Showing papers on "Reagent published in 2012"
TL;DR: This mild, operationally simple, chemoselective, and scalable difluoromethylation method is compatible with a range of nitrogen-containing heteroarene substrates of varying complexity as well as select classes of conjugated π-systems and thiols.
Abstract: Molecular scaffolds containing alkylfluorine substituents are desired in many areas of chemical research from materials to pharmaceuticals. Herein, we report the invention of a new reagent (Zn(SO2CF2H)2, DFMS) for the innate difluoromethylation of organic substrates via a radical process. This mild, operationally simple, chemoselective, and scalable difluoromethylation method is compatible with a range of nitrogen-containing heteroarene substrates of varying complexity as well as select classes of conjugated π-systems and thiols. Regiochemical comparisons suggest that the CF2H radical generated from the new reagent possesses nucleophilic character.
472 citations
TL;DR: The G2 silanes are the best candidates for preparing stable amine-functionalized surfaces and AEAPTES results in more reproducible silane layers in the vapor phase due to its lower sensitivity to water content in the reaction systems.
Abstract: Five functional silanes—3-aminopropyltriethoxysilane (APTES), 3-aminopropyltrimethoxysilane (APTMS), N-(2-aminoethyl)-3-aminopropyltriethoxysilane (AEAPTES), N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEAPTMS), and N-(6-aminohexyl)aminomethyltriethoxysilane (AHAMTES)—were assessed for the preparation of hydrolytically stable amine-functionalized silica substrates. These can be categorized into three groups (G1, G2, and G3) based on the intramolecular coordinating ability of the amine functionality to the silicon center. Silanizations were carried out in anhydrous toluene as well as in the vapor phase at elevated temperatures. Aminosilane-derived layers prepared in solution are multilayers in nature, and those produced in the vapor phase have monolayer characteristics. In general, vapor-phase reactions are much less sensitive to variations in humidity and reagent purity, are more practical than the solution-phase method, and generate more reproducible results. Intramolecular catalysis by the amine fun...
370 citations
TL;DR: Inexpensive nickel-bipyridine complexes were found to be active for the trifluoromethylthiolation of aryl iodides and aryL bromides at room temperature using the convenient [NMe(4]][SCF(3)] reagent.
Abstract: Inexpensive nickel–bipyridine complexes were found to be active for the trifluoromethylthiolation of aryl iodides and aryl bromides at room temperature using the convenient [NMe4][SCF3] reagent.
292 citations
TL;DR: A powerful Fe(III)/NaBH(4)-mediated free radical hydrofluorination of unactivated alkenes is disclosed using Selectfluor reagent as a source of fluorine and resulting in exclusive Markovnikov addition.
Abstract: A powerful Fe(III)/NaBH4-mediated free radical hydrofluorination of unactivated alkenes is disclosed using Selectfluor reagent as a source of fluorine and resulting in exclusive Markovnikov addition In contrast to the traditional and unmanageable free radical hydrofluorination of alkenes, the Fe(III)/NaBH4-mediated reaction is conducted under exceptionally mild reaction conditions (0 °C, 5 min, CH3CN/H2O) The reaction can be conducted open to the air and with water as a cosolvent and demonstrates an outstanding substrate scope and functional group tolerance
238 citations
TL;DR: The synthesis and characterization of three highly active dimagnesium catalysts for the copolymerization of cyclohexene oxide and carbon dioxide, active under just 1 atm of carbon dioxide pressure, are reported.
Abstract: The synthesis and characterization of three highly active dimagnesium catalysts for the copolymerization of cyclohexene oxide and carbon dioxide, active under just 1 atm of carbon dioxide pressure, are reported. The catalysts have turnover numbers up to 6000 and turnover frequencies of up to 750 h–1. These values are, respectively, 75 and 20 times higher than those of the other three known magnesium catalysts. Furthermore, the catalysts operate at 1/500th the loading of the best reported magnesium catalyst. The catalyst selectivities are excellent, yielding polymers with 99% carbonate repeat units and >99% selectivity for copolymer. Using a dimagnesium bis(trifluoroacetate) catalyst, and water as a renewable chain transfer reagent, poly(cyclohexene carbonate) polyols are synthesized with high selectivity.
