- Thermodynamics of Electron Transfer from the Cyclooctatetraene Anion Radical to a Series of Substituted Cyclooctatetraenes and Annulene
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Electron spin resonance has been utilized to measure the free energy, enthalpy, and entropy changes for the electron transfer from the anion radical of cyclooctatetraene (COT) to several substituted cyclooctatetraenes (XCOT) and to annulene in hexamethylphosphoramide (HMPA), where the anion radical are free from ion association effects.There is a correlation between the enthalpy of the electron transfer (ΔH0 for COT-. + XCOT COT + XCOT-) and the magnitude of the splitting of the degeneracy of the nonbonding molecular orbitals due to the presence of the substituent (Δε).However, the fact that ΔH0 for the electron transfer is much more sensitive to the presence of the substituent than is Δε leads us to conclude that Δε is greatly effected by solvation.
- Stevenson, Gerald R.,Forch, Brad E.
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- Simple and convenient one-pot synthesis of cyclooctatetraene
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Cyclooctatetraene is readily synthesized by the oxidation of in situ generated [Li(TMEDA)]2[C8H8] with 1,2-dibromoethane. The product is readily isolated and produced without the use of hazardous or toxic reagents.
- Majumder, Supriyo,Odom, Aaron L.
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- Quantitative Investigation of the Decomposition of Cyclooctene on Pt(111) Using BPTDS
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Other researches have reported (J.Am.Chem.Soc. 1993, 115, 2044; J.Phys.Chem. 1994, 98, 2952) that cyclooctene dehydrogenates on Pt(111) to stable adsorbed cyclooctatetraene, which then undergoes ring contraction to produce benzene but without any calibrated measurements of the yield.Here, quantitative thermal desorption mass spectrometry (TDS) and bismuth postdosing thermal desorption mass spectrometry (BPTDS) are used to investigate the conversion of cyclooctene to benzene on the Pt(111) surface.Our results show that although benzene is formed, it is a very minor product, corresponding to less than 2percent of a monolayer (including both adsorbed and gas-phase benzene).Most of the adsorbed cyclooctene either desorbs intact at low temperatures (ca. 10percent) or simply dehydrogenates (ca. 90percent), ultimately to surface carbon by 800 K, but without going through adsorbed benzene as an intermediate.Stable intermediates with stoichiometries C8H12 and C8H6 are identified by TDS to be present at 350 and 430 - 560 K, respectively, but BPTDS shows that neither of these correspond to a simple molecularly adsorbed state of a stable gaseous molecule.During the conversion between these two species, however, cyclooctatetraene is produced transiently at 430 K, suggesting that both of these species still have an intact C8 ring.
- Frei, Nathan,Campbell, Charles T.
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- ACTIVATION OF C-H BONDS IN SATURATED HYDROCARBONS. THE CATALYTIC FUNCTIONALISATION OF CYCLOOCTANE BY MEANS OF SOME SOLUBLE IRIDIUM AND RUTHENIUM POLYHYDRIDE SYSTEMS
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Homogeneous catalytic dehydrogenation of cyclooctane into cyclooctene has been effected by means of a variety of iridium and ruthenium polyhydrides, at 150 deg C, in the presence of an olefin as the hydrogen acceptor; best results (45-70 catalytic turnovers) have been achieved with (iPr3P)2IrH5, 2IrH5 and 3RuH4.
- Felkin, Hugh,Fillebeen-Khan, Tauqir,Gault, Yvonne,Holmes-Smith, Rupert,Zakrzewski, Janusz
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- Cyclooctatetraene made easy
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Cyclooctatetraene, C8H8, has been made readily available from 1,5-cyclooctadiene in 65% yield without the need of using hazardous or toxic reagents by the straightforward oxidation of the intermediate [Li(tmeda)]2C8/
- Gottfriedsen, Jochen,Miloslavina, Alesia,Edelmann, Frank T.
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- 3 + 2 Cycloaddition via a Diels-Alder/retro-Diels-Alder sequence: Tandem cyclopentadienyl annulation of a 1,5-cyclooctadiyne synthetic equivalent
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A novel method of synthesizing a 1,2-bis(ethano) bridged bis(cyclopentadienyl) compound, 6,13-diisopropylidenetricyclo[9.3.0(1,11).0(4,8]tetradeca-1(14),4,7,11 -tetraene, 5, via a tandem Diels-Alder/retro-Diels-Alder sequence using a 1,5-cyclooctadiyne synthetic equivalent and 6,6-dimethylfulvene is reported.
