- Sustainable Production of o-Xylene from Biomass-Derived Pinacol and Acrolein
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o-Xylene (OX) is a large-volume commodity chemical that is conventionally produced from fossil fuels. In this study, an efficient and sustainable two-step route is used to produce OX from biomass-derived pinacol and acrolein. In the first step, the phosphotungstic acid (HPW)-catalyzed pinacol dehydration in 1-ethyl-3-methylimidazolium chloride ([emim]Cl) selectively affords 2,3-dimethylbutadiene. The high selectivity of this reaction can be ascribed to the H-bonding interaction between Cl? and the hydroxy group of pinacol. The stabilization of the carbocation intermediate by the surrounding anion Cl? may be another reason for the high selectivity. Notably, the good reusability of the HPW/[emim]Cl system can reduce the waste output and production cost. In the second step, OX is selectively produced by a Diels–Alder reaction of 2,3-dimethylbutadiene and acrolein, followed by a Pd/C-catalyzed decarbonylation/aromatization cascade in a one-pot fashion. The sustainable two-step process efficiently produces renewable OX in 79 % overall yield. Analogously, biomass-derived crotonaldehyde and pinacol can also serve as the feedstocks for the production of 1,2,4-trimethylbenzene.
- Hu, Yancheng,Li, Ning,Li, Guangyi,Wang, Aiqin,Cong, Yu,Wang, Xiaodong,Zhang, Tao
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- Poly(ethylene glycol)-Supported Chiral Imidazolidin-4-one: An Efficient Organic Catalyst for the Enantioselective Diels-Alder Cycloaddition
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A tyrosine-derived imidazolidin-4-one was immobilized on a modified poly(ethylene glycol) and converted in situ into a soluble polymer-supported catalyst for the enantioselective Diels-Alder cycloaddition of acrolein to 1,3-cyclohexadiene (up to 92% ee) a
- Benaglia, Maurizio,Celentano, Giuseppe,Cinquini, Mauro,Puglisi, Alessandra,Cozzi, Franco
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- On the Use of Ferrocenyl Cations as Chiral Lewis Acids: Evidence for Protic Acid Catalysis
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The preparation of cation 1 is described, as is the use of this material as a catalyst in the Diels-Alder reaction.While the addition of 1 does promote the Diels-Alder reaction, it is not the catalytic species.Rather, it acts as a source of protic acid wh
- Sammakia, Tarek,Latham, Hallie A.
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Read Online
- Polyesters Containing Chiral Imidazolidinone Salts in Polymer Main Chain: Heterogeneous Organocatalysts for the Asymmetric Diels–Alder Reaction
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Novel main-chain polyesters functionalized with chiral imidazolidinone salts were successfully synthesized. Polycondensation of a chiral imidazolidinone dimer bearing two hydroxyphenyl groups with selected achiral dicarboxylic acid chlorides followed by t
- Haraguchi, Naoki,Nguyen, Thanh Liem,Itsuno, Shinichi
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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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- Selective production of bio-based: Para -xylene over an FeOx -modified Pd/Al2O3catalyst
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para-Xylene (PX) is a basic building block of polyethylene terephthalate, which is currently produced from petroleum resources. Developing a renewable route to PX is highly desirable to address both economic and environmental concerns. Several attempts used noble metal catalysts, e.g. Pd/Al2O3, to synthesize PX from biomass-derived 4-methyl-3-cyclohexene-1-carboxaldehyde (4-MCHCA), but suffered from a severe decarbonylation reaction, resulting in toluene as the main product. In this paper, we report an FeOx modification strategy to suppress the decarbonylation reaction on a Pd/Al2O3 catalyst, leading to a drastic shift in selectivity towards PX with a yield up to 81percent via a cascade dehydroaromatization-hydrodeoxygenation (DHA-HDO) pathway. Characterization and control experiments revealed that the electron density of Pd sites decreased in an FeOx-modified Pd/Al2O3 catalyst compared to Pd/Al2O3, thus tuning the preferential adsorption mode of the substrate from η2-(C,O), the key transition state of the decarbonylation reaction, to the η1-(O) mode that favors the hydrodeoxygenation process. Notably, this designed catalyst is highly stable and is readily applicable in the selective synthesis of a broad range of desired aromatic chemicals via the same DHA-HDO pathway from cyclohex-3-enecarbaldehyde derivatives. Overall, this work develops a controllable catalyst modification strategy that tailors an efficient catalyst for petroleum-independent bio-PX synthesis.
