- Cyanide-Coordination Effect on Photochemical Carbon-Skeleton Rearrangements of Alkyl Ligands Coordinated to Vitamin B12 Model Complexes
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The cyanide ion induced the heterolytic cleavage of the cobalt-carbon bond involved in vitamin B12 model complexes by its coordination to the central cobalt atom and enhanced the carbon-skeleton rearrangements via formation of anionic intermedi
- Murakami, Yukito,Hisaeda, Yoshio,Ozaki, Toshiaki,Ohno, Terubisa,Fan, Sheng-Di,Matsuda, Yoshihisa
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Read Online
- Enantioselective hydrogenation of itaconic acid and its derivates with sol-gel immobilized Rh/BPPM catalysts
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Itaconic acid and some of its derivates were hydrogenated with sol-gel entrapped Rh/BPPM catalysts in methanol solutions. The immobilization process was carried out by different gel building agents: hydrophilic tetramethyl orthosilicate Si(OMe)4 (TMOS) and tetraethyl orthosilicate Si(OEt)4 (TEOS), hydrophobic triethoxyphenylsilane PhSi(OEt) 3/TMOS and trimethoxy(octyl)silane OcSi(OMe)3/TMOS. The choice of the silane precursor influences the enantioselectivity and the rate of the reaction because of the hydrophobic interactions between catalyst, gel and substrate. The immobilized catalyst could be recovered and recycled several times under N2-atmosphere. About 90-99% ee were achieved for the hydrogenation of itaconic acid to (S)-(+)-2-methyl succinic acid, and about 14% ee for the hydrogenation of dimethylitaconate to (S)-(+)-2-methyl-succinic acid dimethylester.
- Volovych,Schwarze,Hamerla,Blum,Schom?cker
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Read Online
- Preparation method and application of sacubitril intermediate
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The invention discloses a preparation method and application of a sacubitril intermediate. The sacubitril intermediate disclosed by the invention is obtained by taking itaconic anhydride as a raw material, performing chiral reduction, esterification, selective hydrolysis and carboxyl activation, and finally conducting coupling with 4-biphenylacetic acid. The invention also provides a method for preparing sacubitril by using the sacubitril intermediate. The preparation method provided by the invention has the advantages of easily available raw materials, simple process, economy, environmental protection and the like, and is more suitable for industrial production compared with other routes.
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- Reduction of Activated Alkenes by PIII/PV Redox Cycling Catalysis
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The carbon–carbon double bond of unsaturated carbonyl compounds was readily reduced by using a phosphetane oxide catalyst in the presence of a simple organosilane as the terminal reductant and water as the hydrogen source. Quantitative hydrogenation was observed when 1.0 mol % of a methyl-substituted phosphetane oxide was employed as the catalyst. The procedure is highly selective towards activated double bonds, tolerating a variety of functional groups that are usually prone to reduction. In total, 25 alkenes and two alkynes were hydrogenated to the corresponding alkanes in excellent yields of up to 99 %. Notably, less active poly(methylhydrosiloxane) could also be utilized as the terminal reductant. Mechanistic investigations revealed the phosphane as the catalyst resting state and a protonation/deprotonation sequence as the crucial step in the catalytic cycle.
- Longwitz, Lars,Werner, Thomas
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supporting information
p. 2760 - 2763
(2020/02/05)
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- Diastereo- and Enantioselective Synthesis of Fluorine Motifs with Two Contiguous Stereogenic Centers
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The synthesis of chiral fluorine containing motifs, in particular, chiral fluorine molecules with two contiguous stereogenic centers, has attracted much interest in research due to the limited number of methods available for their preparation. Herein, we report an atom-economical and highly stereoselective synthesis of chiral fluorine molecules with two contiguous stereogenic centers via azabicyclo iridium-oxazoline-phosphine-catalyzed hydrogenation of readily available vinyl fluorides. Various aromatic, aliphatic, and heterocyclic systems with a variety of functional groups were found to be compatible with the reaction and provide the highly desirable product as single diastereomers with excellent enantioselectivities.
- Ponra, Sudipta,Rabten, Wangchuk,Yang, Jianping,Wu, Haibo,Kerdphon, Sutthichat,Andersson, Pher G.
