Showing papers on "Alkylation published in 2001"
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TL;DR: The use of commercially available polymeric ion-exchange resins for a range of industrially important transformations is described in this paper, including alkylation, transalkylation, isomerization, oligomerization and nitration.
Abstract: In this review article, we describe the use of commercially available polymeric ion-exchange resins for a range of industrially important transformations. Recent developments both on the materials design and applications will be described. Examples of high catalytic activity will be described in areas ranging from alkylation, transalkylation, isomerization, oligomerization, acylation, esterification and nitration. The two main classes of ion-exchange resins are based upon styrene-based sulfonic acids (Amberlyst® and Dow type resins), which show very high activity in the areas of esterification and etherification, to the perfluorosulfonic acid-based catalysts including the recently developed Nafion® resin/silica nanocomposites. These show very high activity in the area of linear alkyl benzene formation, isomerization, and some select acylation type chemistries. These new types of catalysts (which have been used commercially) are adding to the ever-growing portfolio of highly active solid acid catalysts, which couple both economic and environmental drivers to improve organic transformations within the chemical industry.
560 citations
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01 Jan 2001
TL;DR: In this paper, the authors present a method for the preparation of Amines by Reductive Alkylation and the subsequent hydrogenation of Imines, Oximes, and Related Compounds.
Abstract: Preface. Hydrogenation Catalysts. Reactors and Reaction Conditions. Hydrogenation of Alkenes. Hydrogenation of Alkynes. Hydrogenation of Aldehydes and Ketones. Preparation of Amines by Reductive Alkylation. Hydrogenation of Nitriles. Hydrogenation of Imines, Oximes, and Related Compounds. Hydrogenation of Nitro, Nitroso, and Related Compounds. Hydrogenation of Carboxylic Acids, Esters, and Related Compounds. Hydrogenation of Aromatic Compounds. Hydrogenation of Heterocyclic Aromatic Compounds. Hydrogenolysis. General Bibliography. Author Index. Subject Index.
261 citations
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TL;DR: Several diorganoscandium complexes stabilized by the β-diketiminato ligands (Ar)NC(R)CHC(R),N(Ar) (Ar = 2,6-iPr-C6H3; R = CH3 (ligand a), R = tBu (ligands b)) have been synthesized as discussed by the authors.
198 citations
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TL;DR: A series of novel N-alkyl/aryl-N'-[4-(3-aralkylthio-4-ALKyl/ Daryl-4H-1,2,4-triazole-5-yl)phenyl]thioureas synthesized and tested for antimycobacterial activity against Mycobacterium tuberculosis H37Rv as well as Myc Cobacterium fortuitum ATCC 6841 which is a rapid growing opportun
183 citations
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TL;DR: These are the first direct reaction rate measurements of nucleophilic addition to the parent o-quinone methide, and a thermal and photochemical reversibility of the alkylation process opens a new perspective for the use and application of such adducts as o-QM molecular carriers.
Abstract: o-Quinone methide (1) has been produced in water both thermally and photochemically from (2-hydroxybenzyl)trimethylammonium iodide (2). Michael addition reactions of 1 to various amines, and sulfides, including amino acids and glutathione have been carried out, obtaining alkylated adducts (3-16) in fairly good to quantitative yields. The reaction rate and selectivity of 1 toward nitrogen and sulfur nucleophiles, in competition with the hydration reaction, have been investigated at different pH by laser flash photolysis technique. The observed reactivity spans 7 orders of magnitude on passing from water (kNu = 5.8 M-1 s-1) to the most reactive nucleophile (2.8 x 10(8) M-1 s-1, 2-mercaptoethanol under alkaline conditions). These are the first direct reaction rate measurements of nucleophilic addition to the parent o-quinone methide (1). Competition experiments provided strong kinetic support to the involvement of free 1 as an intermediate in both thermal and photochemical reactions. Furthermore, several alkylation adducts regenerate 1 either by heating (9, 10, 13, and 14) or by irradiation (9, 11-13, 16). Such a thermal and photochemical reversibility of the alkylation process opens a new perspective for the use and application of such adducts as o-QM molecular carriers.
167 citations
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TL;DR: These studies indicate that the overall branching observed in polyethylenes produced by these Pd catalysts is governed both by the kinetics of migratory insertion and by the equilibria involving the alkyl ethylene complexes.
