- Oxygen-Oxygen Bond Cleavage and Formation in Co(II)-Mediated Stoichiometric O2 Reduction via the Potential Intermediacy of a Co(IV) Oxyl Radical
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In reactions of significance to alternative energy schemes, metal catalysts are needed to overcome kinetically and thermodynamically difficult processes. Often, high-oxidation-state, high-energy metal oxo intermediates are proposed as mediators in elementary steps involving O-O bond cleavage and formation, but the mechanisms of these steps are difficult to study because of the fleeting nature of these species. Here we utilized a novel dianionic pentadentate ligand system that enabled a detailed mechanistic investigation of the protonation of a cobalt(III)-cobalt(III) peroxo dimer, a known intermediate in oxygen reduction catalysis to hydrogen peroxide. It was shown that double protonation occurs rapidly and leads to a low-energy O-O bond cleavage step that generates a Co(III) aquo complex and a highly reactive Co(IV) oxyl cation. The latter was probed computationally and experimentally implicated through chemical interception and isotope labeling experiments. In the absence of competing chemical reagents, it dimerizes and eliminates dioxygen in a step highly relevant to O-O bond formation in the oxygen evolution step in water oxidation. Thus, the study demonstrates both facile O-O bond cleavage and formation in the stoichiometric reduction of O2 to H2O with 2 equiv of Co(II) and suggests a new pathway for selective reduction of O2 to water via Co(III)-O-O-Co(III) peroxo intermediates.
- Nurdin, Lucie,Spasyuk, Denis M.,Fairburn, Laura,Piers, Warren E.,Maron, Laurent
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Read Online
- Protodesilylation of Arylsilanes by Visible-Light Photocatalysis
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The first visible-light-mediated photocatalytic, metal- and base-free protodesilylation of arylsilanes is presented. The C(sp2)-Si bond cleavage process is catalyzed by a 5 mol % loading of a commercially available acridinium salt upon blue-light irradiation. Two simple approaches have been identified employing either aerobic or hydrogen atom transfer cocatalytic conditions, which enable the efficient and selective desilylation of a broad variety of simple and complex arylsilanes under mild conditions.
- García Manche?o, Olga,Kuhlmann, Jan H.,Uygur, Mustafa
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supporting information
p. 1689 - 1694
(2022/03/14)
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- Preparation method of aromatic silicon organic compound
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The invention provides a preparation method of an aromatic silicon organic compound. The aromatic silicon organic compound is a compound as shown in a formula 3 shown in the specification, the aromatic silicon organic compound is prepared by reacting a compound as shown in a formula 1 with a compound as shown in a formula 2, and the reaction formula is as shown in the specification. In the formulas, a is selected from any integer of 0-5, n is selected from any integer of 1-6, R is selected from one of alkyl, alkoxy, fluorine, trifluoromethyl and trifluoromethoxy; m is any integer selected from 1-3, and R2 is selected from C1-C6 alkyl; a catalyst used in the reaction is MIc, MIc is iodized salt, M is metal ion, and c is selected from 1 or 2 according to the valence state of M; and magnesium is added in the reaction process. The method has the advantages of low cost, effective avoidance of heavy metal residues, simplicity and convenience in operation, high yield, mild reaction conditions and easiness in industrialization.
- -
-
Paragraph 0044-0047
(2021/07/08)
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- Transition-Metal-Free Coupling of Polyfluorinated Arenes and Functionalized, Masked Aryl Nucleophiles
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A chemoselective C(sp2)?C(sp2) coupling of sufficiently electron-deficient fluorinated arenes and functionalized N-aryl-N’-silyldiazenes as masked aryl nucleophiles is reported. The fluoride-promoted transformation involves the in situ generation of the aryl nucleophile decorated with various sensitive functional groups followed by a stepwise nucleophilic aromatic substitution (SNAr). These reactions typically proceed at room temperature within minutes. This catalytic process allows for the functionalization of both coupling partners, furnishing highly fluorinated biaryls in good yields.
- Finck, Lucie,Oestreich, Martin
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p. 11061 - 11064
(2021/06/12)
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- Cobalt-Catalyzed Defluorosilylation of Aryl Fluorides via Grignard Reagent Formation
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Transition-metal-catalyzed transformations of the carbon-fluorine bond not only tackle an interesting problem of challenging bond activation but also offer new synthetic strategies where the relatively inert C-F bond is converted to versatile functional groups. Herein we report a practical cobalt-catalyzed silylation of aryl fluorides that uses a cheap electrophilic silicon source with magnesium. This method is compatible with various silicon sources and can be operated under aerobic conditions. Mechanistic studies support the in situ formation of a Grignard reagent, which is captured by the electrophilic silicon source.
