- Oxygen Transfer by Dialkylperoxonium Ions
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Oxygen-transfer from dialkylperoxonium ions R2O+OH has been demonstrated for three such species, where R2 is a hydrocarbon chain or ring, by oxidation of several dialkyl sulfoxides, methyl phenyl sulfide, and the succinimide anion, with concurrent formation of the corresponding cyclic or bicyclic ether R2O.
- Bloodworth, A. J.,Melvin, T.,Mitchell, John C.
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- Rule of five cyclizations in 5-hexenyl radicals and photocycloadditions of 1,5-hexadienes: Effect of 4-oxa substitution
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The effect of 4-oxa substitution on the regiochemistry and rate of 5-hexenyl radical cyclizations was investigated, as a potential model for [2 + 2] photocycloadditions of 2-acyl-4-oxa-1,5-hexadienes. Increasing the electron density in the alkene decreases the rate of cyclization in the 4-oxa-hexejiyl radicals, relative to the all carbon analogs, but has little effect on the regioselectivity of the cyclization. The radical model does not reproduce the high degree of 1,6 closure, observed in the [2 + 2] photocycloadditions for 4-oxa-1,5-hexadiene la. However, the radical model does reinforce the interpretation that ground state conformational effects, engendered by substitution remote from the reacting centers have important rate consequences for cyclization reactions. Copyright
- Matlin, Albert R.,Brinton, Karen Feit,Nivaggioli, Belinda Tsao
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- Cyclization of 4-Hydroxy-4-methyl-1-pentyl p-Toluenesulfonate as a Model to Evaluate Inherent Medium Effect on SN2 Solvolysis
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Solvent effect on the cyclization of 4-hydroxy-4-methyl-1-pentyl p-toluenesulfonate, a mechanistic equivalent to the SN2 solvolysis, was successfully analyzed by Taft LSER equation as log k=3.2?*+1.4α+1.9β-8.36, indicating that three independent factors are operative, i.e., solvent polarity and H-bond donor ability which promote ionization, and H-bond acceptor ability which enhances nucleophilicity of the internal OH group.
- Shimizu, Nobujiro,Tsutsumi, Toru,Tsuno, Yuho
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- Catalytic formation of C-O bonds by alkene activation: Lewis acid-cycloisomerisation of olefinic alcohols
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Tin(IV) trifluoromethanesulfonate has been found to be an excellent catalyst for the cycloisomerisation of non-activated and differently substituted olefinic alcohols to cyclic ethers. The Royal Society of Chemistry 2005.
- Coulombel, Lydie,Favier, Isabelle,Dunach, Elisabet
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- Water opens the door to organolithiums and Grignard reagents: Exploring and comparing the reactivity of highly polar organometallic compounds in unconventional reaction media towards the synthesis of tetrahydrofurans
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It has always been a firm conviction of the scientific community that the employment of both anhydrous conditions and water-free reaction media is required for the successful handling of organometallic compounds with highly polarised metal-carbon bonds. Herein, we describe how, under heterogeneous conditions, Grignard and organolithium reagents can smoothly undergo nucleophilic additions to γ-chloroketones, on the way to 2,2-disubstituted tetrahydrofurans, "on water", competitively with protonolysis, under batch conditions, at room temperature and under air. The reactivity of the above organometallic reagents has also been investigated in conventional anhydrous organic solvents and in bio-based eutectic and low melting mixtures for comparison. The scope and limitations of this kind of reaction are discussed.
- Cicco, Luciana,Sblendorio, Stefania,Mansueto, Rosmara,Perna, Filippo M.,Salomone, Antonio,Florio, Saverio,Capriati, Vito
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p. 1192 - 1199
(2016/02/09)
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- METHOD FOR PREPARING TRIOLS AND DIOLS FROM BIOMASS-DERIVED REACTANTS
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A method to make triols and diols is described. The method includes the steps of performing an aqueous-phase hydrodeoxygenation reaction on a feedstock containing a biomass-derived reactant in aqueous solution. The feedstock is contacted with a heterogeneous metal-containing bifunctional catalyst or a combination of two or more heterogeneous metal-containing catalysts that catalyze cleavage of C—C and C—O bonds, for a time, temperature, pressure, and weight hourly space velocity to yield a product mix comprising triols, diols, or combinations thereof.
