- Bis-selenonium Cations as Bidentate Chalcogen Bond Donors in Catalysis
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Lewis acids are frequently employed in catalysis but they often suffer from high moisture sensitivity. In many reactions, catalysts are deactivated because of the problem that strong Lewis acids also bond to the products. In this research, hydrolytically stable bidentate Lewis acid catalysts derived from selenonium dicationic centers have been developed. The bis-selenonium catalysts are employed in the activation of imine and carbonyl groups in various transformations with good yields and selectivity. Lewis acidity of the bis-selenonium salts was found to be stronger than that of the monoselenonium systems, attributed to the synergistic effect of the two cationic selenonium centers. In addition, the bis-selenonium catalysts are not inhibited by strong bases or moisture.
- He, Xinxin,Wang, Xinyan,Tse, Ying-Lung Steve,Ke, Zhihai,Yeung, Ying-Yeung
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p. 12632 - 12642
(2021/10/21)
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- The charge-assisted hydrogen-bonded organic framework (CAHOF) self-assembled from the conjugated acid of tetrakis(4-aminophenyl)methane and 2,6-naphthalenedisulfonate as a new class of recyclable Br?nsted acid catalysts
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The acid–base neutralization reaction of commercially available disodium 2,6-naphthalenedisulfonate (NDS, 2 equivalents) and the tetrahydrochloride salt of tetrakis(4-aminophenyl)methane (TAPM, 1 equivalent) in water gave a novel three-dimensional charge-assisted hydrogen-bonded framework (CAHOF, F-1). The framework F-1 was characterized by X-ray diffraction, TGA, elemental analysis, and 1H NMR spectroscopy. The framework was supported by hydrogen bonds between the sulfonate anions and the ammonium cations of NDS and protonated TAPM moieties, respectively. The CAHOF material functioned as a new type of catalytically active Br?nsted acid in a series of reactions, including the ring opening of epoxides by water and alcohols. A Diels–Alder reaction between cyclopentadiene and methyl vinyl ketone was also catalyzed by F-1 in heptane. Depending on the polarity of the solvent mixture, the CAHOF F-1 could function as a purely heterogeneous catalyst or partly dissociate, providing some dissolved F-1 as the real catalyst. In all cases, the catalyst could easily be recovered and recycled.
- Belokon, Yuri N.,Dmitrienko, Artem O.,Gak, Alexander S.,Gerasimov, Igor S.,Kuznetsova, Svetlana A.,Larionov, Vladimir A.,Li, Han,Medvedev, Michael G.,Nelyubina, Yulia V.,North, Michael,Saghyan, Ashot S.,Smol'yakov, Alexander F.,Zhereb, Vladimir P.
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supporting information
p. 1124 - 1134
(2020/07/10)
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- High Activity and Efficient Turnover by a Simple, Self-Assembled "artificial Diels-Alderase"
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The Diels-Alder (DA) reaction is a cornerstone of synthesis, yet Nature does not use catalysts for intermolecular [4+2] cycloadditions. Attempts to create artificial "Diels-Alderases" have also met with limited success, plagued by product inhibition. Using a simple Pd2L4 capsule we now show DA catalysis that combines efficient turnover alongside enzyme-like hallmarks. This includes excellent activity (kcat/kuncat > 103), selective transition-state stabilization comparable to the most proficient DA catalytic antibodies, and control over regio- and chemoselectivity that would otherwise be difficult to achieve using small-molecule catalysts. Unlike other catalytic approaches that use synthetic capsules, this method is not defined by entropic effects; instead multiple H-bonding interactions modulate reactivity, reminiscent of enzymatic action.
- Martí-Centelles, Vicente,Lawrence, Andrew L.,Lusby, Paul J.
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supporting information
p. 2862 - 2868
(2018/03/08)
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- Stereoselectivity in a series of 7-alkylbicyclo[3.2.0]hept-2-enes: Experimental and computational perspectives
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Rate constants for overall decomposition (kd) for a series of exo-7-alkylbicyclo[3.2.0]hept-2-enes are relatively invariant. For the alkyl substituents ethyl, propyl, butyl, isopropyl, and t-butyl, the ratio of the rate constant for [1,3] sigmatropic rearrangement to the rate constant for fragmentation, k13/kf, is significantly lower than k13/kf?=?150 observed for exo-7-methylbicyclo[3.2.0]hept-2-ene. Regardless of the size and mass of the alkyl group, the stereoselectivity of the [1,3] carbon migration appears to be quite stable at 80% to 89% suprafacial inversion (si), an observation consistent with conservation of angular momentum but not conservation of orbital symmetry. This global result comports with the phenomenon of “dynamic matching” espoused by Carpenter and collaborators for [1,3] sigmatropic rearrangements in general.
- Leber, Phyllis,Kidder, Katherine,Viray, Don,Dietrich-Peterson, Eric,Fang, Yuan,Davis, Alexander
-
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- Facile Synthesis of a New Chiral BINOL–Silica Hybrid Catalyst for Asymmetric Diels–Alder and Aza Michael Reactions
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Abstract: A novel chiral BINOL–silica hybrid has been successfully prepared by the reaction of (S)-BINOL and SiCl4 following by gel polymerization under atmosphere condition. The synthesized catalyst was characterized by elemental analysis, Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Catalytic activity of the chiral BINOL–silica hybrid for diastereo- and enantioselective Diels–Alder and aza Michael reactions has been investigated. Mild reaction conditions, high yields, excellent diastereo- and enantiomeric excess make this powerful and effective catalyst as an attractive option for the synthesis of chiral organic compounds. Graphical Abstract: [Figure not available: see fulltext.]