- Cho, Hyungdo,Cho, Seung Hwan,Jang, Minjae,Jeong, Jongheon,Kim, Hyunseok,Lee, Eunsung,Lim, Soobin
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supporting information
p. 7387 - 7392
(2020/10/12)
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- Autocatalytic Carbonyl Arylation through In Situ Release of Aryl Nucleophiles from N-Aryl-N′-Silyldiazenes
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A method for the catalytic generation of functionalized aryl alkali metals is reported. These highly reactive intermediates are liberated from silyl-protected aryl-substituted diazenes by the action of Lewis basic alkali metal silanolates, resulting in desilylation and loss of N2. Catalytic quantities of these Lewis bases initiate the transfer of the aryl nucleophile from the diazene to carbonyl and carboxyl compounds with superb functional-group tolerance. The aryl alkali metal can be decorated with electrophilic substituents such as methoxycarbonyl or cyano as well as halogen groups. The synthesis of a previously unknown cyclophane-like [4]arene macrocycle from a 1,3-bisdiazene combined with a 1,4-dialdehyde underlines the potential of the approach.
- Chauvier, Clément,Finck, Lucie,Irran, Elisabeth,Oestreich, Martin
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supporting information
p. 12337 - 12341
(2020/03/23)
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- Dimethylformamide-stabilised palladium nanoclusters catalysed coupling reactions of aryl halides with hydrosilanes/disilanes
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N,N-Dimethylformamide-stabilised Pd nanocluster (NC) catalysed cross-coupling reactions of hydrosilane/disilane have been investigated. In this reaction, the coupling reaction proceeds without ligands with low catalyst loading. N,N-Dimethylacetamide is a crucial solvent in these reactions. The solvent effect was considered by various techniques, such as transmission electron microscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The Pd NCs can be recycled five times under both hydrosilane and disilane reaction conditions.
- Nagata, Tatsuki,Inoue, Takeru,Lin, Xianjin,Ishimoto, Shinya,Nakamichi, Seiya,Oka, Hideo,Kondo, Ryota,Suzuki, Takeyuki,Obora, Yasushi
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p. 17425 - 17431
(2019/06/24)
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- Nickel-Catalyzed Selective Cross-Coupling of Chlorosilanes with Organoaluminum Reagents
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Nickel-catalyzed cross-coupling reactions of chlorosilanes with organoaluminum reagents were developed. An electron-rich Ni(0)/PCy3 complex was found to be an effective catalyst for the desired transformation. The reaction of dichlorosilanes 1 proceeded to give the corresponding monosubstituted products 2. Trichlorosilanes 4 underwent selective double substitution to furnish the corresponding monochlorosilanes 2. Overall, the selective synthesis of a series of alkylmonochlorosilanes 2 from di- and trichlorosilanes was achieved using the present catalytic systems.
- Naganawa, Yuki,Guo, Haiqing,Sakamoto, Kei,Nakajima, Yumiko
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p. 3756 - 3759
(2019/09/12)
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- Palladium-Catalyzed C?H Silylation through Palladacycles Generated from Aryl Halides
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A highly efficient palladium-catalyzed disilylation reaction of aryl halides through C?H activation has been developed for the first time. The reaction has broad substrate scope. A variety of aryl halides can be disilylated by three types of C?H activation, including C(sp2)?H, C(sp3)?H, and remote C?H activation. In particular, the reactions are also unusually efficient. The yields are essentially quantitative in many cases, even in the presence of less than 1 mol % catalyst and 1 equivalent of the silylating reagent under relatively mild conditions. The disilylated biphenyls can be converted into disiloxane-bridged biphenyls.
