- Diverse Mechanistic Pathways in Single-Site Heterogeneous Catalysis: Alcohol Conversions Mediated by a High-Valent Carbon-Supported Molybdenum-Dioxo Catalyst
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With the increase in the importance of renewable resources, chemical research is shifting focus toward substituting petrochemicals with biomass-derived analogues and platform-molecule transformations such as alcohol processing. To these ends, in-depth mechanistic understanding is key to the rational design of catalytic systems with enhanced activity and selectivity. Here we discuss in detail the structure and reactivity of a single-site active carbon-supported molybdenum-dioxo catalyst (AC/MoO2) and the mechanism(s) by which it mediates alcohol dehydration. A range of tertiary, secondary, and primary alcohols as well as selected bio-based terpineols are investigated as substrates under mild reaction conditions. A combined experimental substituent effect/kinetic/kinetic isotope effect/EXAFS/DFT computational analysis indicates that (1) water assistance is a key element in the transition state; (2) the experimental kinetic isotopic effect and activation enthalpy are 2.5 and 24.4 kcal/mol, respectively, in good agreement with the DFT results; and (3) several computationally identified intermediates including Mo-oxo-hydroxy-alkoxide and cage-structured long-range water-coordinated Mo-dioxo species are supported by EXAFS. This structurally and mechanistically well-characterized single-site system not only effects efficient transformations but also provides insight into rational catalyst design for future biomass processes.
- Bedzyk, Michael J.,Das, Anusheela,Kratish, Yosi,Li, Jiaqi,Ma, Qing,Marks, Tobin J.
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p. 1247 - 1257
(2022/02/07)
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- Boosting the Metathesis Activity of Molybdenum Oxo Alkylidenes by Tuning the Anionic Ligand σ Donation
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The catalytic performances of molecular and silica-supported molybdenum oxo alkylidene species bearing anionic O ligands [ORF9, OTPP, OHMT - where ORF9 = OC(CF3)3, OTPP = 2,3,5,6-tetraphenylphenoxy, OHMT = hexamethylterphenoxy] with different σ-donation a
- De Jesus Silva, Jordan,Pucino, Margherita,Zhai, Feng,Mance, Deni,Berkson, Zachariah J.,Nater, Darryl F.,Hoveyda, Amir H.,Copéret, Christophe,Schrock, Richard R.
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supporting information
p. 6875 - 6880
(2021/02/06)
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- Benchmarked Intrinsic Olefin Metathesis Activity: Mo vs. W
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Combining Surface Organometallic Chemistry with rigorous olefin purification protocol allows evaluating and comparing the intrinsic activities of Mo and W olefin metathesis catalysts towards different types of olefin substrates. While well-defined silica-supported Mo and W imido-alkylidenes show very similar activities in metathesis of internal olefins, Mo catalysts systematically outperform their W analogs in metathesis of terminal olefins, consistent with the formation of stable unsubstituted W metallacyclobutanes in the presence of ethylene. However, Mo catalysts are more prone to induce olefin isomerization, in particular when ethylene is present, probably because of their propensity to undergo more easily reduction processes.
- Zhizhko, Pavel A.,Mougel, Victor,De Jesus Silva, Jordan,Copéret, Christophe
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- Heterogeneous Ketone Hydrodeoxygenation for the Production of Fuels and Feedstocks from Biomass
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In this work, we describe a simple, heterogeneous catalytic system for the hydrodeoxygenation (HDO) of 5-nonanone and 2,5-hexanedione, which we use as model compounds for more complex biomass-derived molecules. We present the stepwise reduction of ketones by using supported metal and solid acid catalysts to identify the intermediates en route to hydrocarbons. Although monoketone HDO can be achieved rapidly using moderate conditions (Ni/SiO2.Al2O3, HZSM-5, 200 °C, 1.38 MPa H2, 1 h), quantitative γ-polyketone HDO requires higher pressures and longer reaction times (Pd/Al2O3, HZSM-5, 2.76 MPa H2, 5 h), although these are more facile conditions than have been reported previously for γ-polyketone HDO. Stepwise HDO of the γ-polyketone shows the reaction pathway occurs through ring-closure to a saturated tetrahydrofuran species intermediate, which requires increased H2 pressure to ring-open and subsequently to fully HDO. This work allows for further understanding of bio-derived molecule defunctionalization mechanisms, and ultimately aids in the promotion of biomass as a feedstock for fuels and chemicals.
