Enynes with Sulfonium Salts via Radical Relay Strategy

A visible-light-induced copper-catalyzed sulfonium salts ring-opening radical-triggered tandem cyclization of 1,7-enynes for the synthesis of three types of highly valuable (distal thioethers-containing) heteropolycyclic compounds is described. Preliminary mechanistic studies suggest that the construction of three C-C bonds and a tetracycle in one pot is based on 6-<i>exo-dig</i> cyclization/1,5-hydrogen-atom transfer/5-<i>endo-trig</i> cyclization radical relay processes under mild conditions. The reaction selectivity shifted to the 6-<i>exo</i>-<i>dig</i> cyclization (rather than 1,5-hydrogen-atom transfer) in the presence of a benzyl group at the 2-position of the acrylamide moiety, enabling the successful synthesis of a diverse range of benzo[<i>j</i>]phenanthridin-6(5<i>H</i>)-one derivatives. Meanwhile, this approach provides a new route to complex cyclopenta[<i>c</i>]quinolin-4-ones derivatives.