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131.
Soluble and insoluble polystyrene-bound triphenylarsine reagents have been prepared from 4-styryldiphenylarsine. The utility of these reagents as ligands for palladium in Suzuki cross-coupling reactions is demonstrated. In these applications, the use of polymeric triphenylarsine simplifies the purification of the coupled product and allows for the ligand to be recycled. Furthermore, the soluble polymeric arsine reagent permits the palladium catalyst to be recovered and reused. 相似文献
132.
A sheath-flow capillary electrophoresis-mass spectrometry (CE-MS) system utilizing a fully integrated large-bore stainless-steel emitter electrode tapered at the end for micro-ionspray operation has been developed and evaluated. A separation capillary with an outer diameter of up to 360 microm was inserted into the electrode thus forming a void volume of less than 15 nL between the capillary end and the electrospray ionisation (ESI) tip. The sheath liquid, usually methanol-water (80:20) with 0.1% formic acid for positive ion mode or methanol for negative ion mode, was delivered at 0.5-1.0 microL/min. Unlike previously reported CE-MS interfaces, the CE-MS probe was incorporated directly onto an Applied Biosystems/MDS SCIEX orthogonal-spray Turbo "V" ion source for ease of use and automatic operation. This integration enables fast and facile coupling and replacement of the separation capillary without interrupting the ion source configuration, and the sheath liquid supply. The reusable electrospray electrode was precisely fabricated and aligned with the length of the nebulizing gas tube for improved reproducibility. Automation was achieved through software control of both CE and tandem MS (MS/MS) for unattended batch sample analysis. The system was evaluated for attomole- to low femtomole-level profiling of model peptides and protein mixtures, bisphosphates, as well as antiviral nucleosidic drugs in cellular extracts. 相似文献
133.
ent‐Erythramine ((?)‐ 1 ), the enantiomer of the alkaloid erythramine, was prepared in 15 steps from known compounds. The first of three pivotal bond‐forming steps in the synthesis was a Suzuki–Miyaura cross‐coupling reaction of the starting materials to give a bis‐silyl ether. The second involved silver(I)‐induced electrocyclic ring opening of the gem‐dichlorocyclopropane formed in the next step and trapping of the ensuing π‐allyl cation by the tethered nitrogen atom to give, following cleavage of the allyloxycarbonyl protecting group, an approximately 5:6 mixture of the chromatographically separable diastereoisomeric spirocyclic products. In the third critical bond‐forming reaction, the iodide formed from one of the diastereoisomers underwent a radical‐addition/elimination reaction sequence that led to (?)‐ 1 in 89 % yield. The application of the same sequence of transformations to the other diastereoisomer afforded 3‐epi‐(+)‐erythramine (3‐epi‐(+)‐ 1 ). 相似文献
134.
The reactivity of SiO produced in a SiCl4/O2 plasma with the surface of a depositing silicon oxide film has been measured to be near zero for surface temperatures of 25–500 °C using the IRIS technique (imaging of radicals interacting with surfaces). This method combines spatially resolved laser-induced fluorescence with molecular beam techniques. The SiO desorbs from the surface with a spatial distribution consistent with a cosine angular distribution. 相似文献
135.
Reactions of oxygenated cobalt(II) complexes. IX. Oxidative properties of tetrakis(ethylenediamine)-μ-peroxo-μ-hydroxo-dicobalt(III) 1 VIII s. [1]. [(en)2Co(O2, OH)Co(en)2]3+ ( a ) reacts with I? in acidic aqueous solution according to: CoIII(O2, OH)CoIII + 21? + 5H+ ? 2CoIII + 3H2O + I2. Using I? in excess first order rate constants are obtained which, to a first approximation, are independent of [I?]. Comparison with kinetic data of deoxygenation of [(en)2Co(O2, OH)Co(en)2]3+ under analogous conditions suggests that both reactions have the same rate determining step. The singly bridged species [(en)2(H2O)CoO2Co(H2O) (en)2]4+ is shown to be the reactive intermediate in the iodide oxidation (Schema 2). 相似文献
136.
C−N Bond Formation from a Masked High‐Valent Copper Complex Stabilized by Redox Non‐Innocent Ligands
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Jérémy Jacquet Pauline Chaumont Geoffrey Gontard Dr. Maylis Orio Dr. Hervé Vezin Dr. Sébastien Blanchard Dr. Marine Desage‐El Murr Prof. Louis Fensterbank 《Angewandte Chemie (International ed. in English)》2016,55(36):10712-10716
The reactivity of a stable copper(II) complex bearing fully oxidized iminobenzoquinone redox ligands towards nucleophiles is described. In sharp contrast with its genuine low‐valent counterpart bearing reduced ligands, this complex performs high‐yielding C?N bond formations. Mechanistic studies suggest that this behavior could stem from a mechanism akin to reductive elimination occurring at the metal center but facilitated by the ligand: it is proposed that a masked high oxidation state of the metal can be stabilized as a lower copper(II) oxidation state by the redox ligands without forfeiting its ability to behave as a high‐valent copper(III) center. These observations are substantiated by a combination of advanced EPR spectroscopy techniques with DFT studies. This work sheds light on the potential of redox ligands as promoters of unusual reactivities at metal centers and illustrates the concept of masked high‐valent metallic species. 相似文献
137.
