Total syntheses of (-)-methyl atis-16-en-19-oate, (-)-methyl kaur-16-en-19-oate, and (-)-methyl trachyloban-19-oate by a combination of palladium-catalyzed cycloalkenylation and homoallyl-homoallyl radical rearrangement

Asymmetric total syntheses of (-)-methyl atis-16-en-19-oate (1c), (-)-methyl kaur-16-en-19-oate (2c), and (-)-methyl trachyloban-19-oate (3c) have been achieved by employing a hybrid strategy of palladium-catalyzed cycloalkenylation and homoallyl-homoallyl radical rearrangement. The common synthetic intermediate 5 was prepared from 2-allylcyclohexanone (4) with 98% ee using d'Angelo's asymmetric Michael addition. A series of functional group modifications in 5 via palladium-catalyzed cycloalkenylation led to (+)-14, which had already been prepared by us as racemate. (-)-Methyl atis-16-ene-19-oate (1c) was generated via homoallyl-homoallyl radical rearrangement. On the other hand, Wolff-Kishner reduction of 18 followed by esterification yielded (-)-methyl kaur-16-en-19-oate (2c) together with (-)-methyl trachyloban-19-oate (3c).     

Effect of disorder in the twist angle on light scattering by a three-dimensional spherulite

Light scattering patterns are calculated for imperfect three-dimensional spherulites with fluctuations in the twist angle. The fluctuations are described in terms of a parameter characterizing the distance correlation function. Cases are considered in which (i) the principal axis of the scattering element makes a constant angle with the radius but there is disorder in the twist angle about the axis, and (ii) there is combined twist disorder and orientation disorder of the scattering elements. Calculations suggest that the disorder in the twist angle may lead to a decrease in the higher-order variation of scattered intensity with scattering angle and deviation from the four-leaf-clover-type scattering characteristic of a perfect spherulite at lower scattering angles. On the other hand, disorder in orientation has little effect on the scattering pattern.     

Palladium-catalysed cascade ring expansion reaction of cyclobutanols that have a propargylic moiety with nucleophiles

Cascade ring rearrangement of four-membered ring systems containing various propargylic components by a palladium catalyst is described. The reactions of cyclobutanols that have a propargylic carbonate moiety with phenols as nucleophiles produce phenoxy-induced cyclopentanones in high yields. The reactions proceed in a regio- and diastereoselective manner to afford the substituted cyclopentanones with high selectivities. Imides also act as nucleophiles to produce the imidyl-induced products. Propargylic bromide successfully reacts with sodium alkoxides to produce the corresponding products in good yields.     

DNA sensors using a ferrocene-oligonucleotide conjugate

Using the redox-active DNA conjugate (ferrocene-modified oligonucleotide 12 mer) as a probe, the novel electrochemical gene sensor, which is sensitive, convenient, and not relying on radio isotope, has been developed. Oligonucleotide (16 mer) complementary to the target (19 mer) was immobilized onto gold electrode through the specific chemisorption of successive phosphorothioates which were introduced into 5'-end of the oligonucleotide. The sequence of the conjugate was designed to be also complementary to another site of the target. Therefore, the conjugate and the oligonucleotide anchoring on the electrode formed a sandwich-type ternary complex with a target DNA to give electric currents based on the ferrocene oxidation. By using this system, we have distinguished the mutant that has one base substitution from the fully complementary target.     

Remarkable control of radical cyclization processes of cyclic enyne: total syntheses of (+/-)-methyl gummiferolate, (+/-)-methyl 7beta-hydroxykaurenoate, and (+/-)-methyl 7-oxokaurenoate and formal synthesis of (+/-)-gibberellin a(12) from a common synthetic precursor.

Total syntheses of (+/-)-methyl gummiferolate (13b), (+/-)-methyl 7beta-hydroxykaurenoate (14b), and (+/-)-methyl 7-oxokaurenoate (14d) and a formal synthesis of (+/-)-gibberellin A(12) (15) have been accomplished through the common synthetic precursor, (3aR,7aR)-3,3-dimethyl-7a-(2-propynyl)-3a,4,7,7a-tetrahydroisobenzofuranone (16). The homoallyl-homoallyl radical rearrangement reaction of the monocyclic enyne 25, derived from 16 in two steps, afforded the bicyclo[2.2.2]octane compound 26, which was converted to (+/-)-methyl gummiferolate (13b). In contrast, the radical cyclization of the bicyclic enyne 16 gave the tricyclic lactone 19, leading to (+/-)-methyl 7beta-hydroxykaurenoate (14b) and (+/-)-methyl 7-oxokaurenoate (14d). Transformation of 14d into lactone 20 was carried out in a single step under bromination conditions. This constitutes a formal total synthesis of gibberellin A(12) (15).     

