- Iridium-catalyzed enantioselective intramolecular hydroarylation of allylic aryl ethers devoid of a directing group on the aryl group
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Although intramolecular hydroarylation is an attractive transformation of allylic aryl ethers, it has suffered from narrow substrate scope. We herein describe Ir/(S)-DTBM-SEGPHOS-catalyzed intramolecular hydroarylation of allylic aryl ethers. The reaction
- Kusaka, Satoshi,Ohmura, Toshimichi,Suginome, Michinori
-
supporting information
p. 13542 - 13545
(2021/12/23)
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- t-BuOK promoted stereoselective isomerization of allyl aryl ethers
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The t-BuOK promoted stereoselective isomerization of allyl aryl ethers has been developed. The reactions proceeded well in methyl tert-butyl ether (MTBE), providing the corresponding products in good to excellent yields (83–96percent). Most of the substra
- Shi, Mingqi,Wang, Liang,Chen, Qun,He, Mingyang,Shen, Minggui,Zhang, Zhi-hui
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- Development of unique dianionic Ir(III) CCC pincer complexes with a favourable spirocyclic NHC framework
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A new type of dianionic Ir(III) CCC pincer complexes (SNHC-Ir, 1a-1c) is successfully designed and synthesized by developing a one-step methodology, which involves an initial coordination of Ir(I) with the NHC and subsequent metallation of double sp2C- H bonds. This method is considerably useful over those reported by using strong coordination ligand or carbonic anion exchange, and would provide an alternative efficient template of organometallics synthesis. Experimental and density functional theory (DFT) calculation results indicate that the spirocyclic framework is a favourable factor for the facile formation and stabilization of these complexes. Primary investigation shows that chloride 1b can well catalyze homo and hetero addition of styrene derivatives and remote olefin isomerization, which represents the first catalytic application of the dianionic CCC pincer complexes.
- Yan, Zhi-Bo,Dai, Kun-Long,Yang, Bin-Miao,Li, Zi-Hao,Tu, Yong-Qiang,Zhang, Fu-Min,Zhang, Xiao-Ming,Peng, Meng,Chen, Qi-Long,Jing, Ze-Ran
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p. 1761 - 1766
(2020/10/29)
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- Potent Reductants via Electron-Primed Photoredox Catalysis: Unlocking Aryl Chlorides for Radical Coupling
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We describe a new catalytic strategy to transcend the energetic limitations of visible light by electrochemically priming a photocatalyst prior to excitation. This new catalytic system is able to productively engage aryl chlorides with reduction potentials hundreds of millivolts beyond the potential of Na0 in productive radical coupling reactions. The aryl radicals produced via this strategy can be leveraged for both carbon-carbon and carbon-heteroatom bond-forming reactions. Through direct comparison, we illustrate the reactivity and selectivity advantages of this approach relative to electrolysis and photoredox catalysis.
- Chernowsky, Colleen P.,Cowper, Nicholas G. W.,Wickens, Zachary K.,Williams, Oliver P.
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supporting information
(2020/02/04)
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- Lewis acid promoted double bond migration in O-allyl to Z-products by Ru-H complexes
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In catalytic double bond migration reaction, E-configuration olefins were normally generated as the dominant product because E-configuration was thermodynamically favored. However, Z-configuration products are sometimes desired in pharmaceutical chemistry owing to the structure-activity relationship. In this paper, we have demonstrated a new strategy that Lewis acid promoted an widely employed and convenient ruthenium(II) complex for the catalytic isomerization of O-allylethers, leading to thermodynamic-unfavored Z-product under mild conditions. The model substrate of allyl phenyl ether can be simply scaled up to 20 mmol to produce Z-product with TON of 2453 and TOF of 13,430 h?1 at 40–60 °C. The system of Ru(II)/Lewis Acid catalysts was suitable for various substituted O-allylethers and other types of substrates. Through mechanism study including kinetic study, ligand inhibition effect and molecular spectroscopy, the dissociation of PPh3 ligand by the addition of Lewis acid, and the formation a five-membered Ru complex from anchimeric assistance were both recognized as essential steps to improve the reactivity and to control the stereoselectivity of catalytic double bond migration reaction through metal hydride addition-elimination mechanism. This new strategy may provide a new opportunity to produce thermodynamic-unfavored product in heterocyclic compounds for pharmaceutical chemistry.