- Fu, Zaihui,Li, Changzhi,Meng, Qingwei,Pan, Xiaoli,Xiao, Yuxue,Zhang, Chao
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supporting information
p. 4341 - 4349
(2020/07/14)
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- TRNA SYNTHETASE INHIBITORS
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Disclosed herein are secondary amine compounds that inhibit tRNA synthetase. The compounds of the invention are useful in inhibiting tRNA synthetase in Gram-negative bacteria and are useful in killing Gram-negative bacteria. The secondary amine compounds of the invention are also useful in the treatment of tuberculosis.
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Paragraph 00470
(2019/07/30)
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- Selective Production of Renewable para-Xylene by Tungsten Carbide Catalyzed Atom-Economic Cascade Reactions
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Tungsten carbide was employed as the catalyst in an atom-economic and renewable synthesis of para-xylene with excellent selectivity and yield from 4-methyl-3-cyclohexene-1-carbonylaldehyde (4-MCHCA). This intermediate is the product of the Diels–Alder reaction between the two readily available bio-based building blocks acrolein and isoprene. Our results suggest that 4-MCHCA undergoes a novel dehydroaromatization–hydrodeoxygenation cascade process by intramolecular hydrogen transfer that does not involve an external hydrogen source, and that the hydrodeoxygenation occurs through the direct dissociation of the C=O bond on the W2C surface. Notably, this process is readily applicable to the synthesis of various (multi)methylated arenes from bio-based building blocks, thus potentially providing a petroleum-independent solution to valuable aromatic compounds.
- Dai, Tao,Li, Changzhi,Li, Lin,Zhao, Zongbao Kent,Zhang, Bo,Cong, Yu,Wang, Aiqin
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supporting information
p. 1808 - 1812
(2018/02/10)
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- Synthesis of Main-Chain Ionic Polymers of Chiral Imidazolidinone Organocatalysts and Their Application to Asymmetric Diels–Alder Reactions
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Main-chain ionic polymers incorporating chiral imidazolidinone moieties in the polymer main chain were successfully synthesized by the polyaddition reaction of a chiral imidazolidinone dimer with a disulfonic acid. The organocatalytic activities of these polymers were investigated in the asymmetric Diels–Alder reaction between trans-cinnamaldehyde and 1,3-cyclopentadiene. The catalytic performance of the polymers was found to be sensitive to the chemical structure of the disulfonate units and the imidazolidinone dimer. With the use of these heterogeneous polymeric chiral organocatalysts, enantioselectivities of up to 99% for the endo isomer were obtained. This result was higher than those obtained with corresponding monomeric and dimeric counterparts in a homogeneous solution. The polymeric chiral organocatalyst was recovered and reused several times, maintaining its high enantioselectivity. (Figure presented.).
- Haraguchi, Naoki,Takenaka, Nagisa,Najwa, Aisyah,Takahara, Yuta,Mun, Mah Kar,Itsuno, Shinichi
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p. 112 - 123
(2017/12/26)
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- Methods for preparing benzene-ring-containing compounds from pinacol
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The invention relates to methods for preparing durene, 1,2,3-trimethylbenzene, o-xylene, pyromellitic acid and trimellitic acid from pinacol. Durene, 1,2,3-trimethylbenzene and o-xylene are prepared through three steps of reaction, and pyromellitic acid and trimellitic acid are prepared through four steps of reaction. A catalytic system used in the invention is green and environment-friendly, andcan be recycled. The raw materials of method, i.e., pinacol, crotonaldehyde, acrolein and crotonate can all be derived from biomass, and are cheap and easily available. All the reaction processes aresimple and are high in activity and selectivity in the dehydration of pinacol and the dehydrogenation, decarbonylation and oxidation of D-A products. The invention provides novel methods for preparingfine chemicals including durene, 1,2,3-trimethylbenzene, o-xylene, pyromellitic acid and trimellitic acid from lignocellulose-based platform chemicals.
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Paragraph 0049; 0050; 0073; 0074
(2018/08/04)
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- Carbocations as Lewis acid catalysts: Reactivity and scope
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One class of potential Lewis acids that has received negligible attention as a catalyst is the carbocation. Here we show the potential of triarylmethylium ions as highly powerful Lewis acid catalysts for organic reactions. The Lewis acidity of the triarylmethylium ion can be easily tuned by variation of the electronic properties of the aromatic rings and the catalytic activity of the carbocation is shown to correlate directly to the level of stabilization of the empty pC-orbital at the cationic carbon. The versatility of triarylmethylium ions as efficient Lewis acid catalysts for organic reactions is demonstrated in Diels-Alder, aza-Diels-Alder, conjugate addition, halogenation, epoxide rearrangement and intramolecular hetro-ene reactions.
