- Inner-Sphere versus Outer-Sphere Coordination of BF4- in a NHC-Gold(I) Complex
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The role of counterions in chemistry mediated by gold complexes stretches much further than merely providing charge balance to cationic gold species. Interplay between their basicities and coordination strengths influences interactions with both the gold center and substrates in catalysis. Actual monogold(I) active species are generally believed to be monocoordinated species, formed from the abstraction or the decoordination of a second ligand from precursor complexes, but only a small amount of experimental evidence exists to underpin the existence of these transient species. The formation of a bench-stable neutral IPrCl-gold(I) tetrafluoroborate complex is reported herein. Experimental studies by X-ray diffraction analysis and NMR spectroscopy and theoretical studies by DFT calculations were conducted to determine the composition, structure, and behavior of this complex. The absence of an auxiliary ligand resulted in inner-sphere coordination of the counterion in the solid state. In solution, an equilibrium between two conformations was found with the counterion occupying inner-sphere and outer-sphere positions, respectively. Stoichiometric and catalytic reactivity studies with the tetrafluoroborate complex have been conducted. These confirmed the lability of the inner-sphere coordinating counterion that gives the IPrCl-gold(I) fragment behavior similar to that of related systems.
- Veenboer, Richard M. P.,Collado, Alba,Dupuy, Stéphanie,Lebl, Tomas,Falivene, Laura,Cavallo, Luigi,Cordes, David B.,Slawin, Alexandra M. Z.,Cazin, Catherine S. J.,Nolan, Steven P.
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- Palladium-catalyzed C-C bond formation: Synthesis of 1,1-dialkylbuta-1,3-dienes and β-phenylstyrenes via organoboron intermediates
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α,β-Unsaturated and α-phenyl acetals show different reactivity when treated with LIC-KOR superbase and trialkylboranes, in the presence of the reagent system PdL4-ArX (Suzuki-Miyaura cross-coupling conditions). In particular, unsaturated acetal
- Deagostino, Annamaria,Prandi, Cristina,Zavattaro, Chiara,Venturello, Paolo
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- Palladium-Catalyzed Reductive Cross-Coupling Reaction of Aryl Chromium(0) Fischer Carbene Complexes with Aryl Iodides
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The first palladium-catalyzed reductive cross-couplings of aryl chromium(0) carbene complexes with aryl iodides have been realized. This coupling reaction shows excellent functional group tolerance and high efficiency. Mechanistically, aryl chromium(0) carbene complexes undergo transmetalation with arylpalladium species to generate palladium(II) carbene intermediates, which is followed by migratory insertion. The catalytic cycle is then completed by hydrogen transfer and reductive elimination. Consistent with the mechanistic hypothesis, density functional theory (DFT) calculations support the involvement of a palladium carbene intermediate, and carbene migratory insertion is a facile step with an energy barrier of 5.1 kcal/mol. The carbene transfer step and the hydrogen transfer step are confirmed as the rate-limiting steps in the catalytic cycle.
- Wang, Kang,Lu, Yu,Hu, Fangdong,Yang, Jinghui,Zhang, Yan,Wang, Zhi-Xiang,Wang, Jianbo
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supporting information
p. 1 - 10
(2018/01/17)
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- Stereoselective gold(I)-catalyzed intermolecular hydroalkoxlation of alkynes
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(Chemical Equation Presented) We report the use of cationic gold complexes [Au(NHC)(CH3CN)][BF4] and [{Au(NHC)}2(μ-OH)][BF4] (NHC = N-heterocyclic carbene) as highly active catalysts in the solvent-free hydroalkoxylation of internal alkynes using primary and secondary alcohols. Using this simple protocol, a broad range of (Z)-vinyl ethers were obtained in excellent yields and high stereoselectivities. The methodology allows for the use of catalyst loadings as low as 200 ppm for the addition of primary alcohols to internal alkynes (TON = 35 000, TOF = 2188 h-1).
- Veenboer, Richard M. P.,Dupuy, Stphanie,Nolan, Steven P.
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p. 1330 - 1334
(2015/02/19)
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- A parahydrogen based NMR study of Pt catalysed alkyne hydrogenation
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A parahydrogen based NMR study of the platinum(ii) bis-phosphine triflate catalysed hydrogenation of alkynes in methanol reveals that platinum bis-phosphine alkyl cations and methanol functionalised platinum bis-phosphine alkylether cations, are responsible for the observed alkene and vinylether products.
