Epoxidation of Electron-Deficient Alkenes Triggered by Visible-Light-Driven Phenol Photooxidation for the Synthesis of Epoxy Dienone Products

This article describes a synthesis of epoxy dienone products starting from para-substituted phenols bearing an electron-deficient alkene at the meta position. This one-pot photooxygenation/epoxidation transformation takes place at room temperature using catalytic amounts of Rose Bengal and cesium carbonate upon green light irradiation. This reaction provides access to a range of functionalized epoxy dienone products with diastereoisomeric ratios ranging from 4:1 to > 12:1. DFT calculations and mechanistic experiments revealed that this reaction would proceed through singlet oxygen-mediated photooxidation of phenols followed by an intramolecular oxygen atom transfer on the alkene side arm.