Molecular transformations of unsaturated thiacrown ethers

Unsaturated thiacrown ethers with 15, 18, and 21 members were oxidized to sulfoxides by the reaction with m-CPBA. The reaction with t-BuOCl at -20 degrees C also afforded sulfoxides, whereas the reaction at room temperature yielded cis-trans isomerized compounds. The cis-trans isomerized compound was also obtained by the photochemical reaction or by the reaction with NCS and NCP. Meanwhile, the reaction with NBS and NBP provided an acetal via 1,2-bridged bromonium intermediate.     

Stabilizing effect of intramolecular lewis base toward racemization of optically active selenoxides

2‐(Methylchalcogenomethyl)diphenyl selenoxides 1 and 2‐{2′‐(N,N‐dimethylamino)ethyl}phenyl alkyl (or aryl) selenoxides 2 , which were expected to be stabilized toward racemization by intramolecular coordination, were synthesized and optically resolved into their enantiomers on an optically active column using high‐performance liquid chromatography. Relationship between the absolute configurations and the chiroptical properties of the enantiomers was clarified by comparing with those of sulfur analogues. Stabilities toward racemization of optically active selenoxides 1a and 1b were nearly equal to that of 2‐{(N,N‐dimethylamino)methyl}diphenyl selenoxide and mesityl phenyl selenoxide. The rates of racemization for optically active selenoxides 2 were found to be faster than that of 2‐{(N,N‐dimethylamino)methyl}phenyl alkyl (or aryl) selenoxides. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:301–311, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20299     

Metal complexes of partially phosphorylated poly(vinyl alcohol) - functions and applications

The highly phosphorylated poly(vinyl alcohol)s (P-PVAs: degree of phosphorylation 70 mol-%) were synthesized by the reaction of PVA, dicyandiamide, urea and orthophosphoric acid in DMF solution. A range of P-PVAs having differents contents (3.3 to 70 mol-%) of phosphoric acid groups can be obtained by the change of reaction time via the same procedure. The complex formation of Cr(III), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) ions with P-PVA thus obtained was investigated by means of potentiometric titration and spectroscopy. By chemical crosslinking reaction of P-PVA with glutaraldehyde, novel anionic polyelectrolyte gels were easily prepared. The degree of swelling and the hardness of hydro-gels can be changed by varying the crosslinking reaction condition. The ion exchange capacity and metal ion selectivities of a cation exchange resin prepared from P-PVA hydrogel have been estimated. Flame-retardation of metal-P-PVA complexes have also studied. The Ni(II)-P-PVA complex showed a good flame-retardation. The molecular composites of the P-PVA salts of cations such as K⁺ or R₄N⁺ (R = CH₃ etc.) were also prepared. These composite polymers showed single ionic conductivity (σ rt > 10⁻⁴ S · cm⁻¹).     

Regioselective Perfluoroalkylation of Heteroaromatic Compounds by Perfluoroalkanesulfonyl Chloride in the Presence of a Ruthenium(II) Complex

Abstract

Regioselective perfluoroalkylation of heteroaromatic compounds by perfluoroalkanesulfonyl chloride in the presence of a catalytic amount of ruthenium(II) phosphine complex is described.     

Optically active telluronium imides: Optical resolution,absolute configuration,and mechanism of racemization

Thermodynamically and kinetically stabilized asymmetric diaryltelluronium imides were synthesized and optically resolved into their enantiomers on an optically active column using medium‐pressure column chromatography. The relationship between the absolute configuration and the optical properties of the chiral telluronium imides was clarified. The mechanism of the racemization, which involves the formation of telluroxides by the hydrolysis of the telluronium imides, was proposed. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:523–529, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10185     

Retro‐Diels–Alder Approach to the Synthesis of π‐Expanded Azuliporphyrins and Their Porphyrinoid Aromaticity

Bicyclo[2.2.2]octadiene (BCOD) fused azuliporphyrins were synthesized by 3+1 porphyrin synthesis of azulitripyrranes with diformylpyrroles. Subsequent retro‐Diels–Alder reaction of the BCOD‐fused azuliporphyrins afforded azulibenzo‐, azulidibenzo‐, and azulitribenzoporphyrins 1 – 5 . NMR and UV/Vis spectra, as well as nucleus‐independent chemical shift (NICS) calculations revealed that 1 – 5 and their diprotonated dications exhibit relatively low porphyrinoid aromaticity, which was dependent on the position and number of fused benzene rings present.     

Kinetics of metal exchange reaction of Cu(II)-poly(vinyl alcohol) complex with Ca(II)-ethylenediamine-N,N,N′,N′-tetraacetic acid in aqueous solution

The kinetics of the metal exchange reaction between the Cu(II)-poly(vinyl alcohol) complex (Cu(II)-PVA) and Ca(II)-ethylenediamine-N,N,N′,N′-tetraacetic acid (Ca(II)-EDTA) were studied by mixing both solutions in a spectrophotometer at pH 9.7–11.0, at μ = 0.10(KNO₃) and at 25°C. The reaction is initiated by the formation of unstable Cu(II)-H-PVA by the attack of H⁺ to Cu(II)-PVA, and while both ligand exchange and metal exchange steps occur, the latter may be rate-determining. The kinetic expression of this reaction was determined as -d[Cu(II)-PVA]/dt = k[Cu(II)-PVA] [H⁺] [PVA]/[Ca(II)-EDTA], where k = k₁ + k′₂[H⁺], k₁ = 3.85 × 10⁻² sec⁻¹, k₂ = k′₂ · K^−H_Cu(II)-H-PVA 9.59 × 10⁵ 1 mol⁻¹ sec⁻¹.     

Experimental demonstration of excitation and propagation of intrinsic localized modes in a mass–spring chain

Excitation and propagation of nonlinear localized oscillations are demonstrated experimentally by using a mass–spring chain to emulate those in the celebrated Fermi–Pasta–Ulam chain of β type. Two types of experiments are performed, one corresponding to a boundary-value problem and the other to an initial-value one. In the former experiment, one end of the chain is driven sinusoidally in the direction of the chain above a cut-off frequency. In the latter experiment, only a number of weights centered around the weight in the middle of the chain are held displaced initially and released suddenly. The experimental results show quantitatively good agreements with the numerical ones. Two videos linked also show visually mobile and stationary localized oscillations.