- Boutain, Marie,Duckett, Simon B.,Dunne, John P.,Godard, Cyril,Hernandez, Jose M.,Holmes, A. Jonathan,Khazal, Iman G.,Lopez-Serrano, Joaquin
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body text
p. 3495 - 3500
(2010/07/03)
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- Dichotomous reactivity in the reaction of triethyl- and triphenylphosphane HBr salts with dimethyl acetals: A novel entry to α-alkoxy-functionalized ylides and general synthesis of vinyl ethers and alkoxy dienes
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The discovery of dichotomous reactivity in the reaction of trialkyl- vs. triphenylphosphane HBr salts with acetals allows entry to functionalized α-methoxy phosphonium salts and a novel process for tertiary phosphane methylation. The new protocol opens a general entry to the synthesis of vinyl ethers and differentially substituted 1,3-dienes via Wittig reactions of the functionalized ylides derived from the α-methoxy phosphonium salts.
- Das, Priyabrata,McNulty, James
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supporting information; experimental part
p. 3587 - 3591
(2010/09/05)
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- Palladium-catalyzed cleavage reaction of carbon-carbon triple bond with molecular oxygen promoted by lewis acid
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A new Lewis acid promoted and palladium-catalyzed cleavage reaction of carbon-carbon triple bond with molecular oxygen was reported, in which alkyne or 1.3-diynes is split into carboxylic ester in various alcohols. Copyright
- Wang, Azhong,Jiang, Huanfeng
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p. 5030 - 5031
(2008/10/09)
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- Heck reactions of α- or β-substituted enol ethers with aryl bromides catalysed by a tetraphosphane/palladium complex - Direct access to acetophenone or 1-arylpropanone derivatives
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cis,cis,cis-1,2,3,4-Tetrakis(diphenylphosphanylmethyl)cyclopentane/ [PdCl(C3H5)]2 efficiently catalyses the Heck reaction of α- and β-substituted enol ethers with aryl bromides. The arylation of 1-phenyl-1-(trimethylsilyloxy) ethylene led directly to the 2-aryl-1-phenylethanones. Similar reaction rates were observed with electron-rich, electron-deficient or sterically congested aryl bromides. Heck reaction with benzyl isopropenyl ether gave a mixture of isomers. However, this mixture gave selectively the 1-arylpropanones after hydrolysis. Employing β-methoxystyrene, 3-ethoxyacrylonitrile or methyl 3-methoxyacrylate, the regioselective α-arylation of these enol ethers was observed in all cases, but mixtures of (Z) and (E) isomers were generally obtained, which in many cases yielded a single ketone product after acid treatment. The stereoselectivity of this reaction depends on steric and electronic factors, and better stereoselectivities in favour of (Z) isomers were observed with electron-rich or sterically congested aryl bromides. Higher yields were obtained for this reaction with electron-rich or sterically congested aryl bromides than with electron-poor aryl bromides. These observations suggest that the rate-limiting step of the catalytic cycle is not the oxidative addition of the aryl bromide to the palladium complex with these substituted enol ethers. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
- Battace, Ahmed,Feuerstein, Marie,Lemhadri, Mhamed,Zair, Touriya,Doucet, Henri,Santelli, Maurice
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p. 3122 - 3132
(2008/02/08)
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- Mild preparation of alkenes from phenyl sulfides: One-pot elimination of phenylthio group via sulfilimine at ambient temperature
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(Chemical Equation Presented) Various alkenes were prepared from phenyl sulfides in a one-pot manner at room temperature by converting them to the corresponding S-aminosulfonium salts with O-mesitylenesulfonylhydroxylamine, followed by treatment with pota
- Matsuo, Jun-Ichi,Kozai, Takaaki,Ishibashi, Hiroyuki
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p. 6095 - 6098
(2007/10/03)
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- Functionalization of alkynes catalyzed by t-Bu-P4 base
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The addition of O- and N-nucleophiles to alkynes catalyzed by a phosphazene base, t-Bu-P4 base, was investigated. Alkynes were easily transformed to enol ethers and enamines in DMSO by the addition of nucleophiles. When phenylacetylene was reacted with di
- Imahori, Tatsushi,Hori, Chieko,Kondo, Yoshinori
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p. 1090 - 1092
(2007/10/03)
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- A New Synthesis of Butadienyl- and Styrylboronic Esters: Highly Reactive Intermediates for Suzuki Cross-Coupling
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(Matrix Presented) Alkoxy-functionalized butadienyl- and styrylboronic esters have been synthesized starting from α,β-unsaturated acetals. These derivatives readily cross-couple with aryl substrates, and the obtained products can be transformed under mild
- Tivola, Paolo Balma,Deagostino, Annamaria,Prandi, Cristina,Venturello, Paolo
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p. 1275 - 1277
(2007/10/03)
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- Alkoxydienylstannanes via metalation of α,β-unsaturated and α-phenyl acetals: Preparation and synthetic uses in the Stille cross-coupling reaction
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Alkoxydienylstannanes via metalation of α,β-unsaturated and α-phenyl acetals were analyzed. Treatment of α,β-unsaturated and α-phenyl acetals with an equimolar mixture of butyllithium and potassium tert-butoxide gave α-metalated 1,3 dienes and vinyl ethers that readily react with chlorotributyltin affording (Z)-functionalized alkoxyvinylstannanes. Stille cross-coupling reaction between these reactants and allyl bromide, iodobenzene, or benzoyl chloride produced derivatives that can be converted into carbonyl compounds according to an umpolung approach.
