An efficient and applicable I₂-catalyzed intramolecular dehydrogenative C–O/C–N coupling reaction via activating the C–H bond adjacent to the N atom has been developed to provide dozens of substituted benzoxazinones (31 examples) and quinazolinones (5 examples) in good to excellent yields (up to 98%). This one-pot methodology has significant advantages, including a metal-free process, broad substrate scope, high atom economy, and simple operation. This strategy goes through an iminium intermediate followed by nucleophilic attack to provide the desired products.