- Cyclization of Ethyne and Propyne over Lanthanide Catalysts Deposited from Eu or Yb Metal Solutions in Liquid Ammonia
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Europium and ytterbium catalysts separated on active carbon from a solution of lanthanide metals dissolved in liquid ammonia were found to be effective for oligomerization of alkynes.Selective cyclic dimerization and trimerization of propyne and ethyne to cyclohexadiene and benzene occurred during the oligomerization, respectively, in which the active catalysts were characterized as lanthanide imides induced by the thermal treatment.
- Imamura, Hayao,Suda, Eisaku,Konishi, Tomohiro,Sakata, Yoshihisa,Tsuchiya, Susumu
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- THE THERMAL REARRANGEMENT OF CIS,CIS-1-FLUORO-2-METHYL-3-VINYLCYLOPROPANE. THE KINETIC EFFECT OF A SINGLE FLUORINE SUBSTITUENT
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It was demonstrated through a kinetic study of the thermal rearrangement of cis,cis-1-fluoro-2-methyl-3-vinylcyclopropane to cis-3-fluoro-1,4-hexadiene that a single fluorine substituent lowers that activation barrier for rearrangement by about 2 kcal/mole as compared to 6.4 kcal/mole for geminal difluoro substitution.
- Elsheimer, Seth,Dolbier, William R.
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- Regioselective Catalytic Transfer Hydrogenation of Dimethyl Bicyclohepta-2,5-diene-2,3-dicarboxylate, Dimethyl Bicyclohept-2-ene-2,3-dicarboxylate, and Related Compounds over Palladium on Carbon
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The catalytic transfer hydrogenation (CTH) of dimethyl bicyclohepta-2,5-diene-2,3-dicarboxylate (3) on palladium on carbon is highly regioselective, giving predominant reduction at the least-substituted olefinic site.The CTH of dimethyl bicyclohept-2-ene-2,3-dicarboxylate also occurs with exclusive suprafacial exo addition of hydrogen to afford the endo isomer.An increase in the relative concentration of palladium on carbon (ca. 40-45 wt/wt percent based on the acceptor) accelerates the rate of CTH while the substituted cyclohexenes undergo CTH faster than cyclohexene with dimethyl bicyclohept-2-ene-2,3-dicarboxylate.
- Tabor, Derrick C.,White, Franklin H.,Collier, L. Warren,Evans, Slayton A.
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- Tellurolate-Induced 1,4-Elimination of 1,4-Dibromo-2-Enes. Syntheses of 1,3-Dienes
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Sodium 2-thienyltellurolate, generated in catalytic amounts from sodium borohydride and bis(2-thienyl) ditelluride, was found to efficiently debrominate 1,4-dibromo-2-olefins to 1,3-dienes under very mild reaction conditions.The required 1,4-dibromo-2-olefins were usually synthesized by allylic α,α'-bromination of olefins.Terminal olefins yielded, via allylic rearrangement, a mixture of 1,4-dibromo-2-olefins and 1,2-dibromo-3-olefins.Both these isomers were converted to 1,3-dienes (E/Z ca. 9/1) by the tellurolate reagent.The syntetic utility of the tellurolate-induced debromination reaction was demonstrated in a two-step synthesis of the main component of the red bollworm moth sex pheromone.
- Engman, Lars,Bystroem, Styrbjoern E.
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- Thermal chemistry of bicyclo[4.2.0]oct-2-enes
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At 300 °C, bicyclo[4.2.0]oct-2-ene (1) isomerizes to bicyclo[2.2.2]oct-2-ene (2) via a formal [1,3] sigmatropic carbon migration. Deuterium labels at C7 and C8 were employed to probe for two-centered stereomutation resulting from C1-C6 cleavage and for one-centered Stereomutation resulting from C1-C8 cleavage, respectively. In addition, deuterium labeling allowed for the elucidation of the stereochemical preference of the [1,3] migration of 1 to 2. The two possible [1,3] carbon shift outcomes reflect a slight preference for migration with inversion rather than retention of stereochemistry; the si/sr product ratio is ~1.4. One-centered stereomutation is the dominant process in the thermal manifold of 1, with lesser amounts of fragmentation and [1,3] carbon migration processes being observed. All of these observations are consistent with a long-lived, conformationally promiscuous diradical intermediate.
- Powers, David C.,Leber, Phyllis A.,Gallagher, Sarah S.,Higgs, Andrew T.,McCullough, Lynne A.,Baldwin, John E.
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- An Experimental and Theoretical Evaluation of the Intramolecular Reactions of Cyclohexyne
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The intramolecular reactions of cyclohexyne (1a) have been explored theoretically by using ab initio calculations at the Mp2/6-31G* level and experimentally by examining the ring expansion of cyclopentylidenecarbene (2a) at elevated temperatures.The calculations indicate that 1a is more stable than 2a by 19.0 kcal/mol and that the barrier for 1a -> 2a is 26.4 kcal/mol.Carbene 2a can rearrange to bicyclohex-5-ene and thence to cyclohexadiene with a barrier of 38.9 kcal/mol.A higher energy reaction of 1a is cleavage to ethylene and butatriene in a retro-Diels-Alder reaction, which is calculated to have a barrier of 46.8 kcal/mol.This retro-Diels-Alder reaction is observed experimentally when 2a is generated by the pyrolysis of the cyclopentylidene adduct of Meldrum's acid.
- Tseng, John,McKee, Michael L.,Shevlin, Philip B.
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- Central and Lateral Bicyclo[1.1.0]butane Bond Cleavage with Subsequent Wagner-Meerwein Rearrangements or Carbene Formation in the 185-nm Photolysis of Tricyclo[3.1.0.02,6]hexane, Tricyclo[4.1.0.02,7]heptane, and Tricyclo[5.1.0.02,8]octane
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The 185-nm photochemistry of tricyclop[3.1.0.02,6]hexane, tricyclo[4.1.0.02,7] heptane, [1,7-d2]tricyclo[4.1.0.02,7]heptane, tricyclo[5.1.0.02,8]octane, and [1-d]tricyclo[5.1.0.02,8]octane was investigated. Tricyclo[5.1.0.02,8]octane yields bicyclo[4.2.0]oct-7-ene, tricyclo[4.1.0.02,7]heptane yields 85% bicyclo[3.2.0]hept-6-ene and 15% 3-methylenecyclohexene, and tricyclo[3.1.0.02,6]hexane yields 39% 3-methylenecyclopentene, 15% 1,3-cyclohexadiene, 26% trans-1,3,5-hexatriene, and 20% cis-1,3,5-hexatriene. From the deuterium-labeling studies, it is concluded that, in the case of the tricyclooctane, the central bicyclobutane bonds cleave in the primary step to give radical cationic or zwitterionic species that undergo a Wagner-Meerwein rearrangement. Also, in the case of tricycloheptane, this is the dominating pathway but lateral C-C bond cleavage with subsequent carbene and product formation takes place to the extent of ca. 15%. For tricyclohexane, this pathway becomes the major route. Our photomechanistic observations are in good agreement with earlier theoretical investigations on the relative energetic ordering of the bicyclobutane HOMOs, in that the product composition reflects this.
