- Pulse Radiolysis Study of the Cycloheptatriene Triplet State: Lifetime, Relaxation, and Nonvertical Excitation
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The triplet state of cycloheptatriene (CHT) has been produced by pulse radiolysis in toluene.Its lifetime of 6 +/- 1 μs is considerably longer than for acyclic trienes, ca. 300 ns, despite a smaller energy gap between the relaxed T1 and S0 surfaces.It is proposed that relaxation is from the boatlike spectroscopic state to an approximately planar species within which spin-orbit coupling factors are minimized.Plots of log ket vs. donor triplet energy for endothermic triplet energy transfer to both CHT and the acyclic neo-alloocimene (NA) show that, whereas the latter is close to being a vertical acceptor of triplet energy, CHT exhibits clear "nonvertical" character.In this respect, NA and CHT mimic trans- and cis-stilbene, respectively.It would appear that, for olefinic systems, established "nonvertical" behavior is currently restricted to nonplanar ? systems, and the possibility is raised that such behavior may, at least in part, reflect higher vibrational level densities in such systems.
- Gorman, A. A.,Hamblett, I.,Irvine, M.,Raby, P.,Standen, M. C.,Yeates, S.
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- Formation of charge-transfer complexes based on a tropylium cation and 2,6-helic[6]arenes: a visible redox stimulus-responsive process
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Charge-transfer (CT) complexes formed from 2,6-helic[6]arene hosts and a tropylium cation are described in detail. In particular, it was found that the binding and release processes of the guest in the complexes could be efficiently controlled by a redox stimulus, and the responsive process could be visually observed by the color change of the solution. To our knowledge, this represents the first visible redox stimulus-responsive host-guest system formed from the tropylium cation.
- Zhang, Geng-Wu,Shi, Qiang,Chen, Chuan-Feng
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- Synthesis of 1,2,3,4,5,6,7-Heptasubstituted Cycloheptatrienes through Cycloaddition Reactions of Substituted Cyclopentadienones
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Two schemes for synthesizing heptasubstituted cycloheptatrienes with various substituents in the ring are suggested. The first method is based on cycloaddition of 2,5-dimethoxycarbonyl-3,4-diphenylcyclopentadienone with substituted cyclopropenes and allows cycloheptatrienes containing two or three electron-withdrawing substituents in the molecule to be obtained. The second method employs a cascade reaction between a substituted cyclopentadienone and appropriate vinyldiazoacetates. It allows the number of electron-withdrawing substituents to be increased to five. In all cases, heptasubstituted cycloheptatrienes are formed as just one of the possible isomers.
- Platonov, Dmitry N.,Belyy, Aleksandr Yu.,Ananyev, Ivan V.,Tomilov, Yury V.
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- Synthesis and characterization of manganese triple-decker complexes
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The use of the highly sterically demanding CpBIG ligand (CpBIG = C5(4-nBuC6H4)5) and white phosphorus (P4) enables the synthesis of new P-rich derivatives of the rare Pn ligand complexes of manganese. The obtained complexes, [{CpBIGMn}2(μ,η5:5-P5)] (2) and [{CpBIGMn}2(μ,η2:2-P2)2] (3), exhibit the highest number of P atoms in this class of manganese compounds identified by X-ray structure analyses. The EPR spectrum of the 29 VE triple-decker complex 2 shows one unpaired electron coupling with two 5/2 spin Mn nuclei.
- Heinl, Sebastian,Balázs, Gábor,Bodensteiner, Michael,Scheer, Manfred
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- Gold Catalysts Can Generate Nitrone Intermediates from a Nitrosoarene/Alkene Mixture, Enabling Two Distinct Catalytic Reactions: A Nitroso-Activated Cycloheptatriene/Benzylidene Rearrangement
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Gold-catalyzed reactions of cycloheptatrienes with nitrosoarenes yield nitrone derivatives efficiently. This reaction sequence enables us to develop gold-catalyzed aerobic oxidations of cycloheptatrienes to afford benzaldehyde derivatives using CuCl and nitrosoarenes as co-catalysts (10-30 mol %). Our density functional theory calculations support a novel nitroso-activated rearrangement, tropylium → benzylidene. With the same nitrosoarenes, we developed their gold-catalyzed [2 + 2 + 1]-annulations between nitrosobenzene and two enol ethers to yield 5-alkoxyisoxazolidines using 1,4-cyclohexadienes as hydrogen donors.
- Cheng, Mu-Jeng,Kardile, Rahul Dadabhau,Kuo, Tung-Chun,Liu, Rai-Shung,More, Sayaji Arjun
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supporting information
p. 5506 - 5511
(2021/07/31)
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- Generation of methylene by the liquid phase oxidation of isobutene with nitrous oxide
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The application of nitrous oxide as an alternative oxidant provides new opportunities for selective oxidation of olefins. Here, we studied for the first time the thermal oxidation of isobutene with N2O in the liquid phase. The study revealed that the oxidation proceeds via 1,3-dipolar cycloaddition of N2O to the C[dbnd]C bond by two routes forming unstable 4,5-dihydro-[1,2,3]-oxadiazole intermediates. The main route (the contribution of 91%) includes the addition of the N2O oxygen to the second carbon atom in olefin. In this case, the oxadiazole decomposes with the C–C bond cleavage yielding acetone, methylene (:CH2), and N2. The methylene then readily reacts with isobutene and benzene (solvent). The minor route involves the addition of the N2O oxygen to the first carbon atom and the oxadiazole decomposition with a hydrogen shift leading to isobutanal and N2. The main distinctive feature of the studied reaction is the formation of methylene in high yield.
