- Influence of Intracrystalline Ionic Strength in MFI Zeolites on Aqueous Phase Dehydration of Methylcyclohexanols
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The impact of the concentration of hydrated hydronium ions and in turn of the local ionic strength in MFI zeolites has been investigated for the aqueous phase dehydration of 4-methylcyclohexanol (E1 mechanism) and cis-2-methylcyclohexanol (E2 mechanism). The E2 pathway with the latter alcohol led to a 2.5-fold higher activity. The catalytic activity normalized to the hydronium ions (turnover frequency, TOF) passed through a pronounced maximum, which is attributed to the increasing excess chemical potential of the alcohols in the pores, increasing in parallel with the ionic strength and the additional work caused by repulsive interactions and charge separation induced by the bulky alcohols. While the maximum in rate observed is invariant with the mechanism or substitution, the reaction pathway is influencing the activation parameters differently.
- Milakovi?, Lara,Hintermeier, Peter H.,Liu, Yue,Baráth, Eszter,Lercher, Johannes A.
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Read Online
- Well-defined dendrimer encapsulated ruthenium SCILL catalysts for partial hydrogenation of toluene in liquid-phase
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Dendrimer encapsulated ruthenium nanoparticles (RuDEN) were prepared and immobilized on silica 60 and silica 100. The size of the supported RuDENs was investigated using HRTEM and the generation six G6-RuDEN was found to be the most stable RuDEN upon immobilization. The catalysts were evaluated in the liquid-phase hydrogenation of toluene at a hydrogen pressure of 30 bar and 110 °C. Several ionic liquids were used as coatings for the G5-RuSil100 catalysts to give various Solid Catalysts with Ionic Liquid Layer (SCILL). In each case the selectivity towards methylcyclohexenes was increased compared to the uncoated catalyst, accompanied by an expected decrease in activity with the highest methylcyclohexene selectivity being observed when using [EMIM][NTf2] as a coating.
- Antonels, Nathan Charles,Benjamin Williams, Marc,Meijboom, Reinout,Haumann, Marco
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Read Online
- Rearrangement of r-5-methyl-c-2-(trimethylsilyl)cyclohexan-t-yl 2,4-dinitrobenzoate in Chloroform
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Isomerisation of the title compound 3 to the ester 4 in deuteriochloroform is believed to occur via rearrangement of an intermediate β-trimethylsilyl substituted carbocation, with subsequent capture by the 2,4-dinitrobenzoate anion.
- Green, Alison J.,Kuan, Yew Leong,White, Jonathan M.
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Read Online
- Depolymerization and hydrodeoxygenation of lignin to aromatic hydrocarbons with a Ru catalyst on a variety of Nb-based supports
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Efficient conversion of lignin to aromatic hydrocarbons via depolymerization and subsequent hydrodeoxygenation is important. Previously, we found that NbOx species played a key role in the activation and cleavage of C–O bonds in lignin and its model compounds. In this study, commercial niobic acid (HY-340), niobium phosphate (NbPO-CBMM) and lab-made layered niobium oxide (Nb2O5-Layer) were chosen as supports to study the effect of Br?nsted and Lewis acids on the activation of C–O bonds in lignin conversion. A variety of Ru-loaded, Nb-based catalysts with different Ru particle sizes were prepared and applied to the conversion of p-cresol. The results show that all the Ru/Nb-based catalysts produce high mole yields of C7–C9 hydrocarbons (82.3–99.1%). What's more, Ru/Nb2O5-Layer affords the best mole yield of C7–C9 hydrocarbons and selectivity for C7–C9 aromatic hydrocarbons, of up to 99.1% and 88.0%, respectively. Moreover, it was found that Lewis acid sites play important roles in the depolymerization of enzymatic lignin into phenolic monomers and the cleavage of the C–O bond of phenols. Additionally, the electronic state and particle size of Ru are significant factors which influence the selectivity for aromatic hydrocarbons. A partial positive charge on the metallic Ru surface and a smaller Ru particle size are beneficial in improving the selectivity for aromatic hydrocarbons.