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p. 13878 - 13883
(2018/10/24)
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- METHOD FOR THE PRODUCTION OF METHYLSUCCINIC ACID AND THE ANHYDRIDE THEREOF FROM CITRIC ACID
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A process for the preparation of methylsuccinic acid in any form, including its salts, its mono- and diester derivatives and the anhydride thereof, which comprises reacting citric acid or a derivative thereof in decarboxylation conditions, said process comprising (i) reacting citric acid or mono- and diester derivatives thereof in a non- aqueous solvent, specifically excluding alcohols, on a metallic catalyst at a temperature between 50 to 400°C and under a partial hydrogen pressure from 0.1 to 50 bar or (ii) reacting citric acid or any salt thereof or mono-, di- and triester derivatives thereof on a metallic catalyst in solvents comprising at least 5% water, at a temperature of from 50 to 400°C under a hydrogen partial pressure from 0.1 to 400 bar
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Page/Page column 16
(2018/04/21)
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- Photoredox radical conjugate addition of dithiane-2-carboxylate promoted by an iridium(III) phenyl-tetrazole complex: a formal radical methylation of Michael acceptors
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A readily accessible iridium(iii) phenyl-tetrazole complex ([Ir(ptrz)2(tBu-bpy)]+, 2; Hptrz = 2-methyl-5-phenyl-tetrazole; tBu-bpy = 4,4′-di-tert-butyl-2,2′-bipyridine) is shown to be a versatile catalyst for a new photocatalytic Michael reaction. Under light irradiation in the presence of 2, a dithiane 2-carboxylic acid, obtained by simple hydrolysis of a commercially available ethyl ester, generates a 1,3-dithiane radical capable of performing addition to a variety of Michael acceptors (e.g., unsaturated ketones, esters, amides and malonates). This broad scope reaction with high yields is a formal photo-redox addition of the elusive methyl radical and the adducts obtained can be starting materials for a variety of functionalized products. The excited-state oxidation potential of catalyst 2 allows selective formation of radicals only from α-heterosubstituted carboxylates. Chemical modification of this metal complex can tune the electrochemical properties, opening a route to new highly selective catalytic photo-oxidation reactions.
- Gualandi, Andrea,Matteucci, Elia,Monti, Filippo,Baschieri, Andrea,Armaroli, Nicola,Sambri, Letizia,Cozzi, Pier Giorgio
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p. 1613 - 1620
(2017/02/10)
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- PROCESS FOR DOUBLE CARBONYLATION OF ALLYL ALCOHOLS TO CORRESPONDING DIESTERS
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The invention relates to a process for doubly carbonylating allyl alcohols to the corresponding diesters, wherein a linear or branched allyl alcohol is reacted with a linear or branched alkanol (alcohol) with supply of CO and in the presence of a catalytic system composed of a palladium complex and at least one organic phosphorus ligand and in the presence of a hydrogen halide selected from HCl, HBr and HI.
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Paragraph 0064; 0067; 0068
(2017/07/14)
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- PROCESS FOR DOUBLE CARBONYLATION OF ALLYL ETHERS TO CORRESPONDING DIESTERS
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The invention relates to a process for doubly carbonylating allyl ethers to the corresponding diesters, wherein a linear or branched allyl ether is reacted with a linear or branched alkanol (alcohol) with supply of CO and in the presence of a catalytic system composed of a palladium complex and at least one organic phosphorus ligand and in the presence of a hydrogen halide selected from HCl, HBr and HI.
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Paragraph 0095; 0097
(2017/07/14)
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- Transfer hydrogenation promoted by N-heterocyclic carbene and water
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N-Heterocyclic carbenes (NHCs) promote the transfer hydrogenation of various activated C=C, C=N, and N=N bonds with water as the proton source. The NHCs act as reducing reagents to be converted into their oxides. A detailed reaction mechanism is proposed on the basis of deuterium-labeling experiments.
- Kato, Terumasa,Matsuoka, Shin-Ichi,Suzuki, Masato
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supporting information
p. 13906 - 13909
(2015/09/07)
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- First pre-functionalised polymeric aromatic framework from mononitrotetrakis(iodophenyl)methane and its applications
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Starting from mononitrotetrakis(iodophenyl)methane as monomer, we report the preparation of the first pre-functionalised porous aromatic frameworks (PAFs) and their application as supports for organometallic catalysts. Neutral coordinate imino-pyridine Schiff base (PAF-NPy) or chiral bis-amino (PAF-NPro) ligands were obtained by post-synthetic treatment of PAF-NH2 and treated with copper(I) or rhodium(I) to yield the corresponding supported transition-metal catalysts. The as-prepared PAF-NN-M catalysts exhibited activity and selectivity similar to that of the corresponding homogeneous catalysts and were easily removed from reaction media and recycled without loss of activity or selectivity. New copper catalysts: The preparation of pre-functionalised porous aromatic frameworks (PAFs) and their application as supports for organometallic catalysts (see figure) is reported for the first time.
