- Raman spectroscopic study of allyl methyl ether (3-methoxy-1-propene), CH2=CHCH2OCH3, and some isotopically labelled analogues
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Fourier-transform Raman spectra of allyl methyl ether, CH2=CHCH2OCH3, three deuterated derivatives and one 13C derivative have been obtained.Comparison of the spectra of the deuterated and protiated compounds in conjunction with polarization data has enabled full vibrational assignments to be made for the carbon-hydrogen modes and the 13C data have identified some skeletal modes of the CO and CC bonds.As a result of the data obtained from the deuterated compounds in particular, some initial suggestions have been revised for tentative literature assignments of molecules of biological interest.In other cases, confirmation of existing assignments have been made.
- Bowen, R. D.,Edwards, H. G. M.,Farwell, D. W.
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Read Online
- Controlling the Lewis Acidity and Polymerizing Effectively Prevent Frustrated Lewis Pairs from Deactivation in the Hydrogenation of Terminal Alkynes
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Two strategies were reported to prevent the deactivation of Frustrated Lewis pairs (FLPs) in the hydrogenation of terminal alkynes: reducing the Lewis acidity and polymerizing the Lewis acid. A polymeric Lewis acid (P-BPh3) with high stability was designed and synthesized. Excellent conversion (up to 99%) and selectivity can be achieved in the hydrogenation of terminal alkynes catalyzed by P-BPh3. This catalytic system works quite well for different substrates. In addition, the P-BPh3 can be easily recycled.
- Geng, Jiao,Hu, Xingbang,Liu, Qiang,Wu, Youting,Yang, Liu,Yao, Chenfei
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p. 3685 - 3690
(2021/05/31)
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- Deoxygenation of Epoxides with Carbon Monoxide
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The use of carbon monoxide as a direct reducing agent for the deoxygenation of terminal and internal epoxides to the respective olefins is presented. This reaction is homogeneously catalyzed by a carbonyl pincer-iridium(I) complex in combination with a Lewis acid co-catalyst to achieve a pre-activation of the epoxide substrate, as well as the elimination of CO2 from a γ-2-iridabutyrolactone intermediate. Especially terminal alkyl epoxides react smoothly and without significant isomerization to the internal olefins under CO atmosphere in benzene or toluene at 80–120 °C. Detailed investigations reveal a substrate-dependent change in the mechanism for the epoxide C?O bond activation between an oxidative addition under retention of the configuration and an SN2 reaction that leads to an inversion of the configuration.
- Maulbetsch, Theo,Jürgens, Eva,Kunz, Doris
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p. 10634 - 10640
(2020/07/30)
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- Piperazine-promoted gold-catalyzed hydrogenation: The influence of capping ligands
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Gold nanoparticles (NPs) combined with Lewis bases, such as piperazine, were found to perform selective hydrogenation reactions via the heterolytic cleavage of H2. Since gold nanoparticles can be prepared by many different methodologies and using different capping ligands, in this study, we investigated the influence of capping ligands adsorbed on gold surfaces on the formation of the gold-ligand interface. Citrate (Citr), poly(vinyl alcohol) (PVA), polyvinylpyrrolidone (PVP), and oleylamine (Oley)-stabilized Au NPs were not activated by piperazine for the hydrogenation of alkynes, but the catalytic activity was greatly enhanced after removing the capping ligands from the gold surface by calcination at 400 °C and the subsequent adsorption of piperazine. Therefore, the capping ligand can limit the catalytic activity if not carefully removed, demonstrating the need of a cleaner surface for a ligand-metal cooperative effect in the activation of H2 for selective semihydrogenation of various alkynes under mild reaction conditions.
- Barbosa, Eduardo C. M.,Camargo, Pedro H. C.,Fiorio, Jhonatan L.,Hashmi, A. Stephen K.,Kikuchi, Danielle K.,Rossi, Liane M.,Rudolph, Matthias
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p. 1996 - 2003
(2020/04/22)
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- A HPPO by-product recycling synthetic 1, 3 - propanediol (by machine translation)
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The invention belongs to the technical field of organic chemical industry, relates to a HPPO by-product recycling synthetic 1, 3 - propanediol, more specifically, relates to a propylene HPPO process with methanol the reaction product of propylene glycol monomethyl ether as the raw material, and sequentially passes through the dewatering, borohydrite oxidation, hydrolysis of the three-step reaction synthesizes the high value added 1, 3 - propylene glycol, 1, 3 - propylene glycol total yield of 80% or more, purity 99.5% or more, the invention has the simple process route, rationalization of resources use, 1, 3 - propylene glycol yield and purity and the like. (by machine translation)
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Paragraph 0030-0035
(2019/07/04)
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- Accessing Frustrated Lewis Pair Chemistry through Robust Gold@N-Doped Carbon for Selective Hydrogenation of Alkynes
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Pyrolysis of Au(OAc)3 in the presence of 1,10-phenanthroline over TiO2 furnishes a highly active and selective Au nanoparticle (NP) catalyst embedded in a nitrogen-doped carbon support, Au@N-doped carbon/TiO2 catalyst. Parameters such as pyrolysis temperature, type of support, and nitrogen ligands as well as Au/ligand molar ratios were systematically investigated. Highly selective hydrogenation of numerous structurally diverse alkynes proceeded in moderate to excellent yield under mild conditions. The high selectivity toward the industrially important alkene substrates, functional group tolerance, and the high recyclability makes the catalytic system unique. Both high activity and selectivity are correlated with a frustrated Lewis pairs interface formed by the combination of gold and nitrogen atoms of N-doped carbon that, according to density functional theory calculations, can serve as a basic site to promote the heterolytic activation of H2 under very mild conditions. This "fully heterogeneous" and recyclable gold catalyst makes the selective hydrogenation process environmentally and economically attractive.
