Visible Light-Promoted Synthesis of Spiroepoxy Chromanone Derivatives via a Tandem Oxidation/Radical Cyclization/Epoxidation Process

A highly efficient and straightforward approach for the synthesis of spiroepoxy chroman-4-one derivatives was developed using a visible light-enabled tandem radical strategy. The reaction is initiated by the formation of an acyl radical that undergoes intramolecular radical cyclization and epoxidation. The optimal result was obtained with 1 mol% of Ru(bpy)(3)Cl(2)6H(2)O, TBHP, and K2CO3 in i-PrOAc at room temperature with irradiation from a blue LED. This unprecedented tandem approach utilizes a broad range of substrates, and provides a convenient and powerful synthetic tool for accessing the synthetically useful spiroepoxy chroman-4-ones and their nitrogen-containing derivatives.