- Wang, Haibin,Liu, Shaodong,Sun, Tingting,Lv, Zhanao,Zhan, Zhen,Yin, Guochuan,Chen, Zhuqi
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- Hydrosilylation of Allyl Ethers in the Presence of Supported Sulfur-Containing Platinum(II) Complexes
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Hydrosilylation of allyl ethyl, allyl butyl, allyl glycidyl, allyl benzyl, and allyl phenyl ethers by 1,1,3,3-tetramethyldisiloxane in the presence of supported sulfur-containing platinum(II) complexes with the general formula [{SiO2}O2S/
- de Vekki,Il’ina,Skvortsov
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- Palladium-catalysed alkene chain-running isomerization
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We report a method for palladium-catalysed chain-running isomerization of terminal and internal alkenes. Using an air-stable 2,9-dimethylphenanthroline-palladium catalyst in combination with NaBAr4 promoter, olefins are converted to the most stable double bond isomer at -30 to 20 °C. Silyl enol ethers are readily formed from silylated allylic alcohols. Fluorinated substituents are compatible with the reaction conditions, allowing the synthesis of fluoroenolates. Catalyst loading as low as 0.05% can be employed on a gram scale.
- Kocen, Andrew L.,Brookhart, Maurice,Daugulis, Olafs
-
supporting information
p. 10010 - 10013
(2017/09/12)
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- Nitrogen-Doped Carbon-Encapsulated Nickel/Cobalt Nanoparticle Catalysts for Olefin Migration in Allylarenes
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Olefin migration in allylarenes is typically performed with precious-metal-based homogeneous catalysts. In contrast, very limited progress has been made with the use of cheap, Earth-abundant base metals as heterogeneous catalysts for these transformations—in spite of the obvious economic and environmental advantages. Herein, we report on the use of an easily prepared heterogeneous catalyst material for the migration of olefins, in particular, for allylarenes. The catalyst material consists of nickel/cobalt alloy nanoparticles encapsulated in nitrogen-doped carbon shells. The encapsulated nanoparticles are stable in air and are easily collected by centrifugation, filtration, or magnetic separation. Furthermore, we demonstrate that the catalysts can be reused several times and provide continuously high yields of the olefin-migration product.
- Kramer, S?ren,Mielby, Jerrik,Buss, Kasper,Kasama, Takeshi,Kegn?s, S?ren
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p. 2930 - 2934
(2017/08/14)
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- An alternative mechanism for the cobalt-catalyzed isomerization of terminal alkenes to (Z)-2-alkenes
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The cobalt-catalyzed selective isomerization of terminal alkenes to the thermodynamically less-stable (Z)-2-alkenes at ambient temperatures takes place by a new mechanism involving the transfer of a hydrogen atom from a Ph2PH ligand to the starting material and the formation of a phosphenium complex, which recycles the Ph2PH complex through a 1,2-H shift.
- Schmidt, Anastasia,N??dling, Alexander R.,Hilt, Gerhard
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supporting information
p. 801 - 804
(2015/03/04)
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- Mechanistic studies of alkene isomerization catalyzed by CCC-pincer complexes of iridium
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Iridium complexes containing CCC-pincer m-phenylene-bridged N-heterocyclic carbene ligands were examined as catalysts for alkene isomerization. Complexes containing either mesityl or adamantyl side groups were found to catalyze the isomerization of a number of alkenes to the internal isomers, including 1-octene, vinylcyclohexane, and allylbenzene. Mechanistic studies indicate a surprising dichotomy, apparently caused by ligand steric effects. For the mesityl-substituted catalyst, several lines of evidence provide strong support for isomerization via an iridium allyl hydride intermediate: (1) H-D crossover experiments indicate that 1,3-hydrogen migration is exclusively intramolecular, (2) the catalyst resting state, a π-allyl hydride species, was isolated and serves as a kinetically competent catalyst, (3) NMR experiments indicate that the π-allyl hydride resting state undergoes reversible C-H reductive elimination that is rapid relative to catalytic turnover, and (4) kinetic studies indicate that the isomerization reaction is first order in substrate and catalyst, consistent with turnover-limiting ligand substitution. H-D crossover experiments for alkene isomerization catalyzed by the adamantyl-substituted complex show selectivity for a 1,3-deuterium shift, as well as the intermolecular transfer of hydrogen. These results are consistent with an insertion/elimination mechanism proceeding selectively through a secondary metal-alkyl or with a π-allyl-type mechanism with an unknown pathway for intermolecular hydrogen crossover.
