title: Photoreactions of 4-(Tribromomethyl)-4-methyl-2,5-cyclohexadienone and Its Derivatives with Amines: Radical Cyclization and Ring Expansion Reactions Promoted through Photoinduced Electron Transfer Processes.
abstract: Photoreactions of 4-(tribromomethyl)-4-methyl-2,5-cyclohexadienone (1) and its derivatives with amines were studied. Irradiation of 1 with amine produced 4-bromo-5-methyltropone (2) along with 4-(dibromomethyl)-4-methyl-2,5-cyclohexadienone (3). The effects of solvent, added water, and the structural variation in amine on the product ratio were explored. Isolation of the amine-derived products revealed that oxidative dealkylation of amine proceeded during the photoreaction. On the basis of the results obtained, a reaction mechanism involving fragmentation of the dienone anion-radical and amine cation-radical pair is proposed. Photoreactions of dienone 4 with amine produced the tropones 6 and 7, whereas tropone 9 was produced from 8. Trialkyltin radical-induced reductions of dienones 1 and 4 with tri-n-butyltin hydride demonstrated common features with the photoreactions. It was also found that irradiation of dienone 3 with amine produced 4-methyltropone (10).
authors.affiliation: Department of Chemistry, Faculty of Science, and Graduate School of Science and Technology, Niigata University, Ikarashi, Niigata 950-2181, Japan.
authors.forename: Eietsu
authors.initials: E
authors.lastname: Hasegawa
authors.forename: Yukinobu
authors.initials: Y
authors.lastname: Tamura
authors.forename: Kimiko
authors.initials: K
authors.lastname: Suzuki
authors.forename: Akira
authors.initials: A
authors.lastname: Yoneoka
authors.forename: Toshio
authors.initials: T
authors.lastname: Suzuki