- Immobilization of a soluble metal complex in an organic network. Remarkable catalytic performance of a porous dialkoxyzirconium polyphenoxide as a functional organic zeolite analogue
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Treatment of anthracenebisresorcinol 1 (a tetraphenol) with Zr(O(t)Bu)4 in THF results in polycondensation to give an O-Zr-O network and affords a poly(dialkoxyzirconium phenoxide), 14- · 2[Zr(O(t)Bu)2] (Zr host), in quantitative yield as an insoluble, amorphous, microporous powder with a particle size of ~0.7 μm, a pore size of ~0.7 nm, and a specific surface area of ~200 m2/g. The powder exhibits reversible Langmuir-type adsorption/desorption of N2 at 77 K and hexane at 298 K. Adsorption and coadsorption of ethyl acetate, benzene, and other polar and apolar guests also occurs readily at 298 K. The Zr host catalyzes the Diels-Alder reaction of acrolein with 1,3-cyclohexadiene in a remarkable manner. As a solid metal- organic catalyst, it has a formula-based turnover rate constant of 40 h-1, which far exceeds those of its components, i.e., the soluble Lewis acid Zr(O(t)Bu)4 (0.1 h-1) and the hydrogen-bonded insoluble organic network 1 (0.3 h-1). The solid catalyst can be easily separated from the organic product, which is not contaminated with Zr or the reactants. The recovered catalyst can be used repeatedly without deactivation. The reaction can also be conducted in a flow system with the insoluble Zr host catalyst and a reactant mixture as a mobile phase. The remarkable catalytic performance of the Zr host and its easy preparation suggest that insoluble microporous metal-organic solid catalysts are workup-free and waste-free as well as resource- and energy-saving.
- Sawaki, Tomoya,Aoyama, Yasuhiro
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Read Online
- 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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- Carbon's Three-Center, Four-Electron Tetrel Bond, Treated Experimentally
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Tetrel bonding is the noncovalent interaction of group IV elements with electron donors. It is a weak, directional interaction that resembles hydrogen and halogen bonding yet remains barely explored. Herein, we present an experimental investigation of the
- Karim, Alavi,Schulz, Nils,Andersson, Hanna,Nekoueishahraki, Bijan,Carlsson, Anna-Carin C.,Sarabi, Daniel,Valkonen, Arto,Rissanen, Kari,Gr?fenstein, Jürgen,Keller, Sandro,Erdélyi, Máté
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p. 17571 - 17579
(2019/01/04)
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- Synthetic studies toward polytwistane hydrocarbon nanorods
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A synthetic strategy toward the intriguing hydrocarbon nanorod polytwistane is outlined. Our approach aims toward the polymerization of acetylene starting from precursors that would provide a helical bias for the formation of polytwistane. Both transition-metal-catalyzed and radical polymerizations were investigated. Two potential initiator molecules were synthesized that could be used for either approach. Although the intended regioselectivities were not observed, unusual organopalladium complexes and numerous compounds with novel carbon skeletons were obtained.
- Olbrich, Martin,Mayer, Peter,Trauner, Dirk
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p. 2042 - 2055
(2015/09/08)
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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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- Bromination and accompanying rearrangement of the polycyclic oxetane 2,4-oxytwistane
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Bromination of the polycyclic oxetane 2,4-oxytwistane (rac-(1R,3S,4R,7S,9R,11S)-2-oxatetracyclo-[5.3.1.03,11.04,9]undecane) was undertaken in order to form 2,4-dibromotwistane. The oxetane was subjected to the mild reagent combinatio
- Rosenberg, Murray G.,Billing, Peter,Brecker, Lothar,Brinker, Udo H.