- Fiorio, Jhonatan Luiz,Gon?alves, Renato Vitalino,Teixeira-Neto, Erico,Ortu?o, Manuel A.,López, Núria,Rossi, Liane Marcia
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p. 3516 - 3524
(2018/04/14)
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- Gold-Ligand-Catalyzed Selective Hydrogenation of Alkynes into cis-Alkenes via H2 Heterolytic Activation by Frustrated Lewis Pairs
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The selective hydrogenation of alkynes to alkenes is an important synthetic process in the chemical industry. It is commonly accomplished using palladium catalysts that contain surface modifiers, such as lead and silver. Here we report that the adsorption of nitrogen-containing bases on gold nanoparticles results in a frustrated Lewis pair interface that activates H2 heterolytically, allowing an unexpectedly high hydrogenation activity. The so-formed tight-ion pair can be selectively transferred to an alkyne, leading to a cis isomer; this behavior is controlled by electrostatic interactions. Activity correlates with H2 dissociation energy, which depends on the basicity of the ligand and its reorganization on activation of hydrogen. High surface occupation and strong Au atom-ligand interactions might affect the accessibility and stability of the active site, making the activity prediction a multiparameter function. The promotional effect found for nitrogen-containing bases with two heteroatoms was mechanistically described as a strategy to boost gold activity. (Graph Presented).
- Fiorio, Jhonatan L.,López, Núria,Rossi, Liane M.
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p. 2973 - 2980
(2017/05/31)
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- Unexpected cleavage of ether bonds of 1,3-dimethoxypropane in Grignard-Wurtz synthesis of a MgCl2-donor adduct
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Diethers are an important group of electron donors in Ziegler-Natta catalysts. A simple diether, 1,3-dimethoxypropane was studied as an electron donor in Grignard-Wurtz synthesis of a MgCl2-donor adduct. 1,3-Dimethoxypropane was unexpectedly found to undergo a cleavage reaction during the synthesis producing methoxy groups (OCH3). Each mole of 1,3-dimethoxypropane produced approximately 2 moles of methoxy groups, which are probably bound to magnesium chloride as methoxymagnesium chloride. A Grignard reagent, BuMgCl formed in the Grignard-Wurtz reaction most likely causes the cleavage of the ether bonds in 1,3-dimethoxypropane and there seem to be at least two parallel reaction paths taking place and producing at least two different by-products. The first step in the cleavage of 1,3-dimethoxypropane is a Grignard reagent (BuMgCl) induced elimination of OCH3, which gives 3-methoxy-1-propene. This intermediate product reacts further in a substitution reaction caused by the Grignard reagent producing 1-heptene as the by-product. The cleavage of the ether bond in 3-methoxy-1-propene and formation of OCH3 can also occur through another reaction path, which produces propene as the by-product.
- Nissinen, Ville,Pirinen, Sami,Pakkanen, Tuula T.
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- Technological method for preparation of allyl ether compounds
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The invention discloses a technological method for preparation of allyl ether compounds; the technological method can obtain the high-purity allyl ether compounds in low cost and high yield, has the advantages of high selectivity of the allyl ether compounds, less side reaction, easy separation and purification of the products, friendly technological process environment and the like, and is suitable for large-scale industrialized production.
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Paragraph 0056-0058
(2017/02/17)
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- Hydrogen-bond-activated palladium-catalyzed allylic alkylation via allylic alkyl ethers: Challenging leaving groups
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C-O bond cleavage of allylic alkyl ether was realized in a Pd-catalyzed hydrogen-bond-activated allylic alkylation using only alcohol solvents. This procedure does not require any additives and proceeds with high regioselectivity. The applicability of this transformation to a variety of functionalized allylic ether substrates was also investigated. Furthermore, this methodology can be easily extended to the asymmetric synthesis of enantiopure products (99% ee).