- Jenkins, Rhodri W.,Moore, Cameron M.,Semelsberger, Troy A.,Sutton, Andrew D.
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p. 2807 - 2815
(2017/07/28)
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- Metathesis of C5–C8 Terminal Olefins on Re2O7/Al2O3 Catalysts
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Abstract: Primary products of the interaction of terminal olefins C5–C8 with Re2O7/Al2O3 catalysts are established. The rupture of the C=C bond of the olefin occurs with formation of a carbene localized at a rhenium ion, with the alkylidene fragment in the produced carbene being the CH2=group of the terminal alkene molecule. Thus M=CH2 species and lower normal α-olefins are formed. Graphical Abstract: [Figure not available: see fulltext.]
- Kustov, Leonid M.,Furman, Daniil B.,Barkova, Aleksandra P.
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p. 1033 - 1039
(2016/06/01)
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- Direct conversion of carboxylic acids (Cn) to alkenes (C2n - 1) over titanium oxide in absence of noble metals
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Carbon-carbon bond formations and deoxygenation reactions are important for biomass up-grading. The classical ketonic decarboxylation of carboxylic acids provides symmetrical ketones with 2n + 1 carbon atoms and eliminates three oxygen atoms. Herein, this reaction is carried out with titanium oxide at 400°C, and an olefin with 2n + 1 carbon atoms is obtained instead of the ketone. For olefin formation hydrogen transfer reactions are required from suitable precursors to form aromatics and coke. Additional aldol condensation reactions increase further molecular weight in the product mixture. Hence, a combination of titanium oxide with a hydrodeoxygenation bed provides double amount of diesel fuel as the combination with zirconium oxide when reacting hexose-derived pentanoic acid.
- Oliver-Tomas, Borja,Renz, Michael,Corma, Avelino
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- Quantitatively Analyzing Metathesis Catalyst Activity and Structural Features in Silica-Supported Tungsten Imido-Alkylidene Complexes
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A broad series of fully characterized, well-defined silica-supported W metathesis catalysts with the general formula [(≡SiO)W(=NAr)(=CHCMe2R)(X)] (Ar = 2,6-iPr2C6H3 (AriPr), 2,6-Cl2C6H3 (ArCl), 2-CF3C6H4 (ArCF3), and C6F5 (ArF5); X = OC(CF3)3 (OtBuF9), OCMe(CF3)2 (OtBuF6), OtBu, OSi(OtBu)3, 2,5-dimethylpyrrolyl (Me2Pyr) and R = Me or Ph) was prepared by grafting bis-X substituted complexes [W(NAr)(=CHCMe2R)(X)2] on silica partially dehydroxylated at 700 C (SiO2-(700)), and their activity was evaluated with the goal to obtain detailed structure-activity relationships. Quantitative influence of the ligand set on the activity (turnover frequency, TOF) in self-metathesis of cis-4-nonene was investigated using multivariate linear regression analysis tools. The TOF of these catalysts (activity) can be well predicted from simple steric and electronic parameters of the parent protonated ligands; it is described by the mutual contribution of the NBO charge of the nitrogen or the IR intensity of the symmetric N-H stretch of the ArNH2, corresponding to the imido ligand, together with the Sterimol B5 and pKa of HX, representing the X ligand. This quantitative and predictive structure-activity relationship analysis of well-defined heterogeneous catalysts shows that high activity is associated with the combination of X and NAr ligands of opposite electronic character and paves the way toward rational development of metathesis catalysts.