- Semikolenov, Sergey,Ivanov, Dmitry,Babushkin, Dmitry,Malykhin, Sergey,Kharitonov, Alexander,Dubkov, Konstantin
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p. 3589 - 3595
(2018/05/24)
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- Gold(I) Carbenoids: On-Demand Access to Gold(I) Carbenes in Solution
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Chloromethylgold(I) complexes of phosphine, phosphite, and N-heterocyclic carbene ligands are easily synthesized by reaction of trimethylsilyldiazomethane with the corresponding gold chloride precursors. Activation of these gold(I) carbenoids with a variety of chloride scavengers promotes reactivity typical of metallocarbenes in solution, namely homocoupling to ethylene, olefin cyclopropanation, and Buchner ring expansion of benzene.
- Sarria Toro, Juan M.,García-Morales, Cristina,Raducan, Mihai,Smirnova, Ekaterina S.,Echavarren, Antonio M.
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supporting information
p. 1859 - 1863
(2017/02/05)
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- Comparison of enzymatic and acid hydrolysis of bound flavor compounds in model system and grapes
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Four synthesized terpenyl-β-D-glycopyranosides (geranyl, neryl, citronellyl, myrtenyl) were subjected to enzymatic (AR 2000, pH 5.5) and acid (citric buffer, pH 2.5) hydrolysis. Decrease of glycosides was measured by HPLC and the volatiles released - by comprehensive gas chromatography-mass spectrometry (GC x GC-ToF-MS). Enzymatic hydrolysis performed for 21 h yielded 100% degree of hydrolysis for all glycosides but citronellyl (97%). Degree of acid hydrolysis was highly dependent on type of aglycone and the conditions. The highest degree was achieved for geraniol, followed by citronellol and nerol. Myrtenylo-β-D-glycopyranoside was the most resistant glycoside to hydrolysis. Acid hydrolysis degree was also related to temperature/time combination, the highest being for 100 °C and 2 h. In a result of enzymatic hydrolysis 85-91% of total peak areas was terpene aglycone, whereas for acid hydrolysis the area of released terpene aglycone did not exceed 1.3% of total peak area indicating almost complete decomposition/transformation of terpenyl aglycone.
- Dziadas, Mariusz,Jeleń, Henryk H.
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p. 412 - 418
(2015/06/17)
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- Synthesis, structure, and reactivity of a gold carbenoid complex that lacks heteroatom stabilization
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Hydride abstraction from the neutral gold cycloheptatrienyl complex [(P)Au(η1-C7H7)] (P=P(tBu) 2(o-biphenyl)) with triphenylcarbenium tetrafluoroborate at -80 C led to the isolation of the cationic gold cycloheptatrienylidene complex [(P)Au(η1-C7H6)]+ BF 4- in 52 yield, which was characterized in solution and by single-crystal X-ray diffraction. This cycloheptatrienylidene complex represents the first example of a gold carbenoid complex that lacks conjugated heteroatom stabilization of the electron-deficient C1 carbon atom. The cycloheptatrienylidene ligand of this complex is reactive; it can be reduced by mild hydride donors, and converted to tropone in the presence of pyridine N-oxide. Hydride abstraction from the neutral gold cycloheptatrienyl complex 1 (P=P(tBu)2 (o-biphenyl)) with Ph3C+ BF 4- formed the cationic gold cycloheptatrienylidene complex 2, which was characterized by single-crystal X-ray diffraction. The cycloheptatrienylidene ligand of 2 is reactive; it can be reduced by mild hydride donors, and converted into tropone in the presence of pyridine N-oxide.
- Harris, Robert J.,Widenhoefer, Ross A.
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supporting information
p. 9369 - 9371,3
(2015/02/05)
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- Nonconventional versus conventional application of pseudo-first-order kinetics to fundamental organic reactions
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Three new analysis procedures for pseudo-first-order kinetics are introduced and applied to eight different fundamental organic reactions. The reactions belong to the following classes: nitroalkane proton transfer, formal hydride ion transfers from NADH model compounds, and SN2 reactions of alkyl halides with ionic and neutral nucleophiles. The three methods consist of (1) half-life dependence of kapp, (2) sequential linear pseudo-first-order correlation, and (3) revised instantaneous rate constant analysis. Each of the three procedures is capable of distinguishing between one- and multistep mechanisms, and the combination of the three procedures provides a powerful strategy for differentiating between the two mechanistic possibilities. The data from the eight reactions chosen as examples clearly show how the procedures work in practice.
- Parker, Vernon D.,Hao, Weifang,Li, Zhao,Scow, Russell
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experimental part
p. 2 - 12
(2012/03/22)
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- Dihydroazulene-buckminsterfullerene conjugates
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The dihydroazulene (DHA)/vinylheptafulvene (VHF) photo/thermoswitch has recently attracted interest as a molecular switch for molecular electronics. In this field, Buckminsterfullerene, C60, has been shown to be a useful anchoring group for adhering a molecular wire to an electrode. Here we have combined the two units with the overall aim to elucidate how C60 influences the DHA-VHF switching events. Efficient synthetic protocols for making covalently linked DHA-C60 conjugates were developed, using Prato, Sonogashira, Hay, and Cadiot-Chodkiewicz reactions. These syntheses provide as well a variety of potentially useful DHA and C60 building blocks for acetylenic scaffolding. The two units were separated by bridges of various lengths, such as oligo(phenyleneethynylene) (OPE2 and OPE3) wires. The distance of separation was found to influence strongly the light-induced ring-opening reaction of DHA to its corresponding VHF. Thus, C60 was found to significantly quench this conversion when situated closely to the DHA unit.