- Huo, Xiaohong,Quan, Mao,Yang, Guoqiang,Zhao, Xiaohu,Liu, Delong,Liu, Yangang,Zhang, Wanbin
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supporting information
p. 1570 - 1573
(2014/04/17)
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- Rate and product studies on the solvolyses of allyl chloroformate
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The solvolysis rate constants of allyl chloroformate (CH 2=CHCH2OCOCl, 3) in 30 different solvents are well correlated with the extended Grunwald-Winstein equation, using the NT solvent nucleophilicity scale and YCl solvent ionizing scale, with the sensitivity values of 0.93 ± 0.05 and 0.41 ± 0.02 for l and m, respectively. These l and m values can be considered to support a S N2 reaction pathway. The activation enthalpies (ΔH≠) were 12.5 to 13.4 kcal·mol-1 and the activation entropies (ΔS≠) were -34.4 to -37.3 cal·mol-1·K -1, which is also consistent with the proposed bimolecular reaction mechanism. The solvent kinetic isotope effect (SKIE, kMeOH/k MeOD) of 2.16 was also in accord with the SN2 mechanism. The values of product selectivity (S) for the solvolyses of 3 in alcohol/water mixtures was 1.3 to 3.9, which is also consistent with the proposed bimolecular reaction mechanism.
- Koh, Han Joong,Kang, Suk Jin
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p. 4117 - 4121
(2013/08/23)
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- Catalytic removal of N-allyloxycarbonyl groups using the [CpRu(IV)(π-C3H5)(2-quinolinecarboxylato)]PF 6 complex. A new efficient deprotecting method in peptide synthesis
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A variety of amines including even sterically less demanding and highly nucleophilic secondary amines have been efficiently deprotected without decarboxylative N-allylation from the corresponding N-allyloxycarbonyl (N-AOC) compounds by using a catalytic amount of [CpRu-(IV)(π-C3H 5)(2-quinolinecarboxylato)]PF6 in the presence of 1 molar amount of trifluoromethanesulfonic acid, the general utility of which has been demonstrated by the efficient synthesis of a collagen protein unit tripeptide, Pro-Pro-Gly.
- Tanaka, Shinji,Saburi, Hajime,Murase, Takanori,Yoshimura, Masahiro,Kitamura, Masato
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p. 4682 - 4684
(2007/10/03)
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- Reaction of orthoesters with alcohols in the presence of acidic catalysts: A study
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Allylic and benzylic alcohols are converted into corresponding unsymmetrical ethers when reacted with various orthoesters in the presence of montmorillonite KSF at ambient temperature. A detailed study has been undertaken to examine the mechanism and generality of these reactions with regard to various acidic catalysts, which reveal interesting competitive reactions mainly O-acetylation, together with trace amount of dimerized product. The type of the side product and their relative quantity depends upon the nature of the catalyst employed. Furthermore, the low yields of the Claisen rearrangement product obtained from allylic alcohols under heating is rationalized due to the formation of some of these products.
- Sampath Kumar,Joyasawal, Sipak,Reddy,Pawan Chakravarthy,Krishna,Yadav
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p. 1686 - 1692
(2007/10/03)
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- Halide-Free Dehydrative Allylation Using Allylic Alcohols Promoted by a Palladium-Triphenyl Phosphite Catalyst
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The triphenyl phosphite-palladium complex was found to effect catalytic substitution reactions of allylic alcohols via a direct C-O bond cleavage. The dehydrative etherification proceeded efficiently without any cocatalysts and bases to give allylic ethers in good to excellent yields.
- Kayaki, Yoshihito,Koda, Takashi,Ikariya, Takao
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p. 2595 - 2597
(2007/10/03)
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- Specific features of solvation effects in monomolecular and bimolecular solvolysis
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A method was suggested for distinguishing monomolecular and bimolecular solvolysis on the basis of reaction kinetics in water, MeOH, EtOH, i-PrOH, cyclohexanol, and t-BuOH. In solvolysis of n-PrBr, CH2=CHCH2Br, PhCOCl, and MeOClO3 (SN2 reactions), a linear correlation is observed between log k and the solvent ionizing power Z, whereas in solvolysis of t-BuBr, t-BuCl, and 1-AdI (SN1, E1 reactions) this correlation is nonlinear. Deviations from linearity are due to steric hindrance decreasing the negative effect of nucleophilic solvation.
- Ponomarev,Michkov,Dvorko
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p. 591 - 598
(2007/10/03)
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- γ-1,4 Addition of substituted methoxyallylcopper reagents to methylvinylketone
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Methoxyallylcopper reagents substituted in α and/or β position of methoxy group reacted regiospecifically with MVK to give γ-1,4 adducts, i.e. ketoenolethers, γ substituted methoxyallylcopper reagents gave mixtures of γ-1,4 and α-1,4 adducts.