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p. 8786 - 8799
(2015/02/19)
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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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scheme or table
p. 4421 - 4428
(2012/04/23)
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- Erbium triflate in ionic liquids: A recyclable system of improving selectivity in Diels-Alder reactions
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The efficiency of Er(OTf)3 in promoting the Diels-Alder reactions between different dienes and dienophiles in ionic liquids has been investigated. Compared with the analogous cycloadditions performed in conventional solvents shorter reaction times are required to obtain good/excellent yields. In most cases an enhancement of regio- and endo:exo selectivity was observed. The role of the ionic liquid, as a function of the cationic part, i.e. the imidazolium based or the pyridinium based, is discussed well. The ILs containing the catalyst can be readily separated from the reaction products and recovered in very high purity for direct reuse, up to six cycles.
- Bortolini, Olga,De Nino, Antonio,Garofalo, Angelo,Maiuolo, Loredana,Procopio, Antonio,Russo, Beatrice
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experimental part
p. 124 - 129
(2011/02/16)
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- Novel tetrahydroisoquinoline based organocatalysts for asymmetric Diels-Alder reactions: Insight into the catalytic mode using ROESY NMR and DFT studies
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For the first time an organocatalyst bearing a secondary nitrogen within a cyclohexane ring has been evaluated in the asymmetric Diels-Alder reaction. This organocatalyst is also the first of its kind based on a (1R,3S)-6,7-dimethoxy- 1-phenyl-1,2,3,4-tetrahydroisoquinoline backbone. These catalysts were tested over a range of dienes and dienophiles and displayed promising chemical conversions of up to 100% with up to 64% ee with triflic acid as the cocatalyst. Density functional theory computational studies and 2D NMR spectroscopy were used to determine the structure of the intermediate iminium ion formed between the most efficient catalyst and cinnamaldehyde. The reaction profile for each of the four possibilities in this reaction were calculated and it was found that the iminium intermediate leading to the major product is higher in energy but kinetically preferred. The activation energies of all possible reaction paths were calculated and the results correlated with the observed products. These experiments revealed that the presence of both (E)- and (Z)-isomers of the cinnamaldehyde were contributing factors for the low enantioselectivity of the reaction products.
- Naicker, Tricia,Petzold, Katja,Singh, Thishana,Arvidsson, Per I.,Kruger, Hendrik G.,Maguire, Glenn E.M.,Govender, Thavendran
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experimental part
p. 2859 - 2867
(2011/03/19)
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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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- 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 general approach to creating soluble catalytic polymers heterogenized in microcapsules
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A general method for preparing site-isolated polymeric catalysts is presented. Linear chloromethyl and azide polymers have been sequestered within polyurea microcapsules and small molecule catalysts soaked through the shell walls to functionalize the soluble polymers. Reaction onto each type of support is quantitative and MacMillan, DMAP, and TEMPO test catalysts are shown to have faster reaction rates than the analogous resin-supported catalysts.
- Mason, Brian P.,Bogdan, Andrew R.,Goswami, Anandarup,McQuade, D. Tyler
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p. 3449 - 3451
(2008/03/12)
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- Bis-phosphine monoxide platinum(II) and palladium(II) cationic complexes as Lewis acid catalysts in Diels-Alder and sulfoxidation reactions
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A series of bis-phosphine monoxide (BPMO) palladium(II) and platinum(II) cationic complexes of the type [M(BPMO-κ2-P,O)2][X]2 (M = Pd, Pt; BPMO = Ph2P-(CH2)n-P(O)Ph2 with n = 1 (dppmO), 2 (dppeO), 3 (dpppO); X = BF4, TfO) were prepared from the corresponding chlorides [MCl2(BPMO-κ1-P)2] upon treatment with 2 equiv. of AgX in wet acetone/CH2Cl2 or MeOH solutions. They were characterized by 1H and 31P{1H} NMR spectroscopies and, in the case of the complex [Pt(dppeO-κ2-P,O)2][BF4]2, also by X-ray crystallography. These complexes were tested as catalysts in some Diels-Alder and oxidation reactions with different substrates. In the latter reaction Pt(II) complexes showed moderate activity, while for the former one, both classes of complexes were active in the C-C coupling, in particular the Pt(II) species showed interesting high endo/exo diasteroselectivity depending on the counteranion.
