- Kinetics and regioselectivity of ring opening of 1-bicyclo[3.1.0] hexanylmethyl radical
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(Chemical Equation Presented) Rate constants for the rearrangement of 1-bicyclo[3.1.0]-hexanylmethyl radical (2) to 3-methylenecyclohexenyl radical (3) and 2-methylenecyclopentyl-1-methyl radical (1) were measured using the PTOC-thiol competition method. The ring-expansion pathway is described by the rate equation, log(k/s-1) = (12.5 ± 0.1) - (4.9 ± 0.1)/θ; the non-expansion pathway is described by log(k/s-1) = (11.9 ± 0.6) - (6.9 ± 0.8)/θ. Employing the slower trapping agent, tri-n-butylstannane, favors methylenecyclohexane over 2-methyl-methylenecyclopentane by more than 120:1 at ambient or lower temperatures.
- Kantorowski, Eric J.,Le, Daniel D.,Hunt, Caleb J.,Barry-Holson, Keegan Q.,Lee, Jessica P.,Ross, Lauren N.
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- Platinacyclobutane chemistry: Cis-disubstituted platinacyclobutane complex from bicyclo[4.1.0] heptane
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The methodology for the preparation, isolation, and characterization of platinacyclobutanes from cis-disubstituted cyclopropane derivatives is established. In this case the metallacyclobutane was successfully prepared and characterized from bicyclo[4.1.0]
- Parsons,Jennings
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Read Online
- Adjusting the features of active metallocene ziegler systems for their potential use as carbon-carbon coupling catalysts in organic synthesis
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A variety of bent metallocene dichloride/methylalumoxane catalysts, derived from the zirconocene complexes 10, 12-18, have been employed in intramolecular olefin-coupling reactions yielding monomeric or dimeric products. This was achieved by using optimized reaction conditions employing low substrate concentrations (1.0-1.8 M) and rather long reaction times. Under these particular conditions, 1,5-hexadiene was cyclodimerized to give l-methylene-3-(cyclopentylmethyl)cyclopentane (11). 1,6-Heptadiene was cleanly converted to methylenecyclohexane, and cis-1,2-divinylcyclopentane (19) and cis-1,2-divinylcyclohexane (22) were cyclized to yield 2-methylenebicyclo[3.3.0]octane (20) and 7-methylenebicyclo[4.3.0]nonane (23), respectively. In many cases, the cyclization products were accompanied by isomers originating from double-bond shift reactions that often occur rapidly at these catalyst systems under the specific reaction conditions chosen to keep the products in the monomeric regime. VCH Verlagsgesellschaft mbH.
- Thiele, Sven,Erker, Gerhard
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- CYCLIZATION OF ALKENYLLITHIUM REAGENTS
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Alkenyllithium species containing a primary chloride group can be generated efficiently.They undergo subsequent cyclization to alkylidene cycloalkanes of various ring sizes.
- Chamberlin, A. Richard,Bloom, Steven H.
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- Wittig Reagents Bound to Cross-Linked Polystyrenes
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Insoluble benzyltriarylphosphonium and methyltriarylphosphonium salts have been prepared on 2percent and 8percent divinylbenzene cross-linked polystyrene and on 20percent divinylbenzene cross-linked macroporous polystyrene.Phosphoranes were generated with sodium methoxide or sodium ethoxide in THF and with the dimethylsulfinyl carbanion in Me2SO from the benzyl- and methylphosphonium salts, respectively.Reactions of the phosphoranes with a variety of aldehydes and ketones provided alkenes in 73-96percent yields (by GLC analysis) with the 2percent cross-linked polymer, 52-77percent yields with the 8percent cros s-linked polymer, and 72-87percent yields with the 20percent cross-linked macroporous polymer.The rates of phosphorane generation and alkene formation depend on the polymer, decreasing in the order 2percent > 20percent macroporous > 8percent cross-linked.The fraction of E double bond product from the benzylphosphonium salt and either benzaldehyde or cinnamaldehyde is greater with the 20percent cross-linked macroporous polymer than with the 2percent cross-linked polymer.The byproduct polymer-bound phosphine oxides were reduced to phosphines with trichlorsilane, and the phosphines were reused for Wittig synthesis.A quantitative 31P-NMR analysis of phosphine and phosphine oxide residues in polystyrene gels is reported.
- Bernard, Margaret,Ford, Warren T.
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- ACTIVATION OF C-H BONDS IN SATURATED HYDROCARBONES. THE SELECTIVE, CATALYTIC FUNCTIONALISATION OF METHYL GROUPS BY MEANS OF A SOLUBLE IRIDIUM POLYHYDRIDE SYSTEM
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The selective, catalytic conversion of methylcyclohexane into methylenecyclohexane at 100 deg C, and of n-hexane into 1-hexene at 45 deg C, has been effected using bis(triisopropylphosphine)iridium pentahydride and an olefin (neohexene) as a hydrogen acceptor; with this system, approximate relative reactivities of C-H bonds in saturated hydrocarbons are: sec-alkyl-H, 1; iso-alkyl-H, 8; n-alkyl-H, >60.
- Felkin, Hugh,Fillebeen-Khan, Tauqir,Holmes-Smith, Rupert,Yingrui, Lin
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- THE EFFECTIVENESS OF A WEAK BASE IN THE OLEFIN SYNTHESIS FROM β-HYDROXYALKYLPHOSPHONATES
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β-Hydroxyalkylphosphonates were treated with a weak base such as potassium carbonate in N,N-dimethylformamide to give the corresponding olefins in good yields.
- Kawashima, Takayuki,Ishii, Takafumi,Inamoto, Naoki
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Read Online
- THE DIMESITYLBORON GROUP IN ORGANIC SYNTHESIS. 4. THE 'BORON WITTIG' REACTION
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Anions generated α- to a dimesitylboron group readily condense with aldehydes and ketones.Elimination of Mes2BOLi then leads to alkenes in a boron analogue of the Wittig reaction.
- Pelter, Andrew,Singaram, Bakthan,Wilson, John W.