- Santella, Marco,Mazzanti, Virginia,Jevric, Martyn,Parker, Christian Richard,Broman, S?ren Lindb?k,Bond, Andrew D.,Nielsen, Mogens Br?ndsted
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p. 8922 - 8932
(2013/01/15)
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- Hyperaromatic stabilization of arenium ions: Cyclohexa- and cycloheptadienyl cations-experimental and calculated stabilities and ring currents
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Measurements of pKR show that the cycloheptadienyl cation is less stable than the cyclohexadienyl (benzenium) cation by 18 kcal mol -1. This difference is ascribed here to "hyperaromaticity" of the latter. For the cycloheptadienyl cation a value of KR = [ROH][H+]/[R+] is assigned by combining a rate constant for reaction of the cation with water based on the azide clock with a rate constant for the acid-catalyzed formation of the cation accompanying equilibration of cycloheptadienol with its trifluoroethyl ether in TFE-water mixtures. Comparison of pKR = -16.1 with pKR = -2.6 for the cyclohexadienyl cation yields the difference in stabilities of the two ions. Interpretation of this difference in terms of hyperconjugative aromaticity is supported by the effect of benzannelation in reducing pKR for the benzenium ion: from -2.6 down to -3.5 for the 1H-naphthalenium and -6.0 for the 9H-anthracenium ions, respectively. MP2/6-311+G* and G3MP2 calculations of hydride ion affinities of benzenium ions show an order of stabilities for substituents at the methylene group consistent with their hyperconjugative abilities, i.e., (H3Si)2 > cyclopropyl > H 2 > Me2> (HO)2 > F2. Calculations of ring currents show a similar ordering. No conventional ring current is seen for the cycloheptadienyl cation, whereas currents in the F 2-substituted benzenium ion are consistent with antiaromaticity. Arenium ions where the methylene group is substituted with a single OH group show characteristic energy differences between conformations, with C-H or C-OH bonds respectively occupying or constrained to axial positions favorable to hyperconjugation. The differences were found to be 8.8, 6.3, 2.4, and 0.4 kcal mol-1 for benzenium, naphthalenium, phenanthrenium, and cyclohexenyl cations, respectively.
- Lawlor, David A.,Bean, David E.,Fowler, Patrick W.,Keeffe, James R.,Kudavalli, Jaya Satyanarayana,More O'Ferrall, Rory A.,Rao, S. Nagaraja
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supporting information; experimental part
p. 19729 - 19742
(2012/01/31)
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- Tropylium ion mediated α-cyanation of amines
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Tropylium ion mediated α-cyanation of amines is described. Even in the presence of KCN, tropylium ion is capable of oxidizing various amine substrates, and the resulting iminium ions undergo salt metathesis with cyanide ion to produce aminonitriles. The byproducts of this transformation are simply cycloheptatriene, a volatile hydrocarbon, and water-soluble potassium tetrafluoroborate. Thirteen total substrates are shown for the α-cyanation procedure, including a gram scale synthesis of 17β-cyanosparteine. In addition, a tropylium ion mediated oxidative aza-Cope rearrangement is demonstrated.
- Allen, Julia M.,Lambert, Tristan H.
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supporting information; experimental part
p. 1260 - 1262
(2011/04/15)
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- Liquid phase oxidation of alkenes with nitrous oxide to carbonyl compounds
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A variety of substrates including linear, cyclic, heterocyclic alkenes and their derivatives were tested in the liquid phase non-catalytic oxidation with nitrous oxide (N2O). The structure and composition of the alkenes have a significant effect on the reaction selectivity. With many alkenes, N 2O oxidation provides a selective way for the preparation of carbonyl compounds. The generation of carbene (or diazomethane) species is a remarkable feature of the oxidation of terminal alkenes.
- Starokon,Dubkov,Babushkin,Parmon,Panov
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p. 268 - 274
(2007/10/03)
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- Unambiguous detection of 2,4,6-cycloheptatrien-1-ol by NMR spectroscopy and trapping with phenyltriazolinedione
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For the first time, the title alcohol 3 was unambiguously detected as a transient intermediate leading to ditropylether (6) in a cation-anion reaction between the tropylium ion (5) and hydroxide ion in an aqueous solution by NMR spectroscopy. It was also found that 6 gives 3 as a transient product in acid-catalyzed disproportionation of 6 into a mixture of tropone (4) and 1,3,5-cycloheptatriene (7) in chloroform containing water. Furthermore the existence of 3 in the latter reaction was confirmed by trapping with 4-phenyl-1,2,4-triazoline-3,5-dione to afford the [4+2]cycloadduct of the norcaradiene form of 3.
- Oda, Mitsunori,Okawa, Kazuya,Tsuri, Hitoshi,Kuroda, Shigeyasu
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p. 795 - 800
(2007/10/03)
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- Reactions of carbocations with unsaturated hydrocarbons: Electrophilic alkylation or hydride abstraction?