237 citations
TL;DR: A mild and practical protocol for the copper-mediated trifluoromethylation of aryl and heteroaryl boronic acids using NaSO(2)CF(3) (Langlois' reagent) and TBHP is described.
177 citations
TL;DR: A metal-free N-hydroxyphthalimide catalyzed aerobic oxidative cleavage of olefins has been developed, showing good economical and environmental advantages and a plausible mechanism is proposed.
177 citations
TL;DR: Methyltrioxorhenium acts as a catalyst for the direct electrophilic trifluoromethylation of various aromatic and hetero-aromatic compounds using the hypervalent iodine reagent 1-(trifluorsocyl)-1,2-benziodoxol-3(1H)-one (1).
Abstract: Methyltrioxorhenium acts as a catalyst (5–10 mol %) for the direct electrophilic trifluoromethylation of various aromatic and heteroaromatic compounds using the hypervalent iodine reagent 1-(trifluoromethyl)-1,2-benziodoxol-3(1H)-one (1). The products are formed in up to 77% yield. Mixtures of regioisomers are obtained in the case of substituted and heteroaromatic substrates. The reaction, typically carried out in chloroform solvent at 70 °C, shows a significant induction period. Monitoring by EPR shows the involvement of radical species. A small kinetic deuterium isotope effect of 1.3 is observed for benzene.
169 citations
TL;DR: A new fluorescent chemosensor based on a helical imide as fluorophore and a cyclen moiety as ionophore was synthesized, which not only showed enhanced fluorescent responses in the presence of Zn, Cd, and Hg but also could simultaneously and selectively distinguish the three cations in a simulated physiological condition with the help of cysteine as an auxiliary reagent.
Abstract: A new fluorescent chemosensor based on a helical imide as fluorophore and a cyclen moiety as ionophore was synthesized, which not only showed enhanced fluorescent responses in the presence of Zn2+, Cd2+, and Hg2+ but also could simultaneously and selectively distinguish the three cations in a simulated physiological condition with the help of cysteine as an auxiliary reagent.
168 citations
TL;DR: It is reported that a simple iron porphyrin complex catalyzes the cyclopropanation of styrenes, enynes, and dienes under the demanding conditions necessary for the in situ generation of diazomethane from a water-soluble diazald derivative.
Abstract: Diazomethane is a common and versatile reagent in organic synthesis whose broader use is generally impeded by its explosiveness and toxicity. Here we report that a simple iron porphyrin complex catalyzes the cyclopropanation of styrenes, enynes, and dienes under the demanding conditions [aqueous 6 molar potassium hydroxide (KOH) solution, open to air] necessary for the in situ generation of diazomethane from a water-soluble diazald derivative. A biphasic reaction medium arising from the immiscibility of the olefin substrates with water appears essential to the overall efficiency of the process. The work we describe highlights an approach to catalysis with untoward reactive intermediates, in which the conditions for their generation under operationally safe regimes dictate catalyst selection.
165 citations
TL;DR: P Powder X-ray diffraction of the particles revealed that they were highly crystalline despite their very short time under hydrothermal flow conditions, and gas sensing substrates showed excellent selectivity toward ethanol.
Abstract: A rapid, clean, and continuous hydrothermal route to the synthesis of ca. 14 nm indium oxide (In2O3) nanoparticles using a superheated water flow at 400 °C and 24.1 MPa as a crystallizing medium and reagent is described. Powder X-ray diffraction (XRD) of the particles revealed that they were highly crystalline despite their very short time under hydrothermal flow conditions. Gas sensing substrates were prepared from an In2O3 suspension via drop-coating, and their gas sensing properties were tested for response to butane, ethanol, CO, ammonia, and NO2 gases. The sensors showed excellent selectivity toward ethanol, giving a response of 18–20 ppm.
TL;DR: A new rhodamine-based receptor, derivatized with an additional fluorophore (quinoline), was synthesized for selective recognition of Hg(2+) and Cr(3+) in an acetonitrile/HEPES buffer medium and allowed detection of these two ions by monitoring changes in absorption and the fluorescence spectral pattern.
