title: Bay-area selective thermal [4+2] and [4+4] cycloaddition reactions of triply linked ZnII diporphyrin with o-xylylene.
abstract: A triply linked ZnII diporphyrin underwent site-selective cycloaddition reactions with thermally generated o-xylylene to provide a triply linked porphyrin-chlorin hybrid and a triply linked chlorin dimer in moderate yields. The former product is a symmetry-allowed [4+2] cycloadduct, while the latter is a symmetry-forbidden [4+4] cycloadduct. Oxidation of the latter product with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) provided a triply linked diporphyrin fused with a benzocyclooctatriene segment. This oxidized product and above [4+2] cycloadduct were structurally characterized by single crystal X-ray diffraction analysis. The observed site-selectivity is considered to arise from the large MO coefficients at the bay-area in the LUMO of the triply linked diporphyrin. The anomalous thermal [4+4] cycloaddition may be ascribed to the highly conjugated and quite perturbed electronic properties of triply linked ZnII diporphyrin.
authors.affiliation: Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Tanaka
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Nakamura
authors.forename: Atsuhiro
authors.initials: A
authors.lastname: Osuka