- Charge-Transfer Quenching of Singlet Excited Complexes
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Rate constants in benzene for quenching of several exciplexes, the pyrene excimer, and the corresponding excited monomeric arenes by organic one-electron donors and acceptors are reported.The results can be explained by a frontier orbital treatment, leadi
- Caldwell, Richard A.,Creed, David,DeMarco, D. C.,Melton, Lynn A.,Ohta, Hiroyuki,Wine, Paul H.
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Read Online
- Method for synthesizing alkyl olefin through coupling of double-bond carbon-hydrogen bond and saturated carbon-hydrogen bond
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The invention discloses a method for synthesizing alkyl olefin through coupling of a double-bond carbon-hydrogen bond and a saturated carbon-hydrogen bond. According to to the method, one-pot reactionis implemented on olefin and sulfoxide in the presence of ferric salt and hydrogen peroxide to generate alkyl olefin; in the method, sulfoxide is simultaneously used as a hydrocarbylation reagent anda solvent of olefin, and a reaction product is alkyl olefin from sulfoxide alkyl coupled with olefin carbon atoms, so that an olefin carbon chain is increased; the reaction conditions are mild, the selectivity is good, the yield is high, and industrial production is facilitated.
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Paragraph 0060-0064; 0080
(2021/02/10)
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- Method for synthesizing 1, 2-disubstituted olefin through reaction of terminal group olefin and sulfoxide
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The invention discloses a method for synthesizing 1, 2-disubstituted olefin by reaction of terminal olefin and sulfoxide. According to the method, terminal olefin with sulfoxide make reaction in one pot in the presence of ferric salt and hydrogen peroxide to generate the 1, 2-disubstituted olefin. sulfoxide is simultaneously used as a hydrocarbylation reagent and a solvent of olefin, and a reaction product is 1, 2-disubstituted olefin of which a terminal carbon atom in terminal olefin is coupled with a sulfoxide alkyl group, so that an olefin carbon chain is increased; the reaction conditionsare mild, the selectivity is high, the yield is high, and industrial production is facilitated.
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Paragraph 0053-0054; 0057-0062; 0065
(2021/02/10)
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- A donor-acceptor complex enables the synthesis of: E -olefins from alcohols, amines and carboxylic acids
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Olefins are prevalent substrates and functionalities. The synthesis of olefins from readily available starting materials such as alcohols, amines and carboxylic acids is of great significance to address the sustainability concerns in organic synthesis. Metallaphotoredox-catalyzed defunctionalizations were reported to achieve such transformations under mild conditions. However, all these valuable strategies require a transition metal catalyst, a ligand or an expensive photocatalyst, with the challenges of controlling the region- and stereoselectivities remaining. Herein, we present a fundamentally distinct strategy enabled by electron donor-acceptor (EDA) complexes, for the selective synthesis of olefins from these simple and easily available starting materials. The conversions took place via photoactivation of the EDA complexes of the activated substrates with alkali salts, followed by hydrogen atom elimination from in situ generated alkyl radicals. This method is operationally simple and straightforward and free of photocatalysts and transition-metals, and shows high regio- and stereoselectivities.
- Chen, Kun-Quan,Shen, Jie,Wang, Zhi-Xiang,Chen, Xiang-Yu
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p. 6684 - 6690
(2021/05/31)
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- Iron Catalyzed Double Bond Isomerization: Evidence for an FeI/FeIII Catalytic Cycle
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Iron-catalyzed isomerization of alkenes is reported using an iron(II) β-diketiminate pre-catalyst. The reaction proceeds with a catalytic amount of a hydride source, such as pinacol borane (HBpin) or ammonia borane (H3N?BH3). Reactivity with both allyl arenes and aliphatic alkenes has been studied. The catalytic mechanism was investigated by a variety of means, including deuteration studies, Density Functional Theory (DFT) and Electron Paramagnetic Resonance (EPR) spectroscopy. The data obtained support a pre-catalyst activation step that gives access to an η2-coordinated alkene FeI complex, followed by oxidative addition of the alkene to give an FeIII intermediate, which then undergoes reductive elimination to allow release of the isomerization product.
- Woof, Callum R.,Durand, Derek J.,Fey, Natalie,Richards, Emma,Webster, Ruth L.