- Saeidian, Hamid,Paghandeh, Hossein,Parvin, Zahra,Mirjafary, Zohreh,Ghaffarzadeh, Mohammad
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p. 1366 - 1374
(2018/05/03)
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- Improving the efficiency of the Diels-Alder process by using flow chemistry and zeolite catalysis
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The industrial application of the Diels-Alder reaction for the atom-efficient synthesis of (hetero)cyclic compounds constitutes an important challenge. Safety and purity concerns, related to the instability of the polymerization prone diene and/or dienophile, limit the scalability of the production capacity of Diels-Alder products in a batch mode. To tackle these problems, the use of a high-pressure continuous microreactor process was considered. In order to increase the yields and the selectivity towards the endo-isomer, commercially available zeolites were used as a heterogeneous catalyst in a microscale packed bed reactor. As a result, a high conversion (≥95%) and endo-selectivity (89:11) were reached for the reaction of cyclopentadiene and methyl acrylate, using a 1:1 stoichiometry. A throughput of 0.87 g h-1 during at least 7 h was reached, corresponding to a 3.5 times higher catalytic productivity and a 14 times higher production of Diels-Alder adducts in comparison to the heterogeneous lab-scale batch process. Catalyst deactivation was hardly observed within this time frame. Moreover, complete regeneration of the zeolite was demonstrated using a straightforward calcination procedure.
- Seghers,Protasova,Mullens,Thybaut,Stevens
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supporting information
p. 237 - 248
(2017/08/14)
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- Borenium ionic liquids as catalysts for Diels-Alder reaction: Tuneable Lewis superacids for catalytic applications
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Ionic liquids based on the tricoordinate borenium cation were used for the first time as Lewis acid catalysts for a model Diels-Alder reaction. The conversion of the dienophile was successfully correlated with the Gutmann acceptor number values of the ionic liquids. Borenium ionic liquids exceeded the performance of catalysts reported in the literature.
- Matuszek,Coffie,Chrobok,Swad?ba-Kwa?ny
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p. 1045 - 1049
(2017/08/15)
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- Electrostatically enhanced phosphoric acids: A tool in Br?nsted acid catalysis
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A novel type of phosphoric acid catalyst with enhanced reactivity is reported. These compounds possess one or two positively charged centers which electrostatically activate them. This is illustrated in several bond-forming transformations including Friedel-Crafts and Diels-Alder reactions as well as a ring-opening polymerization. Rate accelerations corresponding to orders of magnitude are observed.
- Ma, Jie,Kass, Steven R.
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supporting information
p. 5812 - 5815
(2016/11/29)
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- Ruthenium Lewis Acid-Catalyzed Asymmetric Diels–Alder Reactions: Reverse-Face Selectivity for α,β-Unsaturated Aldehydes and Ketones
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Acrolein, methacrolein, methyl vinyl ketone, ethyl vinyl ketone, 3-methyl-3-en-2-one, and divinyl ketone were coordinated to a cationic cyclopentadienyl ruthenium(II) Lewis acid incorporating the electron-poor bidentate BIPHOP–F ligand. Analysis by NOESY and ROESY NMR techniques allowed the determination of conformations of enals and enones present in solution in CD2Cl2. The results were compared to solid-state structures and to the facial selectivities of catalytic asymmetric Diels–Alder reactions with cyclopentadiene. X-Ray structures of four Ru-enal and Ru-enone complexes show the α,β-unsaturated C=O compounds to adopt an anti-s-trans conformation. In solution, enals assume both anti-s-trans and anti-s-cis conformations. An additional conformation, syn-s-trans, is present in enone complexes. Enantioface selectivity in the cycloaddition reactions differs for enals and enones. Reaction products indicate enals to react exclusively in the anti-s-trans conformation, whereas with enones, the major product results from the syn-s-trans conformation. The alkene in s-cis conformations, while present in solution, is shielded and cannot undergo cycloaddition. A syn-s-trans conformation is found in the solid state of the bulky 6,6-dimethyl cyclohexanone-Ru(II) complex. The X-ray structure of divinyl ketone is unique in that the Ru(II) center binds the enone via a η2bond to one of the alkene moieties. In solution, coordination to Ru–C=O oxygen is adopted. A comparison of facial preference is also made to the corresponding indenyl Lewis acids.