- Verde-Sesto, Ester,Pintado-Sierra, Mercedes,Corma, Avelino,Maya, Eva M.,De La Campa, Jose G.,Iglesias, Marta,Sanchez, Felix
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supporting information
p. 5111 - 5120
(2014/05/06)
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- Palladium nanoparticles in glycerol: A versatile catalytic system for C-X bond formation and hydrogenation processes
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Palladium nanoparticles stabilised by tris(3-sulfophenyl)phosphine trisodium salt in neat glycerol have been synthesised and fully characterised, starting from both Pd(II) and Pd(0) species. The versatility of this innovative catalytic colloidal solution has been proved by its efficient application in C-X bond formation processes (X=C, N, P, S) and C-C multiple bond hydrogenation reactions. The catalytic glycerol phase could be recycled more than ten times, preserving its activity and selectivity. The scope of each of these processes has demonstrated the power of the as-prepared catalyst, isolating the corresponding expected products in yields higher than 90%. The dual catalytic behaviour of this glycerol phase, associated to the metallic nanocatalysts used in wet medium (molecular- and surface-like behaviour), has allowed attractive applications in one-pot multi-step transformations catalysed by palladium, such as C-C coupling followed by hydrogenation, without isolation of intermediates using only one catalytic precursor. Copyright
- Chahdoura, Faouzi,Pradel, Christian,Gomez, Montserrat
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supporting information
p. 3648 - 3660
(2014/01/06)
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- Magnetic nanoparticles entrapped in siliceous mesocellular foam: A new catalyst support
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γ-Fe2O3 nanoparticles were formed inside the cage-like pores of mesocellular foam (MCF). These magnetic nanoparticles showed a uniform size distribution that could be easily controlled by the MCF pore size, as well as by the hydrocarbon chain length used for MCF surface modification. Throughout the entrapment process, the pore structure and surface area of the MCF remained intact. The resulting magnetic MCF facilitated the immobilization of biocatalysts, homogeneous catalysts, and nanoclusters. Moreover, the MCF allowed for facile catalyst recovery by using a simple magnet. The supported catalysts exhibited excellent catalytic efficiencies that were comparable to their homogeneous counterparts. Copyright
- Lee, Su Seong,Riduan, Siti Nurhanna,Erathodiyil, Nandanan,Lim, Jaehong,Cheong, Jian Liang,Cha, Junhoe,Han, Yu,Ying, Jackie Y.
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experimental part
p. 7394 - 7403
(2012/07/27)
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- Steric effects on the stereochemistry of old yellow enzyme-mediated reductions of unsaturated diesters: Flipping of the substrate within the enzyme active site induced by structural modifications
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The ene-reductase-mediated reduction of the carbon-carbon double bond of some alkyl 2- substituted butenedioates was investigated. The stereochemical outcome of the reaction was found to be influenced by steric effects. Ethyl and butyl citraconates were converted into the corresponding alkyl (R)-2-methylsuccinates with excellent enantioselectivity, whereas ethyl and butyl mesaconates were completely unreactive. Methyl 2-substituted fumarates were reduced to enantiomerically enriched methyl (S)-2-substituted succinates, whereas the (Z)-stereoisomers were left unreacted by enereductases. Labelling experiments were performed to investigate the mechanism of these bioreductions and explain their stereochemical outcome.
- Brenna, Elisabetta,Gatti, Francesco G.,Manfredi, Alessia,Monti, Daniela,Parmeggiani, Fabio
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p. 2859 - 2864
(2013/01/15)
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- Asymmetric bioreduction of activated carbon-carbon double bonds using Shewanella yellow enzyme (SYE-4) as novel enoate reductase
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Shewanella yellow enzyme (SYE-4), a novel recombinant enoate reductase, was screened against a variety of different substrates bearing an activated double bond, such as unsaturated cyclic ketones, diesters, and substituted imides. Dimethyl- and ethyl esters of 2-methylmaleic acid were selectively reduced to (R)-configured succinic acid derivatives and various N-substituted maleimides furnished the desired (R)-products in up to >99% enantiomeric excess. Naturally occurring (+)-carvone was selectively reduced to (-)-cis- dihydrocarvone and (-)-carvone was converted to the diastereomeric product, respectively. Overall SYE-4 proved to be a useful biocatalyst for the selective reduction of activated CC double bonds and complements the pool of synthetic valuable enoate reductases.
- Iqbal, Naseem,Rudroff, Florian,Brigé, Ann,Van Beeumen, Jozef,Mihovilovic, Marko D.
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experimental part
p. 7619 - 7623
(2012/09/07)
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- Development of homogeneous and heterogenized rhodium(i) and palladium(ii) complexes with ligands based on a chiral proton sponge building block and their application as catalysts
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Chiral compounds prepared from proton sponge building block 8-((2R,5R)-2,5-dimethylpyrrolidin-1-yl)naphthalen-1-amine were found to be effective chiral ligands for obtaining complexes of rhodium(i) and palladium(ii) by reaction with [RhCl(cod)]2, PdCl2(cod) or Pd(OAc) 2. The complexes bearing triethoxysilane groups were immobilized on mesoporous MCM-41 in order to obtain new heterogeneous catalysts. Both materials are active in the hydrogenation of alkenes and could be recycled without loss of activity or enantioselectivity.
