Radical Carbonylation Mediated by Continuous-Flow Visible-Light Photocatalysis: Access to 2,3-Dihydrobenzofurans.

The annulative carbonylation of alkenyl-tethered arenediazonium salts using visible-light photocatalysis in continuous flow is described. The method furnishes a diverse series of novel acetate-functionalized 2,3-dihydrobenzofurans at room temperature and moderate CO pressure (25 atm), delivering these products in a short time with straightforward scale-up. This continuous flow and free-radical approach overcomes the limitation of traditional Pd-catalyzed annulative carbonylation, giving valuable 2,3-dihydrobenzofurans in a predictable and regioselective manner.