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supporting information
p. 5972 - 5977
(2021/03/17)
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- Process for isomerizing and converting (Z)-olefins to (E)-olefins
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The invention belongs to the technical field of metal catalytic synthesis, and discloses a method for isomerizing and converting (Z)-olefins into (E)-olefins. The (E)-olefins are prepared through a reaction at -30-80 DEG C for 0.5-48 h by using a combination of CoX2 and a PNP or PAO ligand as a catalyst in the presence of an activating reagent; and a molar ratio of the (Z)-olefins to the CoX2 to the PNP or PAO ligand to the activating reagent is 1:(0.00001-0.10):(0.00001-0.10):(0.00003-0.30). The catalyst used in the invention is the combination of the cheap metal cobalt salt and the simple and easily available ligand, no other toxic transition metal (such as ruthenium, rhodium and palladium) salt is added in the reaction, and the method also has the advantages of cheap and easily available raw material, good functional group tolerance, mild reaction conditions, simplicity in operation, and e atom economy of 100%.
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Paragraph 0048-0050; 0066-0068; 0075-0077
(2020/03/25)
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- Cobalt-Catalyzed Z to e Isomerization of Alkenes: An Approach to (E)-β-Substituted Styrenes
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An efficient cobalt-catalyzed Z to E isomerization of β-substituted styrenes using the amido-diphosphine ligand was developed, delivering the (E)-isomers with good functional tolerance and high stereoselectivity. The reaction could be scaled up to gram-scale with a catalyst loading of 0.1 mol %, using a mixture of (Z)- and (E)-alkene as the starting material. Preliminary mechanistic studies indicated that cobalt(I)-hydride and a benzylic-cobalt species were probably involved in the reaction, as supported by experiments and DFT calculations.
- Liu, Hongmei,Xu, Man,Cai, Cheng,Chen, Jianhui,Gu, Yugui,Xia, Yuanzhi
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supporting information
p. 1193 - 1198
(2020/02/04)
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- Superelectrophilic Fe(III)-Ion Pairs as Stronger Lewis Acid Catalysts for (E)-Selective Intermolecular Carbonyl-Olefin Metathesis
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An intermolecular carbonyl-olefin metathesis reaction is described that relies on superelectrophilic Fe(III)-based ion pairs as stronger Lewis acid catalysts. This new catalytic system enables selective access to (E)-olefins as carbonyl-olefin metathesis products. Mechanistic investigations suggest the regioselective formation and stereospecific fragmentation of intermediate oxetanes to be the origin of this selectivity. The optimized conditions are general for a variety of aryl aldehydes and trisubstituted olefins and are demonstrated for 28 examples in up to 64% overall yield.
- Albright, Haley,Schindler, Corinna S.,Vonesh, Hannah L.
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supporting information
p. 3155 - 3160
(2020/04/21)
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- Radical Cation Diels-Alder Reactions by TiO2 Photocatalysis
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Radical cation Diels-Alder reactions by titanium dioxide (TiO2) photocatalysis in lithium perchlorate/nitromethane solution are described. TiO2 photocatalysis promotes reactions between electron-rich dienes and dienophiles, which would otherwise be difficult to accomplish due to electronic mismatching. The reactions are triggered by hole oxidation of the dienophile and are completed by the excited electron reduction of the radical cation intermediate at the dispersed surface in the absence of any sacrificial substrate.
- Nakayama, Kaii,Maeta, Naoya,Horiguchi, Genki,Kamiya, Hidehiro,Okada, Yohei
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supporting information
p. 2246 - 2250
(2019/04/10)
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- Stereospecific Iron-Catalyzed Carbon(sp2)-Carbon(sp3) Cross-Coupling with Alkyllithium and Alkenyl Iodides
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An efficient synthetic protocol involving iron-catalyzed cross-coupling reactions between organolithium compounds and alkenyl iodides as key coupling partners was achieved. More than 30 examples were obtained with moderate to good yields and high stereospecificity. Gram-scale and synthetic applications of this procedure are recorded herein to demonstrate its feasibility and potential utilization.
- Lu, Xiao-Lin,Shannon, Mark,Peng, Xiao-Shui,Wong, Henry N. C.