- Lu, Ailan,Ji, Xiaoming,Zhou, Bo,Wu, Zhuo,Zhang, Yanghui
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supporting information
p. 3233 - 3237
(2018/02/23)
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- New transmetalation reagents for the gold-catalyzed visible light-enabled C(sp or sp2)-C(sp2) cross-coupling with aryldiazonium salts in the absence of a photosensitizer
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The scope of photosensitizer-free visible light-driven gold-catalyzed cross-coupling was evaluated by a wide variety of organoboron and organosilicon species using four equivalents of aryldiazonium salts and (4-CF3-C6H4)3PAuCl in MeOH. In addition, a C(sp or sp2)-C(sp2) cross-coupling of organotrimethylsilanes and aryldiazonium salts was investigated. The reactions can be conducted under very mild reaction conditions, with a reduced amount of aryldiazonium salt (1.2 equiv.) by using a catalytic amount of Ph3PAuNTf2 in MeCN under irradiation with blue LEDs at room temperature.
- Witzel, Sina,Sekine, Kohei,Rudolph, Matthias,Hashmi, A. Stephen K.
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supporting information
p. 13802 - 13804
(2018/12/14)
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- Oxidative 1,2-Difunctionalization of Ethylene via Gold-Catalyzed Oxyarylation
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Under the conditions of oxidative gold catalysis, exposure of ethylene to aryl silanes and alcohols generates products of 1,2-oxyarylation. This provides a rare example of a process that allows catalytic differential 1,2-difunctionalization of this feedstock chemical.
- Harper, Matthew J.,Emmett, Edward J.,Bower, John F.,Russell, Christopher A.
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supporting information
p. 12386 - 12389
(2017/09/22)
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- Gold-catalysed oxyarylation of styrenes and mono- and gem-disubstituted olefins facilitated by an iodine(III) oxidant
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1-Hydroxy-1,2-benziodoxol-3(1H)-one (IBA) is an efficient terminal oxidant for gold-catalysed, three-component oxyarylation reactions. The use of this iodine(III) reagent expands the scope of oxyarylation to include styrenes and gem-disubstituted olefins, substrates that are incompatible with the previously reported Selectfluor-based methodology. Diverse arylsilane coupling partners can be employed, and in benzotrifluoride, homocoupling is substantially reduced. In addition, the IBA-derived co-products can be recovered and recycled. The I's have it: The unprecedented use of an iodine(III) reagent as the terminal oxidant for gold-catalysed oxyarylation allows the substrate scope to be significantly expanded; in addition to monosubstituted olefins, styrenes and gem-disubstituted olefins are well tolerated (see scheme). With benzotrifluoride as solvent, unproductive homodimerisation of the arylsilane coupling partner is effectively suppressed. Copyright
- Ball, Liam T.,Lloyd-Jones, Guy C.,Russell, Christopher A.
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supporting information; experimental part
p. 2931 - 2937
(2012/04/23)
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- Palladium-catalyzed direct CH bond arylation of simple arenes with aryltrimethylsilanes
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Direct CH bond arylation of arenes with aryltrimethylsilanes catalyzed by PdCl2 in the presence of CuCl2 as an oxidant has been developed. In addition to the role as the oxidant, CuCl2 is found to be necessary for the selective crosscoupling reaction.
- Funaki, Kenji,Kawai, Hiroshi,Sato, Tetsuo,Oi, Shuichi
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supporting information; experimental part
p. 1050 - 1052
(2011/12/05)
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- Silicon switch approach in TRPV1 antagonist MK-056 and its analogues
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In searching for opportunities to exploit the benefits of silicon in TRPV1 research, we tried to investigate the pharmacological effects of sila-substitution (C/Si exchange) of tert-butyl group in the MK-056 series. Compound 13a, with a 4-positioned trime
- Chang, Minsun,Park, Seol-Rin,Kim, Juhyun,Jang, Mijung,Park, Jeong Hyun,Park, Ji Eun,Park, Hyeung-Geun,Suh, Young-Ger,Jeong, Yeon Su,Park, Young-Ho,Kim, Hee-Doo
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experimental part
p. 111 - 116
(2010/03/30)
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- Arylsilanes: Application to gold-catalyzed oxyarylation of alkenes
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Arylsilanes are efficient reagents for the gold-catalyzed oxyarylation of alkenes (21 examples, up to 85% isolated yield). Using commercially available Ph3PAuCl and readily prepared, benign arylsilanes, these two- and three-component reactions
- Ball, Liam T.,Green, Michael,Lloyd-Jones, Guy C.,Russell, Christopher A.