- Mougel, Victor,Santiago, Celine B.,Zhizhko, Pavel A.,Bess, Elizabeth N.,Varga, Jeno,Frater, Georg,Sigman, Matthew S.,Copéret, Christophe
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supporting information
p. 6699 - 6704
(2015/06/08)
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- Conversion of levulinic acid derived valeric acid into a liquid transportation fuel of the kerosene type
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In the transformation of lignocellulosic biomass into fuels and chemicals carboncarbon bond formations and rising hydrophobicity are highly desired. The ketonic decarboxylation fits these requirements perfectly as it converts carboxylic acids into ketones forming one carboncarbon bond and eliminates three oxygen atoms as carbon dioxide and water. This reaction is used, in a cascade process, together with a hydrogenation and dehydration catalyst to obtain hydrocarbons in the kerosene range from hexose-derived valeric acid. It is shown that zirconium oxide is a very selective and stable catalyst for this process and when combined with platinum supported on alumina, the oxygen content was reduced to almost zero. Furthermore, it is demonstrated that alumina is superior to active carbon, silica, or zirconium oxide as support for the hydrogenation/dehydration/hydrogenation sequence and a palladium-based catalyst deactivated more rapidly than the platinum catalyst. Hence, under optimized reaction conditions valeric acid is converted into n-nonane with 80% selectivity (together with a 10% of C10-C15 hydrocarbons) in the organic liquid phase upto a 100:1 feed to catalyst ratio [w/w]. The oxygen free hydrocarbon product mixture (85% yield) meets well with the boiling point range of kerosene as evidenced by a simulated distillation. In the gas phase, butane was detected together with mainly carbon dioxide.
- Corma, Avelino,Oliver-Tomas, Borja,Renz, Michael,Simakova, Irina L.
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p. 116 - 122
(2014/06/09)
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- Methylformate as replacement of syngas in one-pot catalytic synthesis of amines from olefins
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A new general approach for the one-pot hydroaminomethylation of olefins using methylformate as formylating agent instead of synthesis gas (syngas) has been proposed. Herein we report that a Ru-Rh catalytic system demonstrates high activity in a tandem conversion of a series of n-alkenes into amines using methylformate with yields 58-92% (6 h). The selectivity for the normal amine reached 96% with catalysis by the Ru carbonyl complex Ru3(CO) 12, with an overall yield of 55% with respect to amine in this instance. The addition of the Rh complex to Ru catalytic system, sharply increased the hydroaminomethylation rate of both the terminal and internal alkenes and increased the yield of amines to 82-93% (6-12 h). The Royal Society of Chemistry.
- Karakhanov, Eduard,Maksimov, Anton,Kardasheva, Yulia,Runova, Elena,Zakharov, Roman,Terenina, Maria,Kenneally, Corey,Arredondo, Victor
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p. 540 - 547
(2014/02/14)
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- Catalytic Conversion of Cellulose to Liquid Hydrocarbon Fuels by Progressive Removal of Oxygen to Facilitate Separation Processes and Achieve High Selectivities
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Described is a method to make liquid chemicals, such as functional intermediates, solvents, and liquid fuels from biomass-derived cellulose. The method is cascading; the product stream from an upstream reaction can be used as the feedstock in the next downstream reaction. The method includes the steps of deconstructing cellulose to yield a product mixture comprising levulinic acid and formic acid, converting the levulinic acid to γ-valerolactone, and converting the γ-valerolactone to pentanoic acid. Alternatively, the γ-valerolactone can be converted to a mixture of n-butenes. The pentanoic acid so formed can be further reacted to yield a host of valuable products. For example, the pentanoic acid can be decarboxylated yield 1-butene or ketonized to yield 5-nonanone. The 5-nonanone can be hydrodeoxygenated to yield nonane, or 5-nonanone can be reduced to yield 5-nonanol. The 5-nonanol can be dehydrated to yield nonene, which can be dimerized to yield a mixture of C9 and C18 olefins, which can be hydrogenated to yield a mixture of alkanes. Alternatively, the nonene may be isomerized to yield a mixture of branched olefins, which can be hydrogenated to yield a mixture of branched alkanes. The mixture of n-butenes formed from γ-valerolactone can also be subjected to isomerization and oligomerization to yield olefins in the gasoline, jet and Diesel fuel ranges.
