Showing papers in "Advanced Synthesis & Catalysis in 2010"
TL;DR: The catalytic asymmetric synthesis of the tetrasubstituted carbon stereocenter at the C-3 position of the oxindole framework integrates new synthetic methods and chiral catalysts.
Abstract: The 3,3′-disubstituted oxindole structural motif is a prominent feature in many alkaloid natural products, which include all kinds of tetrasubstituted carbon stereocenters, spirocyclic or not, all-carbon or heteroatom-containing. The catalytic asymmetric synthesis of the tetrasubstituted carbon stereocenter at the C-3 position of the oxindole framework integrates new synthetic methods and chiral catalysts, reflects the latest achievements in asymmetric catalysis, and facilitates the synthesis of sufficient quantities of related compounds as potential medicinal agents and biological probes. This review summarizes the recent progress in this area, and applications in the total synthesis of related bioactive compounds.
1,085 citations
TL;DR: The review examines the chiral amine literature from 2000-2009 concerning enantioselective and diastereoselectives methods for N-acylenamide and enamine reduction, reductive amination, and imine reduction.
Abstract: The review examines the chiral amine literature from 2000-2009 (May) concerning enantioselective and diastereoselective methods for N-acylenamide and enamine reduction, reductive amination, and imine reduction. The reaction steps for each strategy, from ketone to primary chiral amine, are clearly defined, with best methods and yields for starting material preparation and final deprotection noted. Categories of chiral amines have been defined in Section 1 to allow the reader to quickly understand whether their specific target amine falls within a difficult to synthesize, or not, structural class. Amino acids are not considered in this work.
752 citations
TL;DR: In this paper, a review summarizes the progress made essentially these last ten years on heterogeneous palladium catalysis in pure water and discusses the efficiency and reusability of the heterogeneous catalysts as well as the experimental conditions from a sustainable chemistry point of view.
Abstract: This review summarizes the progress made essentially these last ten years on heterogeneous palladium catalysis in pure water. The work covers four important palladium-catalyzed transformations for carbon-carbon bond formation: Suzuki, Heck, Sonogashira and Tsuji-Trost reactions. The discussion focuses on the efficiency and reusability of the heterogeneous catalysts as well as on the experimental conditions from a sustainable chemistry point of view. The review is introduced by a discussion on mechanistic aspects inherent to heterogeneous catalysis.
589 citations
TL;DR: In this article, a series of easily prepared Lewis basic ionic liquids were developed for cyclic carbonate synthesis from epoxide and carbon dioxide at low pressure without utilization of any organic solvents or additives.
Abstract: A series of easily prepared Lewis basic ionic liquids were developed for cyclic carbonate synthesis from epoxide and carbon dioxide at low pressure without utilization of any organic solvents or additives. Notably, quantitative yields together with excellent selectivity were attained when 1,8-diazabicyclo[5.4.0]undec-7-enium chloride ([HDBU]Cl) was used as a catalyst. Furthermore, the catalyst could be recycled over five times without appreciable loss of catalytic activity. The effects of the catalyst structure and various reaction parameters on the catalytic performance were investigated in detail. This protocol was found to be applicable to a variety of epoxides producing the corresponding cyclic carbonates in high yields and selectivity. Therefore, this solvent-free process thus represents an environmentally friendly example for the catalytic conversion of carbon dioxide into value-added chemicals by employing Lewis basic ionic liquids as catalyst. A possible catalytic cycle for the hydrogen bond-assisted ring-opening of epoxide and activation of carbon dioxide induced by the nucleophilic tertiary nitrogen of the ionic liquid was also proposed.
246 citations
TL;DR: Recent progress in the field of catalytic enantioselective fluorination reactions, including their scope and mechanism is reviewed.