- Villaverde, Gonzalo,Arnanz, Avelina,Iglesias, Marta,Monge, Angeles,Sanchez, Felix,Snejko, Natalia
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scheme or table
p. 9589 - 9600
(2011/11/13)
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- Synthesis of electron-rich CNN-pincer complexes, with N-heterocyclic carbene and (S)-proline moieties and application to asymmetric hydrogenation
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New chiral CNN-pincer-type gold, palladium, and rhodium complexes containing N-heterocyclic carbene substituent and (S)-N-tert-butyl- methylpyrrolidine-2-carboxamide as chiral auxiliary have been synthesized and studied for asymmetric hydrogenation. The complexes were prepared by the silver carbene transfer route from the respective silver complex. The reaction with [RhCl(cod)]2 (cod = cycloocta-l,5-diene), PdCl2(CH 3CN)2, or K[AuCl4] affords the corresponding cationic [Rh(cod)(ligand)]Cl, [PdCl(ligand)]Cl, and [AuCl(ligand)]Cl2 complexes in which the ligand functions effectively in a CNN coordination mode. The complexes catalyze the enantioselective hydrogenation of prochiral alkenes. Enantioselectivity is very sensitive to the NHC N-substituent, resulting in a useful switch in the predominant enantiomer.
- Boronat, Merce,Corma, Avelino,Gonzalez-Arellano, Camino,Iglesias, Marta,Sanchez, Felix
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experimental part
p. 134 - 141
(2010/03/03)
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- New chiral ligands bearing two N-heterocyclic carbene moieties at a dioxolane backbone. Gold, palladium and rhodium complexes as enantioselective catalysts
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Biscarbene ligands with two imidazolin-2-ylidene moieties at a chiral dioxolane backbone were used as ligands for gold, rhodium and palladium complexes. All new complexes showed varying degrees of enantioselectivity toward hydrogenation of prochiral alkenes with ees up to 95%. The Royal Society of Chemistry 2010.
- Arnanz, Avelina,Gonzalez-Arellano, Camino,Juan, Alberto,Villaverde, Gonzalo,Corma, Avelino,Iglesias, Marta,Sanchez, Felix
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experimental part
p. 3001 - 3003
(2010/08/04)
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- Immobilization of (NHC)NN-pincer complexes on mesoporous MCM-41 support
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Unsymmetrical pincer-type-ligated {pincer = [C6H 3N(CH2L1)(CH2L2)-2,6], L1 = prolinamide, L2 = NHC} gold and rhodium complexes have proven to be highly effective catalysts for the hydrogenation of alkenes. Immobilization on ordered mesoporous silica (MCM-41) using a grafting process offers significant potential advantages in the application of such catalysts particularly with respect to catalyst separation and recycling. We describe one approach toward such immobilization: covalent bonding to silica via a pendant alkoxysilane group. This approach yields catalysts that are robust, recyclable, and comparable to or even more active than the corresponding species in solution. Spectroscopic evidence (IR spectroscopy, solid-state CP/MAS NMR, SEM), elemental analysis, and studies of catalytic activity support the hypothesis that binding occurs at the prolinamide substituent with no complex degradation. Control experiments showed the true heterogeneous nature of the catalyst in this reaction. Analyses of the hybrid materials revealed that the mesoporous structure of these materials was retained during the immobilization process as well as during catalysis.
- Del Pozo, Carolina,Corma, Avelino,Iglesias, Marta,Sanchez, Felix
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experimental part
p. 4491 - 4498
(2011/01/09)
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- PALLADIUM CATALYSTS
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The invention relates to a particulate substance comprising a particulate porous support coupled to a palladium species. The palladium species may comprise palladium nanoclusters. The particulate substance may be used as a catalyst for conducting a carbon-carbon coupling reaction or a reduction.
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Page/Page column 15; 19
(2010/05/13)
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- Enantioselective hydrogenation of olefins by chiral iridium phosphorothioite complex covalently anchored on mesoporous silica
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Chiral monodentate phosphorous-based ligands have proven effective for the enantioselective hydrogenation of olefins. Binol-derived monodentate phosphorothioite (PS) ligand was synthesized from binol and thiopropyltriethoxysilane, and its iridium complex was covalently anchored to mesoporous silica supports like SBA-15, MCM-41, and MCM-48. These catalysts were characterized by different physicochemical techniques and assessed for their catalytic performances in the heterogeneous asymmetric hydrogenation of itaconic acid and its derivatives. It was found that the catalytic activities and enantioselectivities of the heterogenized iridium complex (IrPSSBA-15) in the hydrogenation reactions were comparable to its homogeneous analogue. Binol-derived monodentate phosphorothioite ligand in heterogeneously anchored form (iridium complex) is a more effective catalyst than the reported monodentate phosphorous ligand systems in the hydrogenation reactions, possibly due to the changes in electronic properties around the iridium metal center. The effects of substrate-to-catalyst molar ratio, solvents, and temperature on substrate conversions and enantioselectivities of the products were investigated in hydrogenation reactions.
