- A Bidentate Iodine(III)-Based Halogen-Bond Donor as a Powerful Organocatalyst**
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In contrast to iodine(I)-based halogen bond donors, iodine(III)-derived ones have only been used as Lewis acidic organocatalysts in a handful of examples, and in all cases they acted in a monodentate fashion. Herein, we report the first application of a bidentate bis(iodolium) salt as organocatalyst in a Michael and a nitro-Michael addition reaction as well as in a Diels–Alder reaction that had not been activated by noncovalent organocatalysts before. In all cases, the performance of this bidentate XB donor distinctly surpassed the one of arguably the currently strongest iodine(I)-based organocatalyst. Bidentate coordination to the substrate was corroborated by a structural analysis and by DFT calculations of the transition states. Overall, the catalytic activity of the bis(iodolium) system approaches that of strong Lewis acids like BF3.
- Heinen, Flemming,Reinhard, Dominik L.,Engelage, Elric,Huber, Stefan M.
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supporting information
p. 5069 - 5073
(2021/02/26)
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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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- Iodine-Catalyzed Diels-Alder Reactions
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The Diels-Alder cycloaddition is the most popular pericyclic reaction with numerous applications in synthesis and catalysis. We now demonstrate that we can perform this reaction under mild and metal-free conditions relying on molecular iodine as the catalyst. Cycloadditions with cyclohexadiene, cyclopentadiene, or isoprene with various dienophiles can be performed typically within minutes in moderate to good yields and high endo selectivity. The mechanistic studies including kinetic and DFT investigations clearly indicate a halogen-bond activation and rule out other modes of activation. Furthermore, iodine performs equally well as typical metallic Lewis acids like AlCl3, SnCl4, or TiCl4.
- Arndt, Thiemo,Wagner, Philip K.,Koenig, Jonas J.,Breugst, Martin
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p. 2922 - 2930
(2021/05/17)
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- STRONGLY LEWIS ACIDIC METAL-ORGANIC FRAMEWORKS FOR CONTINUOUS FLOW CATALYSIS
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Lewis acidic metal-organic framework (MOF) materials comprising triflate-coordinated metal nodes are described. The materials can be used as heterogenous catalysts in a wide range of organic group transformations, including Diels-Alder reactions, epoxide-ring opening reactions, Friedel-Crafts acylation reactions and alkene hydroalkoxylation reactions. The MOFs can also be prepared with metallated organic bridging ligands to provide heterogenous catalysts for tandem reactions and/or prepared as composites with support particles for use in columns of continuous flow reactor systems. Methods of preparing and using the MOF materials and their composites are also described.
- -
-
Paragraph 0186-0187
(2021/02/26)
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- Strongly Lewis Acidic Metal-Organic Frameworks for Continuous Flow Catalysis
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The synthesis of highly acidic metal-organic frameworks (MOFs) has attracted significant research interest in recent years. We report here the design of a strongly Lewis acidic MOF, ZrOTf-BTC, through two-step transformation of MOF-808 (Zr-BTC) secondary building units (SBUs). Zr-BTC was first treated with 1 M hydrochloric acid solution to afford ZrOH-BTC by replacing each bridging formate group with a pair of hydroxide and water groups. The resultant ZrOH-BTC was further treated with trimethylsilyl triflate (Me3SiOTf) to afford ZrOTf-BTC by taking advantage of the oxophilicity of the Me3Si group. Electron paramagnetic resonance spectra of Zr-bound superoxide and fluorescence spectra of Zr-bound N-methylacridone provided a quantitative measurement of Lewis acidity of ZrOTf-BTC with an energy splitting (?E) of 0.99 eV between the ?x? and ?y? orbitals, which is competitive to the homogeneous benchmark Sc(OTf)3. ZrOTf-BTC was shown to be a highly active solid Lewis acid catalyst for a broad range of important organic transformations under mild conditions, including Diels-Alder reaction, epoxide ring-opening reaction, Friedel-Crafts acylation, and alkene hydroalkoxylation reaction. The MOF catalyst outperformed Sc(OTf)3 in terms of both catalytic activity and catalyst lifetime. Moreover, we developed a ZrOTf-BTC?SiO2 composite as an efficient solid Lewis acid catalyst for continuous flow catalysis. The Zr centers in ZrOTf-BTC?SiO2 feature identical coordination environment to ZrOTf-BTC based on spectroscopic evidence. ZrOTf-BTC?SiO2 displayed exceptionally high turnover numbers (TONs) of 1700 for Diels-Alder reaction, 2700 for epoxide ring-opening reaction, and 326 for Friedel-Crafts acylation under flow conditions. We have thus created strongly Lewis acidic sites in MOFs via triflation and constructed the MOF?SiO2 composite for continuous flow catalysis of important organic transformations.