- Adam, Waldemar,Alt, Christine,Braun, Max,Denninger, Uwe,Zang, Gerald
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- Thermal reactions of 7-d- and 8-d-bicyclo[4.2.0]oct-2-enes
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The gas phase thermal reactions exhibited by bicyclo[4.2.0]oct-2-ene and 7-d and 8-d analogues at 300 °C have been followed kinetically through GC and 2H NMR spectroscopic analyses. In contrast to the pattern of transformations exhibited by bicyclo[3.2.0]hept-2-ene and deuterium-labeled analogues, no reactions initiated by C1-C6 bond cleavage are seen, epimerization at C8 is much faster than [1,3] shifts leading to bicyclo[2.2.2]oct-2-ene, and the ratio of rate constants for [1,3] carbon migration with inversion versus migration with retention is ~1.4. Homolysis of C1-C8 to give a conformationally flexible diradical intermediate having a relatively long lifetime and multiple options for further reaction (re-formation of C1-C8 with or without net epimerization, fragmentation to 1,3-cyclohexadiene and ethylene, migration to the original C3 with inversion or retention) accords well with the observations. Clearly, orbital symmetry control does not govern stereochemistry for the [1,3] sigmatropic carbon shifts. Copyright
- Baldwin, John E.,Leber, Phyllis A.,Powers, David C.
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- NMR spectroscopic and computational investigations of RuHCl(CO)(PPh 3)3 catalyzed isomerization of 1,4-cyclohexadiene
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Ruthenium catalysts with bulky ligands are particularly effective for diene isomerization reactions. Thermodynamics and the mechanism of RuHCl(CO)(PPh3)3 catalyzed 1,4-cyclohexadiene isomerization was probed experimentally through NMR spectroscopy and mod
- Mao, James X.,Mathers, Robert T.,Damodaran, Krishnan
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- Kinetics and mechanism of monomolecular heterolysis of commercial organohalogen compounds: XL. Nature of salt effects in dehydrobromination of 3-bromocyclohexene in γ-butyrolactone. Role of solvation effects of dipolar aprotic solvents
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The influence of neutral salts on the rate of heterolysis of 3-bromocyclohexene at 31°C in γ-butyrolactone was studied by the verdazyl method; ν = k[C6H9Br], E1 mechanism. Additions of lithium picrate do not affect the reaction rate;
- Ponomarev,Stambirskii,Dvorko
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- Chemistry of β-functionalized α-nitroso ethylenes. Methyl β-nitroso acrylate as heterodienophile in [4 + 2]-cycloaddition to cyclic dienes
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(equation presented) β-Functionalized nitroso alkene 2, obtained from methyl β-nitropropionate 1 and W,O-bis(trimethylsilyl)acetamide, can function as a good heterodienophile in Diels-Alder reactions. Therefore, 2 was trapped by cyclic dienes to give adducts 4 with the corresponding stereoselectivity. Cycloadduct 4a undergoes refro-[4 + 2]-cycloaddition at 33 °C in solution; thus 4a can be used to generate nitroso alkene 2 in neutral medium. Cyclopentadiene reacts with adduct 4a according to an endo-[4 + 2]-cycloaddition scheme to give cycloadduct 5 in low yield.
- Tishkov, Alexander A.,Lyapkalo, Il'ya M.,Ioffe, Sema L.,Strelenko, Yuri A.,Tartakovsky, Vladimir A.
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- Infrared Multiphoton Isomerization of cis- and trans-1,3,5-Hexatriene
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The laser-induced infrared multiphoton isomerization reactions of cis- and trans-1,3,5-hexatriene have been investigated.Excitation of the trans isomer produces vibrationally excited cis molecules possessing sufficient energy to undergo electrocyclic ring closure to 1,3-cyclohexadiene.The ratio of primary (cis) to secondary (cyclohexadiene) products is dependent upon laser fluence and buffer gas pressure.Excitation of the cis isomer produces both trans and cyclohexadiene products.The fluence dependence of the product ratio is in accord with RRKM calculations for competing reactions of the highly excited (70-100 kcal/mol) cis parent isomer.
- Lewis, Frederick D.,Teng, Peter A.,Weitz, Eric
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- Synthesis and study of zeolites modified with cation metals as catalysts for the reaction of oxidative dehydrogenation of naphthenic hydrocarbons
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A study of the catalytic activity of modified zeolites in the reaction of selective oxidative dehydrogenation of cyclohexane and methyl cyclohexane demonstrated that catalysts prepared based on natural clinoptilolite modified with Cu2+, Zn2+, Co2+, and Cr3+ cations showed the highest activity in the reactions considered. Specifcally, the natural zeolite, clinoptilolite, containing 0.5 wt % Co2+ and 0.25 wt % Cr3+ is an active catalyst for the reaction of oxidative dehydrogenation of methyl cyclohexane into cyclohexadiene-1,3. With the experimental data and the binding energies of the catalyst components with atomic oxygen considered, the active centers in the components of the catalyst for the reaction of oxidative dehydrogenation of cyclohexane, responsible for the formation of cyclohexadiene-1,3-cyclohexene, and benzene can be divided into groups. Principles to be used when selecting high-efficiency catalytic systems for the reaction of oxidative dehydrogenation of alicyclic hydrocarbons to the corresponding dienes are formulated.
- Aliev,Shabanova,Kerimov
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- Kinetics of thermal dimerization of hexatriene
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The thermal isomerization of cis-hexatriene (cHT) to cyclohexadiene (CHD) and the dimerization of CHD and trans-hexatriene (tHT) in the liquid phase in the temperature range 380 K-473 K are reported.
- Bulatov,Oref
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- Dehydrogenation of cyclohexene over carbon deposited on alumina
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The dehydrogenation of cyclohexene over carbon deposited on alumina, C/Al2O3, which was prepared by contacting hydrocarbons such as cyclohexane, cyclohexene, and cyclohexanone with alumina surface at ≥ 823 K, was studied under non-oxidative conditions. At 773 K, the conversion gradually decreased with process time, while the selectivity to the products slightly changed. Because the selectivity to dehydrogenated products such as benzene and 1,3-cyclohexadiene and their yields increased with increasing carbon content, the carbon deposited on alumina had dehydrogenation activity. The selectivities to the dehydrogenated products were maximized at a specific carbon content, while the selectivity to cyclohexane, hydrogenation product, increased with carbon content over the specific carbon content.
- Sato,Amano,Takahashi,Sodesawa
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- Thermal reactions of 8-methylbicyclo[4.2.0]oct-2-enes: Competitive diradical-mediated [1,3] sigmatropic, stereomutation, and fragmentation processes
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At 275 °C, 8-exo-methylbicyclo[4.2.0]oct-2-ene (1a) undergoes a [1,3] sigmatropic rearrangement to 5-methylbicyclo[2.2.2]oct-2-enes, of which the orbital symmetry-allowed si product is only marginally favored over the forbidden sr product; that is, silsr is 2.4. Accompanying the [1,3] shift are significant amounts of epimerization and fragmentation. The 8-endo epimer 1b, which yields no [1,3] product, experiences primarily direct fragmentation and secondarily epimerization. A diradical intermediate can account for all such observations.
- Bogle, Xavier S.,Leber, Phyllis A.,McCullough, Lynne A.,Powers, David C.
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- THE ABSENCE OF ETHYLENEDIONE ON PHOTOCHEMICAL BISCARBONYLATION REACTIONS
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Photolyses of a number of bridged cyclohexenediones and vinylcyclobutanediones in argon or xenon matrices at 10 K at a variety of wavelengths produced carbon monoxide with no evidence for formation of ethylenedione, the elusive dimer of CO.
