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Showing papers in "Advanced Synthesis & Catalysis in 2006"


Journal ArticleDOI
TL;DR: A wide array of forms of palladium has been utilized as precatalysts for Heck and Suzuki coupling reactions over the last 15 years as mentioned in this paper, and there are now many suggestions in the literature that narrow the scope of types of precatalyst that may be considered true catalysts in these coupling reactions.
Abstract: A wide array of forms of palladium has been utilized as precatalysts for Heck and Suzuki coupling reactions over the last 15 years. Historically, nearly every form of palladium used has been described as the active catalytic species. However, recent research has begun to shed light on the in situ transformations that many palladium precatalysts undergo during and before the catalytic reaction, and there are now many suggestions in the literature that narrow the scope of types of palladium that may be considered true “catalysts” in these coupling reactions. In this work, for each type of precatalyst, the recent literature is summarized and the type(s) of palladium that are proposed to be truly active are enumerated. All forms of palladium, including discrete soluble palladium complexes, solid-supported metal ligand complexes, supported palladium nano- and macroparticles, soluble palladium nanoparticles, soluble ligand-free palladium, and palladium-exchanged oxides are considered and reviewed here. A considerable focus is placed on solid precatalysts and on evidence for and against catalysis by solid surfaces vs. soluble species when starting with various precatalysts. The review closes with a critical overview of various control experiments or tests that have been used by authors to assess the homogeneity or heterogeneity of catalyst systems.

1,737 citations


Journal ArticleDOI
TL;DR: A number of chiral acid catalysts have been developed recently as discussed by the authors, with a focus being placed on thiourea, TADDOL, and phosphoric acids, which are rapidly growing areas in organocatalysis.
Abstract: Hydrogen bond catalysis and Bronsted acid catalysis are rapidly growing areas in organocatalysis. A number of chiral acid catalysts has been developed recently. Recent progress in the chiral Bronsted acid catalysis has been reviewed with a focus being placed on thiourea, TADDOL, and phosphoric acids. 1 Introduction 2 Hydrogen Bond Catalysis 2.1 Monofunctional Thiourea Catalysts 2.2 Bifunctional Thiourea Catalysts 2.3 TADDOL Derivatives 2.4 BINOL Derivatives 3 Bronsted Acid Catalysis 3.1 Ammonium Salts 3.2 Phosphoric Acids 4 Conclusion

773 citations


Journal ArticleDOI
TL;DR: A comprehensive overview of the development of gold and platinum catalysis of enyne cycloisomerization can be found in this article, where a discussion of the most recent studies on gold-and platinum-catalyzed cycloisomers of 1,4-and 1,3-enynes is provided.
Abstract: This account provides a comprehensive overview of the development of gold and platinum catalysis of the enyne cycloisomerization. The use of these soft, alkynophilic metals enables mild, chemoselective and efficient transformations of a variety of readily available acyclic enynes to a wide range of synthetically useful carbocyclic and heterocyclic products. The review is organized according to diverse structural types of enynes that undergo skeletal cycloisomerizations. The account begins with an overview of transformations of primarily 1,6-enynes to 1-alkenylcyclopentenes, bicyclo[4.1.0]heptenes, methylenecycloalkenes, bicyclo[4.3.0]nonadienes and bicyclo[3.2.0]heptenes. This section is followed by the discussion of cycloisomerizations of 1,5-enynes, which enable a rapid access to a range of other cyclic products, including bicyclo[3.1.0]hexenes, cyclohexadienes, heterobicycloalkenes, methylenecyclopentenes, naphthalenes and methyleneindenes. In addition, the [3,3] rearrangement of 1,5-enynes provides efficient access to the corresponding allenes. The account concludes with an overview of the most recent studies on gold- and platinum-catalyzed cycloisomerizations of 1,4- and 1,3-enynes. Due to the rapidly increasing interest in this area during the past three to five years, we believe that this review provides a timely and comprehensive discussion of the development gold- and platinum-catalyzed cycloisomerization starting from the initial pioneering investigations to the latest advances in the field. A significant emphasis is placed on the mechanistic discussion of the observed manifolds of skeletal reorganizations.