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Read Online
- Synthesis of sp 3-Enriched β-Fluoro Sulfonyl Chlorides
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A three-step approach to the synthesis of sp 3-enriched β-fluoro sulfonyl chlorides starting from alkenes is reported. The method was successfully applied to a wide range of acyclic and cyclic substrates, bearing either an exocyclic or an endocyclic double bond. The procedure worked with a wide range of substrates and tolerated a number of functional and protecting groups. Moreover, the target cyclic compounds were obtained as single cis diastereomers on a multigram scale. The title compounds are promising building blocks for drug discovery that can be used to obtain sp 3-enriched β-fluoro and α,β-unsaturated sulfonamides.
- Gurbanov, Rustam,Sokolov, Andriy,Golovach, Sergey,Melnykov, Kostiantyn,Dobrydnev, Alexey V.,Grygorenko, Oleksandr O.
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p. 1771 - 1784
(2020/12/28)
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- NOVEL HISTONE METHYLTRANSFERASE INHIBITORS
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The present invention relates to novel compounds of formula (I) as defined herein. The compounds are inhibitors of histone methyltransferases of the seven-beta-strand family, in particular of KMT9.
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Page/Page column 30; 37
(2021/04/01)
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- Stereoselective Diboration of Spirocyclobutenes: A Platform for the Synthesis of Spirocycles with Orthogonal Exit Vectors
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The diastereo- and enantioselective diboration of spirocyclobutenes provides a platform for the rapid preparation of a wide variety of chiral spirocyclic building blocks. The chemoselective functionalization of the carbon-boron bond in the products, including a stereospecific sp3-sp2 Suzuki–Miyaura cross-coupling reaction, provides a powerful tool to control the directionality and the nature of the exit vectors in the spirocyclic framework.
- Nóvoa, Luis,Trulli, Laura,Parra, Alejandro,Tortosa, Mariola
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supporting information
p. 11763 - 11768
(2021/04/26)
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- Beyond Takai's Olefination Reagent: Persistent Dehalogenation Emerges in a Chromium(III)-μ3-Methylidyne Complex
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Reaction of CHI3 with six equivalents of CrCl2 in THF at low temperatures affords [Cr3Cl3(μ2-Cl)3(μ3-CH)(thf)6] as the first isolable high-yield CrIII μ3-methylidyne complex. Substitution of the terminal chlorido ligands via salt metathesis with alkali-metal cyclopentadienides generates isostructural half-sandwich chromium(III)-μ3-methylidynes [CpR3Cr3(μ2-Cl)3(μ3-CH)] (CpR=C5H5, C5Me5, C5H4SiMe3). Side and decomposition products of the Cl/CpR exchange reactions were identified and structurally characterized for [Cr4(μ2-Cl)4(μ2-I)2(μ4-O)(thf)4] and [(η5-C5H4SiMe3)CrCl(μ2-Cl)2Li(thf)2]. The Cl/CpR exchange drastically changed the ambient-temperature effective magnetic moment μeff from 9.30/9.11 μB (solution/solid) to 3.63/4.32 μB (CpR=C5Me5). Reactions of [Cr3Cl3(μ2-Cl)3(μ3-CH)(thf)6] with aldehydes and ketones produce intricate mixtures of species through oxy/methylidyne exchange, which were partially identified as radical recombination products through GC/MS analysis and 1H NMR spectroscopy.
- Anwander, Reiner,Langmann, Jan,Maichle-M?ssmer, C?cilia,Scherer, Wolfgang,Trzmiel, Simon,Werner, Daniel
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supporting information
p. 20049 - 20054
(2021/08/06)
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- A Rare-Earth-Metal Ensemble of the Tebbe Reagent: Scope of Coligands and Carbonyl Olefination
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Treatment of the half-sandwich complexes CpRLn(AlMe4)2 (CpR = C5Me5, C5Me4SiMe3; Ln = Y, La, Lu) with the mild halogenido transfer reagents SiMe3X (X = Cl, Br, I) resulted in efficient and selective halogenido/tetramethylaluminato exchange. Depending on the size of the rare-earth metal, dimeric [CpRLn(AlMe4)(μ-X)]2 (Ln = Y, Lu) and decametallic [CpR3La3(AlMe4)2(μ-X)4]2 could be obtained. Donor (THF)-induced tetramethylaluminato cleavage gave access to methyl-free mixed methylidene/halogenido complexes CpR3Ln3(μ-X)3(μ3-X)(μ3-CH2)(THF)3 for yttrium (X = Cl, Br) and lanthanum (X = Cl, Br, I) in good yields. Additionally, mixed methylidene/halogenido Y(III) complexes could be obtained via methyl/halogenido exchange employing (C5Me5)3Y3(μ-Me)3(μ3-Me)(μ3-CH2)(THF)2 and SiMe3X via tetramethylsilane elimination. All methylidene complexes were probed in olefination reactions and found to act as efficient Schrock-type nucleophilic carbenes converting ketones and aldehydes into the respective terminal alkenes. Such reactivity is as high as that of the prominent Tebbe reagent but is less tolerant toward sterically demanding and functionalized substrates (such as esters). In contrast to the Tebbe reagent, complexes CpR3Ln3(μ-X)3(μ3-X)(μ3-CH2)(THF)3 polymerize δ-valerolactone in an efficient manner, generating polylactones with molecular weight distributions Mw/Mn as low as 1.13. Moreover, the bromido variant of the Tebbe reagent, Cp2Ti(μ-CH2)(μ-Br)AlMe2, is described, underlying similar synthesis limitations: that is, the coformation (and hence cocrystallization) of the trivalent species Cp2Ti(μ-Br)2AlMe2.
- Anwander, Reiner,Birkelbach, Verena M.,Dietrich, H. Martin,Kracht, Felix,Maichle-M?ssmer, C?cilia,Stuhl, Christoph
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p. 3490 - 3504
(2020/10/09)
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- Contra-thermodynamic Olefin Isomerization by Chain-Walking Hydrofunctionalization and Formal Retro-hydrofunctionalization
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We report a contra-thermodynamic isomerization of internal olefins to terminal olefins driven by redox reactions and formation of Si-F bonds. This process involves chain-walking hydrosilylation of internal olefins and subsequent formal retro-hydrosilylation. The process rests upon the high activities of platinum hydrosilylation catalysts for isomerization of metal alkyl intermediates and a new, metal-free process for the conversion of alkylsilanes to alkenes. By this approach, 1,2-disubstituted and trisubstituted olefins are converted to terminal olefins.
- Hanna, Steven,Butcher, Trevor W.,Hartwig, John F.