Abstract: Since the incorporation of fluorine into biologically active compounds often enhances the properties of the parent compounds, there is a considerable demand for efficient enantioselective fluorination reactions. Over the past decade, a range of metal-catalyzed and organocatalyzed fluorination reactions has been developed. Nowadays, fluorine can be catalytically introduced into many compounds in good yield and with high enantioselectivity, and the scope of these reactions is broad. Herein, we review recent progress in the field of catalytic enantioselective fluorination reactions, including their scope and mechanism.
229 citations
TL;DR: In this article, the first one-pot transformation of an olefin into a triazole was described, and the catalyst is easy to prepare, very versatile and reusable at a low copper loading.
Abstract: Copper nanoparticles on activated carbon have been found to effectively catalyze the multicomponent synthesis of 1,2,3-triazoles from different azide precursors, such as organic halides, diazonium salts, anilines and epoxides in water. The first one-pot transformation of an olefin into a triazole is also described. The catalyst is easy to prepare, very versatile and reusable at a low copper loading.
193 citations
TL;DR: In this paper, a review of the recent advances in the synthetic applications of silicon-based, bulky amino organocatalysts in which catalysts containing an organosilicon moiety or group play a formative role in controlling both the course of the reaction as well as the stereoselectivity is presented.
Abstract: Recent years have witnessed an explosive growth in the field of amino organocatalysis, especially in asymmetric enamine and iminium catalysis. Except for the obvious interaction between organo-catalyst and substrate, the impact of bulky side group ons stereoselectivity is not as simple as one could imagine. Within the development of bulky site-stereoselective organocatalysts, functional silyl organocatalysts with a bulky silicon group are promising and meet the high standards of modern synthetic methods. This review focuses on the recent advances in the synthetic applications of silicon-based, bulky amino organocatalysts in which catalysts containing an organosilicon moiety or group play a formative role in controlling both the course of the reaction as well as the stereoselectivity.
189 citations
TL;DR: A series of gold(I) isonitrile complexes were prepared and converted to the corresponding diaminocarbene gold (I) complexes by reactions with primary and symmetrical secondary amines as discussed by the authors.
Abstract: A series of gold(I) isonitrile complexes were prepared and converted to the corresponding diaminocarbene gold(I) complexes by reactions with primary and symmetrical secondary amines. Twelve crystal structure analyses of the gold(I) complexes could be obtained, in addition NMR studies allowed an analysis of the different diastereomers present in solution. In the gold-catalyzed phenol synthesis these complexes were very successful as pre-catalysts, reaching an unprecedented 3050 turnovers with a problematic substrate. Good conversions in the hydration of phenylacetylene could also be achieved.
182 citations
TL;DR: In this article, metal-containing Janus particles are used as interfacial catalyst/emulsifiers that catalyze reac- tions in biphasic systems with controlled phase-specificivity, that is, conversion of the desired reaction on one side of the emulsion.
Abstract: Metal-containing Janus particles are used as interfacial catalyst/emulsifiers that catalyze reac- tions in biphasic systems with controlled "phase se- lectivity", that is, conversion of the desired reaction on one side of the emulsion. The reaction may affect the solubility of the molecule in one phase, causing migration to the opposite phase. As a result, combined reaction and separation can be achieved in a single reaction vessel.
173 citations
TL;DR: In this paper, an efficient method was developed for the direct acylation of arene sp2 CH bonds with aldehydes using palladium acetate as catalyst and peroxide as oxidant.
Abstract: An efficient method was developed for the direct acylation of arene sp2 CH bonds with aldehydes using palladium acetate as catalyst and peroxide as oxidant. The solvent-free oxidative acylation reaction assisted by a pyridine directing group provides an easy access to aromatic, aliphatic, and optical active ketones.
171 citations
TL;DR: Copper(I) bromide-catalyzed amidation of 2-arylpyridine derivatives and 1-methylindoles with a variety of amides was achieved by employing tert-butyl peroxide (TBP) as oxidant Aryl halides under the reaction conditions.