- Bah, Juho,Naidu, Veluru Ramesh,Teske, Johannes,Franzn, Johan
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supporting information
p. 148 - 158
(2015/01/30)
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- Synthesis of Chiral Polyethers Containing Imidazolidinone Repeating Units and Application as Catalyst in Asymmetric Diels-Alder Reaction
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In this study, enantiopure imidazolidinones containing two hydroxyphenyl groups were synthesized, and the Williamson synthesis of the chiral bisphenols thus prepared with dihalides afforded polyethers containing chiral imidazolidinone repeating units. These chiral imidazolidinone polyethers exhibited excellent catalytic activity in the asymmetric Diels-Alder reaction. With the use of these polymeric catalysts, enantioselectivities up to 99% were obtained, higher than those obtained by the corresponding monomeric imidazolidinone catalyst in homogeneous solution. The polymeric catalysts were found to be insoluble in commonly used organic solvents, and they could be repeatedly used without the loss of activity.
- Itsuno, Shinichi,Oonami, Tatsuaki,Takenaka, Nagisa,Haraguchi, Naoki
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supporting information
p. 3995 - 4002
(2016/01/25)
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- PERFUME SYSTEMS
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The present application relates to perfume raw materials, perfume delivery systems and consumer products comprising such perfume raw materials and/or such perfume delivery systems, as well as processes for making and using such perfume raw materials, perfume delivery systems and consumer products. Such perfume raw materials and compositions, including the delivery systems, disclosed herein expand the perfume communities' options as such perfume raw materials can provide variations on character and such compositions can provide desired odor profiles.
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Page/Page column 56
(2015/12/08)
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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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- 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
(2015/02/05)
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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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- Highly enantioselective diels-alder reaction catalyzed by chiral imidazolidinone
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New chiral imidazolidinone with an indole group was synthesized and used to catalyze the Diels-Alder reaction of α,β-unsaturated aldehyde with diene. High enantiomeric excesses and good yields were obtained. The reaction media were also surveyed. The best
- Wang, Yongjiang,Xu, Xiaoliang,Pei, Wen
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experimental part
p. 2032 - 2041
(2009/11/30)
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- Unsaturated aldehydes as alkene equivalents in the Diels-Alder reaction
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A one-pot procedure is described for using α,β-unsaturated aldehydes as olefin equivalents in the Diels-Alder reaction. The method combines the normal electron demand cycloaddition with aldehyde dienophiles and the rhodium-catalyzed decarbonylation of aldehydes to afford cyclohexenes with no electron-with-drawing substituents. In this way, the aldehyde group serves as a traceless control element to direct the cycloaddition reaction. The Diels-Alder reactions are performed in a diglyme solution in the presence of a catalytic amount of boron trifluoride etherate. Subsequent quenching of the Lewis acid, addition of 0.3% of [Rh(dppp)2Cl] and heating to reflux achieves the ensuing decarbonylation to afford the product cyclohexenes. Under these conditions, acrolein, crotonaldehyde and cinnamaldehyde have been reacted with a variety of 1,3-dienes to afford cyclohexenes in overall yields between 53 and 88%. In these transformations, the three aldehydes serve as equivalents of ethylene, propylene and styrene, respectively.
- Taarning, Esben,Madsen, Robert
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supporting information; experimental part
p. 5638 - 5644
(2009/05/30)
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- A recyclable fluorous organocatalyst for Diels-Alder reactions
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Chiral fluorous imidazolidinone catalyst 2 provides consistently high enantioselectivities in Diels-Alder reactions of dienes and α,β-unsaturated aldehydes. The catalyst can be readily separated from the reaction products by fluorous solid-phase extractio
- Chu, Qianli,Zhang, Wei,Curran, Dennis P.