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supporting information
p. 2546 - 2549
(2019/03/26)
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- Radical Cation Cyclopropanations via Chromium Photooxidative Catalysis
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The chromium photocatalyzed cyclopropanation of diazo reagents with electron-rich alkenes is described. The transformation occurs under mild conditions and features specific distinctions from traditional diazo-based cyclopropanations (e.g., avoiding β-hydride elimination, chemoselectivity considerations, etc.). The reaction appears to work most effectively using chromium catalysis, and a number of decorated cyclopropanes can be accessed in generally good yields.
- Sarabia, Francisco J.,Ferreira, Eric M.
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supporting information
p. 2865 - 2868
(2017/06/07)
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- (E)-Selective Wittig Reactions between a Nonstabilized Phosphonium Ylide Bearing a Phosphastibatriptycene Skeleton and Benzaldehydes
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Wittig reactions between benzaldehyde derivatives and a nonstabilized phosphonium ylide bearing a phosphastibatriptycene skeleton, regarded as a tridentate aryl ligand, gave (E)-alkenes with high selectivity in the presence of both lithium and sodium salts. As previously reported, reactions between a triphenylphosphonium ylide and benzaldehyde derivatives under the same conditions afforded mainly (Z)-alkenes. Variable-temperature (VT)31P{1H} NMR spectra showed two signals, assigned to cis- and trans-1,2-oxaphosphetanes, which were observed at different temperatures (–80 °C and –40 °C, respectively) in the Wittig reaction between benzaldehyde and the nonstabilized phosphonium ylide bearing the phosphastibatriptycene skeleton, in the presence of both lithium and sodium salts, and showed the existence of equilibrium between these products at –40 °C. On the other hand, this equilibrium was not clearly observed in the reaction between the triphenylphosphonium ylide and benzaldehyde, for which only one signal was detected. The observed intermediates were confirmed to be 1,2-oxaphosphetanes by deprotonation of the isolated β-hydroxyalkylphosphonium salts bearing a phosphastibatriptycene skeleton and a triphenylphosphine moiety, respectively. Crossover reactions were conducted in the deprotonations of β-hydroxyalkylphosphonium salts with TMS2NNa in the presence of p-chlorobenzaldehyde, resulting in the observation of signals corresponding to 1,2-oxaphosphetanes containing phenyl and p-chlorophenyl groups at the 4-positions, indicating the exchange process between benzaldehyde and p-chlorobenzaldehyde at –40 °C for the phosphastibatriptycene system and at 0 °C for triphenyl derivatives. These results clearly indicated that stereochemical drift occurred at those temperatures, even in reactions using nonstabilized phosphonium ylides. The stereochemical drift in the phosphastibatriptycene system occurred at a lower temperature than in the case of the triphenyl derivative, thus explaining the (E)-selective Wittig reactions between the benzaldehyde derivatives and the nonstabilized phosphastibatriptycene-based phosphonium ylide in the presence of lithium and sodium salts.
- Uchiyama, Yosuke,Ohtsuki, Takemaru,Murakami, Rikiya,Shibata, Munenori,Sugimoto, Jun
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p. 159 - 174
(2017/01/14)
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- Nitrogen-Doped Carbon-Encapsulated Nickel/Cobalt Nanoparticle Catalysts for Olefin Migration in Allylarenes
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Olefin migration in allylarenes is typically performed with precious-metal-based homogeneous catalysts. In contrast, very limited progress has been made with the use of cheap, Earth-abundant base metals as heterogeneous catalysts for these transformations—in spite of the obvious economic and environmental advantages. Herein, we report on the use of an easily prepared heterogeneous catalyst material for the migration of olefins, in particular, for allylarenes. The catalyst material consists of nickel/cobalt alloy nanoparticles encapsulated in nitrogen-doped carbon shells. The encapsulated nanoparticles are stable in air and are easily collected by centrifugation, filtration, or magnetic separation. Furthermore, we demonstrate that the catalysts can be reused several times and provide continuously high yields of the olefin-migration product.