Abstract: Copper(I) bromide-catalyzed amidation of 2-arylpyridine derivatives and 1-methylindoles with a variety of amides was achieved by employing tert-butyl peroxide (TBP) as oxidant Aryl halides could be tolerated under the reaction conditions Neither a special ligand nor a base was required for this amidation process
TL;DR: In this article, simple β-chloroammonium salts in the presence of a weak base were used to obtain NHC complexes from simple metal precursors, such as palladium(II), platinum(II) bis(isonitrile) and gold(I) isonitrile complexes.
Abstract: From palladium(II) or platinum(II) bis(isonitrile) complexes and from gold(I) isonitrile complexes, both easily available from simple precursors, the corresponding mono-N-heterocyclic carbene (NHC) complexes could be obtained selectively in good yields under very mild conditions. The reagents are simple β-chloroammonium salts in the presence of a weak base. Unsymmetric NHC complexes are accessible. Thus over only two steps from simple metal precursors a broad variety of NHC complexes is available, the method is ideal to quickly assemble catalyst libraries. The palladium complexes are active pre-catalysts in Suzuki cross-coupling even with the additional isonitrile ligand on palladium.
TL;DR: Propiolic acids can be synthesized in excellent yields from alkynes and carbon dioxide in the presence of the mild base cesium carbonate under unprecedentedly mild conditions.
Abstract: A highly effective copper catalyst has been developed that promotes the insertion ot carbon dioxide into the C-H bond of terminal alkynes under unprecedentedly mild conditions. For the first time, propiolic acids can thus be synthesized in excellent yields from alkynes and carbon dioxide in the presence of the mild base cesium carbonate. The catalyst, (4,7-diphenyl-1,10-phenanthroline)bis[tris(4-fluorophenyl)phosphine]-copper(I) nitrate, is easy accessible and relatively stable against air and water.
TL;DR: A versatile catalytic system based on pal- ladium(II) acetate/bis(diphenylphosphino)methane (PdA2/dppm) that works "on water" giving site-selective CH arylation of (NH)-indoles with- out protecting or directing groups is described.
Abstract: This communication describes the devel- opment of a versatile catalytic system based on pal- ladium(II) acetate/bis(diphenylphosphino)methane (PdA2/dppm) that works "on water" giving site-selective CH arylation of (NH)-indoles with- out protecting or directing groups. Remarkably, the control of regioselectivity was achieved by small changes in the "extra-catalytic" base/halide part- ners. These innovative methodologies allow a high- yielding access to both C2 and C3-arylindoles, as well as 2,3-diarylindoles, and display high chemo/re- gioselectivities and structural versatility with regard to either indole or aryl moieties.
TL;DR: Potassium hydroxide (KOH) in dimethyl sulfoxide (DMSO) forms a superbasic medium that allows one to access cross-coupling products from reactions between aryl halides with various sulfur-, oxygen- and nitrogen-based nucleophiles under transition metal-free conditions as discussed by the authors.
Abstract: Potassium hydroxide (KOH) in dimethyl sulfoxide (DMSO) forms a superbasic medium that allows one to access cross-coupling products from reactions between aryl halides with various sulfur-, oxygen- and nitrogen-based nucleophiles under transition metal-free conditions.
TL;DR: In this paper, the performance of a metal organic framework (MOF) as a room temperature acetalization catalyst was evaluated. But the structural stability of this catalytic system was not investigated.
Abstract: Room temperature acetalization of aldehydes with methanol has been carried out using metal organic frameworks (MOFs) as solid heterogeneous catalysts. Of the MOFs tested, a copper-containing MOF [Cu 3 (BTC) 2 ] (BTC=1,3,5-benzenetricarboxylate) showed better catalytic activity than an iron-containing MOF [Fe(BTC)] and an aluminium containing MOF [Al 2 (BDC) 3 ] (BDC=1,4-benzenedicarboxylate). The protocol was validated for a series of aromatic and aliphatic aldehydes and used to protect various aldehydes into commercially important acetals in good yields without the need of water removal. In addition, the reusability and heterogeneity of this catalytic system was demonstrated. The structural stability of MOF was further studied by characterization with powder X-ray diffraction, Brunauer-Emmett-Teller surface area measurements and Fourier-transformed infrared spectroscopic analysis of a deactivated catalyst used to convert a large amount of benzaldehyde. The performance of copper MOF as acetalization catalyst compares favourably with those of other conventional homogeneous and heterogeneous catalysts such as zinc chloride, zeolite and clay.
