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Low Catalyst Loading (low + catalyst_loading)
Selected AbstractsA Versatile Palladium/Triphosphane System for Direct Arylation of Heteroarenes with Chloroarenes at Low Catalyst Loading,ANGEWANDTE CHEMIE, Issue 37 2010David Roy Ein luftbeständiger Palladiumkatalysator mit dreizähnigem Phosphanligand aryliert elektronenreiche wie elektronenarme mehrfach substituierte Furane (X=O), Thiophene (X=S) und Pyrrole (X=NR5) sowie Thiazole direkt unter C-H-Aktivierung mit Chlorarenen (siehe Schema; DMAc=N,N -Dimethylacetamid, TBAB=Tetra- n -butylammoniumbromid). [source] Highly Enantioselective Conjugate Addition of Thioglycolate to Chalcones Catalyzed by Lanthanum: Low Catalyst Loading and Remarkable Chiral Amplification,ANGEWANDTE CHEMIE, Issue 25 2010Yonghai Hui Kleineree,große Wirkung: Mit dem Lanthan(III)-Komplex eines chiralen N,N,-Dioxids als Katalysator verlief die Titelreaktion hoch enantioselektiv und mit hohen Ausbeuten. Besonders bemerkenswert war die große asymmetrische Verstärkung: Das Produkt wurde mit 98,%,ee erhalten, wenn 1,Mol-% L/La(OTf)3 mit 2,%,ee für L eingesetzt wurde. Tf=Trifluormethansulfonyl. [source] ChemInform Abstract: Modified Palladium-Catalyzed Regioselective ortho-Arylation of sp2 C,H Bond Substrates with a Low Catalyst Loading.CHEMINFORM, Issue 22 2009Fan Yang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Highly Efficient and Practical Pyrrolidine,Camphor-Derived Organocatalysts for the Direct ,-Amination of AldehydesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 29 2010Pang-Min Liu Abstract A series of pyrrolidine,camphor-derived organocatalysts (1,4) were designed and synthesised. These organocatalysts were used for direct ,-amination of aldehydes with dialkyl azodicarboxylates to give the desired ,-aminated products in high chemical yields (up to 92,%) and with high to excellent levels of stereoselectivity (up to >99,% ee). The reactions proceeded rapidly (within 5 min) with low catalyst loading (5 mol-%) at ambient temperature. Enantioselective aminations of asymmetric ,,,-disubstituted aldehydes in the catalytic system were studied, with reasonable to high stereoselectivities (up to 75,% ee) being obtained. The utility of this methodology was demonstrated with the synthesis of derivatives of ,-amino-,-butyrolactone and a tetrasubstitutedcyclohexane-derived amino alcohol with high stereoselectivities. Transition models were proposed for the asymmetric ,-amination reactions; they involve hydrogen-bond interactions between the nucleophilic enamine formed in situ and the nitrogen source. [source] Alkyne Hydroarylations with Chelating Dicarbene Palladium(II) Complex Catalysts: Improved and Unexpected Reactivity Patterns Disclosed Upon Additive Screening,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 19 2009Andrea Biffis Abstract Palladium(II) complexes with a ligand set made from a chelating N-heterocyclic dicarbene ligand and two weakly coordinating anions (generally introduced in situ upon addition of 2 equiv. of a suitable silver salt) were found to be very active and selective catalysts for the room-temperature hydroarylation of alkynes at low catalyst loading (0.1 mol-%). Moreover, the screening of various strong acids as reaction promoters revealed that both the strength of the acid and the coordinating ability of its conjugated base influence the catalytic performance. Most remarkably, the use of HBF4 together with a dicarbene Pd complex catalyst provides a dramatic change in the selectivity of the reaction, with the prevalent formation of a product stemming from the insertion of two molecules of alkyne into the aromatic C,H bond. The results presented herein highlight the fact that the dicarbene ligand, apart from stabilising the catalyst, is also able to enhance catalytic activity and, most notably, to steer the reaction selectivity towards novel products. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Catalytic Asymmetric Alkylation of Aldehydes by Using TrialkylboranesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 26 2008Takahiro Ukon Abstract Triethylborane can be used in the asymmetric alkylation of aldehydes by using a 3-(3,5-diphenylphenyl)-H8 -BINOL-derived titanium(IV) catalyst in the presence of an excess amount of titanium tetraisopropoxide. The reaction proceeds with a low catalyst loading (2 mol-%), exhibiting high enantioselectivity for aromatic and unsaturated aldehydes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Metal-Containing Ionic Liquids as Efficient Catalysts for Hydroxymethylation in WaterEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 20 2008Katharina Bica Abstract The iron-containing ionic liquid butylmethylimidazolium tetrachloroferrate (bmim-FeCl4) proved to be an efficient and recyclable catalyst for the hydroxymethylation of ,-keto esters using aqueous formaldehyde and a low catalyst loading of up to 0.1 mol-% without co-solvents or additional surfactants. An useful and high-yielding approach to hydroxymethylated keto esters as well as to 3-disubstitued butyrolactones via tandem hydroxymethylation,lactonization could thus be established.