title: Generation and characterization of highly strained dibenzotetrakisdehydro[12]- and dibenzopentakisdehydro[14]annulenes.
abstract: To generate dibenzotetrakisdehydro[12]- and dibenzopentakisdehydro[14]annulenes ([12]- and [14]DBAs) having a highly deformed triyne moiety, [4.3.2]propellatriene-anneleted dehydro[12]- and dehydro[14]annulenes were prepared as their precursors. UV irradiation of the precursors resulted in the photochemical [2 + 2] cycloreversion to generate the strained [12]- and [14]DBAs, respectively. The [12]DBA was not detected by 1H NMR spectroscopy, but it was intercepted as Diels-Alder adducts in solution, suggesting its intermediacy. Its spectroscopic characterization was successfully carried out by UV-vis spectroscopy in a 2-methyltetrahydrofuran (MTHF) glass matrix at 77 K and by FT-IR spectroscopy in an argon matrix at 20 K. On the other hand, the [14]DBA was stable enough for observation by 1H and 13C NMR spectra in solution, though it was not isolated because of the low efficiency of the cycloreversion. The [14]DBA was also characterized by interception as Diels-Alder adducts in solution and by UV-vis spectroscopy in a MTHF glass matrix at 77 K. The kinetic stabilities of the DBAs are compared with the related dehydrobenzoannulenes with respect to the topology of the pi-systems. In addition, the tropicity of the [14]DBA is discussed based on its experimental and theoretical 1H NMR chemical shifts.
authors.affiliation: Division of Frontier Materials Science, Graduate School of Engineering Science, Osaka University, and CREST, Japan Science and Technology Agency (JST), Toyonaka, Osaka 560-8531, Japan.
authors.forename: Ichiro
authors.initials: I
authors.lastname: Hisaki
authors.forename: Takeshi
authors.initials: T
authors.lastname: Eda
authors.forename: Motohiro
authors.initials: M
authors.lastname: Sonoda
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Niino
authors.forename: Tadatake
authors.initials: T
authors.lastname: Sato
authors.forename: Tomonari
authors.initials: T
authors.lastname: Wakabayashi
authors.forename: Yoshito
authors.initials: Y
authors.lastname: Tobe
mesh_terms: D003080:Cold Temperature; D006571:Heterocyclic Compounds / Q000138:chemical synthesis / Q000737:chemistry; D007700:Kinetics; D047028:Macrocyclic Compounds / Q000138:chemical synthesis / Q000737:chemistry; D008956:Models, Chemical; D015394:Molecular Structure; D010782:Photolysis; D011084:Polycyclic Aromatic Hydrocarbons / Q000138:chemical synthesis / Q000737:chemistry; D012997:Solvents; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods
chemical_list: D006571:Heterocyclic Compounds; D047028:Macrocyclic Compounds; D011084:Polycyclic Aromatic Hydrocarbons; D012997:Solvents