- Tivola, Paolo Balma,Deagostino, Anna,Prandi, Cristina,Venturello, Paolo
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p. 437 - 441
(2007/10/03)
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- Ti(η5-C5H5)(η5-C5H4(t)Bu)(CH2Ph)2; a probe of the course of the petasis benzylidenation reaction
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The existence of the proposed benzylidene intermediate 11 in the Petasis benzylidenation procedure is supported by the isolation of cyclometallated product 8. A model is proposed which explains the empirical observation that a large acid residue and a small ester group are needed for good stereoselectivity in benzylidenation reactions.
- Hart,McCamley,Taylor
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- Electronic and Conformational Effects in the Photochemistry of α-Alkenyl-Substituted Vinyl Halides
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The photochemical reactions in methanol of the vinylic halides 2-halo-1-phenyl-1,3-butadienes 1-3Z-X (β-halo-β-alkenylstyrenes) and 1-halo-1,2-diphenylethenes 4Z-X (α-halostilbenes), with X = Cl or Br, have been studied quantitatively.E/Z isomerization, dehydrohalogenation, nucleophilic substitution, a -halogen shift, a -hydrogen shift, and oxidation are observed as the primary reactions.No reductive dehalogenation products are formed.The efficiencies of product formation are dependent on the halogen used, the electron-donating capacity of the α-substituent, the ground state conformation of the starting material, and the wavelength of excitation.Apart from the photoinduced E/Z isomerization and the oxidation reaction typical for alkenes, product formation occurs exclusively via vinyl-cationic intermediates, which are formed upon photolytic cleavage of the carbon-halogen bond.These ionic species, or part of them, are present as vinyl cation/halide anion-pairs.
- Krijnen, Erik S.,Zuilhof, Han,Lodder, Gerrit
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p. 8139 - 8150
(2007/10/02)
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- Cyclopropyl analogs as anti-estrogenic, anti-tumor and female fertility agents
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Anti-estrogenic cyclopropyl analogs such as 1,1-dichlorocis-2,3-diphenylcyclopropane, when administered to a subject function as anti-tumor agents to prevent the development of estrogen-dependent tumors in the subject and substantially arrest the growth and metastatic involvement of existing estrogen-dependent tumors in the subject. Further, the anti-estrogenic cyclopropyl analogs may be used as anti-estrogenic agents and as fertility agents in the treatment of female infertility. The cyclopropyl analogs useful as anti-tumor, anti-estrogenic and female fertility agents have the general structure wherein: X is a halogen or hydrogen atom; R1 is a hydrogen atom, an alkyl group containing from 1 to about 3 carbon atoms, a monocyclic group, a hydroxy substituted monocyclic group, an alkoxy substituted monocyclic group in which the alkyl substituent contains from 1 to about 3 carbon atoms or an acetoxy substituted monocyclic group; R2 is a hydrogen atom, an acetate group, a hydroxyl group, an alkoxy group in which the alkyl substituent contains from 1 to about 3 carbon atoms, a beta-dialkylaminoethoxy group wherein the alkyl substituent contains from 1 to about 6 carbon atoms, a beta-monoaminoheterocycloethoxy group, or pharmaceutically acceptable salts thereof; R3 is a hydrogen atom, an acetate group, a hydroxyl group, or an alkoxy group in which the alkyl substituent contains from 1 to about 3 carbon atoms; R4 is a hydrogen atom, or an alkyl group containing from 1 to about 3 carbon atoms; and the wavy lines ( ) in the structure indicate that the anti-tumor agent can be the cis- or trans-isomers.