- Kramer, S?ren,Mielby, Jerrik,Buss, Kasper,Kasama, Takeshi,Kegn?s, S?ren
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p. 2930 - 2934
(2017/08/14)
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- Direct Olefination of Alcohols with Sulfones by Using Heterogeneous Platinum Catalysts
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Carbon-supported Pt nanoparticles (Pt/C) were found to be effective heterogeneous catalysts for the direct Julia olefination of alcohols in the presence of sulfones and KOtBu under oxidant-free conditions. Primary alcohols, including aryl, aliphatic, allyl, and heterocyclic alcohols, underwent olefination with dimethyl sulfone and aryl alkyl sulfones to give terminal and internal olefins, respectively. Secondary alcohols underwent methylenation with dimethyl sulfone. Under 2.5 bar H2, the same reaction system was effective for the transformation of alcohol OH groups to alkyl groups. Structural and mechanistic studies of the terminal olefination system suggested that Pt0 sites on the Pt metal particles are responsible for the rate-limiting dehydrogenation of alcohols and that KOtBu may deprotonate the sulfone reagent. The Pt/C catalyst was reusable after the olefination, and this method showed a higher turnover number (TON) and a wider substrate scope than previously reported methods, which demonstrates the high catalytic efficiency of the present method. Olefination of alcohols: The first heterogeneous catalytic terminal and internal olefination of primary alcohols and methylenation of secondary alcohols with sulfones, a reusable carbon-supported Pt catalyst, and KOtBu is reported (see scheme).
- Hakim Siddiki,Touchy, Abeda Sultana,Kon, Kenichi,Shimizu, Ken-Ichi
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p. 6111 - 6119
(2016/04/26)
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- Nickel-Catalyzed Allylic C(sp2)–H Activation: Stereoselective Allyl Isomerization and Regiospecific Allyl Arylation of Allylarenes
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Stereoselective allyl isomerization and regiospecific allyl arylation reactions of allylarenes with a catalytic system comprising nickel(II) with an aryl Grignard reagent were studied. Both reactions are triggered by allylic internal C(sp2)–H activation by in-situ-formed Ni0, which is inserted into the C–H bond at the 2-position of the allyl moiety without a directing group. The isomerization of allylarene to 1-propenylarene favors the E isomer and proceeds with quantitative conversion. The arylation takes place through oxidative cross-coupling of allylarenes with excess Grignard reagent. It occurs regiospecifically at the position of C(sp2)–H activation and represents a new method for the synthesis of 1,1-disubstituted olefins. The results of deuterium labeling experiments reveal an alkenyl/alkyl mechanism involving allylic internal C(sp2)–H activation and multiple intermolecular 1,2-, 1,3-, and 2,3-hydride shifts. These methods represent new approaches to the functionalization of olefins, and the mechanistic investigations could be helpful for the discovery and design of new strategies for olefin functionalization.
- Wu, Qiang,Wang, Lanlan,Jin, Rizhe,Kang, Chuanqing,Bian, Zheng,Du, Zhijun,Ma, Xiaoye,Guo, Haiquan,Gao, Lianxun
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p. 5415 - 5422
(2016/11/22)
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- Direct organocatalytic oxo-metathesis, a trans-selective carbocation-catalyzed olefination of aldehydes
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A direct organocatalytic carbonyl/olefin oxo-metathesis has been developed. The reaction is catalyzed by trityl tetrafluoroborate (TrBF4) and utilizes unactivated alkenes for the olefination of aromatic aldehydes to give trans β-alkylstyrenes in yields of 44-85% with only acetone as the byproduct. The pronounced Lewis acidity of the carbocation results in unusual reactivity that is proposed to catalyze a stepwise [2+2] cycloaddition to give an oxetane intermediate. Fragmentation of the latter in a formal retro [2+2] reaction gives the oxo-metathesis product.
- Naidu, Veluru Ramesh,Bah, Juho,Franzén, Johan
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supporting information
p. 1834 - 1839
(2015/05/27)
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- Photocatalytic synthesis of dihydrobenzofurans by oxidative [3+2] cycloaddition of phenols
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We report a protocol for oxidative [3+2] cycloadditions of phenols and alkenes applicable to the modular synthesis of a large family of dihydrobenzofuran natural products. Visible-light-activated transition metal photocatalysis enables the use of ammonium persulfate as an easily handled benign terminal oxidant. The broad range of organic substrates that are readily oxidized by photoredox catalysis suggests that this strategy may be applicable to a variety of useful oxidative transformations.
- Blum, Travis R.,Zhu, Ye,Nordeen, Sarah A.,Yoon, Tehshik P.