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Benzhydryl cations were used as reference electrophiles to determine the hydride donor reactivities of unsaturated hydrocarbons. The kinetics of the reactions were followed by UV-vis spectroscopy and conductivity measurements, and it was found that the second-order rate constants for the hydride transfer processes were almost independent of the solvents or counterions employed. The rate constants correlate linearly with the previously published empirical electrophilicity parameters E of the benzhydrylium ions. Therefore, the linear free energy relationship log k(20 °C) = s(E + N) could be employed to characterize the hydride reactivities of the hydrocarbons by the nucleophilicity parameters N and s. The similarity of the slopes s for hydride donors and π-nucleophiles allows a direct comparison of the reactivities of these different functional groups based on their nucleophilicity parameters N. Since nucleophilicity parameters of -5 N 0 have been found for a large variety of allylic and bisallylic hydride donors, a rule of thumb is derived that hydride transfer processes may compete with carbon-carbon bond-forming reactions when carbocations are combined with olefins of π-nucleophilicity N 0.
- Mayr, Herbert,Lang, Gabriele,Ofial, Armin R.
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p. 4076 - 4083
(2007/10/03)
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- An old but simple and efficient method to elucidate the oxidation mechanism of NAD(P)H model 1-aryl-1,4-dihydronicotinamides by cations 2-methyl-5-nitroisoquinolium, tropylium, and xanthylium in aqueous solution
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Cations 2-methyl-5-mitroisoquinplinium (IQ+), tropylium (T+), and xanthylium (Xn+) were treated by an NAD(P)H model 1-(p-substituted phenyl)-1.4-dihydronicotinamide series (1) in buffered aqueous solution to give the corresponding reduced products by accepting hydride. Effects of the 4-substituents of 1 on the reaction rates were investigated. Hammett's linear free energy relationship analysis on the three reactions of 1 provides the reaction constants of -0.48, -2.2, and -1.4 with IQ+, T+, and Xn+ as the hydride acceptors, respectively. Comparison of the present reactions with the reaction examples whose mechanisms are well-known, such as the reaction of 1 with a one-electron oxidant Fe(CN)6-3, shows that the active site of 1 in the oxidation with IQ+ is at the 4-position on the dihydropyridine ring but that the active site of 1 in the oxidations with T+ and Xn+ is at the 1-position, which is in agreement with the results from the Bronsted-type linear analysis and the relation studies of the logarithm of the second-order rate constants with the oxidation potentials of the hydride donors. According to the dependence of the reaction mechanism on the active site of 1, a conclusion can be made that the reaction of 1 with IQ+ proceeds by direct one-step hydride transfer mechanism, but the reactions of 1 with T+ and Xn+ would take place via multistep hydride transfer mechanism initiated by one-electron transfer.
- Zhu,Liu,Zhao,Cheng
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p. 370 - 375
(2007/10/03)
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- Simple and efficient synthesis of bromine-substituted 1,3-dienes and 1,3,5-cycloheptatriene by vacuum pyrolysis of gem-dibromocyclopropanes
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To establish whether the results obtained by the gas phase pyrolysis of 6,6-dihalobicyclo[3.1.0]hexanes by HeI photoelectron spectroscopy using a high power CW CO2 laser as a directed heat source can be achieved on a preparatory scale using a modified apparatus, we carried out the gas phase pyrolysis of a few representative gem-dibromocyclopropanes such as 1,1-dibromo-2,2,3,3-tetramethylcyclopropane (1), 1,1-dibromo-2,2-dimethyl-cyclopropane (2), 1,1-dibromo-cis-2,3-dimethylcyclopropane (3), 1,1-dibromo-trans-2,3-dimethylcyclopropane (4), 6,6-dibromobicyclo[3.1.0]hexane (5) and 7,7-dibromobicyclo[4.1.0]heptane (6). Except 7,7-dibromobicyclo[4.1.0]heptane, that gave 1,3,5-cycloheptatriene in 72% yield at 525°C, 1, 2, 3, 4 and 5 readily lose HBr at 400-560°C in the gas phase to produce β-bromo-1,3-dienes in high chemical yields and purity. The dienes are potentially useful starting substrates for the Diels-Alder reactions.
- Werstiuk, Nick H.,Roy, Chandra D.
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p. 3255 - 3258
(2007/10/03)
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- Mechanism of the reaction of methylene with benzene: A study of kinetic hydrogen isotope effects and theoretical calculations
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The reaction mechanism of singlet and triplet methylene with benzene and related aromatic compounds was investigated by kinetic isotope effects (KIEs), solvent effects, and product studies. The results are further rationalized by a series of ab initio calculations at MP2/6-31G*//RHF/6-31G* and UMP2/6-31G*//UHF/6-31G* levels of theory. The proposed 1c intermediate for the triplet reaction was found by means of the calculations, whereas no singlet analog 1 could be found.
- Hartz, Nikolai,Surya Prakash,Olah, George A.
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p. 901 - 905
(2007/10/02)
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- SYNTHESIS OF CYCLOHEPTA-1,3,5-TRIENES BY THE REACTION OF AROMATIC HYDROCARBONS WITH DIAZO COMPOUNDS IN THE PRESENCE OF TRANSITION METAL COMPLEXES
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A preparative method has been developed for the synthesis of cyclohepta-1,3,5-trienes, using a reaction of aromatic hydrocarbons with diazomethane, methyldiazoacetate, adamantanoyldiazomethane, and 1-diazo-3-phenylpropan-2-one, with rhodium trifluoroacetate as catalyst.The order of activity and the relative reactivity coefficients of substituted benzenes have been determined, and the link between these characteristics and the energy of the highest occupied molecular orbital of the aromatic ring has been established.In catalyzed reactions of benzenes with diazomethaneor methyldiazoacetate, leading to cycloheptatrienes, effects of chemical polarization of the ring have not been observed.
