- Mechanism of Hydration of Simple Olefins in Aqueous Solution. cis- and trans-Cyclooctene
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Rates of hydration of cis- and trans-cyclooctene and 2,3-dimethyl-2-butene to the corresponding alcohols have been measured in concentrated and dilute aqueous perchloric acid, and those of the latter two olefins in bisulfate ion and phosphoric acid buffer solutions as well.The systems examined in buffers show general-acid catalysis.The reaction of trans-cyclooctene is not reversible, but those of cis-cyclooctene and 2,3-dimethyl-2-butene are; for cis-cycloctene, K=/=1.8 and for 2,3-dimethyl-2-butene, K ca. 4.For hydration of trans-cyclooctene, ΔH*= 22 kcal mol-1, ΔS*= 1 cal K-1 mol-1, and kH(1+)(25 deg C)= 5.2x10-4 M-1 s-1; for the hydration of cis-cyclooctene, ΔH*= 24 kcal mol-1, ΔS*= -10 cal K-1 mol-1, and kH(1+)( 25 deg C)= 2.1x10-7 M-1 s-1; and for the rate of approach to equilibrium in the 2,3-dimethyl-2-butene system, kH(1+)( 25 deg C)= 2.9x10-4 M-1 s-1.The lifetime of tertiary carbocations such as that formed by protonation of 2,3-dimethyl-2-butene is estimated to be τ ca. 10-10 s in dilute aqueous solution, which allows this ion to be a viable, solvationally equilibrated intermediate in the hydration reaction.The secondary cyclooctyl cation is likewise judged to be a solvationally equilibrated species in concentrated aqueous acids, with τ ca. 5x10-8 to 5x10-9 s in the 45-55 wt percent HClO4 solutions used for the hydration of cis-cyclooctene.In dilute aqueous solution, however, carbocation lifetimes are shorter, and τ ca. 5x10-12 s is estimated for the cyclooctyl cation in dilute acids such as those used for the hydration of trans-cyclooctene.Species as short-lived as this can probably still be reaction intermediates, but they are not solvationally equilibrated and may have to react by preassociation mechanisms; an argument is presented that shows that such a mechanism is likely not to be required in the hydration of trans-cyclooctene.
- Chiang, Y.,Kresge, A. J.
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- Primary Alcohols via Nickel Pentacarboxycyclopentadienyl Diamide Catalyzed Hydrosilylation of Terminal Epoxides
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The efficient and regioselective hydrosilylation of epoxides co-catalyzed by a pentacarboxycyclopentadienyl (PCCP) diamide nickel complex and Lewis acid is reported. This method allows for the reductive opening of terminal, monosubstituted epoxides to form unbranched, primary alcohols. A range of substrates including both terminal and nonterminal epoxides are shown to work, and a mechanistic rationale is provided. This work represents the first use of a PCCP derivative as a ligand for transition-metal catalysis.
- Lambert, Tristan H.,Steiniger, Keri A.
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p. 8013 - 8017
(2021/10/25)
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- Application method of Grignard reaction
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The invention discloses an application method of a Grignard reaction, belonging to the technical field of organic synthesis. According to the invention, a two-way dropwise adding mode is adopted, andpreparation of a Grignard reagent and a Grignard reaction are carried out at the same time; as the Grignard reaction is carried out while the Grignard reagent is prepared, the concentration of the Grignard reagent in a reaction system is reduced, and coupling side reactions are reduced; the use amount of a solvent in the reaction system is reduced, the accumulation rate of raw materials is increased, yield is increased and cost is reduced; and meanwhile, in the reaction system, the activity of the Grignard reagent in the system is reduced due to the reduction of the concentration of the Grignard reagent, so an explosion risk caused by over-high concentration of the Grignard reagent during storage and reaction of the Grignard reagent is avoided.
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Paragraph 0026-0039
(2021/03/31)
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- METHOXYCARBONYLATION WITH FORMIC ACID AS CO SOURCE
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Process for methoxycarbonylation with formic acid as the CO source.
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Paragraph 0048-0050
(2019/02/24)
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- Palladium-catalyzed selective generation of CO from formic acid for carbonylation of alkenes
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A general and selective palladium-catalyzed alkoxycarbonylation of all kinds of alkenes with formic acid (HCOOH, FA) is described. Terminal, di-, tri-, and tetra-substituted including functionalized olefins are converted into linear esters with high yields and regioselectivity. Key-to-success is the use of specific palladium catalysts containing ligands with built-in base, e.g., L5. Comparison experiments demonstrate that the active catalyst system not only facilitates isomerization and carbonylation of alkenes but also promotes the selective decomposition of HCOOH to CO under mild conditions.
- Sang, Rui,Kucmierczyk, Peter,Dong, Kaiwu,Franke, Robert,Neumann, Helfried,Jackstell, Ralf,Beller, Matthias
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supporting information
p. 5217 - 5223
(2018/04/24)
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- Oxidation of Alkanes by Periodate Using a MnV Nitrido Complex as Catalyst
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The design of catalytic systems that can selectively oxidize unactivated C?H bonds under mild conditions is a challenge to chemists. We report here that the manganese(V) nitrido complex [MnV(N)(CN)4]2? is a highly efficient catalyst for the oxidation of alkanes by periodate (IO4 ?) at ambient conditions. Excellent yields of alcohols and ketones (>95 %) are obtained with a maximum turnover number (TON) of 3000.