- Sahoo, Suman,Kumar, Pradeep,Lefebvre,Halligudi
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- Palladium nanoclusters supported on propylurea-modified siliceous mesocellular foam for coupling and hydrogenation reactions
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This paper describes the synthesis, characterization and applications of palladium (Pd) nanoparticles supported on siliceous mesocellular foam (MCF). Pd nanoparticles of 2-3 nm and 4-6 nm were used in reactions involving molecular hydrogen (such as hydrogenation of double bonds and reductive amination), transfer hydrogenation of ketones and epoxides, and coupling reactions (such as Heck and Suzuki reactions). They successfully catalyzed all these reactions with excellent yield and selectivity. This heterogeneous catalyst was easily recovered by filtration, and recycled several times without any significant loss in activity and selectivity. The palladium leaching in the reactions was determined to be much less than the FDA-approved limit of 5 ppm. Furthermore, the catalyst can be stored and handled under normal atmospheric conditions. This immobilized catalyst allows for ease of recovery/reuse and minimization of waste generation, which are of great interest in the development of green chemical processes.
- Erathodiyil, Nandanan,Ooi, Samuel,Seayad, Abdul M.,Han, Yu,Lee, Su Seong,Ying, Jackie Y.
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experimental part
p. 3118 - 3125
(2009/04/08)
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- Conjugate reduction of α,β-unsaturated esters and amides with tributyltin hydride in the presence of magnesium bromide diethyl etherate
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We report herein that the conjugate reduction of α,β-unsaturated esters and amides, such as aryl acrylates, pantolactone esters of acrylic acids, diethyl itaconate and N-crotonylcamphorsultam, with tributyltin hydride proceeded in moderate to high yields in the presence of magnesium bromide diethyl etherate. The effect of metal halide enhancing the yields is also described.
- Hirasawa, Satomi,Tajima, Yoshie,Kameda, Yoko,Nagano, Hajime
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p. 10930 - 10938
(2008/02/12)
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- New heterogenized gold(I)-heterocyclic carbene complexes as reusable catalysts in hydrogenation and cross-coupling reactions
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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.
- Corma,Gutierrez-Puebla,Iglesias,Monge,Perez-Ferreras,Sanchez
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p. 1899 - 1907
(2007/10/03)
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- Improved palladium and nickel catalysts heterogenised on oxidic supports (Silica, MCM-41, ITQ-2, ITQ-6)
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Two series of solid catalysts in which a chiral palladium or nickel complex with Schiff bases as ligands have been immobilized on ordered mesoporous silica supports (MCM-41), delaminated ITQ-2, ITQ-6 zeolites and amorphous silica have been prepared. Hydrogenation of alkenes and imines was studied with the homogeneous as well as with the counterpart heterogenized catalysts. The high accessibility introduced by the structure of the supports allows the preparation of highly efficient immobilized catalysts with TOFs of 1,000,000 h -1. A moderate acidity in the support increases the catalytic activity considerably, and the easy recoverable immobilized catalysts can duplicate the activity of the homogeneous analogues. No deactivation of the catalysts was observed after repeated recycling.
- Gonzalez-Arellano,Corma,Iglesias,Sanchez
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p. 1316 - 1328
(2007/10/03)
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- Carbon-carbon bond formation by radical addition-fragmentation reactions of O-alkylated enols
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α-tert-Butoxystyrene [H2C = C(OBut)Ph] reacts with α-bromocarbonyl or α-bromosulfonyl compounds [R 1R2C(Br)EWG; EWG = -C(O)X or -S(O2)X] to bring about replacement of the bromine atom by the phenacyl group and give R 1R2C(EWG)CH2C(O)Ph. These reactions take place in refluxing benzene or cyclohexane with dilauroyl peroxide or azobis(isobutyronitrile) as initiator and proceed by a radical-chain mechanism that involves addition of the relatively electrophilic radical R 1R2(EWG)C* to the styrene. This is followed by β-scission of the derived α-tert-butoxybenzylic adduct radical to give But*, which then abstracts bromine from the organic halide to complete the chain. α-1-Adamantoxystyrene reacts similarly with R 1R2C(Br)EWG, at higher temperature in refluxing octane using dα-tert-amyl peroxide as initiator, and gives phenacylation products in generally higher yields than are obtained using α-tert-butoxystyrene. Simple iodoalkanes, which afford relatively nucleophilic alkyl radicals, can also be successfully phenacylated using α-1-adamantoxystyrene. O-Alkyl O-(tert-butyldimethylsilyl) ketene acetals H2C=C(OR)OTBS, in which R is a secondary or tertiary alkyl group, react in an analogous fashion with organic halides of the type R1R2C(Br)EWG to give the carboxymethylation products R1R2C(EWG)CH 2CO2Me, after conversion of the first-formed silyl ester to the corresponding methyl ester. The silyl ketene acetals also undergo radical-chain reactions with electron-poor alkenes to bring about alkylation-carboxymethylation of the latter. For example, phenyl vinyl sulfone reacts with H2C=C(OBut)OTBS to afford Bu tCH2CH(SO2Ph)CH2CO2Me via an initial silyl ester. In a more complex chain reaction, involving rapid ring opening of the cyclopropyldimethylcarbinyl radical, the ketene acetal H 2C=C(OCMe2C3H5-cyclo)OTBS reacts with two molecules of N-methyl- or N-phenyl-maleimide to bring about [3 + 2] annulation of one molecule of the maleimide, and then to link the bicyclic moiety thus formed to the second molecule of the maleimide via an alkylation-carboxymethylation reaction.
