- Thiourea versus the oxyanion hole as a double H-bond donor
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A novel receptor based on the 4,5-diamine-9,9-dimethylxanthene skeleton functionalised with triflamides has been developed and its hydrogen-bonding donor ability is examined and compared with that of thiourea groups. The novel receptor also shows its potential as an organocatalyst.
- Mu?iz, Francisco M.,Montero, Victoria Alcázar,Fuentes de Arriba, ángel L.,Simón, Luis,Raposo, César,Morán, Joaquín R.
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- Synthesis of novel dendritic 2,2′-bipyridine ligands and their application to lewis acid-catalyzed diels-alder and three-component condensation reactions
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(Chemical Equation Presented) A series of dendritic ligands with a 2,2′-bipyridine core was synthesized through the coupling of 4,4′-dihydroxy-2,2′-bipyridine with poly(aryl ether) dendrons. The corresponding dendritic Cu(OTf)2 catalysts were used for Diels-Alder and three-component condensation reactions. The dendritic Cu(OTf) 2-catalyzed Diels-Alder reaction proceeded smoothly, and these dendritic catalysts could be recycled without deactivation by reprecipitation. Three-component condensation reactions such as Mannich-type reactions also proceeded not only in dichloromethane but also in water. Furthermore, a positive dendritic effect on chemical yields was observed in both Diels-Alder reactions and aqueous-media three-component condensation reactions.
- Muraki, Takahito,Fujita, Ken-Ichi,Kujime, Masato
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- Metal-free, noncovalent catalysis of Diels - Alder reactions by Neutral hydrogen bond donors in organic solvents and in water
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We examined the catalytic activity of substituted thioureas in a series of Diels - Alder reactions and 1,3-dipolar cycloadditions. The kinetic data reveal that the observed accelerations in the relative rates are more dependent on the thiourea substituents than on the reactants or solvent. Although the catalytic effectiveness is the strongest in noncoordinating, nonpolar solvents, such as cyclohexane, it is also present in highly coordinating polar solvents, such as water. In 1,3-dipolar cycloadditions, the thiourea catalysts demonstrate only very moderate selectivity for reactions with inverse electron demand. Our experiments emphasize that both hydrophobic and polar interactions can co-exist, making these catalysts active, even in highly coordinating solvents. This class of catalysts increases the reaction rates and endo-selectivities of Diels - Alder reactions, in a similar manner to weak Lewis acids, without concomitant product inhibition.
- Wittkopp, Alexander,Schreiner, Peter R.
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- NMR study of diastereoisomerism of 2-(1-aminoethyl)bicyclo[2.2.1]heptane and its hydrochloride (deitiforin)
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The assignment of the signals for the H and C atoms of four diastereomers (without their separation) of 2-(1-aminoethyl)bicyclo[2.2.1]heptane (1) and its hydrochloride (2) (the antiviral drug deitiforin) was performed for the first time by two-dimensional 1H and 13C NMR spectroscopy. The effects of the substituent at position 2 of norbornane on the chemical shifts of the α-, β-, and γ-carbon atoms of the bicycle were examined using the increments for alkanes. The changes in the chemical shifts of the C(6) and C(7) atoms are substantially larger than those for the other C atoms, which made it possible to identify the exo and endo forms. Each of these forms exists as a mixture of two diastereomers. The effect of the positive charge of the N atom on the γ-protons, which are closely spaced, but separated by a number of covalent bonds, was considered on going from amine 1 to hydrochloride 2. Based on significant changes in shielding of these H atoms, the configurations of the asymmetric center in the CHMe(NH2) substituent of the diastereomers were established.
- Tandura,Shumsky,Litvin,Kozlova,Shuvalova,Sharf,Kolesnikov
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- Entrapment of cyclopentadiene in zeolite NaY and its application for solvent-free Diels-Alder reactions in the nanosized confined environment
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Nonpolar cyclopentadiene was stably entrapped as a monomer in the hydrophilic supercages of zeolite NaY. A monomer form of cyclopentadiene in the supercages was confirmed by 13C MAS NMR spectroscopy. The adsorbed cyclopentadiene in the confined cavities performed the Diels-Alder reaction with typical dienophiles under solvent-free conditions more effectively than in organic and water media.
