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61.
62.
Highly diastereoselective protonation of chiral lactam enolates of 4-substituted-1,4-dihydroisoquinolin-3-ones is reported. Protonation and alkylation processes of these lactam enolates derived from phenylglycinol occur with opposite diastereofacial selectivity. This diastereoselective protonation has been applied to the asymmetric synthesis of (4S)-N-methyl-4-phenyl-1,2,3,4-tetrahydroisoquinoline 9 obtained in up to 97% ee. 相似文献
63.
Serge Schubert Philippe Renaud Pierre-Alain Carrupt Kurt Schenk 《Helvetica chimica acta》1993,76(7):2473-2489
Radical addition to enamines using Bu3SnH as reducing agent are reported (Schemes 2 and 4). The diastereoselectivity of these reactions was examined in different systems (Tables 1 and 2). Enamines derived from cyclic ketones such as cyclohexanone were alkylated with high diastereoselectivity with preferential formation of the cis-disubstituted cycloalkanes. In acyclic systems such as enamines derived from propiophenone and diethyl ketone, moderate to high stereoselectivities were observed in the H-abstraction step. A model based principally on minimization of allylic 1,3-strain (A1,3 strain) was deduced from the experimental results and semi-empirical (AM1) calculations. 相似文献
64.
The study of the mass analysed ion kinetic energy spectra of deuterated derivatives of aniline, aminopyridines and 2-chloro-5-aminopyridine shows that prior to HCN loss, hydrogen scrambling does not occur for aminopyridines and is limited but noticeable for aniline. In the case of this last compound the extent of scrambling varies markedly for small variations in the energy of the ions studied, these variations being within the energy window corresponding to metastable ions. Furthermore, an examination of the mass analysed ion kinetic energy spectra of monodeuterated derivatives of aminopyridines leads to the rejection of the generally accepted mechanism for HCN loss from the molecular ions of these compounds. 相似文献
65.
The properties of n-type thin polycrystalline films of antimony trisulphide obtained by tarnishing reactions have been studied by photoelectrochemical and spectroellipsometric techniques. The photoelectrochemical behaviour is analysed using a recombination model. 相似文献
66.
Enantiospecific total synthesis of (-)-polyoxamic acid using 2,3-aziridino-gamma-lactone methodology
The non-natural enantiomer of polyoxamic acid was synthesized in six steps from 2,3-aziridino-gamma-lactone 7 with an overall yield of 10%. The key step of the strategy is a deprotection-protection sequence on the nitrogen atom of the aziridine ring required for aziridine activation toward nucleophilic ring opening. 相似文献
67.
Marie E Chevalier Y Brunel S Eydoux F Germanaud L Flores P 《Journal of colloid and interface science》2004,269(1):117-125
The mechanism of action of additives that control the sedimentation of paraffin crystals after their crystallization in model diesel oil has been studied by means of a new experimental approach. The chemical analysis of the crystals and detailed measurements of the sedimentation phenomenon give new insights into this complex process. Thus, the wax antisettling additives used for preventing wax crystal sedimentation adsorb at the surfaces of wax particles and provide them with enhanced colloidal stability. The settling rate is not related to the size of the crystals or the viscosity of the liquid medium, but to the ability of the additives to prevent the aggregation of wax crystals. The reported methodology makes it possible to investigate the fundamental mechanisms, but also to evaluate structure-activity relationships of the various additives used in the petroleum industry. 相似文献
68.
Can one join both ends of a helix? A helical aromatic oligoamide was macrocyclized into a saddle-shaped bifunctional clip molecule that self-assembles into discrete circular dodecamers in the solid state and shows great potential for binding aromatic acid guests in solution. The cyclization step requires that the helix is only partly denatured in the reaction medium. 相似文献
69.
Philippe Quevauviller Gemma Rauret Allan Ure Roser Rubio José-Fírmin López-Sánchez Haidé Fiedler Herbert Muntau 《Mikrochimica acta》1995,120(1-4):289-300
The determination of extractable trace metal contents in soil using single extraction procedures is currently performed in many laboratories to assess the bioavailable metal fraction (and related phytotoxic effects) and the accessability to the environment (e.g. contamination of ground waters). Owing to the need for validation of the extraction schemes used and of the analytical techniques, the EC Measurements and Testing Programme (formerly BCR) has organized a project for improving the quality of determination of extractable trace metal contents in soil, the first step being an interlaboratory study to adopt common extraction procedures and the second being a certification campaign to certify two soils for their extractable trace element contents following these procedures. This paper gives a brief overview of the project organisation and describes the preparation, homogeneity and stability studies of two soil candidate reference materials (sewage sludge-amended and terra rossa soils). 相似文献
70.
Hartl F Mahabiersing T Chardon-Noblat S Da Costa P Deronzier A 《Inorganic chemistry》2004,43(22):7250-7258
IR, UV-vis, and EPR spectroelectrochemistry at variable temperatures and in different solvents were applied to investigate in situ the formation of electroactive molecular chains with a nonbridged Os-Os backbone, in particular, the polymer [Os(0)(bpy)(CO)(2)](n) (bpy = 2,2'-bipyridine), from a mononuclear Os(II) carbonyl precursor, [Os(II)(bpy)(CO)(2)Cl(2)]. The one-electron-reduced form, [Os(II)(bpy(.)(-))(CO)(2)Cl(2)](-), has been characterized spectroscopically at low temperatures. This radical anion is the key intermediate in the electrochemical propagation process responsible for the metal-metal bond formation. Unambiguous spectroscopic evidence has been gained also for the formation of [[Os(0)(bpy(*)(-))(CO)(2)](-)](n), the electron-rich electrocatalyst of CO(2) reduction. The polymer species are fairly well soluble in butyronitrile, which is important for their potential utilization in nanoscience, for example, as conducting molecular wires. We have also shown that complete solubility is accomplished for the monocarbonyl-acetonitrile derivative of the polymer, [Os(0)(bpy)(CO)(MeCN)(2)Cl](n). 相似文献