Showing papers on "Reagent published in 2002"
TL;DR: DMC possesses properties of nontoxicity and biodegradability which makes it a true green reagent to use in syntheses that prevent pollution at the source and avoiding the formation of undesirable inorganic salts as byproducts.
Abstract: Dimethyl carbonate (DMC) is a versatile compound that represents an attractive eco-friendly alternative to both methyl halides (or dimethyl sulfate) and phosgene for methylation and carbonylation processes, respectively. In fact, the reactivity of DMC is tunable: at T = 90 °C, methoxycarbonylations take place, whereas at higher reaction temperatures, methylation reactions are observed with a variety of nucleophiles. In the particular case of substrates susceptible to multiple alkylations (e.g., CH2-active compounds and primary amines), DMC allows unprecedented selectivity toward mono-C- and mono-N-methylation reactions. Nowadays produced by a clean process, DMC possesses properties of nontoxicity and biodegradability which makes it a true green reagent to use in syntheses that prevent pollution at the source. Moreover, DMC-mediated methylations are catalytic reactions that use safe solids (alkaline carbonates or zeolites), thereby avoiding the formation of undesirable inorganic salts as byproducts. The r...
930 citations
TL;DR: The method allows for consecutive cross-coupling processes in one pot, as exemplified by the efficient preparation of compound 12, and has been applied to the first synthesis of the cytotoxic marine natural product montipyridine 8.
Abstract: Simple iron salts such as FeCln, Fe(acac)n (n = 2,3) or the salen complex 4 turned out to be highly efficient, cheap, toxicologically benign, and environmentally friendly precatalysts for a host of cross-coupling reactions of alkyl or aryl Grignard reagents, zincates, or organomanganese species with aryl and heteroaryl chlorides, triflates, and even tosylates. An “inorganic Grignard reagent” of the formal composition [Fe(MgX)2] prepared in situ likely constitutes the propagating species responsible for the catalytic turnover, which occurs in many cases at an unprecedented rate even at or below room temperature. Because of the exceptionally mild reaction conditions, a series of functional groups such as esters, ethers, nitriles, sulfonates, sulfonamides, thioethers, acetals, alkynes, and −CF3 groups are compatible. The method also allows for consecutive cross-coupling processes in one pot, as exemplified by the efficient preparation of compound 12, and has been applied to the first synthesis of the cytotox...
664 citations
TL;DR: This paper presents a meta-analysis of C-C Bond Formation Using Recyclable Resin-Based Reagents and Catalysts using Immobilized Oxidants as a Carrier for Reagent Attachment to Polymer Supports, and some of the mechanisms behind this formation are described.
Abstract: Contents 1.0Introduction
1.1 Polystyrene Supports as Carriers for Reagents and Catalysts
1.2 Catalyst and Reagent Attachment to Polymer Supports
2.0C-C Bond Formation Using Recyclable Resin-Based Reagents and Catalysts
2.1 Palladium-Catalyzed Coupling Reactions
2.2 Other Transition Metal Catalyzed Reactions
2.3 Resin-Supported Olefin Metathesis
2.4 Resin-Mediated Cycloaddition Reactions
2.4.1 Diels-Alder Cycloadditions
2.4.2 Resin-Based Catalysts for 1,3-Dipolar Cycloadditions
2.5 Immobilized Chiral Ligands for Diethylzinc Additions to Aldehydes
2.6 Miscellaneous: Other C-C Bond Forming Reactions
3.0Immobilized Oxidants
3.1Oxidation with Immobilized Transition Metal Complexes
3.2 Alcohol Oxidation
3.3 Alkene Oxidation
3.3.1 Dihydroxylation
3.3.2 Epoxidation
3.3.3 Asymmetric Epoxidation
3.3.4 Other Alkene Oxidation Reactions
3.4 Potpourri: Other Immobilized Oxidants
4.0Immobilized Resin-Based Reductants
4.1 General Reduction Processes
4.2 Asymmetric Reduction of Ketones
4.3 Alkene Reduction
4.4 Resin-Based Tin and Germanium Reductants
5.0Conclusions
6.0Abbreviations
7.0Acknowledgments
8.0References
595 citations
TL;DR: In this paper, the authors reported the preparation of linear and branched DOPA-modified poly(ethylene glycol)s (PEG-DOPAs) containing one to four DOPA endgroups.