755 citations


Journal ArticleDOI
TL;DR: In this article, the authors introduce some general principles describing the fundamentals of the covalent anchoring and give an overview of the most important types of covalently anchored catalysts.
Abstract: Very frequently the most costly components in a chemical reaction are not the starting materials or the reaction products, but the catalyst. In addition to the advantages from the economic point of view, recovery and reuse of the catalyst is equally important in order to avoid wastes, so improving the greenness of the process. There is a current tendency to transform homogeneous into heterogeneous catalysis, that will even be accelerated in the near future. Starting from a successful homogeneous catalyst, one general methodology allowing its recovery and reuse is to immobilize a suitable derivative of the active catalyst on an insoluble solid support. When the catalyst does not deactivate and is sufficiently stable under the reaction conditions, the ultimate immobilization methodology is to attach covalently the catalytically active species to the support. In this contribution, after introducing some general principles describing the fundamentals of the covalent anchoring, the emphasis is placed more on giving an overview of the most important types of covalently anchored catalysts, including Bronsted and Lewis acids, covalently anchored bases and hydrogenation complexes. Hot topics such as silica-bound organocatalysts and the application of periodic mesoporous organosilicas as heterogeneous catalysts is also covered.

615 citations


Journal ArticleDOI
TL;DR: In this article, the general mechanistic aspects of the [2+2++2] cycloaddition reaction are discussed along with the proposed models of asymmetric induction.
Abstract: Recent progress in the synthesis of benzene and 1,3-cyclohexadiene derivatives, and heterocyclic compounds such as pyridines, pyridones, pyrans, pyrimidine diones, etc, has been reviewed. The general mechanistic aspects of the [2+2+2] cycloaddition reaction are discussed. The asymmetric variants of these reactions are also discussed along with the proposed models of asymmetric induction.

574 citations


Journal ArticleDOI
TL;DR: In this article, the main problem of finding a suitable catalyst that is active, selective, and stable under the process conditions is discussed, and the most promising candidate is found to be sulphated zirconia.
Abstract: The advantages of biodiesel as an alternative fuel and the problems involved in its manufacturing are outlined. The pros and cons of making biodiesel via fatty acid esterification using solid acid catalysts are examined. The main problem is finding a suitable catalyst that is active, selective, and stable under the process conditions. Various solid acids (zeolites, ion-exchange resins, and mixed metal oxides) are screened as catalysts in the esterification of dodecanoic acid with 2-ethylhexanol, 1-propanol, and methanol at 130–180 °C. The most promising candidate is found to be sulphated zirconia. The catalyst's stability towards thermal decomposition and leaching is tested and the effects of the surface composition and structure on the catalytic activity are discussed.

529 citations


Journal ArticleDOI
TL;DR: The palladium-catalyzed coupling of amines and aryl halides has matured from an exotic small-scale transformation into a very general, efficient and robust reaction during the last ten years as discussed by the authors.
Abstract: The palladium-catalyzed coupling of amines and aryl halides or aryl alcohol derivatives has matured from an exotic small-scale transformation into a very general, efficient and robust reaction during the last ten years. This article reports several applications of this method from an industrial vantage point, including ligand synthesis, synthesis of arylpiperazines, arylhydrazines and diarylamines. Much emphasis in placed on issues of scale-up and safety to underline the potential of CN couplings as solutions for industrial-scale synthetic problems.

443 citations


Journal ArticleDOI
Franco Cozzi1
TL;DR: In this article, a survey of the literature in the period 2003-2005 in the field of immobilized organic catalysis is presented, and a list of suggestions about how the process of immobilization should be carried out is also included, taking into account several factors such as the properties of the catalyst, the nature of the support, and the mode of connection of the catalysts to the support.
Abstract: This review article is divided in two parts. In the first part (Sections 2 and 3) selected examples of the publications that appeared in the literature in the period 2003-2005 in the field of immobilized organic catalysis are presented. When appropriate, the results of these publications are compared to those reported earlier and already discussed in a previous review article (see ref. [4] ). On the basis of this survey, in Section 4 some general considerations about when and why a supported version of an organic catalyst is worth developing are proposed. In Section 4 a list of suggestions about how the process of immobilization should be carried out is also included, taking into account several factors such as the properties of the catalyst, the nature of the support, and the mode of connection of the catalyst to the support.