- Ji, Pengfei,Feng, Xuanyu,Oliveres, Pau,Li, Zhe,Murakami, Akiko,Wang, Cheng,Lin, Wenbin
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supporting information
p. 14878 - 14888
(2019/10/02)
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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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- BTK INHIBITORS
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Provided are Bruton's Tyrosine Kinase (Btk) inhibitor compounds according to Formula I, or pharmaceutically acceptable salts thereof, or pharmaceutical compositions comprising these compounds and their use in therapy. In particular, provided is the use of Btk inhibitor compounds of Formula I in the treatment of Btk mediated disorders.
- -
-
Page/Page column 143; 144
(2016/07/27)
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- COMPOUNDS USEFUL AS MODULATORS OF TRPM8
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The present invention includes compounds useful as modulators of TRPM8, such as compounds of Formulae (Ia), (Ib) and (Ic), and the subgenus and species thereof; personal products containing those compounds; and the use of those compounds and the personal products, particularly the use of increasing or inducing chemesthetic sensations, such as cooling or cold sensations.
- -
-
Paragraph 0578
(2016/03/29)
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- A Well-Defined Aluminum-Based Lewis Acid as an Effective Catalyst for Diels-Alder Transformations
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A catalytically active aluminum-based system for Diels-Alder transformations is reported. The system was generated by mixing a β-diketiminate-stabilized aluminum bistriflate compound with Na[BArCl4] (ArCl=3,5-Cl2C6H3). Solid-state analysis of the catalytic system reveals a unique structure incorporating a two-dimensional coordination polymer. According to the experimental results obtained from several Diels-Alder transformations, the aluminum-based system appears to be a more practical and more robust alternative to the recently reported compounds based on carbon and silicon cations.
- Liu, Zhizhou,Lee, Jazreen Hui Qi,Ganguly, Rakesh,Vidovic, Dragoslav
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supporting information
p. 11344 - 11348
(2015/08/03)
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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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- Silylium ion-catalyzed challenging Diels-Alder reactions: The danger of hidden proton catalysis with strong Lewis acids
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The pronounced Lewis acidity of tricoordinate silicon cations brings about unusual reactivity in Lewis acid catalysis. The downside of catalysis with strong Lewis acids is, though, that these do have the potential to mediate the formation of protons by various mechanisms, and the thus released Bronsted acid might even outcompete the Lewis acid as the true catalyst. That is an often ignored point. One way of eliminating a hidden proton-catalyzed pathway is to add a proton scavenger. The low-temperature Diels-Alder reactions catalyzed by our ferrocene-stabilized silicon cation are such a case where the possibility of proton catalysis must be meticulously examined. Addition of the common hindered base 2,6-di-tert-butylpyridine resulted, however, in slow decomposition along with formation of the corresponding pyridinium ion. Quantitative deprotonation of the silicon cation was observed with more basic (Mes)3P to yield the phosphonium ion. A deuterium-labeling experiment verified that the proton is abstracted from the ferrocene backbone. A reasonable mechanism of the proton formation is proposed on the basis of quantum-chemical calculations. This is, admittedly, a particular case but suggests that the use of proton scavengers must be carefully scrutinized, as proton formation might be provoked rather than prevented. Proton-catalyzed Diels-Alder reactions are not well-documented in the literature, and a representative survey employing TfOH is included here. The outcome of these catalyses is compared with our silylium ion-catalyzed Diels-Alder reactions, thereby clearly corroborating that hidden Bronsted acid catalysis is not operating with our Lewis acid. Several simple-looking but challenging Diels-Alder reactions with exceptionally rare dienophile/enophile combinations are reported. Another indication is obtained from the chemoselectivity of the catalyses. The silylium ion-catalyzed Diels-Alder reaction is general with regard to the oxidation level of the α,β-unsaturated dienophile (carbonyl and carboxyl), whereas proton catalysis is limited to carbonyl compounds.