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Paragraph 0092; 0093
(2014/09/30)
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- Experimental investigation of the low temperature oxidation of the five isomers of hexane
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The low-temperature oxidation of the five hexane isomers (n-hexane, 2-methyl-pentane, 3-methyl-pentane, 2,2-dimethylbutane, and 2,3-dimethylbutane) was studied in a jet-stirred reactor (JSR) at atmospheric pressure under stoichiometric conditions between 550 and 1000 K. The evolution of reactant and product mole fraction profiles were recorded as a function of the temperature using two analytical methods: gas chromatography and synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). Experimental data obtained with both methods were in good agreement for the five fuels. These data were used to compare the reactivity and the nature of the reaction products and their distribution. At low temperature (below 800 K), n-hexane was the most reactive isomer. The two methyl-pentane isomers have about the same reactivity, which was lower than that of n-hexane. 2,2-Dimethylbutane was less reactive than the two methyl-pentane isomers, and 2,3-dimethylbutane was the least reactive isomer. These observations are in good agreement with research octane numbers given in the literature. Cyclic ethers with rings including 3, 4, 5, and 6 atoms have been identified and quantified for the five fuels. While the cyclic ether distribution was notably more detailed than in other literature of JSR studies of branched alkane oxidation, some oxiranes were missing among the cyclic ethers expected from methyl-pentanes. Using SVUV-PIMS, the formation of C 2-C3 monocarboxylic acids, ketohydroperoxides, and species with two carbonyl groups have also been observed, supporting their possible formation from branched reactants. This is in line with what was previously experimentally demonstrated from linear fuels. Possible structures and ways of decomposition of the most probable ketohydroperoxides were discussed. Above 800 K, all five isomers have about the same reactivity, with a larger formation from branched alkanes of some unsaturated species, such as allene and propyne, which are known to be soot precursors.
- Wang, Zhandong,Herbinet, Olivier,Cheng, Zhanjun,Husson, Benoit,Fournet, Rene,Qi, Fei,Battin-Leclerc, Frederique
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p. 5573 - 5594
(2014/08/18)
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- Calcium catalyzed hydroalkoxylation
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A calcium catalyzed intramolecular hydroalkoxylation reaction is presented, as a transition metal free, inexpensive, and very mild process for the highly atom economic formation of cyclic ethers from γ,δ-unsaturated alcohols. In contrast to most of the previously reported procedures, room temperature conditions are fully sufficient in most cases for a high yielding cycloisomerization in the presence of a combination of 5 mol-% Ca(NTf 2)2 and 5 mol-% Bu4NPF6. Full regioselectivity is observed in all transformations.
- Kena Diba, Anastasie,Begouin, Jeanne-Marie,Niggemann, Meike
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supporting information
p. 6629 - 6632,4
(2012/12/13)
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- Calcium catalyzed hydroalkoxylation
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A calcium catalyzed intramolecular hydroalkoxylation reaction is presented, as a transition metal free, inexpensive, and very mild process for the highly atom economic formation of cyclic ethers from γ,δ-unsaturated alcohols. In contrast to most of the previously reported procedures, room temperature conditions are fully sufficient in most cases for a high yielding cycloisomerization in the presence of a combination of 5 mol-% Ca(NTf 2)2 and 5 mol-% Bu4NPF6. Full regioselectivity is observed in all transformations.