- Rubin, Mordecai B.,Patyk, Andres,Sander, Wolfram
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- Dynamics of the thermal dissociation of unsaturated cyclic ketones: Nascent vibrational energy distributions in the products
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It has been found that in thermal dissociation of both norbornenone and 3-cyclopentenone the CO is formed with less than half its statistical share of the energy released from the transition state. We have used (VV) coupling between the products, 1,3-cyclohexadiene and butadiene, respectively, to probe their nascent vibrational energy. They are both born vibrationally excited. It seems that much of the energy released appears as vibrational energy of these molecules. In the transition state the CO group must have a bond length close to that of the free molecule. These results do not permit a decision between symmetric and asymmetric bond cleavage. However, separate experiments in which the rotational distribution has been measured establish that the dissociation does not occur by symmetric bond rupture.
- Simpson,Price,Holmes,Adam,Martin,Bish
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- THERMAL BEHAVIOR OF TRANS,TRANS,TRANS-1,2,3,4-TETRAVINYLCYCLOBUTANE
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Above 420 deg C the title compound decomposes to trans-hexatriene and cyclohexadiene-1,3.At temperatures above 770 deg C only cyclohexadiene-1,3 and benzene are found.
- Fischer, Evelyn,Gleiter, Rolf
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- 3-Thiabicyclohept-6-ene 3,3-Dioxide: A Novel Synthon for cis-1,2-Divinyl Intermediates and Derived Seven-membered Ring Systems
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Functionalisation of the 6,7-double bond in the novel bicyclic sulphone, 3-thiabicyclohept-6-ene 3,3-dioxide, followed by thermal extrusion of SO2, allows direct entry into seven-membered ring systems via a Cope rearrangement of the resulting cis-1
- Aitken, R. Alan,Cadogan, J. I. G.,Gosney, Ian,Hamill, Brendan J.,McLaughlin, Leo M.
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- One- and Two-Electron Oxidation of Hydrazines by Dimethyldioxirane
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Dimethyldioxirane (1) reacts with sesquibicyclic hydrazine 2 to give the expected (thermally labile) hydrazine N-oxide product and with the homologous hydrazine 5, principally by methyl group transfer, to produce the N-methylated hydrazinium cation acetate 6.
- Nelsen, Stephen F.,Scamehorn, Richard G.,Felippis, James De,Wang, Yichun
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- Evidence for inhomogeneous broadening in vibrational overtone transitions: Formation of 1, 3-cyclohexadiene from cis-1, 3, 5-hexatriene
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By pumping the 4-O and 5-O C-H overtones of cis-1,3,5-hexatriene, the rates of 1,3- cyclohexadiene formation are measured using a Stern-Volmer analysis.While the rate for 5-0 C- H excitation is faster than 4-O C-H excitation, the latter is about one order
- Chuang, Mei-Chen,Zare, Richard N.
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- THE THERMODYNAMIC EFFECT OF FLUORINE AS A SUBSTITUENT VINYLIC CF2 AND CFH AND ALLYLIC CF2C
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I2-catalyzed isomerizations of 3-fluoropropene and 3,3-difluoropropene, and a Cope rearrangement of 1,1-difluoro-1,5-hexadiene provide thermodynamic data which allow the determination of a number of important group values for contributions to ΔHf0 which when combined with those determined in the preceding paper allow the calculations of ΔHf0's of most simple F-substituted hydrocarbons: d-(F)(H)>= -38.4, d(F)2>= -88.0, d)>= -103.9, = -104.9 kcal/mole.A kinetic study of the conversion of 1,1-difluoro- to 3,3-difluoro-1,5-hexadiene provided activation parameters for the process: Log A= 10.8, Ea= 33.0 kcal/mole and ΔS*= -12.2 e. u.Incremental geminal stabilizations of F and other substituents are discussed and contrasted.
- Dolbier, William R.,Medinger, Karl S.,Greenberg, Arthur,Liebman, Joel F.
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- Thermal Decarbonylation of Some Strained Ketones
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Norbornen-7-one derivatives are known to undergo facile decarbonylation reactions, and these reactions are sensitive to the presence of endo-fused carbocyclic structures.MO calculations were performed on endo-tricyclo2,5>nona-3,7-dien-9-one in order to determine the importance of electronic participation of the four-membered ring in the decarbonylation reaction.
- Rubio, M.,Hernandez, Alfonso Garcia,Daudey, J. P.,Cetina, R. R.,Diaz, A.
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- Organic Photochemistry with 6.7-eV Photons: 1,4-Cyclohexadiene and 1,4-Cyclohexadiene-3,3,6,6-d4
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The photolysis of 1,4-cyclohexadiene has been investigated in solution at 185 and 214 nm, as well as by sensitization by benzene in solution at 254 nm or by mercury (3P1) atoms in the vapor phase.The reaction mechanisms under these conditions have been probed by the use of 1,4-cyclohexadiene-3,3,6,6-d4 (4).Both at 185 and 214 nm, the principal products are bicyclohex-2-ene (3), 1,3-cyclohexadiene, 1,3,5-hexatriene, and benzene.NMR analysis of the products formed in the photolysis of 4 at 185 nm shows that the formation of 3 is exclusively by a 1,2-hydrogen migration.The other two decomposition pathways at this wavelength correspond to 1,3- and 1,4-H migration.The relative importance of these reactions is sensitive to the wavelength in the range 185-214 nm.Triplet sensitization of 1,4-cyclohexadiene gives benzene (+H2) as a major product and 3 as a minor product.Deuterium labeling shows that in this instance 3 is formed by a di-?-methane rearrangement.Ab initio calculations on the ground state of 1,4-cyclohexadiene employing a STO-3G basis yield a dihedral angle of about 140 with a relatively flat minimum.The intermediate neglect of differential overlap (INDO-SCF-CI) method was used to calculate the energies of the low-lying singlet and triplet states in 1,4-cyclohexadiene for several values of the dihedral angle.At the experimental dihedral angle of 160, it was computed that there were two triplet states, 3A2 (3.7 eV) and 3B2 (3.8 eV), and three closely spaced singlet states, 1A2 (5.9 eV), 1B2 (6.3 eV), and 1B2 (6.4 eV).This is in reasonably good agreement with recent electron-impact data.The 3B2 state is deduced to undergo the di-?-methane rearrangement under triplet sensitization while all of the hydrogen migration reactions that are observed on direct irradiation are attributed to the higher 1B2 state.This state is derived from the excitation of an electron to the ?1* + ?2* orbital and contains significant C-H antibonding character.
- Srinivasan, R.,White, Lloyd S.,Rossi, Angelo R.,Epling, Gary A.
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- Low Valent Magnesium Chemistry with a Super Bulky β-Diketiminate Ligand
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The steric bulk of the well-known DIPPBDI ligand (CH[C(CH3)N-DIPP]2, DIPP=2,6-diisopropylphenyl) was increased by replacing isopropyl for isopentyl groups. This very bulky DIPePBDI ligand could not stabilize the radical species (DIPePBDI)Mg.: reduction of (DIPePBDI)MgI with Na gave (DIPePBDI)2Mg2 with a rather long Mg-Mg bond of 3.0513(8) ?. Addition of TMEDA prior to reduction gave complex (DIPePBDI)2Mg2(C6H6), which could also be obtained as its THF adduct. It is speculated that combination of a bulky spectator ligand and TMEDA prevents dimerization of the intermediate MgI radical, which then reacts with the benzene solvent. Complex (DIPePBDI)2Mg2(C6H6), which formally contains the anti-aromatic anion C6H62?, reacted with tBuOH as a Br?nsted base to 1,3- and 1,4-cyclohexadiene and with H2 as a two electron donor to (DIPePBDI)2Mg2H2 and C6H6. It also reductively cleaved the C?F bond in fluorobenzene and gave (DIPePBDI)MgPh, (DIPePBDI)MgF, and C6H6.