- Knapp, Spring Melody M.,Shaner, Sarah E.,Kim, Daniel,Shopov, Dimitar Y.,Tendler, Jennifer A.,Pudalov, David M.,Chianese, Anthony R.
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supporting information
p. 473 - 484
(2014/02/14)
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- Synthesis, characterizations and catalytic applications of hydridecarbonyl ruthenium(II) complexes with imidazole carboxylic acid derivative ligands
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The hydridecarbonyl ruthenium(II) [RuH(CO)(MeImCOO)(PPh3) 2]·CH3OH 1 and [RuH(CO)(BImCOO)(PPh 3)2] 2 complexes were synthesized and characterized by IR, 1H, 31P NMR, UV-Vis spectroscopy and X-ray crystallography. The experimental studies were completed by quantum chemical calculations which were used to identify the nature of the interactions between the ligands and the central ion and the orbital compositions in the frontier electronic structures. Based on a molecular orbital scheme, the calculated results allowed the interpretation of the UV-Vis spectra obtained at an experimental level. The luminescence properties of the complexes were determined. The catalytic activity for both of the complexes was tested in the reaction of the double bond migration in O-allyl systems. Complex 1 was significantly more active than complex 2, because of the longer Ru-H bond distance in complex 1 in comparison with complex 2.
- Ma?ecki,Maroń,Krompiec,Filapek,Penkala,Marcol
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p. 190 - 199
(2013/03/14)
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- Stereoselective alkene isomerization over one position
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Although controlling both the position of the double bond and E:Z selectivity in alkene isomerization is difficult, 1 is a very efficient catalyst for selective mono-isomerization of a variety of multifunctional alkenes to afford >99.5% E-products. Many reactions are complete within 10 min at room temperature. Even sensitive enols and enamides susceptible to further reaction can be generated. Catalyst loadings in the 0.01-0.1 mol% range can be employed. E-to-Z isomerization of the product from diallyl ether was only -6 times as fast as its formation, showing the extremely high kinetic selectivity of 1.
- Larsen, Casey R.,Grotjahn, Douglas B.
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supporting information; experimental part
p. 10357 - 10360
(2012/08/08)
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- Benign catalysis with iron: Unique selectivity in catalytic isomerization reactions of olefins
-
The use of noble metal catalysts in homogeneous catalysis has been well established. Due to their price and limited availability, there is growing interest in the substitution of such precious metal complexes with readily available and bio-relevant catalysts. In particular, iron is a "rising star" in catalysis. Herein, we present a general and selective iron-catalyzed monoisomerization of olefins, which allows for the selective generation of 2-olefins. Typically, common metal complexes give mixtures of various internal olefins. Both bulk-scale terminal olefins and functionalized terminal olefins give the corresponding products under mild conditions in good to excellent yields. The proposed reaction mechanism was elucidated by in situ NMR studies and supported by DFT calculations and extended X-ray absorption fine structure (EXAFS) measurements.
- Jennerjahn, Reiko,Jackstell, Ralf,Piras, Irene,Franke, Robert,Jiao, Haijun,Bauer, Matthias,Beller, Matthias
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experimental part
p. 734 - 739
(2012/06/04)
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- [Pd(μ-Br)(PtBu3)]2 as a highly active isomerization catalyst: Synthesis of enol esters from allylic esters
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The dimeric Pd(I)-complex [Pd(μ-Br)(PtBu3)] 2 was found to be highly active for catalyzing double-bond migration in various substrates such as unsaturated ethers, alcohols, amides, and arenes, under mild conditions. It efficiently mediates the conversion of allylic esters into enol esters, rather than inserting into the allylic C-O bond. The broad applicability of this reaction was demonstrated with the synthesis of 22 functionalized enol esters.
- Mamone, Patrizia,Gruenberg, Matthias F.,Fromm, Andreas,Khan, Bilal A.,Goossen, Lukas J.