- Ma, Li,Chen, Lingjing,Lau, Tai-Chu
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p. 2846 - 2848
(2016/10/25)
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- Iron-catalyzed oxidation of unreactive C-H bonds: Utilizing bio-inspired axial ligand modification to increase catalyst stability
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Three different bio-inspired Fe(II) complexes are applied as powerful catalysts for the oxidation of unreactive C-H bonds under ambient conditions. Cyclohexane as the main model substrate is oxidized to cyclohexanol, cyclohexyl hydroperoxide, and cyclohexanone. Alcohol + cyclohexyl hydroperoxide to ketone ratios ((A + H)/K) of up to 26 are obtained with comparatively high turnovers of up to 43. Bio-inspired modification of the Fe(II) complexes in the axial positions is used to increase catalyst stability toward hydrogen peroxide, leading to an increase in turnovers of up to 34%. Several parameters for the catalytic oxidation are investigated, e.g., the amount and type of oxidant, reaction temperature, and the relative catalyst concentration. Among others, 9,10-dihydroantracene and 2,3-dimethylbutane are used as substrates for the catalytic C-H bond oxidation.
- Haslinger, Stefan,Raba, Andreas,Cokoja, Mirza,P?thig, Alexander,Kühn, Fritz E.
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p. 147 - 153
(2015/10/06)
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- Highly efficient alkane oxidation catalyzed by [MnV(N)(CN) 4]2-. Evidence for [MnVII(N)(O)(CN) 4]2- as an active intermediate
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The oxidation of various alkanes catalyzed by [MnV(N)(CN) 4]2- using various terminal oxidants at room temperature has been investigated. Excellent yields of alcohols and ketones (>95%) are obtained using H2O2 as oxidant and CF3CH 2OH as solvent. Good yields (>80%) are also obtained using (NH4)2[Ce(NO3)6] in CF 3CH2OH/H2O. Kinetic isotope effects (KIEs) are determined by using an equimolar mixture of cyclohexane (c-C6H 12) and cyclohexane-d12 (c-C6D12) as substrate. The KIEs are 3.1 ± 0.3 and 3.6 ± 0.2 for oxidation by H2O2 and Ce(IV), respectively. On the other hand, the rate constants for the formation of products using c-C6H12 or c-C6D12 as single substrate are the same. These results are consistent with initial rate-limiting formation of an active intermediate between [Mn(N)(CN)4]2- and H2O2 or CeIV, followed by H-atom abstraction from cyclohexane by the active intermediate. When PhCH2C(CH3)2OOH (MPPH) is used as oxidant for the oxidation of c-C6H12, the major products are c-C6H11OH, c-C6H10O, and PhCH2C(CH3)2OH (MPPOH), suggesting heterolytic cleavage of MPPH to generate a Mn=O intermediate. In the reaction of H2O2 with [Mn(N)(CN)4]2- in CF 3CH2OH, a peak at m/z 628.1 was observed in the electrospray ionization mass spectrometry, which is assigned to the solvated manganese nitrido oxo species, (PPh4)[Mn(N)(O)(CN)4] -·CF3CH2OH. On the basis of the experimental results the proposed mechanism for catalytic alkane oxidation by [MnV(N)(CN)4]2-/ROOH involves initial rate-limiting O-atom transfer from ROOH to [Mn(N)(CN)4]2- to generate a manganese(VII) nitrido oxo active species, [MnVII(N)(O) (CN)4]2-, which then oxidizes alkanes (R'H) via a H-atom abstraction/O-rebound mechanism. The proposed mechanism is also supported by density functional theory calculations.
- Ma, Li,Pan, Yi,Man, Wai-Lun,Kwong, Hoi-Ki,Lam, William W.Y.,Chen, Gui,Lau, Kai-Chung,Lau, Tai-Chu
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p. 7680 - 7687
(2014/06/10)
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- Synthesis, stability and reactivity of the first mononuclear nonheme oxoiron(iv) species with monoamido ligation: A putative reactive species generated from iron-bleomycin
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The preparation and characterisation of an oxoiron(iv) species with monoamido ligation are described. Reactivity studies revealed the important role of the amido ligand in enhancing the ability of oxoiron(iv) complexes to promote hydrogen atom transfer from external alkanes. the Partner Organisations 2014.
- Hitomi, Yutaka,Arakawa, Kengo,Kodera, Masahito
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supporting information
p. 7485 - 7487
(2014/07/07)
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- Formation of a room temperature stable Fev(o) complex: Reactivity toward unactivated c-h bonds
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An FeV(O) complex has been synthesized from equimolar solutions of (Et4N)2[FeIII(Cl)(biuret-amide)] and mCPBA in CH3CN at room temperature. The FeV(O) complex has been characterized by UV-vis, EPR, M?ssbauer, and HRMS and shown to be capable of oxidizing a series of alkanes having C-H bond dissociation energies ranging from 99.3 kcal mol-1 (cyclohexane) to 84.5 kcal mol-1 (cumene). Linearity in the Bell-Evans-Polayni graph and the finding of a large kinetic isotope effect suggest that hydrogen abstraction is engaged the rate-determining step.
- Ghosh, Munmun,Singh, Kundan K.,Panda, Chakadola,Weitz, Andrew,Hendrich, Michael P.,Collins, Terrence J.,Dhar, Basab B.,Sen Gupta, Sayam
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supporting information
p. 9524 - 9527
(2014/07/22)
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- Factors affecting migration of tertiary alkyl groups in reactions of alkylboronic esters with bromomethyllithium
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The reactions of bromomethyllithium with tert-alkylboronic esters could be of great potential for the formation of quaternary carbon centers but often give poor yields/conversions. Calculations and experimental evidence show that tert-alkyl groups migrate less effectively than other types of alkyl group in such reactions and that O-migration competes. Furthermore, slow/incomplete capture of the bromomethyl reagent by the boronic ester is a problem in more hindered systems, and an additional competing reaction, possibly Li-Br exchange on the bromomethylborate species, also leads to lower yields of migrated products. Based on this, experimental protocols have been devised in which the competing reactions are largely suppressed, leading to higher conversions to migrated product for several substrates.
