Shigeru Ohba

Synthesis and properties of 1,8-Di(2-thienyl)-, 1,8-bis(5,2′-bithiophene-2-yl)-, 1,8-bis(5,2′:5′,2″-terthiophene-2-yl)-, and 1,8-bis(5,2′:5′,2″:5″,2″′-quaterthiophene-2-yl)naphthalenes and related compounds

Abstract 1,8-Di(2-thienyl)-, 1,8-bis(5,2′-bithiophene-2-yl)-, 1,8-bis(5,2′:5′,2″-terthiophene-2-yl)-, and 1,8-bis-(5,2′:5′,2″:5″,2″′-quaterthiophene-2-yl)naphthalenes (1a, 1b, 1c and 1d, respectively) were synthesized starting from 1,8-dibromonaphthalene by appliction of NiCl2(dppp)-catalyzed coupling of aryl bromides with thienylmagnesium bromides. For comparison with these compounds, 1-(2-thienyl)-, 1-(5,2′-bithiophene-2-yl)-, 1-(5,2′:5′,2″-terthiophene-2-yl)-, and 1-(5,2′:5′,2″:5″,2″′-quaterthiophene-2-yl)naphthalenes (2a–d) were also prepared. Inspection of 1H and 13C NMR and UV/Vis data of 1a–d and 2a–d including X-ray single crystal structure data of 1b suggests that the planes of two oligothiophene units of 1a–d are approximately parallel to each other and are at large angles to the naphthalene ring. In accordance with these findings, CV oxidation potential data show that the radical cations formed from 1a–d are stabilized by intramolecular electron transfer interaction of the two oligothiophene units.

Electron-density distribution in crystals of p-nitrobenzene derivatives

The electron-density distributions in five nitrobenzene derivatives have been examined by the multipole expansion method based on X-ray diffraction data measured with Mo Kα radiation (λ= 0.70926 A) at 120 K. p-Dinitrobenzene, C 6 H 4 N 2 O 4 , (I), M r =168.1, monoclinic, P2 1 /n, a=10.941 (2), b =5.3813 (5), c=5.6684 (4) A, β=92.116 (8) o , V= 333.51 (7) A 3 , Z=2, D x =1.67 Mg m -3 , μ= 0.13 5 mm -1 , R=0.030 for 2045 unique reflections

Compelled Orientational Control of the Solid-State Photodimerization of trans-Cinnamamides: Dicarboxylic Acid as a Non-covalent Linker

Abstract The 2:1 hydrogen-bonded cocrystals 1a·ox, 1a·su, 1a·pht, 1a·fu, 1b·ox, 1c·ox, 1d·ox between trans-cinnamamides (1a–1d) and dicarboxylic acids (ox, su, gl, fu, pht) were prepared and characterized by IR and powder X-ray techniques. The crystal structures of 1a·pht, 1a·ox and 1a·fu were solved by single crystal X-ray diffraction. Phthalic acid (pht) caused β-type photodimerization of trans-cinnamamide (1a) in the cocrystal and functioned as a non-covalent linker like gauche 1,2-diamines in photodimerization of trans-cinnamic acids. Oxalic acid (ox) enforced 1a to take a bilayer structure that is suitable for β-type photodimerization. In the case of fumaric acid (fu), cross photodimerization with 1a occurred to give a cycloadduct 4. For the cocrystals 1a·pht and 1a·fu, pedal-like motion was assumed to occur prior to the dimerization.

Oxidation of cyclohexane with hydrogen peroxide catalysed by copper(II) complexes containing N,N-bis(2-pyridylmethyl)-β-alanineamide ligands

Abstract In the presence of hydrogen peroxide, a mononuclear copper(II) complex, [Cu(bdpg)Cl]Cl [where (bdpg) represents N,N-bis(2-pyridylmethyl)-β-alanine-amide] exhibits a much higher activity for the oxygenation of cyclohexane than other analogs. Crystal structure determinations and spectroscopic data indicate that the amide group in the (bdpg) ligand, which can interact with a hydroperoxide-ion η1-bonded to copper(II) plays an important role in activation of hydrogen peroxide, leading to the facile oxygenation of cyclohexane.