- Berrien, Jean-Francois,Raymond, Marie-Noelle,Zaari, Fatima,Moskowitz, Henri,Mayrargue, Joelle
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p. 3367 - 3370
(2007/10/03)
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- Transformation of vinyloxirane on Pt-SiO2 and Pd-SiO2
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The transformation of vinyloxirane and ethyloxirane were studied on Pt-SiO2 and Pd-SiO2 catalysts at 273 and 301 K in a recirculation reactor, in the presence of hydrogen or deuterium. There are significant differences, not only in reaction rates, but also in reaction routes, depending upon the nature of the metal. The main reaction routes are: deoxygenation and hydrogen or deuterium addition on Pt-SiO2; isomerization and hydrogenolysis on Pd-SiO2. The reaction routes leading to the formation of the individual products are interpreted on the basis of the experimental results. In the case of the hydrogenolysis of oxiranes, Pd was shown to exhibit a special reactivity, unlike earlier observations described in the literature.
- Bartok, Mihaly,Fasi, Andras,Notheisz, Ferenc
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- Clay catalyzed highly selective O-alkylation of primary alcohols with orthoesters
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Montmorillonite KSF catalyzes the selective O-alkylation of various primary allylic and benzylic alcohols when reacted with different orthoesters at room temperature to afford ethers in moderate to high yields.
- Kumar, H. M. Sampath,Reddy, B. V. Subba,Mohanty, Pradyumna K.,Yadav
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p. 3619 - 3622
(2007/10/03)
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- Hydrolysis and Alcoholysis of Esters of o-Nitrobenzenesulfonic Acid
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The rate of solvolysis of esters of o-nitrobenzenesulfonic acid with water and C1-C4 alcohols is satisfactorily described by two-parametric Hammett-Taft equation with predominating effect of the electronic factor σ*. The effect of the structure of the hydrocarbon rest in the sulfonic ester group does not fit to this relationship.
- Sendega,Makitra,Pirig
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p. 1438 - 1446
(2007/10/03)
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- Synthesis of benzyl/allyl alkyl ethers from corresponding magnesium alkoxides
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In the presence of iodine, alcohols react with magnesium to produce magnesium alkoxides which are then treated with benzyl chloride or allyl bromide to produce benzyl alkyl ethers or allyl alkyl ethers.
- Lin, Ji-Mao,Li, Hui-Hui,Zhou, Ai-Min
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p. 5159 - 5160
(2007/10/03)
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- Tin for organic synthesis. Part 15 : The use of 1,2-bis(trimethylstannyl) -1-alkenes in electrophilic destannylation reactions
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Z-1,2-Bis(trimethylstannyl)-1-alkenes show different types of reaction behaviour towards various electrophiles. p-Tolysulphonyliso-cyanate forms five-membered tin-nitrogen-containing heterocycles. 1,1-Dichloromethylmethyl ether reacts with carbofunctionalised distannylalkenes to yield α,β-unsaturated aldehydes, which are useful tools for the synthesis of further substituted vinylstannanes. Z-1,2-Bis(trimethylstannyl)- 1-alkenes containing heteroatoms such as O or N undergo only protodestannylation with this electrophile. The reaction of Z-1,2-bis (trimethylstannyl)-1-alkenes with trimethylsilyl chlorosulphonate followed by hydrolysis with aqueous NaHCO3 provides the corresponding sodium sulphonates. SO2 and SO3 undergo insertion into both tin-carbon bonds in an ipso- and stereospecific manner to form bis-sulphinic- or bis-sulphonic bis(trialkylstannyl) esters.
- Niestroj, Michael,Neumann, Wilhelm P.,Mitchell, Terence N.
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- EFFICIENT AND/OR SELECTIVE METHYLATION BY DIAZOMETHANE OF ALCOHOLS, HALO ALCOHOLS, GLYCOLS, AMINO ALCOHOLS AND MERCAPTO ALCOHOLS WITH THE USE OF A PROTON-EXCHANGED X-TYPE ZEOLITE AS AN ACID-BASE BIFUNCTIONAL CATALYST
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Reactions of diazomethane with butanol, allyl alcohol and β- and γ-halo alcohols led to efficient methylation (giving the corresponding methyl ethers) with the use of a proton-excahnged X-type zeolite compared with H2SO4.The reactions with propylene and isobutylene glycols using the zeolite provided regioselective methylation of the primary OH rather than the secondary or tertiary OH, whereas regioselectivity was not observed in the reactions using H2SO4.The reactions with 2-aminoethanol and 2-mercaptoethanol showed high chemoselective S-methylation and N-monomethylation, respectively, in the presence of the zeolite instead of H2SO4.The mechanism for the reactions is proposed to involve acid-base bifunctional catalysis of the zeolite in which the acidic site reacts with diazomethane to form its conjugate acid, and the nucleophilicity of OH and SH groups is enhanced by the interaction of the basic site with the proton of the groups.