Abstract: A new rhodamine-based receptor, derivatized with an additional fluorophore (quinoline), was synthesized for selective recognition of Hg(2+) and Cr(3+) in an acetonitrile/HEPES buffer medium of pH 7.3. This reagent could be used as a dual probe and allowed detection of these two ions by monitoring changes in absorption and the fluorescence spectral pattern. In both instances, the extent of the changes was significant enough to allow visual detection. More importantly, the receptor molecule could be used as an imaging reagent for detection of Hg(2+) and Cr(3+) uptake in live human cancer cells (MCF7) using laser confocal microscopic studies. Unlike Hg(ClO(4))(2) or Hg(NO(3))(2) salts, HgCl(2) or HgI(2) failed to induce any visually detectable change in color or fluorescence upon interaction with L(1) under identical experimental conditions. Presumably, the higher covalent nature of Hg(II) in HgCl(2) or HgI(2) accounts for its lower acidity and its inability to open up the spirolactam ring of the reagent L(1). The issue has been addressed on the basis of the single-crystal X-ray structures of L(1)·HgX(2) (X(-) = Cl(-) or I(-)) and results from other spectral studies.
TL;DR: DMSO could serve as an effective methylthiolation reagent for the synthesis of heterocyclic methyl thioethers in the form of a Lewis acid catalyzed reaction between heteroarenes and thiols.
Abstract: A Lewis acid (AgI, NiII, or FeII) catalyzed, CuII-mediated thiolation reaction between heteroarenes and thiols was achieved with good yield under base-free conditions. DMSO could serve as an effective methylthiolation reagent for the synthesis of heterocyclic methyl thioethers.
TL;DR: The C-X bond of α-haloketones is smoothly trifluoromethylated with the fluoroform-derived CuCF(3) reagent recently developed in the laboratories, providing an unprecedentedly easy entry to valuable 2,2,2-trifluoroethylketones.
Abstract: The C–X bond (X = Br, Cl) of α-haloketones is smoothly trifluoromethylated with the fluoroform-derived CuCF3 reagent recently developed in our laboratories. This is the first nucleophilic α-trifluoromethylation reaction of carbonyl compounds and a rare example of CF3–C(sp3) coupling. The transformation employs only low-cost chemicals and cleanly occurs in up to 99% yield at room temperature, thereby providing an unprecedentedly easy entry to valuable 2,2,2-trifluoroethylketones.
TL;DR: The effect of surface modifications on antibacterial activity of ZnO under ambient illumination is investigated, and it is found that nanoparticles coated with different surface modifying reagents could exhibit higher or lower toxicity compared to bare ZNO, depending on the surface modifyingReagent used.
Abstract: In various practical applications, nanomaterials typically have functionalized surfaces. Yet, the studies of toxicity and antibacterial activity of functionalized nanoparticles are scarce. We investigated the effect of surface modifications on antibacterial activity of ZnO under ambient illumination, and we found that nanoparticles coated with different surface modifying reagents could exhibit higher or lower toxicity compared to bare ZnO, depending on the surface modifying reagent used. Different surface modifying reagent molecules resulted in differences in the release of Zn2+ ions and the production of reactive oxygen species (ROS). However, the antibacterial activity did not correlate with the ROS levels or the Zn2+ ion release. One of the surface-modified ZnO samples exhibited significantly lower Zn2+ ion release while at the same time exhibiting improved antibacterial activity. In all cases, damage of the cell wall membranes and/or changes in the membrane permeability have been observed, together with the changes in ATR-FTIR spectra indicating differences in protein conformation. Mechanisms of antibacterial activity are discussed.
TL;DR: A new approach to direct intermolecular allylic amination has been developed using metal-free conditions at room temperature using hypervalent iodine(III) reagent as an oxidant and bistosylimide as a nitrogen source.
Abstract: A new approach to direct intermolecular allylic amination has been developed using metal-free conditions at room temperature. The reaction employs a hypervalent iodine(III) reagent as an oxidant and bistosylimide as a nitrogen source. A series of different allylic aminations are presented with up to a 99% yield. Mechanistic studies including isotope labeling and Hammett correlation suggest that depending on the substrate structure two different mechanisms can be operating.
