Photochemical Desaturation and Epoxidation with Oxygen by Sequential Flavin Catalysis

Abstract

AbstractCatalytic desaturations are important strategies for the functionalization of organic molecules. In nature, flavoenzymes mediate the formation of α,β‐unsaturated carbonyl compounds by concomitant cofactor reduction. Contrary to many laboratory methods for these reactions, such as the Saegusa‐Ito oxidation, no transition metal reagents or catalysts are required. However, a molecular flavin‐mediated variant has not been reported so far. We disclose a photochemical approach for silyl enol ether oxidation, which leads to α,β‐unsaturated ketones (13 examples) in very good yields. The flavin catalysts are stable throughout the desaturation reaction, and we successfully applied them in a subsequent aerobic epoxidation by simply changing the reaction conditions. This protocol allowed us to directly convert silyl enol ethers into α,β‐epoxyketones in a one‐pot fashion (12 examples). Sequential flavin catalysis is not limited to one specific reactivity combination and can, inter alia, couple the photochemical oxidation with radical additions. We anticipate that flavin‐catalyzed desaturation will be applicable to other substrate classes and that its sequential catalytic activity will enable rapid substrate diversification.