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] A Practical Gold-Catalyzed Route to 4-Substituted Oxazolidin-2-ones from N -Boc PropargylaminesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 21 2007Eun-Sun Lee Abstract AuI -catalyzed cyclization of N -Boc propargylamines into 4-alkylidene oxazolidin-2-ones is described. This modularapproach provides access to a variety of nonproteogenic 4-substituted oxazolidinones that are important in asymmetric synthesis and biological applications. The current flexible route is characterized by low catalyst loading, mild conditions, and operational simplicity.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Cyclopalladated Ferrocenylimine as Efficient Catalyst for the Syntheses of Arylboronate EstersADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Lianhui Wang Abstract The cyclopalladated ferrocenylimine I and its phosphine adducts IIa,f were prepared and evaluated in the borylation of aryl halides. The tricyclohexylphosphine adduct IIb exhibited highly catalytic activity for the coupling of aryl and heteroaryl bromides containing various functional groups with low catalyst loading (2,mol%). Aryl and heteroaryl chlorides were smoothly converted into the corresponding boronates in the presence of the monophosphinobiaryl ligand (XPhos) adduct IIf. It was proposed that palladacycle was only a reservoir of the catalytically active species from the investigation on the reaction mechanism. [source] Bismuth Triflate-Catalyzed Addition of Allylsilanes to N -Alkoxycarbonylamino Sulfones: Convenient Access to 3-Cbz-Protected CyclohexenylaminesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2009Thierry Ollevier Abstract Bismuth triflate was found to be an efficient catalyst in the Sakurai reaction of allyltrimethylsilanes with N -alkoxycarbonylamino sulfones. The reaction proceeded smoothly with a low catalyst loading of Bi(OTf)3,4,H2O (2,5,mol%) to afford the corresponding protected homoallylic amines in very good yields (up to 96%). A sequential allylation reaction followed by ring-closing metathesis delivers 6,8 membered 3-Cbz-protected cycloalkenylamines. [source] Effect of Long Chain Fatty Acids on Organocatalytic Aqueous Direct Aldol ReactionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 17 2009Nobuyuki Mase Abstract In an organocatalyzed, aqueous direct aldol reaction, the addition of a long chain fatty acid (1,mol%) such as stearic acid or erucic acid improved the aldol product yield and the enantioselectivity with low catalyst loading (1,mol%). The small particle size of the emulsion (less than 1,,m) was a key to the enhanced reactivity as shown by dynamic light scattering (DLS) analyses. [source] Highly Enantioselective Michael Addition of ,-Substituted Cyano Ketones to ,,,-Unsaturated ,-Keto Esters using Bifunctional Thiourea-Tertiary Amine Catalysts: An Easy Access to Chiral DihydropyransADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 17 2009Sheng-Li Zhao Abstract An asymmetric Michael addition of ,-substituted cyano ketones to ,,,-unsaturated ,-keto esters to form chiral dihydropyrans catalyzed by a series of ,-amino acid-derived thiourea-tertiary amines is presented. A novel tyrosine-derived thiourea catalyst was identified as the optimal catalyst providing the desired product in 91,95% yields and with 90,96% ee at a low catalyst loading of 2.0,mol%. The utility of the reaction was exemplified by facile conversion of the dihydropyran product into pharmaceutically useful dihydropyridine. [source] The First Catalytic Mannich-Type Reaction of N -Alkoxycarbonylamino Sulfones with Silyl EnolatesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 15 2006Thierry Ollevier Abstract Bismuth triflate was found to be an efficient catalyst in the Mannich-type reaction of silyl enolates with N -alkoxycarbonylamino sulfones. The reaction proceeded smoothly with a low catalyst loading of bismuth triflate (0.5,1.0 mol,%) to afford the corresponding protected ,-aminocarbonyl compound in very good yields (up to 96,%). [source] A Highly Effective Bis(sulfonamide),Diamine Ligand: A Unique Chiral Skeleton