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supporting information
p. 11056 - 11059
(2015/03/30)
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- Copper-catalyzed oxidative alkenylation of C(sp3)-H bonds via benzyl or alkyl radical addition to β-nitrostyrenes
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A new method for the preparation of (E)-β-alkylstyrene derivatives has been developed via the addition of a benzyl or alkyl radical to β-nitrostyrenes using di-tert-butyl peroxide (DTBP) as the oxidant in the presence of Cu powder catalyst. The C-H bonds in various toluene derivatives, ethers, alkanes and alcohols were successfully converted into C-C bonds to yield the corresponding (E)-β-alkylstyrene derivatives in moderate to good yields.
- Guo, Shengrong,Yuan, Yanqin,Xiang, Jiannan
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supporting information
p. 3093 - 3097
(2015/04/14)
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- Iron-catalyzed olefin hydrogenation at 1 bar H2 with a FeCl3-LiAlH4 catalyst
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The scope and mechanism of a practical protocol for the iron-catalyzed hydrogenation of alkenes and alkynes at 1 bar H2 pressure were studied. The catalyst is formed from cheap chemicals (5 mol% FeCl3-LiAlH4, THF). A homogeneous mechanism operates at early stages of the reaction while active nanoparticles form upon ageing of the catalyst solution. This journal is
- Gieshoff, Tim N.,Villa, Matteo,Welther, Alice,Plois, Markus,Chakraborty, Uttam,Wolf, Robert,Jacobi Von Wangelin, Axel
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supporting information
p. 1408 - 1413
(2015/03/18)
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- Direct catalytic olefination of alcohols with sulfones
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The synthesis of terminal as well as internal olefins was achieved by the one-step olefination of alcohols with sulfones catalyzed by a ruthenium pincer complex. Furthermore performing the reaction with dimethyl sulfone under mild hydrogen pressure provides a direct route for the replacement of alcohol hydroxy groups by methyl groups in one step.
- Srimani, Dipankar,Leitus, Gregory,Ben-David, Yehoshoa,Milstein, David
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supporting information
p. 11092 - 11095
(2015/03/30)
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- A facile and convenient sequential homobimetallic catalytic approach towards β-methylstyrenes. A one-pot Stille cross-coupling/isomerization strategy
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An efficient one-pot synthetic approach towards β-methylstyrenes is reported. The transformation, based on sequential homobimetallic catalysis, involves a Stille cross-coupling reaction between aryl halides and allyltributylstannane, followed by an in situ palladium-catalyzed conjugative isomerization. The reaction was optimized, and the best results were obtained with 10 mol% Pd(PPh3)2Cl2, 8.0 equiv. LiCl, and 0.5 equiv. PPh3 in diglyme at 130 °C for 12 h. It was demonstrated that the reaction tolerates a wide variety of functional groups. This journal is the Partner Organisations 2014.
- Simonetti, Sebastian O.,Larghi, Enrique L.,Kaufman, Teodoro S.
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p. 3735 - 3743
(2014/06/09)
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- Method for synthesizing (E)-Anethol and Related Compounds By Cross Coupling Reaction of Potassium alllyltrifluroborate and 4-bromoanisole and aryl halides
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Methods of producing substituted and non-substituted beta-methyl styrene by a cross-coupling reaction are provided. The disclosure also provides for methods of preparing (E)-Anethol and related compounds by a cross coupling reaction of potassium allyltrifluoroborate and 4-bromoanisole and aryl halides. Compounds, compositions, and methods of treating disorders utilizing beta-methyl styrene are also provided.
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Page/Page column 4
(2012/01/15)
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- Catalytic isomerization of hydrophobic allylarenes in aqueous microemulsions
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In the course of our attempts to replace the traditional but environmentally disfavored organic solvents in organic processes by water, we studied the double bond isomerization of hydrophobic allylarenes, in aqueous microemulsions. The catalyst for these reactions was the rhodium-trichloride- Aliquat 336 ion pair encaged within hydrophobic silica sol-gel. During the entrapment of the rhodium compound, it was converted into supported catalytically active Rh(0) nanoparticles characterized by TEM and XPS studies. The transformations of the allylarenes to (E)- and (Z)-1-phenyl-1-propenes follows the first order rate law, and proved to be significantly affected by the electronic nature of the substrates and by the hydrophobicity of the sol-gel support. Upon completion of the isomerization the catalyst could be recovered and recycled at least six times without a decrease in the catalytic activity after the first catalytic run.