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supporting information; experimental part
p. 3716 - 3719
(2012/09/08)
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- An isomerization-1,3-dipolar cycloaddition tandem reaction towards the synthesis of 3-aryl-4-methyl-5-O-substituted isoxazolines from O-allyl compounds
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A new strategy for the synthesis of 3-aryl-4-methyl-5-O-substituted isoxazolines via tandem catalytic isomerization of O-allyl systems to O-(1-propenyl) systems-1,3-dipolar cycloaddition (1,3-DC) to nitrile oxides is presented. The influence of the heteroatom in Ph-X-CH=CHCH3 (X=O, S, or Se) on the regio- and stereoselectivity of ArCNO 1,3-cycloaddition to these dipolarophiles is analyzed as well. The dipolarophiles were obtained via [RuClH(CO)(PPh3)3]-, [RuH2(CO)(PPh 3)]- or base (KOH/18-crown-6)-catalyzed double bond migration in corresponding allyl ethers, O-allyl acetals, PhS- and PhSe-allyl systems. Cycloadditions of nitrile oxides to O-(1-propenyl) systems were fully regioselective whereas in the reactions of ArCNO with the PhS-(1-propenyl) and PhSe-(1-propenyl) systems both possible regioisomers were formed. It was established that within the majority of dipolarophiles of ROCHCHCH3 type 1,3-DC is concerted, while for some dipolarophiles of RXCH=CHCH3 (X=O and R=Ph3C, 2,3-dihydroxypropyl, tetrahydropyran-2-yl; X=S or Se and R=Ph) type 1,3-DC turns into a two-step reaction with simultaneous rotation about C-C bond. The results of the experiments have been analyzed theoretically using DFT calculations. The results of these calculations agreed well with the experimental data.
- Krompiec, Stanis?aw,Bujak, Piotr,Malarz, Joanna,Krompiec, Micha?,Skórka, ?ukasz,Pluta, Tadeusz,Danikiewicz, Witold,Kania, Magdalena,Kusz, Joachim
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experimental part
p. 6018 - 6031
(2012/09/22)
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- Ruthenium(IV)-catalyzed isomerization of the C=C bond of O-allylic substrates: A theoretical and experimental study
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A general mechanism to rationalize RuIV-catalyzed isomerization of the C=C bond in O-allylic substrates is proposed. Calculations supporting the proposed mechanism were performed at the MPWB1K/6-311+G(d,p)+SDD level of theory. All experimental observations in different solvents (water and THF) and under different pH conditions (neutral and basic) can be interpreted in terms of the new mechanism. Theoretical analysis of the transformation from precatalyst to catalyst led to structural identification of the active species in different media. The experimentally observed induction period is related to the magnitudes of the energy barriers computed for that process. The theoretical energy profile for the catalytic cycle requires application of relatively high temperatures, as is experimentally observed. Participation of a water molecule in the reaction coordinate is mechanistically essential when the reaction is carried out in aqueous medium.
- Varela-Ulvarez, Adrian,Sordo, Jose A.,Piedra, Estefania,Nebra, Noel,Cadierno, Victorio,Gimeno, Jose
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experimental part
p. 10583 - 10599
(2011/11/06)
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- Encapsulated molecular catalysts in polysiloxane gels: Ruthenium cluster-catalyzed isomerization of alkenes
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Novel ruthenium-encapsulating polysiloxane gels are prepared by treatment of polymethylhydrosiloxane with diols in the presence of (μ3, η2,η3,η5-acenaphthylene)Ru 3(CO)7, and act as reusable catalysts in the isomerization of alkenes without leakage of the catalyst species. The Royal Society of Chemistry.
- Motoyama, Yukihiro,Abe, Motonori,Kamo, Kazuyuki,Kosako, Yusuke,Nagashima, Hideo
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supporting information; experimental part
p. 5321 - 5323
(2009/03/11)
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- Exploring the reactivity of C(sp3)-cyclometalated Ir III compounds in hydrogen transfer reactions
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The manuscript describes the synthesis and full characterization of a new PC(sp3)P-based cyclometalated IrIII complex that manifests an exceptional thermal stability, as well as outstanding reactivity in hydrogen transfer reactions. The described compound represents the first example of a new family of stable C-(sp3)-metalated compounds.
