共查询到20条相似文献,搜索用时 15 毫秒
1.
Roger W. Binkley Michael G. Ambrose David G. Hehemann 《Journal of carbohydrate chemistry》2013,32(2):203-219
Abstract The reactions of bromide, chloride, and iodide ions with 1,3,4, 6-tetra-O-acetyl-2-O-(trifluoromethylsulfonyl) -α-D-glucopyranose (2) and with 1, 3, 4, 6-tetra-O-acetyl-2-O-(trifluoromethylsulfonyl)-β-D-mannopyranose (3) gave good to excellent yields of the corresponding deoxyhalogeno sugars. In contrast, when the gluco triflate 2 and tetra-butylammonium fluoride were heated under reflux in benzene, only 5-(acetoxymethyl)-2-formylfuran (13) was formed. Reaction of the manno triflate 3 under similar conditions produced 1, 3,4, 6-tetra-O-acetyl-2-deoxy-2-fluoro-β-D-gluco-pyranose (17), 1. 3, 4. 6-tetra-O-acetyl-2-deoxy-β-D-erythro-hex-2-eno-pyranose (18), 4,6-di-O-acetyl-1, 5-anhydro-2-deoxy-D-erythro-hex-l-enitol-3-ulose (19), and 1, 2, 3, 4, 6-penta-O-acetyl-β-D-glucopyranose (20). The mechanisms of the reactions of The triflates 2 and 3 with fluoride ion are discussed. 相似文献
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Abstract A synthesis for L-streptose (1) is described. This synthesis differs from those previously reported in several ways, one of which is the use of photochemical reactions in two important steps. These reactions are part of a sequence leading from L-arabinose (2) to 5-deoxy-1,2-O-isopropylidene-β-L-threo-pentofuranos-3-ulose (3). Two other photochemical reactions are considered as a part of the conversion of 3 into L-streptose (1) but neither proved useful. L-Streptose (1) is synthesized from 3 by a sequence of reactions which involves formation of 5-deoxy-l,2-O-isopropylidene-3-C-nitromethyl-β-L-lyxo-furanose (10) and subsequent reaction of 10 with titanium(III) chloride. 相似文献
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光化学反应是以洁净、节能、节约为目标的化学合成方法,它为有机合成化学提供了新途径、新方法和新技术,是合成化学中最活跃、最有生命力的研究领域之一,深入研究光化学反应必将为现代有机合成的发展注入新的活力.本论文重点研究了具有应用价值的烯烃光敏氧化、脱肟成酮光敏氧化及汉斯酯1,4二氢吡啶衍生物芳香化等光化学反应,取得了一系列重要的研究结果. 相似文献
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Dr. Richard Brimioulle M. Sc. Dominik Lenhart M. Sc. Mark M. Maturi Prof. Dr. Thorsten Bach 《Angewandte Chemie (International ed. in English)》2015,54(13):3872-3890
The nature of the excited state renders the development of chiral catalysts for enantioselective photochemical reactions a considerable challenge. The absorption of a 400 nm photon corresponds to an energy uptake of approximately 300 kJ mol?1. Given the large distance to the ground state, innovative concepts are required to open reaction pathways that selectively lead to a single enantiomer of the desired product. This Review outlines the two major concepts of homogenously catalyzed enantioselective processes. The first part deals with chiral photocatalysts, which intervene in the photochemical key step and induce an asymmetric induction in this step. In the second part, reactions are presented in which the photochemical excitation is mediated by an achiral photocatalyst and the transfer of chirality is ensured by a second chiral catalyst (dual catalysis). 相似文献
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In the photolysis of ketene with benzene in the gas phase, Cycloheptatriene (CHT) and totuene (Tol) have been observed as the products. The ratio, (CHT)/(CHT)+(Tol) are studied at various conditions. The difference of activation energy of formation between toluene and cycloheptariene is evaluated to be 4.76 kcal/mole. 相似文献
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Anatoli L. Poznyak Valeri I. Pavlovski 《Angewandte Chemie (International ed. in English)》1988,27(6):789-796
Three types of photochemical reaction of coordination compounds are well-known and have often been discussed: redox reactions, substitutions, and isomerizations. Less well known is a fourth type of reaction, which occurs fairly frequently: reaction of the ligands themselves. It is the purpose of this article to fill the corresponding gap in the photochemical literature and to summarize our current knowledge of such reactions and of their mechanisms and possible applications. 相似文献
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《Analytical letters》2012,45(20):1609-1619
Abstract Spectrophotometric data used in connection with HA acidity function yield pK1=?3.3(K1= [H2SeO3][H+]/[H3SeO3 +]);potentiometric and spectral measurements give for pK2 and pK3 data in agreement with the literature. At pH > 10 selenite undergoes a fast photochemical reaction, preceded by a rapidly established acid-base equilibrium. Products of this reaction undergo a slow reaction which is second order in selenite. 相似文献
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Polymer microcapsule was employed as a reactionmedium to achieve enantioselectivity in photochemical reduction of phenyl cyclohexyl ketone and photoelectrocycliztion of tropolone methyl ether under the influence of various chiral inductors.In all cases,low but evident enantioselectivity was observed.The poor enantioselectivity is probably due to the facts that not all the capsules include simultaneously both the chiral inductor and the reactant molecules,and the wall of the microcapsule is not rigid enough to hold the reactant and the chiral inductor molecules in close contact. 相似文献