- Gentner, Thomas Xaver,R?sch, Bastian,Ballmann, Gerd,Langer, Jens,Elsen, Holger,Harder, Sjoerd
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- Kinetics and mechanism of monomolecular heterolysis of commercial organohalogen compounds: XXVIII. Effect of the nature of the verdazyl indicator on salt effects in dehydrobromination of 3-bromocyclohexene in nitrobenzene
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The salt effect on the rate of dehydrobromination of 3-bromocyclohexene in PhNO2 depends on the nature of the verdazyl indicator. With triphenylverdazyl and its chloro and nitro derivatives in the presence of Et4NClO4, a n
- Ponomarev,Stambirskii,Dvorko
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- Merging Halogen-Atom Transfer (XAT) and Cobalt Catalysis to Override E2-Selectivity in the Elimination of Alkyl Halides: A Mild Route towardcontra-Thermodynamic Olefins
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We report here a mechanistically distinct tactic to carry E2-type eliminations on alkyl halides. This strategy exploits the interplay of α-aminoalkyl radical-mediated halogen-atom transfer (XAT) with desaturative cobalt catalysis. The methodology is high-yielding, tolerates many functionalities, and was used to access industrially relevant materials. In contrast to thermal E2 eliminations where unsymmetrical substrates give regioisomeric mixtures, this approach enables, by fine-tuning of the electronic and steric properties of the cobalt catalyst, to obtain high olefin positional selectivity. This unprecedented mechanistic feature has allowed access tocontra-thermodynamic olefins, elusive by E2 eliminations.
- Zhao, Huaibo,McMillan, Alastair J.,Constantin, Timothée,Mykura, Rory C.,Juliá, Fabio,Leonori, Daniele
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supporting information
p. 14806 - 14813
(2021/09/18)
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- Continuous synthesis method of 1,3-cyclohexadiene
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The invention discloses a continuous synthesis method of 1,3-cyclohexadiene. The synthesis method includes the following steps: in a continuous reactor, a compound defined in the specification and bromine are subjected to an addition reaction, then debromination is performed under a strong alkali condition, and 1,3-cyclohexadiene is distilled out, wherein R1 and R2 are straight-chain or branched-chain alkyl or aryl and are the same or different. With the adoption of the continuous synthesis method, in the continuous reactor, the bromination reaction of cyclohexene, continuous quenching, extraction and concentration processes are achieved, fluidization operation of the production process is achieved, moreover, no highly toxic solvent or no safety hazard exists, the process of eliminating olefin formation is carried out in the continuous reactor, continuous feeding and continuous distillation of the product are achieved, the whole reaction system is still kept in a relatively small reaction volume and is subjected to reaction, and the process safety risk is reduced.
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Paragraph 0038-0068
(2019/01/07)
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- Synthesis, characterization and catalytic performance in cyclohexane transformation by Bi2O3/MCM-41 nanocomposite materials
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The nanoparticles of Bi2O3 supported on mesoporous MCM-41 were prepared in a simple way and were well characterized. The oxidation of cyclohexane to cyclohexanol and cyclohexanone under 1 atmospheric pressure of air in the absence of any solvent and reducing agents with Bi2O3/MCM-41 nanocomposites were considered. These nanoparticles of Bi2O3 supported on mesoporous MCM-41 were found to be the very effective catalysts for cyclohexane oxidation with air in a temperature range of 280–370 ?C. The influences of reaction temperature, the loading amount of Bi2O3 and space velocity on the oxidation of cyclohexane were also studied, and optimized conditions were investigated.
- Mozaffari, Majid,Ebadi, Amin
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p. 1643 - 1651
(2017/11/20)
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- Challenging Thermodynamics: Hydrogenation of Benzene to 1,3-Cyclohexadiene by Ru@Pt Nanoparticles
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Since the earliest reports on catalytic benzene hydrogenation, 1,3-cyclohexadiene and cyclohexene have been proposed as key intermediates. However, the former has never been obtained with remarkable selectivity. Herein, we report the first partial hydrogenation of benzene towards 1,3-cyclohexadiene under mild conditions in a catalytic biphasic system consisting of Ru@Pt nanoparticles (NPs) in ionic liquid (IL). The tandem reduction of [Ru(COD)(2-methylallyl)2] (COD=1,5-cyclooctadiene) followed by decomposition of [Pt2(dba)3] (dba=dibenzylideneacetone) in 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMI?PF6) IL under hydrogen affords core–shell Ru@Pt NPs of 2.9±0.2 nm. The hydrogenation of benzene (60 °C, 6 bar of H2) dissolved in n-heptane by these bimetallic NPs in BMI?PF6 affords 1,3-cyclohexadiene with an unprecedented 21 % selectivity at 5 % benzene conversion. Conversely, almost no 1,3-cyclohexadiene was observed when using monometallic Pt0 or Ru0 NPs under the same reaction conditions and benzene conversions. This study reveals that the selectivity is related to synergetic effects of the bimetallic composition of the catalyst material as well as to the performance under biphasic reaction conditions. It is proposed that colloidal metal catalysts in ILs and under multiphase conditions (“dynamic asymmetric mixtures”) can operate far from the thermodynamic equilibrium akin to chemically active membranes.
- Weilhard, Andreas,Abarca, Gabriel,Viscardi, Janine,Prechtl, Martin H. G.,Scholten, Jackson D.,Bernardi, Fabiano,Baptista, Daniel L.,Dupont, Jairton
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p. 204 - 211
(2017/01/17)
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- The value of 2JP–CO as a diagnostic parameter for the structure and thermal reactivity of carbonyl-stabilised phosphonium ylides
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A survey of 20 carbonyl-stabilised phosphonium ylides with recently reported X-ray structures shows a strong correlation between the C[dbnd]P to C[dbnd]O torsion angle and the value of 2JP–CO, with high values being associated with an anti configuration and low with syn. Seven new X-ray structural determinations are reported, several for types of ylide not crystallographically characterised before, and these also conform to this pattern. The value of 2JP–CO is then correlated with whether or not thermal extrusion of Ph3PO occurs to give alkynes for over 200 ylides and an empirical rule developed that the extrusion never occurs for ylides where this value is > 11 Hz. This is used to rationalise the anomalous behaviour of some trioxo ylides and cyclic ylides, two of which afford cycloalkynes, isolated after rearrangement as the isomeric 1,3-dienes. The rule also holds for a family of novel highly fluorinated ylides which afford fluorinated alkynes in good yield upon flash vacuum pyrolysis.
- Aitken, R. Alan,Boubalouta, Youcef,Chang, Da,Cleghorn, Lee P.,Gray, Ian P.,Karodia, Nazira,Reid, Euan J.,Slawin, Alexandra M.Z.
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p. 6275 - 6285
(2017/09/29)
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- Oxidative dehydrogenation of cyclohexane over modified zeolite catalysts
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The catalytic activity of modified zeolites in selective oxidative dehydrogenation of cyclohexane has been studied. It has been established that polymetallic zeolite catalyst, namely, CuZnCoCr-clinoptilolite (0.5% Cu2+, 0.2% Zn2+; 0.1% Co2+; 0.1% Cr3+) manifests the highest activity in the reaction under consideration. The kinetic scheme of the reaction mechanism has been proposed, and a kinetic model of the process has been developed on the basis of stepwise mechanism schemes. The numerical values of the kinetic parameters are calculated.