- Imachi, Shouhei,Onaka, Makoto
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- Rapid quantification of the activating effects of hydrogen-bonding catalysts with a colorimetric sensor
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A sensor has been developed to quickly and simply assess the relative reactivity of different hydrogen-bonding catalysts. Specifically, blue-shifts seen upon treatment of H-bonding catalysts with the colorimetric compound 7-methyl-2-phenylimidazo[1,2-a]pyrazin-3(7H)-one correlate well to the K eq of binding to the sensor. The blue-shifts also show a high degree of correlation with relative rates in Diels-Alder reactions of methyl vinyl ketone and cyclopentadiene employing the H-bonding catalysts. The relevance of the sensor blue-shifts to the LUMO-lowering abilities of the H-bonding catalysts is discussed.
- Huynh, Phuong N. H.,Walvoord, Ryan R.,Kozlowski, Marisa C.
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p. 15621 - 15623,3
(2012)
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- Diels-Alder reaction using a dendritic copper(II) triflate-catalyst: a positive dendritic effect on the chemical yield
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A series of dendritic ligands with a 2,2′-bipyridine core was synthesized through the coupling of 4,4′-dihydroxy-2,2′-bipyridine with poly(arylether) dendron in fair yields. The corresponding copper(II) trifluoromethanesulfonate (triflate) dendrimers were applied as a Lewis acid catalyst to the Diels-Alder reaction. A positive dendritic effect on the chemical yields of adducts was observed.
- Fujita, Ken-ichi,Muraki, Takahito,Hattori, Hatsuhiko,Sakakura, Toshiyasu
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- Lewis Acidic Boranes, Lewis Bases, and Equilibrium Constants: A Reliable Scaffold for a Quantitative Lewis Acidity/Basicity Scale
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A quantitative Lewis acidity/basicity scale toward boron-centered Lewis acids has been developed based on a set of 90 experimental equilibrium constants for the reactions of triarylboranes with various O-, N-, S-, and P-centered Lewis bases in dichloromethane at 20 °C. Analysis with the linear free energy relationship log KB=LAB+LBB allows equilibrium constants, KB, to be calculated for any type of borane/Lewis base combination through the sum of two descriptors, one for Lewis acidity (LAB) and one for Lewis basicity (LBB). The resulting Lewis acidity/basicity scale is independent of fixed reference acids/bases and valid for various types of trivalent boron-centered Lewis acids. It is demonstrated that the newly developed Lewis acidity/basicity scale is easily extendable through linear relationships with quantum-chemically calculated or common physical–organic descriptors and known thermodynamic data (ΔH (Formula presented.)). Furthermore, this experimental platform can be utilized for the rational development of borane-catalyzed reactions.
- Mayer, Robert J.,Hampel, Nathalie,Ofial, Armin R.
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supporting information
p. 4070 - 4080
(2021/01/29)
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- N-Heterocyclic Iod(az)olium Salts – Potent Halogen-Bond Donors in Organocatalysis
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This article describes the application of N-heterocyclic iod(az)olium salts (NHISs) as highly reactive organocatalysts. A variety of mono- and dicationic NHISs are described and utilized as potent XB-donors in halogen-bond catalysis. They were benchmarked in seven diverse test reactions in which the activation of carbon- and metal-chloride bonds as well as carbonyl and nitro groups was achieved. N-methylated dicationic NHISs rendered the highest reactivity in all investigated catalytic applications with reactivities even higher than all previously described monodentate XB-donors based on iodine(I) and (III) and the strong Lewis acid BF3.
- Boelke, Andreas,Kuczmera, Thomas J.,Lork, Enno,Nachtsheim, Boris J.
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supporting information
p. 13128 - 13134
(2021/08/09)
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- 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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- Preorganization: A Powerful Tool in Intermolecular Halogen Bonding in Solution
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Preorganization is a powerful tool in supramolecular chemistry which has been utilized successfully in intra- and intermolecular halogen bonding. In previous work, we had developed a bidentate bis(iodobenzimidazolium)-based halogen bond donor which featured a central trifluoromethyl substituent. This compound showed a markedly increased catalytic activity compared to unsubstituted bis(iodoimidazolium)-based Lewis acids, which could be explained either by electronic effects (the electron withdrawal by the fluorinated substituent) or by preorganization (the hindered rotation of the halogen bonding moieties). Herein, we systematically investigate the origin of this increased Lewis acidity via a comparison of the two types of compounds and their respective derivatives with or without the central trifluoromethyl group. Calorimetric measurements of halide complexations indicated that preorganization is the main reason for the higher halogen bonding strength. The performance of the catalysts in a series of benchmark reactions corroborates this finding.