- Thamapipol, Sirinporn,Ludwig, Bettina,Besnard, Céline,Saudan, Christophe,Kündig, E. Peter
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p. 774 - 789
(2016/10/17)
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- PRODUCTION METHOD OF EXO-TYPE NORBORNENE COMPOUND
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PROBLEM TO BE SOLVED: To provide a production method of a norbornene compound, in particular, exo-enriched 2-acyl-5-norbornene containing many exo isomers, which is useful as a source material precursor of monomers for electronic materials and optical materials. SOLUTION: The production method of an exo-type norbornene compound is characterized by bringing an endo-type norbornene compound having an acyl group at a second position expressed by the formula below into contact with a tertiary amino compound (B) to carry out epimerization. The production method is carried out in a batch process where distillation purification is performed after the reaction or in a continuous process where purification is performed by reactive distillation. In the formula, R represents a hydrogen atom or an alkyl group or a phenyl group which may have a substituent. COPYRIGHT: (C)2015,JPOandINPIT
- -
-
Paragraph 0039-0041
(2017/01/02)
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- Intramolecularly Sulfur-Stabilized Silicon Cations with Chiral Binaphthyl Backbones: Synthesis of Three Different Motifs and Their Application in Enantioselective Diels-Alder Reactions
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The formation and 29Si NMR spectroscopic characterization of silicon cations that are intramolecularly stabilized by a dialkyl thioether are described. The chemical stability of the silicon-sulfur Lewis pair and, hence, the viability of the approach, were probed with a 2-[(alkylthio)methyl]phenyl-substituted hydrosilane as a proxy before three different motifs with chiral binaphthyl backbones were prepared in multistep sequences. The degree of shielding of the silicon atom in these cations was found to depend on the substitution pattern at the silicon atom and the ring size generated by the silicon-sulfur interaction. These sulfur-stabilized silicon cations are sufficiently reactive to promote Diels-Alder reactions of cyclohexa-1,3-diene with various dienophiles; the same set of reactions with cyclopentadiene is also reported. One of the three chiral Lewis acids induces low, but promising, enantioselectivity, and 24% ee is the highest value so far obtained with a cationic tetracoordinate silicon catalyst.
- Rohde, Volker H. G.,Müller, Maria F.,Oestreich, Martin
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p. 3358 - 3373
(2016/01/15)
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- Carbocations as lewis acid catalysts in diels-alder and Michael addition reactions
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In general, Lewis acid catalysts are metal-based compounds that owe their reactivity to a low-lying empty orbital. However, one potential Lewis acid that has received negligible attention as a catalyst is the carbocation. We have demonstrated the potential of the carbocation as a highly powerful Lewis acid catalyst for organic reactions. The stable and easily available triphenylmethyl (trityl) cation was found to be a highly efficient catalyst for the Diels-Alder reaction for a range of substrates. Catalyst loadings as low as 500 ppm, excellent yields, and good endo/exo selectivities were achieved. Furthermore, by changing the electronic properties of the substituents on the tritylium ion, the Lewis acidity of the catalyst could be tuned to control the outcome of the reaction. The ability of this carbocation as a Lewis acid catalyst was also further extended to the Michael reaction. Copyright
- Bah, Juho,Franzen, Johan
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p. 1066 - 1072
(2014/02/14)
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- Hydrogen-bond-rich ionic liquids as effective organocatalysts for Diels-Alder reactions
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The synthesis and characterisation of new hydrogen-bond-rich ionic liquids and studies of their catalytic performance in Diels-Alder reactions are described. d-Glucose and chloroalcohols were used as the raw materials and as the sources of hydroxyl groups for the synthesis of ionic-liquid cations, whereas weakly coordinating bis(trifluoromethylsulfonyl)imide was used as the anion. The new ionic liquids were analysed by 1H and 13C NMR spectroscopy and by ESI-MS experiments, which confirmed their structures. In addition, the thermal data of the studied ionic liquids measured by differential scanning calorimetry and thermogravimetric analysis showed that these compounds tend to form a glass at temperatures in the range of -29°C to -16°C and are thermally stable from ambient temperature to at least 430°C, most likely because of the presence of bis(trifluoromethylsulfonyl) imide anions. The performance of the ionic liquids in the model reaction of cyclopentadiene with diethyl maleate or methyl acrylate was investigated. The studied ionic liquids showed high activity even when present in catalytic amounts (4 mol% with respect to the dienophile). An increase in the number of hydroxyl groups present in the ionic liquid structure resulted in higher reaction rates. This journal is the Partner Organisations 2014.
- Erfurt, Karol,Wandzik, Ilona,Walczak, Krzysztof,Matuszek, Karolina,Chrobok, Anna
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p. 3508 - 3514
(2014/07/08)
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- Quantification of electrophilic activation by hydrogen-bonding organocatalysts
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A spectrophotometric sensor is described that provides a useful assessment of the LUMO-lowering provided by catalysts in Diels-Alder and Friedel-Crafts reactions. A broad range of 33 hydrogen-bonding catalysts was assessed with the sensor, and the relative rates in the above reactions spanned 5 orders of magnitude as determined via 1H- and 2H NMR spectroscopic measurements, respectively. The differences between the maximum wavelength shift of the sensor with and without catalyst (Δλmax-1) were found to correlate linearly with ln(krel) values for both reactions, even though the substrate feature that interacts with the catalyst differs significantly (ketone vs nitro). The sensor provides an assessment of both the inherent reactivity of a catalyst architecture as well as the sensitivity of the reaction to changes within an architecture. In contrast, catalyst pKa values are a poor measure of reactivity, although correlations have been identified within catalyst classes.
- Walvoord, Ryan R.,Huynh, Phuong N. H.,Kozlowski, Marisa C.
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supporting information
p. 16055 - 16065
(2015/02/19)
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- 31P NMR Spectroscopically Quantified Hydrogen-Bonding Strength of Thioureas and Their Catalytic Activity in Diels-Alder Reactions
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The hydrogen-bonding strength of a variety of commonly employed thiourea catalysts was quantified by using a trialkylphosphine oxide as a 31P NMR probe. Simple diarylthioureas and more complex bifunctional amine- and hydroxy-substituted thiourea derivatives were examined. Their catalytic activity was determined in a Diels-Alder reaction, and the obtained pseudo-first-order rate constants were correlated with the 31P NMR chemical shifts. A linear correlation between both variables was observed throughout the functionalized thioureas. The 31P NMR probe correlation fared better in comparison to a pK a correlation. Accordingly, the quantification presented herein by using a 31P NMR probe offers an elegant way to estimate the catalytic activity of thiourea catalysts in hydrogen-bond-activated reactions such as the Diels-Alder reaction. The correlation of 31P NMR shift values [Δδ(31P)] for the determination of hydrogen-bond strengths of thiourea derivatives with kinetic data [ln (k rel)]of thiourea-catalyzed Diels-Alder reactions is evaluated. A Hammett-type plot provides a more reliable correlation than the correlation of kinetic data with the pK a values of the thiourea derivatives.
