A selective reductive amination of aldehydes by the use of Hantzsch dihydropyridines as reductant

Direct reductive amination of an aldehyde was carried out using a Hantzsch dihydropyridine as the reductant in the presence of a catalytic amount of scandium triflate. The reaction was highly selective towards aldehydes over ketones, and other reducible functional groups did not affect the reaction.     

Rigid-rod polymers with polysiloxane side chains. I. Synthesis and characterization of rigid-rod polyimides with polysiloxane side chains and their compatibility with linear polysiloxanes

Rigid-rod aromatic polyimdies having polydimethylsiloxane side chains were prepared for the purpose of dispersing rigid-rod molecules in silicone matrices for molecular reinforcement. The polyimides were obtained by imidizing the polyamide-acids bearing the side chains either thermally or chemically, which were synthesized by reacting 4,4′-diaminobiphenyl-terminated polysiloxane macromonomers with pyromellitic dianhydride in THF. The polyamide-acid films obtained by removing the solvent were soluble in THF, but the polyimides were insoluble in any common solvent. The polyimides showed no melting transition below 350°C on DSC analysis, at which temperature the side chain started decomposing. Although all the polyimides were anisotropic as observed by a polarizing microscope, x-ray diffraction analysis suggested the presence of only limited chain organization. Blends with linear polydimethylsiloxanes were prepared by casting the THF solution containing the polyamide-acid and the polydimethylsiloxane, followed by solvent evaporation and thermal imidization. With relatively longer side chains, the polyimides were proved to be compatibilized with polydimethylsiloxanes. © 1994 John Wiley & Sons, Inc.     

Efficient copper-catalyzed coupling of aryl iodides and thiobenzoic acid

A highly efficient copper-catalyzed coupling reaction of aryl iodides and thiobenzoic acid, using 10 mol % of copper iodide, 20 mol % of 1,10-phenanthroline, and ⁱPr₂NEt in toluene, was developed. This methodology is applicable to a variety of aryl iodides.     

Glycosides of benzyl and salicyl alcohols from Alangium chinense

From the water-soluble fraction of the dried leaves of Alangium chinense, three new glycosides, benzyl alcohol beta-D-glucopyranosyl-(1 --> 2)-[beta-D-xylopyranosyl-(1 --> 6)]-beta-D-glucopyranoside, 2'-O-beta-D-glucopyranosylsalicin, and 2'-O-beta-D-glucopyranosyl-6'-O-beta-D-xylopyranosylsalicin were isolated along with seven known glycosides. The structures of the new compounds were determined by spectroscopic and chemical means.     

Selective vinyl cationic polymerization of monomers with two cationically polymerizable groups. II. p-vinylphenyl glycidyl ether: An epoxy-functionalized styrene

p-Vinylphenyl glycidyl ether (VPGE), a styrene derivative with an epoxy pendant, was polymerized by various cationic initiators, and its selective vinyl polymerization was investigated at low temperatures below ?15°C. BF₃OEt₂ (a metal halide) and CF₃SO₃H (a strong protonic acid) polymerized both vinyl and epoxy groups of VPGE, and produced cross-linked insoluble polymers. The HI/I₂ initiating system and iodine, in contrast, polymerized its vinyl group in polar solvents (CH₂Cl₂ and nitroethane) highly selectively in the temperature range of ?15 to ?40°C to give soluble polymers with a polystyrene backbone and epoxy pendants; however, under these conditions, 10–15% of the epoxy groups of the polymers were consumed during the polymerization by the reaction with the growing species. The polymerization by HI/I₂ in CH₂CI₂ involved a long-lived propagating species, as indicated by a progressive increase in the molecular weight (M?_n) of the polymers with monomer conversion and their fairly narrow molecular weight distributions (M?_w/M?_n ～ 1.6). The differences between the polymerizations of VPGE and p-isopropenylphenyl glycidyl ether, an α-methylstyrene-type counterpart of VPGE, were also discussed with an emphasis on the effects of the α-methyl group in the latter monomer.     