- Cai, Yudong,Roberts, Brian P.,Tocher, Derek A.,Barnett, Sarah A.
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p. 2517 - 2529
(2007/10/03)
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- Effect of supramolecular inclusion on the 1,2-rearrangement of free radicals
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The free radicals 3-ethoxy-2-(ethoxycarbonyl)-3-oxopropyl (1′) and 3-ethoxy-2-(ethoxycarbonyl)-2-methyl-3-oxopropyl (2′) were generated by photolysis of perester precursors in i) hexane solution, ii) in the presence of β-cyclodextrin, and iii) in NaY zeolite. While free radicals in solution are reluctant to rearrange, they do so when encapsulated in β-cyclodextrin or NaY zeolite. The coenzyme-B12-dependent enzymic rearrangement of methylmalonyl-CoA to succinyl-CoA could be mimicked by photochemical generation of an analogue of the putative intermediate radical in a molecular container.
- Chen, Ying,Kervio, Eric,Retey, Janos
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p. 552 - 558
(2007/10/03)
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- Enzymatic Synthesis of 4-Methyl- and 4-Ethyl-L-glutamic Acids
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This paper reports the activity of glutamic oxalacetic aminotransferase (GOT) from pig heart and bacteria for racemic 4-hydroxy-, 4-methyl-, and 4-ethyl-2-ketoglutaric acids.These compounds are good substrates for GOT with Vmax values of, respectively, 70, 90, and 130 percent relative to the natural substrate, 2-ketoglutaric acid.GOT displays high enantioselectivity toward 4-methyl-2-ketoglutaric acid and 4-ethyl-2-ketoglutaric acid; the synthesis of both diastereoisomers of the corresponding 4-substituted L-glutamic acids is thus possible.
- Echalier, Frederique,Constant, Olivier,Bolte, Jean
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p. 2747 - 2750
(2007/10/02)
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- Carbonylation of alkyl sulfonates catalyzed by cobalt complexes
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Alkyl sulfonates (R1-OSO2R2) react with carbon monoxide and alcohol (R3-OH) in the presence of catalytic amounts of Co complex and Nal to afford the corresponding esters (R1-COOR3) in moderate to good yields.
- Urata, Hisao,Goto, Daisuke,Fuchikami, Takamasa
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p. 3091 - 3094
(2007/10/02)
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- TRANSITION METAL COMPLEX CATALYZED CARBONYLATION OF ORGANIC HALIDES IN THE PRESENCE OF MOLECULAR SIEVES INSTEAD OF BASE
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In the presence of molecular sieves under base free conditions organic halides are successfully carbonylated under carbon monoxide pressure with water or alcohols catalyzed by Co or Pd complex to generate the corresponding carboxylic acids or esters, respectively, in good yields.
- Urata, Hisao,Hu, Nan-Xing,Maekawa, Hisayuki,Fuchikami, Takamasa
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p. 4733 - 4736
(2007/10/02)
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- Electroorganic Chemistry. 124. Electroreductive Intramolecular Coupling of α-(ω-Bromoalkyl) β-Keto Esters
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Intramolecular coupling occurs when cyclic α-(bromomethyl) β-keto esters are electrochemically reduced in the presence of trimethylsilyl chloride and one-carbon ring-enlarged products are obtained in reasonable yields.Electroreduction of α-(γ-bromopropyl) β-keto esters also affords the corresponding five-membered cyclized products and/or the corresponding ring-opened compounds.The ease of ring opening of the cyclized products is highly influenced by their stereoconfiguration.Electroreduction of α-(β-bromoethyl) β-keto ester gives the product formed by the reductive elimination of the bromoethyl group whereas α-(δ-bromobutyl) β-keto ester yields the product of the reductive elimination of bromine.This electroreductive intramolecular coupling is initiated by the reduction of the carbon-bromine bond and proceeds through a carbanion intermediate.
