共查询到20条相似文献,搜索用时 31 毫秒
1.
2.
Silver‐Catalyzed Allylation of Ketones and Intramolecular Cyclization through Carbene Intermediates from Cyclopropenes Under Ambient Conditions
下载免费PDF全文
![点击此处可从《化学:亚洲杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Tandem C?C bond formation was achieved through silver‐catalyzed ring‐opening of cyclopropenes via carbene intermediates. The reaction of cyclopropenes in the presence of a silver catalyst gave indene derivatives under ambient conditions. In contrast, the insertion of organozinc reagents to silver carbene or allylic cation intermediates afforded allylmetal intermediates for the tandem allylation of carbonyl compounds. 相似文献
3.
Folding of Synthetic Homogeneous Glycoproteins in the Presence of a Glycoprotein Folding Sensor Enzyme
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Simone Dedola Dr. Masayuki Izumi Dr. Yutaka Makimura Dr. Akira Seko Dr. Akiko Kanamori Dr. Masafumi Sakono Prof. Dr. Yukishige Ito Prof. Dr. Yasuhiro Kajihara 《Angewandte Chemie (International ed. in English)》2014,53(11):2883-2887
UDP‐glucose:glycoprotein glucosyltransferase (UGGT) plays a key role in recognizing folded and misfolded glycoproteins in the glycoprotein quality control system of the endoplasmic reticulum. UGGT detects misfolded glycoproteins and re‐glucosylates them as a tag for misfolded glycoproteins. A flexible model to reproduce in vitro folding of a glycoprotein in the presence of UGGT in a mixture containing correctly folded, folding intermediates, and misfolded glycoproteins is described. The data demonstrates that UGGT can re‐glucosylate all intermediates in the in vitro folding experiments, thus indicating that UGGT inspects not only final folded products, but also the glycoprotein folding intermediates. 相似文献
4.
Min CHEN Rong QIAN Hai‐Yan JIANG Xiang ZHANG Jing ZHOU Wei‐Guo CAO Yin‐Long GUO 《中国化学》2008,26(5):923-928
Electrospray ionization mass spectrometry (ESI‐MS) was utilized to perform monitoring of the intermediates in the reaction of 1,2,3‐trisubstituted electron‐deficient cyclopropane derivatives, cis‐1‐thien‐2′‐oyl‐2‐(p‐subustituted phenyl‐6,6‐dimethyl)‐5,7‐dioxaspiro[2.5]‐4,8‐octadiones, with methanol. Key intermediates, either cationic or protonated forms of neutral species, were intercepted and characterized by ESI‐MS and its tandem version (ESI‐MS/MS). Therefore, the mechanism of the ring‐opening process for electron‐deficient cyclopropane derivatives was fully confirmed by the intermediates monitored. 相似文献
5.
A Study of Heterogeneous Catalysis by Nanoparticle‐Embedded Paper‐Spray Ionization Mass Spectrometry
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Shibdas Banerjee Prof. Chanbasha Basheer Prof. Richard N. Zare 《Angewandte Chemie (International ed. in English)》2016,55(41):12807-12811
We have developed nanoparticle‐embedded paper‐spray mass spectrometry for studying three types of heterogeneously catalyzed reactions: 1) Palladium‐nanoparticle‐catalyzed Suzuki cross‐coupling reactions, 2) palladium‐ or silver‐nanoparticle‐catalyzed 4‐nitrophenol reduction, and 3) gold‐nanoparticle‐catalyzed glucose oxidation. These reactions were almost instantaneous on the nanocatalyst‐embedded paper, which subsequently transferred the transient intermediates and products to a mass spectrometer for their detection. This in situ method of capturing transient intermediates and products from heterogeneous catalysis is highly promising for investigating the mechanism of catalysis and rapidly screening catalytic activity under ambient conditions. 相似文献
6.
Four N‐formamido‐containing mono‐and diheterocyclic pyrrole‐ and imidazole‐2‐containing acids 1–4 were synthesized as intermediates for the preparation of polyamide molecules. The N‐formamido‐moiety forces the compounds to bind strongly as a stacked dimer, and in a staggered fashion, at specific sequences in the minor‐groove of DNA. The acid moiety at the C‐terminus of compounds enables these molecules to be coupled to amine‐containing intermediates to form the amide linkages of the target polyamide. This convergent approach increases the synthetic diversity in polyamide chemistry by enabling one acid to be used with a variety of different C‐terminus‐functionalized intermediates. 相似文献
7.