for the Enantioselective Cu-Catalyzed Henry ReactionCHEMISTRY - A EUROPEAN JOURNAL, Issue 28 2010Wei Jin A skeleton in the closet! As a unique chiral skeleton, the newly developed bis(sulfonamide),diamine, which contains both diamine and bis(sulfonamide) moieties, was a highly effective ligand for the asymmetric Cu(OAc)2 -catalyzed Henry reaction between nitromethane and aldehydes with a low catalyst loading at room temperature (see scheme). Both aliphatic and aromatic aldehydes gave excellent enantioselectivities of up to 99,%,ee. [source] Rhodium-Catalyzed Formation of Stereocontrolled Trisubstituted Alkenes from Baylis,Hillman AdductsCHEMISTRY - A EUROPEAN JOURNAL, Issue 18 2009Thomas Gendrineau Abstract Efficient and general conditions for the formation of stereodefined trisubstituted alkenes by using the rhodium-catalyzed reaction of unactivated Baylis,Hillman adducts with either organoboronic acids or potassium trifluoro(organo)borates are reported (see scheme). We report here efficient and general conditions for the formation of stereodefined trisubstituted alkenes using the rhodium-catalyzed reaction of unactivated Baylis,Hillman adducts with either organoboronic acids and potassium trifluoro(organo)borates. The use of the [{Rh(cod)OH}2] precursor gave very fast coupling reactions under low catalyst loading, very mild reaction conditions (from room temperature up to 50,°C) and without the need of additional phosphane ligands. Based on the new reaction conditions, the reaction, originally limited to Baylis,Hillman adducts derived from esters, could be extended to a large variety of Baylis,Hillman adducts, bearing either keto, cyano or amido functionalities. Moreover, the reaction of Baylis,Hillman adducts bearing esters functionality was improved and could be conducted at lower temperature using lower catalyst loading. [source] Au-Catalyzed Tandem Cyclization/[1,2]-Alkyl Migration Reaction of Epoxy Alkynes: Synthesis of SpiropyranonesCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2008Xing-Zhong Shu Dr. Abstract A novel gold-catalyzed tandem cyclization/[1,2]-alkyl migration process of epoxy alkynes to spiropyranones has been discovered. From this process, the construction of adjacent multiple stereocenters with a new quaternary carbon atom is achieved. The gold-catalyzed domino process is stereospecific with respect to the migrating carbon atom. A type of unusual CC bond cleavage of epoxide systems has also been discovered, which can lead to the formation of two Z,alkenes and a carbonyl functional group in one step with excellent stereoselectivity. Furthermore, this efficient domino process could be achieved in the presence of the simplest and least expensive gold catalyst [NaAuCl4],2,H2O with a low catalyst loading. [source] Water Compatible Gold(III)-Catalysed Synthesis of Unsymmetrical Ethers from AlcoholsCHEMISTRY - A EUROPEAN JOURNAL, Issue 5 2008Abstract An efficient and broad-scoped method for the preparation of unsymmetrical ethers from alcohols catalysed by the simplest and least expensive gold catalyst, NaAuCl4, is described for the first time. The procedure enables the etherification of benzylic and tertiary alcohols with moderate to good yields under mild conditions with low catalyst loading. Symmetrical ethers, the usual side products in the etherification of alcohols, were not detected in this case. The formation of the racemic ether from a chiral benzyl alcohol suggests the intermediacy of a carbocation, which has not previously been postulated for gold-catalysed reactions involving alcohols. [source] Homo-coupling of Aryl Iodide and Bromide Catalyzed by Immobilized Palladium with a Bidentate Nitrogen LigandCHINESE JOURNAL OF CHEMISTRY, Issue 10 2009Xiaofang Chen Abstract The immobilized palladium onto organic-inorganic hybrid material, which contains bidentate nitrogen ligands, was a very effective catalyst for homo-coupling of aryl iodide and bromide. The protocol involved the use of N,N -dimethylacetamide as a solvent, and n -tributylamine as a base. The reaction generated the corresponding homo-coupling products in good to excellent yields at low catalyst loading (0.20 mol%). Furthermore, the silica-supported palladium catalyst could be recovered and recycled by a simple filtration of the reaction solution and used for five consecutive trials without loss of its activity. [source] Enantioselective Ag-Catalyzed Allylation of Aldimines,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 30 2009Marina Naodovic Abstract A highly enantioselective synthesis of homoallylic amines, using allyltrimethoxysilane under AgI catalytic conditions, has been developed. Among the chiral ligands investigated, a remarkable difference in the resulting AgI complexes was observed. Under mild conditions and low catalyst loadings, homoallylamines were produced in high ee values (up to 80,%) and good yields. The methodology can be further extended to a diastere- and enantioselective crotylation of aldimines.