- Davila, Alfonso,Ramezanian, Merrikh S.,Fronczek, Frank R.,McLaughlin, Mark L.
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- Trapping of 1,3,5,7-Cyclooctatetraene Valence Tautomers. Thermodynamic Stability of Bicycloocta-2,4,7-triene
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High-temperature equilibrium constants of trapped mixtures of 1,3,5,7-cyclooctatetraene and its valence tautomer bicycloocta-2,4,7-triene were obtained by using a high-temperature thermal trapping technique and gave values for the thermodynamic parameters ΔS0 and ΔH0 of -4.3 +/- 0.7 eu and 5.5 +/- 0.6 kcal/mol, respectively.
- Squillacote, Michael E.,Bergman, Adelle
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- Photochemical Unmasking of Polyyne Rotaxanes
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Bulky photolabile masked alkyne equivalents (MAEs) are needed for the synthesis of polyyne polyrotaxanes, as insulated molecular wires and as stabilized forms of the linear polymeric allotrope of carbon, carbyne. We have synthesized a novel MAE based on phenanthrene and compared it with an indane-based MAE. Photochemical unmasking of model compounds was studied at different wavelengths (250 and 350 nm), and key products were identified by NMR spectroscopy and X-ray crystallography. UV irradiation at 250 nm leads to unmasking of both MAEs. Irradiation of the phenanthrene system at 350 nm results in quantitative dimerization via [2 + 2] cycloaddition to form a [3]-ladderane; irradiation of this ladderane at 250 nm generates a dihydrotriphenylene, which can be oxidized easily to a triphenylene. Irradiation of the indane-based MAE at 350 nm in the presence of traces of oxygen forms an endoperoxide and a bisepoxide. Both MAEs have been incorporated into rotaxanes via copper-mediated active metal template Glaser or Cadiot-Chodkiewicz coupling. The identity of the rotaxanes was confirmed by NMR spectroscopy and mass spectrometry. The phenanthrene rotaxane decomposes during attempted photochemical unmasking, whereas photolysis of the indane rotaxane results in unmasking of the polyyne thread to form a rotaxane with a chain of 16 sp-hybridized carbon atoms. This approach opens avenues toward the synthesis of encapsulated carbon allotropes.
- Woltering, Steffen L.,Gawel, Przemyslaw,Christensen, Kirsten E.,Thompson, Amber L.,Anderson, Harry L.
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supporting information
p. 13523 - 13532
(2020/09/02)
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- Cyclooctatetraene dianion from 1,5-cyclooctadiene. A synthesis in the presence of naphthalene radical anion
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A novel synthesis of cyclooctatetraene dianion from 1,5-cyclooctadiene (1,5-COD) is described. The reaction of the potassium-naphthalene adduct with 1,5-COD proceeds at room temperature over 3 days in heptane/tetrahydrofuran to produce the target compound.
- Simons, Leslie H.,Lagowski
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p. 1771 - 1773
(2007/10/03)
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- The rearrangement of the cubane radical cation in solution
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The rearrangement of the cubane radical cation (1.+) was examined both experimentally (anodic as well as (photo)chemical oxidation of cubane 1 in acetonitrile) and computationally at coupled cluster, DFT, and MP2 [BCCD(T)/cc-pVDZ//B3LYP/6-31G* + ZPVE as well as BCCD(T)/cc-pVDZ//MP2/6-31G* + ZPVE] levels of theory. The interconversion of the twelve C2v degenerate structures of 1.+ is associated with a sizable activation energy of 1.6 kcal mol-1. The barriers for the isomerization of 1.+ to the cuneane radical cation (2.+) and for the C-C bond fragmentation to the secocubane-4,7-diyl radical cation (10.+) are virtually identical (ΔH0? = 7.8 and 7.9 kcal mol-1, respectively). The low-barrier rearrangement of 10.+ to the more stable syn-tricyclooctadiene radical cation 3.+ favors the fragmentation pathway that terminates with the cyclooctatetraene radical cation 6.+. Experimental single-electron transfer (SET) oxidation of cubane in acetonitrile with photoexcited 1,2,4,5-tetracyanobenzene, in combination with back electron transfer to the transient radical cation, also shows that 1.+ preferentially follows a multistep rearrangement to 6.+ through 10.+ and 3.+ rather than through 2.+. This was confirmed by the oxidation of syn-tricyclooctadiene (3), which, like 1, also forms 6 in the SET oxidation/rearrangement/electron-recapture process. In contrast, cuneane (2) is oxidized exclusively to semibullvalene (9) under analogous conditions. The rearrangement of 1.+ to 6.+ via 3.+, which was recently observed spectroscopically upon ionization in a hydrocarbon glass matrix, is also favored in solution.