- Sgarbossa, Paolo,Pizzo, Erika,Scarso, Alessandro,Sbovata, Silvia Mazzega,Michelin, Rino A.,Mozzon, Mirto,Strukul, Giorgio,Benetollo, Franco
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p. 3659 - 3666
(2007/10/03)
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- Titanium(IV) and zirconium(IV) sulfato complexes containing the Klaeui tripodal ligand: Molecular models of sulfated metal oxide surfaces
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Treatment of titanyl sulfate in about 60 nM sulfuric acid with NaL, (L OEt = [(η5-C5H5)Co-{(P(O)(OEt) 2}3]-) afforded the μ-sulfato complex [(LOEtOEtTi)2(μ-O)2(μ-SO 4)] (2). In more concentrated sulfuric acid (> 1 M), the same reaction yielded the di-μ-sulfato complex [(LOEtTi) 2(μ-O)(μ-SO4)2] (3). Reaction of 2 with HOTf (OTf = triflate, CF3SO3) gave the tris-(triflato) complex [LOEtTi(OTf)3] (4), whereas treatment of 2 with Ag(OTf) in CH2Cl2 afforded the sulfato-capped trinuclear complex [{(LOEt)3Ti3(μ-O) 3}(μ3-SO4){Ag(OTf)}][OTf] (5), in which the Ag(OTf) moiety binds to a μ-oxo group in the Ti3(μ-O) 3 core. Reaction of 2 in H2O with Ba(NO3) 2 afforded the tetranuclear complex (LOEt) 4Ti4(μ-O)6 (6). Treatment of 2 with [{Rh(cod)Cl}2] (cod = 1,5-cyclooctadiene), [Re(CO)5Cl], and [Ru(tBu2-bpy)(PPh3)2Cl2] (tBu2bpy = 4,4′-dl-tert-butyl-2,2′-dipyridyl) in the presence of Ag(OTf) afforded the heterometallic complexes [(L OEt)2Ti2(O)2(SO4){Rh- (cod)}2][OTf]2 (7), [(LOEt)2Ti(O) 2-(SO4){Re(CO)3}][OTf] (8), and [{(L OEt)2Ti2(μ-O)}(μ3-SO 4)(μ-O)2{Ru-(PPh3)(tBu2bpy)}] [OTf]2 (9), respectively. Complex 9 is paramagnetic with a measured magnetic moment of about 2.4 μB. Treatment of zirconyl nitrate with NaLOEt in 3.5 M sulfuric acid afforded [(LOEt) 2Zr(NO3)][LOEtZr(SO4)-(NO 3)] (10). Reaction of ZrCl4 in 1.8 M sulfuric acid with NaLOEt in the presence Na2SO4 gave the μ-sulfato-bridged complex [LOEtZr(SO4)(H 2O)]2(μ-SO4) (11). Treatment of 11 with triflic acid afforded [(LOEt)2Zr][OTf]2 (12), whereas reaction of 11 with Ag(OTf) afforded a mixture of 12 and trinuclear [{LOEtZr(SO4)(H2O)}3(μ 3-SO4)][OTf] (13). The ZrIV triflato complex [LOEtZr-(OTf)3] (14) was prepared by reaction of L OEtZrF3 with Me3SiOTf. Complexes 4 and 14 can catalyze the Diels-Alder reaction of 1,3-cyclohexadiene with acrolein in good selectivity. Complexes 2-5, 9-11, and 13 have been characterized by X-ray crystallography.