- N?dling, Alexander R.,Jakab, Gergely,Schreiner, Peter R.,Hilt, Gerhard
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supporting information
p. 6394 - 6398
(2016/02/18)
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- Hexameric capsule of a resorcinarene bearing fluorous feet as a self-assembled nanoreactor: A Diels-Alder reaction in a fluorous biphasic system
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A Diels-Alder reaction in a fluorous biphasic system was accelerated by a hexameric capsule of resorcinarene bearing fluorous feet. The reaction takes place predominantly within the capsule, which can be recovered as a fluorous solution and recycled after simple decantation. Copyright
- Shimizu, Shoichi,Usui, Asuka,Sugai, Masae,Suematsu, Yuki,Shirakawa, Seiji,Ichikawa, Hayato
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p. 4734 - 4737
(2013/08/23)
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- Enantioselective catalytic diels-alder reactions with enones as dienophiles
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The aqua complexes (SM,RC)-[(η5-C 5Me5)M(PROPHOS)(H2O)][SbF6] 2 [PROPHOS = (R)-propane-1,2-diylbis(diphenylphosphane); M = Rh (1), Ir (2)] are active catalysts for the asymmetric Diels-Alder reaction between ketones and dienes. At low temperatures, enantioselectivities of up to 89% ee are achieved. The intermediate Lewis acid-dienophile complexes (S M,RC)-[(η5-C5Me 5)M(PROPHOS)(MVK)][SbF6]2 (MVK = methyl vinyl ketone; M = Rh (3), Ir (4)) and (SIr,RC)- [(η5-C5Me5)Ir(PROPHOS)(EVK)][SbF 6]2 (EVK = ethyl vinyl ketone (5)) have been isolated and characterized by analytical and spectroscopic means, including the determination of the crystal structure of the iridium complexes 4 and 5 by X-ray diffractometric methods. Structural parameters indicate that the dispositions of the coordinated dienophiles are controlled by the CH/π attractive interactions established between a phenyl group of the PROPHOS ligand and the α-vinyl proton of the ketones. Proton NMR parameters indicate that these interactions are maintained in solution. From these data, the stereoselectivity of the catalytic reaction is discussed.
- Carmona, Daniel,Viguri, Fernando,Asenjo, Ainara,Lahoz, Fernando J.,García-Ordu?a, Pilar,Oro, Luis A.
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experimental part
p. 4551 - 4557
(2012/08/08)
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- N-hexylpyridinium bis(trifluoromethylsulfonyl)imide and Lewis acids - Catalytic systems for Diels-Alder reaction
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A comparative study of the Diels-Alder reactions between cyclopentadiene (1) and dienophiles (2 a - c) in N-hexylpyridinium bis(trifluoromethylsulfonyl) imide in a temperature range of 20-45°C is reported. The reaction rate constants and activation energies were calculated. Moreover, the catalytic systems based on N-hexylpyridinium bis(trifluoromethylsulfonyl)imide and Lewis acids were tested as a reaction media to perform the Diels-Alder reaction. Yb, Y, Mg, Zn triflates and chlorides (0.005 to 0.1 mmol) were used as catalysts. The recycling of catalytic system consisted of YCI3 and ionic liquid was performed. Versita Sp. z o.o.
- Bittner, Bozena,Janus, Ewa,Milchert, Eugeniusz
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scheme or table
p. 192 - 198
(2012/04/04)
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- Microwave-assisted solvent-free Diels-Alder reaction - A fast and simple route to various 5,6-substituted norbornenes and polychlorinated norbornenes
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A series of 5,6-substituted norbornenes and 5,6-substituted polychlorinated norbornenes was prepared by using a microwave-assisted Diels-Alder reaction. This procedure proved very versatile, fast, and with an easy workup step, and therefore suitable even for large-scale synthesis. Georg Thieme Verlag Stuttgart · New York.
- Dejmek, Milan,Hrebabecky, Hubert,Sala, Michal,Drainsky, Martin,Nencka, Radim
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experimental part
p. 4077 - 4083
(2012/01/05)
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- Triethylsulfonium bistriflimide as the reaction medium in catalyzed and uncatalyzed cycloaddition [4 + 2]
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Triethylsulfonium bistriflimide, [S2.2.2][NTf2], has been tested and compared with other ionic liquids and molecular solvents as a medium in Diels-Alder reaction between cyclopentadiene and dimethyl maleate. Triflates and chlorides of different metals have been combined with [S 2.2.2][NTf2] and the catalytic activity of the systems formed have been determined. The effect of concentration of the catalysts in sulfonium ionic liquid and reactants on the yield and endo:exo ratio has been established. The representative catalyst-Yb(OTf)3?xH 2O in [S2.2.2][NTf2] has been examined in the reaction of cyclopentadiene with various dienophiles. The use of sulfonium ionic liquids permitted recycling the catalysts. For the best four catalytic systems, the products have been isolated.