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p. 9287 - 9290
(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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- Ionic liquids and their use
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Ionic compounds having a freezing point of no more than 50° C., formed by the reaction of at least one amine salt of the formula R1R2R3R4N+X? (I) with at least one hydrated salt, which is a chloride, nitrate, sulphate or acetate of Li, Mg, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb, Bi, La or Ce; wherein R1, R2 and R3 are each independently a C1 to C5 alkyl or a C6 to C10 cycloalkyl group, or wherein R2 and R3 taken together represent a C4 to C10 alkylene group, thereby forming with the N atom of formula (I) a 5 to 11 membered heterocyclic ring, and wherein R4 is hydrogen, or phenyl, or C1 to C12 alkyl or cycloalkyl group, optionally substituted with at least one group selected from OH, Cl, Br, F, I, phenyl, NH2, CN, NO2, COOR5, CHO, COR5 and OR5, wherein R5 is a C1 to C10 alkyl or cycloalkyl group, and X? is an anion capable of being complexed by the said hydrated salt. The compounds are useful as solvents, electrolytes, and catalysts, and have particular application in solvents/electrolytes for metal plating and electropolishing processes, in particular in chromium plating.
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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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- 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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- Iminium ion catalysis: Use of the α-effect in the acceleration of the Diels-Alder reaction
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The α-effect can be used in the acceleration of the DielsAlder reaction between a series of dienes and electron deficient dienophiles using iminium ion catalysis, providing a novel molecular scaffold capable of performing this class of catalytic process.
- Cavill, Julie L.,Peters, Jens-Uwe,Tomkinson, Nicholas C. O.
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p. 728 - 729
(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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- Aluminum trisphenoxide polymer as a Lewis acidic, solid catalyst
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A newly introduced, solid polymer of an aluminum trisphenoxide has been demonstrated an efficient catalyst for promoting the Diels-Alder reaction of α,β-enals.
- Saito, Susumu,Murase, Masaaki,Yamamoto, Hisashi
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- Design of bronsted acid-assisted chiral Lewis acid (BLA) catalysts for highly enantioselective Diels-Alder reactions
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Bronsted acid-assisted chiral Lewis acid (BLA) was highly effective as a chiral catalyst for the enantioselective Diels-Alder reaction of both α- substituted and α-unsubstituted α,β-enals with various dienes. Hydroxy groups in optically active binaphthol derivatives and boron reagents with electron-withdrawing substituents were used as Bronsted acids and Lewis acids, respectively. Intramolecular Bronsted acids in a chiral BLA catalyst played an important role in accelerating the rate of Diels-Alder reactions and in producing a high level of enantioselectivity. In particular, excellent enantioselectivity was achieved due to intramolecular hydrogen bonding interaction and attractive π-π donor-acceptor interaction in the transition-state assembly by hydroxy aromatic groups in a chiral BLA catalyst.
- Ishihara, Kazuaki,Kurihara, Hideki,Matsumoto, Masayuki,Yamamoto, Hisashi
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p. 6920 - 6930
(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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- Macromolecular materials in heterogeneous catalysis: An aluminium silasesquioxane gel as active catalyst in Diels-Alder reactions of enones
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A highly active, genuinely heterogeneous catalyst for liquid-phase Diels-Alder reactions of enones results from the silanol centred modification of an incompletely condensed silasesquioxane with trimethylaluminium, the resulting catalytic material being a gel that contains aluminium(III) siloxy functions (Al-O-Si) which are incorporated in a well defined, three-dimensional SiO framework.
- Abbenhuis, Hendrikus C. L.,Van Herwijnen, Hendrikus W. G.,Van Santen, Rutger A.
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p. 1941 - 1942
(2007/10/03)
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- Synthesis of a polymer-bound iron Lewis acid and its utilization in Diels-Alder reactions
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The first polymer-bound iron Lewis acid 3 was synthesized in two steps from (η5-vinylcyclopentadienyl)dicarbonylmethyliron. Preliminary studies for catalysis of Diels-Alder reactions by the polymer-bound iron Lewis acid 3 are also reported.