- Azerraf, Clarite,Gelman, Dmitri
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scheme or table
p. 10364 - 10368
(2009/12/05)
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- Convenient synthesis of isoxazolines via tandem isomerization of allyl compounds to vinylic derivatives and 1,3-dipolar cycloaddition of nitrile oxides to the vinylic compounds
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A novel effective method for the synthesis of new isoxazolines via tandem isomerization of QCH(X)CH{double bond, long}CH(Y) to QC(X){double bond, long}CHCH2(Y) (Q = RO, RS, R2N, R3Si, etc.; X = H, R, OR; Y = H, R; R = alkyl, aryl) catalyzed by ruthenium complexes and 1,3-dipolar cycloaddition of the latter compounds to arenenitrile oxides is presented. The cycloaddition of QCH(X)CH{double bond, long}CH(Y) to 2,6-dichlorobenzonitrile oxide is also described. The regio- and stereoselectivity of the cycloaddition of nitrile oxide to allyl and 1-propenyl (vinylic in general) compounds is discussed.
- Krompiec, Stanis?aw,Bujak, Piotr,Szczepankiewicz, Wojciech
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supporting information; experimental part
p. 6071 - 6074
(2009/04/11)
-
- New selectivities from old catalysts. Occlusion of Grubbs' catalysts in PDMS to change their reactions
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This article describes new selectivities for Grubbs' first and second generation catalysts when occluded in a hydrophobic matrix of polydimethylsiloxane (PDMS). Occlusion of catalysts in mm-sized slabs of PDMS is accomplished by swelling with methylene chloride then removing the solvent under vacuum. The catalysts are homogenously dissolved in PDMS yet remain catalytically active. Many substrates that react by olefin metathesis with Grubbs' catalysts freely dissolved in methylene chloride also react by olefin isomerization with occluded catalysts. Eleven examples of substrates that exhibit dual reactivity by undergoing olefin isomerization with occluded catalysts and olefin metathesis with catalysts dissolved in methylene chloride are reported. Most of these substrates have olefins with allylic phosphine oxides, carbonyls, or ethers. Control experiments demonstrate that isomerization is occurring in the solvent by decomposition of the catalyst from a ruthenium carbene to a proposed ruthenium hydride. This work was extended by heating occluded Grubbs' first generation catalyst to 100 °C in 90% MeOH in H2O in the presence of various alkenes to transform the Grubbs' catalyst into an isomerization catalyst for unfunctionalized olefins. This work demonstrates that occlusion of organometallic catalysts in PDMS has important implications for their reactions and can be used as a method to control which reactions they catalyze.
- Brett Runge,Mwangi, Martin T.,Bowden, Ned B.
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p. 5278 - 5288
(2007/10/03)
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- SmI2/water/amine mediates cleavage of allyl ether protected alcohols: application in carbohydrate synthesis and mechanistic considerations.
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[reaction: see text]. SmI2/H2O/amine provides selective cleavage of unsubstituted allyl ethers in good to excellent yields. This method is therefore useful in deprotection of alcohols and carbohydrates.
- Dahlen, Anders,Sundgren, Andreas,Lahmann, Martina,Oscarson, Stefan,Hilmersson, Goeran
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p. 4085 - 4088
(2007/10/03)
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- Synthesis, characterization, and reactivity of half-sandwich Ru(II) complexes containing phosphine, arsine, stibine, and bismutine ligands
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The synthesis and some reactions of the Ru(II) and Ru(IV) half-sandwich complexes [RuCp(EPh3)(CH3CN)2]+ (E = P, As, Sb Bi) and when the former is weaker, that is in going down the series. Thus in the case of Bi,
- Becker, Eva,Slugovc, Christian,Rüba, Eva,Standfest-Hauser, Christina,Mereiter, Kurt,Schmid, Roland,Kirchner, Karl
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- A concise synthesis of carpanone using solid-supported reagents and scavengers
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The synthesis of the natural product carpanone by utilization of polymer supported reagents, eliminating the need for conventional purification techniques was reported. The synthesis and crystal structure of a polymer-supported iridium catalyst for isomerization was also reported. The observations showed that isomerization of electron-rich aromatic compounds by the catalyst resulted in products with predominantly trans alkene geometry. However, the electron-poor derivatives were found to be less prone to rearrangement.
- Baxendale, Ian R.,Lee, Ai-Lan,Ley, Steven V.
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p. 1850 - 1857
(2007/10/03)
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- A polymer-supported iridium catalyst for the stereoselective isomerisation of double bonds
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A polymer-supported iridium catalyst has been prepared and used in the isomerisation of the double bonds in aryl allylic derivatives with excellent trans selectivity and without the need for conventional work-up procedures.
- Baxendale, Ian R.,Lee, Ai-Lan,Ley, Steven V.