- Janus, Ewa,Bittner, Bozena
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experimental part
p. 147 - 154
(2010/11/05)
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- A Tin-tungsten mixed oxide as an efficient heterogeneous catalyst for C-C Bond Bond-Forming reactions
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The tin-tungsten mixed oxide prepared by the calcination of the tin-tungsten hydroxide precursor with a Sn/W molar ratio of 2 at 800 °C (SnW2-800) acts as an effective and reusable solid catalyst for C-C bond-forming reactions, such as the cyclization of citronellal, the Diels-Alder reaction, and the cyanosilylation of carbonyl compounds with trimethylsilyl cyanide (TMSCN). Various kinds of structurally diverse aliphatic, aromatic, and unsaturated, heteroatom-containing substrates could be converted into the desired products in high to excellent yields. The observed catalyses for these reactions were truly heterogeneous and the recovered catalyst could be reused several times without an appreciable loss of its high catalytic performance. The Bronsted acid sites generated on the aggregated polytungstate species on SnW2-800 likely play an important role in the C-C bond-forming reactions.
- Ogasawara, Yoshiyuki,Uchida, Sayaka,Yamaguchi, Kazuya,Mizuno, Noritaka
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supporting information; experimental part
p. 4343 - 4349
(2009/11/30)
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- Biodegradable pyridinium ionic liquids: Design, synthesis and evaluation
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A range of ionic liquids (ILs) with a pyridinium cation were synthesised and their biodegradability was evaluated using the CO2 Headspace test (ISO 14593). ILs bearing an ester side chain moiety were prepared from either pyridine or nicotinic acid and showed high levels of biodegradation under aerobic conditions and can be classified as 'readily biodegradable'. In contrast, pyridinium ILs with alkyl side chains showed significantly lower levels of biodegradability in the same test. The utility of the biodegradable IL 6c as a reaction solvent for the Diels-Alder reaction was also investigated.
- Harjani, Jitendra R.,Singer, Robert D.,Garcia, M. Teresa,Scammells, Peter J.
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experimental part
p. 83 - 90
(2010/04/22)
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- Oxazaborolidinone-catalyzed enantioselective Diels-Alder reaction of acyclic α,β-unsaturated ketones
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(Chemical Equation Presented) allo-Threonine-derived O-acyl-β-phenyl- oxazaborolidinones are demonstrated to be powerful and highly enantioselective Lewis acid catalysts for the Diels-Alder reaction of simple acyclic enone dienophiles, expanding the scope of ketone dienophiles and dienes. With 10 to 20 mol % of catalyst, the Diels-Alder adducts are obtained in 76-98% ee with high endo-selectivity. The catalyst exhibits high activity for the reaction with the less reactive β-substituted dienophiles and the less reactive 1,3-cycohexadiene and 1,3-butadiene derivatives. The application of the catalysts to the Diels-Alder reaction of furan is also described.
- Singh, Ram Shanker,Adachi, Shinya,Tanaka, Fumi,Yamauchi, Toyonao,Inui, Chieko,Harada, Toshiro
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p. 212 - 218
(2008/09/18)
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- Ionic liquids as powerful solvent media for improving catalytic performance of silyl borate catalyst to promote Diels-Alder reactions
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(Chemical Equation Presented) Use of the acidic chloroaluminate ionic liquid, including the recycled ones, can improve the catalytic activity of the toluene-coordinated silyl borate in enhancing rates, stereo-selectivities, and yields of Diels-Alder reactions.
- Kumar, Anil,Pawar, Sanjay S.
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p. 8111 - 8114
(2008/03/11)
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- Enhanced Diels-Alder reactions: on the role of mineral catalysts and microwave irradiation in ionic liquids as recyclable media
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This manuscript explores in detail the combined effect of solid supports or microwave irradiation in ionic liquids on a series of Diels-Alder reactions involving 1,3-cyclopentadiene and numerous dienophiles.
- López, Ignacio,Silvero, Guadalupe,Arévalo, María José,Babiano, Reyes,Palacios, Juan?Carlos,Bravo, José Luis
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p. 2901 - 2906
(2007/10/03)
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- An in-depth look at the effect of Lewis acid catalysts on Diels-Alder cycloadditions in ionic liquids
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The present work explores in detail the Diels-Alder reaction between cyclopentadiene and a series of dienophiles, performed in an innovative medium such as an ionic liquid. The potential activation of different Lewis acid catalysts and their load effect when used in combination with this solvent have been explored, in order to settle the improvement on rates and selectivities.
- Silvero, Guadalupe,Arévalo, María José,Bravo, José Luis,ávalos, Martín,Jiménez, José Luis,López, Ignacio
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p. 7105 - 7111
(2007/10/03)
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- Enantioselective diels-alder reaction of acyclic enones catalyzed by allo-threonine-derived chiral oxazaborolidinone
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An allo-threonine-derived O-(p-biphenylcarbonyloxy)-B-phenyl- oxazaborolidinone is demonstrated to be a powerful and highly enantioselective Lewis acid catalyst for the enantioselective Diels-Alder reaction of simple acyclic enone dienophiles, expanding the scope of ketone dienophiles and dienes. With 10-20 mol% of the catalyst, the Diels-Alder adducts are obtained with up to 94 % ee and high endo selectivity. The catalyst exhibits a high activity in the reaction with the less reactive β-substituted dienophiles and the less reactive 1,3-cycohexadiene and 1,3-butadiene derivatives. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.