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supporting information; experimental part
p. 4724 - 4727
(2010/12/25)
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- New achiral phenylacetylene monomers having an oligosiloxanyl group most suitable for helix-sense-selective polymerization and for obtaining good optical resolution membrane materials
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To develop new phenylacetylene monomers more suitable for helix-sense-selective polymerization (HSSP) we reported previously and to improve the efficiency of the HSSP and membrane performance of the resulting polymers, novel phenylacetylenes having a flexible oligosiloxanyl group (SnBDHPA)together with the other related three series of monomers were synthesized and polymerized by using a chiral catalytic system and enantioselectivity in permeation of the membranes from the resulting chiral polymers were examined. SnBDHPA was the most suitable for the HSSP and the CD absorptions (G values) of poly- (SnBDHPA) were stronger and more stable than those of the corresponding polymers having rigid alkyl groups. The polymers could be fabricated to flexible self-supporting membranes by using solvent-casting method. In addition, enantioselectivity in permeation of one of poly(SnBDHPA) membranes was much higher than that of a poly(phenylacetylene) membrane having alkyl groups. This was because the polymers having oligosiloxane groups had high regularity of structures, i.e., chemical structures of the macromolecules such as one handedness and high order structures such as columnar contents in the membranes, and the membranes were flexible and had almost no defects. These good properties as optical resolution membrane materials were caused by flexibility, hydrophobicity, and bulkiness of the oligosiloxane chains. S3BDHPA having a trisiloxanyl group was found to be the best monomer for the HSSP and for obtaining good optical resolution membrane materials.
- Liu, Lijia,Zang, Yu,Hadano, Shingo,Aoki, Toshiki,Teraguchi, Masahiro,Kaneko, Takashi,Namikoshi, Takeshi
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scheme or table
p. 9268 - 9276
(2011/11/14)
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- Regiocontrolled cobalt-catalyzed Diels-Alder reactions of silicon-functionalized, terminal, and internal alkynes
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(Chemical Equation Presented) The efficient control of the regiochemistry of the Diels-Alder adducts which are formed in excellent yields from 1,3-dienes and alkynylsilanes can be realized utilizing cobalt complexes with a pyridine-imine ligand or a dppe ligand, respectively. The application of 2-trimethylsilyloxy-1,3-butadiene leads to a very interesting cyclohexenone derivative suitable for further transformations.
- Hilt, Gerhard,Janikowski, Judith
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supporting information; experimental part
p. 773 - 776
(2009/08/19)
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- Prediction of perception: Probing the hOR17-4 olfactory receptor model with silicon analogues of bourgeonal and lilial
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(Figure Presented) Sense and sensibility: Silicon analogues of the lily-of-the-valley odorants lilial and bourgeonal demonstrate that the electronic surface structure determines the interaction of an odorant with its olfactory receptor. The subtle changes
- Doszczak, Leszek,Kraft, Philip,Weber, Hans-Peter,Bertermann, Ruediger,Triller, Annika,Hatt, Hanns,Tacke, Reinhold
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p. 3367 - 3371
(2008/02/13)
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- meta-directing cobalt-catalyzed diels-alder reactions
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(Chemical Equation Presented) Overcoming the ortho/para rule? The regioselectivity of Diels-Alder reactions with neutral electron demand between 1,3-dienes with alkynes can be controlled by simple cobalt diimine complexes so that the meta-substituted cycloadducts are generated in good yields and excellent regioselectivity (see scheme; DDQ=2,3-dichloro-5,6-dicyano-1,4- benzoquinone).
- Hilt, Gerhard,Janikowski, Judith,Hess, Wilfried
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p. 5204 - 5206
(2007/10/03)
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- Development of Odorless Thiols and Sulfides and Their Applications to Organic Synthesis
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Development of new odorless thiols (dodecanethiol, 4-n- heptylphenylmethanethiol, 4-trimethylsilylphenylmethanethiol, 4-trimethylsilylbenzenethiol) and an odorless sulfide (1-methylsulfanyldodecane) and their applications to dealkylation, Michael addition, Swern oxidation, and Corey-Kim oxidation are described.