- Kena Diba, Anastasie,Begouin, Jeanne-Marie,Niggemann, Meike
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supporting information
p. 6629 - 6632
(2013/01/15)
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- Efficient intramolecular hydroalkoxylation of unactivated alkenols mediated by recyclable lanthanide lriflate ionic liquids: Scope and mechanism
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Lanthanide triflate complexes of the type [Ln(OTf)3] (Ln = La, Sm, Nd, Yb, Lu) serve as effective, recyclable catalysts for the rapid intramolecular hydroalkoxylation (HO)/cyclization of primary/secondary and aliphatic/aromatic hydroxyalkenes in imidazolium-based room-temperature ionic liquids (RTILs) to yield the corresponding furan, pyran, spirobicyclic furan, spirobicyclic furan/pyran, benzofuran, and isochroman derivatives. Products are straightforwardly isolated from the catalytic solution, conversions exhibit Markovnikov regioselectivity, and turnover frequencies are as high as 47 h -1 at 120°C. The ring-size rate dependence of the primary alkenol cyclizations is 5>6, consistent with a sterically controlled transition state. The hydroalkoxylation/cyclization rates of terminal alkenols are slightly more rapid than those of internal alkenols, which suggests modest steric demands in the cyclic transition state. Cyclization rates of aryl-functionalized hydroxyalkenes are more rapid than those of the linear alkenols, whereas five- and five/six-membered spirobicyclic skeletons are also regioselectively closed. In cyclization of primary, sterically encumbered alkenols, turnoverfrequency dependence on metal-ionic radius decreases by approximately 80fold on going from La3+ (1.160 A) to Lu3+ (0.977 A), presumably reflecting steric impediments along the reaction coordinate. The overall rate law for alkenol hydroalkoxylation/cyclization is v≈[catalys] 1[alkenol]1. An observed ROH/ROD kinetic isotope effect of 2.48 (9) is suggestive of a catalytic pathway that involves kinetically significant intramolecular proton transfer. The present activation parameters-enthalpy (ΔH≠) = 18.2 (9) Kcal mol-1, entropy (ΔS≠) = -17.0 (1.4) eu, and energy (E,) = 18.2 (8) kcal mol-1-suggest a highly organized transition state. Proton scavenging and coordinative probing results suggest that the lanthanide inflates are not simply precursors of free triflic acid. Based on the kinetic and mechanistic evidence, the proposed catalytic pathway invokes hydroxyl and olefin activation by the electron-deficient Ln3+ center, and intramolecular H+ transfer, followed by alkoxide nucleophilic attack with ring closure.
- Dzudza, Alma,Marks, Tobin J.
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supporting information; experimental part
p. 3403 - 3422
(2010/06/21)
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- Copper-catalysed intramolecular O-H addition to unactivated alkenes
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Intramolecular cyclisation of ω-alkenoic acids and alkenols can be achieved using a catalytic amount of Cu(OTf)2 to afford lactones and cyclic ethers, offering a practical alternative to existing catalysts.
- Adrio, Luis A.,Quek, Louisa Shuyi,Taylor, Jason G.,Kuok (Mimi) Hii, King
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experimental part
p. 10334 - 10338
(2010/02/28)
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- On the 6-endo selectivity in 4-penten-1-oxyl radical cyclizations
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Regioselectivities in cyclizations of 4-substituted 4-penten-1-oxyl radicals have been investigated in a combined experimental and computational study (density functional theory). The progressive increase of the 6-endo-trig selectivity along the series of 4-substituents H 3 3)3 6H5 has been interpreted to originate from a balance between strain and FMO interactions. Torsional strain, which is associated with geometrical changes upon an approach of the reacting entities, is relevant for the 6-endo-trig but not for the 5-exo-trig reactions, as seen, for instance, in selective tetrahydrofuran formation from the 4-penten-1-oxyl radical and its 4-methyl derivative. The preference for tetrahydropyran formation in cyclizations of the 4-tert-butyl and the 4-phenyl-4-penten-1-oxyl radical has been attributed to FMO interactions between the terminal carbon atom of the π bond and the O-radical center thus favoring the 6-endo-trig reaction on the basis of lower transition state energies.
