- Flow Chemistry-Enabled Divergent and Enantioselective Total Syntheses of Massarinolin A, Purpurolides B, D, E, 2,3-Deoxypurpurolide C, and Structural Revision of Massarinolin A
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Massarinolin A and purpurolides are bioactive bergamotane sesquiterpenes condensed with a variety of synthetically challenging ring systems: a bicyclo[3.1.1]heptane, an oxaspiro[3.4]octane, and a dioxaspiro[4.4]nonane (oxaspirolactone). Herein, we report the first enantioselective total syntheses of massarinolin A, purpurolides B, D, E, and 2,3-deoxypurpurolide C. Our synthesis and computational analysis also led to a structural revision of massarinolin A. The divergent approach features an enantioselective organocatalyzed Diels–Alder reaction to install the first stereogenic center in high ee, a scalable flow photochemical Wolff rearrangement to build the key bicyclo[3.1.1]heptane, a furan oxidative cyclization to form the oxaspirolactone, a late-stage allylic C?H oxidation, and a Myers’ NBSH-promoted sigmatropic elimination to install the exo methylene group of massarinolin A.
- Cui, Chengsen,Dai, Mingji,Wang, Ye-Cheng
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supporting information
p. 24828 - 24832
(2021/09/18)
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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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- Viable route and DFT study for the synthesis of optically active limonaketone: A barely available natural feedstock in Cedrus atlantica
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Herein, we report a novel, easy and efficient synthesis pathway of optically active limonaketone, a high added value monoterpene, starting from limonene, natural and low-cost feedstock. The strategy was developed in an excellent three-step total synthesis of limonaketone, potentially important intermediate in limonene ozonolysis and barely available in Cedrus atlantica essential oil (0.1% yield). The first step was the epoxidation of limonene which proceed in 91% yield. The ozonolysis of the prepared limonene oxide leads to the formation of the characteristic ketone function of limonaketone in 92% yield. The last step was performed by a deoxygenation in the presence of Zn and gave limonaketone in quantitative yield. The optically pure limonaketone has been efficiently synthesized from limonene and the overall yield was 84%. A molecular electron density theory (MEDT) analysis was carried out by using density functional theory (DFT) calculations at the M06–2X/6–311G(d,p) (LANL2DZ for Zn) level to understand the observed chemoselectivity in the Zn-deoxygenation reaction as well as its corresponding mechanistic pathway.
- Mekkaoui, Ayoub Abdelkader,Ben El Ayouchia, Hicham,Anane, Hafid,Chahboun, Rachid,El Firdoussi, Larbi,El Houssame, Soufiane
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- Identification of the early intermediates formed in ozonolysis of: Cis-2-butene and limonene: A theoretical and matrix isolation study
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This study combined quantum chemical calculations and the matrix isolation technique to identify the formation of primary intermediates from the ozonolysis of cis-2-butene and limonene. Quantum chemical calculations were conducted under the framework of density functional theory (DFT) at M06-2x/6-311+(d, p) level of theory to predict the possible mechanism as well as the new absorption bands. New bands whose intensity increased with annealing, were observed in twin jet deposition, which indicated the formation of primary ozonides, CI and secondary ozonides in the investigated systems. Isotopic labeling (18O) experiments further supported the assignment of observed bands. The results and findings in this study would enrich the understanding of the reaction mechanism of alkene ozonolysis.
- Li, Shan-Shan,Yang, Xiao-Yang,Xu, Yi-Sheng,Jiang, Lei
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p. 20100 - 20106
(2019/07/09)
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- Synthesis of 9-geranylterpinolene as a mixture of isomers, and synthesis of α- and β-springene, possible kairomones of the beech leaf-mining weevil, Orchestes fagi (L.)
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The beech leaf-mining weevil, Orchestes fagi (L.), also known as the beech flea weevil, is a common and widespread pest of beech, Fagus sylvatica L., in its native Europe. It now appears to be well established in Nova Scotia, Canada. We have previously reported the synthesis of 9-geranyl-p-cymene and 9-geranyl-α-terpinene, as they are both found in eclosing beech buds, and have researched the synthesis of other diterpenes that are isomers of 9-geranyl-α-terpinene. We now wish to report a synthesis of the diterpene 9-geranylterpinolene as a mixture of isomers, as a novel diterpene, and as a possible kairomone of O. fagi. Also, all trans-α-springene, its 3Z-isomer, and β-springene were synthesized as a mixture, as well as pure β-springene, utilizing known methods.