- Ma, Di,Lu, Shenglu,Liu, Xiaohui,Guo, Yong,Wang, Yanqin
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p. 609 - 617
(2019/04/03)
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- PROCESS FOR PHOTOCATALYTIC ACCEPTOR-FREE DEHYDROGENATION OF ALKANES AND ALCOHOLS
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A process for photocatalytic acceptor-free dehydrogenation of alkanes and alcohols, in which an alkane or an alcohol is irradiated in the presence of a rhodium complex containing organic phosphorus(III) compounds as ligands as a catalyst, and in the presence of at least one Lewis base is provided.
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Paragraph 0065
(2015/09/23)
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- Towards a practical development of light-driven acceptorless alkane dehydrogenation
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The efficient catalytic dehydrogenation of alkanes to olefins is one of the most investigated reactions in organic synthesis. In the coming years, an increased supply of shorter-chain alkanes from natural and shale gas will offer new opportunities for inexpensive carbon feedstock through such dehydrogenation processes. Existing methods for alkane dehydrogenation using heterogeneous catalysts require harsh reaction conditions and have a lack of selectivity, whereas homogeneous catalysis methods result in significant waste generation. A strong need exists for atom-efficient alkane dehydrogenations on a useful scale. Herein, we have developed improved acceptorless catalytic systems under optimal light transmittance conditions using trans-[Rh(PMe3) 2(CO)Cl] as the catalyst with different additives. Unprecedented catalyst turnover numbers are obtained for the dehydrogenation of cyclic and linear (from C4) alkanes and liquid organic hydrogen carriers. These reactions proceed with unique conversion, thereby providing a basis for practical alkane dehydrogenations.
- Chowdhury, Abhishek Dutta,Weding, Nico,Julis, Jennifer,Franke, Robert,Jackstell, Ralf,Beller, Matthias
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supporting information
p. 6477 - 6481
(2014/06/24)
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- Enantioselective synthesis of chiral sulfones by ir-catalyzed asymmetric hydrogenation: A facile approach to the preparation of chiral allylic and homoallylic compounds
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A highly efficient and enantioselective Ir-catalyzed hydrogenation of unsaturated sulfones was developed. Chiral cyclic and acyclic sulfones were produced in excellent enantioselectivities (up to 98% ee). Coupled with the Ramberg-Baecklund rearrangement, this reaction offers a novel route to chiral allylic and homoallylic compounds in excellent enantioselectivities (up to 97% ee) and high yields (up to 94%).
- Zhou, Taigang,Peters, Byron,Maldonado, Matias F.,Govender, Thavendran,Andersson, Pher G.
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p. 13592 - 13595
(2012/10/08)
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- {(1 R,2 R,4 R)-4-Methyl-1,2-cyclohexanediamine}oxalatoplatinum(II): A Novel Enantiomerically Pure Oxaliplatin Derivative Showing Improved Anticancer Activity in Vivo
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Novel derivatives of the clinically established anticancer drug oxaliplatin were synthesized. Cytotoxicity of the compounds was studied in six human cancer cell lines by means of the MTT assay. Additionally, most promising complexes were also investigated in cisplatin- and oxaliplatin-resistant human cancer cell models. The therapeutic efficacy in vivo was studied in the murine L1210 leukemia model. Most remarkably, {(1R,2R,4R)-4-methyl-1,2-cyclohexanediamine} oxalatoplatinum(II), comprising an equatorial methyl substituent at position 4 of the cyclohexane ring, was as potent as oxaliplatin in vitro but distinctly more effective in the L1210 model in vivo at the optimal dose. The advantage observed in the in vivo situation was mainly based on a more favorable therapeutic index. The maximum tolerated dose of the novel analogue was higher than that of oxaliplatin and caused a greater increase in life span (>200% versus 152%), with more animals experiencing long-term survival (5/6 versus 2/6). These data support further (pre)clinical development of the methyl-substituted oxaliplatin analogue with improved anticancer activity.
- Abramkin, Sergey A.,Jungwirth, Ute,Valiahdi, Seied M.,Dworak, Claudia,Habala, Ladislav,Meelich, Kristof,Berger, Walter,Jakupec, Michael A.,Hartinger, Christian G.,Nazarov, Alexey A.,Galanski, Markus,Keppler, Bernhard K.