- -
-
Page/Page column 14
(2010/12/31)
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- High yield of liquid range olefins obtained by converting i-propanol over zeolite H-ZSM-5
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Methanol, ethanol, and i-propanol were converted under methanol-to-gasoline (MTH)-like conditions (400°C, 1-20 bar) over zeolite H-ZSM-5. For methanol and ethanol, the catalyst lifetimes and conversion capacities are comparable, but when i-propanol is use
- Mentzel, Uffe V.,Shunmugavel, Saravanamurugan,Hruby, Sarah L.,Christensen, Claus H.,Holm, Martin S.
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experimental part
p. 17009 - 17013
(2010/03/23)
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- Reduction of alkyl and vinyl sulfonates using the CuCl2· 2H2O-Li-DTBB(cat.) system
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The reduction of a series of alkyl mesylates, dimesylates and triflates to the corresponding hydrocarbons was efficiently performed using a reducing system composed of CuCl2·2H2O, an excess of lithium sand and a catalytic amount (5 mol%) of 4,4′-di-tert-butylbiphenyl (DTBB), in tetrahydrofuran at room temperature. The process was also applied to enol and dienol triflates affording alkenes and dienes, respectively. The use of the deuterated copper salt CuCl2·2D2O allowed the simple preparation of the corresponding deuterated products.
- Radivoy, Gabriel,Alonso, Francisco,Moglie, Yanina,Vitale, Cristian,Yus, Miguel
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p. 3859 - 3864
(2007/10/03)
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- The simultaneous in-situ generation of aldehydes and phosphorus ylides: A convenient multi-step one-pot olefination protocol
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The lithium α-(dimethylamino)alkoxides resulting from the nucleophilic addition of an organolithium reagent to N,N-dimethylformamide are basic enough to deprotonate alkyltriphenylphosphonium salts suspended in tetrahydrofuran. The aldehydes liberated by t
- Wang, Qian,Wei, Heng-Xu,Schlosser, Manfred
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p. 3263 - 3268
(2007/10/03)
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- Radical Addition of N-Chlorophthalimide and N-Bromophthalimide to Alkenes
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The addition of N-chlorophthalimide (1b) to alkenes 3 via phthalimidyl radicals introduces a chlorine atom and an imidyl moiety to vicinal C-atoms of a carbon chain. The yields depend on the substituents of the alkene 3. The regioselectivity can be explained by steric and electronic effects; differences in the behavior of the addition of N-chlorophthalimide (1b) and N-bromophthalimide (1a) can be explained by a reversible attack of the phthalimidyl radical to the double bond.