TL;DR: A chiral squaramide catalysts-promoted asymmetric sulfa-Michael conjugated addition of thiols to trans-chalcones is presented and high enantioselectivities were achieved under mild conditions.
Abstract: A chiral squaramide catalysts-promoted asymmetric sulfa-Michael conjugated addition of thiols to trans-chalcones is presented. Moderate to excellent yields and high enantioselectivities (up to 99% ee) were achieved under mild conditions.
TL;DR: A copper-catalyzed intermolecular aerobic oxidative CH bond amination of various polyfluorobenzenes with an array of primary aromatic amines was achieved for the first time as discussed by the authors.
Abstract: A copper-catalyzed intermolecular aerobic oxidative CH bond amination of various polyfluorobenzenes with an array of primary aromatic amines was achieved for the first time. The reactivity of the polyfluorobenzenes was observed to depend on the acidity of CH bonds. Under similar reaction conditions, the CH bond amination of azoles also occurred.
TL;DR: In this article, an internal aryl-substituted ortho-alkynylphenol and a similar aniline with stoichiometric amounts of N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene-gold tosylate [(IPr)AuOTs] and triethylamine gave the aurated heterocycles as stable intermediates of the corresponding gold(I)-catalysed hydrooxylation and hydroamination reactions.
Abstract: An internal aryl-substituted ortho-alkynylphenol and a similar aniline with stoichiometric amounts of N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene-gold tosylate [(IPr)AuOTs] and triethylamine gave the aurated heterocycles as stable intermediates of the corresponding gold(I)-catalysed hydrooxylation and hydroamination reactions. X-ray crystal structure analyses of both products could be obtained. A similar internal alkyl-substituted ortho-alkynylphenol gave only the cycloisomerised product, no aurated intermediate could be detected.
TL;DR: In this paper, water-soluble palladium catalyst complexes, in situ obtained from the respective sulfonated imidazolinium salt, sodium tetrachloropalladate (Na 2 PdCl 4 ) and potassium hydroxide (KOH) in water, were successfully applied in the copper-free Sonogashira coupling reaction in isopropyl alcohol/water mixtures using 0.2 mol% catalyst loading.
Abstract: The reactions of the N,N'-diarylimidazolium and N,N'-diarylimidazolinium salts with chlorosulfonic acid result in the formation of the respective disulfonated N-heterocyclic carbene (NHC) precursors in reasonable yields (46-77%). Water-soluble palladium catalyst complexes, in situ obtained from the respective sulfonated imidazolinium salt, sodium tetrachloropalladate (Na 2 PdCl 4 ) and potassium hydroxide (KOH) in water, were successfully applied in the copper-free Sonogashira coupling reaction in isopropyl alcohol/water mixtures using 0.2 mol% catalyst loading. The preformed (disulfonatedNHC)PdCl(cinnamyl) complex was used in aqueous Suzuki-Miyaura reactions at 0.1 mol% catalyst loading. The coupling protocol reported here is very useful for Sonogashira reactions of N- and S-heterocyclic aryl bromides and chlorides with aryl- and alkylacetylenes.
