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51.
Lucien Stella 《Angewandte Chemie (International ed. in English)》1983,22(5):337-350
Many N-chloroalkylamines with double bond(s) dissociate homolytically to give chlorine atoms and aminyl radicals which undergo intramolecular cyclization reactions. Here, the nature of the aminyl radicals (neutral, protonated, or complexed to metal salts) appears to be important. The reactivity varies strongly from one species to another, and their selectivities can be different towards addition, substitution, abstraction, or dimerization reactions. A good synthetic tool appears to be the “complexed radical”, which is generated under mild conditions. A variety of β-functionalized, substituted, fused, or bridged azaheterocycles with alkaloid part structures thus become easily accessible in high yields, in a regio- and, possibly, stereoselective manner. Many examples are discussed illustrating the synthetic possibilities, limitations, and mechanistic features of this cyclization process. 相似文献
52.
西松烷型二萜类化合物是一大类广泛分布于松脂、烟草、陆地动物及海洋生物体中的具有十四元碳环骨架的化合物.其结构新颖复杂,且大多具有显著和广谱的生物活性.近几十年来,有关这类化合物的研究已引起了人们的极大兴趣.因此,开展这类天然产物及其类似物的全合成及构效关系的研究不仅具有重要的学术价值,而且具有潜在的应用前景. 相似文献
53.
54.
We achieved the total synthesis of the histone deacetylase inhibitor spiruchostatin A, as the prelude to the preparation of a combinatorial library of its analogues. Two key reactions were an asymmetric acetate aldol reaction using a Zr-enolate and macrolactonization using the Shiina method. 相似文献
55.
Dieter Seebach 《Angewandte Chemie (International ed. in English)》1988,27(12):1624-1654
The chemistry of lithium enolates is used to demonstrate that complex structures held together by noncovalent bonds (“supramolecules”) may dramatically influence the result of seemingly simple standard reactions of organic synthesis. Detailed structural data have been obtained by crystallographic investigations of numerous Li enolates and analogous derivatives. The most remarkable features of these structures are aggregation to give dimers, tetramers, and higher oligomers, complexation of the metal centers by solvent molecules and chelating ligands, and hydrogen-bond formation of weak acids such as secondary amines with the anionoid part of the enolates. The presence in nonpolar solvents of the same supramolecules has been established by NMR-spectroscopic, by osmometric, and by calorimetric measurements. The structures and the order of magnitude of the interactions have also been reproduced by ab-initio calculations. Most importantly, supramolecules may be product-forming species in synthetic reactions of Li enolates. A knowledge of the complex structures of Li enolates also improves our understanding of their reactivity. Thus, simple procedures have been developed to avoid complications caused by secondary amines, formed concomitantly with Li enolates by the common methods. Mixtures of achiral Li enolates and chiral Li amides can give rise to enantioselective reactions. Solubilization by LiX is observed, especially of multiply lithiated compounds. This effect is exploited for alkylations of N-methylglycine (sarcosine) CH2 groups in open-chain oligopeptides. Thus, the cyclic undecapeptide cyclosporine, a potent immunosuppressant, is converted into a THF-soluble hexalithio derivative (without epimerization of stereogenic centers) and alkylated by a variety of electrophiles in the presence of either excess lithiumdiisopropyl amide or of up to 30 equivalents of lithium chloride. Depending on the nature of the LiX additive, a new stereogenic center of (R) or (S) configuration is created in the peptide chain by this process. A structure-activity correlation in the series of cyclosporine derivatives thus available is discussed. 相似文献
56.
A practical and efficient stereoselective synthesis of the side chain of neomarinone is reported. The synthesis was achieved in six steps (41% overall yield) from 2-methyl-2-cyclohexenone. The key step is a novel stereoselective 1,4-conjugate addition/enolate alkylation by an epoxide-opening reaction. 相似文献
57.
接枝和交联对纳米Si02改性NR/PP共混型热塑弹性体的影响 总被引:2,自引:0,他引:2
动态硫化制备纳米二氧化硅(SiO2)改性天然橡胶,聚丙烯共混型热塑性弹性体(NR/PPTPE).研究了马来酸酐,苯乙烯,过氧化二异丙苯(MAH/St/DCP)多单体“就地”熔融接枝、交联对TPE力学性能、耐溶剂性能和耐热变形性能的影响,并用SEM分析了TPE的断面形貌.结果表明:纳米SiO2和MAH/St/DCP的最佳质量分数分别为0.03和0.0375/0.0188/0.00375时,MAH/St/DCP接枝、交联改性NR/PP/纳米SiO:TPE的力学性能、耐溶剂性能和耐热变形性能最佳.MAH/St/DCP“就地”接枝、交联通过细化交联NR分散相、改善交联NR分散的均匀性和增加两相之间的共交联,使NR与PP两相界面结合强度明显提高,NR/PPTPE的综合性能得到明显的改善. 相似文献
58.
天然沸石在水污染控制中的应用 总被引:20,自引:0,他引:20
本文综合评述了天然沸石在水污染控制中的应用,包括去除城市废水和工业废水中的氮和磷、放射性废水中的铯和锶以及工业废水中的重金属等。 相似文献
59.
Summary The effect of pre-adsorbed benzene and ethanol on the adsorptive properties of natural zeolite (clinoptilolite) has been studied
by gas-solid chromatography. It has been shown that modification of the solid surface by volatile organics has a significant
influence on the adsorptive properties. The modification is of the same order as the more difficult modification by inorganics,
as illustrated here by clinoptilolite modification with Co2+. Energy distribution of surface adsorptive sites appears to be continuous and confirms previous finding that only a small
proportion of active sites is responsible for most adsorbate retention.
Part II reference [4] 相似文献
60.
Matej Babjak 《Tetrahedron》2005,61(9):2471-2479
A total synthesis of (+)-goniothalesdiol, a 3,4-dihydroxy-2,5-disubstituted tetrahydrofuran isolated from Goniothalamus borneensis (Annonaceae), and its 7-epimer is reported using oxycarbonylation methodology for construction of polyhydroxylated substituted heterocycles. Diastereoselectivity of addition of organometallic reagents to 2,3-O-isopropylidene-d-threose derivatives using theoretical calculations based on the semiempirical PM5 was studied. 相似文献