- Singh, Ram Shanker,Harada, Toshiro
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p. 3433 - 3435
(2007/10/03)
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- Recyclable organotungsten Lewis acid and microwave assisted Diels-Alder reactions in water and in ionic liquids
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The water-soluble, organotungsten Lewis acid, [OP(2-py)3W(CO) (NO)2](BF4)2 (1), was synthesized and characterized. A series of 1-catalyzed Diels-Alder reactions were investigated under conventional heating or microwave heating conditions. The cycloaddition reactions were efficiently conducted in either water or in an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate. The ionic liquid acts as a powerful medium not only for rate- and selectivity enhancements but also for facilitating catalyst recycling. Dramatic rate acceleration via microwave flash heating as compared to thermal heating was observed. Graphical Abstract
- Chen, I-Hon,Young, Jun-Nan,Yu, Shuchun Joyce
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p. 11903 - 11909
(2007/10/03)
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- Planar chiral PHANOLs as double hydrogen bonding donor organocatalysts: Synthesis and catalysis
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4,12-Dihydroxy[2.2]paracyclophanediol (PHANOL; 1), and its para-substituted derivatives 2, 5 and 7, were found to catalyse Diels-Alder cyclo-additions of α,β-unsaturated aldehydes or ketones with dienes and/or epoxide ring opening reactions with amines. The mode of catalysis by the PHANOLs is via double hydrogen bonding to the two sp2 lone pairs of a carbonyl group or the two lone pairs of the epoxide. The order of activity of the PHANOLs for catalysis of the Diels-Alder reaction essentially correlates with the expected hydrogen-bond donor strength based on the degree of electron-withdrawing capability of the group(s) in the para position. In contrast, ortho-substituted PHANOLs 10, 11 and 14 were not active as catalysts due to steric interference with the double hydrogen bonding mode. 1H NMR and IR spectral data for the various PHANOLs are discussed in support of the proposed double hydrogen bond mode.
- Braddock, D. Christopher,MacGilp, Iain D.,Perry, Benjamin G.
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p. 1117 - 1130
(2007/10/03)
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- I2 as an efficient catalyst in ionic Diels-Alder reactions of α,β-unsaturated acetals
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A variety of protected and unprotected α,β-unsaturated aldehydes react with 1,3-dienes in the presence of I2 to give the corresponding cycloadducts.
- Chavan, Subhash P.,Sharma, Pallavi,Rama Krishna,Thakkar, Mahesh
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p. 3001 - 3003
(2007/10/03)
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- Kinetics study and theoretical modeling of the diels-alder reactions of cyclopentadiene and cyclohexadiene with methyl vinyl ketone. The effects of a novel organotungsten catalyst
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The Diels-Alder reaction rate constants of methyl vinyl ketone with cyclopentadiene and cyclohexadiene in the presence of a novel organotungsten catalyst, [P(2-py)3W(CO)(NO)2]2+, have been measured experimentally and modeled theoretically at several temperatures. The uncatalyzed systems were also studied for direct comparison. When 0.0022 M of catalyst is present at room temperature, the rate constants were found to be approximately 5.3 and 5300 times higher than the corresponding uncatalyzed reactions for cyclopentadiene and cyclohexadiene systems, respectively. Experimental data suggested that the catalyst reduced the activation energies by 5-10 kcal/mol. However, the preexponential factors showed reduction of more than 3 orders of magnitude upon catalysis due to the entropic effects. The energy barriers and the rate constants of the uncatalyzed systems were accurately modeled by correlated electronic structure and dual-level variational transition state theory calculation. The calculated endo selectivity is in good agreement with the observed product distribution. Theoretical calculation also suggested the catalyzed reactions proceeded in a highly asynchronous or even stepwise fashion.
- Fu, Yaw-Shien,Tsai, Shih-Chung,Huang, Chun-Huei,Yen, Shih-Yao,Hu, Wei-Ping,Yu, Shuchun Joyce
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p. 3068 - 3077
(2007/10/03)
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- Asymmetric Lewis Acid-Catalyzed Diels-Alder Reactions of α,β-Unsaturated Ketones and α,β-Unsaturated Acid Chlorides
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(Equation presented) Conformational analysis, van der Waals attractions, and transition structure calculations are combined to design an asymmetric Lewis acid-catalyzed Diels-Alder reaction for simple acyclic α,β-unsaturated ketones and α,β-unsaturated acid chlorides, giving up to 83 and 92% ee, respectively. The two-point-binding chiral recognition mechanism, Lewis acid-Lewis base coordination with boron and a van der Waals attraction with the naphthyl group, uses the inherent enone unit of simple α,β-unsaturated carbonyl compounds, ending the need for auxiliary oxygen binding sites on the dienophile.
- Hawkins, Joel M.,Nambu, Mitch,Loren, Stefan
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p. 4293 - 4295
(2007/10/03)
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- Evaluation of Lewis acidity of "Naked" lithium ion through Diels-Alder reaction catalyzed by lithium TFPB in nonpolar organic solvents
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The Diels-Alder reaction of cydopentadiene with methyl vinyl ketone was remarkably promoted by anhydrous LiTFPB as a Lewis acid catalyst both in dichloromethane and in toluene. Experimental and computational investigations revealed the effects of solvent, hydrating water molecules, and counter anions on the Lewis acidity of the "naked" lithium ion.