- Takeuchi, Hiroshi,Kishioka, Hiroaki,Kitajima, Kunio
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p. 121 - 126
(2007/10/02)
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- In situ NMR study of the rhodium(I)-catalyzed hydrogenation of the allene 1-methoxy-propa-1,2-diene using parahydrogen
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The homogeneous hydrogenation of 1-methoxy-propa-1,2-diene was investigated via in situ 1H-NMR spectroscopy using different rhodium(I) catalysts and parahydrogen (p-H2). The detected polarization signals allow the determination of the hydrogenation products due to their characteristic patterns.
- Harthun,Bargon,Selke
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p. 7755 - 7758
(2007/10/02)
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- Relative Thermodynamic Stabilities of Isomeric Alkyl Allyl and Alkyl (Z)-Propenyl Ethers
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The relative thermodynamic stabilities of ten allyl ethers (ROCH2CH=CH2) and the corresponding isomeric (Z)-propenyl ethers (where R is an alkyl group, or a methoxysubstituted alkyl group) have been determined by chemical equilibration in DMSO solution with t-BuOK as catalyst.From the variation of the equilibrium constant with temperature, the values of the thermodynamic parameters ΔG, ΔH and ΔS of isomerization at 298.15 K were evaluated.The propenyl ethers are highly favored at equilibrium, the values of both ΔG and ΔH for the allyl -> propenyl reaction being ca. -18 to 25 kJ mol-1.The favor of the propenyl ethers is increased by bulky alkyl substituents, and decreased by methoxysubstituted alkyl groups.In most cases the entropy contribution is negligible; however, for R=(MeO)2CH and R=(MeO)3C the values of ΔS are ca. -5 J K-1 mol1-.
- Taskinen, Esko
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p. 11389 - 11394
(2007/10/02)
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- CHEMISTRY OF SYSTEMS OF THE ALLYL TYPE I. SYNTHESIS OF ALLYL AND 2-PROPYNYL ETHERS UNDER PHASE-TRANSFER CATALYSIS CONDITIONS
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A convenient method was developed for the synthesis of allyl and 2-propynyl ethers under phase-transfer catalysis conditions, which make it possible to dispense with the use of an inert organic solvent and to ensure the practically complete conversion of the alkylating agent.
- Ibragimov, I. I.,Tarasov, V. A.,Aliev, A. G.,Belyaeva, V. I.
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p. 1398 - 1402
(2007/10/02)
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- Catecholborane reductive cleavage of allyl and propargyl acetals and ketals: A simple route to allyl and prop-2-ynyl ethers
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The chemoselective conversion of allyl and prop-2-ynyl acetals as well as ketals by reductive cleavage with catecholborane into the corresponding allyl and prop-2-ynyl ethers is described.
- Bovicelli,Mincione,Patamia
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p. 907 - 913
(2007/10/02)
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- Carbonylation of allylic ethers to esters
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A method is disclosed for the production of esters by reaction of an allylic ether with carbon monoxide in the presence of a catalytically effective amount of a Group VIII noble metal catalyst and halide compound to obtain esters. The halide compound is present in an amount sufficient to prevent the catalyst from being converted into a Group VIII metal during the reaction. When the reaction is conducted in the presence of a quaternary ammonium salt the ester may be extracted by solvent extraction to minimize catalyst decomposition caused when extractive distillation is used to separate the ester.
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- Gas-Phase Addition of the Vinyl Cation to Hydrogen and Methane. A Nuclear Decay Study
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A nuclear technique based on the spontaneous decay of multitritiated precursors that allows the generation of free carbenium ions of exactly the same nature in different enviroments has been employed for generating the labeled vinyl cation (C2X3(1+), X = H,T) from multitritiated ethylene and for investigating its reactivity toward hydrogen and methane at pressures ranging from 60 to 720 Torr.Kinetic data for the addition of C2X3(1+) to H2 and CH4 and the ensuing product distributions are obtained by intercepting the ionic species with different gaseous nucleophiles, i.e., 1,4-dibromobutane, benzene, and methanol, and by isolating the corr esponding neutral end products.The results are consistent with the intermediacy of the vinyl cation, formed by the β(1-) transition with a limited excess of vibrational energy, which insert into the ?-bonds of H2 and CH4 yielding respectively C2H5(1+) and sC3H7(1+) ions.The experiments provide no evidence for the occurrence of alternative C3H7(1+) structures, i.e., protonated cyclopropane, from the C2X3(1+) attack on CH4.At CH4 pressures below 200 Torr, a fraction of the C3H7(1+) adducts fragments diretly into allyl cations and H2.A definition of the C2X3(1+) + H2(or CH4) addittion and fragmentation mechanism is obtained by comparison of the present data with those arisisng from previous experimental studies based on different approaches (i.e., radiolysis, ICR, SIFT, HMPS, etc.) and with those of ab initio calculations.