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supporting information; experimental part
p. 7356 - 7364
(2011/01/12)
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- Low-valent titanium-mediated stereoselective alkylation of allylic alcohols
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We have developed low-valent titanium-mediated 1,3-transpositive cross-coupling reactions of acyclic and cyclic allylic alcohols for the stereoselective introduction of ethyl, 2-silylethyl, 2-phenethyl, and alkenyl groups. Cross-coupling of an allylic alcohol with a vinylsilane or styrene derivative is particularly noteworthy, as an efficient cross-selective coupling of two alkenes has been elusive. The stereochemistry of the cross-coupling alkylation is consistent with syn addition/β-elimination.
- Lysenko, Ivan L.,Kim, Keunho,Hyung, Goo Lee,Jin, Kun Cha
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supporting information; scheme or table
p. 15997 - 16002
(2009/05/15)
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- Transformations of β-alkylcyclohexane hydrocarbons on modified pentasils with participation of methanol and oxidants
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The reactions of dehydroalkylation of methylcyclohexane, ethylcyclohexane, and methylcyclohexene isomers and toluene alkylation with methanol on platinum-and gallium-modified pentasil in the presence of an O 2-CO2 mixture was studied. Optimum conditions were found for the one-step dehydroalkylation of methylcyclohexane on the ring. Under these conditions, the degree of conversion of methylcyclohexane and methylcyclohexene isomers into xylene isomers is above that of toluene alkylation to afford xylene. According to the discussed reaction mechanism, the dehydroalkylation of cyclohexane hydrocarbons on Pt, Ga-pentasil involves both the steps of formation of unsaturated intermediates and toluene in status nascendi. Nauka/Interperiodica 2006.
- Alimardanov,Velieva,Dadasheva,Rustamov
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p. 353 - 361
(2008/04/18)
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- Silica-supported dendrimer-palladium complex-catalyzed selective hydrogenation of dienes to monoolefins
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The selective hydrogenation of cyclic and acyclic dienes to monoolefins occurs under very mild conditions, in the presence of silica-supported PAMAM-Pd complexes. The activity and selectivity of this reaction is sensitive to the dendrimer structure. These dendritic complexes display excellent recycle properties, retaining activity for up to eight recycles.
- Zweni, Pumza P.,Alper, Howard
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p. 725 - 731
(2007/10/03)
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- Stereochemistry of oxachlorocarbene SNi reactions
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(Chemical Equation Presented) 3-Nortricyclyloxychlorocarbene and trans-4-methylcyclohexyloxychlorocarbene both fragment in hydrocarbon solvents with extensive loss of stereochemical integrity to the corresponding chlorides via competitive and nearly isoenergetic SNi-like transition states.
- Moss, Robert A.,Fu, Xiaolin,Tian, Jingzhi,Sauers, Ronald,Wipf, Peter
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p. 1371 - 1374
(2007/10/03)
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- Dehydroalkylation of methylcyclohexane by methanol on modified zeolites: Kinetic features and reaction mechanism
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The reaction of methylcyclohexane dehydroalkylation by methanol on modified forms of mordenite and pentasil was studied. The kinetic features of the process in the presence of HNa-pentasil modified by gallium and iron oxides and phosphorus were investigated. A kinetic model that fairly well describes the process at 430-570°C is suggested. The reaction mechanism is considered, which involves the dehydroalkylation of methylcyclohexane by methanol via the intermediate dehydrogenation of both hydrocarbons and alcohol and the subsequent interaction of the unsaturated compounds formed with formaldehyde adsorbed on the catalyst surface. Copyright
- Alimardanov,Velieva,Suleimanova,Tairova,Sh Sadygova
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- Multicatalytic processes using diverse transition metals for the synthesis of alkenes
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A series of cascade processes for the synthesis of alkenes from alcohols is described. Each individual step is catalyzed with a specific transition metal complex. The oxidation-methylenation one-pot procedure took place in the presence of a palladium and a rhodium catalyst to produce the desired terminal alkenes in high yields. A methylenation-ring-closing metathesis allowed the synthesis of cyclic alkenes from carbonyl derivatives, using the second-generation metathesis catalyst. Finally, an oxidation-methylenation-RCM process that involves up to three different transition metal catalysts in the same vessel is presented. Copyright
- Lebel, Helene,Paquet, Valrie
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p. 11152 - 11153
(2007/10/03)
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- Thermal isomerization of (3-butenyl)cyclopropane to norbornane
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equation presented (3-Butenyl)cyclopropane isomerizes thermally to norbornane and gives rise to many other products. Deuterium and carbon-13-labeled versions of (3-butenyl)cyclopropane have been prepared and isomerized, establishing that the formation of
- Baldwin, John E.,Burrell, Richard C.,Shukla, Rajesh
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p. 3305 - 3307
(2007/10/03)
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- Polyoxometalates as reduction catalysts: Deoxygenation and hydrogenation of carbonyl compounds
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Excellent deoxygenation of ketones and aldehydes is achieved with Keggin-type polyoxometalates in the presence of hydrogen (see Equation (1) for an example). The mixed addenda phosphovanadomolybdate [PV2Mo10O4]5- was found to be the best catalyst. X-ray diffraction and IR studies suggest that the polyoxometalates are structurally stable under the strongly reducing conditions.