Abstract: A series of stable dialkyl complexes of Pd, (α-diimine)PdR2 (α-diimine = aryl-substituted diimine, R = n-Pr, n-Bu, i-Bu), have been prepared via Grignard alkylation of the corresponding (α-diimine)PdCl2 complexes Protonation of these dialkyl species at low temperature results in loss of alkane and formation of cationic Pd β-agostic alkyl complexes, which have been observed as intermediates in the polymerization of ethylene and propylene by these Pd catalysts Studies of the structure and dynamic behavior of these alkyl complexes are presented, along with the results of trapping reactions of these species with ligands such as NCMe, CO, and C2H4 Trapping with ethylene results in formation of cationic alkyl ethylene complexes which model the catalyst resting state in these systems These complexes have been used to obtain mechanistic details and kinetic parameters of several processes, including isomerization of the alkyl ethylene complexes, associative and dissociative exchange with free ethylene, and mig
157 citations
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TL;DR: A regioselective synthesis has been developed for the preparation of unsymmetrical 1,3,5-triaryl-4-alkylpyrazolines and -pyrazoles by treatment of alpha-benzotriazolyl-alpha,beta-unsaturated ketones with monosubstituted hydrazines followed by alkylation at the 4-position of the pyrazoline ring.
Abstract: A regioselective synthesis has been developed for the preparation of unsymmetrical 1,3,5-triaryl-4-alkylpyrazolines and -pyrazoles by treatment of α-benzotriazolyl-α,β-unsaturated ketones with monosubstituted hydrazines followed by alkylation at the 4-position of the pyrazoline ring. Reaction of α-benzotriazolyl-α,β-unsaturated ketones with hydroxylamine gives 3,5-disubstituted isoxazoles regioselectively.
157 citations
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143 citations
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TL;DR: In this article, the synthesis of a complete triad of Group 4 carbenes is reviewed and their reaction chemistry demonstrating nucleophilic alkylation, Lewis acidity of the metal, 1,2 addition across the MC carbene bond and [2+2] cycloaddition across this double bond.
139 citations
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TL;DR: Ferrocene-modified chiral pocket ligands have been studied in the palladium-catalyzed asymmetric alkylation of simple ketone enolates, in which (R,R,Sp,Sp)-1 containing two pairs of matched chiralities, central chirality and planar chiralality, behaved very efficiently in this reaction and up to 95% ee value was achieved.
133 citations
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TL;DR: Linear alkylbenzene technology has almost completely replaced the older branched alkylenzene for production of surfactants due to improved biodegradability and cost-effectiveness.
Abstract: Linear alkylbenzene technology has almost completely replaced the older branched alkylbenzene technology for production of surfactants due to improved biodegradability and cost-effectiveness. The technology of choice today is dehydrogenation of n-paraffins to n-olefins followed by benzene alkylation to produce linear alkylbenzene. Solid acids catalyst-based systems are emerging to slowly replace hydrofluoric acid units in order to ensure environmental safety and improve economics. Numerous materials have been evaluated as solid acid catalysts for this alkylation process including zeolites, clays, various metal oxides, and supported aluminum chloride. At this time, only the UOP Detal technology has been commercialized. Because of ongoing fundamental studies on reaction mechanism and catalyst properties, significant progress is being made to improve the selectivity, catalytic stability, and long-term stability of these solid acids under commercial operating conditions.
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TL;DR: The first example of palladium-catalyzed allylic alkylation of an imino ester with simple allyl esters in the presence of a chiral quaternary ammonium salt is reported in this article.
Abstract: The first example of palladium-catalyzed allylic alkylation of an imino ester with simple allyl esters in the presence of a chiral quaternary ammonium salt is reported. The presence of molecular sieves was found to have a beneficial effect on the enantioselectivity of the reaction by scavenging water from the system. Alkylated products with e.e.s of up to 61% were obtained.
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TL;DR: Two stereoselective routes to a series of diastereomeric inhibitors of HIV protease, monofluorinated analogues of the Merck HIV proteases inhibitor indinavir, are described and variation of potency as a function of inhibitor stereochemistry is discussed.