15 Jul 2012
TL;DR: CNTs/λ-Fe(2)O(3) hybrid is a promising magnetic nanomaterial for preconcentration and separation of organic pollutants for environmental remediation and a new photocatalytic regeneration technology can be enabled by the high nanoscale iron oxide loading.
Abstract: We report a simple and easy method to fabricate magnetic carbon nanotubes (CNTs) by Fenton's reagent method without the addition of any cations. H(2)O(2) was added slowly into the FeSO(4) solution mixed with purified CNTs, and the resulting reactants were placed into a quartz tube to undergo heat treatment under a nitrogen/hydrogen flow. Iron oxide (Fe(2)O(3)) nanoparticles were uniformly dispersed on CNTs without any pretreatment such as strong acid or covalent functionalization processes. The as-produced magnetic CNTs were used as an adsorbent for removal of methyl orange (MO) dye from aqueous solutions. Adsorption experiments indicated that the magnetic CNTs have good adsorption capacity (q(e)) of MO (28 mg/g). The Freundlich isotherm model fitted the experiment data better than the Langmuir isotherm mode. The mean energy of adsorption was calculated as 3.72 kJ/mol based on the Dubinin-Radushkevich model, which suggests that the removal process was dominated by physical adsorption. Kinetic regression results showed that the adsorption kinetics was more accurately represented by a pseudo second-order model. Intra-particle diffusion was involved in the adsorption process, but it was not the only rate-controlling step. More importantly, a new photocatalytic regeneration technology can be enabled by the high nanoscale iron oxide loading (50%). The magnetic CNT adsorbents could be effectively and quickly separated by applying an external magnetic field and regenerated by UV photocatalysis. Therefore, CNTs/λ-Fe(2)O(3) hybrid is a promising magnetic nanomaterial for preconcentration and separation of organic pollutants for environmental remediation.
TL;DR: 3-Methyl-1-sulfonic acid imidazolium nitrate ([Msim]NO(3) as a new Brønsted acidic ionic liquid and nitrating agent was prepared and used for the efficient nitration of aromatic compounds.
Abstract: 3-Methyl-1-sulfonic acid imidazolium nitrate ([Msim]NO3) as a new Bronsted acidic ionic liquid and nitrating agent was prepared and used for the efficient nitration of aromatic compounds (even aniline derivatives). The dramatic effect of this reagent by in situ generation of nitrogen dioxide as a radical on aromatic compounds to give nitroarenes has been studied.
TL;DR: Iron-copper cooperative catalysis is shown to be effective for an alkene-Grignard exchange reaction and alkylmagnesiation of alkynes and isomerization of Grignard reagents from 2-alkyl to 1-alksyl catalyzed by Fe-Cu also is applicable as the first 1-alky Grignards formation step.
Abstract: Iron–copper cooperative catalysis is shown to be effective for an alkene–Grignard exchange reaction and alkylmagnesiation of alkynes. The Grignard exchange between terminal alkenes (RCH═CH2) and cyclopentylmagnesium bromide was catalyzed by FeCl3 (2.5 mol %) and CuBr (5 mol %) in combination with PBu3 (10 mol %) to give RCH2CH2MgBr in high yields. 1-Alkyl Grignard reagents add to alkynes in the presence of a catalyst system consisting of Fe(acac)3, CuBr, PBu3, and N,N,N′,N′-tetramethylethylenediamine to give β-alkylvinyl Grignard reagents. The exchange reaction and carbometalation take place on iron, whereas copper assists with the exchange of organic groups between organoiron and organomagnesium species through transmetalation with these species. Sequential reactions consisting of the alkene–Grignard exchange and the alkylmagnesiation of alkynes were successfully conducted by adding an alkyne to a mixture of the first reaction. Isomerization of Grignard reagents from 2-alkyl to 1-alkyl catalyzed by Fe–Cu...
TL;DR: In this article, high-porosity gallium oxide was synthesized by reconstructing its surface and body with mesopores and macropores, which achieved a 300% higher CO2 adsorption capacity, as well as a 200% increased surface area, compared to the bulk nanoparticles.
