A metal-free method for the construction of 3,3-dimethyl isoindolinones via radical-mediated intramolecular coupling of two C-H bonds of N,N-diisopropyl benzamides was developed. The reactions can proceed in moderate to high yield and with excellent chemoselectivity. A reaction sequence of the formation of an alkyl radical via oxidative cleavage of alkyl C-H bond and the formation of lactam ring via intramolecular homolytic aromatic substitution was proposed.