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Hypervalent iodine reagents are powerful tools in contemporary organic synthesis. They have found numerous applications in modern oxidative transformations. The unique reactivity of hypervalent iodine allows access to unconventional electrophilic synthons. For example, electrophilic halogenation chemistry has been greatly expanded by the study of various haloiodanes. Cyclic λ3-haloiodanes are versatile reagents which can promote reactions such as halogenations, halocyclizations and oxidations. Their peculiar reactivity sets them apart from traditional sources of electrophilic halogens. Furthermore, they offer a broad range of reactivities which have been exploited in more diversified transformations. This review summarizes the different syntheses and derivatives of these cyclic haloiodanes, their applications and mechanistic insights as well as the relevant computational, structural and kinetic studies. 相似文献
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Reactivities of mononuclear non-heme iron intermediates including evidence that iron(III)-hydroperoxo species is a sluggish oxidant 总被引:1,自引:0,他引:1
There is an intriguing, current controversy on the involvement of iron(III)-hydroperoxo species as a "second electrophilic oxidant" in oxygenation reactions by heme and non-heme iron enzymes and their model compounds. In the present work, we have performed reactivity studies of the iron-hydroperoxo species in nucleophilic and electrophilic reactions, with in situ-generated mononuclear non-heme iron(III)-hydroperoxo complexes that have been well characterized with various spectroscopic techniques. The intermediates did not show any reactivities in the nucleophilic (e.g., aldehyde deformylation) and electrophilic (e.g., oxidation of sulfide and olefin) reactions. These results demonstrate that non-heme iron(III)-hydroperoxo species are sluggish oxidants and that the oxidizing power of the intermediates cannot compete with that of high-valent iron(IV)-oxo complexes. We have also reported reactivities of mononuclear non-heme iron(III)-peroxo and iron(IV)-oxo complexes in the aldehyde deformylation and the oxidation of sulfides, respectively. 相似文献
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本文计算的σ_(ΔE)~(HO)和σ_(ΔE)~(LU)值,应用于苯系Ph(x)_n六十多个分子的亲电或亲核反应活性比较,结果同文献实验数据。σ_(ΔE)~(HO)值与分子间或分子内亲电反应活性呈正平行关系,而σ_(ΔE)~(LU)值则正好相反,但是CN、CF_3和F取代基则例外。 相似文献
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2-Iminothiazole, an isoform of 2-aminothiazole, is a scaffold of synthetic and medicinal significance. We have reported an efficient method by which alkyl group of 2-alkyliminothiazoles is changed into other alkyl groups by isothiocyanates. In this article, a detailed mechanistic aspect, and the scopes and limitations were disclosed. All the reactions were carried out in toluene at 105 °C without any additive. The reaction is a reversible process and the equilibrium is determined by the reactivity of both reactants, in which the more electron-withdrawing alkyl or aryl groups at the 2-imino group or isothiocyanate showed higher reactivities. With this simple method, we effectively altered the alkyl group attached on the imine nitrogen. A synthetic problem in 2-iminothiazole chemistry, synthesis of amino acid-derived 2-iminothiazole was solved in a very simple manner. Using suitably designed 2-iminothiazole substrate, the electrophilic reactivity of various isothiocyanates could be empirically compared by this exchange reaction. Moreover, successful exchange reaction using isocyanates instead of isothiocyanates broadened the utility of this reaction. 相似文献
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本文计算的σ~△~E^H^O和σ△E^L^U值, 应用于苯系Ph(X)n六十多个分子的亲电或亲核反应活性比较, 结果同文献实验数据。σ~△~E^H^O值与分子间或分子内亲电反应活性呈正平行关系, 而σ~△~E^L^U值则正好相反, 但是CN、CF3和F取代基则例外。 相似文献
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Koder RL Walsh JD Pometun MS Dutton PL Wittebort RJ Miller AF 《Journal of the American Chemical Society》2006,128(47):15200-15208
Flavins are central to the reactivity of a wide variety of enzymes and electron transport proteins. There is great interest in understanding the basis for the different reactivities displayed by flavins in different protein contexts. We propose solid-state nuclear magnetic resonance (SS-NMR) as a tool for directly observing reactive positions of the flavin ring and thereby obtaining information on their frontier orbitals. We now report the SS-NMR signals of the redox-active nitrogens N1 and N5, as well as that of N3. The chemical shift tensor of N5 is over 720 ppm wide, in accordance with the predictions of theory and our calculations. The signal of N3 can be distinguished on the basis of coupling to 1H absent for N1 and N5, as well as the shift tensor span of only 170 ppm, consistent with N3's lower aromaticity and lack of a nonbonding lone pair. The isotropic shifts and spans of N5 and N1 reflect two opposite extremes of the chemical shift range for "pyridine-type" N's, consistent with their electrophilic and nucleophilic chemical reactivities, respectively. Upon flavin reduction, N5's chemical shift tensor contracts dramatically to a span of less than 110 ppm, and the isotropic chemical shift changes by approximately 300 ppm. Both are consistent with loss of N5's nonbonding lone pair and decreased aromaticity, and illustrate the responsiveness of the 15N chemical shift principal values to electronic structure. Thus. 15N chemical shift principal values promise to be valuable tools for understanding electronic differences that underlie variations in flavin reactivity, as well as the reactivities of other heterocyclic cofactors. 相似文献
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Yongqang Wang 《大学化学》2020,35(7):142-150
亲电取代反应是一类基本的有机反应,其中以苯环上的亲电取代反应最常见。该反应的反应活性及反应的位点与苯环上已有的取代基有很大的关系。本文从波谱学的角度,利用核磁数据,阐述了已有的取代基如何影响苯环的电子云密度,进而影响苯环亲电取代反应的活性和取代的位置。本文视角新颖,将对学生的学习及科研产生启发。 相似文献