349 citations


Journal ArticleDOI
TL;DR: Candida antarctica lipase B (CAL-B) is an ideal tool for the synthesis and resolution of a wide range of nitrogenated compounds that can be used for the production of pharmaceuticals and interesting manufactures in the industrial sector.
Abstract: Candida antarctica lipase B (CAL-B) is a very effective catalyst for the production of amines and amides using different enzymatic procedures. Simplicity of use, low cost, commercial availability and recycling possibility make this lipase an ideal tool for the synthesis and resolution of a wide range of nitrogenated compounds that can be used for the production of pharmaceuticals and interesting manufactures in the industrial sector.

337 citations


Journal ArticleDOI
TL;DR: A review of positive dendrimer effects from the literature can be found in this article, where the authors highlight the appearance of these properties as well as prospects for future work in the field.
Abstract: The immobilization of catalytic groups onto a dendritic support either at the core or at the periphery gives rise to unique properties that affect rates of reaction, substrate activation or selectivity, etc. When advantageous, these properties can be classified as a positive dendrimer effect. Positive dendrimer effects can arise from site isolation, transition state stabilization and/or dielectric effects in the case of core-modified dendrimers, while peripherally modified dendrimers usually benefit from steric crowding or cooperativity for catalytic residues confined to the surface of the polymer. In this review, the appearance of positive dendrimer effects from the literature will be highlighted as well as prospects for future work in the field.

319 citations


Journal ArticleDOI
TL;DR: The application and performance of conceptual and qualitative theories and quantitative quantum mechanical methods to the study of mechanism, reactivity and selectivity of 1,3-dipolar and Diels-Alder cycloadditions are reviewed in this paper.
Abstract: The application and performance of conceptual and qualitative theories and quantitative quantum mechanical methods to the study of mechanism, reactivity, and selectivity of 1,3-dipolar and Diels-Alder cycloadditions are reviewed. This review emphasizes the application of conceptual density functional theory (DFT) for predicting reactivity and regioselectivity, and highly accurate quantum mechanical methods for predicting barrier heights and reaction energetics. Applications of computations to solvation effects, metal and organocatalysis, are also described.

Journal ArticleDOI
TL;DR: The reaction of N-alkylimidazole with alkyl sulfonates at room temperature affords 1,3-dialkyliminidazolium alkanesulfonates as crystalline solids in high yields.
Abstract: The reaction of N-alkylimidazole with alkyl sulfonates at room temperature affords 1,3-dialkylimidazolium alkanesulfonates as crystalline solids in high yields. The alkanesulfonate anions can be easily substituted by a series of other anions [BF4, PF6, PF3(CF2CF3)3, CF3SO3 and N(CF3SO2)2] by simple reaction of anions, salts, or acids in water at room temperature. Extraction with dichloromethane, filtration through a short basic alumina column and solvent evaporation affords the desired ionic liquids in 80–95% yield. The purity (>99.4%) of these ionic liquids can be determined by 1H NMR spectra using the intensity of the 13C satellites of the imidazolium N-methyl group as internal standard.

Journal ArticleDOI
TL;DR: In this article, the authors make a tutorial review on catalyst immobilization from the viewpoint of the catalyst designer, emphasizing the use of promising concepts in this area, rather than trying to be exhaustive.
Abstract: In this review the authors intend to make a tutorial review on catalyst immobilisation from the viewpoint of the catalyst designer, emphasizing the use of promising concepts in this area, rather than trying to be exhaustive. The following topics are covered.

Journal ArticleDOI
TL;DR: The Pauson-Khand-type reaction as discussed by the authors is a cycloaddition involving an alkyne, an alkene and carbon monoxide catalyzed or mediat- ed by transition metal complexes.
Abstract: The Pauson-Khand-type reaction is for- mally a (2 + 2 + 1) cycloaddition involving an alkyne, an alkene and carbon monoxide catalyzed or mediat- ed by transition metal complexes. This review focus- es on the catalytic reaction and describes the recent research on the Pauson-Khand-type reaction.

