Photocycloaddition and Photoaddition Reactions of Aromatic Compounds
Photocycloaddition and photoaddition can be utilized for new carbon-carbon and carbon-heteroatom bond formation under mild conditions from synthetic view points. In last three decades, a large number of these photoreactions between elec tron-donating and electron-accepting molecules have been appeared and dis cussed in the literature, reviews, and books [1-10]. In these photoreactions, a variety of reactive intermediates such as excimers, exciplexes, triplexes, radical ion pairs, and free-radical ions have been postulated and some of them have been detected as transient species to understand the reaction mechanism. Most of reac tive species in solution have been already characterized by laser flash photolysis techniques, but still the prediction for the photochemical process is hard to visu alize. In preparative organic photochemistry, the dilemma that the transient species including emission are hardly observed in the reaction system giving high chemical yields remains in most cases [1 1 ,1 2 ].