- Kirsch, Andre,Luening, Ulrich
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p. 129 - 134
(2007/10/03)
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- Reductive Deoxygenation of Ketones and Secondary Alcohols by Organoaluminum Lewis Acids
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The reductive deoxygenation of ketones and secondary alcohols to the corresponding methylene hydrocarbons has been achieved in good to excellent yield by the combined action of an aluminum hydride source and a strongly Lewis-acidic aluminum reagent.Such reductions were successful with diaryl ketones, alkyl aryl ketones, and dialkyl ketones, as exemplified by the reduction of benzophenone, acetophenone and 5-nonanone, respectively.The corrresponding secondary alcohols of these ketones, namely benzhydrol, 1-phenyl-1-ethanol, and 5-nonanol, could also be converted into their respective methylene hydrocarbons by Lewis-acidic sources of aluminum hydride.All such reductions of ketones could be conducted in a single reaction flask in a one-, two-, or three-step process.In the one-step process, which is most suitable for diaryl ketones, i-BuAlCl2 may be employed as both the hydride source and the Lewis acid.For alkyl aryl ketones a two-step process, consisting first of reduction with i-Bu2AlH and then treatment with AlBr3 (with or without catalysis of Cp2TiCl2), leads to better yields.Finally, for dialkyl ketones a three-step process proved to be preferred, wherein a sequential treatment with i-Bu2AlH, AlBr3 and then additional i-Bu2AlH (with a Ni(acac)2 catalyst) gives the highest conversion to alkane.If required, residual alkene may be removed by a brief catalytic hydrogenation or treatment with BH3THF.The ease of deoxygenating the foregoing ketones and secondary alcohols appears to be governed by the ease of forming, and the relative stability of, the corresponding carbenium ion intermediates, namely Ar2HC+ > ArRHC+ > R2HC+.The driving force for such deoxygenations by these aluminum reagents undoubtedly is the exothermic formation of the dialuminoxane system, R2Al-O-AlR2.
- Eisch, John J.,Liu, Zhi-Rong,Boleslawski, Marek P.
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p. 2143 - 2147
(2007/10/02)
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- 1,2-DIALKYLVINYLSILANES FROM α-SILYL EPOXIDES VIA ORGANOLITHIUM REAGENTS
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The reactions of cis-α-epoxysilanes (1) with an excess of alkyllithium reagents were found to cleanly provide 1,2-dialkylvinylsilanes (3).A model for this reductive alkylation is advanced which explains the role of substituents in determining the product stereochemistry.
- Santiago, Braulio,Lopez, Carlos,Soderquist, John A.
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p. 3457 - 3460
(2007/10/02)
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- Hydroboration. 86. Convenient Conversion of Aldehydes and Ketones into the Corresponding Alkenes via Hydroboration of their Enamines. A Remarkably Simple Synthesis of Either (Z)- or (E)-Alkenes
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Aldehydes and ketones are converted into the corresponding alkenes via hydroboration of their enamines.Hydroboration of aldehyde enamines by 9-borabicyclononane (9-BBN), followed by methanolysis, affords the corresponding terminal alkenes in 75-90percent yields.Unsaturated aldehyde enamines produce the corresponding dienes under these conditions.Enamines derived from substituted cyclic ketones and heterocyclic ketones are readily accommodated in this reaction to afford the corresponding alkenes in very good yields.The synthesis of pure (Z)- or (E)-alkenes is readily achieved from the same acyclic ketone enamine by modification of the hydroboration-elimination procedure: (A) hydroboration by 9-BBN followed by methanolysis or (B) hydroboration by borane methyl sulfide (BMS) followed by methanolysis and hydrogen peroxide oxidation.Mechanistic rationale is provided.
- Singaram, Bakthan,Rangaishenvi, Milind V.,Brown, Herbert C.,Goralski, Christian G.,Hasha, Dennis L.
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p. 1543 - 1549
(2007/10/02)
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- Dehydration of Alcohols Catalysed by Metallic Sulphates Supported on Silica Gel
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Many metallic sulphates and hydrogen sulphates supported on silica gel efficiently catalyse dehydration of secondary and tertiary alcohols under mild conditions.The sulphates of CeIV, TiIV, and FeIII were most active.Silica gel was essential for the efficient dehydration in each case.The dehydration catalysed by Fe2(SO4)3, CuSO4, and NaHSO4 on silica gel was studied in detail.The order of the reactivity of alcohols was tertiary > secondary > primary.The dehydration activity of methanesulphonic acid was also enhanced (ca. 14 times at 90 deg C) by the presence of silica gel.Some mechanistic investigations were carried out.