- Aliev,Shabanova,Nadzhaf-Kuliev,Medzhidova
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p. 639 - 645
(2016/08/16)
-
- Chemical Synthesis and Self-Assembly of a Ladderane Phospholipid
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Ladderane lipids produced by anammox bacteria constitute some of the most structurally fascinating yet poorly studied molecules among biological membrane lipids. Slow growth of the producing organism and the inherent difficulty of purifying complex lipid mixtures have prohibited isolation of useful amounts of natural ladderane lipids. We have devised a highly selective total synthesis of ladderane lipid tails and a full phosphatidylcholine to enable biophysical studies on chemically homogeneous samples of these molecules. Additionally, we report the first proof of absolute configuration of a natural ladderane.
- Mercer, Jaron A. M.,Cohen, Carolyn M.,Shuken, Steven R.,Wagner, Anna M.,Smith, Myles W.,Moss, Frank R.,Smith, Matthew D.,Vahala, Riku,Gonzalez-Martinez, Alejandro,Boxer, Steven G.,Burns, Noah Z.
-
p. 15845 - 15848
(2016/12/23)
-
- A general and efficient method for the palladium-catalysed conversion of allylic alcohols into their corresponding dienes
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A general method was established, converting a broad range of allylic alcohols directly and quantitatively into their corresponding dienes. The developed protocol allows the direct use of allylic alcohols, circumventing the need for their derivatisation into more reactive precursors, thereby minimising waste production with water as the sole co-product.
- Ostrowski, Karoline A.,Vogelsang, Dennis,Vorholt, Andreas J.
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p. 1302 - 1305
(2016/03/09)
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- Streamlining the conversion of biomass to polyesters: Bicyclic monomers with continuous flow
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A three-step transformation of 1,4-cyclohexadiene (1,4-CHD) using continuous flow produced an aliphatic bicyclic monomer for polyester synthesis. The monomer synthesis involved catalytic alkene isomerization of 1,4-CHD to 1,3-CHD using a heterogeneous Na
- Dakshinamoorthy, Deivasagayam,Lewis, Stewart P.,Cavazza, Michael P.,Hoover, Aaron M.,Iwig, David F.,Damodaran, Krishnan,Mathers, Robert T.
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p. 1774 - 1783
(2014/04/17)
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- Rhodium-catalyzed alkene hydrosilylation via a hydride shuttle process by diene ligands: Dramatic enhancement of regio- and diastereoselectivity
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A cooperative ligand-assisted, Rh-catalyzed intramolecular alkene hydrosilylation of homoallylic silyl ethers (1) was developed to provide 1,3-trans-oxasilacyclopentanes (trans-2) in a highly regio- and diastereoselective manner. The modification of metal-ligand architecture employing an inner-sphere functional diene ligand (1,3-cyclohexadiene) and a supporting phosphine ligand (BINAP) was identified as responsible for dramatic enhancement of selectivities. Mechanistic details of a diene ligand-mediated hydride shuttle process are presented as the potential mechanistic driving force behind the high level of the selectivities.
- Hua, Yuanda,Nguyen, Hiep H.,Trog, Gabriela,Berlin, Adam S.,Jeon, Junha
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supporting information
p. 5890 - 5895
(2015/03/30)
-
- Bromination and accompanying rearrangement of the polycyclic oxetane 2,4-oxytwistane
-
Bromination of the polycyclic oxetane 2,4-oxytwistane (rac-(1R,3S,4R,7S,9R,11S)-2-oxatetracyclo-[5.3.1.03,11.04,9]undecane) was undertaken in order to form 2,4-dibromotwistane. The oxetane was subjected to the mild reagent combinatio
- Rosenberg, Murray G.,Billing, Peter,Brecker, Lothar,Brinker, Udo H.
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p. 8786 - 8799
(2015/02/19)
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- PLANT BASED MONOMERS AND POLYMERS
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The preparation of cyclohexadienes from one or more plant oils is disclosed. The cyclohexadiene can be used to form polymers or derivatized to form other monomers that can be used to form polymeric materials.
- -
-
Paragraph 0026; 0035; 0039; 0066-0067
(2014/01/07)
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- Expanding the scope of biomass-derived chemicals through tandem reactions based on oxorhenium-catalyzed deoxydehydration
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New modes of DODH: Oxorhenium compounds act as deoxydehydration(DODH)/acid dual-purpose catalysts to transform biomass-derived diol substrates into a variety of commodity chemical precursors. The power of this approach is highlighted by a tandem [1,3]-OH shift/DODH of 2-ene-1,4-diols and 2,4-diene-1,6-diols, and by a DODH/esterification sequence of sugar acids to unsaturated esters for the production of polymers and plasticizers. Copyright
- Shiramizu, Mika,Toste, F. Dean
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p. 12905 - 12909
(2014/01/06)
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- Synthesis, characterization, and catalytic behavior of dioxomolybdenum complexes bearing AcAc-type ligands
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A series of [MoO2(acac′)2] [acac′ = acetylacetonato-type ligand: dibenzoylmethane (3), 1-benzoylacetone (4), bis(p-methoxybenzoyl)methane (5), 2-acetylcyclopentanone (6), 2-acetylcyclohexanone (7), and 2-acetyl-1-tetralone (8)] complexes have been synthesized in yields of 44-83 % by a simple synthetic method by using sodium molybdate and the desired acac-type ligand as starting materials. All the complexes were characterized by IR, UV/Vis, NMR, and high-resolution ESI-MS, and for compounds 3, 4, and 8, solid-state structures were obtained by X-ray diffraction. All the complexes contain a cis-dioxomolybdenum moiety, as proven by the characteristic Mo=O vibrations in the IR spectra and the occurrence of four sets of signals in the NMR spectra of the complexes bearing asymmetrical ligands (4 and 6-8), and confirmed by the solid-state structures. The complexes were found to be active as catalysts in the dehydration of 1-phenylethanol to styrene using technical-grade toluene as the solvent in air at 100 °C. The highest catalytic activity was found for [MoO2{(tBuCO) 2CH}2] (2), followed by [MoO2{(C 6H5CO)2CH}2] (3). Both complexes were also found to be active in the dehydration of other alcohols, including allylic, aliphatic, and homoallylic alcohols, as well as secondary and tertiary alcohols, with 2 generally showing better activity and selectivity than 3. These catalytic results were compared with those previously obtained with the metal-based catalyst Re2O7 and the benchmark acid catalyst H2SO4. The results were dependent on the substrate: By using 2, good selectivities but lower activities were generally obtained with tertiary alcohols, whereas good activities but lower selectivities were obtained with secondary alcohols. The industrially important dehydration of 2-octanol to octenes was very efficiently catalyzed by 2. Overall, the [MoO 2(acac′)2] complexes reported herein could offer a cheaper and more abundant metal-based catalyst alternative to the previously reported rhenium-based catalytic system for the dehydration reaction. Copyright
- Korstanje, Ties J.,Folkertsma, Emma,Lutz, Martin,Jastrzebski, Johann T.B.H.,Klein Gebbink, Robertus J.M.
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p. 2195 - 2204
(2013/05/22)
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- A unique Au-Ag-Au triangular motif in a trimetallic halonium dication: Silver incorporation in a gold(I) catalyst
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As a result of explorations into the solution chemistry of silver/gold mixtures, a unique diphosphine trimetallic chloronium dication was discovered that incorporates silver-arene chelation and a triangular mixed gold/silver core in the solid state. Notably, it was isolated from a Celite prefiltered solution initially thought to be silver-free. The crystal structure also incorporates the coordination to silver of one fluorine atom of one SbF6 - counterion. The structure was compared to two new, but well-precedented, phosphine digold chloride cations. DFT calculations supported significant silver-halide and silver-arene interactions in the mixed gold/silver complex and metallophilic interactions in all three complexes. Comparison of computed data revealed that the ωB97X-D functional, which has a long-range corrected hybrid with atom-atom dispersion corrections, gave a better fit to the experimental data compared with the PBE0 functional, which has previously failed to capture aurophilic interactions. Preliminary studies support the presence of the mixed gold/silver structure in solution. Silver lining! As a result of explorations into the solution chemistry of silver/gold mixtures, a unique trimetallic chloronium dication was discovered that incorporates silver-arene chelation and a triangular mixed gold/silver core (see figure). Notably, it was isolated from a previously Celite-filtered solution, a procedure generally believed to be efficient at removing silver. The solid-state and solution structure, as well as DFT calculations are reported herein. Copyright
- Zhu, Yuyang,Day, Cynthia S.,Zhang, Lin,Hauser, Katarina J.,Jones, Amanda C.