Journal ArticleDOI
TL;DR: In this paper, a mechanism of glucose oxidation on gold nanoparticles is presented, where the gold-catalysed aerobic oxidation of glucose occurs through a two-electrons mechanism leading to gluconate and hydrogen peroxide.
Abstract: Careful analytical determinations show that the gold-catalysed aerobic oxidation of glucose occurs through a two-electrons mechanism leading to gluconate and hydrogen peroxide. This latter decomposes before reaching the critical concentration for competing with O 2 in glucose oxidation. A mechanism of glucose oxidation on gold nanoparticles is presented.

Journal ArticleDOI
TL;DR: In this article, a review summarizes the oxidation methods of organic compounds carried out in the presence of a catalyst using ionic liquids or molten ammonium salts as solvents, where the catalyst is efficiently immobilized in the solvent, thus leading to a reusable system.
Abstract: This review summarizes the oxidation methods of organic compounds carried out in the presence of a catalyst using ionic liquids or molten ammonium salts as solvents. From an ecological point of view, these procedures are particularly interesting when the catalyst is efficiently immobilized in the solvent, thus leading to a reusable system.

Journal ArticleDOI
TL;DR: In this article, the first time that a heterogeneous gold catalyst showed activity in the gold-catalysed phenol synthesis was reported, and the surface bound, cationic gold species is still active and can reach turnover numbers of up to 391.
Abstract: Nanoparticles of gold supported on nanocrystalline CeO 2 catalyse the isomerisation of ω-alkynylfurans to phenols. Initial leaching of gold was observed, which could be minimised by calcining. Subsequent runs showed that once all soluble species had leached, the surface-bound, cationic gold species is still active and can reach turnover numbers of up to 391. This is the first time that a heterogeneous gold catalyst showed activity in the gold-catalysed phenol synthesis.

Journal ArticleDOI
TL;DR: In this paper, simple Bronsted acids such as p-toluenesulfonic acid monohydrate (PTS) or polymer-bound P-Toluene sulfonic acid (PSO) were used to catalyze the direct nucleophilic substitution of the hydroxy group of allylic and benzylic alcohols with a large variety of carbon-and heteroatom-centered nucleophiles.
Abstract: Simple Bronsted acids such as p-toluenesulfonic acid monohydrate (PTS) or polymer-bound p-toluenesulfonic acid efficiently catalyze the direct nucleophilic substitution of the hydroxy group of allylic and benzylic alcohols with a large variety of carbon- and heteroatom-centered nucleophiles. Reaction conditions are mild, the process is conducted under an atmosphere of air without the need for dried solvents, and water is the only side product of the reaction.

Journal ArticleDOI
TL;DR: It was shown that only one oxygen atom of the nitro group is bound to the thiourea moiety, in juxtaposition to the working hypothesis known from the literature which involves a bonding of both oxygens.
Abstract: A highly enantioselective (84–92% ee) organocatalytic Michael addition of acetone to aromatic nitroolefins has been described. The transition state geometries for formation of R and S enantiomers in this Michael addition have been calculated and analyzed. It was shown that only one oxygen atom of the nitro group is bound to the thiourea moiety, in juxtaposition to the working hypothesis known from the literature which involves a bonding of both oxygens. The theoretical and experimental enantiomeric excess values show good agreement, rendering the computations an efficient tool for predicting the ee values in similar reactions.

Journal ArticleDOI
TL;DR: Ionic-liquid-anchored (2S,4R)-4-hydroxyproline 12 catalyzes direct asymmetric aldol reactions with comparable enantioselectivities in DMSO, and with superior enantiosity in neat acetone or 2-butanone, than (S)-proline (8) (up to 28 % ee difference).
Abstract: Ionic-liquid-anchored (2S,4R)-4-hydroxyproline 12 catalyzes direct asymmetric aldol reactions with comparable enantioselectivities in DMSO, and with superior enantioselectivities in neat acetone or 2-butanone, than (S)-proline (8) (up to 28 % ee difference) itself. Furthermore, the supported catalyst 12 can be easily recycled and reused for at least four times without significant loss of yields and enantioselectivity.