- Schreiner, Peter R.,Wittkopp, Alexander,Gunchenko, Pavel A.,Yaroshinsky, Alexander I.,Peleshanko, Sergey A.,Fokin, Andrey A.
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p. 2739 - 2744
(2007/10/03)
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- Preparation of 1,5-Cyclooctadiyne and 1,3,5,7-Cylooctatetraene from 1,5-Cyclooctadiene
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Bromination of 1,5-cyclooctadiene (1) and stepwise dehydrobromination first with KOtBu and then with KOtBu/18-crown-6 yields 1,5-cyclooctadiyne (5).A prolonged interaction of the base causes a complete transformation to cyclooctatetraene (6).Diyne 5 and even more the intermediate enyne 4 are highly reactive dienophiles.The cycloadducts 10-14 formed with 1,3-cyclohexadiene, carbon disulphide, and tetraphenylcyclopentadienone were isolated and characterized.Treatment of 5 with titanium tetrachloride induces a vigorous polymerization. - Key Words: Cycloalkynes / Dehydrohalogenation / Cycloaddition
- Detert, Heiner,Rose, Bernd,Mayer, Winfried,Meier, Herbert
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p. 1529 - 1532
(2007/10/02)
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- 1-Thia-3,4-diazolidine-2,5-dione Functionality: A Photochemical Synthon for the Azo Group
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The 1-thia-3,4-diazolidine-2,5-dione functional group was shown to yield azo compounds upon photolysis.This photoreaction when combined with the known ability of this group to react in a Diels-Alder fashion or as a dinucleophile toward alkylating agents greatly increases the utility of this functionality.The dual reactivity of this group was demonstrated in the synthesis of a number of 3,4-dialkyl-1-thia-3,4-diazolodone-2,5-diones.The photolysis of these compounds produced either thermally stable cyclic azo compounds or the decomposition products of thermally unstable azo compounds.
- Squillacote, Michael,Felippis, James De
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p. 3564 - 3571
(2007/10/02)
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- Isotopic Exchange Involving the Annulene Anion Radical and Its Dimerization to the Annulene Anion Radical
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The addition of D2O to hexamethylphosphoramide solutions of the potassium salt of the annulene anion radical results in the slow (days) formation of the monodeuteriated anion radical (C8H7D1.1-).However, several days after a similar addition to the sodium salt solution, no C8H7D1.1- is present.Instead, the anion radical of annulene is found.These observations led to EPR and NMR studies, which have revealed the mechanism of each process.The mechanisms are based upon the facts that ion association is necessary for the isotope exchange reaction and the absence of ion association is required for the dimerization.Solutions of deuteriated annulene anion radical, annulene dianion, annulene anion radical, and annulene dianion can be readily generated from reduced solutions of annulene for EPR, NMR, etc. studies by making use of the isotopic exchange and dimerization mentioned above.
- Stevenson, Cheryl D.,Burton, Richard D.,Peters, Steve J.,Reiter, Richard C.
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p. 5838 - 5842
(2007/10/02)
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- Contrasting Free Energies of Electron Transfer from - and Annulenes to Their Perdeuteriated and Per-(13)C Analogues
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A very large equilibrium isotope effect (confirmed via physical, separation oof the isotopes involved) was observed via the EPR analysis of a mixture of benzene and perdeuteriated-per-(13)C-benzene competing for a deficient number of electrons in tetrahyydrofuran (THF) in the presence of 18-crown-6 (18C6).The Keq for the reaction C6H6.-, K+(18C6) + (13)C6D6 = C6H6 + (13)C6D6.-, K+(18C6) is 0.096 +/- 0.008 at 100 deg C.An analogous competition for electrons exists between annulene and perdeuteriated-per-(13)C-annulene.In contrast to the benzene system the Keq for the reaction C8H8.-, Na+ + (13)C8D8 = C8H8 + (13)C8D8.-,Na+ in liquid ammonia is 1.20 +/- 0.04 at -100 deg C.Similar contrasting results (but smaller in magnitude) were observed for the benzene and cyclooctatetraene perdeuteriated and per -(13)C systems.The results are interpreted in terms of the divergence of the annulene system from aromatic character upon electron addition and the convergence of the annulene system toward aromatic character upon electron addition.