- Dzhemilev, U. M.,Dokichev, V. A.,Sultanov, S. Z.,Sadykov, R. A.,Tolstikov, G. A.,Nefedov, O. M.
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p. 945 - 950
(2007/10/02)
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- THE USE OF 1,1,2,2,3,3,4,4-OCTAPHENYLTETRASILANE IN THE IONIC HYDROGENOLYSIS OF ALKYL HALIDES
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1,1,2,2,3,3,4,4-Octaphenyltetrasilane is a hydride ion donor in the ionic hydrogenolysis of alkyl halides which are capable of forming relatively stable carbocations.The reaction takes place at room temperature in the presence of catalytic amounts of aluminum chloride and leads to the formation of the corresponding hydrocarbon with a high yield.In the light of the properties of octaphenyltetrasilane a method was developed for hydrogenolysis in a heterogenous medium in a column filled with a mixture of octaphenyltetrasilane and aluminum chloride.The spent silane is regenerated by reduction with lithium aluminum hydride and is used repeatedly
- Bolestova, G. I.,Shevchenko, N. V.,Parnes, Z. N.,Vol'pin, M. E.
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p. 2224 - 2227
(2007/10/02)
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- A Comparison of the Rates of Intramolecular Hydrogen Migration in the Molecules (n+) to give (n+), n=0 or 1: Crystal Structures of , , and
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Co-condensation of molybdenum atoms with cycloheptatriene gives (7), which rearranges thermally to , (8).Oxidation of (7) gives the cation (1+), (9), which rearranges thermally to give (1+), (10).The crystal structures of (7), (8), and (9) have been determined.The isomerizations of (7) to (8), and of (9) to (10) are clean, first-order, intramolecular processes, and, surprisingly, the rate of conversion of (9) to (10) (Eact.=115 kJ mol-1) is slower than for the conversion of (7) to (8) (Eact.=101 kJ mol-1).
- Green, Malcolm L. H.,Newman, Paul A.,Bandy, Judith A.
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p. 331 - 344
(2007/10/02)
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- Metal-templated synthesis of macrocyclic (triphosphine)molybdenum complexes
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Reaction of CH2=CHCH2PH2, CH2=CHCH2CH2PH2, and CH≡CCH2PH2 with (mesitylene)Mo(CO)3 or (cycloheptatriene)Mo(CO)3 yields the complexes (CH2=CHCH2PH2)3Mo(CO)3 (1), (CH2=CHCH2CH2PH2) 3Mo(CO)3 (2), and (CH≡CCH2PH2)3Mo(CO)3 (3), respectively. Reaction of CH2=CHCH2PH2 and CH≡CCH2PH2 with cis-(piperidine)2Mo(CO)4 yields cis-(CH2=CHCH2PH2)2Mo(CO) 4 (4) and cis-(CH≡CCH2PH2)2Mo(CO)4 (5). Free-radical-initiated cyclooligomerization of 1 and 2 yields the triligated macrocyclic secondary-phosphine complexes fac-[HP(CH2)3]3Mo(CO)3 (6) and fac-[HP-(CH2)4]3Mo(CO)3 (7). Under similar conditions, reaction of 4 yields an acyclic diphosphine complex characterized tentatively as cis-[H2P(CH2)3PH(CH2CH=CH 2)]Mo(CO)4 (8). Compounds 1-7 and 10 have been characterized by spectral (31P, 13C, and 1H NMR and IR and mass) data. 6 has been characterized in the solid state by single-crystal X-ray analysis. Crystalline 6 is monoclinic, space group P21/c, with a = 12.606 (3) ?, b = 8.508 (2) ?, c = 15.420 (2) ?, β = 93.39 (2)°, do = 1.61 g/mL, dc = 1.616 g/mL, Z = 4, and R = 0.026, Rw = 0.032 for 2685 unique observed reflections. In the crystal, the P3 macrocycle assumes a partial crown structure in which the complex has approximate Cs point symmetry. 31P NMR spectral studies of the cyclooligomerization of 1 show the partially cyclized intermediates formed prior to 6. The macrocyclic complexes 6 and 7 are kinetically stable, showing no sign of ligand displacement in reactions with Ph3P, PF3, KCN, or P(OMe)3.
- Diel, Bruce N.,Brandt, Paul F.,Haltiwanger, R. Curtis,Hackney, Michael L. J.,Norman, Arlan D.
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p. 2811 - 2816
(2008/10/08)
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- A solvent effect in reactions of singlet methylene
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The effect of several solvents on the selectivity of singlet methylene (1:CH2) was investigated. It was found that product ratios from reactions in pentane, ethyl ether and cyclohexene solutions were identical; however, product ratios from reactions carried out in benzene were slightly different.