- Elliott, Mark C.,Smith, Keith,Heulyn Jones,Hussain, Ajaz,Saleh, Basil A.
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p. 3057 - 3064
(2013/06/27)
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- Tuning a P450 enzyme for methane oxidation
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A new spin: The addition of chemically inert perfluoro carboxylic acids (green; see picture) to P450 enzymes results in dramatic activation of their catalytic activity as a result of the conversion of the Fe/heme from a low-spin to a high-spin state, and the reduction of the binding-pocket size. Together these effects allow otherwise inert substrates such as propane and even methane to be oxidized. Copyright
- Zilly, Felipe E.,Acevedo, Juan P.,Augustyniak, Wojciech,Deege, Alfred,Reetz, Manfred T.
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supporting information; experimental part
p. 2720 - 2724
(2011/06/10)
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- Alkane hydroxylation by a nonheme iron catalyst that challenges the heme paradigm for oxygenase action
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A nonheme iron catalyst catalyzed stereoselective oxidation of alkanes with H2O2 with remarkable efficiency and exhibiting an unprecedented high incorporation of water into the oxidized products. The present results challenge the canonical description of oxygenases, the standard oxo-hydroxo tautomerism that applies to heme systems and serves as a precedent for alternative pathways for the oxidation of hydrocarbons at nonheme iron oxygenases. Copyright
- Company, Anna,Gomez, Laura,Gueell, Mireia,Ribas, Xavi,Luis, Josep M.,Que Jr., Lawrence,Costas, Miquel
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p. 15766 - 15767
(2008/09/19)
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- Nonheme FeIVO Complexes That Can Oxidize the C-H Bonds of Cyclohexane at Room Temperature
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Nonheme oxoiron(IV) complexes of two pentadentate ligands, N4Py (N,N-bis(2-pyridylmethyl)-bis(2-pyridyl)methylamine) and Bn-tpen (N-benzyl-N,N′,N′-tris(2-pyridylmethyl)-1,2-diaminoethane), have been generated and found to have spectroscopic properties similar to the closely related tetradentate TPA (tris(2-pyridylmethyl)amine) complex reported earlier. However, unlike the TPA complex, the pentadentate complexes have a considerable lifetime at room temperature. This greater thermal stability has allowed the hydroxylation of alkanes with C-H bonds as strong as 99.3 kcal/mol to be observed at room temperature. Furthermore, a large deuterium KIE value is found in the oxidation of ethylbenzene. These observations lend strong credence to postulated mechanisms of mononuclear nonheme iron enzymes that invoke the intermediacy of oxoiron(IV) species. Copyright
- Kaizer, Jozsef,Klinker, Eric J.,Oh, Na Young,Rohde, Jan-Uwe,Song, Woon Ju,Stubna, Audria,Kim, Jinheung,Muenck, Eckard,Nam, Wonwoo,Que Jr., Lawrence
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p. 472 - 473
(2007/10/03)
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- Mechanism of ene reactions of singlet oxygen. A two-step no-intermediate mechanism
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The mechanism of the ene reaction of singlet (1Δg) oxygen with simple alkenes is investigated by a combination of experimental isotope effects and several levels of theoretical calculations. For the reaction of 2,4-dimethyl-3-isopropyl-2-pentene, the olefinic carbons exhibit small and nearly equal 13C isotope effects of 1.005-1.007, while the reacting methyl groups exhibit 13C isotope effects near unity. In a novel experiment, the 13C composition of the product is analyzed to determine the intramolecular 13C isotope effects in the ene reaction of tetramethylethylene. The new 13C and literature 2H isotope effects are then used to evaluate the accuracy of theoretical calculations. RHF, CASSCF(10e, 8o), and restricted and unrestricted B3LYP calculations are each applied to the ene reaction with tetramethylethylene. Each predicts a different mechanism, but none leads to reasonable predictions of the experimental isotope effects. It is concluded that none of these calculations accurately describe the reaction. A more successful approach was to use high-level, up to CCSD(T), single-point energy calculations on a grid of B3LYP geometries. The resulting energy surface is supported by its accurate predictions of the intermolecular 13C and 2H isotope effects and a very good prediction of the reaction barrier. This CCSD(T)//B3LYP surface features two adjacent transition states without an intervening intermediate. This is the first experimentally supported example of such a surface and the first example of a valley-ridge inflection with significant chemical consequences.
- Singleton, Daniel A.,Hang, Chao,Szymanski, Michael J.,Meyer, Matthew P.,Leach, Andrew G.,Kuwata, Keith T.,Chen, Jenny S.,Greer, Alexander,Foote, Christopher S.,Houk
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p. 1319 - 1328
(2007/10/03)
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- Direct formation of pinacols from olefins over various titano-silicates
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The epoxidation and successive pinacol formation of tri- and tetraalkyl-substituted olefins using Ti-β/H2O2/H2O as the catalytic system has been investigated. Aluminum-free Ti-β exhibits better activity and pinacol selectivity than TS-1, TS-2, Ti-MCM-22, and mesoporous Ti-MCM-41. Pinacol (vic-diol) is obtained as the major product with small amounts of the side products pinacolone, alcohol (via hydration), and oligomers. The conversion and pinacol selectivity increase with an increase in reaction temperature and time. The change in product distribution with reaction time over Ti-β shows that the epoxide is the initial product which undergoes a secondary reaction to give pinacol as the major product. The conversion and H2O2 selectivity decrease with the bulkiness of the substituents at the C=C bond but the selectivity of pinacol is not significantly affected. The reactivity of cyclic 1-methyl-1-cyclohexene is considerably lower than that of the corresponding open-chain analogue 2-methyl-2-butene. The symmetrical tetramethyl-substituted 2,3-dimethyl-2-butene led to the formation of small amount of dimers over medium-pore titanium silicates TS-1, TS-2, and Ti-MCM-22. The epoxidation of these substituted olefins proceeded more rapidly when using acetonitrile as a cosolvent than under triphase conditions. Mechanistically, the primary epoxide product undergoes acid-catalyzed nucleophilic ring opening by H2O molecules to give pinacol.