- Stevenson, Gerald R.,Peters, Steven J.,Reidy, Kerry A.,Reiter, Richard C.
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p. 1877 - 1882
(2007/10/02)
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- Contrasting free energies of electron transfer from [6] and [8]annulenes to their perdeuteriated-per-13C analogues
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EPR analyis shows that the equilibrium isotope effect upon the equilibrium constant for electron transfer between isotopic isomers is much larger in [6]annulene (i.e. C6H6-·+13C6D6 = C6H6 + 13C6D6-·) than in the [8]annulene systems (i.e. C8H8-· + 13C8D8 = C8H8 + 13C8D8-·). This is due to the effects of aromaticity.
- Stevenson,Peters,Reidy
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p. 6151 - 6154
(2007/10/02)
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- Is pseudorotation the operational pathway for bond shifting within [8]annulenes? Probe of planarization requirements by 1,3-annulation of the cyclooctatetraene ring. Kinetic analysis of racemization and 2-D NMR quantitation of π-Bond alternation and ring inversion as a function of polymethylene chain length
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The chiral 1,3-bridged cyclooctatetraenes 9a-c have been prepared in nine steps from the appropriate 2-cycloalkenone precursors. Following annulation with ethyl acetoacetate to give 15, trans-1,2-dichloroethylene was cycloadded photochemically in a [2 + 2] reaction and a cyclobutene ring was ultimately formed. Once reduction to alcohol 19 was accomplished, dehydration was effected and the bicyclo[4.2.0]octatrienes so generated underwent disrotatory ring opening to deliver the [8]annulenes. The rates of this electrocyclic ring opening were determined in two examples. Polarimetric studies provided quantitative measure of the readiness with which planar dianion formation occurs as a function of loop size. Unexpectedly, attempts to resolve these molecules failed to deliver them in optically active condition because of too rapid enantiomerization via ring inversion and/or bond shifting. The rates of these processes were determined by 2-D dynamic NMR methods, the data revealing that both processes are accelerated relative to nonbridged models. These and related findings are interpreted in terms of a pseudorotation scheme leading to flattened saddle and not planar-alternate transition states. The unique features associated with this mechanistic phenomenon are discussed.
- Paquette,Wang,Luo,Cottrell,Clough,Anderson
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p. 239 - 253
(2007/10/02)
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- 2,6-Dicyano-1,5-tetramethylenesemibullvalenes
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The Propellane-8,11-dione (10) reacts with thiophenols in the presence of titanium tetrachloride/triethylamine to afford equal amounts of the vinyl sulfides C2/Cs-11 (yield 87-93percent).Equilibration of the 1:1 mixture of C2/Cs-11 is catalyzed by trifluoroacetic acid and produces a 3:2 ratio of C2- and Cs-11.Sodium perborate tetrahydrate in acetic acid oxidizes the vinyl sulfides C2/Cs-11 to the vinyl sulfones C2/Cs-12 in 81-93percent yield.Potassium cyanide on aluminium oxide in boiling 2-methyl-2-butanol converts the 4-chlorosulfones C2/Cs-12b into a mixture of the α,β-unsaturated dinitriles 14-17 and 19, which are separated through chromatography.The intermediates 13 and 18 are isolated in the same way.The major product 14 is brominated by N-bromosuccinimide to afford a mixture of exo-20, endo-20, exo,exo-21, exo,endo-21, endo,endo-21, and 22, which are separated through chromatography.The configurations of the γ-bromodinitriles exo-20 and endo,endo-21 are established by X-ray diffraction analyses.The γ,γ'-dibromodinitrile endo,endo-21 is very reluctant towards the zinc/copper couple as well as powdered lithium.The reaction with tetracarbonylnickel affords a novel semibullvalene dimer for which one of the regioisomeric structures 26 and 27 is proposed.Both γ-bromodinitriles exo-20 and endo-20 are dehydrobrominated by potassium tert-butoxide in ether/tert-butyl alcohol yielding 38percent of dicyanosemibullvalene 1c, which closely resembles the non-bridged dicyanosemibullvalene 1a.In the same way the mixture of γ-bromodinitriles, obtained by bromination of 14 with two mol of N-bromosuccinimide, produces 10percent of 1c and 28percent of bromodicyanosemibullvalene 32 (based on 14) after chromatography.As anticipated, 1c is thermally more stable (up to about 440 K) than 1a lacking the tetramethylene bridge.The IR bands of the nitril groups of 1c undergo a reversible change in the temperature range between 293 and 437 K.This temperature dependence of the IR spectrum appears to be related to the extremely high rate (1011 s-1) of the degenerate Cope rearrangement. - Key Words: Semibullvalenes, 1,5-bridged and dimeric / Propellanes / Vinyl sulfides and sulfones / Nitriles, γ-brominated α,β-unsaturated / IR spectra, temperature-dependent
- Quast, Helmut,Mayer, Andreas,Peters, Eva-Maria,Peters, Karl,von Schnering, Hans Georg
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p. 1291 - 1306
(2007/10/02)
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- REDUCTIVE TRANSFORMATIONS - 11. STEREOSELECTIVE CYCLOANNELATION AND BRIDGING OF THE CYCLOOCTATETRAENE DIANION.