- Shono, Tatsuya,Kise, Naoki,Uematsu, Nobuyuki,Morimoto, Shinji,Okazaki, Eiichi
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p. 5037 - 5041
(2007/10/02)
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- Redox Behavior of Simple Vitamin B12 Model Complexes and Electrochemical Catalysis of Carbon-Skeleton Rearrangements
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Various cobalt complexes of 4,10-dipropyl-5,9-diazatrideca-4,9-diene-3,10-dione dioxime, (C2C3)(DOH)2pn, were prepared, and redox behavior of them was investigated by means of cyclic voltammetry; Co(II)/Co(I) redox potentials in the range of -0.69 through -0.7 V vs.Ag/AgCl.The monomethylated complex, which has a cobalt-carbon bond at one axial site of the nuclear cobalt, was disproportionated to the dimethylated complex, involving two cobalt-carbon bonds at both axial sites, and the CoI species by one-electron reduction.The dimethylated complex was inactive for electrochemical reduction, but transformed into the monomethylated complex via cleavage of a cobalt-carbon bond upon electrochemical oxidation.The electrolyses of 1-bromo-2,2-bis(ethoxycarbonyl)propane, 1-bromo-2-cyano-2-ethoxycarbonylpropane, and 2-acetyl-1-bromo-2-ethoxycarbonylpropane in the presence of IIIBr2> in N,N-dimethylformamide did not proceed in a divided cell at -2.0 vs.Ag/AgCl, since the corresponding dialkylated complexes, inactive for electrochemical reduction, were formed in the course of reaction.When imidazole was added to solutions for the electrolysis, the reaction proceeded efficiently by the trans effect arising from the coordinated axial base and the corresponding carbon-skeleton rearrangement products were obtained.On the other hand, the carbon-skeleton rearrangement proceeded in an undivided cell even in the absence of imidazole; the dialkylated complex was decomposed to give the monoalkylated complex and the reduction and rearrangement products by electrochemical ocxidation on the anode.
- Murakami, Yukito,Hisaeda, Yoshio,Fan, Sheng-Di,Matsuda, Yoshihisa
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p. 2219 - 2228
(2007/10/02)
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- Carbon -Skeleton Rearrangement of an Alkyl Ligand Coordinated to Simple Vitamin B12 Model Complexes in Synthetic Bilayer Membrane
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The carbon-skeleton rearrangement of an alkyl ligand coordinated to the nuclear cobalt of simple vitamin B12 model complexes formed with diimine-dioxime-type ligands took place efficiently in a synthetic bilayer membrane under irradiation with visible light.
- Murakami, Yukito,Hisaeda, Yoshio,Song, Xi-Ming,Fan, Sheng-Di
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p. 877 - 880
(2007/10/02)
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- Electrochemical Carbon-skeleton Rearrangements catalysed by Hydrophobic Vitamin B12 immobilised in a Polymer-coated Electrode
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A glassy carbon electrode was coated with a polymer species derived from a hydrophobic vitamin B12 and Araldite CT-200, and the immobilised cobalt complex catalysed the electrochemical carbon-skeleton rearrangements of alkyl halides having electron-withdrawing groups.
- Murakami, Yukito,Hisaeda, Yoshio,Ozaki, Toshiaki,Matsuda, Yoshihisa
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p. 1094 - 1096
(2007/10/02)
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- CONFORMATION OF SUCCINIC ACID DERIVATIVES BY DOUBLE 13C-LABELLING
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Three-bonded carbon/carbon couplings (3Jcc) are used, in conjunction with MM2 calculations, to examine conformational equilibria in several di-13C-labelled succinic acid derivatives.
- Menger, F.M.,Lee, L. H.
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p. 757 - 760
(2007/10/02)
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- OPTICALLY ACTIVE α-ALKYLSUCCINATES FROM THE STEREOSELECTIVE ALKYLATION OF CHIRAL IMIDE ENOLATES.
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The chiral oxazolidinones 1 and 2 were alkylated by methyl bromoacetate, then subsequent removal of the chiral auxiliary provided readily with high stereoselectivity the α-alkylated succinates 7 and 8.Acyloin condensation and bromination gave the optically active α-t-butylcyclobutanedione 10.
- Fadel, Antonine,Salauen, Jacques
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p. 6257 - 6260
(2007/10/02)
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- Redox Behavior of Simple Vitamin B12 Model Complexes with Cobalt-Carbon Bonds and Catalytic Carbon-Skeleton Rearrangements
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The cobalt complex of 2,10-diethyl-3,9-dipropyl-1,4,8,11-tetraaazaundeca-1,3,8,10-tetraene-1,11-diol catalyzed electrolyses of alkyl halides with electron-withdrawing groups at the β-position to afford rearrangement products via oxidation of the corresponding dialkylated complexes as intermediates.