- Saha, Anjan K.,Hossain, M. Mahmun
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p. 3833 - 3836
(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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- Chromium and tungsten pentacarbonyl groups as reactivity auxiliaries in the Diels-Alder reactions of alkenyl carbene complexes with 1,3-dienes
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The Diels-Alder reactions of Fischer carbene complexes of the group 6 metals bearing alkenyl substituents on the carbene ligand are surveyed for 10 chromium, molybdenum, and tungsten complexes with 11 1,3-dienes. The reactions of complexes of the type R1CH=CHC(OMe)=M(CO)5 (R1 = H, CH3 (trans), M = Cr, Mo, W) have been examined with isoprene, and it was found that the rates can be as much as 2 × 104 faster than their organic ester analogues. The regioselectivity of the cycloadditions of alkenyl carbene complexes with isoprene were also found to be significantly higher(≥91:9) than their organic esters analogues and comparable to that observed with Lewis acid mediated cycloadditions of acrylates esters with isoprene. The cycloadditions of the seven complexes of the type R1R2C=CR3C(OMe)=M(CO)5 (R1, R2, R3 = H; R1 = CH3, R2, R3 = H; R1, R3 = H, R2 = CH3 (cis and trans); R1 = H, R2, R3 = CH3: M = Cr, W) were investigated with 2,3-dimethyl-1,3-butadiene and cyclopentadiene. The reactions with cyclopentadiene were found to be stereoselective in favor of the Alder endo adduct at a level much higher than is observed for the corresponding α,β-unsaturated esters. The reaction with cyclopentadiene was also found to be stereospecific with cis- and trans-propenyl tungsten complexes where the stereochemistry about the olefin in each carbene complex was retained in the cycloadducts. The cycloadditions of six complexes of the type R1R2C=CR3C(OMe)=M(CO)5 were also investigaed with three monooxygenated dienes: 1-methoxy-, 2-methoxy-, and 1-acetoxy-1,3-butadiene. It was found that these carbene complexes display greatly enhanced reactivity compated to α,β-unsaturated esters with these dienes under either thermal or high-pressure conditions. All of the reactions of these three acyclic dienes with alkenyl carbene complexes were highly regioselective; however, like their organic ester analogues, they occured with relatively low stereoselectively. The endo adduct (but not the exo) from the reaction of the trans-propenyl chromium (but not tungsten) complex 12 with 1-methoxy-1,3-butadiene forms a methoxyl-chelated tetracarbonyl carbene complex. Several cycloadditions were examined for four complexes of the type R1R2C=CR3C(OMe)=W(CO)5 with Danishefsky's diene and trans,trans-1-methoxy-2-[(trimethylsilyl)oxy]-4-ethoxy-1,3-butadiene (27). The reaction of the trans-propenyl tungsten complex with diene 27 occurs with retention of the stereochemistry in both the diene and the carbene complex. The reaction of the cis-propenyl tungsten complex with 27 occurs with competing isometrization to the trans-propenyl complex prior to cycloaddition. The chromium and tungsten cyclohexenyl complexes C6H9C(OMe)=M(CO)5 were found to dispaly different chemoselectivities toward derivatives of Danishefsky's diene; the chromium complex produced divinylcyclopropanes, whereas the tungsten complex gave rise to Diels-Alders adducts. The reaction of the vinyl tungsten complex CH2=CHC(OMe)=W(CO)5 with 6,6-dimethyl-6-sila-α-pyran (28) illustrates the advantages of rate and tolerance of sensitive organic functionality that are possible when alkenyl carbene complexes are employed as synthons in the Diels-Alder reaction. Finally, the versatility with which the metal unit can be removed from cycloadducts 43 and 44 demonstrates that alkenyl carbene complexes can serve as synthons in the Diels-Alder reaction for esters, aldehydes, ketones, methoxyallens, 2-methoxybutadiene, and simple alkenes.
- Wulff, William D.,Bauta, William E.,Kaesler, Ralph W.,Lankford, Peter J.,Miller, Ross A.,Murray, Christopher K.,Yang, Dominic C.
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p. 3642 - 3659
(2007/10/02)
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- Catalysis of Diels-Alder Reactions with Acrolein as Dienophile by Iron(III)-Doped Montmorillonite
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Acrolein is improved as a dienophile in the presence of the K10 montmorillonite exchanged with iron(III).Cycloaddition occurs with a number of dienes at room temperature and in high yield.Dienes tested include butadiene, isoprene, cyclopentadiene, cyclohexadiene, 1-methoxycyclohexadiene, anthracene.
- Laszlo, Pierre,Moison, Helene
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p. 1031 - 1034
(2007/10/02)
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- Chiral (Acyloxy)borane (CAB): A Powerful and Practical Catalyst for Asymmetric Diels-Alder Reactions
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Chiral (acyloxy)borane complexes catalyze the Diels-Alder reaction of α,β-unsaturated aldehydes to bring about remarkable induction.