- Meltzer, Diana,Avnir, David,Fanun, Monzer,Gutkin, Vitaly,Popov, Inna,Schom?cker, Reinhard,Schwarze, Michael,Blum, Jochanan
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experimental part
p. 8 - 13
(2011/04/15)
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- Efficient double bond migration of allylbenzenes catalyzed by Pd(OAc) 2-HFIP system with unique substituent effect
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A novel catalyst system of Pd(OAc)2-HFIP induces double-bond migration of allylbenzenes under mild conditions with low catalytic loading to afford 1-propenylbenzenes. The reaction shows a unique substituent effect that is highly dependent on the distance of substituents from the allylic moiety. Thus, the reactivity of substrates bearing a methyl group is ordered in para > meta > ortho, whereas it is entirely reversed as ortho > meta > para for methoxy and chloro substituents.
- Nishiwaki, Nagatoshi,Kamimura, Ryuichiro,Shono, Kimihiro,Kawakami, Toshihiko,Nakayama, Katsuhisa,Nishino, Kohei,Nakayama, Takayuki,Takahashi, Keisuke,Nakamura, Aki,Hosokawa, Takahiro
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supporting information; experimental part
p. 3590 - 3592
(2010/08/19)
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- Remarkable regioselectivity in microwave-enhanced palladium-catalyzed allylation reaction involving allyltrifluoroborates and aryl halides
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An unprecedented cross-coupling reaction of potassium allyltrifluoroborates and aryl halides to the corresponding trans-β-methylstyrenes in the presence of PdCl2(dtbpf) catalyst under microwave heating was developed.
- Al-Masum, Mohammad,Alam, Shahrina
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experimental part
p. 5201 - 5204
(2009/12/06)
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- Catalytic amide-mediated methyl transfer from silanes to alkenes in Fujiwara-Moritani oxidative coupling
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(Chemical Equation Presented) Intramolecular assistance: Carbon-bound trimethylsilyl groups are activated intramolecularly by a carbonyl group and can participate in Heck reactions under oxidative conditions. Good stereoselectivities are obtained for a range of di-and trisubstituted alkenes (see example).
- Rauf, Waqar,Brown, John M.
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supporting information; experimental part
p. 4228 - 4230
(2009/03/12)
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- Manganese-catalyzed cross-coupling reaction between aryl grignard reagents and alkenyl halides
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(Chemical Equation Presented) Aryl Grignard reagents react stereospecifically with alkenyl halides in the presence of manganese chloride (10%) to afford good yields of cross-coupling products.
- Cahiez, Gerard,Gager, Olivier,Lecomte, Fabien
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supporting information; experimental part
p. 5255 - 5256
(2009/05/30)
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- Nickel catalyzed cross-coupling of modified alkyl and alkenyl Grignard reagents with aryl- and heteroaryl nitriles: Activation of the C-CN bond
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The nickel catalyzed cross-coupling of alkyl and alkenyl Grignard reagents with aryl nitrile derivatives affords good yields of the corresponding aryl alkanes or aryl alkenes via activation of the C-CN bond. To prevent direct addition of the nucleophile to the nitrile group, the reactivity of the Grignard reagent was modulated by reaction with either LiOt-Bu or PhSLi prior to cross-coupling. The optimum catalyst was determined to be NiCl2(PMe3)2, which is a convenient air stable commercially available complex.
- Miller, Joseph A.,Dankwardt, John W.
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p. 1907 - 1910
(2007/10/03)
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- Convenient preparation of trans-arylalkenes via palladium(II)-catalyzed isomerization of cis-arylalkenes
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A convenient method for the isomerization of cisarylalkenes to their trans isomers using a palladium(II) catalyst is described. The reaction conditions are mild and general across a range of arylalkenes. The synthesis of a trans-resveratrol derivative from a mixture of alkene isomers was also completed.
- Yu, Jinquan,Gaunt, Matthew J.,Spencer, Jonathan B.