- Kogan, Vladimir,Aizenshtat, Zeev,Neumann, Ronny
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p. 3331 - 3334
(2007/10/03)
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- Reactions of nucleophiles with 5-(alkoxy)thianthrenium ions
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Reactions of 5-(alkoxy)thianthrenium perchlorates (1) with weakly basic nucleophiles Br-, I- and PhS- (X-) in MeCN and DMSO led to SN2 substitution, E2C elimination, and reaction at sulfornium sulfur to extents depending on the structure of the alkoxy group (RO) in 1 and the nucleophile. Three types of reaction occurred with R = cyclopentyl (1a), cyclohexyl (1b), cis- (1c) and trans- 4-methylcyclohexyl (1d) and cycloheptyl (1e), and X- = Br and I-. That is, SN2 reaction gave RX and thianithrene 5-oxide (ThO), E2C reaction gave cycloalkene and ThO and reaction at sulfonium sulfur gave X2, thianthrene (Th) and cycloalkanol (ROH). Earlier work with R = Me (1f) and Et (1g) and X- = I-. Br- had shown that only SN2 reaction occurred. In contrast with reactions of halide ions, reactions of PhS- with 1b-g occurred only at sulfonium sulfur, giving Th, ROH and PhSSPh (DPDS). For comparison with 1, reactions of Ph2S+OMe (2) with I- and PhS- were carried out. Reaction with I- gave only Ph2S=O and Mel (SN2), Reaction with PhS- gave very little PhSMe (SN2) but mainly Ph2S, MeOH, and DPDS from reaction at sulfonium sulfur. The differences in nucleophilic pathways (PhS- vs Br- and I-) in reactions with 1 and 2 are attributed to differences in thiophilicities of the nucleophiles. The thiophilicity of PhS- dominates its reactions with 1 and 2. The direction toward products (Th, ROH and DPDS) in these reactions is compounded by the ease of displacement of alkoxide from 1 and 2 by PhS-, and the ease with which, subsequently, thiophilic PhS- attacks sulfenyl sulfur in the resulting phenylthiosulfonium ion. Copyright
- Liu, Bo,Shine, Henry J.,Zhao, Wenyi
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p. 827 - 836
(2007/10/03)
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- Structure and Thermal Decomposition of Some 5-(Cyclohexyloxy)thianthreniumyl Perchlorates
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Five sets of cis- and trans-substituted cyclohexanols were used for reaction with thianthrene cation radical perchlorate, namely, cis- and trans-cyclohexane-1,2-diol, cis- and trans-2-methyl-, 3-methyl-, and 4-methylcyclohexanol, and cis,cis- and trans,trans-3,5-dimethylcyclohexanol. Reaction in CH2-Cl2 solution and precipitation with ether gave the corresponding crystalline 5-(cyclohexyloxy)-thianthreniumyl perchlorate salts. The configuration of each salt in CDCl3 was shown by 1H and 13C NMR spectroscopy to correspond with the configuration of the cyclohexanol from which it was made. X-ray Ortep diagrams of four of the salts confirmed the structure deduced from NMR spectroscopy. In the NMR, inequivalence of the 1H and 13C signals from the thianthreniumyl 4-and 6-, 1- and 9-, 2- and 8-, and 3- and 7-positions was found when the 1′-position of the cyclohexyl ring was stereogenic. In the four Ortep diagrams, the orientation of the S-O bond was psuedoaxial. Thermal decomposition of the salts made from the monosubstituted cyclohexanols at 100°C in CH3CN solution gave products consistent with the assigned structures.