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Haichao Huang Prof. Dr. Yu-Mei Lin Prof. Dr. Lei Gong 《Chemical record (New York, N.Y.)》2023,23(12):e202300275
Over the past decades, asymmetric photochemical synthesis has garnered significant attention for its sustainability and unique ability to generate enantio-enriched molecules through distinct reaction pathways. Photochemical asymmetric three-component reactions have demonstrated significant potential for the rapid construction of chiral compounds with molecular diversity and complexity. However, noteworthy challenges persist, including the participation of high-energy intermediates such as radical species, difficulties in precise control of stereoselectivity, and the presence of competing background and side reactions. Recent breakthroughs have led to the development of sophisticated strategies in this field. This review explores the intricate mechanisms, synthetic applications, and limitations of these methods. We anticipate that it will contribute towards advancing asymmetric catalysis, photochemical synthesis, and green chemistry. 相似文献
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光化学反应是最基本也是最重要的物理化学过程之一,在诸多领域有着广泛的应用。由于计算方法的限制以及光化学反应过程的错综复杂性,光化学反应机理的从头算研究是极具挑战性的国际前沿课题之一。本文综述了近20年来羰基化合物光化学反应机理从头算研究的一些进展,总结了羰基化合物电子激发态的特性和光化学反应过程的规律性,为深入研究光化学反应提供一些有用的信息。 相似文献
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Three new photoproducts, ethyl O-benzoyl mandelate (5a), ethyl O-acetylmandelate (6a), and biphenyl triketone (7a) are isolated and identified in the reactions of ethyl phenylglyoxylate (1a) in benzene. Quantum yields and initial rate constants of product formation are shown to be concentration dependent. For the formation of carbonyl product 3 at lower starting material concentrations (<0.01 M), quantum yields greater than 1 are observed. Variations in the quantum yields as a function of reaction time are due to the accumulation of alpha-hydroxyphenyl ketene (D). The relative reactivities of triplet excited states of phenylglyoxylates 1 and phenyl ketones are compared. A mechanism involving both intramolecular gamma-H abstraction and intermolecular H abstraction, which leads to radical chain reaction, is proposed. Rate constants for intramolecular gamma-H abstraction (k(N)) and intermolecular H abstraction (k(I)) of methyl phenylglyoxylate (1d) are measured. 相似文献
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SN2 Displacement of Carbohydrate Triflates by 9-Oximes of Erythromycin A and Of a Tylosin Derivative
ABSTRACT The preparation of 9-O-glycosyloxime derivatives of erythromycin A (1) and tylosin (2) is reported. Access to this new class of macrolides was achieved from (E)-9-oxime of erythromycin A (3) and 9-oxime of tylosin 20-(1,3-dithiane) (4), by successful displacement of triflates of suitably protected carbohydrates. 相似文献
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In order to discuss the free radicals formation mechanism of Hypocrellin A(HA)with amino derivatives,the electron-spin resonance( ESR) spectroscopy was adopted to study the photochemistry on HA with dibenzyl amine(DBA)and N-methyl benzyl amine(NMBA),respectively. When HA with DBA or NMBA in chloroform solution was illuminated with visible light,singlet oxygen,semiquinone radical and oxynitride radical were formed depending on the condition of the solvent system containing the amino-substituted and solved oxygen. The signal intensity of oxynitride radical decreased with increasing the illumination time,and the signal intensity of semiquinone radical increased with increasing the illumination time. The oxynitride radical content was in inverse ratio with the semiquinone radical generated by being irradiated. In the aerobic system of chloroform solution containing DBA/HA,smiquinone radical was the main radical irradiated. The results indicated that HA induced amino derivatives into HA semiquinone radical. 相似文献
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Shaoming Duan Roger W. Binkley Edith R. Binkley 《Journal of carbohydrate chemistry》2013,32(3):391-396
Abstract Imidazylates 1-3 were irradiated in methanol in the presence and in the absence of the electron donortriethylamine. In each case photochemical deprotection occurred in excellent yield to form the partially protected sugar from which the imidazylate was synthesized. Reactions in the presence of triethylamine required much shorter irradiation times. 相似文献
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Zhen Yang Yujing Guo Prof. Dr. Rene M. Koenigs 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(27):6703-6706
Sigmatropic rearrangement reactions constitute one of the most fundamental reactions of carbenes. While state-of-the-art synthetic methods require the use of expensive precious metal catalysts, the application of visible light for the photolysis of α-aryldiazoacetates is much less investigated and provides an operationally simple entry to carbenes under mild reaction conditions. Herein, we report on blue-light induced sigmatropic rearrangement reactions of sulfur compounds with α-aryldiazoacetates. This process, depending on the substitution pattern of the sulfide, opens up formal insertion reactions of carbenes into S−N, S−C, or C−H bonds. 相似文献