Charge distribution and atomic thermal vibration in lead chalcogenide crystals

Charge distribution in crystals of lead chalcogenides, PbX (X = S, Se and Te), has been studied by X-ray diffraction. The structure of PbX is of the rock salt type: cubic, Fm3m, a = 5.934 (1), 6.128 (1) and 6.462 (1)A for PbS, PbSe and PbTe, respectively. Final agreement factors for PbS, PbSe and PbTe were R = 0.015, 0.011 and 0.015 for 144, 147 and 130 independent reflections, respectively. The direct integration of charge density, the observed atomic scattering factors, and the population analysis of the valence electrons unanimously indicated that the Pb atom is negatively charged. This observation suggests predominant covalency for the chemical bond in lead chalcogenide crystals. No overlap density was observed in the deformation density map. The bonding electrons in these crystals may be delocalized like free electrons in metals. The thermal parameters of the Pb atoms were found to be larger than those of the chalcogen atoms and the ratio Bpb/B x increases in the order: PbS < PbSe < PbTe. Anharmonic thermal vibration of the Pb atom was detected in the difference electron density maps. A positive peak of 2 (0.3) e A -3 was observed in the (111) direction at 0.4 A from the Pb nucleus for all three compounds. Its height was reduced to 1 (0-3) e A -3 by introducing anharmonic potential parameters for the Pb atom.

Diterpenes from Euphorbia helioscopia

Abstract A number of diterpenes have been isolated from Euphorbia helioscopia and their stereostructures elucidated on the basis of the spectral data together with some chemical evidence. The absolute configuration of cuphoscopin A and euphornin in particular have been unambiguously determined by means of X-ray crystallographic analysis.

Polyoxypeptin isolated from Streptomyces: A bioactive cyclic depsipeptide containing the novel amino acid 3-hydroxy-3-methylproline

Abstract Polyoxypeptin, a potent inducer of apoptosis in human pancreatic carcinoma cells, was isolated from an ethyl acetate extract of a Streptomyces culture broth. Structural determination by 2D-NMR and X-ray crystallographic analysis revealed that it is a novel cyclic hexadepsipeptide containing five hydroxylated amino acids. The unusual and hitherto unreported amino acid 3-hydroxy-3-methylproline was one of them.

AgAsF6 as safe alternative to AgClO4 for generating cationic zirconocene species: Utilities in lewis acid-promoted selective CC bond forming reactions

For generating cationic zirconocene species that are useful for organic synthesis, AgAsF6 proved to be an efficient catalyst that serves as a safe alternative to AgClO4. Scope and limitation is discussed on this new catalyst in the processes including (1) alkyl/alkenyl transfer reaction from organozirconocene chloride to aldehyde, (2) two- and four-carbon homologation of aldehyde, (3) dual synthetic methods of 1,3-dienes from aldehydes/ketones via 1,3-bimetallic species, and (4) three-component alkylative cycloaddition via o-quinodimethane species.

Stereochemistry of ptaquiloside, a novel norsesquiterpene glucoside from bracken, Pteridium aquilinum var. latiusculum

Abstract The absolute stereostructure of ptaquiloside ( 1 ), a novel norsesquiterpene glucoside isolated from bracken, Pteridium aquilinum var. latiusculum has been elucidated by the 1H NMR spectral method and an X-ray crystallographic analysis of ptaquiloside tetraacetate ( 2 ).

Single-crystal-to-single-crystal photodimerization of 4-chlorocinnamoyl-O,O'-dimethyldopamine.

[2+2]Photodimerization of the title compound, C(19)H(20)ClNO(3), has been observed in situ by single-crystal X-ray diffraction. Pairs of monomers related by centers of symmetry have parallel C=C bonds at a C.C distance of 4.155 (17) A. Irradiation of a single crystal with a mercury lamp achieves 100% conversion to the dimer. Redetermination of the structure during the course of the reaction revealed a linear correlation between the percent conversion to the dimer and the decrease in the cell Volume. The displacement parameters for the pure dimer structure are substantially smaller than those for the pure monomer structure. The dimerization reaction is also induced by irradiation with X-rays, the induction being stronger with Cu Kalpha than with Mo Kalpha radiation.