- Voelkel, Martin H. H.,Wonner, Patrick,Huber, Stefan Matthias
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p. 214 - 224
(2020/03/10)
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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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- Iodine(III) Derivatives as Halogen Bonding Organocatalysts
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Hypervalent iodine(III) derivatives are known as versatile reagents in organic synthesis, but there is only one previous report on their use as Lewis acidic organocatalysts. Herein, we present first strong indications for the crucial role of halogen bonding in this kind of catalyses. To this end, the solvolysis of benzhydryl chloride and the Diels–Alder reaction of cyclopentadiene with methyl vinyl ketone served as benchmark reactions for halide abstraction and the activation of neutral compounds. Iodolium compounds (cyclic diaryl iodonium species) were used as activators or catalysts, and we were able to markedly reduce or completely switch off their activity by sterically blocking one or two of their electrophilic axes. Compared with previously established bidentate cationic halogen bond donors, the monodentate organoiodine derivatives used herein are at least similarly active (in the Diels–Alder reaction) or even decidedly more active (in benzhydryl chloride solvolysis).
- Heinen, Flemming,Engelage, Elric,Dreger, Alexander,Weiss, Robert,Huber, Stefan M.
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supporting information
p. 3830 - 3833
(2018/03/09)
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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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- 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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- 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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- 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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- 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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- 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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- 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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- 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
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Paragraph 0039-0041
(2017/01/02)
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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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- Small molecule regulation of self-association and catalytic activity in a supramolecular coordination complex
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Herein, we report the synthesis and characterization of the first weak-link approach (WLA) supramolecular construct that employs the small molecule regulation of intermolecular hydrogen bonding interactions for the in situ control of catalytic activity. A biaryl urea group, prone to self-aggregation, was functionalized with a phosphinoalkyl thioether (P,S) hemilabile moiety and incorporated into a homoligated Pt(II) tweezer WLA complex. This urea-containing construct, which has been characterized by a single crystal X-ray diffraction study, can be switched in situ from a rigid fully closed state to a flexible semiopen state via Cl- induced changes in the coordination mode at the Pt(II) structural node. FT-IR and 1H NMR spectroscopy studies were used to demonstrate that while extensive urea self-association persists in the flexible semiopen complex, these interactions are deterred in the rigid, fully closed complex because of geometric and steric restraints. Consequently, the urea moieties in the fully closed complex are able to catalyze a Diels-Alder reaction between cyclopentadiene and methyl vinyl ketone to generate 2-acetyl-5-norbornene. The free urea ligand and the semiopen complex show no such activity. The successful incorporation and regulation of a hydrogen bond donating catalyst in a WLA construct open the doors to a vast and rapidly growing catalogue of allosteric catalysts for applications in the detection and amplification of organic analytes.
- McGuirk, C. Michael,Stern, Charlotte L.,Mirkin, Chad A.
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supporting information
p. 4689 - 4696
(2014/04/17)
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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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- 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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- 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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- 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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- 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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- 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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- 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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- 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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- 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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- 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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- Monomeric metal aqua complexes in the interlayer space of montmorillonites as strong Lewis acid catalysts for heterogeneous carbon-carbon bond-forming reactions
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Montmorillonite-enwrapped copper and scandium catalysts (Cu2-- and Sc3+-monts) were easily prepared by treating Na--mont with the aqueous solution of the copper nitrate and scandium triflate, respectively. The resulting Cu2+- and Sc3+-monts showed outstanding catalytic activities for a variety of carbon-carbon bond-forming reactions, such as the Michael reaction, the Sakurai-Hosomi allylation, and the Diels-Alder reaction, under solvent-free or aqueous conditions. The remarkable activity of the mont catalysts is attributable to the negatively charged silicate layers that are capable of stabilizing metal cations. Furthermore, these catalysts were reusable without any appreciable loss in activity and selectivity. The Cu2+-mont-catalyzed Michael reaction proceeds via a ternary complex in which both the 1,3-dicarbonyl compound and the enone are coordinated to a Lewis acid Cu2+ center.