- Fornarini, Simonetta,Speranza, Maurizio
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p. 2154 - 2160
(2007/10/02)
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- Deamination Reactions, 42. Addition of Diazocyclopropanes to Carbonyl Compounds
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Diazocyclopropanes (6, 38, 57) were generated in equilibrium with cyclopropanediazonium ions by base-induced cleavage of the analogous nitrosoureas in methanol.Efficient trapping of the diazocyclopropanes occurred in dilute solution with a slight excess of carbonyl compounds.The reactivity of the resulting 1-(α-hydroxyalkyl)cyclopropanediazonium ions (10) depended strongly on the α-substituents.Pinacol rearrangements predominated with aldehyde adducts, the migratory aptitudes being H > Ph > CH3.These 1,2-shifts are thought to proceed with inversion at the terminus - the preferred exo-attack of acetaldehyde at 7-diazonorcarane (38) led to the endo-ketone 40.The major product derived from the acetone adduct 22 was the epoxide 26 whose reaction(s) with metanol were also examined.The intramolecular addition of 8-diazobicyclooctan-4-one (57) gave rise to 6-methoxybicyclooct-4-en-1-ol (60).Due to steric constraints, the intermediate 58 underwent exclusive cyclopropyl-allyl transformations (otherwise a minor reaction).
- Kirmse, Wolfgang,Hellwig, Georg,Chiem, Pham van
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p. 1511 - 1524
(2007/10/02)
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- Deamination Reactions, 44. Decomposition of 1-Alkylcyclopropanediazonium Ions
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1-Methyl- (17), 1,2-dimethyl- (41, 44), 1-propyl- (64), 1-(1-methylethyl)cyclopropanediazonium ions (80), and -1-diazonium ions (93) have been generated by alkaline cleavage of the analogous nitrosocarbamates in methanol.Cyclopropyl-allyl transformation and nucleophilic displacement were the only reactions of 17, 41, 44, and 93 while elimination and 1,2-shifts of an α-hydrogen compete increasingly with 64 and 80.The stereochemistry of ring cleavage and nucleophilic displacement has been explored, using 2-D labels in the case of 17 and 93.Cyclopropanediazonium ions (1) and 41 react stereospecifically, 17 and 44 are moderately stereoselective (ca. 85:15), and 93 is entirely unselective.The data indicate a gradual changeover from concerted to stepwise mechanisms.Appreciable stabilization of the positive charge is required to reach the SN1 extreme.
- Kirmse, Wolfgang,Rode, Jutta,Rode, Klaus
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p. 3672 - 3693
(2007/10/02)
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- The Elimination Kinetics of Methoxyalkyl Chlorides in the Gas Phase. Evidence for Neighboring Group Participation
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The rates of elimination of 3-methoxy-1-chloropropane and 4-methoxy-1-chlorobutane have been determined in a seasoned, static reaction vessel over the temperature range of 410-490 deg C and the pressure range of 56-181 torr.The reactions are homogeneous and unimolecular, follow a first-order rate low, and are invariant to the presence of a twofold or greater excess of the radical chain inhibitor toluene.The overall rate coefficients are given by the following Arrhenius equations: for 3-methoxy-1-chloropropane, logk1(s-1)=(12.92+/-0.48)-(226.0+/-6.8) kJ mol-1(2.303RT)-1; for 4-methoxy-1-chlorobutane, logk1(s-1)=(12. 9+/-0.26)-(218.1+/-3.5) kJ mol-1(2.303RT)-1.The CH3O group in 4-methoxy-1-chlorobutane has been found to assist anchimerically the elimination reaction, where dehydrochlorination and tetrahydrofuran formation arise from an intimate ion pair type of mechanism.The partial rates for these parallel eliminations have been determined and reported.Participation of the CH3O in 3-methoxy-1-chloropropane is barely detected.The present results give further evidence of intimate ion pair mechanism through neighboring group perticipation in the gas-phase elimination of certain types of organic molecules.
- Chuchani, Gabriel,Martin, Ignacio
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p. 431 - 433
(2007/10/02)
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- Solvolysis of Allyl Arenesulfonates. Cautionary Comments concerning the NOTs Scale of Solvent Nucleophilicities
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The rates of solvolysis of five allyl arenesulfonates are analysed in terms of the extended Grunwald-Winstein equation.The l values are constant but the m values decrease slightly as the nucleofugality of the leaving group increases.The solvent nucleophilicity (NOTs) values presently available in the literature are based upon a m value for methyl p-toluenesulfonate (tosylate) solvolysis of 0.3; it is demonstrated that a value of 0.55 is more appropriate.The previously reported l values and correlation coefficients for tosylate ester solvolyses are accurate and the "ap parent" sensitivities to solvent ionizing power (m values) are easily corrected.However, for use in conjunction with solvent ionizing power scales for other leaving groups, NTs values based on the appropriate m value or, alternatively, NEt3O+%& values (based on triethyloxonium ion solvolysis) are required.
