A novel catalyst-free photochemical strategy for the direct synthesis of benzoxazin-4-ones intramolecular hydrogen atom transfer (HAT) between aldehyde and phthalimide groups is reported. The reaction proceeds under mild conditions (365 nm, DMSO, room temperature) and involves an unusual skeletal rearrangement of the phthalimide unit. A series of benzoxazin-4-one, benzothiazin-4-one and benzoxazepin-5-one derivatives were synthesized (24 examples, up to 88% yield), and their activity as AMPA receptor modulators was evaluated, identifying a halogenated derivative as a potent micromolar-range antagonist (IC = 14 µM).