Journal ArticleDOI
TL;DR: The most active copper triethanolamine (H 3 tea) complexes for the peroxidative oxidation of cyclohexane, in acetonitrile, were reported in this paper.
Abstract: The mono-, di-, tri-, tetra- and polynuclear copper(II) triethanolamine (H 3 tea) complexes [Cu(H 2 tea)(N 3 )] (1), [Cu 2 (H 2 tea) 2 (XC 6 H 4 COO) 2 ]. 2 H 2 O (X=4-H 2a, 4-CH 3 2b, 3-Cl 2c), [Cu 3 (H 2 tea) 2 -(4-OC6H4COO) 2 (H 2 O)].4H 2 O (3), [O C Cu 4 (tea) 4 -(BOH) 4 ][BF 4 ] 2 (4) and [Cu 2 (H 2 tea) 2 {μ-C 6 H 4 (COO) 2 -1,4} n ].2n H 2 O (5), respectively, are highly active and selective catalysts or catalyst precursors for the peroxidative oxidation of cyclohexane, in acetonitrile, to a cyclohexanol and cyclohexanone mixture, by aqueous hydrogen peroxide in acidic medium (liquid biphasic catalysis) at room temperature and atmospheric pressure. The effects on the catalytic activity of various factors, e.g., the relative amounts of cyclohexane, oxidant, catalyst, solvent and nitric acid, reaction time, catalyst recycling and impact of both carbon- and oxygen-centred radical traps (supporting mainly radical mechanisms) were investigated and allowed us to achieve yields and TONs up to ca. 39% and 380, respectively, corresponding to the most active copper systems so far reported for the oxidation of cyclohexane under mild conditions. The catalysts can be reused for recycling and, at least complex 4 maintains almost the same level of activity even after five reaction cycles. The preparation of the new complexes 1, 2b and 2c by self-assembly at room temperature, and their full characterization by IR spectroscopy, FAB-MS + , elemental and X-ray diffraction structural (for 1 and 2c) analyses are also reported.

Journal ArticleDOI
TL;DR: One-pot, single-step deracemization of sec-alcohols can be achieved by using bio- or chemo-catalysts or combinations thereof and is applicable to secondary alcohols, amines and α-substituted carboxylic acids as mentioned in this paper.
Abstract: The stereoinversion of one enantiomer into its mirror-image counterpart within a racemate furnishes a single stereoisomeric product in 100 % theoretical yield. This extremely efficient type of deracemization, whereby substrate and product possess an identical chemical structure, can be achieved by using bio- or chemo-catalysts or combinations thereof and is applicable to secondary alcohols, amines and α-substituted carboxylic acids. Special emphasis is devoted to the theoretical background of the one-pot, single-step deracemization of sec-alcohols.

Journal ArticleDOI
TL;DR: The extension to an intramolecular variant of this procedure provides a valuable route to substituted fluorenes and renders this environment friendly process an attractiv approach to diarylmethane derivatives.
Abstract: A highly efficient Bi(OTf) 3 -catalyzed benzylation of arenes and heteroarenes has been developed. The mild reaction conditions, high yields, operational simplicity and practicability, broad scope, and remarkably low catalyst loading render this environment friendly process an attractiv approach to diarylmethane derivatives. The extension to an intramolecular variant of this procedure provides a valuable route to substituted fluorenes.

Journal ArticleDOI
TL;DR: The reaction of the binuclear gold(I) complex with ω-alkynylfurans furnished phenols as the major product and anellated furans as the side-products as mentioned in this paper.
Abstract: Reaction of the cationic binuclear gold(I) complex [(Ph3PAu)2Cl]BF4 with ω-alkynylfurans furnished phenols as the major product and anellated furans as the side-products. The analogous trimesitylphosphane complex [(Mes3PAu)2Cl]BF4 selectively afforded only the phenols. The latter catalyst then enabled the first intermolecular gold-catalyzed phenol synthesis.