One‐pot synthesis of a new high vinyl content hybrid silica monolith dedicated to nanoliquid chromatography
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El‐Debs Racha Pauline Gay Vincent Dugas Claire Demesmay 《Journal of separation science》2016,39(5):842-850
A new vinyltrimethoxysilane‐based hybrid silica monolith was developed and used as a reversed‐phase capillary column. The synthesis of this rich vinyl hybrid macroporous monolith, by cocondensation of vinyltrimethoxysilane with tetramethoxysilane, was investigated using an unconventional (formamide, nitric acid) porogen/catalyst system. A macroporous hybrid silica monolith with 80% in mass of vinyltrimethoxysilane in the feeding silane solution was obtained and compared to a more conventional low vinyl content hybrid monolith with only of 20% vinyltrimethoxysilane. Monoliths were characterized by scanning electron microscopy, 29Si nuclear magnetic resonance spectroscopy and N2 adsorption–desorption. About 80% of the vinyl precursor was incorporated in the final materials, leading to 15.9 and 61.5% of Si atoms bonded to vinyl groups for 20% vinyltrimethoxysilane and 80% vinyltrimethoxysilane, respectively. The 80% vinyltrimethoxysilane monolith presents a lower surface area than 20% vinyltrimethoxysilane (159 versus 551 m2/g), which is nevertheless compensated by a higher vinyl surface density. Chromatographic properties were evaluated in reversed‐phase mode. Plots of ln(k) versus percentage of organic modifier were used to assess the reversed‐phase mechanism. Its high content of organic groups leads to high retention properties. Column efficiencies of 170 000 plates/m were measured for this 80% vinyltrimethoxysilane hybrid silica monolith. Long capillary monolithic columns (90 cm) were successfully synthesized (N = 120 000). 相似文献
138.
The development of C1-symmetric aminosulfoximines, their highly modular synthesis, and their application in enantioselective copper-catalyzed Mukaiyama-type aldol reactions between pyruvates and enolsilanes is described. In this context, the influence of the ligand architecture as well as the optimization of the reaction conditions are discussed. In detail, the dependence of the catalyst efficiency on the solvent, the metal source and the temperature are reported, and an interesting additive effect is highlighted. Furthermore, the substrate scope will be presented. With the optimized catalyst system, a number of aldol products with quaternary stereogenic centers have been obtained in high yields and with enantiomeric excesses up to 99 %. 相似文献
139.
Intramolecular (4+3) Cycloadditions of Pyrroles and Application to the Synthesis of the Core of Class II Galbulimima Alkaloids
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Jiayun He Zhihua Chen Wenfei Li Kam‐Hung Low Prof. Dr. Pauline Chiu 《Angewandte Chemie (International ed. in English)》2018,57(19):5253-5256
The first intramolecular (4+3) cycloaddition of pyrroles with epoxy enolsilanes as the electrophiles was developed and used to generate optically‐enriched cycloadducts containing the nortropane substructure in good yields. Using this pyrrole cycloaddition as the key step, we achieved the asymmetric synthesis of a nortropane compound bearing the BCDEF ring structure common to the Class II galbulimima alkaloids. 相似文献
140.
Chemoselective Activation of Diethyl Phosphonates: Modular Synthesis of Biologically Relevant Phosphonylated Scaffolds
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Dr. Pauline Adler Dr. Amandine Pons Dr. Jing Li Jörg Heider Bogdan R. Brutiu Prof. Dr. Nuno Maulide 《Angewandte Chemie (International ed. in English)》2018,57(40):13330-13334
Phosphonates have garnered considerable attention for years owing to both their singular biological properties and their synthetic potential. State‐of‐the‐art methods for the preparation of mixed phosphonates, phosphonamidates, phosphonothioates, and phosphinates rely on harsh and poorly selective reaction conditions. We report herein a mild method for the modular preparation of phosphonylated derivatives, several of which exhibit interesting biological activities, that is based on chemoselective activation with triflic anhydride. This procedure enables flexible and even iterative substitution with a broad range of O, S, N, and C nucleophiles. 相似文献