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Extremely Efficient Cross-Coupling of Benzylic Halides with Aryltitanium Tris(isopropoxide) Catalyzed by Low Loadings of a Simple Palladium(II) Acetate/Tris(p -tolyl)phosphine SystemADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Chi-Ren Chen Abstract Highly efficient coupling reactions of benzylic bromides or chlorides with aryltitanium tris(isopropoxide) [ArTi(O- i- Pr)3] catalyzed by a simple palladium(II) acetate/tris(p -tolyl)phosphine [Pd(OAc)2/ P(p -tolyl)3] system are reported. The coupling reactions proceed in general at room temperature employing low catalyst loadings of 0.02 to 0.2,mol%, affording coupling products in excellent yields of up to 99%. For benzylic bromides bearing strong electron-withdrawing cyano (CN) or trifluoromethyl (CF3) substituents, the reactions require a higher catalyst loading of 1,mol%, or the reactions are carried out at 60,°C. The catalytic system also tolerates (1-bromoethyl)benzene bearing ,-hydrogen atoms while using a catalyst loading of 1,mol% to afford the coupling product in a 70% yield. [source] Palladium-Catalyzed Aerobic Oxidation of Naturally Occurring Allylbenzenes as a Route to Valuable Fragrance and Pharmaceutical CompoundsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2010Luciana Abstract A palladium-catalyzed, aerobic oxidation of naturally occurring allylbenzenes, i.e., eugenol, methyleugenol, safrole, and estragole, in dimethylacetamide/water solutions under mild conditions has been developed, in which palladium(II) chloride is used in the absence of co-catalysts or special stabilizing ligands as the sole and recyclable catalyst. Methyl ketones that are important for the flavour and pharmaceutical industries have been obtained in good to excellent yields with low catalyst loadings (1,2,mol%) and high average turnover frequencies. This simple catalytic method represents an ecologically benign and economically attractive route to industrially valuable compounds starting from renewable substrates easily available from essential oils. [source] Highly Enantioselective Hydrogenation of Quinoline and Pyridine Derivatives with Iridium-(P-Phos) CatalystADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2010Wei-Jun Tang Abstract The use of a chiral iridium catalyst generated in situ from the (cyclooctadiene)iridium chloride dimer, [Ir(COD)Cl]2, the P-Phos ligand [4,4,-bis(diphenylphosphino)-2,2,,6,6,-tetramethoxy-3,3,-bipyridine] and iodine (I2) for the asymmetric hydrogenation of 2,6-substituted quinolines and trisubstituted pyridines [2-substituted 7,8-dihydroquinolin-5(6H)-one derivatives] is reported. The catalyst worked efficiently to hydrogenate a series of quinoline derivatives to provide chiral 1,2,3,4-tetrahydroquinolines in high yields and up to 96% ee. The hydrogenation was carried out at high S/C (substrate to catalyst) ratios of 2000,50000, reaching up to 4000,h,1 TOF (turnover frequency) and up to 43000 TON (turnover number). The catalytic activity is found to be additive-controlled. At low catalyst loadings, decreasing the amount of additive I2 was necessary to maintain the good conversion. The same catalyst system could also enantioselectively hydrogenate trisubstituted pyridines, affording the chiral hexahydroquinolinone derivatives in nearly quantitative yields and up to 99% ee. Interestingly, increasing the amount of I2 favored high reactivity and enantioselectivity in this case. The high efficacy and enantioselectivity enable the present catalyst system of high practical potential. [source] Highly Efficient Ion-Tagged Catalyst for the Enantioselective Michael Addition of Aldehydes to NitroalkenesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 17 2009Marco Lombardo Abstract The ion-tagged diphenylprolinol silyl ether 6 very efficiently catalyzes the asymmetric Michael addition of aliphatic aldehydes to nitroalkenes with ee of up to>99.5% at low catalyst loadings (0.25,5,mol%) and using only a slight excess of aldehydes (1.2,2,equiv.). This new organocatalyst can be used with the same outstanding efficiency in a wide variety of solvents and reaction conditions. [source] Palladium-Catalyzed Oxidation of Phenyl-Substituted Alkenes using Molecular Oxygen as the Sole OxidantADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Aline