Syntheses totales et etudes de lignanes biologiquement actifs—I : Application de la reaction d'ullmann a la synthese de biaryles precurseurs de lignanes bisbenzocyclooctadienes

Several biaryls bearing various substituents on both rings were synthesized in a preparative fashion, and in yields up to 88% by a technical improvement on the classical Ullmann reaction. All these biaryls bear reactive functional groups (i.e. formyl, methoxycarbonyl, dimethoxycarbonylpropyl and butanolidylmethyl) in both the o and o′ positions. The biaryls 9, 13, 21 and 26–33 are plausible synthons for bisbenzocyclooctadiene lignans such as schizandrin and steganacin.     

Kinetics of polymerization of acrylonitrile initiated by the Mn3+-thioacetamide redox system

Kinetics of the polymerization of acrylonitrile has been investigated in aqueous sulfuric acid in a temperature range of 25–45°C. The rate of polymerization (R_p) and the rate of managanic ion disappearance, etc., have been measured. The effect of the various additives, such as water-miscible organic solvents, neutral electrolytes, complexing agents, and surfactants, on the rate has been thoroughly studied. A mechanism that involves the initial complex formation between the thiol form of the thioamide and Mn³⁺, whose decomposition yields the initiating free radical with the polymer chain terminated by mutual combination of growing radicals, has been suggested.     

Glycidyl methacrylate–tert-butyl acrylate copolymers: Synthesis,characterization, and thermal studies

Glycidyl methacrylate was copolymerized with tert-butyl acrylate in bulk at 60°C using benzoyl peroxide as free radical initiator. The copolymer composition was determined by chemical analysis as well as from ¹³C-NMR data. The monomer reactivity ratios were calculated by using the YBR method. The number average sequence length of the copolymers was determined from ¹³C-NMR data and compared with those obtained from reactivity ratios. The intrinsic viscosity of the copolymers was determined in DMF, and thermal stability as well as mechanism of thermal degradation of the copolymers were evaluated.     

First asymmetric synthesis of a 6-alkoxy-5,6-dihydro-1,3-oxazine: a promising enantioselective route to beta-amido aldehydes

[reaction: see text] The 1,3-oxazine route to enantiopure beta-amido aldehydes was investigated. Heterocycloaddition of the N-acyl imine 1 with (R)-O-vinylpantolactone provided the stable dihydroxazine 4c. High diastereocontrols were observed when using Yb(fod)3-catalyzed or SnCl4-mediated conditions, thus leading after quantitative hydrolysis to (R)-N-benzoyl-3-phenylpropanal with >98% ee.     

Fresnel coherent diffractive imaging

We present an x-ray coherent diffractive imaging experiment utilizing a nonplanar incident wave and demonstrate success by reconstructing a nonperiodic gold sample at 24 nm resolution. Favorable effects of the curved beam illumination are identified.     

Loss of collectivity in 79Rb

High-spin states in ⁷⁹Rb were populated in the reaction at E(beam) = 60 MeV. The lifetimes of the excited states of the positive-parity yrast band and of the negative-parity band in ⁷⁹Rb were measured by the Doppler Shift Attenuation Method. The deduced transition quadrupole moments Q_t are found to have a decreasing trend with rotational frequency for both the bands, consistent with those found experimentally in neighbouring nuclei. An erratum to this article is available at .