Abstract: Two stereoselective routes to a series of diastereomeric inhibitors of HIV protease, monofluorinated analogues of the Merck HIV protease inhibitor indinavir, are described. The two routes feature stereoselective construction of the fluorinated core subunits by asymmetric alkylation reactions. The first-generation syntheses were based on the conjugate addition of the lithium enolate derived from pseudoephedrine α-fluoroacetamide to nitroalkene 12, a modestly diastereoselective transformation. A more practical second-generation synthetic route was developed that is based on a novel method for the asymmetric synthesis of organofluorine compounds, by enolate alkylation using optically active fluoroiodoacetic acid as the electrophile in combination with a chiral amide enolate. Resolution of fluoroiodoacetic acid with ephedrine provides either enantiomeric form of the electrophile in ≥96% ee. Alkylation reactions with this stable and storable chiral fluorinated precursor are shown to proceed in a highly stereos...
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TL;DR: In this article, a catalytic enantioselective alkylation of heteroaromatic compounds using alkylidene malonates has been developed; the reaction is shown to yield high yield and enantiomeric excess.
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TL;DR: Ag(I) salts significantly enhance palladium-catalyzed Suzuki-Miyaura cross-couplings of n-alkylboronic acids with a wide variety of aryl and alkenyl halides/triflates as discussed by the authors.
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TL;DR: In this paper, a dimeric Cinchona alkaloid ammonium salt was developed as a new efficient phase-transfer catalyst; the catalytic enantioselective alkylation of N-(diphenylmethylene)glycine tert-butyl ester using 4======provided 7 in a high enantiomeric excess (90-99% ee).
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TL;DR: In this article, it was shown that the N-alkylation of aniline, carboxamides and heterocyclic compounds bearing an acidic hydrogen atom attached to nitrogen can be accomplished with alkyl halides in acetonitrile and cesium fluoride-celite employed as a solid base.
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TL;DR: O(2)-aryl diazeniumdiolates proved capable of reacting with the nucleophilic sulfur of the HIV-1 p7 nucleocapsid protein's zinc finger assembly to eject the zinc, disrupting a structural motif critical to viral replication and suggesting possible utility in the drug discovery realm.
Abstract: Ions of structure R2N[N(O)NO]- and their alkylation products have seen increasing use as nitric oxide (NO)-generating agents for biomedical research applications. Here we show that such diazeniumdiolate anions can readily displace halide from a variety of electrophilic aza- or nitroaromatic substrates to form O2-arylated derivatives of structure R2N−N(O)N−OAr. The site of arylation and the cis arrangement of the oxygens were confirmed by X-ray crystallography. Displacement by various nucleophiles showed R2N[N(O)NO]- to be a reasonably good leaving group, with rate constants for displacement by hydroxide, methoxide, and isopropylamine that were between those of chloride and fluoride in the SNAr reactions we surveyed. The Meisenheimer intermediate could be spectrally observed. These O2-aryl diazeniumdiolates proved capable of reacting with the nucleophilic sulfur of the HIV-1 p7 nucleocapsid protein's zinc finger assembly to eject the zinc, disrupting a structural motif critical to viral replication and sug...
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TL;DR: The results led to the conclusion that planar chirality influences the stereochemical outcome by changing or even inverting the ratio of two rotamers because of the steric interaction between a planarChiral group and the coordination site.
Abstract: A series of novel planar chiral 2‘-substituted 1,1‘-P,N-ferrocene ligands 9−11, 14, and 16 were prepared with diastereopurity >99:1 and found to be effective in asymmetric allylic alkylation and amination reactions. Ligand 14 furnished the highest enantiomeric excess, 98.5% and 96.5% ee in alkylation and amination reactions, respectively. The role of planar chirality in asymmetric reactions has been examined, and decisive effects on enantioselectivity as well as the control of absolute configuration in palladium-catalyzed allylic alkylation and amination reactions were observed. To clarify why and how the planar chirality governed the stereochemical outcome, X-ray crystallographic structures of η3-diphenylallyl Pd complexes, 1H NMR, 31P NMR spectra of palladium dichloride complexes, and η3-diphenylallyl Pd complexes of three 1,1‘-P,N-ferrocene ligands were analyzed with the aid of COSY and 2D NOESY experiments. All results led to the conclusion that planar chirality influences the stereochemical outcome b...
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TL;DR: Variation of solvent and reaction temperature revealed that the highest regio- and enantioselectivities are found using coordinating solvents of -40 degrees C.
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TL;DR: Measurements of protein alkylation by matrix assisted laser desorption/ionisation‐time of flight‐mass spectrometry (MALDI‐TOF‐MS) and its implications on 2‐D gel analysis in particular and proteomics in general are discussed.