Abstract: Highly porous gallium oxide was synthesized by reconstructing its surface and body with mesopores and macropores. For the first time, the efficient photocatalytic conversion of CO2 into a high energy carrier, CH4, using the porous gallium oxide was realized without any co-particle or sacrificial reagent. The enhanced photocatalytic activity is mainly attributed to the 300% higher CO2 adsorption capacity, as well as the 200% increased surface area, compared to the bulk nanoparticles. Furthermore, we propose the new reaction pathway based on the result that the carbon dioxide was converted directly into methane without going through carbon monoxide intermediates.
TL;DR: For the title reaction, O(2), the ideal oxidant, was used as the only oxidizing reagent and the dimer intermediate and isotopic labeling control experiments with (18)O(2) partially disclosed the reaction mechanism.
Abstract: Clear cut: For the title reaction, O(2), the ideal oxidant, was used as the only oxidizing reagent. The dimer intermediate (see scheme) and isotopic labeling control experiments with (18)O(2) partially disclosed the reaction mechanism.
TL;DR: A direct metal-free amination of arylalkynes has been developed, which proceeds by reaction of the terminal alkyne with the hypervalent iodine reagent PhI(OAc)NTs(2) within a single-step operation, which provides rapid access to the important class of ynamides.
Abstract: A direct metal-free amination of arylalkynes has been developed, which proceeds by reaction of the terminal alkyne with the hypervalent iodine reagent PhI(OAc)NTs2 within a single-step operation. This unprecedented intermolecular C–H to C–N bond conversion provides rapid access to the important class of ynamides. In addition to the title reaction, the related transformation between alkylated alkynes and the iodine(III) reagent is also discussed.
TL;DR: A copper-catalyzed trifluoromethylation reaction to prepare various branched allylic CF3 products from allylsilanes is described, finding that this reaction is broad in scope and tolerant of various functional groups.
Abstract: The trifluoromethylation reactions are performed with Togni reagent (II) to give branched allylic trifluoromethylated products.
TL;DR: It is surmised that a transition-metal-catalyzed 2,2,2-trifluoroethylation using readily available trifluoromethyl iodide (CF3CH2I) and organoboronic acids could provide an alternative method for the preparation of (2,1,2 -trifloroethyl)arenes; a process that has not been reported to date.
Abstract: Aryl boronic acids are efficiently converted into the corresponding (trifluoroethyl)arenes by treatment with the readily available reagent CF3CH2I (19 examples).
TL;DR: Kinetically controlled labeling offers a high potential for addressing a broad range of native proteins and peptides in a site-selective fashion and complements the portfolio of recombinant techniques or chemoenzymatic approaches.
TL;DR: The iron-catalyzed 2-arylbenzoxazole formation from o-nitrophenols and benzylic alcohols using hydrogen transfer is described and tolerated a wide range of functionalities.
TL;DR: The results of the three-step process of biomass degradation show the necessity of applying a chemical pretreatment such as oxidation with Fenton's reagent, while the coagulation of residual Fe(3+) ions is not required for high biogas production.
TL;DR: In this article, a halogen-free Bronsted acidic deep eutectic solvents (DES) were prepared by mixing new quaternary ammonium methanesulfonate salts with p-toluenesulfonic acid (PTSA).
TL;DR: The solid-state structures of the chloride and less sensitive hydrogen sulfate were determined by single-crystal X-ray diffraction in an effort to provide some insight into the different properties of the materials.
Abstract: Imidazole-1-sulfonyl azide hydrochloride, an inexpensive and effective diazotransfer reagent, was recently found to be impact sensitive. To identify safer-to-handle forms of this reagent, several different salts of imidazole-1-sulfonyl azide were prepared, and their sensitivity to heat, impact, friction, and electrostatic discharge was quantitatively determined. A number of these salts exhibited improved properties and can be considered safer than the aforementioned hydrochloride. The solid-state structures of the chloride and less sensitive hydrogen sulfate were determined by single-crystal X-ray diffraction in an effort to provide some insight into the different properties of the materials.