Tailoring flavins for visible light photocatalysis: organocatalytic [2+2] cycloadditions mediated by a flavin derivative and visible lightElectronic supplementary information (ESI) available: Experimental procedures, characterization data and copies of NMR and UV-VIS spectra. See DOI: 10.1039/c5cc01344e

A new application of flavin derivatives in visible light photocatalysis was found. 1-Butyl-7,8-dimethoxy-3-methylalloxazine, when irradiated by visible light, was shown to allow an efficient cyclobutane ring formation via an intramolecular [2+2] cycloaddition of both styrene dienes, considered as electron-rich substrates, and electron-poor bis(arylenones), presumably proceeding via an energy transfer mechanism. A new application of flavins in visible light photocatalysis: excited alloxazine allows fast cycloaddition of both electron-poor and electron-rich dienes.