Abstract The palladium-catalyzed aerobic oxidation of styrene and 2-vinylnaphthalene in dimethylacetamide/water or dimethylformamide/water solutions under mild conditions has been developed, in which palladium(II) chloride is used in the absence of co-catalysts or special stabilizing ligands as the sole and recyclable catalyst. The corresponding methyl ketones have been obtained in good to excellent yields with low catalyst loadings (0.2,5,mol%) and high turnover numbers (up to ca. 1000 to palladium). This simple and efficient catalytic method represents an ecologically benign and economically attractive synthetic pathway to industrially important compounds used in the manufacture of various polymers and drugs. [source] Highly Convenient, Clean, Fast, and Reliable Sonogashira Coupling Reactions Promoted by Aminophosphine-Based Pincer Complexes of Palladium Performed under Additive- and Amine-Free Reaction ConditionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2009Jeanne Abstract Sequential addition of 1,1,,1,,-phosphinetriyltripiperidine and 1,3-diaminobenzene or resorcinol to toluene solutions of (cyclooctadiene)palladium dichloride [Pd(cod)(Cl)2] under nitrogen in "one pot" almost quantitatively yielded the aminophosphine-based pincer complexes {[C6H3 -2,6-(XP{piperidinyl}2)2]Pd(Cl)} (X=NH 1; X=O 2). Complex 1 (and to a minor extent 2) proved to be efficient Sonogashira catalysts, which allow the quantitative coupling of various electronically deactivated and/or sterically hindered and functionalized aryl iodides and aryl bromides with several alkynes as coupling partners within very short reaction times and low catalyst loadings. Importantly, in contrast to most of the Sonogashira catalysts, which either are both air- and moisture-sensitive and/or require the addition of co-catalysts, such as copper(I) iodide [CuI], for example, or a large excess of an amine, the coupling reactions were carried out without the use of amines, co-catalysts or other aditives and without exclusion of air and moisture. Moreover, the desired products were exclusively formed (no side-products were detected) without employing an excess of one of the substrates. Ethylene glycol and potassium phosphate (K3PO4) were found to be the ideal solvent and base for this transformation. Experimental observations strongly indicate that palladium nanoparticles are not the catalytically active form of 1 and 2. On the other hand, their transformation into another homogeneous catalytically active species cannot be excluded. [source] Reduction of Alkyl Halides by Triethylsilane Based on a Cationic Iridium Bis(phosphinite) Pincer Catalyst: Scope, Selectivity and MechanismADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2009Jian Yang Abstract A highly efficient procedure for the reduction of a broad range of alkyl halides by triethylsilane based on a cationic iridium bis(phosphinite) pincer catalyst has been discovered and developed. This reduction chemistry is chemoselective and has unique selectivities compared with conventional radical-based processes and the aluminum trichloride/triethylsilane (AlCl3/Et3SiH) and triphenylmethyl tetrakis[pentafluorophenyl]borate/triethylsilane {[Ph3C] [B(C6F5)4]/Et3SiH} systems. Reductions use three equivalents of triethylsilane relative to the halide and can be carried out with very low catalyst loadings and in a solvent-free manner, which may provide an environmentally attractive and safe alternative to many currently practiced methods for reduction of alkyl halides. Mechanistic studies reveal a unique catalytic cycle. The cationic iridium hydride 2,6-bis[di-(tert -butyl)phosphinyloxy)phenyl(hydrido)iridium, (POCOP)IrH+ {POCOP= 2,6-[OP(t- Bu)2]2C6H3} binds and activates the silane. This complex serves as a potent silylating reagent to generate silyl halonium ions, Et3SiXR+, which are reduced by the neutral iridium dihydride to yield alkane product and regenerate the cationic (POCOP)IrH+, thus closing the catalytic cycle. All key intermediates have been identified by in situ NMR monitoring and kinetic studies have been completed. An application of this reduction system to the catalytic hydrodehalogenation of a metal chloride complex is also described. [source] Diphosphines of dppf-Type Incorporating Electron-Withdrawing Furyl Moieties Substantially Improve the Palladium-Catalysed Amination of Allyl AcetatesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2005Aziz Fihri Abstract Highly active Pd/diphosphine catalytic systems incorporating new, air-stable ferrocenyl-furylphosphines allow nucleophilic allylic amination at room temperature with unprecedented