A photoinduced intramolecular cyclization of allyl acrylates to synthesize fully substituted spiro-γ-butyrolactone compounds is described. The reaction is believed to proceed through activation of the carbonyl group upon ultraviolet irradiation, 1,4-hydrogen atom transfer, and intramolecular cyclization of diradical species, an intramolecular hydrogen abstraction strategy, based on a series of control and isotope studies as well as DFT calculations.