Chemoselective Oxygen-Centered Radical Cyclizations onto Silyl Enol Ethers

A new oxygen-centered radical cyclization onto silyl enol ethers has been developed and utilized for the synthesis of versatile siloxy-substituted tetrahydrofurans. The reactions display excellent chemoselectivity for cyclization onto the electron-rich silyl enol ether when competing terminal alkene cyclization, 1,5-hydrogen abstraction, and β-fragmentation pathways are present. The increased chemoselectivity also allows for the synthesis of tetrahydropyrans, a challenging substrate class to access using oxygen-centered radical alkene cyclizations due to competing 1,5-hydrogen abstractions.