N-Phenyl phthalimide and 3, 4-Dihydroisocoumarins were obtained by irradiation of N- phenyl phthalonimide in the presence of tertiary amines. The δ-lactone structure was demonstrated via an alternative synthesis that gave the isomeric γ-lactone as well. The key steps of the photoreaction, and the role of the amine, oxygen and several potential intermediates are discussed.
[Seijas, Julio A.; Vazquez-Tato, M. Pilar; Martinez, M. Montserrat; Nunez-Corredoira, Gonzalo Journal of Chemical Research - Part S, 1999 , # 7 p. 420 - 421]