- Nishiguchi, Takeshi,Kamio, Chizuko
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p. 707 - 710
(2007/10/02)
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- BASE-PROMOTED ELIMINATION OF HYDROGEN FLUORIDE FROM ALKYL FLUORIDES: REACTIVITY AND STEREOCHEMISTRY
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- The alcoholate-promoted dehydrohalogenation of 5-nonyl fluoride and cyclododecyl fluoride, typical straight-chain and, respectively, medium-size cyclic substrates, leads to cis- and trans-alkenes in an approximate ratio of 1:3.With bulky bases such as lithium diisopropylamide the trans isomer may be obtained almost exclusively.In general, the elimination of hydrogen fluoride proceeds very slowly.Increase of the base strength has only a moderate effect on the rates.Electrophilic assistance as provided by lithium cations in media of low polarity can, however, considerably accelerate the reaction. - Cyclododecyl fluoride cannot be prepared from cyclododecanol.It is, however, readily accessible by bromofluorination of cyclododecene and subsequent reduction of the adduct with stannane.
- Matsubara, Seijiro,Matsuda, Hiroyuki,Hamatani, Takeshi,Schlosser, Manfred
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p. 2855 - 2864
(2007/10/02)
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- Synthesis of Alkenes via Peterson Reaction
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The α-phenylthiosilanes (2) have been used to prepare the α-silyl anions (1) by reaction with lithium naphthalenide; subsequent condensation with a carbonyl compound gave the alkene (8) via the Peterson reaction.The α-phenylthiosilanes (2) were prepared from n,n-bis(phenylthio)acetals (4) by reaction with lithium naphthalenide and chlorotrimethylsilane.The n,n-bis(phenylthio)acetals (4) were obtained, in turn, from 1,1-bis(phenylthio)acetals (5) by anion formation with butyl-lithium-N,N,N',N'-tetramethylethylenediamine complex in hexane followed by reaction with an alkyl halide.The Peterson reaction was also used to prepare vinyl sulphides (9) and vinyl sulphones (13).
- Ager, David J.
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p. 183 - 194
(2007/10/02)
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- A SIMPLIFIED WITTIG SYNTHESIS USING A SOLID-LIQUID TRANSFER PROCESS: V - THE USE OF FORMAMIDE AS CATALYST FOR THE SYNTHESIS OF ALKENES FROM CARBONYL COMPOUNDS.
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A new synthetic metod of preparation of alkenes with good yields, using formamide as phase transfer catalyst is described.
- Bigot, Y. Le,Hajjaji, N.,Rico, I.,Lattes, A.,Delmas, M.,Gaset, A.
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p. 495 - 498
(2007/10/02)
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- Double Bond Geometry of the Alkenes produced by Oxidative Elimination of Alkyl Phenyl Selenides and Tellurides
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Treatment of secondary-alkyl phenyl selenides with various oxidants affords the corresponding trans-alkene highly selectively irrespective of the amount of oxidant, while in the case of the tellurium analogues the double bond geometry of the product alkene depends markedly on the amount of oxidant, the trans-isomer being formed highly selectively with 1 equiv. oxidant and the proportion of the cis-isomer being increased with excess (2-10 equiv.) of oxidant.
- Uemura, Sakae,Hirai, Yasuyuki,Ohe, Kouichi,Sugita, Nobuyuki
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p. 1037 - 1038
(2007/10/02)
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- HOMOALLYLIC SUBSTITUTION REACTIONS OF LITHIUM DIALKYL CUPRATES WITH CYCLOPROPYLCARBINYL HALIDES: MECHANISTIC CONSIDERATIONS
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Highly reactive lithium dialkyl cuprates and 1-bromo-1-cyclopropylalkanes, 4, react to give good yields of the homoallylic substitution product, 6.Less reactive organocuprates react with 4 to give mixtures of 6 and the direct substitution product 7.These results are consistent with a copper(I) radical intermediate which undergoes facile rearrangement prior to reductive coupling.
- Hrubiec, Robert T.,Smith, Michael B.