TL;DR: This critical review with 439 references covers developments in this hot area of research up to July 2009 and includes a description of synthetically important, regioselective transition metal-catalyzed Csp2-N, Csp-N
Abstract: Functionalized imidazole derivatives include compounds that are known to possess a broad range of significant biological properties or are important templates in medicinal chemistry. In the light of the importance of these heteroaromatic compounds a great deal of attention has been given to their synthesis and, in the past years, a number of methods has been described in the literature allowing for the construction of the heteroaromatic core of these substances by cyclization protocols. However, in recent years, much more attention has been focused on the design and development of efficient protocols that are based on the selective functionalization of the imidazole ring at the N-1, C-2, C-4 or C-5 position via transition metal-catalyzed reactions and enable the synthesis of imidazole derivatives, including bioactive and/or naturally occurring compounds, which cannot be accessed by other means. This critical review with 439 references covers developments in this hot area of research up to July 2009 and includes a description of synthetically important, regioselective transition metal-catalyzed Csp2-N, Csp-N, Csp3-N, Csp2-Csp2, and Csp-Csp2 bond forming methods, their applications, and limitations.
TL;DR: In this article, a new protocol for the thioarylation of structurally diverse alkyl bromides such as benzyl, cinnamyl, n-octyl, cyclohexyl and cyclopentyl was developed.
Abstract: In this article, we have developed a new protocol for the thioarylation of structurally diverse alkyl bromides such as benzyl, cinnamyl, n-octyl, cyclohexyl, cyclopentyl, and tert-butyl bromides with aryl iodides, bromides and an activated chloride using thiourea catalyzed by copper(I) iodide in wet polyethylene glycol (PEG 200) as an eco-friendly medium in the presence of potassium carbonate at 80 and 100 °C under an inert atmosphere. The process is free from foul-smelling thiols which makes this method more practical for the thioetherification of aryl halides. Another important feature of this method is the variety of alkyl bromides which are commercially available for the in situ generation of thiolate ions with respect to the existing protocols in which the less commercially available thiols are directly used for the preparation of arylthio ethers.
TL;DR: The application of combination catalysis in enantioselective trifluoromethylation reactions is illustrated in this paper, where four ground-breaking studies have described the efficient catalytic enanti-selective nucleophilic TRM reactions of ketones and azomethine imines.
Abstract: The application of combination catalysis in enantioselective trifluoromethylation reactions is illustrated. Four ground-breaking studies have described the efficient catalytic enantioselective nucleophilic trifluoromethylation of ketones and azomethine imines in the presence of the combination of a Cinchona alkaloid-derived ammonium salt and different nucleophilic initiators, whereas the highly enantioselective electrophilic and radical trifluoromethylation of aldehydes could be achieved via the combination of chiral organocatalysts and metal salts.
TL;DR: An organic-inorganic hybrid heterogeneous nanocatalyst system was synthesized by covalent grafting a palladium dichloride complex of the type (L) 2 PdCl 2 (L = trimethoxysilyl-functionalized triphenylphosphine) on silica-coated magnetic nanoparticles as discussed by the authors.
Abstract: An organic-inorganic hybrid heterogeneous nanocatalyst system was synthesized by covalent grafting a palladium dichloride complex of the type (L) 2 PdCl 2 (L = trimethoxysilyl-functionalized triphenylphosphine) on silica-coated magnetic nanoparticles. It is a highly active and recyclable catalyst for the Suzuki-Miyaura cross-coupling reaction. The new catalyst can easily be separated from the reaction mixture by applying an external magnetic field and can be recycled many times without any loss of activity.
TL;DR: Copper/cobalt phthalocyanines were established for the first time as catalysts for the very efficient chemo-and regioselective reduction of aromatic nitro compounds to generate the corresponding amines.
Abstract: Copper/cobalt phthalocyanines were established for the first time as catalysts for the very efficient chemo- and regioselective reduction of aromatic nitro compounds to generate the corresponding amines. The selective reduction of nitro compounds was observed in the presence of a large range of functional groups such as aldehyde, keto, acid, amide, ester, halogen, lactone, nitrile and heterocyclic functional groups. Furthermore, the present method was found to be highly regioselective towards the reduction of aromatic dinitro compounds in a short time with high yields. In most of the cases the conversion and selectivity were > 99% as monitored by GC-MS. The reduction mechanism was elucidated by UV-vis and electrospray ionization quadrupole time-of-flight tandem mass spectrometry.