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Bifunctional electrophiles with C4-, C6-, and C8-chains are reacted with the cyclooctatetraene dianion to selectively give novel cycloannelation and bridging products which possess a surprising stereochemistry and are useful starting compounds for further synthesises.
- Krummel, Guenter,Muellen, Klaus
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p. 2809 - 2812
(2007/10/02)
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- Thermal Behaviour of C8H8 Hydrocarbons. - Gas-Phase Thermolysis of Cuneane, a New Example of a High-Strain Energy Release Process
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The kinetics of thermal decomposition of cuneane (1) in the gas phase have been investigated in the temperature range 180-220 deg C.The reaction is a clean first-order homogeneous process leading to the formation of two C8H8 isomers, viz., semibullvalene (2) and cyclooctatetraene (3).The rate constant varies with temperature according to the Arrhenius equation log(k/s-1)=(13.82+/-0.09)-(37.7+/-0.2 kcal*mol-1)/RTln10.The Arrhenius parameters are consistent with a biradical mechanism leading to the formation of semibullvalene (2).The product proportions are pressure-dependent which strongly suggests that semibullvalene (2) is initially formed with high vibrational energy content (ca. 74 kcal*mol-1) and can react further to give cyclooctatetraene (3).
- Hassenrueck, Karin,Martin, Hans-Dieter,Walsh, Robin
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p. 369 - 372
(2007/10/02)
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- SPECIAL PROPERTIES IMPARTED TO THE 9-PHOSPHABICYCLONONATRIENE SYSTEM BY A P-(2,4,6-TRI-t-BUTYLPHENYL) SUBSTITUENT; (17)O NMR SPECTRUM OF A BICYCLIC PHOSPHIRANE OXIDE
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9-(2,4,6-Tri-t-butylphenyl)-9-phosphabicyclonona -2,4,6-triene gave an observable P-oxide with t-butyl hydroperoxide.Decomposition occurred by expulsion of the phosphorus fragment, possibly as ArP=O, rather than by the expected ring expansion to a phosphonin oxide.The (17)O NMR shift of 18.0 is the most upfield known for a phosphine oxide.
- Quin, Louis D.,Yao, En-Yun,Szewczyk, Jerzy
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p. 1077 - 1080
(2007/10/02)
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- On the Mechanism of the Cyclooctatetraene Synthesis from Ethyne Employing Nickel Catalysts
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The mechanism of the Reppe cyclization to cyclooctatetraene was investigated by employing ethyne-1-13C as a substrate in the nickel-catalyzed reaction.The specific catalytic systems studied were nickel acetylacetonate-calcium carbide and nickel acetylacetonate-diethylaluminum ethoxide.In both cases, the label pattern in the cyclooctatetraene produced was consistent with either a stepwise coupling or concerted "zipper-type" mechanism of formation.These results preclude the possibility of cyclobutadiene or benzene intermediates or any carbon-carbon bond cleavage processes which do not leave the original connectivity in the alkyne intact.These conclusions were based upon analysis of the isotopic label in C4 fragments, obtained by chemical degradation of the cyclooctatetraene produced.
- Colborn, Robert E.,Vollhardt, K. Peter C.
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p. 5470 - 5477
(2007/10/02)
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- STRAINED CYCLOALKENYNES
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Presently known strained cycloalkynes with one, two or three additional cis- or trans-configurated double bonds are summarized in Table 3.The main topics of the article are the geometrical ring strain, the preparation or in situ generation of these compounds by fragmentation of the corresponding 1,2,3-selendiazoles, and the thermal isomerisation processes performed at room temperature or in flash pyrolysis experiments at 440-640 deg C.