- Zhang, Qian-Feng,Lam, Tony C. H.,Yi, Xiao-Yi,Chan, Eddie Y. Y.,Wong, Wai-Yeung,Sung, Herman H. Y.,Williams, Ian D.,Leung, Wa-Hung
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p. 101 - 111
(2007/10/03)
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- Thermal reactions of 8-methylbicyclo[4.2.0]oct-2-enes: Competitive diradical-mediated [1,3] sigmatropic, stereomutation, and fragmentation processes
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At 275 °C, 8-exo-methylbicyclo[4.2.0]oct-2-ene (1a) undergoes a [1,3] sigmatropic rearrangement to 5-methylbicyclo[2.2.2]oct-2-enes, of which the orbital symmetry-allowed si product is only marginally favored over the forbidden sr product; that is, silsr is 2.4. Accompanying the [1,3] shift are significant amounts of epimerization and fragmentation. The 8-endo epimer 1b, which yields no [1,3] product, experiences primarily direct fragmentation and secondarily epimerization. A diradical intermediate can account for all such observations.
- Bogle, Xavier S.,Leber, Phyllis A.,McCullough, Lynne A.,Powers, David C.
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p. 8913 - 8918
(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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- 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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- Ring-opening-ring-closing metathesis of bicyclo[2.2.2]octenes: A novel synthesis of decalins and hydrindanes
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Bicyclo[2.2.2]octenes containing an olefinic side-chain undergo ring-opening-ring-closing metathesis to give decalins and hydrindanes in reasonable yields.
- Minger, Timothy L,Phillips, Andrew J
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p. 5357 - 5359
(2007/10/03)
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- Asymmetric Organocatalytic Diels-Alder Reactions on Solid Support
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Asymmetric organocatalysis on solid support combines the environmental advantages of metal-free catalysts and the ease of operation of solid-supported reagents. Enantioselective organo-catalytic Diels-Alder reactions have been demonstrated by two differen
- Selkaelae, Sami A.,Tois, Jan,Pihko, Petri M.,Koskinen, Ari M. P.
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p. 941 - 945
(2007/10/03)
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- Catalysis by organic solids. Stereoselective Diels-Alder reactions promoted by microporous molecular crystals having an extensive hydrogen- bonded network
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Anthracenebisresorcinol derivative 1 as an organic network material shows a novel catalysis in the solid state for the acrolein-cyclohexadiene Diels-Alder reaction. The suggested mechanism involves a catalytic cycle composed of sorption of the reactants in the cavities of polycrystalline host 1, preorganized intracavity reaction, and desorption of the product. The host also promotes stereoselective intracavity reactions for alkyl acrylates and cyclohexadiene but, in this case, not in a catalytic manner. Relevance of the present system as a functional organic analog of zeolites is discussed in light of the kinetics of respective elementary processes and the effects of pulverization of the catalyst thereupon as well as X-ray crystal structures.
- Endo, Ken,Koike, Takashi,Sawaki, Tomoya,Hayashida, Osamu,Masuda, Hideki,Aoyama, Yasuhiro
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p. 4117 - 4122
(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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- 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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- 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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- 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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- 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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- Facial (syn-anti) stereoselectivity in the Diels-Alder reactions of spiro(bicyclooctane-2,1'-cyclopentadiene)
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Spiro(bicyclooctane-2,1'-cyclopentadiene) (3) has been synthesized in ten steps, and its Diels-Alder cycloadditions, both thermal and catalysed, have been studied with a variety of Z-ethylenic dienophiles.No significant differences in facial stereoselectivity were observed.This suggests that, in the exo region, the distance between the addends at the transition state is approximately the same in all the cases studied.
- Burnell, D. Jean,Goodbrand, H. Bruce,Kaiser, Stephanie M.,Valenta, Zdenek
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p. 154 - 165
(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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- RATE OF REACTION OF ORGANIC ACIDS WITH UNSATURATED BRIDGED BICYCLIC HYDROCARBONS
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The rate constants were determined for the addition of acetic acid and trifluoroacetic acid to 15 unsaturated hydrocarbons with the bicycloheptane, bicyclo- and bicyclooctane, and cyclohexene structures.The reactivity of the compounds
- Bobyleva, A. A.,Belikova, N. A.,Dzhigirkhanova, A. V.,Plate, A. L.
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p. 797 - 804
(2007/10/02)
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