- Zhao, Wenyi,Shine, Henry J.,Whittlesey, Bruce R.
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p. 8693 - 8701
(2007/10/03)
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- Process for the preparation of optically active cycloolefins
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A process for the preparation of optically active cycloolefins based upon reaction of optically active dienes in the presence of catalyst compositions comprising molybdenum and tungsten complexes.
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- Practical catalyst for cyclic metathesis. Synthesis of functional and/or enantiopure cycloalkenes
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The oxo-tungsten complex trans-WOCl2(OAr)2 (Ar = 2,6-dibromophenyl) is prepared by reaction of WOCl4 with 2 equiv of 2,6-dibromophenol. A variety of nonconjugated dienes are cleanly cyclized to the corresponding cycloalkenes using 2 mol % of this catalyst in combination with 4 mol % of tetraethyllead. All three components of the catalyst system are commercially available. The catalytic reactions are typically complete in 1 h at 90 °C and allow the synthesis of chiral cycloalkenes with little or no loss in optical activity. For example, (R)-and (5)-citronellene have been cyclized to the corresponding (R)- or (S)-3-methylcyclopentenes in 97% enantiomeric excess. The cyclization is compatible with a variety of functional groups including some ester, amide, and ether derivatives. Tri- (but not tetra-) substituted cycloalkenes could be prepared using this catalyst.
- Nugent, William A.,Feldman, Jerald,Calabrese, Joseph C.
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p. 8992 - 8998
(2007/10/02)
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- Reaction of thianthrene cation radical with alcohols: Cyclohexanols
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Cyclohexanol (1), 4-methylcyclohexanol (2), 4-tert-butylcyclohexanol (3), cis-2-methyl- (4) and trans-2-methylcyclohexanol (5) reacted cleanly with thianthrene cation radical perchlorate (Th·+ClO4-) in the presence of 2,6-di-tert-butyl-4-methylpyridine (DTBMP). The alcohols were converted quantitatively into cyclohexenes, while Th·+ was converted quantitatively into thianthrene (Th) and thianthrene 5-oxide (ThO). The oxygen atom of ThO came from the alcohol, as was demonstrated with the use of [18O]cyclohexanol.
- Shine, Henry J.,Yueh, Wang
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p. 6583 - 6586
(2007/10/02)
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- Hydrogen Transfer Reactions, 19. - The Catalysis of Hydrogen Transfer and 1,5-H Shift by Rhodium(III) Chloride in Homogeneous Organic Systems
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In homogeneous solution, partly in the presence of a phase-transfer catalyst, rhodium(III) chloride catalyzes the disproportionation of 1,3-cyclohexadiene and to a lesser extent 1,5-H shifts.In the start phase the catalyst is reduced to the active monovalent state.In these catalytic systems the dehydrogenation proceeds stereoselectively. - This was shown by tracer experiments and isotopes effects using deuterated 1,3-cyclohexadienes 1a-d, which were synthesized with high isotopomeric purity.Key Words: Rhodium chloride / Hydrogen transfer / Deuterated 1,3-cyclohexadienes / Isotope effects
- Wehage, Hubert,Heesing, Albert
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p. 209 - 215
(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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- Electrophilic substitution with allylic rearrangement (SE′) stereochemistry of trifluoroacetolysis of some cyclohex-2-enylmetal compounds
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A range of (4-alkylcyclohex-2-enyl)-, (5-alkylcyclohex-2-enyl)-, and (6-alkylcyclohex-2-enyl)silanes, (4-alkylcyclohex-2-enyl)-, (5-alkylcyclohex-2-enyl)-, and (6-alkylcyclohex-2-enyl)germanes, and (4-alkyl-cyclohex-2-enyl)-, (5-alkylcyclohex-2-enyl)-, and (6-alkylcyclohex-2-enyl)stannanes were cleaved to the cycloalkene (and R3MX) with trifluoroacetic acid-d in various solvents. Complete allylic rearrangement (γ-attack) was observed, and the preferred direction of delivery of the electrophile (formally D+) to the γ-carbon of the allylic triad was determined by detailed 1H, 13C, and 2H NMR analyses of the derived dibromides of the various alkyl-substituted cyclohexenes or by direct 2H NMR analysis and comparisons with 2H-substituted alkylcyclohexenes of established relative configurations. A highly preferred γ-anti mode of acidolysis is established for all systems, except for the trans-4-tert-butylcyclohex-2-enyl derivatives, such exception being ascribed to steric impedance of electrophile approach, promoting syn attack. Thus, overall, highly γ-regioselective and anti-stereoselective substitutions (SE′) are observed.