- Sasidharan,Wu, Peng,Tatsumi, Takashi
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p. 260 - 265
(2007/10/03)
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- Unusual rapid hydroboration of alkenes using diborane in chlorohydrocarbon solvents
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Diborane dissolves in chlorohydrocarbon solvents, such as dichloromethane, 1,2-dichloroethane and 1,1,2,2-tetrachloroethane to form ~0.5 M solutions of B2H6. In these solutions, diborane is in equilibrium with solvent-BH3 adducts (8-15%) and these solutions hydroborate representative olefins almost instantaneously, even at -16°C. The alcohol products can be obtained by standard oxidation of these organoboranes. (C) 2000 Elsevier Science Ltd.
- Kanth,Brown
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p. 9361 - 9364
(2007/10/03)
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- An Efficient Aerobic Oxidation of Isobutane to t-Butyl Alcohol by N-Hydroxyphthalimide Combined with Co(II) Species
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Highly selective aerobic oxidation of isobutane to t-butyl alcohol was successfully achieved by the use of a radical catalyst, N-hydroxyphthalimide (NHPI) in the presence of Co(II) salt under relatively mild conditions. The oxidation of isobutane by NHPI combined with Co(acac)2 under a pressure of air (10 atm) in benzonitrile at 100°C gave t-butyl alcohol in high yield (84%) along with acetone (13%). The reaction is thought to proceed via hydrogen abstraction from isobutane by the phthalimidooxyl radical (PINO). which seems to be a key active species. The formation of acetone can be explained by a partial β-scission of the t-butoxy radical, generated from the redox decomposition of t-butyl hydroperoxide by cobalt ion. Alkyl-substituted butanes and pentanes were difficult to be oxidized selectively under these conditions because of easy degradation to smaller fragments of the resulting alkoxyl radical intermediates.
- Sakaguchi, Satoshi,Kato, Susumu,Iwahama, Takahiro,Ishii, Yasutaka
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p. 1237 - 1240
(2007/10/03)
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- Hydration of olefins in excess water catalyzed by an insoluble cesium hydrogen salt of dodecatungstophosphoric acid
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A solid acid, Cs2.5H0.5PW12O40, efficiently catalyzed hydration of 2,3-dimethylbut-2-ene in excess water at 343 K, while typical oxide-based catalysts such as Nb2O5, SiO2-Al2O3, TiO2-SiO2, and SO42- / ZrO2 were almost inactive. The activity (per unit weight) of Cs2.5H0.5PW12O40 was found to be higher than those of liquid acids like H3PW12O40 and H2SO4, and of a commercial solid acid, H-ZSM-5, for hydration of cyclohexene.
- Okuhara, Toshio,Kimura, Mutsuko,Nakato, Teruyuki
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p. 839 - 840
(2007/10/03)
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- OH Radical Induced Oxidation of 2,3-Dimethylbutane in Air
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The product distribution resulting from the OH induced oxidation of 2,3-dimethylbutane in air was measured and compared with predictions based on a general reaction mechanism.Relative rates derived for the abstraction of primary and tertiary hydrogen atoms by OH radicals from the parent compound are 17percent and 83percent, respectively.The branching ratio for the alcohol versus alkoxyl radical producing pathsways of the self-reaction of 2-propylperoxy radicals was determined to be (0.61 +/- 0.08):(0.39 +/- 0.08); the corresponding ratio for the self-reaction of primary 2,3-dimethylbutylperoxy radicals is (0.56 +/- 0.07): 0.44 +/- 0.07).Large amounts of 2,3-dimethyl-2-hydroperoxybutane and small amounts of 2,3-dimethyl-2-butanol were found, the latter as a product of the cross combination reactions of 2,3-dimethyl-2-butylperoxy with 2-propylperoxy and 2,3-dimethyl-1-butylperoxy radicals.Rate constants of 3.5 * 10-17 and 2 * 10-16 cm-3/(molecule s), respectively, were estimated for these reactions with the help of computer simulations.
- Heimann, Gerald,Warneck, Peter
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p. 8403 - 8409
(2007/10/02)
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- Synthesis, Structure, Reactivity and Electrochemistry of cis-Dioxoruthenium-(VI) and -(V) Complexes containing N,N,N',N',3,6-Hexamethyl-3,6-diazaoctane-1,8-diamine
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The complexes cis-VILO2>2+, cis-VLO2>+ and cis-IIL(MeCN)2>2+ (L = N,N,N',N',3,6-hexamethyl-3,6-diazaoctane-1,8-diamine) have been prepared and their structures determined.The two Ru=O bonds in cis-VILO2>2+ are equivalent and the O-Ru-O angle is 112.0(4) deg.In cis-VLO2>+ the two Ru=O distances are 1.751(3) and 1.756(4) Angstroem, and the O-Ru-O angle is 115.1(2) deg.The N(MeCN)-Ru-N(MeCN) angle in cis-IIL(MeCN)2>2+ is 86.1(2) deg.The cyclic voltammogram of cis-VILO2>2+ in acetonitrile exhibits a reversible one-electron RuVI-RuV couple at 0.53 V vs.Ag-AgNO3 (0.1 mol dm-3).In aqueous solutions, proton-coupled electron-transfer redox couples are observed.This complex is capable of oxidizing a wide variety of organic substrates including 2,3-dimethylbutane and adamantane.Oxidation of saturated alkanes occured preferentially at the tertiary C-H bond.