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supporting information
p. 7129 - 7133
(2019/09/12)
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- Preparation method of food additive capsaicin
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The invention provides a preparation method of a food additive capsaicin. The preparation method utilizes a one-pot method to synthesize capsaicin, changes the existing two synthesis processes into one-step synthesis and greatly improves production efficiency. A novel catalyst MHZ004 used in the preparation method is an efficient catalyst, can effectively catalyze the reaction at a use ratio of 1%mol and can be recovered and recycled so that a catalyst cost is reduced. The preparation method has a high raw material use rate, produces less three wastes and satisfies green chemistry development trend. The capsaicin obtained by the preparation method has low impurity content and high purity. The capsaicin obtained by the preparation method in a GMP workshop satisfies the standards of the food grade capsaicin.
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Paragraph 0020-0021
(2017/10/07)
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- Toward a mild dehydroformylation using base-metal catalysis
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Dehydroformylation, or the reaction of aldehydes to produce alkenes, hydrogen gas, and carbon monoxide, is a powerful transformation that is underdeveloped despite the high industrial importance of the reverse reaction, hydroformylation. Interestingly, nature routinely performs a related transformation, oxidative dehydroformylation, in the biosynthesis of cholesterol and related sterols under mild conditions using base-metal catalysts. In contrast, chemists have recently developed a non-oxidative dehydroformylation method; however, it requires high temperatures and a precious-metal catalyst. Careful study of both approaches has informed our efforts to design a base-metal catalyzed, mild dehydroformylation method that incorporates benefits from each while avoiding several of their respective disadvantages. Importantly, we show that cooperative base metal catalysis presents a powerful, mechanistically unique approach to reactions which are difficult to achieve using conventional catalyst design.
- Abrams, Dylan J.,West, Julian G.,Sorensen, Erik J.
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p. 1954 - 1959
(2017/03/09)
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- Synthesis of 1,3-Substituted Cyclobutanes by Allenoate-Alkene [2 + 2] Cycloaddition
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A method for the [2 + 2] cycloaddition of terminal alkenes with allenoates is presented. This process allows for the rapid synthesis of 1,3-substituted cyclobutanes in high yield under simple and robust reaction conditions.
- Conner, Michael L.,Brown, M. Kevin
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p. 8050 - 8060
(2016/09/09)
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- Sulfur mediated allylic C-H alkylation of tri- and disubstituted olefins
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A novel transition-metal-free, sulfur mediated allylic C-H alkylation reaction through a one-pot procedure involving an ene-like step between simple olefins and activated sulfoxides to generate allylic sulfonium intermediates, and a subsequent [2,3]-sigmatropic rearrangement step under basic conditions to give allylic C-H alkylation products, has been developed. This method is applicable to tri- and disubstituted olefin substrates in both inter- and intramolecular fashions.
- Hu, Gang,Xu, Jiaxi,Li, Pingfan
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supporting information
p. 6036 - 6039
(2015/01/08)
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- Organic reactivity of alcohols in superheated aqueous salt solutions: An overview
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The low dielectric constant and high self-dissociation constant of water in a temperature range between 150 and 250 °C make it a very appealing solvent for synthesis. Surprisingly, while organic chemistry in water at low temperature or around its critical point has been investigated in detail, very little seems to be known about the behaviour of organic molecules under hydrothermal conditions. The present work thus aims at shading some light on this field. As a start, we decided to investigate the reactions in which alcohols can undergo in water in the above-mentioned temperature range. Knowing that very strong salt effects on organic reactions have already been observed in super critical water, the impact of salt on the outcome of our tests was also investigated in detail.
- Avola, Sabine,Goettmann, Frederic,Antonietti, Markus,Kunz, Werner
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scheme or table
p. 1568 - 1573
(2012/10/07)
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- Ruthenium acetate complexes as versatile probes of metal-ligand interactions: Insight into the ligand effects of vinylidene, carbene, carbonyl, nitrosyl and isocyanide
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Reaction of cis-Ru(2-OAc)2(PPh3) 2 with two-electron donor ligands L results in the formation of complexes trans-[Ru(1-OAc)(2-OAc)L(PPh3) 2] (L = CO, NO+, CNtBu). Vinylidene complexes (L = C=CHR) may be prepared from the corresponding reaction with terminal alkynes HC=CR, and species containing hydroxyvinylidene ligands (L = C=CHCR1R 2{OH}) may be prepared from related reactions with propargyl alcohols HC=CCR1R2{OH}. Treatment of cis-Ru(κ2- OAc)2(PPh3)2 with ω-alkynols HC=C(CH 2)nOH (n = 2-4) results in the formation of oxacyclocarbene complexes [L = CCH2(CH2)nO]. An analysis of the spectroscopic data and the structural metrics (as determined by X-ray crystallography) of this series of complexes allows for the relative donor/acceptor properties of the ligand L to be evaluated. This comparison indicates that the vinylidene ligand behaves in a similar fashion to the isocyanide ligand. The complex cis-[Ru(2-OAc)2(PPh 3)2] acts as a precursor for the formation of the complexes trans-[Ru(1-OAc)(2-OAc)L(PPh3) 2] where L is a two-electron donor, σ-donor/π-acceptor ligand. The structural and spectroscopic data of these species provide insight into the relative electron demand of the ligands L.
- Welby, Christine E.,Eschemann, Thomas O.,Unsworth, Christopher A.,Smith, Elizabeth J.,Thatcher, Robert J.,Whitwood, Adrian C.,Lynam, Jason M.
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experimental part
p. 1493 - 1506
(2012/06/16)
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- Ruthenium-catalyzed functionalization of pyrroles and indoles with propargyl alcohols
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Several ruthenium-catalyzed atom-economic transformations of propargyl alcohols with pyrroles or indoles leading to alkylated, propargylated, or annulated heteroaromatics are reported. The mechanistically distinct reactions are catalyzed by a single ruthenium(0) complex containing a redox-coupled dienone ligand. The mode of activation regarding the propargyl alcohols determines the reaction pathway and depends on the alcohols' substitution pattern. Secondary substrates form alkenyl complexes by a 1,2-hydrogen shift, whereas the transformation of tertiary substrates involves allenylidene intermediates. 1-Vinyl propargyl alcohols are converted by a cascade allylation/cyclization sequence. The environmentally benign processes are of broad scope and allow the selective synthesis of highly functionalized pyrroles and indoles generating water as the only waste product. Copyright
- Thies, Nora,Hrib, Cristian G.,Haak, Edgar
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supporting information; experimental part
p. 6302 - 6308
(2012/06/18)
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- Ruthenium-catalyzed addition of carboxylic acids or cyclic 1,3-dicarbonyl compounds to propargyl alcohols
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Monomeric ruthenium(O) complexes containing redox-coupled dienone ligands were found to catalyze the regio-selective addition of carboxylic acids or cyclic 1,3-dicarbonyl compounds to propargyl alcohols.
