Photochemistry of cyclic vicinal tricarbonyl compounds. Photochemical reaction of 1,2,3-Indanetrione with 2,3-dimethyl-2-butene: hydrogen abstraction and photocycloaddition

UV irradiation of 1,2,3-indanetrione, in CH2Cl2, in the presence of 2,3-dimethyl-2-butene yields a complex mixture of products arising from hydrogen abstraction, [2pi+2pi] photocycloaddition (Paternò-Büchi reaction), and [4pi +2pi] photocycloaddition. The reaction is dependent on electronic and steric effects, with the later accounting for the high chemical yield observed for the formation of the dioxene-type product