Abstract: All existing protocols for protein separation by two-dimensional (2-D) gel electrophoresis require the full reduction, denaturation, and alkylation as a precondition for an efficient and meaningful separation of such proteins Existing literature provides a strong evidence to suggest that full reduction and denaturation can be achieved in a relatively short time; the same thing, however, can not be said for the alkylation process, which the present study shows that more than 6 h are required for a complete alkylation We have used matrix assisted laser desorption/ionisation-time of flight-mass spectrometry (MALDI-TOF-MS) to monitor protein alkylation by iodoacetamide over the period 0-24 h at pH 9 The present, fast and specific MS method provided clear indication on the extent and speed of alkylation which reached approximately 70% in the first 2 min, yet the remaining 30% resisted complete alkylation up to 6 h The use of sodium dodecyl sulfate (SDS) during the alkylation step resulted in a strong quenching of this reaction, whereas 2% 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) exerted a much reduced inhibition The implications of the present measurements on 2-D gel analysis in particular and proteomics in general are discussed
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TL;DR: Investigating the most nucleophilic site of dA (N1) preferentially, but reversibly, conjugates to a model ortho-quinone methide indicates that the most readily observed products of DNA modification resulting from reversible reactions may reflect thermodynamic rather than kinetic selectivity.
Abstract: Alkylating agents that react through highly electrophilic quinone methide intermediates often express a specificity for the weakly nucleophilic exocyclic amines of deoxyguanosine (dG N(2)) and deoxyadenosine (dA N(6)) in DNA. Investigations now indicate that the most nucleophilic site of dA (N1) preferentially, but reversibly, conjugates to a model ortho-quinone methide. Ultimately, the thermodynamically stable dA N(6) isomer accumulates by trapping the quinone methide that is transiently regenerated from collapse of the dA N1 adduct. Alternative conversions of the dA N1 to the dA N(6) derivative by a Dimroth rearrangement or other intramolecular processes are not competitive under neutral conditions, as demonstrated by studies with [6-(15)N]-dA. Both a model quinone methide precursor and its dA N1 adduct yield a similar profile of deoxynucleoside products when treated with an equimolar mixture of dC, dA, dG, and T. Consequently, the most readily observed products of DNA modification resulting from reversible reactions may reflect thermodynamic rather than kinetic selectivity.
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TL;DR: In this article, the Friedel-Crafts alkylation of benzene, toluene and p -xylene by benzyl chloride was performed with zinc catalysts.
Abstract: ZnCl 2 , NiCl 2 and CuCl 2 supported on hydroxyapatite (HAP), as a new solid support, catalyse the Friedel–Crafts alkylation of benzene, toluene and p -xylene by benzyl chloride. The reaction proceeds selectively to monoalkyl-compounds and in a short reaction time. The best catalytic activities were observed with the zinc catalysts.
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TL;DR: The a-alkylation of aldehyde-SAMP/RAMP hydrazones has been used in the enantioselective synthesis of two epimers of stenusine, a 3-substituted piperidine alkaloid and spreading reagent of the beetle Stenus comma.
Abstract: Recent advances in the diastereo- and enantioselective synthesis of piperidine, pyrrolidine, and indolizidine alkaloids, based on the highly stereoselective 1,2-addition to the CN double bond of chiral aldehyde-SAMP/RAMP hydrazones, are described. The enantio- selective syntheses of the pyrrolidine alkaloids bgugaine and (2 S,12'R)-2-(12'-aminotride- cyl)-pyrrolidine, a defense alkaloid of the Mexican bean beetle are reported. Furthermore, the SAMP/RAMP-hydrazone method was applied to the syntheses of two 5,8-disubstituted indolizidine alkaloids that have been extracted from neotropical poison-dart frogs. The α - alkylation of aldehyde-SAMP/RAMP hydrazones has been used in the enantioselective syn- thesis of two epimers of stenusine, a 3-substituted piperidine alkaloid and spreading reagent of the beetle Stenus comma. ENANTIOSELECTIVE SYNTHESIS OF AMINES BY DIASTEREOSELECTIVE 1,2-ADDITION TO THE CN DOUBLE BOND OF ALDEHYDE-SAMP/RAMP-HYDRAZONES Amines of high enantiomeric purity are important chiral building blocks for the synthesis of naturally occurring and biologically active substances and for the synthesis of chiral auxiliaries, ligands, etc. For that reason, the asymmetric synthesis of amines has been receiving much interest, and a lot of work is still being carried out toward the development of new methods that can provide these important com- pounds. The approach to the asymmetric synthesis of α -branched amines pursued by our group involves
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TL;DR: It is desirable and practical to produce both enantiomers of a target from the same chiral starting material by stereodifferentiation of prochiral compounds, for instance utilizing a chiral ligand derived from a natural (L) amino acid.
