This paper reports a room temperature visible-light-driven protocol for the intermolecular [2+2] cycloadditions between coumarin-3-carboxylates and acrylamides analogs by an energy-transfer process. Using an iridium complex FIrPic as a photosensitizer and a 3？W blue LED as a light source, an array of cyclobutabenzocypyranones were prepared in moderate to excellent yields. 

Chemistry - A European Journal,2015

Visible-light-driven protocol for [2+2] cycloaddition of coumarins with acrylamides and compounds containing partially hydrogenated dibenzofuran.