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- Metalation of Alkynes. Part 2. Behaviour of Alkynes with Mercury(II)Acetate in Methanol: a Systematic Reinvestigation
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The reaction of a series of alkynes with mercury(II)acetate, both in equimolar and catalytic amounts, were investigated in methanol.Hex-1-yne, oct-1-yne, oct-4-yne, 1,4-diacetoxybut-2-yne, methyl oct-2-ynoate, methyl 3-phenylpropynoate, oct-2-ynoic acid, phenylpropynoic acid, oct-1-yn-3-ol, 1-ethynylcyclohexanol, 1-ethynylcyclohexamine, phenylethyne, diphenylethyne, and ethynylferrocene were the examined substrates.The non-mercuriated products from the reaction were the corresponding vinyl ether, dialkoxyalkane, and ketone, isolated under preparative conditions.The presence of 0.1percent toluene-p-sulphonic acid increased the reactivity.The reactions of oct-1-yne and oct-4-yne were studied in detail by following with time the formation of the products under a variety of conditions, and a mechanistic scheme was drawn.For comparison, styrene, trans-oct-4-ene, and trans-β-methylstyrene were treated with 5 molpercent mercury(II) acetate.The reaction of alkenes was found to be non-catalytic.
- Bassetti, Mauro,Floris, Barbara
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p. 227 - 234
(2007/10/02)
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- Photolysis of Vinyl Halides. Preferential Formation of Vinyl Cations by Copper(II) Salts
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Photolysis of vinyl halides in the presence of copper(II) salts in a significant suppression of product formation derived from vinyl radicals.Photolysis of 1,1-diaryl-2-bromopropenes in the presence of copper(II) salts yielded no 1,1-diaryl-2-propenes.Photolysis of other vinyl halides, i.e., 1,1-diaryl-2-iodopropenes, 1,1-diaryl-2-bromoethylenes, and 1-bromo-2-(p-methoxyphenyl)ethylene, also led to a large decrease in the yields of the reduced olefins derived from the vinyl radicals.Copper(II) triflate was found to be more effective for the oxidation of vinyl radicals than copper(II) acetate.These reactions are explained by the intervention of vinylcopper intermediates and the formation of vinyl cations.
- Kitamura, Tsugio,Kobayashi, Shinjiro,Taniguchi, Hiroshi
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p. 2641 - 2645
(2007/10/02)
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- Peterson Olefination of (α-Methoxybenzyl)silane with Aldehydes and Ketones Leading to Vinyl Ethers
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(α-Methoxybenzyl)trimethylsilane is deprotonated with butyllithium and then allowed to react with a variety of carbonyl compounds giving vinyl ethers which are convertible into methyl ketones under mild conditions.
- Kanemasa, Shui,Tanaka, Junji,Nagahama, Hideki,Tsuge, Otohiko
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p. 3385 - 3386
(2007/10/02)
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- Chemistry of O-Alkyl Selenoesters. Reaction with Triethylphosphine
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The reaction between triethylphosphine and a number of aliphatic and aromatic selenoesters under oxygen-free conditions have been investigated.The purple intermediate formed in the reaction with the aliphatic selenoesters was quenched with atmospheric oxygen and gave the corresponding esters, whereas quenching with methyl iodide gave the corresponding 1-alkoxy-1-iodoalkyltriethylphosphonium iodides (13)-(16).The 1-alkoxy-1-iodoalkyltriethylphosphonium iodides gave the 1-alkoxyalkyltriethylphosphonium iodides (17)-(20) upon treatment with methanol, and treatment with benzaldehyde at -70 deg C gave α-alkoxyalkyl phenyl ketones (22)-(25).The reaction between the selenobenzoates and triethylphosphine gave α-dialkoxy-stilbenes and -dibenzyls.When the reaction was carried out in cyclohexene 7-alkoxy-7-phenylbicycloheptanes were formed.The presence of benzaldehyde in the reaction mixture led to α-alkoxystilbenes.An explanation for these different reactions is presented.
- Hansen, Per-Egil
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p. 1627 - 1634
(2007/10/02)
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