- Neugebauer,DeLuca
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p. 7169 - 7172
(2007/10/02)
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- The Reaction of (CH2(3B1) with C6H6
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The kinetics of the reaction CH2(3B1) + C6H6 --> products (1) has been studied in a discharge flow reactor using Laser Magnetic Resonance (LMR) detection for CH2.The experiments yielded the overall rate constant k1exp = (4.7 +/- 2.4)* E13 exp(-(37.5 +/- 2.4) kJ mol-1/RT) in the temperature range 448 K 1A1) + C6H6 --> products (2) in a stationary photolysis reactor employing gas chromatographic analysis by photolyzing mixtures of CH2CO and C6H6 at λ1 = 366 nm and λ2 = 313 nm.The relative yields of the products cycloheptatriene (CHT) and toluene (T) were found to depend on the wavelength, /( + ) = (0.13 +/- 0.02) and (0.23 +/- 0.02) at λ1 and λ2, respectively.The implications of these results and mechanisms are discussed. - Keywords: Chemical Kinetics / Elementary Reactions / Laser Magnetic Resonance / Methylene / Radicals
- Boehland, T.,Heberger, K.,Temps, F.,Wagner, H. Gg.
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- 7-METHYL- AND 7-PHENYLCYCLOHEPTA-1,3,5-TRIENES FROM BENZVALENE VIA 3,3a,4,5,6,6a-HEXAHYDRO-4,5,6-METHENOCYCLOPENTAPYRAZOLES AND TETRACYCLO2,4.03,5>HEPTANES
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The addition of benzvalene (1) to diazomethane, diazoethane, 2-diazopropane, phenyldiazomethane, and diphenyldiazomethane afforded the 1-pyrazolines 2a-g in good yields.By means of competition experiments, the relative reactivities of benzvalene (1) and norbornene with regard to diazomethane and 2-diazopropane have been determined.The fact that benzvalene reacts about twice as fast as norbornene with both diazoalkenes cannot be rationalized on the basis of frontier orbital energies.On direct photolysis, the pyrazolines 2a-g were converted into the tetracyclo2,4.03,5>heptanes 4a-g exclusively.These compounds gave the 1,3,5-cycloheptatrienes 5a,b,d,e,g in high yields on treatment with silver ions, thus providing better access to 7,7-dimethyl-(5d) and 7,7-diphenylcycloheptatriene (5g) than before.Surprisingly, the latter compound is in equilibrium with a substantial quantity of the norcaradiene form.The heat of reaction for the rearrangement of 4a to 5a has been determined, which allows to derive the heat of formation of tetracyclo2,4.03,5>heptane (4a).
- Christl, Manfred,Brunn, Erich,Roth, Wolfgang R.,Lennartz, Hans-Werner
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p. 2905 - 2916
(2007/10/02)
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- Reactions of 11C atoms with benzene. II. Formation of 11C-labelled toluene and cycloheptatriene
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The reactions of recoil 11C atoms with liquid C6H6 result in the production of 11C-labelled cycloheptatriene (CHT) and toluene in equal amounts of approximately 3percent.From the effect of O2 on the product yields it is concluded that recoil labelling proceeds via both singlet and triplet 11CH2 intermediates, whereas 11CH may also contribute specifically to the formation of C6H5CH3.Addition of H2S increases the C6H5CH3 yield by ca. 5percent, probably due to reactions of triplet phenylcarbene (C6H5CH).The reactions of singlet CH2, produced via the photolysis of CH2N2, with liquid C6H6 were also investigated in the presence of N2, O2 and I2.
- Kuipers, P.,Halteren, B. W. van,Lindner, L.,Brinkman, G. A.
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- Homoaromatic Delocalization in the Transition State for Norcaradiene Formation
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The kinetics for the extrusion of benzene from norcaradiene adducts 11 and 12 have been measured.The high 11/12 rate ratio, 8.9E3, was shown to be due to homoaromatic interactions in the cycloreversion transition state emanating from 11.This conclusion was reached after studying the benzene extrusion kinetics for several model compounds, including 20.The syntheses of the requisite compounds are fully described.
- Bertsch, Achim,Grimme, Wolfram,Reinhardt, Gerd,Rose, Hermann,Warner, Philip M.
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p. 5112 - 5117
(2007/10/02)
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- CONTROL OF PHOTOREACTIONS OF EIGHT MEMBERED RING DI- AND TRIENONES IN A CRYSTALLINE INCLUSION COMPLEX WITH OPTICALLY ACTIVE 1,6-DI(o-CHLOROPHENYL)-1,6-DIPHENYLHEXA-2,4-DIYNE-1,6-DIOL
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By complexing with the title host compound, flipping equilibrium of cycloocta-2,4,6-trien-1-one was frozen in one optical conformer as a 2:1 complex, which upon irradiation gave optically active bicycloocta-4,7-dien-2-one.Irradiation of a 1:2 complex of cycloocta-2,4-dien-1-one and the same host compound gave an optically active dimer, anti-tricyclo2,9>hexa-deca-7,11-diene-3,16-dione.
- Toda, Fumio,Tanaka, Koichi,Oda, Masaji
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p. 653 - 654
(2007/10/02)
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- PHOTOCHEMISTRY OF BRIDGED CYCLOHEPTADIENES. MULTIPLICITY DEPENDENT PERICYCLIC REARRENGEMENTS OF EXCITED BICYCLONONA-2,4-DIENE-7,7,8,8-TETRACARBONITRILE
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Bicyclonona-2,4-diene-7,7,8,8-tetracarbonitrile rearranges selectively under direct irradiation in acetonitrile to tricyclo2,4>non-6-ene-8,8,9,9-tetracarbonitrile, and upon acetone sensitization to bicyclonona-2,6-diene-8,8,9,9-tetracarbonitrile.Both products are derived from sigma bond cleavage, in contrast to the parent unsubstituted diene where only the ?-bonds react.