Metal carbenes derived from transition metal‐catalyzed decomposition of diazo compounds react with nucleophiles with heteroatoms, such as alcohols and amines, to generate highly active oxonium/ammonium ylides intermediates. These intermediates can be trapped by appropriate electrophiles to provide three‐component products. Based on this novel trapping process, we have developed novel multicomponent reactions (MCRs) of diazo compounds, alcohols/anilines, and electrophiles. The nucleophiles were also extended to electron‐rich heterocycles (indoles and pyrroles)/arenes, in which the resulting zwitterionic intermediates were also trapped by electrophiles. By employing efficient catalysis strategy, the reactions were realized with excellent stereocontrol and wide substrate scope. In this personal account, we introduce our breakthroughs in the development of novel asymmetric MCRs via trapping of the active ylides and zwitterionic intermediates with a number of electrophiles, such as imines, aldehyde, and Michael acceptors, under asymmetric catalysis. Transition metal/chiral Lewis acid catalysis, transition metal/Brønsted acid catalysis, and chiral transition‐metal catalysis, enable excellent stereocontrolled outcomes. The methodologies not only provide experimental evidence to support the existence of protic onium ylides intermediates/zwitterionic intermediates and the stepwise pathways of carbene‐induced O?H, N?H and C?H insertions, but also offer a novel approach for the efficient construction of chiral polyfunctional molecules. 相似文献
8.
Paolo Pirovano Adriana M. Magherusan Ciara McGlynn Andrew Ure Amy Lynes Dr. Aidan R. McDonald 《Angewandte Chemie (International ed. in English)》2014,53(23):5946-5950
Metal‐bound superoxide intermediates are often implicated as electrophilic oxidants in dioxygen‐activating metalloenzymes. In the nonheme iron α‐ketoglutarate dependent oxygenases and pterin‐dependent hydroxylases, however, FeIII–superoxide intermediates are postulated to react by nucleophilic attack on electrophilic carbon atoms. By reacting a CuII–superoxide complex ( 1 ) with acyl chloride substrates, we have found that a metal–superoxide complex can be a very reactive nucleophile. Furthermore, 1 was found to be an efficient nucleophilic deformylating reagent, capable of Baeyer–Villiger oxidation of a number of aldehyde substrates. The observed nucleophilic chemistry represents a new domain for metal–superoxide reactivity. Our observations provide support for the postulated role of metal–superoxide intermediates in nonheme iron α‐ketoglutarate dependent and pterin‐dependent enzymes. 相似文献
9.
《Journal of mass spectrometry : JMS》2018,53(6):511-517
Reactive intermediates play key roles for reaction mechanism elucidation. A suitable tool for identifying the key intermediates is crucial and highly desirable. In this study, surface desorption dielectric‐barrier discharge ionization (reactive SDDBDI) was developed for characterization of the reactive intermediates. In reactive SDDBDI, the plasma is doped with a reagent before the plasma ions are directed at a cover slip surface bearing another analyte. Different from SDDBDI, reactive SDDBDI can be used both as an ambient ionization source and as a means to produce reagent ions for ambient ion/molecule reactions. The online derivation of 4‐aminophenol with trifluoroacetic anhydride demonstrated that reactive SDDBDI can be used for chemical analysis where improved specificity or sensitivity is required. The utility of this approach for real‐time detection of reactive intermediate was demonstrated by the Schiff‐base and Eberlin reactions. The formed intermediates and products could be readily detected and identified by tandem mass spectrometry. These results indicate that reactive SDDBDI can be used to generate reagent ions that undergo ion/molecule reactions in the open air with an analyte at condensed phase on a surface. Reactive SDDBDI has high‐efficiency ion transmission and high MS sensitivity. It is thus a potential tool to perform ambient ion/molecule reactions and detect reactive intermediates. 相似文献
10.
The retinal chromophore (11Z)‐3‐diazo‐4‐oxoretinal ( 1 ) with two photo‐labile moieties has been synthesized by semi‐hydrogenation of an 11‐yne precursor with activated Zn in aqueous media. Incorporation of 1 into opsin yielded diazoketo rhodopsin (DK‐Rh), which, upon bleaching, gave rise to intermediates batho‐Rh, lumi‐Rh, meta‐Rh, and meta‐II‐Rh corresponding to those of native Rh but at lower temperatures. Photoaffinity labeling of DK‐Rh and these bleaching intermediates showed that the ionone ring cross‐linked to Trp265 of helix F in DK‐Rh and batho intermediate, and to Ala169 of helix D in lumi, meta‐I, and meta‐II intermediates. These results demonstrate the occurrence of large conformational changes along the visual transduction path, which, in turn, is responsible for activation of the G‐protein. 相似文献
11.
Aminocoumarin derivatives 3‐10 were condensed with diethyl ethoxymethylenemalonate to give intermediates 11‐18. Thermal cyclizations of intermediates give benzopyranopyridinecarboxylates 19‐26. These esters were hydrolyzed to the corresponding benzopyranopyridine carboxylic acids 27‐34. 相似文献
12.