- Berger, Stefanie,Haak, Edgar
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scheme or table
p. 6630 - 6634
(2011/02/21)
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- Oxidative cleavage of gabapentin with N-bromosuccinimide in acid medium: A kinetic and mechanistic study
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The kinetics of oxidative degradation of gabapentin with N-bromosuccinimide in HClO4 medium has been studied at 308 K. The experimental rate law obtained is-d[NBS]/dt = [NBS][GBP]x[H+]y, where x and y are less than unity. dt The reaction was subjected to changes in concentration of succinimide, the reduction product of NBS, concentration of the added neutral salt, dielectric permittivity and ionic strength of the medium. Solvent isotope effect has been studied using D2O. The stoichiometry of the reaction has been found to be 1:1, and oxidation products have been identified and characterized by FTIR and H NMR spectral studies. Activation parameters for the overall reactions have been computed from Arrhenius plot. (CH 2CO)2N+HBr has been postulated as the reactive oxidizing species. The oxidation reaction fails to induce polymerization of the added acrylonitrile. The proposed mechanism and the derived rate law are consistent with the observed kinetic data.
- Bhandarkar, P. M. Ramdas,Mohana
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experimental part
p. 1107 - 1112
(2010/03/05)
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- Cationic rearrangements controlled by the presence of a silyl group
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1,1-Disilylcarbinols having two alkyl groups on the adjacent carbon atom react with thionyl chloride in sulfur dioxide to give the product in which one of the alkyl groups has migrated towards the two silyl groups, and one of the silyl groups has been removed from the resultant cation. The reaction is seen in ring-expansion, as in the conversion of cyclohexylbis[dimethyl(phenyl)silyl]carbinol (7) into 1-dimethyl(phenyl) silylcycloheptene (11), and in open chains, as in the conversion of 1,1-bis[dimethyl(phenyl)silyl]-2-methylpropanol (26) into (E)- and (Z)-2-dimethyl(phenyl)silylbut-2-ene (27). Phenyldimethylsilyllithium reacts with pinacolone to give the α-silyl carbinol (44), which rearranges in the same way to give 2,3-dimethylbut-2-ene (46), effectively achieving a pinacolone-to-pinacol rearrangement.
- Chénedé, Alain,Fleming, Ian,Salmon, Roger,West, Mark C.
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- Flash vacuum pyrolysis over magnesium. Part 1 - Pyrolysis of benzylic, other aryl/alkyl and aliphatic halides
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Flash vacuum pyrolysis over a bed of freshly sublimed magnesium on glass wool results in efficient coupling of benzyl halides to give the corresponding bibenzyls. Where an ortho halogen substituent is present further dehalogenation gives some dihydroanthracene and anthracene. Efficient coupling is also observed for halomethylnaphthalenes and halodiphenylmethanes while chlorotriphenylmethane gives 4,4′-bis(diphenylmethyl)biphenyl. By using α,α′-dihalo-o-xylenes, benzocyclobutenes are obtained in good yield, while the isomeric α,α′-dihalo-p-xylenes give a range of high thermal stability polymers by polymerisation of the initially formed p-xylylenes. Other haloalkylbenzenes undergo largely dehydrohalogenation where this is possible, in some cases resulting in cyclisation. Deoxygenation is also observed with haloalkyl phenyl ketones to give phenylalkynes as well as other products. With simple alkyl halides there is efficient elimination of HCl or HBr to give alkenes. For aliphatic dihalides this also occurs to give dienes but there is also cyclisation to give cycloalkanes and dehalogenation with hydrogen atom transfer to give alkenes in some cases. For 5-bromopent-1-ene the products are those expected from a radical pathway but for 6-bromohex-1-ene they are clearly not. For 2,2-dichloropropane and 1,1-dichloropropane elimination of HCl occurs but for 1,1-dichlorobutane, -pentane and -hexane partial hydrolysis followed by elimination of HCl gives E, E-, E,Z- and Z,Z- isomers of the dialk-1-enyl ethers and fully assigned 13C NMR data are presented for these. With 6-chlorohex-1-yne and 7-chlorohept-1-yne there is cyclisation to give methylenecycloalkanes and -cycloalkynes. The behaviour of 1,2-dibromocyclohexane and 1,2-dichlorocyclooctane under these conditions is also examined. Various pieces of evidence are presented that suggest that these processes do not involve generation of free gas-phase radicals but rather surface-adsorbed organometallic species.
- Aitken, R. Alan,Hodgson, Philip K.G.,Morrison, John J.,Oyewale, Adebayo O.
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p. 402 - 415
(2007/10/03)
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- Ruthenium-assisted synthesis of gem-deuterated alkenes from monosubstituted propargyl alcohols and D2O
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The cyclohexenylvinylidene complex fac,cis-[(PNP)RuCl2{C=CH(C=CHCH2CH2CH2CH2)}] (2) is synthesized by reaction of mer,trans-[(PNP)RuCl2(PPh3)] (1) with 1-ethynylcyclohexanol [PNP
- Bianchini, Claudio,De los Rios, Isaac,Lopez, Carlos,Peruzzini, Maurizio,Romerosa, Antonio
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p. 485 - 488
(2007/10/03)
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- The Olefin Synthesis from β-Hydroxyalkylphosphonates Induced by Fluorides or Relatively Weak Bases
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β-Hydroxyalkylphosphonates, which were prepared readily from alkylphosphonates and carbonyl compounds, were treated with a fluoride ion such as CsF or with relatively weak bases such as K2CO3 in N,N-dimethylformamide to give the corresponding olefins in good yields. One molar equivalent of water to bases is effective for increasing the yields of olefins. The stereochemistry of erythro-dimethyl (2-hydroxy-1-methyl-2-phenyl)ethylphosphonate was determined by X-ray crystallographic analysis. Use of threo-isomer gave (E)-olefin exclusively, while that of erythro-enricned isomer afforded predominantly (Z)-olefin, indicating that the present olefination proceeds stereospecifically in a manner of syn-elimination.