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supporting information
p. 12264 - 12271
(2013/09/23)
-
- Photolytic C-H activation and dehydrogenation of alkanes at cyclopentadienyl iridium complexes in a perfluorinated solvent
-
The fluorinated complex [(Cpf)Ir(CO)2] (2) [Cp f = C5H4(CH2)2(CF 2)5CF3] serves as a precursor for the photolytic activation of C-H bonds in alkanes to give [(Cpf) Ir(CH3)(H)(CO)] (3), [(Cpf)Ir(C5H 9)(H)(CO)] (4), [(Cpf)Ir(C6H 11)(H)(CO)] (5) or [(Cpf)Ir(C8H 15)(H)(CO)] (6). In C7F14 as a solvent the latter react to yield the corresponding olefins as well as [(Cp f)Ir(H)2(CO)] (7). Photocatalytic experiments revealed that [(Cpf)Ir(CO)2] (2) and the non-fluorinated compound [(Cp)Ir(CO)2] (1) dehydrogenate cyclohexane in C7F 14. In C6H12 as a solvent a decomposition of the catalysts was observed.
- Rabay, Battist,Braun, Thomas,Falkenhagen, Jan P.
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p. 8058 - 8065
(2013/07/28)
-
- Synthesis and transformations of di-endo-3-aminobicyclo-[2.2.2]oct-5-ene-2- carboxylic acid derivatives
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all-endo-3-amino-5-hydroxybicyclo[2.2.2]octane-2-carboxylic acid (13) and allendo-5-amino-6-(hydroxymethyl)bicyclo[2.2.2]octan-2-ol (10) were prepared via dihydro-1,3-oxazine or γ-lactone intermediates by the stereoselective functionalization of an Nprotected derivative of endo-3-aminobicyclo[2.2.2]oct- 5-ene-2-carboxylic acid (2). Ring closure of β-amino ester 4 resulted in tricyclic pyrimidinones 15 and 16. The structures, stereochemistry and relative configurations of the synthesized compounds were determined by IR and NMR.
- Palko, Marta,Sohar, Pal,Fueloep, Ferenc
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experimental part
p. 7691 - 7705
(2011/11/04)
-
- Mechanistic studies on fluorocyclohexene conversion to fluorobenzene under Pd-catalyzed dehydrogenation
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The chemical reactivity and reaction mechanism of fluorobenzene formation by dehydrogenation of fluorocyclohexenes was investigated. 1-Fluorocyclohexene reacted with oxidants such as nitrobenzene and oxygen to give fluorobenzene in good yields under moderate conditions in the presence of a Pd catalyst. A detailed comparison of oxidative dehydrogenation with non-oxidative dehydrogenation proved that the oxidants effectively suppressed isomerization and disproportionation, and offered a selective synthesis of fluorobenzene.
- Tojo, Masahiro,Fukuoka, Shinsuke,Tsukube, Hiroshi
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experimental part
p. 89 - 94
(2011/04/21)
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- Mechanistic studies on fluorobenzene synthesis from 1,1-difluorocyclohexane via pd-catalyzed dehydrofluorodehydrogenation
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The chemical reactivity and reaction mechanism of fluorobenzene synthesis via dehydrofluorodehydrogenation of 1,1-difluorocyclohexane was investigated. 1,1-Difluorocyclohexane reacted with molecular oxygen to give fluorobenzene in good yields in the presence of both Pd and metal fluoride catalysts. The reaction proceeded with dehydrofluorination of 1,1-difluorocyclohexane to yield 1-fluorocyclohexene as the sole intermediate species, followed by oxidative dehydrogenation. The present system offers a selective synthesis of fluorobenzene.
- Tojo, Masahiro,Fukuoka, Shinsuke,Tsukube, Hiroshi
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experimental part
p. 333 - 340
(2011/05/05)
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- Dioxygen activation by a non-heme iron(II) complex: Formation of an iron(IV)-oxo complex via C-H activation by a putative iron(III)-superoxo species
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Iron(III)-superoxo intermediates are believed to play key roles in oxygenation reactions by non-heme iron enzymes. We now report that a non-heme iron(II) complex activates O2 and generates its corresponding iron(IV)-oxo complex in the presence of substrates with weak C-H bonds (e.g., olefins and alkylaromatic compounds). We propose that a putative iron(III)-superoxo intermediate initiates the O2-activation chemistry by abstracting a H atom from the substrate, with subsequent generation of a high-valent iron(IV)-oxo intermediate from the resulting iron(III)-hydroperoxo species.
- Lee, Yong-Min,Hong, Seungwoo,Morimoto, Yuma,Shin, Woonsup,Fukuzumi, Shunichi,Nam, Wonwoo
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supporting information; experimental part
p. 10668 - 10670
(2010/11/17)
-
- Palladium-catalyzed asymmetric synthesis of allylic fluorides
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The enantioselective fluorination of readily available cyclic allylic chlorides with AgF has been accomplished using a Pd(0) catalyst and Trost bisphosphine ligand. The reactions proceed with unprecedented ease of operation for Pd-mediated nucleophilic fluorination, allowing access to highly enantioenriched cyclic allylic fluorides that bear diverse functional groups. Evidence that supports a mechanism in which C-F bond formation occurs by an SN2-type attack of fluoride on a Pd(II)-allyl intermediate is presented.
- Katcher, Matthew H.,Doyle, Abigail G.
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supporting information; experimental part
p. 17402 - 17404
(2011/02/23)
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- Redox reaction of the Pd0 complex bearing the Trost ligand with meso-cycloalkene-1,4-biscarbonates leading to a diamidato PdII complex and 1,3-cycloalkadienes: Enantioselective desymmetrization versus catalyst deactivation
-
The Pd0 complex 1 that bears the Trost ligand 2 undergoes a facile redox reaction with 1,4-biscarbonates 5b-d and rac-22 under formation of the diamidato-PdII complex 7 and the corresponding 1,3-cycloalkadienes 8b-d. The redox deacti
- Tsarev, Vasily N.,Wolters, Dennis,Gais, Hans-Joachim
-
experimental part
p. 2904 - 2915
(2010/06/17)
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- Birch reduction of benzene in a low-temperature plasma
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(Chemical Equation Presented) Selective and specific dihydrogenation of benzene and other arenes has been observed in a low-temperature helium plasma. A surface Birch reduction mechanism has been proposed in which benzene molecules adsorbed on the dischar
- Na, Na,Xia, Yu,Zhu, Zhenli,Zhang, Xinrong,Cooks, R. Graham
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supporting information; experimental part
p. 2017 - 2019
(2009/07/25)
-
- Effect of a methoxy substituent on the vinylcyclobutane carbon migration
-
(Chemical Equation Presented) Over the temperature range 250-300°C, 8-exo-methoxybicyclo[4.2.0]oct-2-ene (1a) undergoes a [1,3] sigmatropic rearrangement to 5-exo- and 5-endo-methoxybicyclo[2.2.2]oct-2-enes, 2a and 2b, respectively, with a clear preference for the si product: si/sr = 3.2. Both 1a and its 8-endo epimer 1b experience appreciable epimerization and fragmentation. A long-lived intermediate with weakly interacting diradical centers, one of which is stabilized by a methoxy substituent, can account for all such observations.
