Visible-Light Induced Oxidative Annulation of Enamides to 2,4,5-Trisubstituted Oxazole Skeletons

A novel approach to various trisubstituted oxazoles (28 examples, up to 88% yield) has been developed via 9H-thioxanthen-9-one (TX) mediated oxidative annulation of N-acetyl enamide under visible light irradiation in the presence of BF3 center dot Et2O (2.0 equiv) and 40 mol% of PhNO2. This metal-free procedure features high atom and step economy, green and mild conditions and broad substrate scope.