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p. 516 - 518
(2007/10/03)
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- Determination of rate constants for the reaction of aryl radicals with enolate ions
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The rate of ring closure (kC) of o-(ω-alkenyl)aryl radicals by means of an intramolecular attack of the intermediate phenyl-type radical at the tethered double bond was found to be 4.2 × 108 S-1 (for 1?) and 7.6×107 S-1 (for 8?), both being 6-exo-trig processes, and 9.6 × 109 S-1 for the 5-exo-trig process of 3?. The kC rate constant of these radicals was calibrated with respect to a known rate of H-atom abstraction (kH). The photostimulated SRN1 reactions of radical clock precursor 1 with anions PhS- and (EtO)2PO- in Me2SO at 25 °C provided the rates of addition of these nucleophiles (kY) to intermediate 1? (3.2 × 108 and 2.5 × 109 M-1 S-1, respectively). In contrast, the analogous reaction of a ketone enolate ion with precursor 1 did not take the expected SRN1 course; instead an elimination reaction was favoured. Similarly, the reactions of radical clock precursors 3 or 8 with the enolate ion failed. However, investigation of the distribution of 9-anthracenyl (11?) or 1-naphthyl (12?) radicals between two competing reactions, namely combination with a nucleophile and H abstraction from the solvent (Me2SO), was successful and eventually enabled us to find the kY values for the addition of the enolate ion to these two aryl radical intermediates (4.4 × 108 and 2.9 × 109 M-1 S-1, respectively).
- Annunziata, Alfonso,Galli, Carlo,Marinelli, Manuela,Pau, Tullia
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p. 1323 - 1329
(2007/10/03)
-
- Thermodynamic, spectroscopic, and density functional theory studies of allyl aryl and prop-1-enyl aryl ethers. Part 1. Thermodynamic data of isomerization
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A chemical equilibration study of the relative thermodynamic stabilities of seventy isomeric allyl aryl ethers (a) and (Z)-prop-1-enyl aryl ethers (b) in DMSO solution has been carried out. From the variation of the equilibrium constant with temperature the Gibbs energies, enthalpies, and entropies of isomerization at 298.15 K have been evaluated. Because of their low enthalpies, the (Z)-prop-1-enyl aryl ethers are strongly favored at equilibrium, the Gibbs energies of the a→b isomerization ranging from -12 to -23 kJ mol-1. The entropy contribution is negligible in most reactions, but occasionally small positive values less than +10 J K-1 mol-1 of the entropy of isomerization are found. The equilibration studies were also extended to involve two pairs of related isomeric ethers with a Me substituent on C(2) of the olefinic bond. The Me substituent was found to increase the relative thermodynamic stability of the allylic ethers by ca. 3.4 kJ mol-1.
- Taskinen, Esko
-
p. 1824 - 1834
(2007/10/03)
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- Convenient criterion for the distinction between electrophilic and electron transfer reactions of electron-rich alkenes
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Both experimental and theoretical studies confirm that the formation of aryl vinyl ether and aryl vinyl sulfide cation radicals from the corresponding neutral substrates correlates with the Brown σ+ parameters as opposed to Hammett σ values. Peak oxidation potentials for both classes of substrates correlate preferentially with σ+, as do gas-phase ionization energies calculated by both semi-empirical and ab initio methods. In contrast, the protonation energies of the same substrates, which relate to carbocation formation, correlate preferentially with σ values, as do rates of protonation and other electrophilic additions. These observations permit a sharp distinction between electrophilic and electron transfer reactions of these two common classes of electron-rich substrates. Using this criterion, the cycloadditions of tetracyanoethylene to these substrates are found to proceed via an electrophilic mechanism, rather than by a previously proposed electron transfer mechanism.
