Intramolecular benzylic C−O bond formation was developed using 2,4,6-triphenylpyrylium tetrafluoroborate (TPT), which allows construction of cyclic ethers and lactones. The reaction is supposed to proceed through the single-electron oxidation of the phenyl group, followed by the formation of a benzylic radical, thus preventing a competing 1,5-hydrogen abstraction pathway. Detailed mechanistic studies suggest that molecular oxygen is used to trap the radical intermediate to form benzyl alcohol, which undergoes cyclization. This new approach serves as a powerful platform by providing efficient access to valuable 5- and 6-membered cyclic ethers and lactones with a unified protocol.
Im, H.; Kang, D.; Choi S.; Shin S.; Hong, S.* Org. Lett. 2018, 20, 7437.