Writing of crystal line patterns in glass by laser irradiation

We examined the laser-induced crystallization to form the fresnoite type Ba₂TiGe₂O₈ crystal line patterns in transition metal ion doped BaO–TiO₂–GeO₂ glass. Ba₂TiGe₂O₈ crystal line was written in 0.6FeO–33.3BaO–16.7TiO₂–50GeO₂ glass by continuous wave yttrium–aluminum–garnet (YAG) laser irradiation. We obtained polarization dependence of Raman spectra in crystal line pattern. Second harmonic generation (SHG) indicated unique fringe patterns from Ba₂TiGe₂O₈ crystal lines.     

Highly dispersed anodes for solid oxide fuel cells using NiO/YSZ/BZY triple-phase composite powders prepared by spray pyrolysis

NiO/Y₂O₃-stabilized ZrO₂ (YSZ)/Y-doped BaZrO₃ (BZY) triple-phase composite powders were prepared by spray pyrolysis and evaluated for Ni/YSZ/BZY cermet anodes, which are considered effective for dry CH₄ operation in solid oxide fuel cells. The structure of the particles in these powders was fine crystal fragments, and the individual material phases were clearly separated and highly dispersed within the particles. The Ni/YSZ/BZY cermet anodes fabricated with these composite powders maintained a fine electrode microstructure equivalent to that in a simple Ni/YSZ cermet anode manufactured using a composite powder prepared by spray pyrolysis. Furthermore, the addition of BZY improved the anode performance in humidified H₂ and dry CH₄ operation.     

Recognition of critical pairs of polycyclic aromatics on crystalline, liquid-crystalline and isotropic regions of silica-supported polymer in HPLC

Summary The silica-supported comb-shaped polymer (Sil-ODA₁₈) with a “crystalline-to-isotropic” phase transition showed the characteristic behaviors of both polymeric and monomeric ODS phases. This was examined using a SRM 869 test mixture. Furthermore, Sil-ODA₁₈ exhibited a specific selectivity towards the critical pairs of polycyclic aromatic hydrocarbons (PAHs), such as acenaphthene and fluorene, or benz(a)anthracene and chrysene, or benzo(ghi)perylene, indeno(1,2,3-cd)pyrene and dibenz(a,h)anthracene. The separation of these solutes was controlled by selecting temperature and solvent systems. The selectivity on Sil-ODA₁₈ was also compared with a conventional ODS (octadecylsilyl silica gel) column. The selectivity on a Sil-ODA₁₈ matrix is attributable to an orientation change of the long-chain alkyl substituents on the surface of the silica base material on transition from crystalline to isotropic state.     

Kinetics of Helix‐Handedness Inversion: Folding and Unfolding in Aromatic Amide Oligomers

A series of helically folded oligoamides of 8‐amino‐2‐quinoline carboxylic acid possessing 6, 7, 8, 9, 10 or 16 units are prepared following convergent synthetic schemes. The right‐handed (P) and the left‐handed (M) helical conformers of these oligomers undergo an exchange slow enough to allow their chromatographic separation on a chiral stationary phase. Thus, the M conformer is isolated for each of these oligomers and its slow racemization in hexane/CHCl₃ solutions is monitored at various temperatures using chiral HPLC. The kinetics of racemization at different temperatures in hexane/CHCl₃ (75:25 vol/vol) are fitted to a first order kinetic model to yield the kinetic constant and the Gibbs energy of activation for oligomers having 6, 7, 8, 9, 10 or 16 quinoline units. This energy gives the first quantitative measure of the exceptional stability of the helical conformers of an aromatic amide foldamer with respect to its partly unfolded conformations that occur between an M helix and a P helix. The trend of the Gibbs energy as a function of oligomer length suggests that helix‐handedness inversion does not require a complete unfolding of a helical strand and may instead occur through the propagation of a local unfolding separating two segments of opposite handedness.