- Li, Chi-Keung,Che, Chi-Ming,Tong, Wai-Fong,Tang, Wai-Tong,Wong, Kwok-Yin,Lai, Ting-Fong
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p. 2109 - 2116
(2007/10/02)
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- Enthalpies of Hydration of Alkenes. 4. Formation of Acyclic tert-Alcohols
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The enthalpies of hydration of a series of acyclic alkenes that lead to tert-alcohols were determined.Several pairs of alkenes that give the same alcohol were studied and gave the differences in enthalpy of formation of the alkenes.A consistent difference in Δ Hf of 1.84 kcal/mol was found between di- and trisubstituted alkenes.It was related to the difference in Δ Hf for pairs of exocyclic and endocyclic alkenes.The enthalpies of formation of the alcohols were obtained and were related to data for primary and secondary alcohols.
- Wiberg, Kenneth B.,Hao, Shide
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p. 5108 - 5110
(2007/10/02)
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- Syntheses, Electrochemistry and Reactivities of Pyridine Amide Complexes of Chromium(III) and Manganese(III)
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Reactions of anhydrous CrCl3 with H2bpb and H2bpc in dimethylformamide and manganese(III) acetate with H2bpc in methanol, yielded the respective *xH2O, *H2O and complexes.The electrochemistry of the chromium(III) amide complexes has been studied by cyclic voltammetry.They exhibit reversible oxidation couples with E0 values ranging from 0.28 to 0.80 V vs. ferrocenium-ferrocene.Except for (1-) which has a quasireversible reduction couple at -1.97 V, the electrochemical reductions are irreversible.The complexes ClO4, and have been shown to catalyse olefin epoxidation by iodosobenzene.With , catalytic oxidation of alkanes by PhIO has also been observed.An oxygen-rebound mechanism involving a Mn(V)=O or a Cr(V)=O intermediate is proposed for the PhIO oxidation reactions.
- Leung, Wa-Hung,Ma, Ji-Xiang,Yam, Vivian Wing-Wah,Che, Chi-Ming,Poon, Chung-Kwong
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p. 1071 - 1076
(2007/10/02)
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- Synthesis, Reactivities and Electrochemistry of trans-Dioxoruthenium(VI) Complexes of ?-Aromatic Diimines
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The synthesis and electrochemistry of trans-2 are described.Oxidation of trans-2+ by Ce(IV) in water gave trans-2 is a powerful oxidant with E0(Ru(VI)-Ru(IV)) = 1.0 V vs. saturated calomel electrode at pH 1.0.In acetonitrile or acetone, it oxidizes alcohols to ketones/aldehydes, tetrahydrofuran to γ-butyrolactone, alkenes to epoxides and saturated or aromatic hydrocarbons to alcohol/ketones.Oxidation of saturated alkanes occurs preferentially at the tertiary C-H bond.In the presence of CCl4, cyclohexane is oxidized to cyclohexyl chloride instead of cyclohexanone.The mechanisms of alcohol and cyclohexane oxidation were investigated by kinetic experiments and by isotope labelling studies.
- Che, Chi-Ming,Leung, Wai-Ho,Li, Chi-Keung,Poon, Chung-Kwong
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p. 379 - 384
(2007/10/02)
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- Mechanism of the Grignard Adddition Reaction. XVI. Homolytic and Concerted Mechanisms in the Reaction of α,β-Unsatureted Carbonyl Compounds with Grignard Reagents
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Kinetic measurements have shown that the addition of Grignard reagents to α,β-unsaturated carbonyl compounds takes place either by a concerted mechanism or by a homolytic mechanism.Phenylmagnesium bromide, which is incapable of homolysis, reacts rapidly in a 1,4-fashion if an s-cis conformation exists between the C=C and the C=O bonds, but only 1,2-addition takes place if the conformation is s-trans.tert-Butylmagnesium bromide is unsuited to the concerted reaction, but 1,4-addition takes place via homolysis.Primary and secondary Grignard reagents, like phenyl, react rapidly in a concerted manner with s-cis substrates, but unlike phenyl, these Grignard reagents may, with s-trans substrates, produce some 1,4-adduct via the homolytic mechanism.
- Holm, Torkil
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p. 925 - 929
(2007/10/02)
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- LiBH4-promoted Hydroboration of Alkenes with 1,3,2-Benzodioxaborole
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In the presence of a small amount of LiBH4 mono-, di-, tri- and tetr-substituted ethenes were hydroborated almost quantitatively with 1,3,2-benzodioxaborole (catecholborane) under very mild conditions.
- Arase, Akira,Nunokawa, Yutaka,Masuda, Yuzuru,Hoshi, Masayuki
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p. 205 - 206
(2007/10/02)
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- Oxidations by Methyl(trifluoromethyl)dioxirane. 2. Oxyfunctionalization of Saturated Hydrocarbons
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The reaction of methyl(trifluoromethyl)dioxirane (1b), a novel dioxirane species, with two open-chain, four cyclic, and five polycyclic saturated hydrocarbons and two aralkyl hydrocarbons in CH2Cl2/1,1,1-trifluoropropanone has been studied; under mild conditions (-22 to 0 deg C), it gives alcohols and/or ketones (deriving from further oxidation of secondary alcohols) in high yields and within very short reaction times.Primary C-H bonds are not appreciably oxidized and high regioselectivities were determined for attack at tertiary over secondary C-H bonds, with theexception of norbornane, which showed opposite regioselectivity.The reaction is also highly stereoselective, since hydroxylations of cis- and trans-decalin and of cis- and trans-1,2-dimethylcyclohexane were found to be in each case stereospecific with retention.From kinetic data, Ea = 14.3 kcal mol-1 and log A = 9.9 were estimated for cyclohexane oxidation.Relative rates change in the order cyclohexane (0.78) octane (9.2) adamantane (146); cis-1,2-dimethylcyclohexane was observed to be 7-fold more reactive than its trans isomer, demonstrating remarkable discrimination for equatorial vs axial C-H attack (also noticed in the case of cis- and trans-decalin).The relative rate of oxidation of cumene vs ethylbenzene was found to be ca. 3.1 (after statistical correction), i.e., in sharp excess over values usually recorded in classical radical H-atom abstraction from benzylic position.Rate constants determined for the reactions of cumene and of ethylbenzene show the title dioxirane (1b) is more reactive than dimethyldioxirane (1a) by factors of ca. 600 and over 700, respectively.The whole of theobservations is better accommodated by an "oxenoid" mechanism, involving concerted O-atom insertion by dioxirane into C-H bonds of hydrocarbons.