- Nishide, Kiyoharu,Ohsugi, Shin-Ichi,Miyamoto, Tetsuo,Kumar, Kamal,Node, Manabu
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p. 189 - 200
(2007/10/03)
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- Arylcalcium hydrides as precursors to alkoxides and aryloxides of calcium
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Calcium atoms react with +I-substituted benzene derivatives under cocondensation conditions to yield arylcalcium hydrides. With toluene, tert-butylbenzene, and trimethyl(phenyl)silane the reaction showed no selectivity for C-H activation, resulting in the formation of each of the three possible isomers, while with m-xylene the reaction resulted in selective activation of the bond meta to the CH3 groups. Treatment of (tert-butylphenyl)calcium hydride with di- and trisubstituted phenols such as 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-4-methylphenol, and 2,4,6-tri-tert-butylphenol resulted in the formation of calcium aryloxides in yields > 95%. [Ca(2,4,6-tBu3C6H2O)2 (THF)3] crystallises from a THF solution as a distorted trigonal bipyramid, with two THF ligands in the trans-axial positions and the third THF ligand and both aryloxide groups in equatorial positions. The Ca-OAryl bond length was found to average at 2.181(3). A. The Ca-O-CAryl angles are almost linear, with Cal-O1-C1 and Ca1-O2-C19 being 173.9(3)° and 178.8(3)°, respectively, while the O1-Cal-O2 angle was determined as 157.04(12)°. A reaction between (tert-butylphenyl)calcium hydride and triphenylmethanol resulted in the formation of the corresponding monomeric calcium bis(alkoxide) Ca(OCPh3)2(THF)4 in 95% yield. The structure was determined as a distorted octahedron with the alkoxide ligands in a cis-equatorial arrangement. The Ca-O bond length was determined at 2.1609(17) A. The Ca-O-CAryl angle of 177.46(16)° is almost linear, while the O1-Cal-O1A angle was determined at 110.12(19)°. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).
- Dunne, John P.,Tacke, Matthias,Selinka, Carola,Stalke, Dietmar
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p. 1416 - 1425
(2007/10/03)
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- Reactions of trimethylstannide and trimethylsiliconide anions with aromatic and heteroarornatic substrates
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A parallel study was carried out on the reactions of Me3Sn- and Me3Si- ions towards aromatic and heteroaromatic substrates in hexamethylphosphoramide (HMPA) as solvent. It was found that Me3Si- ions are more reactive and therefore less selective than Me3Sn- ions. In HMPA, PhI and PhBr react with Me3Sn- ions through an HME pathway. PhCl also reacts by an HME reaction, but under photostimulation the SRN1 mechanism competes with the HME process, With PhF as sabstrate, Me3Sn- ions afford (4-fluorophenyl)trimethylstannane, presumably through a hypervalent tin species. Under irradiation, the SRN1 mechanism operates concurrently with the formation of the hypervalent tin species. Me3Si- ions, on the other hand, react with PhX (X = Cl, Br, I) to yield the ipso substitution product, presumably through the intermediacy of a hypervalent silicon species. PhF affords, upon reaction with Me3Si- ions, o- and p-fluorotrimethylsilylbenzenes together with the ipso substitution product PhSiMe3. A novel type of nucleophilic substitution mechanism takes place with Me3Si- ions upon reaction with aromatic and heteroaromatic substrates without classical leaving groups in HMPA. Copyright
- Postigo, Al,Vaillard, Santiago E.,Rossi, Roberto A.
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p. 889 - 893
(2007/10/03)
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- Synthetic equivalents of benzenethiol and benzyl mercaptan having faint smell: Odor reducing effect of trialkylsilyl group
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Syntheses and odor tests of the trialkylsilylated benzyl mercaptans and benzenethiols have revealed that the trimethylsilyl substituent on the benzene ring has a remarkable effect in reducing the foul smell of the parent benzyl mercaptan and benzenethiol.
- Nishide, Kiyoharu,Miyamoto, Tetsuo,Kumar, Kamal,Ohsugi, Shin-Ichi,Node, Manabu
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p. 8569 - 8573
(2007/10/03)
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- A novel type of nucleophilic substitution reactions on nonactivated aromatic compounds and benzene itself with trimethylsiliconide anions.
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[reaction: see text]. The reaction of fluorobenzene with Me3Si- anion (1) in HMPA at room temperature surprisingly affords o- and p-fluorotrimethylsilylbenzenes (substitution of aromatic H for TMS, 76% yield) 7a and 7b and also 14% of trimethylsilylbenzene (2). Benzene itself reacts at 50 degrees C to furnish 4 in 45% yield. Pyridine affords p-trimethylsilylpyridine quantitatively. Mechanistic studies are presented.