- Kawashima, Takayuki,Ishii, Takafumi,Inamoto, Naoki,Tokitoh, Norihiro,Okazaki, Renji
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p. 209 - 219
(2007/10/03)
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- Halogenated Terpenoids. XXIX the 1-Bromo 1-Bromomethyl Cyclohexyl System
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Bromination of methylene groups exocyclic to cyclohexyl systems normally affords two isomeric products; the axial 1-bromo equatorial 1-bromomethyl compound and the axial 1-bromomethyl equatorial 1-bromo derivative. Free energy differences between these two isomers, and the conformations adopted by the axial 1-bromomethyl group, have been explored by n.m.r. spectroscopy, by X-ray crystallography and by MM3 calculations. Evidence is presented to show that the ax-bromomethyl group exists primarily as those rotamers which site the bromine atom synclinal to the vicinal bromine. The A value for a bromomethyl group in this system is then similar to that of an unsubstituted methyl group.
- Brecknell, Douglas J.,Carman, Raymond M.,Edwards, Ross A.,Hansford, Karl A.,Karoli, Tomislav,Robinson, Ward T.
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p. 689 - 700
(2007/10/03)
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- Formation of three-membered rings by SHi displacement. Reverse of cyclopropyl ring opening
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The general methods, photoinitiated or peroxide-initiated free radical chain additions of halomethanes to olefins, yield 1,2-addition products at temperatures ranging from 20 to 100°C. At lower temperatures, -42 to -104°C, a competitive reaction, subsequent to the addition of CCl2X., yields alkylcyclopropanes. The reactions of 1-octene or 1-hexene and 1-methylcyclohexene with atomic hydrogen carried out in the presence of several transfer agents (CCl4, CCl3Br, CCl2Br2) initiate a radical chain addition of CCl2X. and yield cyclized materials resulting from the SHi displacement of halogen by a carbon-centered radical. The radical displacement of a halogen on carbon, the reverse of homolytic displacement on cyclopropyl carbon, is dominant at low temperatures. The rate constants for cyclization (kc) vs transfer with halomethane (kt) showed isokinetic temperatures of -46°C (CCl4, 1-hexene); -35°C (CCl4, 1-methylcyclohexene). The isokinetic temperatures for the reactions of the two substrates carried out in the presence of BrCCl3 were calculated as -204 °C (1-octene) and -109°C (1-methylcyclohexene).
- Tanner, Dennis D.,Zhang, Liying,Hu, Li Qing,Kandanarachchi, Pramod
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p. 6818 - 6824
(2007/10/03)
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- Absolute rate constants for the addition of atomic hydrogen to monosubstituted and trisubstituted olefins
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A mechanism is established for the formation of the products resulting from the solution phase regioselective addition of atomic hydrogen to 1-methylcyclohexene. From this data and new data for the reactions of 1-octene, the absolute rates and activation parameters for the addition of hydrogen atom to an olefin can be extracted. A method was established to determine the absolute rate of addition of a hydrogen atom to a terminal olefin in the solution phase. The addition rate constants, ka (25°C), to 1-octene [ka = (4.2 ± 3.6) × 109 M-1 s-1] and 1-methylcyclohexene [ka = (4.6 ± 0.8) × 106 M-1 s-1, -78°C] are found to be in reasonable agreement with the published values for the vapor phase rate of addition to ethylene. The large rate constants are supported by the observation that the activation parameters (Ea = 5.3 ± 2.9 kcal/mol and log A = 14 ± 3.5 M-1 s-1 for 1-octene) are consistent with the values expected for this fast reaction.
- Tanner, Dennis D.,Zhang, Liying,Kandanarachchi, Pramod
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p. 11319 - 11324
(2007/10/03)
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- Organic reactions catalyzed by methylrhenium trioxide: Dehydration, amination, and disproportionation of alcohols
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Methylrhenium trioxide (MTO) is the first transition metal complex in trace quantity to catalyze the direct formation of ethers from alcohols. The reactions are independent of the solvents used: benzene, toluene, dichloromethane, chloroform, acetone, and in the alcohols themselves. Aromatic alcohols gave better yields than aliphatic. Reactions between two different alcohols could also be used to prepare unsymmetric ethers, the best yields being obtained when one of the alcohols is aromatic. MTO also catalyzes the dehydration of alcohols to form olefins at room temperature, aromatic alcohols proceeding in better yield. When primary (secondary) amines were used as the limiting reagent, direct amination of alcohols catalyzed by MTO gave good yields of the expected secondary (tertiary) amines at room temperature. Disproportionation of alcohols to alkanes and carbonyl compounds was also observed for aromatic alcohols in the presence of MTO. On the basis of the results of this investigation and a comparison with the interaction between MTO and water, a concerted process and a mechanism involving carbocation intermediates have been suggested.
- Zhu, Zuolin,Espenson, James H.
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p. 324 - 328
(2007/10/03)
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- Carbenes in Constrained Systems, 3. Solid-State Photolysis of Cycloheptane- and Cyclooctanespirodiazirine within Cyclodextrins and Zeolites
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Inclusion complexes of cycloheptanespirodiazirine (1) and cyclooctanespirodiazirine (8) in α-, β-, and γ-cyclodextrin, and faujasite type zeolites (NaX and NaY), have been prepared.The guest-host complexes (1- and 8CD and 1- and 8zeolite) were irradiated with UV light in the solid state and the reaction products were separated from the host and analyzed.Product ratios from photolysis of complexes were compared with those obtained from pure compounds and in solution.Cycloheptanespirodiazirine (1) gives cycloheptene (2), bicycloheptane (3), and methylenecyclohexane (4).Photolysis products from cyclooctanespirodiazirine (8) are cyclooctene (9), bicyclooctane (10), and bicyclooctane (11). 10 results from a 1,5-C-H insertion reaction of the carbene derived from 8.As the cavity size of the cyclodextrins becomes larger, the formation of 10 seems to increase.In β-cyclodextrin and in non-polar solvents substantial amounts of azine were found.In addition to hydrocarbons, photolyses in zeolites afforded alcohols and small amounts of the corresponding ketones. - Keywords: Diazirines / Zeolites / Cyclodextrins / Photochemistry / Carbenes
- Kupfer, Rene,Brinker, Udo H.
