An oxidative desymmetrization of isoindolines was realized by TBN initiated radical sp3 C–H activation relay (CHAR), providing a series of ω-hydroxylactams in high yields. This reaction exhibits broad substrate scope and functional group tolerance, and even N-alkyl isoindolines can be well tolerated. The mechanistic study shows that the C–H bond oxidation, dioxygen trapping and intramolecular 1,5-H