title: Substituent effect on reactivity of triplet excited state of 2,3-diazabicyclo[2.2.1]hept-2-enes, DBH derivatives: α C-N bond cleavage versus β C-C bond cleavage.
abstract: The photoreaction of a series of 2,3-diazabicyclo[2.2.1]hept-2-ene (DBH) derivatives, in which various substituents (X) were introduced at the methano bridge carbon of C(7), was investigated under direct (>290 nm) and triplet-sensitized (Ph2CO, >370 nm) irradiation conditions of the azo chromophore (−Cβ–Cα–N═N–Cα–Cβ−). The azo compounds offered a unique opportunity to see the substituent X effect at the remote position of the azo chromophore on the reactivity of the triplet excited state of bicyclic azoalkanes. The present study led to the first observation of the unusual Cα–Cβ bond-cleavage reaction without the ring stiffness, that is, the structural rigidity, in the triplet state of the cyclic azoalkanes. The stereoelectronic effects were found to play an important role in lowering the activation energy of the Cα–Cβ bond-cleavage reaction. NBO analyses at the M06-2X/cc-PVDZ level of theory confirmed the stereoelectronic effect.
authors.affiliation: Department of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan. mabe@hiroshima-u.ac.jp
authors.forename: Manabu
authors.initials: M
authors.lastname: Abe
authors.forename: Shinji
authors.initials: S
authors.lastname: Watanabe
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Tamura
authors.forename: Srikanth
authors.initials: S
authors.lastname: Boinapally
authors.forename: Kousei
authors.initials: K
authors.lastname: Kanahara
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Fujiwara