- Bauld, Nathan L.,Aplin, J. Todd,Yueh, Wang,Endo, Stephanie,Loving, Angie
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-
- Applications of High-Temperature Aqueous Media for Synthetic Organic Reactions
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Preparative organic synthesis was investigated in aqueous media at temperatures up to 300°C. Experiments were conducted with a recently disclosed pressurized microwave batch reactor (MBR) or in conventionally heated autoclaves. Thirty-six examples are presented. Among these, methods were developed for a Fischer synthesis, an intramolecular aldol condensation that was scaled up, decarboxylation of indole-2-carboxylic acid, Rupe rearrangement of 1-ethynyl-l-cyclohexanol, isomerization of carvone to carvacrol, and conversion of phenylacetylene to acetophenone. The applicability of high-temperature water was also demonstrated for biomimetic processes important in food, flavor, and aroma chemistry and for tandem reactions such as formation of 2-methyl-2,3- dihydrobenzofuran from allyl phenyl ether. When addition of acid or base was necessary, less agent was usually required for high-temperature processes than for those at and below boiling, and the reactions often proceeded more selectively. In some instances the requirement was orders of magnitude lower, with obvious consequences for safe, economic processing and for lowering costs of effluent disposal. The diversity of reactions indicates that high-temperature aqueous media could play an increasingly important role in the development of new preparative processes.
- An, Jingyi,Bagnell, Laurence,Cablewski, Teresa,Strauss, Christopher R.,Trainor, Robert W.
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p. 2505 - 2511
(2007/10/03)
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- Isomerization of Olefins Catalyzed by the Hexaaquaruthenium(2+) Ion
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Isomerization of olefins, in particular the useful transformation of allyl to vinyl ethers is catalyzed by the hexaaquaruthenium(2+) ion, producing the (E)-isomers under mild conditions.
- Karlen, Thomas,Ludi, Andreas
-
p. 1604 - 1606
(2007/10/02)
-
- Electroreductive Dehalogenation of Chlorinated Aromatic Ethers. Unexpected Electrogenerated Base Catalyzed Reactions
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The electroreductive dehalogenation of several mono- and polychlorinated aromatic ethers that serve as models of dioxins has been studied.The dechlorination was achieved by a simple constant-current electrolysis using a lead cathode in dimethylformamide.It was shown that 2,4,6-trichloroanisole undergoes successive dechlorination and the chlorine in the 2-position is selectively eliminated.Competitive reactions and cyclic voltammetric measurements suggested the increasing reactivity order of mono- di- trichloride for the reductive dechlorination.Use of allyl 2-chloro phenyl ether as a probe for radical cyclization indicated that free radical intermediates are of little importance.Thus, incipient radicals are immediately reduced to anionic intermediates.The electrolyses in the presence of deuterium oxide revealed proton sources for the present dechlorination.In these attempts, novel phenomena due to electrogenerated base (EGB) were found: di- and trichlorides underwent an unexpected overincorporation of deuterium in their dechlorinated products; a selective formation of Z-enol ethers from the allylic ethers was encountered.The mechanistic features of the present electroreductive dechlorination are discussed.
- Kimura, Makoto,Miyahara, Hiroyoshi,Moritani, Noriyuki,Sawaki, Yasuhiko
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p. 3897 - 3902
(2007/10/02)
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- DOUBLE BOND MIGRATION IN 3-FUNCTIONAL SUBSTITUTED PROPENES IN THE PRESENCE OF RUTHENIUM TRIS(2,4-PENTANEDIONATE)
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The question of the range in which ruthenium tris(2,4-pentanedionate) can be used as a catalyst of isomerization of 3-functional substituted propenes to 1-substituted propenes has been studied.The possibility of using 2,4-pentanedionates of other metals f
- Krompiec, Stanislaw,Suwinski, Jerzy
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p. 505 - 514
(2007/10/02)
-
- ARYLATION OF CYCLIC ETHERS BY GASEOUS PHENYLIUM IONS. FORMATION AND BEHAVIOR OF PHENOXENIUM IONS IN THE GAS PHASE
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Free, unsolvated phenylium ions formed by the spontaneous decay of 1,4-ditritiobenzene have been allowed to react with gaseous cyclic ethers (oxirane, propene oxide, and oxetane) and acetaldehyde in the pressure range 30-250 Torr and in the presence of a thermal radical scavenger (O2, 4 Torr).The effects of a gaseous base (NMe3, 20 Torr) and of an energy moderator (He, 630-720 Torr) were also investigated.Phenylium ion confirms its considerable site selectivity, demonstrated by the distinct preference for the n-type center of the substrate, although appreciable insertion into the carbocyclic structure of propene oxide and oxetane is observed as well.The stability features of the ionic intermediates from addition of phenylium ion to selected substrates have been evaluated as well as their fragmentation and isomerization mechanisms.The behavior of gaseous phenylium ion toward cyclic ethers, in particular its ability to formally abstract an oxygen atom from the ether to give the phenoxenium ion, a reaction first observed in the present study, is discussed and compared with previous mechanistic investigations carried out in the gas phase and in solution.