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p. 1721 - 1726
(2007/10/03)
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- Reactions of Thianthrene Cation Radical with Acyclic and Cyclic Alcohols
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Thianthrene cation radical perchlorate (Th(.+)*ClO4(-)) reacted readily with cycloalkanols (C5, C7, C8, and C12), alkan-2-ols (C3, C5, C6, and C8), 3-hexanol, neopentyl alcohol, a number of benzyl alcohols, dl- and (S)-1-phenylethanol, cyclopentyl- and cyclohexylmethanols, the exo- and endo-borneols, and norborneols.Reactions were carried out with an excess of the alcohol in acetonitrile solution containing 2,6-di-tert-butyl-4-methylpyridine.Products were alkenes, ethers, and N-substituted acetamides, depending on the structure of the alcohol.Thianthrene (Th) and its 5-oxide (ThO) were formed in equal amounts.The sum of amounts of products from the alcohol was equal to the amount of ThO.All reactions are interpretable on the basis of the ultimate formation and further reactions of a 5-alkoxythianthreniumyl ion (ROTh(+)).The predominant formation of nortricyclene from the norborneols is striking and is discussed.Swern-Moffatt-type oxidations of the alcohols were not observed.
- Shine, Henry J.,Yueh, Wang
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p. 3553 - 3559
(2007/10/02)
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- Efficient Syntheses of Multisubstituted Methylenecyclopropanes via Novel Ultrasonicated Reactions of 1,1-Dihaloolefins and Metals
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Ultrasonicated reactions of 1,1-dihaloolefins with lithium, magnesium or sodium in the presence of alkenes rapidly afford multisubstituted methylenecyclopropanes.
- Xu, Linxiao,Lin, Guoying,Tao, Fenggang,Brinker, Udo H.
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p. 650 - 653
(2007/10/02)
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- Unusual Directive Effects in the Hydroboration of β,β-Disubstituted Enamines. Conversion of α-Substituted Aldehydes to the Corresponding Alkenes and β-Amino Alcohols
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A comprehensive study of the conversion of β,β-disubstituted enamines into the corresponding alkenes and β-amino alcohols by hydroboration-elimination and hydroboration-oxidation, respectively, has been carried out.The amine moiety of β,β-disubstituted enamines was found to exert a decisive influence on the regioselectivity of the hydroboration reaction involving borane methyl sulfide (BMS).Thus, in the hydroboration of morpholino and piperidino enamines, the boron atom is initially placed predominantly in the α-position.Conversely, the pyrrolidino enamines direct the boron atom exclusively to the β-position.Three oxidizing agents, trimethylamine N-oxide, sodium perborate, and 30 percent hydrogen peroxide-solid sodium hydroxide, were tried in order to optimize the oxidation of the intermediate organoborane derivatives to the corresponding amino alcohols.Our results clearly indicated that 30 percent hydrogen peroxide-solid sodium hydroxide is best suited for this transformation.The yield of amino alcohol ranged from good to essentially quantitative.Enamines derived from β-aryl aldehydes, upon hydroboration with BMS followed by methanolysis and oxidation with neutral hydrogen peroxide, gave the corresponding 1,1-disubstituted alkenes.Contrary to the regioselectivity observed in the hydroboration reactions involving BMS, the hydroboration of β,β-disubstituted enamines using 9-borabicyclononane (9-BBN) gave the trialkylborane intermediates in which the boron atom was placed exclusively at the β-position regardless of the amine moiety of the enamine.These trialkylborane derivatives were very stable and did not undergo the usual elimination reaction with either methanol or sodium hydroxide.However, on thermal decomposition, these afforded the corresponding 1,1-disubstituted alkenes in high yields.
- Singaram, Bakthan,Goralski, Christian T.,Fisher, Gary B.
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p. 5691 - 5696
(2007/10/02)
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- Synthetically Useful β-Lithioalkoxides from Reductive Lithiation of Epoxides by Aromatic Radical Anions
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Epoxides are reductively cleaved by means of lithium 4,4'-di-tert-butylbiphenylide.Ethylene oxide itself cleaves to lithium 2-lithioethoxide (15) in less than 5 min at -95 deg C.Epoxides possessing one unsubstituted carbon atom reduce in a matter of minutes at -78 deg C.When both carbon atoms are monosubstituted, at least 1 h is required.Epoxides with one or with two geminal saturated substituents open mainly between the oxygen atom and the least substituted carbon atom.Ring opening in the other direction leads to an unstable β-lithioalkoxide which very rapidly forms an olefin.Acyclic 1,2-disubstituted epoxides yield only olefins.Cyclooctene oxide produces, after protonation, a 3:7 ratio of cyclooctanol and cyclooctene.Cyclohexene oxide gives a 3:1 ratio of cyclohexanol and cyclohexene.Vinyloxiranes, on the other hand, open at the most substituted C-O bond to produce an allylic anion associated with an alkoxide.The carbanionic centers of the resulting dianions add to the carbonyl groups of aldehydes and ketones; however, when a hydrogen atom is present on the carbon atom which is attached to both negatively charged atoms, some reduction of the carbonyl group competes with the nucleophilic addition.The allylic anions derived from vinyloxiranes, after treatment with titanium tetraisopropoxide or cerium(III) chloride, add to aldehydes mainly at the most or least substituted terminus, respectively.In the former case, the configuration of the resulting glycols is predominantly anti.A number of adducts of the dianions with conjugated unsaturated aldehydes and ketones can be converted to unsaturated cyclic 6-membered ring ethers in the presence of acid or methanesulfonyl chloride.
- Cohen, Theodore,Jeong, In-Howa,Mudryk, Boguslaw,Bhupathy, M.,Awad, Mohamed M. A.