577 citations
TL;DR: In this paper, high surface area nickel−iron nanoparticles (1:3 Ni:Fe) have been studied as a reagent for the dehalogenation of trichloroethylene (TCE).
Abstract: High surface-area nickel−iron nanoparticles (1:3 Ni:Fe) have been studied as a reagent for the dehalogenation of trichloroethylene (TCE). Ni−Fe (0.1 g) nanoparticles reduced TCE from a 40-mL saturated aqueous solution (24 ppm) to <6 ppb in 120 min. The dehalogenation reaction, based on the surface area normalized rate constant, was 50−80 times slower using nanoiron or iron filings, respectively. On the bimetallic particles, the reaction occurs by nickel-catalyzed hydrodechlorination. As the iron actively corrodes, the cathodically protected nickel surface chemisorbs hydrogen ions. TCE adsorbed to the Ni surface is thus hydrogenated. This reaction competes kinetically with the evolution of molecular hydrogen. Hydrogenation of the C−Cl bond results in the formation of linear as well as branched saturated and unsaturated hydrocarbons. The final TCE degradation products are predominantly even-numbered saturated hydrocarbons, such as butane, hexane, and octane. The toxic dehalogenation products vinyl chloride ...
554 citations
TL;DR: The kinetic problem was solved by including cystamine as a "mediator" between the protein sulfhydryl and Ellman's reagent, as previously applied in an enzymatic thiol assay, and 4,4′-dithiodipyridine (DTDP) was used in place of Ellmans reagent.
Abstract: Since its introduction in 1959, Ellman's reagent (5,5′-dithio-bis(2-nitrobenzoic acid)) has been the favorite reagent for spectrophotometric measurement of protein sulfhydryls. Meanwhile however, evidence has accumulated that many protein sulfhydryls give an incomplete reaction with Ellman's reagent, even during prolonged assay times. In the present study, the kinetic problem was solved by including cystamine as a "mediator" between the protein sulfhydryl and Ellman's reagent, as previously applied in an enzymatic thiol assay [9]. As an alternative, 4,4′-dithiodipyridine (DTDP) was used in place of Ellman's reagent. Due to its small size, amphiphilic nature, and lack of charge, DTDP quickly reacts with poorly accessible protein sulfhydryls, without any catalysis by cystamine. The DTDP method and the Ellman/cystamine method were both optimized for maximal sensitivity, minimal sample consumption (detection limit 0.2 nmol mL–1, determination limit 0.6 nmol mL–1), and minimal assay time (5 min). In validation experiments, both methods gave identical results and the measured sulfhydryls/protein matched the expected values. Electronic supplementary material to this paper can be obtained by using the Springer Link server located at http://dx.doi.org/10.1007/s00216-002-1347-2.
515 citations
TL;DR: Fine-tuning of the reaction conditions allowed remarkably selective transformations within multifunctional substrates, elevating the status of this reagent to that of a highly useful and chemoselective oxidant.
Abstract: o-Iodoxybenzoic acid (IBX), a readily available hypervalent iodine(V) reagent, was found to be highly effective in carrying out oxidations adjacent to carbonyl functionalities (to form α,β-unsaturated carbonyl compounds) and at benzylic and related carbon centers (to form conjugated aromatic carbonyl systems). Mechanistic investigations led to the conclusion that these new reactions are initiated by single electron transfer (SET) from the substrate to IBX to form a radical cation which reacts further to give the final products. Fine-tuning of the reaction conditions allowed remarkably selective transformations within multifunctional substrates, elevating the status of this reagent to that of a highly useful and chemoselective oxidant.
379 citations
TL;DR: A new method for the cross-coupling reaction of Grignard reagents with alkyl chlorides, bromides, and tosylates has been developed by the use of a nickel catalyst in the presence of a diene as an additive.