- Kevill, Dennis N.,Rissmann, Thomas J.
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p. 3062 - 3064
(2007/10/02)
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- Deamination Reactions, 41. Reactions of Aliphatic Diazonium Ions and Carbocations with Ethers
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Aliphatic diazonium ions and carbocations were generated by deacylation of appropriate nitrosoureas (1, 5, 9) in alcohol-ether mixtures or in 2-alkoxyethanols.Ethers were generally inferior to alcohols in capturing cationic intermediates.Formation of trialkyloxonium ions led to alkyl exchange or ring opening.The observed reactivity orders were n-butyl > isobutyl for the diazonium ions, allyl > sec-butyl > tert-butyl for the carbocations, methoxy > ethoxy and oxirane > oxetane > tetrahydrofuran for the ethers, indicating the predominance of steric effects.Neighboring group participation in 4-methoxy-1-butanediazonium ions (58) and 4,5-epoxy-1-pentanediazonium ions (74) was detectable but inefficient ( 20percent of cyclic oxonium ions).
- Kirmse, Wolfgang,Jansen, Ulrich
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p. 2607 - 2625
(2007/10/02)
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- OXYGEN YLIDES-I. REACTIONS OF CARBENES WITH OXETANE
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The ylides generated from carbenes (:CH2, :CHCO2Et, :CHPh) and oxetane in the presence of methanol undergo Stevens rearrangement and protonation competitively, yielding tetrahydrofurans and 1,3-dialkoxycyclopropanes as major products.
- Friedrich, Klaus,Jansen, Ulrich,Kirmse, Wolfgang
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p. 193 - 196
(2007/10/02)
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- CORRELATION OF THE RATES OF SOLVOLYSIS OF ALLYL AND BENZYL ARENESULPHONATES
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Analysis of the specific rates of solvolysis of allyl arenesulphonates in terms of the extended Grunwald-Winstein equation indicates a marked dependence on both the solvent nucleophilicity (high/value) and the solvent ionizing power (high m value).As the charge delocalization in the leaving group increases, both l and m values fall.For allyl toluene-p-sulphonate solvolysis in 28 solvents at 50.0 deg C, values for l(0.83) and for m (0.63), based on the use of NKL and Y values, are very similar to the equivalent values of 0.90 and 0.67 previously reported for benzyl toluene-p-sulphonate solvolysis.Related extended Grunwald-Winstein analyses are considered and the need for variety in the choice of solvents is emphasized.
- Kevill, Dennis N.,Rissmann, Thomas J.
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p. 717 - 720
(2007/10/02)
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- Alkali-induced decomposition of (2-alkoxyalkyl)cobaloximes
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Decomposition of tetrahydrofurfuryl(pyridine)cobaloxime by aqueous sodium hydroxide results in fragmentation to 4-penten-1-ol and cobaloxime(III). Several other (2-alkoxyalkyl)(pyridine)cobaloximes behave analogously. The reaction is of mixed kinetic orde
- Mock, William L.,Bieniarz
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p. 1279 - 1284
(2008/10/08)
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- KINETICS OF THE THERMAL GAS-PHASE DECOMPOSITION OF METHOXYCYCLOPROPANE
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In the temperature range 635-694 K, 70-80 percent of the methoxycyclopropane decomposing initially results in the formation of the isomerization products(E)- and (Z)-1-methoxyprop-1-ene and 3-methoxyprop-1-ene.THe residual decomposition results from approximately equal contributions from methyl-oxygen bond fission and the subsequent radical abstraction reactions.THe isomerization products are formed by homogeneous, non-radical, unimolecular pathways with high-pressure rate constants given by the equations k/s-1 = 1013.29+/-0.75 exp(-226.5+/-9.5kJ mol-1/RT) and k(3-methoxyprop-1-ene)/s-1 = 1014.0+/-1.1exp(-254+/-14 kJ mol-1/RT).The methoxy group lowers the activation energy for opening the cyclopropane ring adjacent to the point of substitution by ca. 45 kJ mol-1.
- Iftikhar, A.Awan,Flowers, Michael
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p. 1413 - 1420
(2007/10/02)
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- aIRON CATALYSIS OF GRIGNARD REDUCTIONS. MECHANISM OF 1,3-REDUCTIVE ELIMINATIONS FROM γ-PROPYL HALIDES
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The iron-catalyzed reduction of various 3-substituted propyl bromides by Grignard reagents affords propylene and cyclopropane.The reduction to propylene is particularly noteworthy since it formally represents a 1,2-hydrogen shift.Two key intermediates have been identified in propylene formation, in which 3-methoxypropyl bromide is first catalytically reduced to the magnesium derivative by Grignard reagent.The iron-catalyzed β-elimination of the 3-methoxypropylmagnesium intemediate affords allyl methyl ether, which is then reductively cleaved to propylene.Extensive studies of deuterium labeling in the reactants, as well as in both intermediates, allow the course of the hydrogen shift to be followed unequivocally.The mechanism of iron catalysis is proposed in Schemes 2 and 3, representing the first and second stages of the reduction to propylene.