Direct and Single‐Molecule Visualization of the Solution‐State Structures of G‐Hairpin and G‐Triplex Intermediates
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Arivazhagan Rajendran Prof. Dr. Masayuki Endo Kumi Hidaka Prof. Dr. Hiroshi Sugiyama 《Angewandte Chemie (International ed. in English)》2014,53(16):4107-4112
We present the direct and single‐molecule visualization of the in‐pathway intermediates of the G‐quadruplex folding that have been inaccessible by any experimental method employed to date. Using DNA origami as a novel tool for the structural control and high‐speed atomic force microscopy (HS‐AFM) for direct visualization, we captured images of the unprecedented solution‐state structures of a tetramolecular antiparallel and (3+1)‐type G‐quadruplex intermediates, such as G‐hairpin and G‐triplex, with nanometer precision. No such structural information was reported previously with any direct or indirect technique, solution or solid‐state, single‐molecule or bulk studies, and at any resolution. Based on our results, we proposed a folding mechanism of these G‐quadruplexes. 相似文献
13.
Andreas T. Messmer Katharina M. Lippert Sabrina Steinwand Dr. Eliza‐Beth W. Lerch Kira Hof David Ley Dr. Dennis Gerbig Dr. Heike Hausmann Prof. Dr. Peter R. Schreiner Prof. Dr. Jens Bredenbeck 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(47):14989-14995
Determining the structure of reactive intermediates is the key to understanding reaction mechanisms. To access these structures, a method combining structural sensitivity and high time resolution is required. Here ultrafast polarization‐dependent two‐dimensional infrared (P2D‐IR) spectroscopy is shown to be an excellent complement to commonly used methods such as one‐dimensional IR and multidimensional NMR spectroscopy for investigating intermediates. P2D‐IR spectroscopy allows structure determination by measuring the angles between vibrational transition dipole moments. The high time resolution makes P2D‐IR spectroscopy an attractive method for structure determination in the presence of fast exchange and for short‐lived intermediates. The ubiquity of vibrations in molecules ensures broad applicability of the method, particularly in cases in which NMR spectroscopy is challenging due to a low density of active nuclei. Here we illustrate the strengths of P2D‐IR by determining the conformation of a Diels–Alder dienophile that carries the Evans auxiliary and its conformational change induced by the complexation with the Lewis acid SnCl4, which is a catalyst for stereoselective Diels–Alder reactions. We show that P2D‐IR in combination with DFT computations can discriminate between the various conformers of the free dienophile N‐crotonyloxazolidinone that have been debated before, proving antiperiplanar orientation of the carbonyl groups and s‐cis conformation of the crotonyl moiety. P2D‐IR unequivocally identifies the coordination and conformation in the catalyst–substrate complex with SnCl4, even in the presence of exchange that is fast on the NMR time scale. It resolves a chelate with the carbonyl orientation flipped to synperiplanar and s‐cis crotonyl configuration as the main species. This work sets the stage for future studies of other catalyst–substrate complexes and intermediates using a combination of P2D‐IR spectroscopy and DFT computations. 相似文献
14.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(11):3105-3109
A single‐flask procedure for the generation of α‐keto‐N ‐alkenylnitrones through a Chan–Lam coupling and subsequent spontaneous 6π electrocyclization of these intermediates for the synthesis of 2H ‐1,4‐oxazine N ‐oxides has been developed for a variety of α‐ketooximes and alkenylboronic acids. This transformation provides a new approach to C‐substituted unsaturated morpholine derivatives that are poised to undergo further functionalization for the preparation of a diverse array of novel heterocyclic structures. The scope of the new method for the synthesis of 2H ‐1,4‐oxazine N ‐oxides is discussed, in addition to initial studies describing the cycloaddition reactivity of these new heterocyclic intermediates. 相似文献
15.
Elusive Reaction Intermediates in Solution Explored by ESI‐MS: Reverse Periscope for Mechanistic Investigations
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Claudio Iacobucci Dr. Samantha Reale Prof. Francesco De Angelis 《Angewandte Chemie (International ed. in English)》2016,55(9):2980-2993
Just as periscopes allow a submarine to visually search for objects above the surface of the sea, in a reversed periscope fashion electrospray mass spectrometry (ESI‐MS) can analyze the compounds at the gas phase/liquid phase interface for chemical entities which may exist in solution. The challenge is the identification and structural characterization of key elusive reaction intermediates in chemical transformations, intermediates which are able to explain how chemical processes occur. This Minireview summarizes recent selected publications on the use of ESI‐MS techniques for studying solution intermediates of homogeneous chemical reactions. 相似文献
16.