Abstract: A new method for the cross-coupling reaction of Grignard reagents with alkyl chlorides, bromides, and tosylates has been developed by the use of a nickel catalyst in the presence of a diene as an additive. This reaction proceeds efficiently at 0−25 °C in THF using primary and secondary alkyl and aryl Grignard reagents. Nickel complexes bearing no phosphine ligands, such as NiCl2, Ni(acac)2, and Ni(COD)2, afford the coupling products in good yields, whereas NiCl2(PPh3)2 and NiCl2(dppp) were less effective. 1,3-Butadiene shows the highest activity as an additive for the present coupling reaction. A plausible reaction pathway was proposed.
293 citations
TL;DR: In this article, three-component (photosensitizer/gold/phase transfer reagent) nanoparticles were shown to generate singlet oxygen with enhanced quantum yields as compared to the free Pc.
Abstract: Gold nanoparticles have been stabilized with a phthalocyanine (Pc) photosensitizer. Transmission electron microscopy confirmed that the coated particles were in the 2-4 nm size regime. Energy-dispersive X-ray analysis revealed that the Pc macrocycle was present on the gold surface and also that the TOAB phase transfer reagent, used during the synthesis, was associated with the nanoparticles. The three-component (photosensitizer/gold/phase transfer reagent) nanoparticles were shown to generate singlet oxygen with enhanced quantum yields as compared to the free Pc. Additionally, the association of the transfer reagent promoted the solubility of the surface-bound hydrophobic sensitizer in polar solvents which would facilitate their systemic injection. The results suggest that these three-component structures have potential as a useful vehicle for the delivery of photosensitizer agents in photodynamic therapy.
292 citations
TL;DR: The results show that modified Fenton's reactions act through a reductive mechanism to degrade compounds that are not reactive with OH*, which broadens the scope of this process for hazardous waste treatment and remediation.
221 citations
TL;DR: A chromogenic reagent for cyanide determination in water based on the reaction of this anion with a squaraine derivative functionalized with ether chains has been developed.
TL;DR: The enantioselective addition reaction of terminal acetylenes and aldehydes mediated by Zn(OTf)2 and N-methyl ephedrine can be conducted with reagent grade solvent containing 84-1000 ppm H2O.
TL;DR: The utilization of 1 as a catalyst for amination of aryl chlorides and bromides with a variety of amine coupling partners under mild conditions is described, and the amination reactions show a remarkable insensitivity to oxygen and water.
TL;DR: The combination of P4S10 and hexamethyldisiloxane efficiently converts esters, lactones, amides, lactams, and ketones to their corresponding thiono derivatives and 3-oxoesters are converted to dithiolethiones by this reagent.
Abstract: The combination of P4S10 and hexamethyldisiloxane efficiently converts esters, lactones, amides, lactams, and ketones to their corresponding thiono derivatives. In the presence of elemental sulfur, 3-oxoesters are converted to dithiolethiones by this reagent. Yields are comparable to or superior to those obtained with Lawesson's reagent. The method has the advantage that reagent-derived byproducts may be removed by a simple hydrolytic workup or by filtration through silica gel, rather than by chromatography, as required for Lawesson's reagent.
TL;DR: The improvement in the decomposition levels of carbofuran reached by the combined processes in relation to the single oxidants, due to the generation of the very reactive hydroxyl radicals, is also established in every process.
TL;DR: In this article, a reaction mechanism was proposed for the interaction between Fenton reagents and the aromatic compounds, which involves the generation and redox cycle of hydroquinone-like intermediates in the Fenton reaction.
Abstract: Fenton degradation of malachite green (MG) catalyzed by various kinds of aromatic additives was examined. It was found that the aromatic additives exhibited catalysis immediately or after an induction period to accelerate the MG degradation in the Fenton reaction. EPR, GC−MS, and redox potential measurements were employed to obtain details of the reaction process. A reaction mechanism is proposed for the interaction between Fenton reagents (Fe2+/Fe3+, H2O2) and the aromatic compounds, which involves the generation and redox cycle of hydroquinone-like intermediates in the Fenton reaction. The Fenton reaction rates of MG after addition of various kinds of aromatic additives were in the following order: hydroquinone > salicylic acid > p-hydroxylbenzoic acid > m-hydroxylbenzoic acid > p-benzoquinone > carboxylic aromatics > amido aromatics, which is also quite consistent with their ability to be transformed into hydroquinone-like compounds. Hydroquinone-like compounds can react with ferric ions to regenerate...