- Kawabata, Tomonori,Kato, Masaki,Mizugaki, Tomoo,Ebitani, Kohki,Kaneda, Kiyotomi
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p. 288 - 297
(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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- Dendrimer-Palladium complex catalyzed oxidation of terminal alkenes to methyl ketones
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Silica-supported polyamidoamine (PAMAM) dendrimers with different spacer lengths were prepared. After the introduction of diphenylphosphino groups, complexation to dibenzylidenepalladium(0) gave the desired silica-supported dendrimer - palladium catalyst complexes G0 to G4-C2-Pd. These catalysts showed activity towards the oxidation of terminal alkenes to methyl ketones. A dependence of catalytic activity on the spacer length of the diamine in PAMAM was observed.
- Zweni, Pumza P.,Alper, Howard
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p. 849 - 854
(2007/10/03)
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- Diels-Alder reaction in air- and moisture-stable zinc-containing ionic liquids
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Diels-Alder reactions in a number of air- and moisture-stable dialkylimidazolium halide-ZnCl2 ionic liquids are reported. High yields and high endo selectivities have been observed. The ionic liquids could then be recyclable without loss of reactivity.
- Sun, I.-Wen,Wu, Shin-Yi,Su, Chia-Hao,Shu, Yu-Lin,Wu, Pei-Lin
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p. 367 - 370
(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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- 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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- Planar chiral PHANOLS as organocatalysts for the Diels-Alder reaction via double hydrogen-bonding to a carbonyl group
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Planar chiral PHANOLs have been shown to catalyze Diels-Alder reactions of α,β-unsaturated aldehydes and ketones with various dienes. Rate accelerations of up to ca. 30-fold were obtained using the electron deficient 4,12-dihydroxy-7,15-dinitro[2.2]paracyclophane as a catalyst. It is proposed that the carbonyl group of the dienophile is activated via a double hydrogen-bonding mode. Although the PHANOLs are inherently chiral, little or no asymmetric induction was observed when using enantiopure (R)-PHANOL.
- Braddock, D. Christopher,MacGilp, Iain D.,Perry, Benjamin G.
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p. 1121 - 1124
(2007/10/03)
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- Hydroxyapatite-bound cationic ruthenium complexes as novel heterogeneous Lewis acid catalysts for Diels-Alder and aldol reactions
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Creation of a stable and well-defined active center on a solid surface is a promising protocol for designing more efficient hybrid-catalysts that bridge the gap between homogeneous and heterogeneous catalysis. Treatment of a hydroxyapatite-bound Ru complex (RuHAP) with an aqueous solution of AgX (X = SbF6-, TfO-) afforded a new type of cationic Ru phosphate complex, having potentially vacant coordination sites. These cationic RuHAPs exhibited Lewis acidity toward carbonyl and cyano groups, promoting Diels-Alder and Aldol reactions with high efficiencies. Moreover, no Ru leaching was detected in the above organic reactions, and then the catalysts were recyclable. Copyright
- Mori, Kohsuke,Hara, Takayoshi,Mizugaki, Tomoo,Ebitani, Kohki,Kaneda, Kiyotomi
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p. 11460 - 11461
(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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- Enantioselective Diels-Alder reactions with N-hydroxy-N-phenylacrylamide
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Matrix presented The use of hydroxamic acids as templates for Lewis acid catalyzed enantioselective Diels-Alder reactions has been examined. A very simple chiral Lewis acid, prepared by mixing optically pure binaphthol with 3 equiv of trimethylaluminum, catalyzes the [4 + 2] cycloaddition of N-hydroxy-N-phenylacrylamide with cyclopentadiene at 0°C in high yield (>96%) and with a fairly good level of enantioselectivity (91% ee). Facile conversion of the products to the corresponding alcohols or aldehydes makes the hydroxamic acid intermediates particularly useful.
- Corminboeuf, Olivier,Renaud, Philippe
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p. 1731 - 1733
(2007/10/03)
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- N-alkoxyacrylamides as substrates for enantioselective Diels-Alder reactions
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Matrix presented The use of N-alkoxyacrylamides as substrates for Lewis acid catalyzed Diels-Alder reactions has been examined. Enantioselectivities up to 92% ee have been achieved using very simple chiral Lewis acids prepared from triisobutylaluminum and 2,2-dimethyl-α,α,α′,α′-tetra-1-naphthalenyl- TADDOL (1-NaphtTADDOL). The use of Yamamoto's Zn-BINOL, easily prepared from Et2Zn and 1,1′-bi-2-naphthol (BINOL), proved to be even more efficient, and enantioselectivities up to 96% ee were achieved.
- Corminboeuf, Olivier,Renaud, Philippe
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p. 1735 - 1738
(2007/10/03)
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