- Wickham, Geoffrey,Young, David,Kitching, William
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p. 1187 - 1195
(2008/10/08)
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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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p. 1435 - 1437
(2008/10/08)
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- Cyclic Olefins by Anodic Oxidation of β-(Trimethylsilyl)carboxylic Acids. - β-(Trimethylsilyl)acrylic Acid Derivatives as Acetylene Equivalents in Diels-Alder Reactions
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Trimethylsilyl-substituted dienophiles 1, 2, and 4 react with dienes 6-14 in 66-100percent yields to give β-trimethylsilyl-substituted carboxylic acids 15-25, some of which are hydrogenated to 26-31.These are decarboxylated-desilylated to cyclic olefins 35-47 by Non-Kolbe electrolysis in 45-91percent yields.The dienophiles 1, 2, and 4 are thus suitable acetylene equivalents for Diels-Alder reactions.
- Hermeling, Dieter,Schaefer, Hans J.
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p. 1151 - 1158
(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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- DEHYDRATION OF ALCOHOLS CATALYZED BY COPPER(II) SULFATE ADSORBED ON SILICA GEL.
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Copper(II) sulfate adsorbed on silica gel efficiently dehydrated secondary and tertiary alcohols under mild conditions to give olefins.The rate of dehydration of tertiary alcohols is much faster than that of secondary alcohols.
- Nishiguchi, Takeshi,Machida, Nakahira,Yamamoto, Etsuko
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p. 4565 - 4568
(2007/10/02)
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- THE REDUCTION OF 2-VINYL-1,1-BIS(BROMOMETHYL)CYCLOPROPANE
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A study was carried out on the reduction of 2-vinyl-1,1-bis(bromomethyl)cyclopropane by various methods including electrochemical procedures.The major reaction pathways ential opening and expansion of the cyclopropane ring, while the product of the formation of a second three-membered ring, namely, vinylspiropentane, is formed in low yield.The probable radical mechanism for this reaction is discussed.
- Zefirov, N. S.,Kozhushkov, S. I.,Kuznetsova, T. S.,Sosonkin, I. M.,Domarev,A. M.,et al
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p. 1863 - 1873
(2007/10/02)
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- Studies on Hydrogenation by Nickel Complexes. 5. The Selective Hydrogenation of 1,4-Cyclohexadienes to Cyclohexenes Catalyzed by a Nickel Complex
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1,4-Cyclohexadiene was hydrogenated selectively to cyclohexene with a nickel catalyst generated from bis(acetylacetonato)nickel(II), triethyldialuminium trichloride, and triphenylphosphine at 40 deg C under an atmospheric pressure of hydrogen.The hydrogenation of eleven kinds of alkyl-substituted 1,4-cyclohexadienes gave the corresponding cyclohexenes in good yields by the nickel catalyst.The structural factors of the alkyl substituent on the diolefin are shown to affect the hydrogenation rate.The homogeneous nickel catalyst system, in which a nickel hydride complex NiH(PPh3)(AlCl4) is supposed to be an active species, was effective for the selective hydrogenation of the diolefin to the olefin.A plausible pathway involving ?-allylnickel complexes for the hydrogenation is proposed.