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p. 1457 - 1468
(2007/10/02)
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- PALLADIUM COMPLEXES OF PHOSPHORUS ACID DISUBSTITUTED ETHERS. SYNTHESIS, STRUCTURE, CATALYSIS
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Complexes of the type of have been prepared by the reaction of bis-(?-allylpalladiumchloride) with phosphorous acid disubstituted ethers; their structure has been studied by IR- and NMR- spectroscopy and X-ray analysis.The complexes have a dimeric centro-symmetric structure which is usual for bivalent palladium compounds with a slightly distorted flat-square coordination of the central atom.These compounds are active catalysts for hydrogenation of unsaturated compounds.Complexes of biphosphites of sugars can impart asymmetry in hydrogenation of prochiral substrates.
- Nifant'ev, E. E.,Kukhareva, T. S.,Antipin, M. Yu.,Struchkov, Yu. T.,Klabunovsky, E. I.
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p. 797 - 803
(2007/10/02)
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- VACUUM FLASH PYROLYSIS (VFP) OF MALONYL PEROXIDES: DECARBOXYLATION VERSUS DECARBONYLATION OF THE INTERMEDIARY α-LACTONES
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Vacuum Flash Pyrolysis (VFP) at ca. 450-500 deg C and ca. 0.1-0.3 Torr of spirocyclic malonyl peroxides (2a,b) affords high yields of allenes (5a,b), while the simple malonyl peroxide (2c) leads to ketone (4), derived respectively from decarboxylation of the intermediary α-lactones (3).
- Adam, Waldemar,Cadiz, Carlos,Mazenod, Francois
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p. 1203 - 1206
(2007/10/02)
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- THE EFFECT OF CROWN ETHER ON STERIC HINDRANCE TO BASE APPROACH IN BIMOLECULAR ELIMINATION: EVIDENCE AGAINST CLUMP AGGREGATE MODEL OF ION-PAIRED ALKOXIDE BASE
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The effect of 18-crown-6-ether upon geometrical orientation and rates was investigated in tert-C4H9OK-tert-C4H9OH promoted anti-elimination from two homologous series of tosylates, RCH2CHOTsC5H11 and RCHOTsCH2C5H11 (R = H, CH3, C2H5, n-C3H5, iso-C3H7, tert-C4H9).Steric requirements of the cis- and trans-stereoselective base species operating in the reaction in the absence and in the presence of the crown ether, respectively, have been assessed.An unambiguous distinction has been made between two pending models of the cis-stereoselective (ion-paired) base.
- Pankova, Magdalena,Zavada, Jiri
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p. 3150 - 3159
(2007/10/02)
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- The effect of steric size of leaving group on rates of the competing syn- and anti-pathways in bimolecular elimations
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Approximate rates of the competing syn- and anti-pathways have been determined in t-C4H9OK-t-C4H9OH promoted elimination from two homologous series of tosylates: I-OTs -> trans-III ( R=H, CH3, C2H5, n-C3H7, i-C3H7, t-C4H9) and II-OTs -> trans-IV ( R=CH3, C2H5, n-C3H7, i-C3H7, t-C4H9).A comparison has been made with rates of the same processes in the elimination of the corresponding trimethylammonium salts: I-N(+)(CH3)3 -> trans-III and II-N(+)(CH3)3 -> trans IV.The title effect is demonstrated by a comparative analysis of the rate patterns obtained for the two leaving groups.
- Zavada, Jiri,Pankova, Magdalena
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p. 2171 - 2178
(2007/10/02)
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- Synthesis of Olefins from α-Chlorocarbonyl Compounds
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Olefins or diolefins with the double bonds in predetermined positions are obtained in moderate to good yields by treatment of α-chlorocarbonyl compounds with Grignard reagents and lithium in a single process.
- Barluenga, Jose,Yus, Miguel,Concellon, Jose M.,Bernad, Pablo
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p. 677 - 692
(2007/10/02)
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