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p. 4627 - 4629
(2007/10/03)
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- Mechanistic aspects of aminium salt-catalyzed Diels-Alder reactions: The substrate ionization step
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Substituent effects in the aminium salt catalyzed Diels-Alder reactions of 2,3-dimetnyl-1,3-butadiene with a series of meta and para substituted β-methylstyrenes are used to probe detailed mechanistic aspects of these reactions. Kinetic studies were carried out using two different aminium salt catalysts and also electrochemically, using anodic potentials corresponding to the oxidation potentials of the aminium salts. Substituent effects in the equilibrium oxidations of the styrene substrates to the corresponding cation radicals were also studied, via oxidation potential measurements. The results indicate rate determining one electron oxidation of the sytrenes to their cation radicals via an outer sphere electron transfer.
- Yueh, Wang,Bauld, Nathan L.
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p. 529 - 538
(2007/10/03)
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- Radical-Stabilization-Energy - the MMEVBH Force Field
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Making use of the VB method of Malrieu et al. a force field has been developed, which allows to calculate heats of formation of hydrocarbons (conjugated and non-conjugated olefins, radicals and diradicals) with high accuracy.With this method radical stabilization energies (RSE) for a great number of delocalized radicals are calculated and compared with experimental values, derived from shock-tube measurements of dissociation energies or from rotational barriers of substituted olefins.A detailed analysis of the RSE with respect to structure, substituents, strain, and aromaticity is presented. - Key Words: Resonance energy / Heats of formation / Single pulse shock tube / Intrisic rotational barrier
- Roth, Wolfgang R.,Staemmler, Volker,Neumann, Martin,Schmuck, Carsten
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p. 1061 - 1118
(2007/10/02)
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- Alkyliron and Alkylcobalt Reagents, VII. - On the Substitution of the Halogen of Alkenyl Chlorides, Alkenyl Fluorides, and Alkynyl Halides by Reagents of the Type R4MLi2 (M = Fe, Co)
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Me4FeLi2 and Me4CoLi2, which are favourable reagents for the substitution of Br in alkenyl bromides, also proved to be favourable for the substitution of the halogen in alkenyl chlorides (yields 68-99 percent; nearly complete retention of configuration in the case of Me4FeLi2), β-fluorostyrene (best yield 92 percent), and 1-fluoronaphthalene (best yield 47 percent).Me4FeLi2 differentiates between various alkenyl chlorides in 1:1 competition experiments better than Me4CoLi2 and is the optimal reagent for the substitution of halogen in 1-chloro-2-phenylethyne (12), 1-bromo-2-phenylethyne (13), and 1-chloro-3-phenoxypropyne (15) by methyl (yields 70, 46, and 80 percent, respectively).Substitution of the halogen in 12 by the n-butyl, n-octyl, and phenyl residue is better achieved by the catalytic systems RMgBr + 2.5 mol percent FeCl2 (R = nBu, nOct, Ph; yields 75, 63, and 96 percent, respectively) than by the reagents nBu4FeLi2, nBu4Fe(MgBr)2, nOct4Fe(MgBr)2, or Ph4Fe(MgBr)2 (yields 18-28 percent). Key Words: Iron, organo complexes / Cobalt, organo complexes
- Kauffmann, Thomas,Saelker, Reiner,Voss, Karl-Uwe
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p. 1447 - 1452
(2007/10/02)
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- Oxidation by Cobalt(III) Acetate. Part 12. Stereoselective Formation of threo-1-Phenylpropane-1,2-diol Monoacetate in Oxidation of β-Methylstyrenes Unsubstituted and Substituted with Electron-donating Groups by Cobalt(III) and Manganese(III) Acetate in Acetic Acid
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Stereochemistry in oxidation of β-methylstyrenes unsubstituted and substituted with electron-donating groups (H, p-MeO, and p-Me) by cobalt(III) and mangenese(III) acetate in acetic acid or in acetic acid containing trifluoroacetic acid has been studied. threo-1-Arylpropane-1,2-diol monoacetates were the main products in the oxidations of both E- and Z-alkenes by these oxidants.These results are explained in terms of the difference in stabilities between intermediate (11) and (14).