- Sakai, Mutsuji,Hirano, Nobuo,Harada, Fumiya,Sakakibara, Yasumasa,Uchino, Norito
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p. 2923 - 2926
(2007/10/02)
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- Factors Influencing Conformational Preferences in Cyclohexenes
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Conformational preferences have been measured for the first time for 4-substituted cyclohexenes in a solvent of low polarity.Measurements were made for the substituents Cl, Br, I, OH, OSiMe3, and CN and were compared with conformational preferences in cyclohexyl and exo-methylenecyclohex-3-yl.In the nearly nonpolar solvent CF2Cl2, in which intramolecular interactions are maximized, there is a much larger axial population for cyclohexen-4-yl than in cyclohexyl or exo-methylenecyclohex-3-yl.In particular, the dipolar interaction of the endocyclic double bond is reduced from that of the exocyclic double bond.This observation is confirmed by the almost negligible effect of symmetrizing the endocyclic double bond through 1,2-dimethyl substitution, in contrast with the large effect of symmetrizing the exocyclic double bond through 7,7-dimethyl substitution.Polar solvents increase the proportion of the axial conformer to a smaller extent for the endocyclic than for the exocyclic system, again in agreement with a lower dipolar effect in the endocyclic case.These results emphasize the anisotropic nature of the steric effects of double bonds.
- Lambert, Joseph B.,Marko, Dale E.
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p. 7978 - 7982
(2007/10/02)
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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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p. 1999 - 2000
(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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- Protium-deuterium exchange of cyclic and acyclic alkanens in dilute acid medium at elevated temperatures
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A modification of the high temperature - dilute acid (HTDA) method for deuterium labelling of aromatic compounds has been applied to the H-D exchange of a number of cyclic and acyclic alkenes.Cyclopentene, cyclohexene, cyclododecene, and tetramethylethylene have been completely exchanged in excellent yield. 1-Methylcyclopentene and 1-methylcyclohexene have also been perdeuterated and cycloheptene and cyclooctene partially labelled but require spinning band distillation or preparative glpc for separation from rearrangement products.A variety of C5-C8 acyclic alkeneshave also been treated under HTDA conditions.
- Werstiuk, Nick Henry,Timmins, George
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p. 530 - 533
(2007/10/02)
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- 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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- SYNTHETIC TRANSFORMATIONS OF THE DIELS-ALDER ADDUCTS OF 1,2-BIS(BENZENESULPHONYL)ETHYLENES
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While a number of procedures has recently been described for the reductive bisdesulphonylation of the Diels-Alder adducts of both (Z)- and (E)-1,2-bis(benzenesulphonyl)ethylenes 1 and 2 to the corresponding carbon-carbon double bond, herewith are presented and discussed different synthetic transformations such as, for example, direct reduction of the adducts to the carbon-carbon single bond and base-induced elimination to the unsaturated sulphone that may readily be transformed into the corresponding saturated sulphone.As a consequence of these results, reagents 1 and 2 may be regarded as very reactive synthetic equivalents of ethylene, ethynyl and vinyl sulphone in cycloaddition reactions.Since saturated and unsaturated sulphones are amenable to a variety of synthetically useful transformations, a new entry to a large number of molecules is made available.
- Lucchi, Ottorino De,Pasquato, Lucia
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p. 349 - 354
(2007/10/02)
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- MECHANISM OF THE REACTION OF GLYCIDYL ESTERS WITH CARBOXYLIC ACIDS
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The kinetics of the reactions of 1-phenoxy-2,3-epoxypropane and 2,3-epoxypropylbenzoate with carboxylic acids were investigated.A new reaction mechanism is proposed to explain the anomalously high reactivity of the glycidyl esters.The mechanism involves protonation of the oxygen of the carbonyl group in the ester followed by intramolecular electrophilic attack on the oxirane oxygen by the carbonyl carbon atom, accompanied by opening of the epoxide ring and transfer of the acyl fragment in the glycidyl ester molecule.
- Klebanov, M. S.,Kir'yazev, F. Yu.,Chervinskii, A. Yu.,Shologon, I. M.