- Goldschmidt, Zeev,Genizi, Elisheva
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p. 4867 - 4870
(2007/10/02)
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- THERMAL REACTIONS OF CYCLOBUTANEDIONES
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Thermolysis of cyclobutanediones in hydrocarbon solvents shows marked dependence on structure and may involve bis-decarbonylation to olefins, monodecarbonylation with rearrangement to cyclopentenone derivatives, or rearrangement without loss of carbon monoxide.
- Rubin, Mordecai B.,Harel, Yaakov
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p. 5373 - 5376
(2007/10/02)
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- Kinetics of the Reaction of Organosilyl Hydrides with Carbenium Ions in an Inert Solvent. Silicocation Intermediacy. Single Electron Transfer versus Synchronous Hydride Transfer
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The rate of reduction of carbenium center with various organosilyl hydrides and one organogermyl hydride in methylene chloride solution was studied.Triphenylmethylium and cycloheptatrienylium salts having metal-halogen complex anions were used as the carbenium substrates.Although the net result of the process at silicon and germanium centers is the formal substitution of H- by halide ion originating from the decomposition of halometallate ion, this substitution proceeds stepwise and one or more silicocation (germanium cation) intermediates are formed.It is possible that one of them has a structure of silylenium (germylenium) ion *Si+ (*Ge+), which may be modified by interaction with solvent.The process which occurs at the carbon center is the hydride-transfer reduction.The kinetic data indicate that the single electron transfer pathway involving the radical silicocation intermediate is followed rather than a synchronous H- transfer from silicon to the carbenium center.
- Chojnowski, J.,Fortuniak, W.,Stanczyk, W.
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p. 7776 - 7781
(2007/10/02)
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- CYCLOHEPTATRIENYL-PHOSPHORUS DERIVATIVES. AN ABNORMAL PHOSPHONIUM SALT HYDROLYSIS.
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A variety of cycloheptatrienyl-phosphorus derivatives have been prepared.In no case was evidence obtained of contribution from norcaradiene forms.Attempts to prepare the corresponding ylide from cycloheptatrienyltriphenylphosphonium salts led to substitution of phospine, as did reactions with a variety of nucleophiles, including hydroxide ion where the observed reaction is in conflict with earlier reports.
- Gilheany, Declan G.,Thompson, Norris T.,Walker, Brian J.
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p. 3843 - 3844
(2007/10/02)
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- Norpinenes (Bicyclohept-2-enes) from Homobenzvalenes (Tricyclo2,7>hept-3-enes)
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4,5-Dibromo-(1b) and 4,5-dichlorohomobenzvalene (1c) were converted into the tetrahalonorpinenes 2b, c by elemental bromine.In the case of unsubstituted homobenzvalene (1a) the analogous reaction could be achieved in 1percent yield only by pyridinium perbromide.Treatment of 1a, b as well as of chlorohomobenzvalenyl nitrobenzoate 1d with iodine furnished the diiodonorpinenes 3a - c.However, 7,7-dibromotetracyclo2,4.03,5>heptane (4) and bromine gave the tetrabromo-trans-tricyclo2,4>heptane derivative 5. - On irradiation in the presence of thiophenol, the homobenzvalenes 1a, c, e, f were transformed into the 6-(phenylthio)norpinenes 6a - d.The hydroxyhomobenzvalenes 1g, h afforded the 6-(phenylthio)norpinenes 6e, g as major products, the configuration at C-4 of which is inverted as compared to that of 6b - d.By using 2>-1a it was shown that with respect to stereochemistry the addition of thiophenol does not proceed uniformly.Without irradiation, 1a was consumed by thiophenol rather slowly at 20 deg C with formation of the norcarene derivatives 9 and 10 in addition to 6a. - By treatment with LiAlH4 the dichloro compound 6b gave the monochloro derivative 6h.Both 6b and 6h, however the latter one with a better yield, were converted into unsubstituted norpinene (11a) by means of sodium in liquid ammonia, thus providing a new and preparatively useful synthesis for 11a.Analogously, 6c, d furnished 4-phenylnorpinene (11b).The reaction of norpinenes 3a and 11a with N-bromosuccinimide produced the allylbromides 3d and 11c, respectively. - 13C NMR spectra of the 4-substituted norpinenes revealed a diagnostically important γ-anti-substituent effect.
- Herzog, Clemens,Lang, Reinhard,Brueckner, Dieter,Kemmer, Petra,Christl, Manfred
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p. 3027 - 3044
(2007/10/02)
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- The Pyrolyses of 1,1,4,4-Tetraphenyl-1,4-butanediol and 1,1,4,4-Tetraphenyl-2-butene-1,4-diol Derivatives. Decomposition Reactions to Form Olefins via the Elimination of Two Mole Equivalents of the Hydroxydiphenylmethyl Radical
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The pyrolysis of 1,1,2,4,4-pentaphenyl-1,4-butandiol, trans-1,2-bis(hydroxydiphenylmethyl)hexane, trans-1,2-bis(hydroxydiphenylmethyl)indan, and cis-endo- and trans-1,2-bis(hydroxydiphenylmethyl)bicycloheptane gave styrene, cyclohexene, indene, and norbornene respectively, accompanied by benzophenone and benzhydrol.The pyrolysis of trans-1,2-bis(hydroxydiphenylmethyl)spironona-4,6,8-triene afforded indene via rearrangement to form trans-1,2-bis(hydroxydiphenylmethyl)indan.The pyrolysis of cis-1,1,4,4-tetraphenyl-2-butene-1,4-diol afforded 2,2,5,5-tetraphenyl-2,5-dihydrofuran.On the other hand, trans-1,1,4,4-tetraphenyl-2- butene-1,4-diol afforded 1,2,4,4-tetraphenyl-3-buten-1-one.The mechanisms of these decomposition reactions are discussed.