- Meier, Herbert,Hanold, Norbert,Molz, Thomas,Bissinger, Hans Joachim,Kolshorn, Heinz,Zountsas, Johannes
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p. 1711 - 1720
(2007/10/02)
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- Heats of Generation of Substituted Annulene Dianions
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Calorimetric studies have shown that either a phenyl or tert-butoxy substituent on annulene () increases the heat of generation (ΔHgen0) of the respective dianion 0 for R-(HMPA) + 2Na(s) --> R-2- + 2Na+(HMPA)> in hexamethylphosphoramide relative to that of .The values for ΔHgen0 are -51, -38, and -42 kcal/mol respectively for R=H, C4H9, and C6H5.The destabilization of the dianion relative to the neutral molecule due to the presence of a phenyl group is accounted for by the fact that the phenyl group is nearly orthogonal to the charged eight-member ring system.This is supported by the NMR spectrum of Ph-2-. 1H NMR studies carried out upon the solvent (HMPA) in the presence of *- show that the Knight shift is very close to that predicted from changes in bulk paramagnetic susceptibility.This confirms the facts that *-(HMPA) is free of ion association and that ion association must be present to provide a mechanism of spin transfer from the anion radical to the solvent.The previously reported dissociation enthalpy of 2-,K+ in HMPA has been combined with several calorimetrically determined values and an extra thermodynamic parameter to obtain a value of -195 kcal/mol for a single ion heat of solvatation of the dianion of annulene in HMPA.
- Stevenson, Gerald R.,Nebgen, Mark A.
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p. 5509 - 5513
(2007/10/02)
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- Tricyclo2,8>oct-3-ene, -oct-4-ene, and -octane: Preparation and Thermolysis of the Hydro Derivatives of Octavalene
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On treatment of 2,3,7,8-tetrabromobicyclooct-3-ene (7) with LiAlH4 an allylic rearrangement occurred with formation of tribromide 8, which was converted into 4-bromotricyclo2,8>oct-3-ene (9) by n-butyllithium.Sodium/tert-butyl alcohol and 9 reacted to give tricyclo2,8>oct-3-ene (4).Hydrogenation of 4 was achieved with diimine and afforded tricyclo2,8>octane (6) along with some bicyclooct-2-ene (10).Sodium iodide transformed 7 into the unrearranged iodide 12.Reduction of 7 with sodium in liquid ammonia led to bicycloocta-3,7-diene (11) in low yield.An allylic rearrangement took place when 7 was treated with AgNO3 to give nitrate 13.In another allylic rearrangement tribromide 14 was formed from 13 and LiAlH4.The reaction of 14 with n-butyllithium afforded 4-bromotricyclo2,8>oct-4-ene (15), and from 15 tricyclo2,8>oct-4-ene (5) was obtained by means of sodium/tert-butyl alcohol.By treatment of 4-bromooctavalene (16) with tert-butyllithium and subsequent hydrolysis, a new route to octavalene (1) was elaborated with virtually no formation of cyclooctatetraene as side product. - At 100 deg C 4 rearranged (t1/2 ca. 40 min) almost quantitatively to dihydrosemibullvalene (17).The decomposition of 5 at 200 deg C (t1/2 ca. 25 h) gave a complex mixture, in which only 11 has been identified.The saturated hydrocarbon 6 was converted virtually quantitatively into a 5.5 : 1 mixture of 3-methylenecycloheptene (18) and 1,3-cyclooctadiene (19) at 160 deg C (t1/2 ca. 8 h).Possible mechanisms of these rearrangements are discussed.