- Schmidt, Ruth K.,Muether, Kristine,Mueck-Lichtenfeld, Christian,Grimme, Stefan,Oestreich, Martin
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supporting information; experimental part
p. 4421 - 4428
(2012/04/23)
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- Taming the silylium ion for low-temperature diels-alder reactions
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Some like it hot: A novel silicon-based Lewis acid having a trivalent silicon cation stabilized by an electron-rich transition metal as the "hot" Lewis acidic site catalyzes challenging Diels-Alder reactions at low temperatures with excellent reaction rat
- Klare, Hendrik F. T.,Bergander, Klaus,Oestreich, Martin
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supporting information; experimental part
p. 9077 - 9079
(2010/03/03)
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- A new approach to promoting sluggish Diels-Alder reactions: Dihapto-coordination of the diene
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The cycloaddition between 1,3-cyclohexadiene and various enones and enals (methyl vinyl ketone, ethyl vinyl ketone, methacrolien) is accomplished at room temperature in yields ranging from 51 to 68% without the use of Lewis acids, high pressures, or microwave reactors. This normally sluggish cyclization is accomplished by precoordination of the diene to a π-basic molybdenum complex. The η2-bound metal is thought to promote a Michael reaction between the uncoordinated portion of the diene and the enone, and the resulting enolate then closes to form the cycloalkene product. The organic cycloadduct is removed by oxidation with air or with silver triflate in nearly quantitative yield. For more sterically hindered enones (e.g., mesityl oxide) and for methyl acrylate, the desired outcome requires the use of BF3·OEt2, and yields are significantly lower (15-35%) Copyright
- Liu, Weijun,You, Fei,Mocella, Christopher J.,Harman, W. Dean
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p. 1426 - 1427
(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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- Strong counteranion effects on the catalytic activity of cationic silicon lewis acids in Mukaiyama aldol and Diels-Alder reactions
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(Graph Presented) A toluene-coordinated silyl borate, [Et 3Si(toluene)]B(C6F5)4, demonstrated catalytic activities significantly higher than those of Me3SiOTf and Me3SiNTf2 in Mu
- Hara, Kenji,Akiyama, Ryuto,Sawamura, Masaya
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p. 5621 - 5623
(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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- 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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- Ionic liquids as powerful media in scandium triflate catalysed Diels-Alder reactions: Significant rate acceleration, selectivity improvement and easy recycling of catalyst
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Ionic liquids act as powerful media (or additives) in scandium triflate catalysed Diels-Alder reactions not only for facilitating of catalyst recovery but also for accelerating reaction rate and improving selectivity.
- Song,Shim,Roh,Lee,Choi
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p. 1122 - 1123
(2007/10/03)
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- Scandium perfluoroalkanesulfonate-catalyzed Diels-Alder reactions in an organic solvent
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Scandium perfluoroalkanesulfonate-catalyzed Diels-Alder reactions proceeded smoothly in dry dichloromethane in the presence of molecular sieves (MS) 5 ?. It was found that water interfered with the reactions, contrary to most rare earth-catalyzed reactions that proceed smoothly in aqueous media. Among scandium perfluoroalkanesulfonates tested, scandium triflate (Sc(OTf)3), scandium pentafluoroethanesulfonate (Sc(OSO2C2F5)3), and scandium nonafluorobutanesulfonate (Sc(OSO2C4F9)3) gave the highest yields and selectivities.
- Kobayashi, Shu,Tsuchiya, Takehiro,Komoto, Ichiro,Matsuo, Jun-Ichi
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p. 392 - 394
(2007/10/03)
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- An FT-IR study on Diels-Alder reactions catalysed by heteropoly acid containing sol-gel silica
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Following the general trend of using heterogeneous catalysts whenever possible, the replacement of traditional homogeneous Lewis acid catalysts for the Diels-Alder reaction is currently considered in the literature. In this contribution, we report the suc
- Kukovecz,Kónya,Kiricsi
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p. 121 - 124
(2007/10/03)
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- Ytterbium trichloride-catalyzed Diels-Alder reactions of unactivated dienes
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Ytterbium chloride (YbCl3) is an effective and reusable catalyst for Dieis-Alder reactions of unactivated dienes with α,β-unsaturated ketones and aldehydes at room temperature, leading to products with high regio- and stereoselectivities.
- Fang, Xinggao,Warner, Benjamin P.,Watkin, John G.
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p. 2669 - 2676
(2007/10/03)
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- Lewis acid catalysis in supercritical carbon dioxide. Use of scandium tris(heptadecafluorooctanesulfonate) as a Lewis acid catalyst in Diels-Alder and aza Diels-Alder reactions
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Diels-Alder reactions of carbonyl dienophiles with dienes and aza Diels-Alder reactions of imines with a diene have been successfully carried out using scandium tris(heptadecafluorooctanesulfonate) (Sc(OSO2C8F17)3) as a Lewis acid catalyst in supercritical carbon dioxide (scCO2). It was revealed that the length of perfluorocarbon chains of the scandium catalyst was an essential factor for the catalytic activity in scCO2.