- Rollick, K. L.,Nugent, W. A.,Kochi, J. K.
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p. 279 - 300
(2007/10/02)
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- Solvomercuration-Demercuration. 8. Oxymercuration-Demercuration of Methoxy-, Hydroxy-, and Acetoxy-Substituted Alkenes
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The oxymercuration-demercuration (OM-DM) of a series of methoxy-, hydroxy-, and acetoxy-substituted alkenes was examined.The systems examined were the allyl, crotyl, 3-buten-1-yl, 4-penten-1-yl, and 5-hexen-1-yl.The methoxyalkenes undergo hydration with very high regioselectivity and almost quantitative yield in all cases.However, a small -I effect is observed in the case of the allylalkene (97.1percent Markovnikov vs. 99.5percent in 1-hexene).Moreover, in the crotyl case, a major directing effect is observed: 97.7percent 3-ol, 2.3percent 2-ol.The other three alkenes undergo the OM reaction with no effect from the methoxy group (99.5percent Markovnikov isomer).In contrast, only allyl-, crotyl-, and 3-buten-1-yl alcohols produce major amounts of hydrated products, the diols.While no hydroxyl group directing effect is observed in the allyl system, a major one is again seen in the case of the crotyl: 93.5percent l,3-diol and 6.5percent l,2-diol.The major products from the 4-penten-1-yl and 5-hexen-1-yl and alcohols are 2-methyltetrahydrofuran and 2-methyltetrahydropyran, respectively, resulting from OH-5 and OH-6 neighboring group participation in the OM stage.The acetoxy alkenes undergo hydration to give diols in ca. 80percent yield with ca. 20percent unreacted starting material.This is the result of a competitive deoxymercuration reaction which is occurring in the DM stage.However, the yield of hydrated products can be increased by varying the amount of base used in the DM.Neighboring-group participation, AcO-5, is observed in the allyl system only, resulting in a 65percent yield of the Markovnikov oxymercurial, by 1H NMR analysis, and a 35percent yield of the acetoxy-exchanged mercurial.Again, a major -I-directing effect of the acetoxy group was observed in the crotyl system but not in the others.In addition to the expected l,2- and l,3-diols, the OM-DM of crotyl acetate also resulted in small amounts of the unexpected 2,3-diol under kinetic conditions.Finally, a modified DM procedure has been developed which is compatible with the acetoxy group.
- Brown, Herbert C.,Lynch, Gary J.
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p. 531 - 538
(2007/10/02)
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- Reaction of Allylic and Benzylic Methyl Ethers with Sodium and Trimethylchlorosilane. Evidence for the Intermediacy of Allylic Radicals and Anions
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Allyl methyl ether and benzyl methyl ether react with sodium and trimethylchlorosilane to yield, respectively, allyltrimethylsilane and benzyltrimethylsilane. α,α-Dimethylallyl methyl ether and γ,γ-dimethylallyl methyl ether react with sodium and trimethylchlorosilane to yield γ,γ-dimethylallyltrimethylsilane. α-Methylallyl methyl ether and trans-γ-methylallyl methyl ether react with trimethylchlorosilane and sodium to yield similar product mixtures of α-methylallyltrimethylsilane and cis- and trans-γ-methylallyltrimethylsilane.These results are discussed in ter ms of a mechanism involving electron transfer to yield allylic radicals and allylic anion intermediates.
- Tzeng, Dongjaw,Weber, William P.
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p. 265 - 267
(2007/10/02)
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- Regiospecific Synthesis of Allylic Dimethylmethoxysilanes
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Photochemically generated dimethylsilylene reacts regiospecifically with allylic methyl ethers to yield allylic dimethylmethoxysilanes.Reaction of allylic methyl ethers with dimethyldichlorosilane and sodium metal likewise gives allylic dimethylmethoxysilanes in preparatively useful yields.Regiospecificity, however, is not always observed in this latter reaction.Such allylic dimethylmethoxysilanes can be converted to allylic trimethylsilanes easily by reaction with methyllithium.
- Tzeng, Dongjaw,Weber, William P.
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p. 693 - 696
(2007/10/02)
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- HOMOGENEOUS CATALYTIC HYDROGENATION OF DIOLEFINS AND ALKYNES IN THE PRESENCE OF PALLADIUM(II) COMPLEXES
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Palladium(II)chloride in dimethylformamide catalyzes the hydrogenation of conjugated diolefins and alkynes in homogeneous solution.Monoolefins are formed selectively.
- Sisak, A.,Jablonkai, I.,Ungvary, F.
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