Journal ArticleDOI
TL;DR: In this paper, an unsymmetrical N-heterocyclic carbene-gold complexes and corresponding solid catalysts in which a gold-carbene complex has been immobilized on silica gel, ordered mesoporous silica (MCM-41), and delaminated zeolite (ITQ-2) have been prepared.
Abstract: Mononuclear unsymmetrical N-heterocyclic carbene-gold complexes and the corresponding solid catalysts in which a gold-carbene complex has been immobilized on silica gel, ordered mesoporous silica (MCM-41), and delaminated zeolite (ITQ-2) have been prepared. These new catalysts have been tested in the hydrogenation of alkenes and the Suzuki cross-coupling reaction to afford selectively non-symmetrical biaryls. These reactions were studied with the soluble as well as with the heterogenized counterpart catalysts. The high accessibility introduced by the structure of the supports allows the preparation of highly efficient immobilized catalysts with TOFs up to 400 h -1 . Moreover, the heterogenized complexes were reused and no deactivation of the catalysts can be observed.

Journal ArticleDOI
Xun Guo1, Honghua Rao1, Hua Fu1, Yuyang Jiang1, Yufen Zhao1 
TL;DR: An inexpensive and efficient catalyst system for Narylation of nitrogen-containing compounds including a variety of amines, amides, indole and imidazole was developed in this paper.
Abstract: An inexpensive and efficient catalyst system has been developed for the N-arylation of nitrogen-containing compounds including a variety of amines, amides, indole and imidazole. This simple protocol uses CuI as the catalyst, commercial available pipecolinic acid as the new ligand, K2CO3 as the base and DMF as the solvent.

Journal ArticleDOI
TL;DR: In this paper, the direct formation of amides from amines and carboxylic acids without catalyst does occur under relatively low temperature conditions, but is highly substrate dependent, and initial results indicate that bifunctional catalysts show even greater potential.
Abstract: Kinetic studies show that the direct formation of amides from amines and carboxylic acids without catalyst does occur under relatively low temperature conditions, but is highly substrate dependent. Boric and boronic acid-based catalysts improve the reaction, especially for less reactive acids, and initial results indicate that bifunctional catalysts show even greater potential.

Journal ArticleDOI
TL;DR: In this article, the Lewis acid-mediated direct amination of benzylic alcohols is described, providing various amine derivatives in good yields under mild and environmentally benign conditions.
Abstract: The Lewis acid-mediated direct amination of benzylic alcohols is described, providing various benzylic amine derivatives in good yields under mild and environmentally benign conditions. Among the different Lewis acids tested, gold(III) proved to be the catalyst of choice for both chemical (yield, conversion) and practical reasons (a filtration over a silica pad is generally sufficient to obtain the corresponding benzylic amine in analytically pure form).

Journal ArticleDOI
TL;DR: The first stereoselective [3 + 2] dipolar cycloadditions of azomethine imines with alpha,beta-unsaturated aldehydes catalyzed by readily available alpha,alpha-diarylprolinol salts are reported, providing a facile route to the synthesis of various chiral bipyrazolidin-3-one derivatives under mild conditions.
Abstract: Bipyrazolidin-3-one derivatives are biologically significant compounds and their importance has increased in the past decades. In this paper, the first stereoselective [3 + 2] dipolar cycloadditions of azomethine imines with alpha,beta-unsaturated aldehydes catalyzed by readily available alpha,alpha-diarylprolinol salts are reported, providing a facile route to the synthesis of various chiral bipyrazolidin-3-one derivatives under mild conditions. The organocatalyst 1g with strongly electron-withdrawing groups exhibited the best stereoselectivity (exo:endo up to 98:2, for exo product up to 97% ee), in the combination with trifluoroacetic acid.

Journal ArticleDOI
TL;DR: In this article, the L-proline has been supported on the surface of modified silica gels with a monolayer of covalently attached ionic liquid with or without additional adsorbed ionic liquids.
Abstract: New materials for L-proline recycling have been developed. These materials have been applied to the L-proline-catalyzed aldol reaction between acetone and several aldehydes. The L-proline has been supported on the surface of modified silica gels with a monolayer of covalently attached ionic liquid with or without additional adsorbed ionic liquid. Good yields and ee values, comparable with those obtained under homogeneous conditions, have been obtained especially with imidazolinium-modified and 4-methylpyridinium-modified silica gels. Moreover, these materials have been easily recovered by simple filtration and studies about their reuse have been carried out. These studies showed that these materials can be used at least up to seven times. Finally, in the case of imidazolinium-modified silica gel, investigations showed that this support can be regenerated giving again a recyclable material with high isolated yields and reproducible ee values up to 13 cycles.