- Matsuo, Jun-Ichi,Tsuchiya, Takehiro,Odashima, Kazunori,Kobayashi, Shu
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p. 178 - 179
(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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- Syntheses and chemistry of Tris(2-pyridyl)phosphine complexes of Group VI transition metals. X-ray structural studies of the molybdenum complexes
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Treatment of P(2-py)3 with Mo(CO)6 or M(CO)3(CH3CN)3 (M=Cr, W) in CH3CN affords compounds of the type P(2-py)3M(CO)3 (1a, M=Cr; 1b, M=Mo; 1c, M=W). Complex P(2-py)3Mo(CO)3·CH2Cl2 was structurally characterized, and its ORTEP drawing shows an almost perfect octahedral arrangement around the Mo center, and the P(2-py)3 ligand occupying the facial position of the octahedron through the coordination of three pyridyl nitrogen atoms. Substitution of CO ligands can take place when treating compounds 1b and 1c with one or two equiv. of NOBF4 in CH3NO2 solvent to afford [P(2-py)3M(CO)3-n(NO)n](BF4) n (2a, M=Mo, n=1; 2b, M=W, n=1; 3a, M=Mo, n=2; 3b, M=W, n=2). These singly and doubly charged cationic species have been characterized by 1H-, 13C-, 31P-, 19F-NMR and IR spectroscopy, as well as elemental analysis. The CO lability of 3a and 3b generated the 16-electron species, [P(2-py)3M(NO)2]2+, which binds to most Lewis basic donor ligands to give complexes of the type, [P(2-py)3M(L)(NO)2](BF4)2 (L=nitriles, aldehydes). A single crystal of [P(2-py)3M(CH3CH2CN)(NO)2](BF 4)2·CH3NO2 was also isolated and structurally characterized. The crystallographic analysis indicated an octahedral arrangement about the Mo metal center. The 1H-NMR downfield shift of the metal-coordinated crotonaldehyde in compounds 4c and 5c is used as a qualitative measurement of relative Lewis acidity, and the acid strength of [P(2-py)3M(NO)2]2+ is comparable to that of TiCl4 when M=Mo and to BF3 and AlCl3 when M=W. The Diels-Alder reactions between cyclohexadienes and methyl vinyl ketone were catalyzed by 0.3 mol% of [P(2-py)3W(CO)(NO)2](BF4)2 (3b) to afford an average 94% conversion and 83% isolated yield.
- Kuo, Cheng-Yi,Fuh, Yaw-Shyan,Shiue, Jay-Yun,Yu, S. Joyce,Lee, Gene-Hsiang,Peng, Shie-Ming
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p. 260 - 267
(2007/10/03)
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- Cycloadditions with clays and alumina without solvents
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The utilization of unactivated K-10 montmorillonite or alumina for Diels-Alder reactions in the absence of solvents, either with symmetrically- or unsymmetrically-substituted carbonyl dienophiles, constitutes an environmentally-friendly alternative providing excellent selectivities under mild conditions.
- Avalos, Martin,Babiano, Reyes,Bravo, Jose L.,Cintas, Pedro,Jimenez, Jose L.,Palacios, Juan C.,Ranu, Brindaban C.
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p. 2013 - 2016
(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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- 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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- Unexpected fragmentations leading to quinanes and hydrindanes mediated by a silyl radical
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Useful bicyclic ring systems are obtained by tris-trimethylsilylsilyl radical (TMS3Si·) mediated fragmentation of strained alkene precursors.
- Dufour, Claire,Iwasa, Seiji,Fabre, Agnes,Rawal, Viresh H.