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p. 2193 - 2196
(2007/10/02)
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- The Selective Catalytic Conversion of Cycloalkanes into Cycloalkenes using a Soluble Rhenium Polyhydride System
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Selective catalytic dehydrogenation (up to 9 turnovers) of cycloalkanes CnH2n (n = 6, 7, and 8) to the corresponding cycloalkenes is achieved, under mild conditions (30 - 80 deg C), using dilute (ca. 3 mM) solutions of the bis(phosphine)rhenium heptahydrides (Ar3P)2ReH7 (Ar=p-F-C6H4, Ph, and p-Me-C6H4) in the cycloalkane, with an olefin as the hydrogen acceptor.
- Baudry, Denise,Ephritikhine, Michel,Felkin, Hugh,Holmes-Smith, Rupert
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p. 788 - 789
(2007/10/02)
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- Experimental and calculated thermodynamic data for the isomeric methylenecyclohexenes and methylenecyclohexane
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The equilibria in the isomerisation of the methylcyclohexenes and methylenecyclohexane have been investigated in the temperature range of 413 to 523 K. ΔrH and ΔrS have been calculated from the experimental data for the following equilibria: methylenecyclohexane1-methylcyclohexene, 3-methylcyclohexene1-methylcyclohexene and 4-methylcyclohexene1-methylcyclohexene.The resulting values for ΔrH and ΔrS are respectively: 7.3+-1.7, 7.6+-0.5, and 6.7+-0.4 kJ mol-1 and -15.9+-0.3, 1.0+-1.6 and 1.5+-1.4 J mol-1 K-1.These data are compared with values calculated using molecular mechanics.
- Peereboom, M.,Graaf, B. van de,Baas, J.M.A.
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p. 336 - 338
(2007/10/02)
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- Methyltriphenoxyphosphonium Iodide (MTPI); Induced Dehydration and Dehydrohalogenation in Aprotic Solvents
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Methyltriphenoxyphosphonium iodide (MTPI) is an effective dehydration and dehydrohalogenation reagent under mild conditions when 1,3-dimethylimidazolidin-2-one is used as an aprotic solvent in place of the more normally used hexamethylphosphoric triamide (HMPT).Since previosly suggested mechanisms had proposed alcohol-HMPT interaction as an important mechanistic step, this result coupled with comparative product geometric isomer distributions and the conjugated: non-conjugated triene product ratios leads to the conclusion that MTPI-alcohol interaction with displacement of phenoxide is the primary step in the reaction.In dimethyl sulphoxide (DMSO) alcohol dehydratation is hindered by DMSO-MTPI interaction yielding dimethyl sulphide.
- Spangler, Charles W.,Kjell, Douglas P.,Wellander, Lori L.,Kinsella, Mary A.
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p. 2287 - 2289
(2007/10/02)
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- Catalylic Conversion of Alcohols. Part 10.-Influence of Pretreatment on the Selectivity of MgO and CaO
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With both CaO and MgO catalysts, the hydrogen pretreated material is a selective dehydrogenation catalyst while the oxygen pretreated material has about the same activity for both dehydrogenation and dehydration.Initially the air (or oxygen) pretreated MgO sample produces an alkene distribution from 2-ols that resembles that obtained with alumina; as the reaction temperature is increased a similar alkene distribution, different from the equilibrium value, is obtained with both pretreatments.The three temperatures used with CaO yield an alkene distribution, with either pretreatment, that resembles the highest temperature run with MgO.Pure cis-2- or trans-2-methylcyclohexanol undergoes extensive cis-trans isomerisation; the different alkene distributions from the two alcohols suggest that a trans elimination pathway contributes to the dehydration mechanism.
- Davis, Burtron H.
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- Asymmetric Induction in Liquid Crystals: Optically Active trans-Cyclooctene from Hofmann Elimination in New Cholesteric Mesophases
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Optically active trans-cyclooctene was obtained by Hofmann elimination of trimethylcyclooctyl ammonium hydroxide in new cholesteric liquid crystals.The extent of asymmetric induction rose 7 percent.Enantiomeric equilibration of racemic trans-cyclooctene in cholesteric medium, at 180 deg C, leads to a 2 percent enantiomeric excess.These asymmetric induction results are interpreted in terms of solute-solvent interactions enhanced by the local ordering of the mesophase.
- Seuron, Patrick,Solladie, Guy
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p. 715 - 719
(2007/10/02)
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