- Furuta, Kyoji,Shimizu, Sadahiro,Miwa, Yoshikazu,Yamamoto, Hisashi
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p. 1481 - 1483
(2007/10/02)
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- Diels-Alder Reaction in the Presence of Zeolite
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Cu(I) ion exchanged Y-zeolite catalyzed Diels-Alder reaction of furan, cyclopentadiene, 1,3-cyclohexadiene, isoprene and 2,3-dimethylbutadiene with a series of acrylic and acetylenic dienophiles is reported.The cycloadducts are obtained in high yield and selectivity. - Keywords: Cycloaddition Reactions, Copper(I)-zeolite
- Ipaktschi, Junes
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p. 496 - 498
(2007/10/02)
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- Factors Influencing Conformational Preferences in Cyclohexenes
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Conformational preferences have been measured for the first time for 4-substituted cyclohexenes in a solvent of low polarity.Measurements were made for the substituents Cl, Br, I, OH, OSiMe3, and CN and were compared with conformational preferences in cyclohexyl and exo-methylenecyclohex-3-yl.In the nearly nonpolar solvent CF2Cl2, in which intramolecular interactions are maximized, there is a much larger axial population for cyclohexen-4-yl than in cyclohexyl or exo-methylenecyclohex-3-yl.In particular, the dipolar interaction of the endocyclic double bond is reduced from that of the exocyclic double bond.This observation is confirmed by the almost negligible effect of symmetrizing the endocyclic double bond through 1,2-dimethyl substitution, in contrast with the large effect of symmetrizing the exocyclic double bond through 7,7-dimethyl substitution.Polar solvents increase the proportion of the axial conformer to a smaller extent for the endocyclic than for the exocyclic system, again in agreement with a lower dipolar effect in the endocyclic case.These results emphasize the anisotropic nature of the steric effects of double bonds.
- Lambert, Joseph B.,Marko, Dale E.
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p. 7978 - 7982
(2007/10/02)
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- CATALYSIS OF HOMO DIELS-ALDER REACTIONS BY YB(FOD)3
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The use of Yb(fod)3 to catalyze Diels-Alder reactions of acrolein with sensitive dienes in nearly stoichiometric ratio and with high stereoselectivity is described.
- Danishefsky, Samuel,Bednarski, Mark
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p. 2507 - 2508
(2007/10/02)
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- ACCELERATION OF THE DIELS-ADLER REACTION BY CLAYS SUSPENDED IN ORGANIC SOLVENTS
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Rapid and stereoselective Diels-Alder reactions can be run in ethanol or methylene chloride in the presence of FeIII-doped K10 montmorillonite.
- Laszlo, Pierre,Lucchetti, Jean
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p. 2147 - 2150
(2007/10/02)
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- A New Total Synthesis of Epifenchone and Dehydrocamphenilone
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A new and simple method with good yields for the total synthesis of the title substances 5 and 9 is described.Methylation of 3, 4, and 8 with CH3I/LCIA in THF under reflux yields the geminal dimethylnorbornanones 5, 6, and 9.
- Dworan, Erich,Buchbauer, Gerhard
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p. 2357 - 2359
(2007/10/02)
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- Synthesis of Norbornanones with a Geminal Dimethyl Group
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The synthesis of gem-dimethylnorbornanones is described.One synthetic pathway after a Diels-Alder reaction involves the transformation of the nitro group into the oxo group with subsequent methylation into the geminal dimethyl product.A shorter way by -cycloaddition of cyclopentadiene with a suitable dimethylated dienophile (e.g. 2-methyl-1-nitropropene) failed, probably by steric hindrance of the dienophile. 7-Oxanorbornanones with a gem -dimethyl group could not be prepared.A second synthetic approach to gem-dimethylnorbornanones is opened by Lewis acid catalyzed rearrangement of cyclohexenylcarbaldehydes. - Keywords: Camphenilone; Diels-Alder reaction; Homonorbornanone; α-Methylation of carbonyls; Nef-reaction; Norepifenchone
- Buchbauer, Gerhard,Dworan, Erich
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p. 1165 - 1174
(2007/10/02)
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- Relationships between structure of some cyclohexene derivatives and attractiveness for the males of Ceratitis capitata
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Derivatives of 3 cyclohexene 1 carboxaldehyde variously substituted with methyl and phenyl groups at the 3, 4 and 6 positions, the corresponding 3 cyclohexene 1 methanol derivatives and their acetates were prepared and the relationships between their structure and their attractiveness for Ceratitis capitata males was investigated. Activity almost disappeared in the alcoholic derivatives, while some of the aldehydes and the acetates showed slight to strong attractiveness. Introduction of methyl or phenyl groups at the 3, 4 and 6 positions caused alteration of activity; the bulky phenyl group at position 6 caused loss of attractiveness in all cases.
- Guiotto,Rodighiero,Fornasiero
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