- Christl, Manfred,Herzog, Clemens,Kemmer, Petra
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p. 3045 - 3058
(2007/10/02)
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- THE SYNTHESIS OF OCTAVALENE (TRICYCLO2,8>OCTA-3,5-DIENE) AND SEVERAL SUBSTITUTED OCTAVALENES
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The first synthesis of octavalene (1a) is reported.The starting material is homobenzvalene (5), to which monobromocarbene is added.The resulting compound 3a takes up bromine across the central bicyclobutane bond to form the tribromide 7a which undergoes a cyclopropyl bromide-allyl bromide rearrangement on heating.From the product (10a) HBr is eliminated to give 1,3-dibromocyclobutane with a 1,3-butadiene bridge across its 2- and 4-position (11a).Finally, t-butyllithium removes the two Br atoms from 11a and converts it into 4:1 mixture of 1a and cyclooctatetraene.This reaction sequence represents the first application of protective group strategy in bicyclobutane chemistry.Octavalene (1a) is shown to rearrange to cyclotetraene at 50 deg.Deuterium-labeled 1a (1a) is used to prove that a sigmatropic shift does not occur in 1a.Utilizing the above methodology 4-bromooctavalene (1b) and 3-phenyl-5-bromooctavalene (1c) are synthesized from dibromocarbene adducts 3b and c of homobenzvalene (5) and 5-phenylhomobenzvalene (6), respectively.Surprisingly, 1c was accompanied by a small quantity of 3-bromo-1-phenyloctavalene (1d).Possible mechanisms for the addition of bromine to the bicyclobutane system of compounds 3 and for the formation of the octavalenes 1 are discussed.In the (13)C-NMR spectra of 1 and 11 chemical shifts at unexpectedly high field are observed for C-6 of the 1,3-cycloheptadiene moieties.
- Christl, Manfred,Lang, Reinhard,Herzog, Clemens
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p. 1585 - 1596
(2007/10/02)
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- The Pyrolysis of Cubane; an Example of a Thermally Induced Hot Molecule Reaction
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The pressure dependence of the product distribution of cubane pyrolysis supports a mechanism involving cyclo-octatetraene formed in a highly vibrationally excited state through the release of ring strain energy.
- Martin, Hans-Dieter,Urbanek, Thomas,Pfoehler, Peter,Walsh, Robin
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p. 964 - 965
(2007/10/02)
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- Reactive E=C (p-p)?-Systems, IV: Retro Diene Cleavage of Diels-Alder Adducts of the Phosphaalkene F3CP=CF2
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Pyrolysis of the Diels-Alder adducts 2-4 yields F3CP=CF2 (1) and the corresponding dienes.For the thermal cleavage of 3 an alternative pathway in addition to the retro-diene reaction is observed, giving the new phosphetane F3CP-CF2 and C4H4 dimers.The enthalpy of the cyclo-reversion reaction of 2 as well as estimated bond energies for the phosphorus-carbon ?- and ?-bond have been determined from appearance potentials and thermochemical literature data.The products were characterized by mass and NMR spectra. - Keywords: Retro Diene Reactions, Phospha-Heterocycles, Mass Spectra, Thermochemical Data, NMR Spectra
- Binnewies, Michael,Grobe, Joseph,Van, Duc Le
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p. 927 - 933
(2007/10/02)
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- The Reductive Decyclizations of Semibullvalene
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Reduction of semibullvalene (5) with potassium more closely resembles deprotonation of tetrahydropentalenes by n-butyl-lithium-potassium t-pentoxide than it does the reduction of (5) with lithium; the former processes both provide the cyclo-octatetraenyl dianion (4), plausibly via the intermediate bicyclooctadienediyl dianion (3).
- Goldstein, Melvin J.,Wenzel, Timothy T.
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p. 1654 - 1655
(2007/10/02)
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- Electrochemical Syntheses, X. Catalytic Application of Electrochemical Systems: Cyclooligomerization of Acetylene
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Following known procedures for the preparation of nickel complexes as precursors to active contact species for the cyclooligomerization of acetylene we report the electrochemical formation of Ni(CO)2(PPh3)2 and its use in a one-pot trimerization of acetylene to benzene.Further investigations demonstrate the possibility to simultaneously produce and use as catalysts active nickel solvates generated from nickel anodes for the cyclization of acetylene to benzene and/or cyclooctatetraene. - Keywords: Electrochemical Synthesis, Homogeneous Catalysis, Nickel Complexes, Acetylene Cyclooligomerization
- Grobe, Joseph,Schneider, Bernd Heinz,Zimmermann, Heinz
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p. 957 - 961
(2007/10/02)
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- ATTEMPTS TO GENERATE A HOMOCYCLOHEPTATRIENYLIDENE
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Attempts to generate homocycloheptatrienylidene by dehydrohalogenation of 8-chlorobicyclooctadiene led to cyclooctatetraene, styrene and heptafulvene.
- Parker, Richard H.,Jones, W. M.