- Leber, Phyllis A.,Lasota, Celina C.,Strotman, Neil A.,Yen, Gloria S.
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p. 912 - 919
(2007/10/03)
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- Allylic amination via decarboxylative C-N bond formation
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This manuscript details the development of a palladium-catalyzed allylic amination that proceeds via decarboxylation of allylic carbamates. Both saturated and aromatic heterocycles undergo decarboxylative rearrangement in good yields. The mechanism of allylation of heteroaromatic amines involves the formation of π-allyl palladium complexes followed by decarboxylation of the carbamate. Finally, the heteroaromatic anion equivalent is allylated to provide allylic amines. Georg Thieme Verlag Stuttgart.
- Mellegaard-Waetzig, Shelli R.,Rayabarapu, Dinesh Kumar,Tunge, Jon A.
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p. 2759 - 2762
(2007/10/03)
-
- Allyl, methallyl, prenyl, and methylprenyl ethers as protected alcohols: Their selective cleavage with diphenyldisulfone under neutral conditions
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Diphenyldisulfone is a mild and efficient reagent for selective cleavage of methylprenyl (2,3-dimethylbut-2-en-1-yl), prenyl (3-methylbut-2-en1-yl), and methallyl (2-methylallyl) ethers. These reaction conditions are compatible with the presence of other protecting groups such as acetals, acetates, and allyl, benzyl, and TBDMS ethers. Exposure of 2,3-dimethylbut-2-en-1-yl and 3-methylbut-2-en1-yl ethers to diphenyldisulfone led to the formation of 2,3-dimethylbuta-1,3-diene and isoprene, respectively. 2-Methylallyl ethers undergo isomerization to 2-methylpropenyl ethers, which are easily hydrolyzed into the corresponding free alcohols and isobutyraldehyde.
- Markovic, Dean,Vogel, Pierre
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p. 2693 - 2696
(2007/10/03)
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- Novel concerted fragmentation upon alcoholysis of a urazole
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(Chemical Equation Presented) Instead of yielding the expected hydrazine, alcoholysis of the above heterocycle results in fragmentation via a highly unusual pathway.
- Wei, Yanjun,Lemal, David M.
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p. 3837 - 3839
(2007/10/03)
-
- A new route to control product selectivity in the oxidative dehydrogenation of cyclohexane and cyclohexene
-
The product selectivity can be controlled by adding acetic acid in feed over vanadium phosphate (VPO) in gas phase oxidative dehydrogenation (ODH), in which cyclohexane and cyclohexene are oxidized to cyclohexene and 1,3-cyclohexadiene (1,3-CHD), respectively, at almost 100% selectivity. This approach is also an efficient method to capture the very unstable intermediates in the mechanism study.
- Zhu, Yujun,Li, Jing,Yang, Xiangguang,Wu, Yue
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p. 822 - 823
(2007/10/03)
-
- NMDA receptor antagonists and their use in inhibiting abnormal hyperphosphorylation of microtubule associated protein tau
-
Aminocyclohexane and aminoalkylcyclohexane compounds, which are systemic-ally-active as NMDA receptor antagonists, are effective in inhibiting abnormal hyperphosphorylation of microtubule associated protein tau, method of treating disorders resulting from or associated with abnormal hyperphosphorylation of microtubule associated protein tau, and pharmaceutical compositions comprising the same.
- -
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-
- Kinetics and mechanism of monomolecular heterolysis of cage-like compounds: XVIII. Solvent effect on the rate of heterolysis of 3-bromocyclohexene. Correlation analysis of solvation effects
-
The kinetics of E1 dehydrobromination of 3-bromocyclohexene in 23 aprotic and 9 protic solvents were studied by the verdazyl technique. The reaction rate is described by the polarity, electrophilicity, and ionizing power parameters of the solvent. Nucleop
- Ponomarev,Stambirskii,Dvorko,Bazil'chuk
-
p. 489 - 496
(2007/10/03)
-
- SIMPLIFIED METHODS OF MAKING 1,3-CYCLOHEXADIENE
-
Novel condensation reactions used to produce 1,3-cyclohexadiene. Such a compound is an important precursor in the manufacture of high performance plastics, as one example, are provided. In the past, the production methods for such 1,3-cyclohexadiene required very complex reactions involving numerous process steps. Such a method has proven costly, difficult to properly monitor and control, and less than reliable to provide even low amounts of such a precursor compound. The inventive production methods thus permit a reduction in complexity and cost, and, with a single reaction step, facilitate quality measurements as to the product purity itself.
- -
-
-
- Palladium-Catalyzed Equilibrium Addition of Acidic OH Groups across Dienes
-
Mildly acidic O-H groups undergo transition-metal-catalyzed reversible addition across the C=C bonds of cyclic and acyclic dienes. For example, the simple complex [Pd(PPh3)4] (1 mol%) effectively catalyzes both the forward addition o
- Utsunomiya, Masaru,Kawatsura, Motoi,Hartwig, John F.
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p. 5865 - 5868
(2007/10/03)
-
- Flash vacuum pyrolysis over magnesium. Part 1 - Pyrolysis of benzylic, other aryl/alkyl and aliphatic halides
-
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)
-
- Allylic CH oxidation versus epoxidation of 2-cyclohexenols, catalyzed by chromium- and manganese-substituted polyoxometalates and salen complexes
-
2-Cyclohexenol (1) is oxidized chemoselectively to 2-cyclohexenone (2a) by the α-Keggin chromium-substituted polyoxometalate (POM) Ia as the catalyst and iodosobenzene as the oxygen source. For the chromium(salen) catalyst IIa the same chemoselectivity in favor of allylic CH oxidation is observed. The manganese-substituted POM Ib and the manganese(salen) complex IIb, however, afford appreciable amounts of the epoxy alcohol 2b. For the stereolabeled 5-tert-butyl-2-cyclohexenols 5, the diastereoselectivity of the epoxidation was appreciable (syn:anti 82:18) in the case of the manganese (salen) complex IIb with the cis isomer, while the manganese-substituted POM Ib exhibited no syn versus anti π-facial differentiation for the cis or trans diastereomer of the cyclohexenol 5. The observed syn hydroxy directivity for the manganese(salen) complex IIb is rationalized in terms of optimal hydrogen bonding between the MnV oxo complex IIb and the trans diastereomer of the allylic alcohol substrate 5. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany 2002.
- Adam, Waldemar,Herold, Marike,Hill, Craig L.,Saha-Moeller, Chantu R.
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p. 941 - 946
(2007/10/03)
-
- Kinetic and thermodynamic stability of naphthalene oxide and related compounds. A comparative microcalorimetric and computational (DFT) study
-
The kinetics of the acid-catalyzed ring opening of naphthalene 1,2-oxide (5) in highly aqueous media to give naphthols has been measured by heat-flow microcalorimetry. The reaction enthalpy of this aromatization reaction was measured as ΔH = -51.3 ± 1.7 kcal mol-1. The unexpectedly low reactivity of naphthalene oxide is suggested to be due to an unusually large thermodynamic stability. A crude estimate of the stabilization effect, ~1 kcal mol-1(not a significant stabilization), is obtained by using the measured reaction enthalpies of structurally related substrates as references. A larger value (2.7 kcal mol-1) was obtained by calculation using the B3LYP hybrid functional corrected with solvation energies derived from semiempirical AM1/SM2 calculations. The origin of this effect is discussed in terms of homoconjugative stabilization and homoaromaticity. There is a good linear correlation (with slope = 0.63) between the experimentally measured free energy of activation and the calculated enthalpy of carbocation formation in water.