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p. 1528 - 1536
(2007/10/02)
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- Photochemical Dehydrogenation of Alkanes Catalyzed by trans-Carbonylchlorobis(trimethylphosphine)rhodium: Aspects of Selectivity and Mechanism
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The photochemical dehydrogenation of alkanes is catalyzed in solution by trans-Rh(PMe3)2(CO)Cl with high efficiency; quantum yields up to 0.10 and turnover numbers as high as 5000 are achieved with cyclooctane as substrate.The intramolecular regioselectivity of the reaction is investigated with methyl-, ethyl-, and isopropylcyclohexane.In competition experiments, cyclooctane is found to be 17 times as reactive as cyclohexane; under carbon monoxide atmosphere, the selectivity is enhanced to a factor of 130.A kinetic isotope effect, kH/kD=5.3, is found for thedehydrogenation of C6H12/C6D12.Both intra- and intermolecular selectivities are consistent with a pathway involving a reversible C-H oxidative addition followed by a β-hydrogen elimination. trans-Rh(PMe3)2(CO)Cl is demonstrated to be the only significant photoactive species in solution.The dehydrogenation reaction is quenched by carbon monoxide with Stern-Volmer kinetics.On the basis of these results, a mechanism is proposed in which the enrgy needed to drive these thermodynamically unfavorable dehydrogenations is obtained only from Rh-CO bond photolysis.
- Maguire, John A.,Boese, William T.,Goldman, Alan S.
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p. 7088 - 7093
(2007/10/02)
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- METHYLENATION OF CARBONYL COMPOUNDS WITH METHYLENEDIMAGNESIUM IODIDE IN THE PRESENCE OF Et2AlCl
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A method has been developed for the methylenation of carbonyl compounds with methylenedimagnesium iodide in the presence of Et2AlCl in 35-70percent yield.In the presence of catalytic amounts of Ti and Pd complexes the yield of methylenation products is increased by 15-20percent.
- Dzhemilev, U. M.,Ibragimov, A. G.,Morozov, A. B.,Muslukhov, R. R.,Tolstikov, G. A.
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p. 2350 - 2352
(2007/10/02)
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- METHYLENECYCLOALKANES. STRAIN AND PROPERTIES
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The synthesis of methylenecycloalkanes and of epoxides based on them was studied.The role of angular strain in the electron density distribution and the reactivity of the alkenes was investigated by quantum-chemical calculation by the LCAO-MO SCF method in the MINDO/3 valence approximation.The data from the calculation are compared with the spectral and kinetic parameters of the epoxidation of methylene-cycloalkanes by peracetic acid in ethyl acetate.
- Kas'yan, L. I.,Seferova, M. F.,Gorb, L. G.,Kozina, M. P.,Dryuk, V. G.
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p. 1019 - 1025
(2007/10/02)
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- Alkylenation with Geminal Dialuminoalkane Reagents: The Synthesis of Olefins from Ketones
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Bis(dichloroalumino)methane (BDAM, 1) has been synthesized in high yield from aluminum powder and methylene chloride by a published procedure carefully modified for safety.By the screening away of aluminum metal fine particles and the gradual addition of methylene bromide promoter over the course of reaction, a safe procedure was attained.Although 1 itself was a poor methylenating agent for ketones, its dietherate complex was distinctly more reactive.By exchanging half the halogens of 1 with Me3Al, MeMgBr, or Et3Al, two very effective methylenating agents for ketones, namely CH2(AlClMe)2 (2) and CH2(AlClEt)2 (3), were obtained.As diether ates with Et2O or THF, 2 and 3 smoothly converted a broad variety of ketones (aliphatic, alicyclic, and aromatic) into their corresponding methylene derivatives, with little or no competitive alkylation or reduction.A titanium-modified reagent, Cl2AlCH2TiCl3 (4), was also effective toward ketones, but gave only low conversions of esters to vinyl ethers.Finally, as an example of a multicarbon, alkylenating agent, the reagents 5-7 ((R2Al)2CH(CH2)4CH3, 5, R = Et; 6, R = Cl; and 7, R = Cl or Et) were examined.Good to fair yields of alkylenation were obtained with aromatic ketones, but aliphatic ketones underwent alkylation, hydride reduction, and/or aldol condension.The great influence of alkyl groups and donor solvent on the reactivity of 1-3 is briefly discussed.
- Piotrowski, Andrzej M.,Malpass, Dennis B.,Boleslawski, Marek P.,Eisch, John J.
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p. 2829 - 2835
(2007/10/02)
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- CHLOROMETHYL-LITHIUM AND 1-CHLORO-2-METHYLPROP-1-ENYL-LITHIUM: USEFUL INTERMEDIATES IN THE SYNTHESIS OF UNSATURATED AND BIFUNCTIONALIZED COMPOUNDS
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The reaction of in situ generated chloromethyl-lithium with ketones (5) at -78 deg C afforded, after lithiation with lithium naphthalenide at the same temperature, β-oxidoalkyl-lithium compounds (6), which on reaction with electrophiles (deuterium oxide, dimethyl disulphide, carbon dioxide, cyclohexanone, and allyl bromide) yielded bifunctionalized compounds (7).When the lithiation step was carried out with lithium powder and at temperatures ranging between -60 deg C and 20 deg C, the corresponding decomposition of intermediates (6) derived from aldehydes and ketones (5) took place spontaneously giving the corresponding terminal or exocyclic olefins (11) regioselectively.The use of in situ generated 1-chloro-2-methylprop-1-enyl-lithium as organolithium reagent in the addition to carbonyl compounds (5) at -110 deg C, followed by transformation of the resulting chlorohydrin (13) into the corresponding methyl ether (14) (successive treatment with sodium hydride and methyl iodide at 0-20 deg C) gave, after lithiation with lithium phenanthrenide at room temperature, the corresponding substituted cumulenes (12).
- Barluenga, Jose,Fernandez-Simon, Jose L.,Concellon, Jose M.,Yus, Miguel
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p. 3339 - 3344
(2007/10/02)
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- Thermal Decomposition and Cobalt-Carbon Bond Dissociation Energies of Organocobalamins: Neopentyl-, (Cyclopentylmethyl)-, (Cyclohexylmethyl)-, (Tetrahydrofurfuryl)- and ((Tetrahydro-2H-pyryl)methyl)cobalamin
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The title compounds were prepared and characterized and their thermal decomposition reactions were studied in aqueous solutions of varying pH and containing varying concentrations of cob(II)alamin (B12) and of bis(dimethylglyoximato)cobalt(II), .