- Murakami, Yukito,Hisaeda, Yoshio,Fan, Sheng-Di,Matsuda, Yoshihisa
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p. 835 - 838
(2007/10/02)
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- 1,2-Migrations in Free Radicals Related to Coenzyme B12 Dependent Rearrangements
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The free radicals XC(CH3)(COOR)CH2., where X=C(=O)Me (1), C(=O)SEt (2), C(=O)OEt (3), C(=CH2)Me (4), and C6H5 (5), were generated by reaction of the corresponding bromides with (n-Bu)3SnH.The rates of rearrangement involving 1,2-migration of X (to form .C(CH3)(COOR)(CH2X)) were measured in competition with trapping by (n-Bu)3SnH.The measurements yielded the following rearrangement rate constants, kr, and activation parameters, ΔH+ and ΔS+: (1) 1.2E4 s-1 at 45 deg C, 11.0 kcal/mol, -4 cal/mol.K; (2) 23.5 s-1 at 60.5 deg C, 13.8 kcal/mol, -11 cal/mol.K; (3) -1 at 113 deg C; (4) 3.0E5 s-1 at 45 deg C, 10.0 kcal/mol, -2 cal/mol.K; (5) 5.0E3 s-1 at 61 deg C.From the results of crossover experiments it is concluded that the rearrangements of 1 and 2 are intramolecular processes, probably proceeding through cyclopropyloxy radical intermediates or transition states.The carbanions corresponding to 1-5 (i.e., XC(CH3)(COOR)CH2-, generated by reduction of the corresponding bromides with sodium naphthalene) also rearrange rapidly but, in each case, with some contribution from migration of the ester group.This represents the first demonstration of spontaneous 1,2-migration of a thioester group in a free radical and models the coenzyme B12 dependent methylmalonyl-CoA mutase rearrangement.The results support a free-radical rearrangement mechanism for the latter reaction.
- Wollowitz, Susan,Halpern, Jack
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p. 3112 - 3120
(2007/10/02)
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- Hydrophobic Vitamin B12. V. Electrochemical Carbon-Skeleton Rearrangement as Catalyzed by Hydrophobic Vitamin B12: Reaction Mechanisms and Migratory Aptitude of Functional Groups
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The carbon-skeleton rearrangements as catalyzed by heptamethyl cobyrinate perchlorate, 1ester>ClO4, were investigated under electrochemical conditions.The controlled-potential electrolysis of 2,2-bis(ethoxycarbonyl)-1-bromopropane, which is considered to be a model substrate for methylmalonyl-CoA mutase, was catalyzed by 1ester>ClO4 in N,N-dimethylformamide to give the rearrangement product, 1,2-bis(ethoxycarbonyl)propane, as a major one at -1.5 V vs.SCE in the presence of acetic acid and at potentials more cathodic than -1.8 V vs.SCE without acetic acid in the dark.The electrochemical carbon-skeleton rearrangement was postulated to proceed via formation of anionic intermediates.The electrolyses of 1-bromo-2-cyano-2-ethoxycarbonylpropane, 2-acetyl-1-bromo-2-ethoxycarbonylpropane, and 1-bromo-2-propane with 1ester>ClO4 also afforded the corresponding carbon-skeleton rearrangement products.The results indicated that substrates with two electron-withdrawing groups placed on the β-carbon atom with combination of one carboxylic ester and one of carboxylic ester, acetyl, and cyano moieties readily gave the corresponding rearrangement products which were derived from individual migration of the substituent groups.Substrates with only one of the electron-withdrawing groups, carboxylic ester, acetyl, and cyano, did not give any rearrangement product, but a substrate with one thioester group afforded the corresponding rearrangement product.The migratory aptitude of electron-withdrawing groups was found to decrease in the order: COSR>COR>COOR>CN.Both electronic character and steric bulkiness of the migrating groups are apparently reflected on this tendency, even though relative contributions of these effects are much dependent on the nature of β-substituents.
- Murakami, Yukito,Hisaeda, Yoshio,Ozaki, Toshiaki,Tashiro, Takako,Ohno, Teruhisa,et al.
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p. 311 - 324
(2007/10/02)
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- Characterization of a Simple Vitamin B12 Model Complex and Its Catalysis in Electrochemical Carbon-Skeleton Rearrangement
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The electrochemical carbon-skeleton rearrangement reaction of 2,2-bis(ethoxycarbonyl)-1-bromopropane was catalyzed by the cobalt complex of 2,10-diethyl-3,9-dipropyl-1,4,8,11-tetraazaundeca-1,3,8,10-tetraene-1,10-diol, which was characterized by ESR spectroscopy and cyclic voltammetry.
- Murakami, Yukito,Hisaeda, Yoshio,Fan, Sheng-Di
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p. 655 - 658
(2007/10/02)
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- REACTION MECHANISMS FOR ELECTROCHEMICAL CARBON-SKELETON REARRANGEMENT AS CATALYZED BY HYDROPHOBIC VITAMIN B12 IN NONAQUEOUS MEDIA
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Reaction mechanisms for the controlled-potential electrolysis of 2,2-bis(ethoxycarbonyl)-1-bromopropane at -1.0, -1.5, and -2.0 V vs.SCE as catalyzed by a hydrophobic vitamin B12 were clarified.
- Murakami, Yukito,Hisaeda, Yoshio,Tashiro, Takako,Matsuda, Yoshihisa
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p. 555 - 558
(2007/10/02)
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