TL;DR: The readily available and inexpensive BINOL in combination with Ti(O(i)Pr)(4) is found to catalyze the reaction of an alkynylzinc reagent with various types of aldehydes to generate chiral propargyl alcohols with 91-99% ee at room temperature.
TL;DR: In this paper, a novel nickel-catalyzed carboxylation of bis-1,3-dienes using carbon dioxide (CO2) was investigated in the presence of catalytic amounts of Ni(acac)2 and PPh3.
Abstract: Novel nickel-catalyzed carboxylation of bis-1,3-dienes using carbon dioxide (CO2) was investigated. In the presence of catalytic amounts of Ni(acac)2 and PPh3, various bis-1,3-dienes smoothly reacted with CO2 and an organozinc reagent (Et2Zn, Me2Zn, or Ph2Zn) under mild conditions. This catalytic carboxylation process was accompanied by carbocyclization of bis-1,3-diene followed by alkylation by an organozinc reagent to afford cyclic carboxylic acid derivatives in high yields with high regio- and stereoselectivities.
TL;DR: A new reagent for the enantioselective allylation of aliphatic aldehydes has been developed that is easily prepared in a single step from commercially available materials and may be stored without significant decomposition.
Abstract: A new reagent for the enantioselective allylation of aliphatic aldehydes has been developed. The reagent is easily prepared in a single step from commercially available materials and may be stored without significant decomposition. The reactivity of the reagent is attributed to strain-release Lewis acidity.
TL;DR: A simple electro-Fenton system has been used and tested for its efficiency in producing hydroxyl radicals and atrazine was chosen as a model organic compound as its reaction with OH(o) has been extensively studied.
TL;DR: Heterogeneous, catalytic, selective alkane functionalization can be used to modify polymer properties and indicates that scission of the main chain does not occur.
Abstract: The rhodium-catalyzed, terminal-selective borylation of alkanes has been used to modify polyolefins. The functionalization of two materials, polyethylethylene (PEE) of molecular weights 1200 and 37 000, was conducted by combining bis-pinacoldiboron and 2.5 mol % [Cp*RhCl2]2 in neat polymer and heating at 150 °C. This procedure causes the polymer and boron reagent to melt, the catalyst to dissolve, and the reaction to form material with boryl groups at the terminal position of the polymer side chains. Oxidation of the borylated material generated polymers with hydroxyl groups at the terminal position of the side chains. The functionalization was conducted at various ratios of boron reagent to monomer. The resulting borylated and subsequent hydoxylated materials were characterized by 1H and 13C NMR spectroscopy, as well as MALDI-MS and GPC. Little change in polymer molecular weight and polydispersity was observed, and these data indicate that scission of the main chain does not occur. Measurements of the Tg...
TL;DR: Chemoselective acetalization of an aldehyde in the presence of ketone, unsymmetrical acetal formation, shorter reaction times, mild reaction conditions, the stability of acid-sensitive protecting groups, high efficiencies, facile isolation of the desired products, and the catalytic nature of the reagent make the present methodology a practical alternative.
Abstract: Acyclic and cyclic acetals of various carbonyl compounds were obtained in excellent yields under a mild reaction condition in the presence of trialkyl orthoformate and a catalytic amount of tetrabutylammonium tribromide (TBATB) in absolute alcohol. Chemoselective acetalization of an aldehyde in the presence of ketone, unsymmetrical acetal formation, shorter reaction times, mild reaction conditions, the stability of acid-sensitive protecting groups, high efficiencies, facile isolation of the desired products, and the catalytic nature of the reagent make the present methodology a practical alternative.
TL;DR: The indium hydride generated from NaBH4 and InCl3, is a promising candidate of alternative to Bu3SnH and catalytic performance in the dehalogenation of alkyl and aryl halides, intramolecular cyclization and intermolecular coupling reaction are noteworthy.
Abstract: The indium hydride generated from NaBH4 and InCl3, is a promising candidate of alternative to Bu3SnH. In particular, the catalytic performance of InCl3 in the dehalogenation of alkyl and aryl halides, intramolecular cyclization and intermolecular coupling reaction are noteworthy.