- Saito, Katsuhiro,Horie, Yoichi,Mukai, Toshio,Toda, Takashi
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p. 3118 - 3124
(2007/10/02)
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- SKATTEBOL TYPE REARRANGEMENT VIA α-BROMOTRIMETHYLSTANNYL CYCLOPROPANE THERMOLYSIS. WHAT IS THE MECHANISM?
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Solution thermolysis of the epimers 5 gave rise to separate sets of products, including, for one, Skattebol-type rearrangement.However, neither epimer produced a free carbene.
- Warner, Philip M.,Herold, Robert D.
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p. 4897 - 4900
(2007/10/02)
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- Stereochemistry of the Bicyclopentane Ringopening; Thermolysis of Tricyclo2,4>heptane Derivatives
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Thermolysis of the anti-tricyclic compounds 6, 22 and 34 proceeds preferentially by concerted 2s+?2a>-reactions and leads to cis,trans-olefines 8, 24 and 37.The rearrangement of the syn-isomers on the other hand seems to be a nonconcerted reaction yielding the diradicals 15, 27 and 36.
- Roth, Wolfgang R.,Klaerner, Frank-Gerit,Grimme, Wolfram,Koeser, Hans G.,Busch, Ralf,et al.
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p. 2717 - 2737
(2007/10/02)
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- REGIOSPEZIFISCHES UMLAGERUNGSVERHALTEN BUTADIENYL- UND VINYLSUBSTITUIERTER CYCLOPRPILYDENE
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The reaction of the mono- and bis-dibromocarbene adducts of trans- and cis-hexatriene with methyllithium proceed regiospecifically.The results are supported by labelling (12C > 99.95percent) experiments.
- Fleischhauer, Ilona,Brinker, Udo H.
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p. 3205 - 3208
(2007/10/02)
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- Organic Photochemistry with 6.7-eV Photons. The Divergent Photobehavior of exo- and endo-7-Methyl-2-norcarene
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The photochemistry of exo- and endo-7-methylbicyclohept-2-ene (7-methyl-2-norcarene) upon direct and toluene-sensitized photolysis has been investigated.Direct photolysis of the two isomers in hydrocarbon solution with monochromatic 214-nm light leads to widely divergent photobehavior.Ring opening, yielding cis-5-methyl-1,3,6-heptatriene (via a formal process), and exo-endo isomerization are major decomposition pathways in both cases, accounting for 30-45percent of the observed products.The formation of 7-methylnorbornene and 4-methylbicyclohept-2-ene is observed to proceed stereospecifically in each case, while the formation of cyclopropyl ring opening/hydrogen migration products appears to depend strongly on the orientation of the methyl group in the starting isomer.Common biradical intermediates are thus believed not to be involved in the direct photolyses of 2 and 3.Toluene-sensitized photolysis of the two isomers leads to formation of exo-4-methylbicyclohept-2-ene (the photochemical vinylcyclopropane rearrangement) and exo-endo isomerization.These results are rationalized in terms of the expected behavior of two common biradical intermediates, which are formed with different efficiencies from the isomeric 2 and 3 upon triplet sensitization.
- Leigh, William J.,Srinivasan, R.
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p. 3970 - 3979
(2007/10/02)
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- Coalescence phenomena in the NMR spectra of some cycloheptatrienes
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Coalescence phenomena have been observed in the NMR spectra of a variety of 7-substituted 1,3,5-cycloheptatrienes upon varying temperature and/or solvent.Using two different methods, the energy of activation of the process responsible for coalescence has been determined.Within a group of structurally similar para-substituted phenyl sulphides a linear relation has been found between the energy of activation and the acidity constant of the corresponding benzenethiol, suggesting the occurrence of ion pairs.The relatively low energy of activation for the phenyl sulphides, when compared with the values of the phenyl sulphones, may rewsult from the structure of the intermediate ion pairs.In addition to the above, a digfferent exchange process between cycloheptatrienyl sulphides and tropylium salt via sulphonium ions has been observed.
- Zwaard, A. W.,Smits, H. J. E.,Kloosterziel, H.
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p. 187 - 191
(2007/10/02)
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- Organic Photochemistry with 6.7 eV Photons: Tetracyclo2,7.04,6>heptane (Quadricyclene)
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Irradiation of quadricyclene in solution leads to isomeric products in addition to bicyclohepta-2,5-diene, which reduces its usefulness in solar energy storage.
- Srinivasan, Ra.,Baum, Thomas,Epling, Gary
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p. 437 - 438
(2007/10/02)
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- A FACILE AND EFFICIENT PREPARATION OF TROPONE FROM DI-7-CYCLOHEPTATRIENYL ETHER USING TRIFLUOROACETIC ACID AS A CATALYST
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Tropone is prepared by an improved method in high yields without troublesome workup processes.Thus, di-7-cycloheptatrienyl ether is treated at room temperature with a small amount of trifluoroacetic acid as a catalyst.
- Machiguchi, Takahisa
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p. 1021 - 1026
(2007/10/02)
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