- Mello, Rossella,Fiorentino, Michele,Fusco, Caterina,Curci, Ruggero
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p. 6749 - 6757
(2007/10/02)
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- Homolytic Decomposition of t-Alkyl 2,2-Dimethylperoxypropionates
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Decomposition rates and products of t-alkyl 2,2-dimethylperoxypropionates were measured in cumene at several temperatures.The peroxyesters decomposed homolitycally, depending on the structure of the t-alkyl moiety.The relative rates of the t-alkyl moieties to the 1,1-dimethylethyl one were: 1,1-dimethylbutyl (1.14), 1,1-dimethylpropyl (1.19), 1,1,2-trimethylpropyl (1.85), 1,1,3,3-tetramethylbutyl (2.10), and 1,1-dimethyl-2-phenylethyl (2.34).The decomposition showed an isokinetic relationship and the importance of stabilization by hyperconjugation.Based on these data, the decomposition mechanism, which contains a slight stretching of the Cα-Cβ bond to the peroxyl oxygen at the transition state is, discussed.
- Komai, Takeshi,Matsuyama, Kazuo,Matsushima, Masaru
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p. 1641 - 1646
(2007/10/02)
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- Catalysis of Non-chain Olefin Oxidation Reactions by Metal Porphyrins
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Studies of the catalytic activity of metal porphyrins in the presence of a reducing agent towards the oxidation of olefins of different types are discussed.The factors which determine the catalytic properties of metal porphyrins in the presence of reducing agent in non-aqueous media are analysed.Mechanisms and a kinetic scheme are proposed, and used to calculate the rate constants of the separate steps.It is suggested that the oxidation of olefins in the presence of metal porphyrins and of a reducing agent is not a chain process.The catalytic properties of polymer catalysts containing metal porphyrins are described.
- Enikolopyan, N. S.,Solov'eva, A. B
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p. 1183 - 1193
(2007/10/02)
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- STUDIES ON THE CHEMISTRY OF DIOLS AND CYCLIC ETHERS-52. MECHANISM AND STEREOCHEMISTRY OF DEHYDRATION OF OXOLANES TO DIENES
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On γ-Al2O3, BPO4 and NaX zeolite, the dehydration of (+/-)-2,2,3,4,5,5-hexamethyloxolane (2) in the vapour phase leads to the formation of 2,3,4,5-tetramethyl-1,5-hexadiene (8) in a slow process, while meso-2,2,3,4,5,5-hexamethyloxolane (3) is converted to 2,3,4,5-tetramethyl-2,4-hexadiene (7) with high selectivity in a fast reaction.These differences in reaction rate and selectivity indicate that the dehydration of 2 takes place by an E2 mechanism.In contrast, the steric strain in 3 results in ring opening by an E1 mechanism.These conclusions are supported by the nonselective transformations of 2,2,5,5-tetramethyloxolane (1) and 2,2,6,6-tetramethyloxane (4), and the dehydration of 1, 2 and 3 in the presence of formic acid in the liquid phase.The experimental observation prove that both the reactivity and the reaction directions in the dehydration of stereoisomeric oxolanes are determined by steric factors.
- Molnar, Arpad,Bartok, Mihaly
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p. 131 - 142
(2007/10/02)
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- Photoinduced Nitrene, Carbene, and Atomic Oxygen Transfer Reactions Starting from the Corresponding Pyridinium N-, C-, and O-Ylides
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Ultraviolet irradiation of the pyridinium ylides 1, 2, and 3 led to fragmentation of the exocyclic polar bonds, as well as to skeletal rearrangements.The photoinduced fragmentation processes gave the corresponding pyridines and highly reactive intermediates, i. e. ethoxycarbonylnitrene, dicyanocarbene and atomic oxygen (oxene), respectively.Trapping of the reactive intermediates by alkanes and alkenes permitted the determination of their spin multiplicity.Ethoxycarbonylnitrene was in its triplet ground state at the moment of its formation.Dicyanocarbene occurred as a mixture of singlet and triplet, as determined by dilution experiments with variable amounts of alkenes.As to atomic oxygen, all collected data point to its formation in solution in its triplet ground state.
- Strub, Henri,Strehler, Christiane,Streith, Jacques
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p. 355 - 364
(2007/10/02)
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- Shape Selective Alkane Hydroxylation by Metalloporphyrin Catalysts
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A series of manganese and iron porphyrins with sterically protected pockets are shown to be shape selective alkane hydroxylation catalysts.With iodosobenzene as oxidant, good regioselectivity is observed for hydroxylation of alkanes at the least hindered methyl group by using the very sterically hindered (5,10,15,20-tetrakis(2',4',6'-triphenylphenyl)porphyrinato)manganese(III) acetate (MnTTPPP(OAc)) as catalyst; The moderately hindered (5,10,15,20-tetrakis(2',4',6'-trimethoxyphenyl)porphyrinato)manganese(III) acetate shows little selectivity toward terminal CH3 hydroxylation but does show enhancement for the adjacent, ω - 1, CH2 site.Primary selectivity is dependent on the size and shape of the alkane substrate, with more bulky substituents giving greater primary selectivity.Substituting pentafluoroiodosobenzene or m-chloroperbenzoic acid as oxidants yields similar selectivity, thus conclusively demonstrating metal based oxidation via a common intermediate for these three systems.In contrast, tert-butyl hydroperoxide or 2,2,2-trifluoroethanol solubilized pentafluoroiodosobenzene show no primary carbon selectivity, and reaction product ratios are independent of the metalloporphyrin catalyst; this demonstrates that the site of oxidation with these oxidants is not metal based.The iron porphyrin derivatives also show good primary selectivity, although to a lesser degree than with the Mn derivatives, proving that these oxidations too are metal based.The regioselectivities for alkane hydroxilation shown by TTPPP derivatives are comparable to or better than those found for some isozymes of cytochrome P-450 which are responsible for primary alcohol biosynthesis from steroids, fatty acids, and alkanes.