- Hartung, Jens,Kneuer, Rainer,Rummey, Christian,Bringmann, Gerhard
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p. 12121 - 12129
(2007/10/03)
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- Lithium diisopropylamide solvated by monodentate and bidentate ligands: Solution structures and ligand binding constants
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6Li and 15N NMR spectroscopic studies of lithium diisopropylamide ([6Li]LDA and [6Li,15N]LDA) in toluene/pentane solutions containing a variety of mono- and polydentate ligands are reported. LDA forms exclusively dimers in the presence of n-BuOMe, Et2O, t-BuOMe, THF, 2- methyltetrahydrofuran, 2,2-dimethyltetrahydrofuran, tetrahydropyran, dimethoxyethane, N,N,N',N'-tetramethylethylenediamine, and MeOCH2CH2NR2 (NR2 = NMe2, NEt2, pyrrolidino). Addition of 1,2-dipyrrolidinoethane and (2-pyrrolidinoethyl)dimethylamine provides monomer-dimer mixtures. Treatment of LDA with trans-N,N,N',N'-tetramethylcyclohexanediamine (TMCDA) or trans- 1-(dimethyl-amino)-2-isopropoxycyclohexane in hydrocarbons afford exclusively monomers. Sparteine binds only reluctantly, giving a mixture of unsolvated oligomers and monomer. Competitions of the ethereal ligands vs TMCDA afford binding constants and associated free energies for dimer solvation which are correlated with those obtained previously for lithium hexamethyldisilazide.
- Remenar, Julius F.,Lucht, Brett L.,Collum, David B.
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p. 5567 - 5572
(2007/10/03)
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- Mechanistic Aspects of Oxygen Transfer by gem-Dialkylperoxonium Ions
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Monocyclic gem-dialkylperoxonium ion 2 has been generated from the reaction of 1-bromo-4-hydroperoxy-4-methylpentane (1) with silver tetrafluoroborate or trifluoroacetate, and related bicyclic ion 4 has been formed from the reaction of 5-hydroxyperoxycyclooctene (3) with N-bromosuccinimide.These species have been shown to oxidize efficiently both dialkyl sulfoxides and methyl phenyl sulfide.Reaction with thianthrene 5-oxide afforded XNu values of 0.10 for 2 and 0.72 for 4, while competition reactions with (p-XC6H4)2SO (X=Me, H, F, and Cl) yielded Hammett ρ values (versus ?) of -0.83+/-0.11 and -1.77+/-0.58.These results indicate that gem-dialkylperoxonium ion salts,R2O+-OH,X-, are electrophilic oxygen transfer reagents, tunable to some extent by choice of R1, R2, and X, but provide no evidence of deprotonation to the corresponding dioxygen ylide under the conditions studied.
- Bloodworth, A. J.,Melvin, T.,Mitchell, John C.
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p. 1078 - 1082
(2007/10/02)
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- Oxonium Ions. Solvation by Single Acetonitrile Molecules in the Gas Phase and by Bulk Solvents
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The standard free energy of formation of gaseous complexes between monoprotonic oxonium ions and acetonitrile have been obtained by using the ion cyclotron resonance equilibrium constant method for exchange of acetonitrile between the ions.The results show that the "solvation" by a single molecule of acetonitrile in the gas phase reproduces the important diverse effects of molecular structure on oxonium ion solvation by bulk water.It is estimated from the present results that the effects of solvation by bulk water are only about three times as great as the corresponding effects of "solvation" by a single water molecule in the gas phase.Internal charge delocalization from the protonic site of the oxonium ions may be reversed by differential solvation, both with single H-bonding molecules in the gas phase and with bulk solvent.Further evidence for the site of preffered protonation of esters and amides is provided.
- Bromilow, J.,Abboud, J. L. M.,Lebrilla, C. B.,Taft, R. W.,Scorrano, G.,Lucchini V.
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p. 5448 - 5453
(2007/10/02)
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