- Postigo,Rossi
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p. 1197 - 1200
(2007/10/03)
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- A mild and efficient protocol for the catalytic silylation of aryl bromides
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New catalyst systems were developed which facilitate palladium-catalyzed silylation of various functionalized aryl and heteroaryl bromides with hexamethyldisilane under unprecedented mild conditions. The use of two different sets of ligands and bases for electron-rich and electron-poor substrates, respectively, is crucial for achieving excellent product selectivities at 100 °C and atmospheric pressure. For electron-rich substrates, diphenyl-2'-pyridylphosphine in combination with K2CO3 gives the best results, whereas for electron-poor substrates, 2-(di-t-butylphosphino)biphenyl/KF is preferred. Even base-sensitive arylsilanes, which are inaccessible by the traditional routes via organolithium species or Grignard reagents, can be prepared in a single step and high yields.
- Goossen,Ferwanah
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p. 1801 - 1803
(2007/10/03)
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- Diphenylphosphinophenolate: A ligand for the palladium-catalysed silylation of aryl halides activating simultaneously both palladium and silicon
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Diphenylphosphinophenolate was found to be an effective ligand for the palladium-catalysed silylation of aryl halides, activating not only palladium but also silicon of a disilane, where aryl bromides and iodides having such substituents as methyl, methoxy, amino, ethoxycarbonyl, trifluoromethyl, formyl or phenyl are applicable to the reaction with hexamethyldisilane to give the corresponding trimethylsilylarenes.
- Shirakawa,Kurahashi,Yoshida,Hiyama
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p. 1895 - 1896
(2007/10/03)
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- The gas-phase reactivity of p-Me3Si-substituted 1,3-diphenylpropane towards charged electrophiles: Intra- and interannular hydrogen migrations
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The gas-phase reaction of p-Me3SiC6H4(CH2)3C6H5 (p-TSDPP) with gaseous cations, including C2H5+, Me2Cl+ and DCO+, has been studied in the pressure range from 10-8 to 103 Torr by Fourier-transform ion cyclotron resonance (FT-ICR) and by the radiolytic technique. The protonated or alkylated intermediates undergo intramolecular migration and intermolecular transfer of protons and/or Me3Si+. The results underline the role of the spectator ring in providing internal solvation to an arenium moiety, as evidenced by the noticeable stability towards Me3Si loss with respect to a single-ring model substrate, p-Me3SiC6H4Me (p-TST), upon reaction with the same gaseous ions. The extent of the alkylation route relative to the alkyldesilylation processes, measured as a function of the arenium ion lifetime, permits derivation of the rate constant for the conversion by proton transfer of the originally formed arenium ions to ipso-silylated isomers (k(i)). The estimated values of k(i(p-TST)) = 5 x 109 s-1 and k(i(p-TSDPP)) = 2 x 108 s-1 at 120°C suggest that interannular H shifts are faster than ring-to-ring H transfer, in agreement with previous evidence from tert-butylated arenium ions. The reactivity of [Me3Si=arene]+ adducts, adequately described by the Wheland σ-complex model, does not exclude the intermediacy of an ion-neutral noncovalent complex.
- Crestoni, Maria Elisa
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p. 993 - 999
(2007/10/03)
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- The nucleophilic silyl radical: Dual-Parameter correlation analysis of the relative rates of bromine-atom abstraction reactions as measured by a rigorous methodology
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The relative rates [k(R)(Y) values] of bromine-atom abstraction reactions of 13 p-Y-substituted benzyl bromides (1Y's : Y = H, Et, tBu, Me3Si, MeS, Ph, P, Cl, Br, CF3, CN, CO2Me,SO2Me) by tris(trimethylsilyl) silyl radicals [(Me3Si)3Si.] in cyclohexane at 80°C have been measured by a rigorous methodology. Correlation analysis of the kinetic data by the dual-parameter equation (log k(H)/k(H) = ρ(x)σ(x)+ρ.σ.) shows that the silyl radical is distinctly nucleophilic and the transition states of the bromine-atom abstraction reactions are affected by both the polar and spindelocalization effects of the Y-substituents. Comparison of the |ρ(p) / ρ(jj).| values suggests that the contribution of the spin-delocalization effects in this Br-atom abstraction reaction may be greater than the spin-delocalization effects in some H-atom abstraction reactions.