TL;DR: The first organocatalytic diastereo- and enantioselective Michael addition reaction of 4-substituted-pyrazolin-5-ones to nitroolefins has been developed with a chiral bifunctional thiourea as organoc atalyst.
Abstract: The first organocatalytic diastereo- and enantioselective Michael addition reaction of 4-substituted-pyrazolin-5-ones to nitroolefins has been developed with a chiral bifunctional thiourea as organocatalyst. A wide variety of desired multi-substituted pyrazolin-5-one derivatives with contiguous quaternary and tertiary stereocenters are smoothly obtained in very good yields (up to 98%) with excellent enantioselectivities (up to > 99% ee) and acceptable diastereoselectivities (up to 80:20). This experimentally simple process facilitates the access to various enantioenriched, multiply substituted pyrazolin-5-one derivatives, potential biologically active molecules, starting from readily available starting materials.
TL;DR: In this article, four polystyrene-supported amino acids have been synthesized and applied to the chemical fixation of carbon dioxide for the first time, and two series of experiments were conducted to study the effect of the reaction conditions on the carboxylation of propylene oxide/carbon dioxide.
Abstract: Four new polystyrene-supported amino acids have been synthesized and applied to the chemical fixation of carbon dioxide for the first time. Two series of experiments with polystyrene-supported threonine (PS-Thr) and polystyrene-supported tyrosine (PS-Tyr) as catalyst, respectively, were conducted to study the effect of the reaction conditions on the carboxylation of propylene oxide/carbon dioxide. There was no considerable decrease in the yield of propylene carbonate after the polystyrene-supported amino acids were used five times, indicating that these catalysts are very stable. It was demonstrated that these catalysts were very efficient in the carboxylation of various epoxides and aziridines with carbon dioxide under mild conditions without any solvents. The mechanism for this carboxylation is also discussed.
TL;DR: Chiral N-heterocyclic carbenes were found to be efficient catalysts for the formal [2+2] cycloaddition reaction of disubstituted ketenes and isatins to give the corresponding spirocyclic oxindole-β-lactones in good yields with good diastereo-selectivities and excellent enantioselectivities.
Abstract: Chiral N-heterocyclic carbenes were found to be efficient catalysts for the formal [2+2] cycloaddition reaction of disubstituted ketenes and isatins to give the corresponding spirocyclic oxindole-β-lactones in good yields with good diastereo-selectivities and excellent enantioselectivities. Ring opening with Grignard reagents or decarboxylation of the oxindole spirocyclic-β-lactone gave the corresponding 3-hydroxy- or 3-alkylenyloxindoles in good yields.
TL;DR: Aniline-substituted diethynylarenes directly produce aryl- and heteroaryl-annulated[a]carbazoles by the gold-catalyzed intramolecular cascade hydroamination/cycloisomerization without producing theoretical by-products.
Abstract: Aniline-substituted diethynylarenes, which are readily synthesized through Sonogashira coupling reactions from commercially available 1,2-dihaloarenes, directly produce aryl- and heteroaryl-annulated[a]carbazoles by the gold-catalyzed intramolecular cascade hydroamination/cycloisomerization without producing theoretical by-products. This new atom-economical route is easily applicable to various aryl-annulated[a]carbazoles containing an alkyl, aryl or ester substituent.
TL;DR: In this paper, a catalyst-free synthesis of 2-substituted quinazolines and 4H-benzo[d][1,3]oxazines using commericially available sodium hypochlorite as oxidant is described.
Abstract: This communication describes a catalyst-free synthesis of 2-substituted quinazolines and 4H-benzo[d][1,3]oxazines using commericially available sodium hypochlorite as oxidant. Operational simplicity, mild reaction conditions and the ability to construct structurally diverse 2-quinazolines and 2-substituted 4H-benzo[d][1,3]oxazines by this method render it to be a practical alternative for the synthesis of these heterocycles.