- Fornarini, Simonetta,Speranza, Maurizio
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p. 2506 - 2514
(2007/10/02)
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- Chemical Reactivities of Coordinatively Unsaturated Hydridotris(phosphonite)cobalt(I) Species Photogenerated towards Allylic and Related Compounds
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Pyrex-filtered photoirradiation with a high-pressure Hg lamp was performed for a thermally inert hydridocobalt(I) CoH4 in the presence of some allylic compounds.Allyl benzoate and allyl phenyl ether showed the cleavage of allylic-O bonds to give propene in a stoichiometric quantity to the complex charged.Photoassisted catalytic double-bond migration occured for N-allylacetamide, N,N-diethylallylamine, and allylbenzene to afford the respective (E)- and (Z)-1-propenyl derivatives with kinetically controlled, E, Z compositions, and the fractions of Z isomers at the initial stage of the reaction proceeding were near 79, 30, and 20percent, respectively.Laser flash photolysis study revealed that the double-bond migration was initiated by the coordination of the substrates through C=C double bond rather than nitrogen or oxygen donor-atom to the coordinatively unsaturated species "CoH3" photogenerated.
- Onishi, Masayoshi,Oishi, Shigero,Sakaguchi, Mitoshi,Takaki, Isato,Hiraki, Katsuma
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p. 3925 - 3930
(2007/10/02)
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- ELIMINATION AND ADDITION REACTIONS. PART 39. VARIATION OF NUCLEOFUGALITY WITH TRANSITION STATE STRUCTURE-1,3- AND 1,2-ELIMINATIONS FROM CARBANIONS COMPARED.
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Phenylsulphonyl-activated 1,3-eliminations have been investigated with the objective of determining nucleofugalities of six leaving groups.In cyclohexane-1,3-diyl and propane-1,3-diyl system unactivated 1,2-elimination of 'poor' leaving groups occurs faster than 1,3-elimination.In 2,2-dimethylpropane-1,3-diyl substrates, however, quantitative 1,3-eliminations occur and the nucleofugalities of Br, Cl, OTs, PhSO2, PhS, PhO, have been determined.In a linear free energy relationship extending over 15 pKa units and 12 rank units, an excellent correlation of nucleofugality with the pKa of the conjugate acid of the leaving group is found.It is concluded from the comparison with 1,2-eliminations previously studied that 1,3-elimination involves considerable leaving group separation and ring formation in the transition state.With bromide as leaving group, the 2,2-dimethylpropane-1,3-diyl system is 1000 times more reactive in cyclopropane formation than the propane-1,3-diyl system; this is the first quantitation of the Thorpe-Ingold effect in homocyclic ring formation.With chloride and tosylate leaving groups, smaller accelerations are observed.
- Issari, Bahram,Stirling, Charles J. M.
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p. 1043 - 1052
(2007/10/02)
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- RHODIUM(I)-CATALYZED REACTION OF 2-PROPENYL CHLOROACETATE. FORMAL ELIMINATION OF ALLENE AND INSERTION INTO THE C-O BOND OF THE ESTER FUNCTION
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Treatment of 2-propenyl chloroacetate with catalytic amount of RhCl(PPh3)3 in boiling tetrahydrofuran gave 2-methylene-4-pentenyl chloroacetate, a product which is derived via a formal insertion of allene unit into the C-O bond of the starting chloroacetate, with concomitant formation of chloroacetic acid.
- Miyamo, Sotaro,Mori, Atsuo,Kato, Katsumi,Kawashima, Yasuhiko,Hashimoto, Harukichi
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p. 1379 - 1382
(2007/10/02)
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- Isomerisation of Allyl Ethers to Vinyl Ethers catalysed by Palladium on Carbon
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Several allyl ethers are cleanly converted into the corresponding prop-1-enyl ethers on heating in benzene or toluene in the presence of palladium on carbon.
- Carless, Howard A. J.,Haywood, David J.
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p. 980 - 981
(2007/10/02)
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- Process for the isomerization of aromatic alkenyl compounds
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Aromatic alkenyl compounds, for example, eugenol and safrole, are isomerized, for example to isoeugenol and isosafrole, by contact with a ruthenium or osmium catalyst.
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