- Hirano, Masao,Hamaguchi, Takayoshi,Zhang, Xiumin,Morimoto, Takashi
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p. 2141 - 2146
(2007/10/02)
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- Reaction of 1-Aryl-3-chloropropenes with Grignard Reagents. Nucleophilic Substitution versus Single-electron Transfer
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The reactions of ambident 1-aryl-3-chloropropenes (1a-e) with a series of Grignard reagents, R'MgY (R' = Me, Pr, Ph, Pri, But; Y = Br, I), were carried out in diethyl ether (EE) and tetrahydrofuran (THF).The products were a mixture of two alkylation products (2) and (3), and three dimerization products (4)-(6).The alkylation:dimerization ratio and the composition of the two alkylation products were a marked function of substituent electronic effects in the chlorides (1a-e), R' or Y of R'MgY, and solvent.On the basis of the stereochemistry of alkylation, cyclizable probe experiments, and the effect of the addition of FeCl3 on product composition, the following conclusions were obtained.First, dimers (4)-(6) are most likely to be produced by a mechanism involving single-electron transfer (SET).Second, for the formation of alkylation products (2) and (3), three alternative pathways contribute depending on the nature of R'MgY and solvent, (a) competitive SN2-SN2' pathways in the reaction of R'MgBr in EE, (b) a process involving SET in the reaction with R'MgI in EE, and (c) SN2 pathways in the reaction of R'MgBr in THF.
- Muraoka, Kiyoshige,Nojima, Masatomo,Kusabayashi, Shigekazu,Nagase, Shigeru
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p. 761 - 768
(2007/10/02)
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- REACTIONS EN MILIEU HETEROGENE SOLIDE-LIQUIDE FAIBLEMENT HYDRATE III - LA REACTION DE WITTIG DANS LE SYSTEME CARBONATES ALCALINS/SOLVANT ORGANIQUE PROTIQUE
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The use of alkaline carbonates in a slighty hydrated solid-liquid protic organic media allowed the synthesis of alkenes from polyfunctional aldehydes with high yield in a E preferential stereochemistry specially with non-stabilized ylides.It has been shown that the decomposition of the threo betain acts as the determining step of the reaction.
- Le Bigot, Y.,El Gharbi, R.,Delmas, M.,Gaset, A.
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p. 3813 - 3824
(2007/10/02)
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- 4,14-DIVINYL-(E,E)-PARACYCLOPHANE-1,11-DIENE. AN UNUSUAL PRODUCT FROM A 1,10-HOFMANN ELIMINATION
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The isolation of 4,14-divinyl-(E,E)-paracyclophane-1,11-diene from the cyclodimerization reaction of 7,8-divinyl-p-quinodimethane and its characterization are described.The title compound features head-to-tail, cofacially paired styryl moieties and its UV spectrum is compared in terms of electronic and structural characteristics with that of its head-to-head analogue and an open chain model compund.
- Glatzhofer, Daniel T.,Longone, Daniel T.
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p. 5923 - 5926
(2007/10/02)
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- WITTIG-REAKTION VON TRIPHENYLPHOSPHONIO-ALKYLIDEN MIT SUBSTITUIERTEN BENZALDEHYDEN: HAMMETT-BEZIEHUNG UND TEILWEISE REVERSIBILITAT DER ADDUKT-BILDUNG
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Bei Abwesenheit loslicher Lithium-Salze vereinigen sich Triphenylphosphonio-methylid und -ethylid bereits bei -75 deg C mit Aldehyden. Elektronenanziehende Liganden beschleunigen, elektronenspendende Liganden verzogern die Anlagerung der Ylide an die substituierten Benzaldehyde.Die Addukte(Oxaphosphetane) zerfallen erst oberhalb -30 deg C zu Olefin und Triphenylphosphinoxid.Wird vor dem Zerfall ein zweiter Aldehyd oder ein zweites Ylid zugesetzt, so findet ein teilweiser Austausch der Komponenten statt.
- Piskala, Alois,Rehan, Abdul Hamid,Schlosser, Manfred
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p. 3539 - 3551
(2007/10/02)
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- Catalytic Double Bond Isomerization by Polystyrene-Anchored RuCl2(PPh3)3
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Dichlorotris(triphenylphosphine)ruthenium has been anchored to diphenylphosphinated styrene-divinylbenzene copolymer.The resulting leaching-resistant catalyst was employed successfully for the isomerization of allylbenzenes and allyl alcohols in numerous turnovers.The stability of the catalyst was examined in different media, and its performances were compared with those of homogeneous RuCl2(PPh3)3 and with those of polymer-bound as well as of free RhCl(PPh3)3 and IrCl(CO)(PPh3)2
- Zoran, Amikam,Sasson, Yoel,Blum, Jochanan
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p. 255 - 260
(2007/10/02)
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