- Jiang, Xi-Kui,Ding, William Fa-Xiang,Zhang, Yu-Huang
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p. 8479 - 8490
(2007/10/03)
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- New deoxynojirimycin derivatives as potent inhibitors of intestinal α-glucohydrolases
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New N-alkyl, alkenyl and benzyl substituted DNJ derivatives incorporating a silicon atom in the substituent were synthesised. Kinetic parameters (K(i), t( 1/4 )) for inhibition of rat intestinal α-glucohydrolases as well as human lysosomal α-glucosidases
- Lesur, Brigitte,Ducep, Jean-Bernard,Lalloz, Marie-Noelle,Ehrhard, Anne,Danzin, Charles
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p. 355 - 360
(2007/10/03)
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- Kinetic Control in the Cleavage of Unsymmetrical Disilanes
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A series of 12 phenyl-substituted arylpentamethyldisilanes 1a-1 have been synthesized in order to examine the regioselectivity of their nucleophilic Si,Si bond cleavage reactions under Still's conditions (MeLi/HMPA/0°C). It has been found that the sensitivity of these reactions to the electronic effects of the substituents in the phenyl ring could be described by the Hammett-type equation log(kA/kB) = 0.4334 + 2.421(Σσ); (correlation coefficient R = 0.983). The kA/kB ratio represents the relative rate of attack at silicon atom A (linked to the aryl ring) or at silicon atom B (away from the aryl ring) of the unsymmetrical disilanes. Thus, the present investigation shows that the earlier belief according to which the nucleophilic cleavage of unsymmetrical disilanes always produces the more stable silyl anionic species (thermodynamic control) should be abandoned, or at least seriously amended: kinetic factors appear to exert a primary influence on the regioselectivity of such reactions. Since the two major kinetic factors (i.e., electrophilic character of and steric hindrance at a given silicon atom) have opposite effects on the orientation of the reaction, it may happen that kinetic and thermodynamic control lead to the same result. For some of the unsymmetrical disilanes studied, the major reaction path was not the Si,Si bond cleavage; instead, Si-aryl bond breaking occurred, producing the corresponding aryl anions.
- Hevesi, Laszlo,Dehon, Michael,Crutzen, Raphael,Lazarescu-Grigore, Adriana
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p. 2011 - 2017
(2007/10/03)
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- Analogues of capsaicin with agonist activity as novel analgesic agents: Structure-activity studies. 4. Potent, orally active analgesics
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Structural features of three regions of the capsaicin molecule necessary for agonist properties were delineated by a previously reported modular approach. These in vitro agonist effects were shown to correlate with analgesic potency in rodent models. Comb
- Wrigglesworth, Roger,Walpole, Christopher S. J.,Bevan, Stuart,Campbell, Elizabeth A.,Dray, Andy,Hughes, Glyn A.,James, Iain,Masdin, Kay J.,Winter, Janet
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p. 4942 - 4951
(2007/10/03)
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- Synthesis of new 7-benzofuranmethanamines as heterocyclic analogues of the squalenepoxidase-inhibitor Butenafine
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Selected title compounds (6a-f, 7a-d) were synthesized by RedAl(R)-reduction of the carboxamides 4a-f and 5a-d, easily available from the corresponding (2,3-dihydro-)7-benzofurancarboxylic acids 1a-f or 2a-d, respectively. For practical reasons, the preparation of the 2,3-dihydro-2-methyl-7-benzofuranmethanamines 6h-k with varied N-substitution by alkylation of the N-methyl-benzofuranmethanamine 6g with preformed aralkylbromides 9a-d was preferred.
- Stanetty,Koller,Purstinger,Grubner
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p. 351 - 358
(2007/10/02)
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- The Electrochemical Reductive Trimethylsilylation of Aryl Chlorides: A Good Route to Aryltrimethylsilanes and a Novel Route to Tris(trimethylsilyl)cyclohexadienes
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The electroreductive trimethylsilylation of aryl chlorides R-C6H4Cl (R = H, o-Me, m-Me, p-Me) can be controlled so as to give, in good yields, either the corresponding aryltrimethylsilanes (products of the reduction of the carbon-chlorine bond) or mixtures of cis- and trans-tris(trimethylsilyl)cyclohexa-1,3(or 1,4)-dienes (products of the successive reduction of the carbon-chlorine bond and the partial reduction of the aromatic ring).Which of the two products is formed depends upon how much electricity is passed during the constant current electrolysis, in a one-compartment cell equipped with a sacrificial aluminum anode, of an aryl chloride in 80:20 THF/HMPA solution that also contains Et4NBF4 as the supporting electrolyte and excess Me3SiCl.The electroreductive trimethylsilylation of phenyltrimethylsilane gave, in 62percent yield, a mixture of three 3,5,6-tris(trimethylsilyl)cyclohexa-1,3-dienes, of which the trans, pseudo a-a isomer constituted 89percent.Such products cannot be obtained by the chemoreductive trimethylsilylation of phenyltrimethylsilane.The electroreductive trimethylsilylation of benzene and toluene produced the corresponding bis(trimethylsilyl)cyclohexa-1,4-dienes.The regio- and stereochemical outcomes of the electroreductive trimethylsilylation of the various substrates can be explained in terms of the electronic and steric effects of the substituents originally attached to the aromatic ring and the steric effects of the trimethylsilyl groups that are subsequently attached.