Steering Surface Reaction Dynamics with a Self‐Assembly Strategy: Ullmann Coupling on Metal Surfaces
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(42):13032-13036
Ullmann coupling of 4‐bromobiphenyl thermally catalyzed on Ag(111), Cu(111), and Cu(100) surfaces was scrutinized by scanning tunneling microscopy as well as theoretical calculations. Detailed experimental evidence showed that initial formation of organometallic intermediates on the surface, as self‐assembled structures or sparsely dispersed species, is determined by the subsequent reaction pathway. Specifically, the assembled organometallic intermediates at full coverage underwent a single‐barrier process to directly convert into the final coupling products, while the sparsely dispersed intermediates at low coverage went through a double‐barrier process via newly identified clover‐shaped intermediates prior to formation of the final coupling products. These findings demonstrate that a self‐assembly strategy can efficiently steer surface reaction pathways and dynamics. 相似文献
17.
Daojin Zhou Shiyuan Wang Yin Jia Xuya Xiong Hongbin Yang Song Liu Jialun Tang Junming Zhang Dong Liu Lirong Zheng Yun Kuang Xiaoming Sun Bin Liu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(3):746-750
The binding strength of reactive intermediates with catalytically active sites plays a crucial role in governing catalytic performance of electrocatalysts. NiFe hydroxide offers efficient oxygen evolution reaction (OER) catalysis in alkaline electrolyte, however weak binding of oxygenated intermediates on NiFe hydroxide still badly limits its catalytic activity. Now, a facile ball‐milling method was developed to enhance binding strength of NiFe hydroxide to oxygenated intermediates via generating tensile strain, which reduced the anti‐bonding filling states in the d orbital and thus facilitated oxygenated intermediates adsorption. The NiFe hydroxide with tensile strain increasing after ball‐milling exhibits an OER onset potential as low as 1.44 V (vs. reversible hydrogen electrode) and requires only a 270 mV overpotential to reach a water oxidation current density of 10 mA cm?2. 相似文献
18.
Yi‐Feng Wang Wei Zhang Shu‐Ping Luo Dr. Bai‐Lin Li Ai‐Bao Xia Ai‐Guo Zhong Dr. Dan‐Qian Xu Dr. 《化学:亚洲杂志》2009,4(12):1834-1838
Generally, amine‐catalyzed enantioselective transformations rely on chiral enamine or unsaturated iminium intermediates. Herein, we report a protocol involving dual activation by an aromatic iminium and hydrogen‐bonding. An enantioselective aza‐Michael–Henry domino reaction of 2‐aminobenzaldehydes with nitroolefins has been developed through this protocol using primary amine thiourea catalysts to provide a variety of 3‐nitro‐1,2‐dihydroquinolines in moderate yields and with up to 90 % ee. The mechanism for the catalytic enantioselective reaction was confirmed by ESI mass spectrometric detection of the reaction intermediates. The products formed are substructures found in skeletons of important biological and pharmaceutical molecules. 相似文献
19.
Microwave and Ultrasound‐Assisted Synthesis of Thiosemicarbazones and Their Corresponding (4,5‐Substituted‐thiazol‐2‐yl)hydrazines
下载免费PDF全文
![点击此处可从《Journal of heterocyclic chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Simone Carradori Daniela Secci Melissa D'Ascenzio Paola Chimenti Adriana Bolasco 《Journal of heterocyclic chemistry》2014,51(6):1856-1861
Hantzsch cyclization of thiosemicarbazone intermediates is a very popular approach to the synthesis of substituted thiazoles. We developed a convenient microwave and ultrasound‐assisted method both for the synthesis of 1‐(alkyliden/cycloalkyliden/aryliden)thiosemicarbazone intermediates and their cyclization into (4,5‐substituted‐thiazol‐2‐yl)hydrazines. The search for optimal reaction conditions included the use of different catalysts (Lewis acids and resins) and solvents at discrete temperatures, pressures, and irradiation powers. Comparing yields, reaction times, and efforts proved that microwave and ultrasound‐assisted techniques outmatch conventional heating and have a remarkable influence on the synthesis. 相似文献
20.
Dipl.‐Chem. Pascal Nösel M.Sc. Tobias Lauterbach Dr. Matthias Rudolph Prof. Dr. A. Stephen K. Hashmi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(26):8634-8641
We report the gold‐catalyzed synthesis of highly functionalized iodofulvenes from iododialkynes under mild conditions. The catalytic cycle involves the formation of gold acetylides and vinylgold intermediates. These intermediates can then undergo an unprecedented iodine/gold exchange. This new pathway for catalyst transfer in dual gold catalysis opens up the possibility of highly regioselective transformations directed by the gold in the organogold intermediates. The resulting products are well suited for further metal‐mediated coupling reactions, allowing the synthesis of extended π‐systems. 相似文献