- Brandt, Peter,Jia, Zhi Sheng,Thibblin, Alf
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p. 7676 - 7682
(2007/10/03)
-
- Equilibrium constants for dehydration of water adducts of aromatic carbon-carbon double bonds
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Equilibrium constants (Kde) are reported for the dehydration of hydrates of benzene, naphthalene, phenanthrene, and anthracene. Free energies of formation of the hydrates (ΔG°f(aq)) are derived by combining free energies of formation of the parent (dihydroaromatic) hydrocarbon with estimates of the increment in free energy (ΔGOH) accompanying replacement of a hydrogen atom of the hydrocarbon by a hydroxyl group. Combining these in turn with free energies of formation of H2O and of the aromatic hydrocarbon products furnishes the desired equilibrium constants, The method depends on the availability of thermodynamic data (i) for the hydrocarbons from which the hydrates are derived by hydroxyl substitution and (ii) for a sufficient range of alcohols to assess the structural dependence of ΔGOH. The data comprise chiefly heats of formation and standard entropies in the gas phase and free energies of transfer from the gas phase to aqueous solution (the latter being derived from vapor pressures and solubilities). They also include experimental measurements of equilibrium constants for dehydration of alcohols, especially cyclic, allylic, and benzylic alcohols. In general ΔGOH depends on whether the alcohol is (a) primary, secondary, or tertiary; (b) allylic or benzylic; and (c) open chain or cyclic. Differences in geminal interactions of the hydroxyl group of the alcohol with α-alkyl and vinyl or phenyl groups account for variations in ΔGOH of 5 kcal mol-1. Weaker variations which arise from β-vinyl/OH or β-phenyl/OH interactions present in the aromatic hydrates but not in experimentally studied analogues are estimated as 1.0 kcal mol-1. Equilibrium constants for dehydration may be expressed as their negative logs (pKde). Reactions yielding the following aliphatic, aromatic, and antiaromatic unsaturated products then have pKde values: +4.8, ethene; +15.0, ethyne; +22.1, cyclopropene; +28.4 cyclobutadiene; -22.2, benzene; -14.6, naphthalene; -9.2, phenanthrene; -7.4, anthracene. Large positive values are associated with formation of strained or antiaromatic double bonds and large negative values with aromatic double bonds. Trends in pKde parallel those of heats of hydrogenation. The results illustrate the usefulness of a substituent treatment for extending the range of currently available free energies of formation. In addition to hydroxyl substituent effects, ΔGOH, values of ΔGπ for substitution of a π-bond in a hydrocarbon are reported.
- Dey, Joykrishna,O'Donoghue, AnnMarie C.,More O'Ferrall, Rory A.
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p. 8561 - 8574
(2007/10/03)
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- Selective hydrogenation of benzene to cyclohexadiene and cyclohexene by lanthanide precipitates obtained from Eu or Yb metal solutions in liquid ammonia
-
Lanthanide precipitates obtained by decomposition of Eu or Yb metal solutions in liquid ammonia were active at 393 K for the partial liquid-phase hydrogenation of benzene to cyclohexene with high selectivity (≥90%). When the reaction temperature decreased to 323 K, cyclohexadienes were preferentially formed. The reducing behavior was markedly enhanced by the addition of ammonia to the reaction system.
- Imamura, Hayao,Nishimura, Kouzi,Sumioki, Kenji,Fujimoto, Mitoshi,Sakata, Yoshihisa
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p. 450 - 451
(2007/10/03)
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- Palladium-catalyzed arylation of allylic benzoates using hypervalent siloxane derivatives
-
Palladium-catalyzed cross-coupling of hypervalent arylsiloxane derivatives proceeded in good to excellent yields with allylic benzoates. Arylation occurred with complete inversion of configuration. The scope and limitations of this reaction, an alternative to the Stille coupling, is summarized.
- Correia,DeShong
-
p. 7159 - 7165
(2007/10/03)
-
- Flash vacuum thermolysis - Synthesis and characterization of unstabilized cycloalkenethiones
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The flash vacuum thermolysis (FVT) of cydoalkenyl allyl (or propargyl) sulfides 8, 9, 12, and 13 led, as the main thermal pathway, to the conjugated cycloalkenethiones 1, 3, and 5, resulting from a retro-ene reaction. These reactive thioketones, thus obtained in ca. 70% yield, have been characterized in the gas phase by mass spectrometry, and at low temperature by IR, UV/Vis and NMR spectroscopy. The polymerization of 1, 3, and 5 upon warming is generally more rapid than the other attempted reactions and only the [2 + 3] dipolar cycloaddition with diazomethane led in low yield, besides polymeric materials, to isomeric 1,3-dithiolanes 20 from cyclopentenethione 1. The obtention of the nonconjugated cycloalkenethiones 2 and 4, expected in the FVT of sulfides 10 and 11, has been confirmed only by UV/Vis spectroscopy at -196 °C, due to their rapid enethiolization. In the case of the large-ring sulfide 14, the (E) geometry of the double bond favoured the competitive retro-ene reaction yielding cyclododecene and propynethial; on the other hand, the FVT of the tricyclic gem-dithiol 15, a possible precursor of cyclobutenethione (7), led to vinyl thioketene (18), obtained by thermal ring opening of 7.
- Briard, Emmanuelle,Levillain, Jocelyne,Ripoll, Jean-Louis,Dat, Yves,Marcual, Albert,Lange, Catherine
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p. 869 - 874
(2007/10/03)
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- Pyrolysis of tricyclic cyclobutane-fused sulfolanes as a route to cis-1,2-divinyl compounds and their Cope-derived products
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Functionalisation of the double bond of 3-thiabicyclohept-6-ene 3, readily formed by hydrolysis of the cycloadduct 1 of 3-sulfolene and maleic anhydride followed by oxidative bis-decarboxylation, gives tricyclic sulfones 5-7 and 9 with the bicyclo2,4> skeleton. FVP of 3 results in stereospecific extrusion of SO2 to give Z-hexa-1,3,5-triene which undergoes electrocylisation to give cyclohexa-1,3-diene while reaction of 3 with LiAlH4 results in non-stereospecific extrusion to give Z- and E-hexa-1,3,5-triene. Upon FVP the tricyclic sulfones 5-7 and 9 lose SO2 to give 7-membered ring products 16-19 by Cope rearrangement of the initially formed cis-1,2-divinyl intermediates 15. The 1,3-dipolar cycloaddition of nitrile oxides and a nitrone to the double bond of 3 gives tricyclic sulfones with the tricyclo2,6> skeleton and a wider variety of these can be prepared by conventional reactions of 1. Upon FVP these lose SO2 to give stable cis-1,2-divinyl compounds 23, 24, 37-40 and 41-44. The Diels-Alder adducts 48 and 49 have been prepared from 3 and these behave differently upon FVP, losing SO2 and butadiene to give tetrasubstituted benzenes, in the latter case by way of an unexpected tetracyclic intermediate.
- Aitken, R. Alan,Cadogan, J. I. G.,Gosney, Ian,Humphries, Caroline M.,McLaughlin, Leo M.,Wyse, Stuart J.
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p. 605 - 614
(2007/10/03)
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