- Bordeau, Michel,Biran, Claude,Pons, Pierrette,Leger-Lambert, Marie-Pierre,Dunogues, Jacques
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p. 4705 - 4711
(2007/10/02)
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- Catalytic C-H Activation. Silylation of Arenes with Hydrosilane or Disilane by RhCl(CO)(PMe3)2 under Irradiation
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Direct silylation of arenes with triethylsilane or hexamethyldisilane were catalyzed by RhCl(CO)(PMe3)2 under irradiation.
- Sakakura, Toshiyasu,Tokunaga, Yuko,Sodeyama, Touru,Tanaka, Masato
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p. 2375 - 2378
(2007/10/02)
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- Palladium-mediated silylation of organic halides with disilane/F- reagent
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Under catalytic influence of tetrakis(triphenylphosphine)palladium, tris(diethylamino)sulfonium trimethyldiflourosilicate promoted the reaction of vynil halides with hexamethyldisilane to give corresponding vinyl silanes in good yields chemoselectivity and stereospecifically.
- Hatanaka, Yasou,Hiyama, Tamajiro
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p. 4715 - 4718
(2007/10/02)
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- SYNTHESIS AND SPECTROSCOPIC CHARACTERISTICS OF ARYLTRIMETHYL-SILICON, -GERMANIUM, AND -TIN COMPOUNDS
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The synthesis and spectroscopic characteristics of 28 para-substituted aryltrimethyl-silicon, -germanium, and -tin compounds are described.The infrared spectra show characteristic bands at 1245-1165 (methyl bend), 840-765 (methyl rock), and 1105-1020 (in-plane aromatic H bend) cm-1; the frequency of the last band was found to depend on the sum of the aromatic substituent masses, the presence or absence of metallic constituents in the substituent having little influence.The mass spectral fragmentation patterns are interpreted in terms of localization of positive charge on the metal atom, with subsequent bond cleavage behavior which obeys the rules for mass spectra of carbon compounds.
- Moerlein, S. M.
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- SYNTHESIS OF ORGANOTRIALKYLSTANNANES. THE REACTION BETWEEN ORGANIC HALIDES AND HEXAALKYLDISTANNANES IN THE PRESENCE OF PALLADIUM COMPLEXES
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The aryl halides YC6H4X (X=Br or I) have been shown to react with the distannanes (R3Sn)2 (R=n-Bu or Me) in toluene in the presence of or to give the compounds YC6H4SnR3 for (a) R=n-Bu, Y=H, p-OMe, o-Me, p-Me, m-Cl, p-Cl, m-CN, p-COCH3 and m-NO2, and (b) R=Me, Y=H, p-OMe, p-Me, p-CN, p-COCH3, m-NO2 and p-NO2.Benzyl halides YC6H4CH2X (X=Cl or Br) similarly give YC6H4CH2SnR3 for (a) R=n-Bu, Y=H, m-OMe, p-OMe, m-Cl, m-CN, and m-NO2, and (b) R=Me, Y=m-Cl, m-CN, p-CN and m-NO2.These reactions are of special value as preparative procedures in cases in which Grignard or organolithium reagents cannot be used.Allyl chloride and bromide were likewise shown to react with (n-Bu3Sn)2 to give CH2=CHCH2SnBu3, but n-BuCl and n-BuBr gave only a trace of n-Bu4Sn.The mixed dimetallo species n-Bu3SnSiMe3 was shown to react with aryl bromides YC6H4Br (X=H, p-OMe, p-Me, or p-Cl) to give the arylsilicon compounds YC6H4SiMe3, with no aryltin products.
- Azizian, Hormoz,Eaborn, Colin,Pidcock, Alan
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