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p. 1245 - 1248
(2007/10/02)
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- Ring Opening of a Bicyclooctadienediyl Dianion
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The bicyclooctadienediyl dianion (3) ring opens to give the cyclo-octatetraene dianion (4), the reverse of the behaviour shown by the corresponding dication.
- Wilhelm, Dieter,Clark, Timothy,Schleyer, Paul von Rague,Davies, Alwyn G.
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p. 558 - 559
(2007/10/02)
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- Thermolysis of Ansarane, Ansarene and Cubane
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The thermolysis and kinetics of decomposition of cubane 4 and of ring enlarged cubanes, the ansarenes 1 - 3, are described.The relief of strain which will be observed breaking specific bonds has been estimated by the aid of force-field calculations thereby disclosing probable reaction pathways.The gas phase pyrolysis of cubane 4 yields vibrationally excited cyclooctatetraene 5 which fragmentates to benzene and acetylene.The gas kinetics of cyclooctatetraene 5 is reported on as well.
- Martin, Hans-Dieter,Pfoehler, Peter,Urbanek, Thomas,Walsh, Robin
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p. 1415 - 1421
(2007/10/02)
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- PHOTOCHEMICAL TRANSFORMATION OF TETRACYCLO2,4.03,6>OCT-7-ENE
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Cyclooctatetraene is a common product of photolysis of the title compound 1a.Depending on reaction conditions it is accompanied by benzene solvent: cyclohexane, λ = 253.7 nm), benzene plus semibullvalene (acetone, 300 nm), and an oxetane (cyclohexane, 350 nm, presence of equimolar amount of benzophenone).
- Stapersma, J.,Klumpp, G. W.
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p. 274 - 275
(2007/10/02)
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- MECHANISM OF THE THERMAL CONVERSION OF TETRACYCLO(3.3.0.02,4.03.6)OCT-7-ENE INTO DIHYDROPENTALENES
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One of a number of possible mechanisms has been established for the title reaction.
- Stapersma, J.,Rood, I. D. C.,Klumpp, G. W.
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p. 2201 - 2212
(2007/10/02)
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- Absorption Spectra and Photochemical Rearrangements in Phenylalkene Cations in Solid Argon
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Matrix photoionization experiments with phenylalkenes produced and trapped the parent molecular cations in solid argon at 20 K.In the substituted styrene cation cases, structure was resolved in red and ultraviolet absorption bands and assigned to Ph-C stretching and Ph-C=C bending modes.Molecular ion rearrangements were observed during sample formation and upon the photolysis of the cold sample; allylbenzene cation rearranged to β-methylstyrene cation and indan cation with 290 nm irradiation.The matrix absorption bands were substantially sharper than photodissociati on spectra, which suggests that excess internal energy may contribute substantially to the bandwidth of gaseous molecular ions produced by electron impact.
- Andrews, Lester,Harvey, James A.,Kelsall, Benuel J.,Duffey, Donald C.
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p. 6415 - 6422
(2007/10/02)
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- Heats of Formation of the Annulene Dianion and Neutral Molecule
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The enthalpy of reaction of the disodium salt of annulene with water and the heat of combustion of neutral annulene were both measured calorimetrically.These measurements were utilized in a thermochemical cycle to yield the heat of reaction of sodium metal with annulene to give the solid dianion salt.The enthalpy of reaction of the dianion with water (-10.9 kcal/mol) is much less exothermic than that for the dianion of annulene.The results indicate that the annulene dianion is greatly stabilized via aromatization.Further, its relative thermodynamic stability over that of the annulene dianion has been attributed to a reduced electron-electron repulsion force in the larger annulene dianion.The combustion measurements indicate that the neutral annulene does not possess any conjugative stability.The heat of combustion of annulene (-2182.2 kcal/mol) is more exothermic by 9 kcal/mol than that for two annulenes.
- Stevenson, Gerald R.,Forch, Brad E.
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p. 5985 - 5988
(2007/10/02)
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- SYN TO ANTI ISOMERIZATION AND DEGRADATION OF PHOSPHINES OF THE 7-PHOSPHANORBORNENE SYSTEM BY ACTION OF METHANOL
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Syn-Substituted phosphines of the 7-phosphanorbornene system form unstable phosphorane adducts with methanol that either fragment by retro-McCormick cycloaddition or undergo polytopal rearrangement and loss of methanol to give the first example of anti phosphines.
- Mesch, Keith A.,Quin, Louis D.
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p. 4791 - 4794
(2007/10/02)
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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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p. 150 - 154
(2007/10/02)
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