turnover frequencies. For instance, in the presence of 0.01,mol,% catalyst the coupling of aniline to allyl acetate occurs at a TOF of more than 10,000,h,1; even the addition of the less nucleophile morpholine to allyl acetate is observed with a TOF of 4250,h,1. The amination of the sterically demanding geranyl acetate, a monoterpene derivative of interest in the flavour industry, at low catalyst loadings demonstrates the scope of this methodology, which provides in addition noticeable advantages in terms of economical (resource- and energy-saving) and sustainable chemistry (high selectivity, no additive, low metal content, and thus easier purification). [source] Palladium-Catalyzed Cross-Coupling Reactions of Amines with Alkenyl Bromides: A New Method for the Synthesis of Enamines and IminesCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2004José Barluenga Prof. Dr. Abstract The palladium-catalyzed cross-coupling reaction of alkenyl bromides with secondary and primary amines gives rise to enamines and imines, respectively. This new transformation expands the applicability of palladium-catalyzed CN bond forming reactions (the Buchwald,Hartwig amination), which have mostly been applied to aryl halides. After screening of different ligands, bases, and solvents, the catalytic combination [Pd2(dba)3]/BINAP in the presence of NaOtBu in toluene gave the best results in the cross-coupling of secondary amines with 1-bromostyrene (dba=dibenzylideneacetone, BINAP=2,2,-bis(diphenylphosphino)-1,1,-binaphthyl). The corresponding enamines are obtained cleanly and in nearly quantitative yields. However, steric hindrance seems to be a limitation of the reaction, as amines carrying large substituents are not well converted. The same methodology can be applied to the coupling of secondary amines with 2-bromostyrene. Moreover, the reaction with substituted 2-bromopropenes allows regioselective synthesis of isomerizable terminal enamines without isomerization of the double bond. The best catalytic conditions for the cross-coupling of 1-bromostyrene with primary amines include again the use of the Pd0/BINAP/NaOtBu system. The reaction gives rise to the expected imines in very short times and with low catalyst loadings. A set of structurally diverse imines can be prepared by this methodology through variations in the structure of both coupling partners. However, 2-bromostyrene failed to give good results in this coupling reaction, probably due to product inhibition of the catalytic cycle. Competition experiments of vinyl versus aryl amination reveal that the reaction occurs preferentially on vinyl bromides. La reacción de acoplamiento cruzado de bromuros de alquenilo con aminas secundarias y primarias da lugar a enaminas e iminas respectivamente. Esta nueva transformación expande las aplicaciones de la reacción de formación de enlaces CN catalizada por paladio (aminación Buchwald,Hartwig), que se había limitado fundamentalmente a haluros de arilo. Después de un estudio de diferentes ligandos. bases y disolventes, los mejores resultados en la reacción de acoplamiento cruzado de aminas secundarias con 1-bromoestireno, se obtuvieron para el catalizador constituido por la combinación Pd/BINAP en presencia de NaOtBu en tolueno. Las correspondientes enaminas se obtienen limpiamente y con rendimientos prácticamente cuantitativos. Sin embargo, los impedimentos estéricos en la amina parecen ser una limitación de la reacción, puesto que aminas con sustituyentes voluminosos proporcionan conversiones bajas. La misma metodología puede aplicarse al acoplamiento de aminas secundarias con 2-bromoestireno. Además, la reacción con 2-bromopropenos sustituidos permite obtener de forma regioselectiva enaminas terminales isomerizables, sin que la isomerización del doble enlace tenga lugar. Las mejores condiciones catalíticas para el acoplamiento de aminas primarias con 1-bromoestireno incluyen de nuevo la utilización del sistema Pd(0)/BINAP/NaOtBu. La reacción proporciona las iminas esperadas en tiempos de reacción muy cortos y con baja carga del catalizador. Mediante esta metodología pueden prepararse un conjunto de iminas de gran diversidad estructural, permitiendo variaciones en ambos reactivos de acoplamiento. Sin embargo, la reacción con 2-bromoestireno no produce buenos resultados en este acoplamiento, probablemente debido a inhibición del ciclo catalítico por parte del producto de reacción. Finalmente, experimentos de competencia de aminación vinílica frente a aminación arílica, ponen de manifiesto que esta reacción se produce de forma preferente sobre los bromuros de vinilo. [source] | ||||||||||||||||||||||