Abstract: It is desirable and practical to produce both enantiomers of a target from the same chiral starting material by stereodifferentiation of prochiral compounds, for instance utilizing a chiral ligand derived from a natural (l) amino acid. During the past 7 years, excellent results have been achieved in several cases by multiple stereodifferentiation of chiral ligands derived from (S)-indoline-2-carboxylic acid: highly diastereo- and enantioselective pinacol coupling reactions of chiral α-ketoamides gave both (S,S)- and (R,R)-quaternary tartaric acid for the first time; asymmetric Diels−Alder cyclization of chiral acrylamides in the presence of Lewis acid afforded extremely high diastereoselectivities of both opposite configurations of the cyclized diastereomers depending upon the structures of chiral ligands and Lewis acids; and asymmetric alkylation of aldehydes to both enantiomers of secondary alcohols and asymmetric hydrogenation of ketones to both enantiomers of chiral secondary alcohols have been achie...
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TL;DR: Asymmetric synthesis of (S)-2′,6′-dimethyltyrosine (DMT), DMT, DMP, α-TMT, α,2.6′, 6′-trimethylphenylalanine (α-TMP) via reactions of 4′-benzyloxy-2,6,dimethylbromide with Ni(II)-complexes of the chiral Schiff base of glycine or alanine as mentioned in this paper.
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TL;DR: Aromatic electrophilic substitution reactions such as alkylation, acylation, benzoylation, and sulfonylation were studied in the presence of a catalytic amount of Cu(OTf) 2 and Sn(OTF) 2 as mentioned in this paper.
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TL;DR: In this paper, the direct alkylation of a Ni(II)-complex of the chiral Schiff base of alanine with (S)-o-[N-(N-benzylprolyl)amino]benzophenone, with racemic α-alkyl benzyl bromides, is a synthetically feasible and methodologically advantageous approach to the target α,β-dialkylphenylalanines over previously reported methods.
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TL;DR: Thioethers are reasonably good donors to zinc in either a tetrahedral or octahedral geometry in the absence of superior anionic ligands, and the suggestion that reactivity in enzymes with multiple zinc-bound thiols could be controlled by differences in thiol pK(a).
Abstract: A series of zinc complexes using a new tripodal, N(2)S, heteroscorpionate ligand (L3SH) that is isostructural and isoelectronic with the well-known N(3) trispyrazolylborates have been methylated in solution and the coordination properties of the resulting thioether examined. This system models the reactivity of zinc-containing enzymes involved in alkyl group transfers such as the DNA repair protein Ada from E. coli, or farnasyl transferase where it has been shown that the thioether resulting from alkyl group transfer remains in the coordination sphere of the zinc. The following complexes have been structurally characterized: [(L3S)ZnI] (1), [(L3SCH(3))ZnI(2)] (2), [(L3SCH(3))ZnI]BF(4) (3), [(L3SCH(3))Zn-mu-bis-acetato-mu-hydroxo-Zn(L3SCH(3))]BF(4) (5), [(L3SCH(3))ZnSPh(F5)]ClO(4) (7), and [(L3SCH(3))(2)Zn](BF(4))(2) (8). Complexes 3, 4, 5, 7, and 8 all display thioether coordination. Thus in the absence of superior anionic ligands, thioethers are reasonably good donors to zinc in either a tetrahedral or octahedral geometry. The methylation of the complex [(L3S)ZnSPh(F5)], which contains two different thiols, produces a single product, 7, where only the aliphatic thiol has been alkylated. This observation validates the suggestion that reactivity in enzymes with multiple zinc-bound thiols could be controlled by differences in thiol pK(a) (Hammes, B. S.; Warthen, C. R.; Crans, D.; Carrano, C. J. J. Biol. Inorg. Chem. 2000, 6, 82. Compound 7 is also of interest in that it resembles the metal ion-binding site of the blue copper protein, azurin.