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p. 7867 - 7870
(2007/10/03)
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- The Catalytic Diels-Alder Reaction Using Combined Catalyst System of Diphenyltin Sulfide or Lawesson's Reagent and Silver Perchlorate
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Catalytic Diels-Alder reaction between several 1,3-dienes and α,β-unsaturated ketones are effectively promoted by the combined use of diphenyltin sulfide (Ph2Sn=S) and silver perchlorate or Lawesson's reagent (2,4-bis(4-methoxyphenyl)-1,3-dithia-2,4-dipho
- Mukaiyama, Teruaki,Watanabe, Kimitoshi,Shiina, Isamu
-
-
- Activated cycloheptenone dienophiles. A versatile approach to 6,7-fused ring targets
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Several 2-carbalkoxy-2-cyclohepten-1-ones were prepared and their Diels-Alder characteristics examined in order to develop a facile general approach to the synthesis of cycloheptane ring-containing polycyclic natural products.Substitution pattern on the seven-membered ring was found to greatly affect the Diels-Alder behavior.In addition, some extraordinary facial stereoselectivity was observed.Key words: Diels-Alder reaction, 2-carbalkoxy-2-cyclohepten-1-ones, 6,7-fused ring system.
- Liu, Hsing-Jang,Yeh, Wen-Lung,Browne, Eric N. C.
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p. 1135 - 1147
(2007/10/03)
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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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- Homogeneous catalysis. Transition metal based lewis acid catalysts
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Transition metal based Lewis acids provide catalysts for the Diels-Alder and Mukaiyama reactions. These catalysts must possess an electron deficient axophilic metal center and a labile coordination position. Unlike traditional Lewis acids, those derived from transition metals can function in the presence of water and have well defined structures. It is shown how a normally electron rich ruthenium atom can be converted to a Lewis acid by incorporation of electron withdrawing ligands and ligands with hard donor atoms. This ruthenium complex, [Ru(salen)(NO)(H2O)]+, is an efficient catalyst for the Diels-Alder reaction, but in the Mukaiyama reaction, it tends to be reduced and thereby deactivated by the silyl enol ether. It is shown that the complex [TiCp*2(H2O)2]2+ (Cp* is pentamethylcyclopentadienyl) is an efficient catalyst for the Diels-Alder reaction even when water is present. Similarly, the triflato complexes [TiCp2(CF3 SO3)2] and [ZrCp2(CF3SO3)2] (Cp is cyclopentadienyl) are efficient catalysts for both the Diels-Alder and Mukaiyama reactions. All of these catalysts are effective at very low loadings of ≈ 1 mol%. Catalysis has been shown to occur via substrate-catalyst adducts and moreover these adducts are formed rapidly and reversibly as required for efficient catalysis.
- Hollis, T. Keith,Odenkirk, William,Robinson,Whelan, John,Bosnich
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p. 5415 - 5430
(2007/10/02)
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- Scandium trifluoromethanesulfonate (Sc(OTf)3). A novel reusable catalyst in the Diels-Alder reaction
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Scandium trifluoromethanesulfonate (Sc(OTf)3) is found to be quite effective as a Lewis acid catalyst in the Diels-Alder reaction. The novel catalyst is available in both aqueous and organic media, is easily recovered from aqueous layer after the reaction is completed, and can be reused.
- Kobayashi, Shu,Hachiya, Iwao,Araki, Mitsuharu,Ishitani, Haruro
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p. 3755 - 3758
(2007/10/02)
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- EFFICIENT CYCLOADDITION DURING ADSORPTION ON CHROMATOGRAPHIC SOLVENTS
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An essentially new method was developed for carrying out cycloaddition on the surface of chromatographic adsorbents in the absence of solvent.This method permits the use of much milder reaction conditions and to increase the reaction's selectivity.
- Veselovskii, V. V.,Gybin, A. S.,Lozanova, A. V.,Moiseenkov, A. M.,Smit, V. A.
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- DRAMATIC ACCELERATION OF THE DIELS-ALDER REACTION BY ADSORPTION ON CHROMATOGRAPHY ADSORBENTS
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The development of a new method for effecting cycloadditions on the surface of chromatographic adsorbents in the absence of solvents that leads to a moderation of the reaction conditions and an increase in selectivity is described.
- Veselovsky, V. V.,Gybin, A. S.,Lozanova, A. V.,Moiseenkov, A. M.,Smit, W. A.,Caple, R.
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p. 175 - 178
(2007/10/02)
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- On Baldwin's Kinetic Barrier Against 5-(Enol-endo)-exo-trigonal Closures: a Comparison of Ionic and Analogous Radical Reactions, and a New Synthesis of Cyclopentanones
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The kinetic barrier that impedes ionic 5-(enol-endo)-exo-trigonal closures does not play such a dominant role in the case of α-oxo radicals (17); these radicals cyclize directly to cyclopentanones in a process that constitutes a synthetic method for conve
- Clive, Derrick L. J.,Cheshire, David R.
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p. 1520 - 1523
(2007/10/02)
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