TL;DR: All reactions were carried out under an atmosphere of argon in flame-dried glassware with reaction solvents: THF, Et2O, CH2Cl2 were purified by passage over activated alumina.
Abstract: General Information. All reactions were carried out under an atmosphere of argon in flame-dried glassware. The reaction solvents: THF, Et2O, CH2Cl2 were purified by passage over activated alumina. Reagents were used as received from the manufacturer unless otherwise stated. Flash chromatography was carried out using EM reagent silica gel 60 (230-400 mesh). Analytical thin layer chromatography was performed on EM Reagent 0.25 mm silica gel 60-F plates. All TLC plates were visualized by UV fluorescence quenching and were stained with either p-anisaldehyde or ceric ammonium molybdate (CAM). Optical rotations were measured on a Jasco DIP-0181 digital polarimeter with a sodium lamp and are reported as follows: [α]λ °C (c=g/100 mL solvent). Infrared spectra were recorded on a Perkin-Elmer 1600 series FT-IR spectrometer. H-NMR spectra were recorded on a Varian Inova-500 (500 MHz) spectrometer and are reported in ppm using solvent as an internal standard (CDCl3=7.26 ppm). Data are reported as: [δ shift]([s= singlet, d=doublet, t=triplet, q=quartet, m=multiplet, b=broad], [integration], and [J=coupling constant in Hz]). Proton decoupled C-NMR spectra were recorded on a Varian Mercury 400 (100 MHz) spectrometer and are reported in ppm using solvent as internal standard (CDCl3=77.0 ppm). Low and high resolution mass spectra were obtained at the Harvard University Mass Spectrometry Laboratory.
Patent•
15 Jan 2002
TL;DR: In this paper, a quantitative analyzing method for electrochemically measuring the concentration of a component being examined in a sample liquid introduced to a reagent layer (30) containing a reactive reagent reacting on that component using a sensor comprising the reagent layers and a first electrode (22) and a second electrode (23) for applying a voltage between the first and second electrodes (22, 23) is presented.
Abstract: A quantitative analyzing method for electrochemically measuring the concentration of a component being examined in a sample liquid introduced to a reagent layer (30) containing a reagent reacting on that component using a sensor comprising the reagent layer (30), and a first electrode (22) and a second electrode (23) for applying a voltage to the reagent layer (30). The method comprises a step for applying a voltage between the first electrode (22) and the second electrode (23) and measuring a current flowing between the first and second electrodes (22, 23), a step for deriving a parameter based on a measured current, and a step for judging the state of a sample liquid introduced to the reagent layer (30) based on the parameter and at least one predetermined constant.
TL;DR: In situ generation of CuH ligated by Takasago's new nonracemic ligand, DTBM-SEGPHOS, leads to an especially reactive reagent capable of effecting asymmetric hydrosilylation of heteroaromatic (H) ketones under very mild conditions.
Patent•
07 May 2002
TL;DR: In this paper, an ammonium salt of the carboxylic acid is heated in the presence of an organic reagent to split the salt and form the acid or the corresponding ester.
Abstract: Processes for preparing carboxylic acids and derivatives thereof in which an ammonium salt of the carboxylic acid is heated in the presence of an organic reagent to split the salt and form the acid or, where the organic reagent is an esterifying agent, the corresponding ester. Both the acid and the ester may be dehydrated to form unsaturated counterparts.
Patent•
22 Nov 2002
TL;DR: In this paper, an automated staining system and a reagent container are designed for use with the automatic staining apparatus, which includes a two-dimensional data element containing reagent information.
Abstract: An automated staining system and a reagent container designed for use with the automated staining apparatus. The reagent container includes a reagent containment section capable of containing a volume of a reagent. The reagent containment section includes an upper wall and a base wall that are spaced apart along an axis. The base wall includes a well having a nadir that is aligned axially with an access opening in the upper wall so that a reagent probe entering the opening parallel to said axis will travel toward the nadir. In another aspect of the invention, the reagent container may include a two-dimensional data element containing reagent information. The staining apparatus may include one removable drawer for holding reagent containers and another removable drawer holding slides.
TL;DR: This work reports on stereoselective reagent-controlled iodolactonizations applying a new method using a combination of ICl and a primary amine leading to the highest selectivities known so far.