- Kim, Sook-Hui,Chen, Hui Lan,Feilchenfeld, Natalie,Halpern, Jack
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p. 3120 - 3126
(2007/10/02)
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- Selective Catalytic Dehydrogenation of Alkanes to Alkenes
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Linear and cyclic alkanes can be selectively dehydrogenated to the corresponding alkenes both thermally and photochemically (254 nm) with iridium complexes as catalysts.In the photochemical case, a sacrificial hydrogen acceptor is not required and H2 is evolved directly.Preferential initial formation of the least stable alkene (e.g., methylenecyclohexane from methylcyclohexane) is explained by attack at unhindered C-H bonds by an oxidative addition to the metal.A subsequent β-elimination gives the alkene.A key feature of the catalyst, 2-O2CCF3)(PR3)2> (4), is that the chelating acetate group can open up to allow β-elimination to take place in the alkyl hydride intermediate 2-O2CCF3)(PR3)2>.Prolonged reaction times lead to progressive isomerization of the alkene to give the thermodynamic product (e.g., 1-methylcyclohexene from methylcyclohexane).Up to 32 turnovers of dehydrogenation are seen.Deactivation of the catalyst takes place by P-C hydrogenolysis of the PAr3 ligand in the thermal case; the rise in the amount of ArH formed parallels the fall-off in activity of the catalyst.P-C cleavage does not take place in the photochemical system (R = cyclohexyl).A reversiblecyclometalation of the catalyst 4a (R = p-FC6H4) is observed after removal of the hydride ligands with t-BuCH=CH2.In the presence of C6H6, a C-H oxidative addition product, 2-O2CCF3)(PR3)2>, is formed instead (kH/kD = 4.5) and can be isolated from the reaction mixtures; This supports the oxidative addition pathway proposed for the alkanes.Equilibrium constants for the reaction of 4a with alkenes to give 1-O2CCF3)(PR3)2> are reported.
- Burk, Mark J.,Crabtree, Robert H.
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p. 8025 - 8032
(2007/10/02)
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- HOMOLYTIC PYRIDYLETHYLATION OF CYCLOHEXANE AND TETRALIN
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The homolytic pyridylethylation of cyclohexene and tetraline with 2-vinylpyridine under conditions of peroxide and thermal initiation was investigated.In addition to the main reaction products, i.e., cycloalkylethylpyridines (1 : 1 adducts), compounds indicating rearrangement of the radicals with H migration were also isolated and identified.
- Il'yasov, E.A.,Galust'yan, G.G.
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p. 326 - 330
(2007/10/02)
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- Copper(II) Triflate, a New Reagent for Mild Dehydration of Alcohols: Synthetic Usefulness and Mechanistic Insight
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The effectiveness of copper(II) triflate (copper(II) trifluoromethanesulfonate) as a new dehydrating reagent for a variety of alcohols has been demonstrated.Based on several control experiments, a possible mechanism is suggested.
- Laali, Khosrow,Gerzina, Robert J.,Flajnik, Christine M.,Geric, Cynthia M.,Dombroski, Ann Marie
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p. 607 - 611
(2007/10/02)
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- REACTION OF CYCLIC EPOXIDE COMPOUNDS WITH TRIPHENYLPHOSPHINE
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Significant differences were found in the reactivity of a series of epoxides of cycloalkenes and methylenecycloalkanes and diepoxides in reaction with triphenylphosphine, depending both on the steric effects of the cyclic fragments and on their strain.The level of the strain can be judged indirectly from the chemical shifts of the 1H and 13C nuclei and the spin-spin coupling constants of the C-H bonds in the epoxide ring.
- Kas'yan, L. I.,Stepanova, N. V.,Galafeeva, M. F.,Boldeskul, I. E.,Trachevskii, V. V.,Zefirov, N. S.
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p. 109 - 112
(2007/10/02)
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- KINETICS AND MECHANISM OF SOME VINYL RADICAL CYCLISATIONS
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The vinyl radicals 2a, 2b, and 11 each undergo fast exo ring closure to give 5a, 5b, and 12, the first two of which readily rearrange to ring-expanded radicals.
- Beckwith, Athelstan L.J.,O'Shea, Dennis M.
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p. 4525 - 4528
(2007/10/02)
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- Synthesis of Alkenes via Peterson Reaction
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The α-phenylthiosilanes (2) have been used to prepare the α-silyl anions (1) by reaction with lithium naphthalenide; subsequent condensation with a carbonyl compound gave the alkene (8) via the Peterson reaction.The α-phenylthiosilanes (2) were prepared from n,n-bis(phenylthio)acetals (4) by reaction with lithium naphthalenide and chlorotrimethylsilane.The n,n-bis(phenylthio)acetals (4) were obtained, in turn, from 1,1-bis(phenylthio)acetals (5) by anion formation with butyl-lithium-N,N,N',N'-tetramethylethylenediamine complex in hexane followed by reaction with an alkyl halide.The Peterson reaction was also used to prepare vinyl sulphides (9) and vinyl sulphones (13).
- Ager, David J.
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p. 183 - 194
(2007/10/02)
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- Methylenation of Carbonyl Compounds Using Chloromethyl-lithium; a New Method for Terminal and Exocyclic Olefins
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The in situ generated chloromethyl-lithium reacts at -78 deg C with different aldehydes and ketones to afford, after lithiation with lithium powder, terminal and exocyclic olefins.
- Barluenga, Jose,Fernandez-Simon, Jose L.,Concellon, Jose M.,Yus, Miguel
-
-
- Hydrogenolysis of Small Cycloalkanes, X. - Catalytic Hydrogenation of Bicycloalkanes
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Dependent on n different products are obtained from bicycloalkanes by hydrogenation on Pt and Pd/C catalysts: from n = 5 onward only methylcycloalkanes of the same ring size; with n = 4 additionally 2-7 percent of cycloheptane is formed; with n = 3 ring enlargement increases to 5-20 percent and with n = 2 cyclopentane is the only product.Mainly butane is formed from bicyclobutane and no intermediate could be detected.Explanations are attempted.The expected products are produced on hydrogenation of methyl-substituted derivatives and spiroalkanes.
- Stahl, Karl-Johannes,Hertzsch, Winfried,Musso, Hans
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p. 1474 - 1484
(2007/10/02)
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- Thermal and Photochemical Catalytic Dehydrogenation of Alkanes with (R = C6H4F-p and Cyclohexyl)
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(cy = cyclohexyl) catalyses the photochemical dehydrogenation of cyclo-octane both in the presence and absence of a hydrogen-acceptor.
- Burk, Mark J.,Crabtree, Robert H.,McGrath, Dominic V.
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p. 1829 - 1830
(2007/10/02)
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