- Cook, Bruce R.,Reinert, Thomas J.,Suslick, Kenneth S.
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p. 7281 - 7286
(2007/10/02)
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- ORGANOBORANES FOR SYNTHESIS. 5. STOICHIOMETRICALLY CONTROLLED REACTION OF ORGANOBORANES WITH OXYGEN UNDER MILD CONDITIONS TO ACHIEVE QUANTITATIVE CONVERSION TO ALCOHOLS
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The reaction of organoboranes with oxygen under mild conditions can be controlled to give an essentially quantitative conversion of all three alkyl groups on boron to the corresponding alcohol.The controlled oxidation is a very clean reaction, with only minor amounts of carbonyl and hydrocarbon products formed.All organoboranes react quite rapidly in the initial stages, but vary considerably in the time required to achieve the desired uptake of oxygen.In contrast to oxidation by alkaline hydrogen peroxide, a portion of this reaction proceeds through alkyl radicals, thus resulting in some loss of stereospecificity.Oxidation of mixed organoboranes reveals that the relative rates of oxidation of alkyl groups on boron are consistent with a radical mechanism, with tertiary > secondary > primary in the rate of oxidation.The selective oxidation of one alkyl group in the presence of the other is not possible, due to small differences in relative rates of oxidation.However, thexyl and cyclohexyl groups can be selectively removed from boron in the presence of alkenyl groups.Thus, controlled oxidation of thexyldialkenylborane affords pure dialkenylborinic acid.
- Brown, Herbert C.,Midland, M. Mark,Kabalka, George W.
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p. 5523 - 5530
(2007/10/02)
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- Shape-selective Alkane Hydroxylation
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A series of sterically hindered manganese porphyrins have been used to catalyse shape-selective alkane hydroxylation, increasing the production of primary alcohols.
- Suslick, Kenneth,Cook, Bruce,Fox, Mary
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p. 580 - 582
(2007/10/02)
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- Solvomercuration-Demercuration. 11. Alkoxymercuration-Demercuration of Representative Alkenes in Alcohol Solvents with the Mercuric Salts Acetate, Trifluoroacetate, Nitrate, and Methanesulfonate
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The alkoxymercuration-demercuration of seven representative olefins with the mercuric salts acetate, trifluoroacetate, nitrate, and methanesulfonate, in methyl, ethyl, isopropyl, and tert-butyl alcohols was examined.Mercuric acetate was effective only in methanol and ethanol.On the other hand, mercuric trifluoroacetate was effective in all four solvents, giving in most cases high yields of the corresponding ethers.Both mercuric nitrate and mercuric methanesulfonate were effective in methanol, ethanol, and 2-propanol.However, in several cases poor selectivity for the ether was observed, as evidenced by the formation of significant amounts of side products.Both electronic and steric effects are important factors in the reaction.Moreover, the structure of the olefin has a pronounced effect, both on the types of oxymercurials formed and on their stability to the reaction conditions.
- Brown, Herbert C.,Kurek, Joseph T.,Rei, Min-Hon,Thompson, Kerry L.
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p. 2551 - 2557
(2007/10/02)
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- Catalytic Replacement of Unactivated Alkane Carbon-Hydrogen Bonds with Carbon-X Bonds (X = Nitrogen, Oxygen, Chlorine, Bromine, or Iodine). Coupling of Intermolecular Hydrocarbon Activation by MnIIITPPX Complexes with Phase-Transfer Catalysis
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A simple system has been devised to facilitate the first processes for the catalytic replacement of unactivated alkane C-H bonds with C-X bonds, X = nitrogen and iodine.The system also enables alkane C-H bonds to be replaced by C-X bonds, X = chlorine, bromine, and oxygen.The system is composed of two liquid phases and the oxidant iodosylbenzene (iodosobenzene).The alkane substrate, the MnIIITPPX catalyst, and the organic solvent (dichloromethane, chlorobenzene, or other aromatic hydrocarbon) constitute one phase, a saturated aqueous solution of the sodium salt of the anion to be incorporated into the alkane, NaX, X = N3(1-), NCO(1-), I(1-), Br(1-), or Cl(1-), constitutes the second phase, and the sparingly soluble oxidant iodosylbenzene constitutes a third phase.When the two liquid phases and the oxidant iodosylbenzene are stirred under an inert atmosphere, both RX and ROH products are produced catalytically based on MnTPP and in reasonable yield based on iodosylbenzene.The MnTPP moiety functions as a catalyst for C-H bond cleavage and for phase transfer of X(1-) from the aqueous phase to the organic phase where the functionalization chemistry takes place.The oxidant hypochlorite can be used in place of, but is less effective than, iodosylbenzene, and the oxidants hydrogen peroxide, periodate, and persulfate are ineffective.Product distributions obtained from the oxidation of cyclohexane, isobutane, 2,3-dimethylbutane, and tert-butylbenzene are most consistent with a product-determining step that involves transfer of X from manganese to a free alkyl radical intermediate.