AMPHIPHILIC COPOLYMERS AS MEDIA FOR LIGHT-INDUCED ELECTRON TRANSFER-II. ELECTROSTATIC EFFECT ON THE BACK ELECTRON TRANSFER

Abstract— Photosensitized reduction of zwitterionic viologen (SPV) and methyl viologen (MV²⁺) was investigated using an amphiliphilic copolymer having phenanthryl and sulfonate groups (APh) as photosensitizer in aqueous solutions. In the presence of triethanolamine the accumulation of SPV * (photoproduct) was found to be faster than that of MV⁺. This attributed to the electrostatic repulsion between SPV. and anionic segments of APh. Such difference between SPV and MV²⁺ was minimized in the case of the related monomer model. Retardation of the back reaction for the APh-SPV system was also demonstrated by laser photolysis, k _b= 8.7 × 10⁷ M ^-1 s^-1 for the polymer system as compared to k _b= 2.8 × 10⁹ M ^-1 s^-1 for the monomer model system. Strong salt-effects on the yield of the photoreduction and the rate of back reaction confirm the strong electrostatic interaction between the photoproducts and polyanions. This remarkable electrostatic effect of the polyanions was simulated by electrochemical redox reactions by using a graphite electrode coated with APh.     

Preferential Uniplanar Orientation of Cellulose Microfibrils Reinvestigated by the FTIR Technique

A simple detection method to observe the uniplanar orientation behavior of native cellulose microfibrils to the cell wall surface by using Fourier transform infrared (FTIR) spectroscopy in the transmission mode is reported. Four bands at 1372, 1355, 1337, and 1317 cm⁻¹ (the latter two have been mentioned previously by Liang and Marchessault (1960, J. Polym. Sci. 43: 85–100)) were found to be sensitive to such orientation: the two middle bands at 1355 and 1337 cm⁻¹ increase remarkably when the 0.60–61 nm lattice planes lie parallel to the cell wall surfaces. The reverse was true when the 0.53–54 nm lattice planes oriented preferentially. Polarization of the two bands at 1372 and 1355 cm⁻¹ was parallel, while that of the other two bands at lower wavenumbers, i.e., at 1337 and 1317 cm⁻¹, was perpendicular to the molecular axis of cellulose. These bands were assigned to OH-related motion, probably to in-plane OH bending, as reported by Maréchal and Chanzy (2000, J. Mol. Spectrosc. 523: 183–196).     

Conformations and steric and stacking interactions of trisubstituted ureas and thioureas with alkyl and phenyl groups

The monomeric ν(N—H) vibrations of various trisubstituted ureas of the R₂UPh type and -thioureas of the R₂TUPh type have been studied. The trans—out isomerism in the former and the trans—out—cis isomerism in the latter are discussed from the point of view of steric effect. The monomeric ν(N—H) vibrations of RPhUPh and RPhTUPh are also examined. The single band appearing in the spectrum of both ureas is characteristic of the cis form; this suggests the existence of phenyl—phenyl interaction (the stacking interaction proposed by Galabov et al. [10]). Behavior of ν(N—H) vibrations at several concentrations is shown to be clearly different in the three forms (trans, out and cis). The presence of the cis form is confirmed by solvent effect experiments.     

Self-assembly patterning of silica colloidal crystals

We developed a self-assembly process of silica particles to fabricate desired patterns of colloidal crystals having high feature edge acuity and high regularity. A micropattern of colloidal methanol prepared on a self-assembled monolayer in hexane was used as a mold for particle patterning, and slow dissolution of methanol into hexane caused shrinkage of molds to form micropatterns of close-packed SiO2 particle assemblies. This result is a step toward the realization ofnano/micro periodic structures for next-generation photonic devices by a self-assembly process.     

Solution viscosity behavior of polystyrene-based cationic ionomers. Effects of ion content and solvent

Dilute-solution viscosities of polystyrene-based cationic ionomers containing ammonio or phosphonio groups were measured in several solvents. In polar solvents with dielectric constant (ε_r) beyond 10, the ionomers showed a typical polyelectrolyte behavior, indicating that a large part of ionic groups were dissociated into ions. In nonpolar solvents with low ε_r, the reduced viscosity of the ionomers linearly decreased with a decreasing ionomer concentration. At low polymer concentrations, every ionomer gave a reduced viscosity lower than that of the corresponding chloromethylated polystyrene. With an increasing ion content, the intrinsic viscosity progressively decreased if the nonpolar solvents had a low acceptor number (A_N), such as toluene or tetrahydrofran (THF). In the halogenated solvents with high A_N value, such as chloroform, however, the intrinsic viscosity was hardly dependent on the ion content. This indicates that the intramolecular aggregation among the ionic groups is inhibited in the halogenated solvents due to a strong anion solvation. An addition of a protic solvent to a nonpolar solvent eliminates the aggregation between ionic groups and leads to polyelectrolyte behavior. © 1994 John Wiley & Sons, Inc.