Visible Light-Induced Aerobic Epoxidation of alpha,beta-Unsaturated Ketones Mediated by Amidines

An aerobic photoepoxidation of alpha,beta-unsaturated ketones driven by visible light in the presence of tetramethylguanidine (3b), tetraphenylporphine (H2TPP), and molecular oxygen under mild conditions was revealed. The corresponding alpha,beta-epoxy ketones were obtained in yields of up to 94% in 96 h. The reaction time was shortened to 4.6 h by flow synthesis. The mechanism related to singlet oxygen was supported by experiments and density functional theory (DFT) calculations.