- Fujiki, Kanji,Ikeda, Shin-Ya,Kobayashi, Hiroshi,Mori, Akira,Nagira, Akihisa,Nie, Jin,Sonoda, Takaaki,Yagupolskii, Yurii
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- Catalysis by lithium cation: Lithium trifluoromethanesulfonate as a substitute for lithium perchlorate in cycloadditions
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Lithium trifluoromethanesulfonate, an easily accessible lithium salt, is shown to be a safe alternative to lithium perchlorate as a promotor in organic Diels-Alder and hetero Diels-Alder reactions.
- Augé, Jacques,Gil, Richard,Kalsey, Sophie,Lubin-Germain, Nadège
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p. 877 - 879
(2007/10/03)
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- A simple route to selective Diels-Alder reactions using modified zeolite Y
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Synthetically useful Diels-Alder reactions of different dienophiles with cyclopentadiene in the presence of chirally modified zeolite Y as simple and accessible medium led to high rate and diastereoselectivity and low to moderate enantioselectivity.
- Najafi, H. Mahmoudi,Ghandi,Farzaneh
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p. 358 - 359
(2007/10/03)
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- Homogeneous Diels-Alder catalysis by organotungsten Lewis acid containing tris(2-pyridyl)phosphine ligand
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The complex [P(2-py)3W(CO)(NO)2](BF4)2 (1) is an excellent catalyst precursor for Diels-Alder reactions of 1,3-diene and α,β-unsaturated ketones and/or aldehydes with a catalyst loading as low as 0.3 mol%.
- Kuo, Cheng-Yi,Fuh, Yaw-Shyan,Chaen, Ming-Cheng,Yu, Shuchun Joyce
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p. 6451 - 6454
(2007/10/03)
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- Silica-Promoted Diels-Alder Reactions in Carbon Dioxide from Gaseous to Supercritical Conditions
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Amorphous fumed silica (SiO2) was shown to increase yields and selectivities of several Diels-Alder reactions in gaseous and supercritical CO2. Pressure effects on the Diels-Alder reaction were explored using methyl vinyl ketone and penta-1,3-diene at 80°C. The selectivity of the reaction was not affected by pressure/ density. As pressure was increased, the yield decreased. At the reaction temperature, adsorption isotherms at various pressures were obtained for the reactants and the Diels-Alder adduct. As expected when pressure is increased, the ratio of the amount of reactants adsorbed to the amount of reactants in the fluid phase decreases, thus causing the yield to decrease. The Langmuir adsorption model fit the adsorption data. The Langmuir equilibrium partitioning constants all decreased with increasing pressure. The effect of temperature on adsorption was experimentally determined and traditional heats of adsorption were calculated. However, since supercritical CO2 is a highly compressible fluid, it is logical to examine the effect of temperature at constant density. In this case, entropies of adsorption were obtained. The thermodynamic properties that influence the real enthalpy and entropy of adsorption were derived. Methods of doping the silica and improving yields and selectivities were also explored.
- Weinstein, Randy D.,Renslo, Adam R.,Danheiser, Rick L.,Tester, Jefferson W.
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p. 2878 - 2887
(2007/10/03)
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- Catalysis by solid acid: Selective Diels-Alder reactions are promoted by mesoporous aluminosilicate with zinc ions and nanometer honeycomb openings
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Zinc ion-exchanged mesoporous aluminosilicate has been designed specifically to accelerate the Diels-Alder reaction between cyclopentadiene and poor dienophiles such as methyl acrylate and methyl methacrylate. Catalysis on this aluminosilicate is more effective than on a K10-based solid acid catalyst.
- Onaka, Makoto,Yamasaki, Ryota
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p. 259 - 260
(2007/10/03)
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- A cationic palladium(II) complex-catalyzed diels-alder reaction
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A cationic palladium(II) complex, [PdL2(RCN)2](BF4)2, has been found to catalyze the Diels-Alder reaction of α, β-unsaturated carbonyl compounds with dienes, affording the corresponding cycloadducts in good yields. Excellent enanlioselectivity can be achieved in the reaction of N- acryloyloxazolidinone and cyclopentadiene by use of a chiral ligand, BINAP.
- Oi, Shuichi,Kashiwagi, Kenji,Inoue, Yoshio
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p. 6253 - 6256
(2007/10/03)
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- Dilithium 2,2'-methylenebis(4,6-di-tert-butylphenoxide) as a bidentate Lewis acid in organic synthesis
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Dilithium 2,2'-methylenebis(4,6-di-tert-butylphenoxide) can be successfully utilized as a bidentate Lewis acid for simultaneous coordination to carbonyl groups, thereby accelerating the Diels-Alder reactions. The double activation ability of the bidentate lithium reagent toward carbonyls is emphasized in comparison with the corresponding monodentate lithium reagent.
- Ooi, Takashi,Saito, Akira,Maruoka, Keiji
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p. 3745 - 3748
(2007/10/03)
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- Aqueous catalysis: Methylrhenium trioxide (MTO) as a homogeneous catalyst for the Diels-Alder reaction
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The title compound proves to be an effective and efficient catalyst for the Diels-Alder reaction when the dienophile is an α,β-unsaturated ketone or aldehyde. It is especially effective in water. Equal amounts of any such dienophile and any of six representative dienes (isoprene, 2-methyl-1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, cyclopentadiene, 1,2,3,4,5-pentamethylcyclopentadiene, and 1,3-cyclohexadiene) were used, along with 1% MTO. The reactions gave usually > 90% isolated yield of the cycloaddition product except for the larger dienophiles. Nearly exclusively, there was formed one product isomer, the same one that usually predominates. The reactions were often run in chloroform (mostly) and in other organic solvents. A select number were carried out in water, where the reactions gave a greater product yield in a considerably shorter time. Water, itself, is known to enhance the rates of Diels-Alder reactions, but MTO exerts an additional accelerating effect. Kinetics studies were carried out to show that the rate is proportional to the catalyst concentration. The products do not inhibit the reaction. The desirability of MTO as a Diels-Alder catalyst stems from a combination of favorable properties: the inertness to air/oxygen, the tolerance for many substrates, the use of an aqueous medium, and the absence of product inhibition. The initial step appears to be the (weak) coordination of the carbonyl oxygen to the electropositive rhenium center. Steric crowding around rhenium inhibits reactions of the larger dienophiles.