- Hill, Craig L.,Smegal, John A.,Henly, Timothy J.
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p. 3277 - 3281
(2007/10/02)
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- Hydroboration. 59. Thexylchloroborane-Methyl Sulfide. A New Stable Monohydroborating Agent with Exceptional Regioselectivity
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Under selected conditions, the hydroboration of 2,3-dimethyl-2-butene with 1 equiv of BH2Cl*SMe2 proceeds cleanly in solution (CH2Cl2, ClCH2CH2Cl, Et2O) or under neat conditions to give exclusively the monohydroboration product, thexylchloroborane-methyl sulfide (ThxBHCl*SMe2).Stock solutions of ThxBHCl*SMe2 in CH2Cl2 or Et2O have unusual thermal stability at ambient temperatures or below.The hydroboration of reactive olefins, such as terminal or unhindered disubstituted alkenes, with ThxBHCl*SMe2 proceeds quantitatively with high regiospecificity in CH2Cl2,ClCH2CH2Cl, Et2O, and THF to produce isomerically pure thexylalkylchloroborane intermediates.Subsequent oxidation produces the desired alcohols in nearly quantitative yield with high regiospecificity.With less reactive olefins, such as 1-methylcyclopentene, cyclohexene, or α-pinene, 11B NMR showed that the desired thexylalkylchloroborane products were contaminated with alkyldichloroborane species, indicating that a significant amount of product redistribution had occured.This was reflected in a lower observed regioselectivity in the hydroboration of some less reactive alkenes with ThxBHCl*SMe2.
- Brown, Herbert C.,Sikorski, James A.,Kulkarni, Surendra U.,Lee, Hsiupu D.
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p. 863 - 872
(2007/10/02)
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- Hydroboration of Sterically Hindered Olefins under High Pressure
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Hydroboration of sterically hindered olefins such as tetramethylethylene, tetraisopropylethylene, trans-1,2-di-tert-butylethylene, and 1,2-dimethyldi-tert-butylethylene has been investigated at high pressure (6000 atm).The previously unknown trithexylborane was prepared.The boron of trithexylborane was found to be isomerized much faster to a terminal carbon than that of dithexyl- and thexylboranes. trans-1,2-Di-tert-butylethylene yields a monoalkylborane at both 1 atm and high pressure (5000-6000 atm).Evidence is presented that is consistent with the hypothesis thata multialkylborane is formed at high pressure that dissociates without an isomerization upon releasing the pressure to 1 atm.Tetraisopropylethylene was found to give no hydroborated products at 1 atm or at high pressure (3500-6000 atm). (E)- and (Z)-1,2-Dimethyldi-tert-butylethylene was prepared, characterized, and hydroborated.A monoalkylborane is formed at 1 atm.At high pressure a trialkylborane is formed, which after returning to 1 atm, yields mainly the isomerized borane. 5β-Chol-9(11)-ene was synthesized from deoxycholic acid.This was found to yield a monoalkylborane after hydroboration at 1 atm or high pressure, in contrast to a literature report for a structurally similar steroid.An isomerized olefin was isolated after oxidation of the steroidal borane.
- Rice, Joseph E.,Okamoto, Yoshiyuki
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p. 4189 - 4194
(2007/10/02)
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- Solvomercuration-Demercuration. 10. Oxymercuration-Demercuration of Olefins with the Mercuric Salts Acetate, Trifluoroacetate, Nitrate, and Methanesulfonate
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The oxymercuration-demercuration of a series of representative olefins has been examined with four mercuric salts: acetate, trifluoroacetate, nitrate, and methanesulfonate.Mono- and 1,2-disubstituted olefins undergo hydration with all four mercuric salts in 90-100percent yields with a regioselectivity for the Markovnikov alcohol (from monoolefins) of >99.5percent.Only styrene was found to be an exception.In marked contrast, only mercuric acetate is effective for the Markovnikov hydration of 1,1-di-, tri- ,and tetrasubstituted olefins.The other three mercuric salts provide loweryields of the tertiary alcohols, yields which decrease rapidly with time. 1-Phenylcyclopentene undergoes only allylic oxidation with the mercuric salts trifluoroacetate, nitrate, and methanesulfonate.Mercuric acetate does give the normal hydration product but only in trace amounts.In this case, allylic oxidation is the major reaction pathway with this salt as well.
- Brown, Herbert C.,Geoghegan, Philip J.,Kurek, Joseph T.
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p. 3810 - 3812
(2007/10/02)
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- Stereochemistry of Aliphatic Carbocations, 14. Alkyl Shifts from Secondary to Primary Carbon Atoms
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Alkyl shifts from secondary to primary carbon atoms have been induced by the nitrous acid deamination of suitable amines (4, 22, 39, 51); they include sequential rearrangements (-CH3,CH3 and -CH3,H).Predominant although incomplete inversion at the migration origin has been observed (Me 70percent, Et 62-64percent, nPr 65percent, iPr 64percent, tBu 55percent).Our results require the intervention of open secondary carbocations which may be preceded by less stable bridged intermediates.
- Kirmse, Wolfgang,Guenther, Bernd-Rainer,Knist, Johannes,Kratz, Sigrid,Loosen, Karin,et al.
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p. 2127 - 2139
(2007/10/02)
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- Cp2TiCl2-catalyzed grignard reactions. 2. Reactions with ketones and aldehydes
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The reaction of Grignard reagents with ketones or aldehydes in the presence of a catalytic amount of Cp2TiCl2 leads to the corresponding reduction products in high yields. Cp2TiH intermediate was proposed to account for this observation.
- Sato, Fumie,Jinbo, Takamasa,Sato, Masao
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p. 2171 - 2174
(2007/10/02)
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