- Zhu, Zuolin,Espenson, James H.
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p. 3507 - 3512
(2007/10/03)
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- Solvent effects on Diels-Alder reactions. the use of aqueous mixtures of fluorinated alcohols and the study of reactions of acrylonitrile
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Rate, endolexo, regio- and diastereo-facial selectivities of several Diels-Alder reactions were measured in a series of fluorinated alcohol-water mixtures, whose solvophobicity has been determined by means of the solvophobic power (Sp) parameter. Solvophobicity is the main factor influencing the reaction rate, although in some reactions hydrogen bond donating (HBD) ability may also play a role. Both solvophobicity and HBD ability are important to account for changes in endolexo selectivity. HBD ability is the main factor responsible for the changes in regio- and diastereo-facial selectivities, induced by the reaction medium. On the other hand, the kinetic rate constants and endolexo selectivity of the reaction of acrylonitrile with cyclopentadiene, as well as the regioselectivity of the reaction of acrylonitrile with isoprene, have been determined in 23 reaction media. The analysis of the results using empirical solvent parameters show that the reaction rate depends on solvophobic, HBD and dipolarity interactions, whereas endolexo selectivity is influenced by solvophobic and dipolarity interactions, and the regioselectivity only by HBD effects.
- Cativiela, Carlos,Garcia, Jose I.,Gil,Martinez, Rosa M.,Mayoral, Jose A.,Salvatella, Luis,Urieta, Jose S.,Mainar,Abraham, Michael H.
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p. 653 - 660
(2007/10/03)
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- Methylalumoxane as a Highly Lewis Acidic Reagent for Organic Synthesis
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Methylalumoxane (MAO) is an extremely strong Lewis acid and is a useful reagent for organic reactions such as the Diels-Alder reaction and the amidation of esters. Reactions using MAO proceed much faster than those using Me3Al.
- Akakura, Matsujiro,Yamamoto, Hisashi
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p. 277 - 278
(2007/10/03)
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- Indium trichloride (InCl3) catalysed Diels-Alder reaction in water
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Indium trichloride (InCl3) is found to catalyse the Diels-Alder reaction in water; the catalyst can be easily recovered from water after the reaction is completed and can be reused.
- Loh, Teck-Peng,Pei, Jian,Lin, Mei
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p. 2315 - 2316
(2007/10/03)
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- Metal Bis((perfluoroalkyl)sulfonyl)amides as Novel Lewis Acid Catalysts in Diels-Alder Reaction
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Some stable and lipophilic metal bis((perfluoroalkyl)-sulfonyl)amides are prepared and employed as remarkable Lewis acid catalysts in the Diels-Alder reaction of cyclopentadiene with methyl vinyl ketone.
- Kobayashi, Hiroshi,Nie, Jin,Sonoda, Takaaki
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p. 307 - 308
(2007/10/02)
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- Synthesis of dipeptides containing α-substituted amino acids; their use as chiral ligands in Lewis-acid-catalyzed reactions
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L-α-Methylphenylalanine, obtained by enzymatic resolution of the corresponding racemic amide with amidase from Ochrobactrum anthropi NCIMB 40321, was used in the synthesis of dipeptides containing α-substituted amino acids.The 2-hydroxynaphthalene-1-carboxaldehyde Schiff bases of the dipeptides (1 and 2) were tested as Ti(IV) and Al(III) complexes in asymmetric Lewis-acid-catalyzed reactions.Only the Al(III) complex of 2 showed moderate enantioselectivity in the cyanation reaction of benzaldehyde with TMS-CN.
- Kaptein, Bernard,Monaco, Vania,Broxterman, Quirinus B.,Schoemaker, Hans E.,Kamphuis, Johan
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p. 231 - 238
(2007/10/02)
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- Diels-Alder Reactions Catalysed by Cation-exchanged Clay Minerals
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Catalysis of Diels-Alder reactions by various clay minerals exchanged with a variety of transition metal cations was shown to occur readily at ambient temperatures in a variety of solvents.Non-transition and lanthanide cation-exchanged clays were found to be ineffective. α,β-Unsaturated carbonyl compounds (such as methyl vinyl ketone, methyl acrylate and methyl methacrylate) were used as dienophile.Cyclopentadiene, furan, pyrrole, isoprene and cyclohexa-1,3-diene were successfully employed as the diene, whilst thiophene was unreactive.Such reactions (except that with isoprene which produces a mixture of 1,3- and 1,4-isomers) produced a mixture of endo- and exo-isomers, the ratios of which could be altered by manipulation of the inter-layer reaction space of the clay catalyst.Choosing a clay with a higher layer charge, and hence lower basal spacing, δd, gave increased selection for the kinetically less favoured, but less bulky isomer.
- Adams, John M.,Dyer, Stuart,Martin, Keith,Matear, W. Alan,McCabe, Richard W.
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p. 761 - 766
(2007/10/02)
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