- Mayo,Silk,Abeysekera,MaGee
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p. 1766 - 1776
(2018/06/18)
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- Odor-active constituents of Cedrus atlantica wood essential oil
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The main odorant constituents of Cedrus atlantica essential oil were characterized by GC-Olfactometry (GC-O), using the Aroma Extract Dilution Analysis (AEDA) methodology with 12 panelists. The two most potent odor-active constituents were vestitenone and 4-acetyl-1-methylcyclohexene. The identification of the odorants was realized by a detailed fractionation of the essential oil by liquid-liquid basic extraction, distillation and column chromatography, followed by the GC-MS and GC-O analyses of some fractions, and the synthesis of some non-commercial reference constituents.
- Uehara, Ayaka,Tommis, Basma,Belhassen, Emilie,Satrani, Badr,Ghanmi, Mohamed,Baldovini, Nicolas
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p. 208 - 215
(2017/10/06)
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- Pursuing the active species in an aluminium-based Lewis acid system for catalytic Diels-Alder cycloadditions
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Several Al-based complexes supported by a bis(imino)aryl NCN pincer ligand have been prepared. Systematic structural and experimental evidence identified a cationic species, supported by a THF molecule, as the best Lewis acid precatalyst for a range of Diels-Alder cycloadditions. This highlighted the importance of fully isolating and characterizing the active species in any catalytic process especially when Lewis acids are used due to the presence of hidden Br?nsted acids (HBAs). Finally, the control experiments conducted in order to eliminate HBA activity that involve a bulky pyridine base should be performed with caution as the corresponding protonated pyridinium salt could also serve as a proton source.
- Liu, Zhizhou,Ganguly, Rakesh,Vidovi?, Dragoslav
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p. 753 - 759
(2017/02/05)
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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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- Encapsulation of an organometallic cationic catalyst by direct exchange into an anionic MOF
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Metal-Organic Frameworks (MOFs) are porous crystalline materials that have emerged as promising hosts for the heterogenization of homogeneous organometallic catalysts, forming hybrid materials which combine the benefits of both classes of catalysts. Herein, we report the encapsulation of the organometallic cationic Lewis acidic catalyst [CpFe(CO)2(L)]+ ([Fp-L]+, Cp = η5-C5H5, L = weakly bound solvent) inside the pores of the anionic [Et4N]3[In3(BTC)4] MOF (H3BTC = benzenetricarboxylic acid) via a direct one-step cation exchange process. To conclusively validate this methodology, initially [Cp2Co]+ was used as an inert spatial probe to (i) test the stability of the selected host; (ii) monitor the stoichiometry of the cation exchange process and (iii) assess pore dimensions, spatial location of the cationic species and guest-accessible space by single crystal X-ray crystallography. Subsequently, the quasi-isosteric [Fp-L]+ was encapsulated inside the pores via partial cation exchange to form [(Fp-L)0.6(Et4N)2.4][In3(BTC)4]. The latter was rigorously characterized and benchmarked as a heterogeneous catalyst in a simple Diels-Alder reaction, thus verifying the integrity and reactivity of the encapsulated molecular catalyst. These results provide a platform for the development of heterogeneous catalysts with chemically and spatially well-defined catalytic sites by direct exchange of cationic catalysts into anionic MOFs.
- Grigoropoulos, Alexios,Whitehead, George F. S.,Perret, Noémie,Katsoulidis, Alexandros P.,Chadwick, F. Mark,Davies, Robert P.,Haynes, Anthony,Brammer, Lee,Weller, Andrew S.,Xiao, Jianliang,Rosseinsky, Matthew J.
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p. 2037 - 2050
(2016/03/05)
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- Lewis Acids as Activators in CBS-Catalysed Diels–Alder Reactions: Distortion Induced Lewis Acidity Enhancement of SnCl4
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The effect of several Lewis acids on the CBS catalyst (named after Corey, Bakshi and Shibata) was investigated in this study. While2H NMR spectroscopic measurements served as gauge for the activation capability of the Lewis acids, in situ FT-IR spectroscopy was employed to assess the catalytic activity of the Lewis acid oxazaborolidine complexes. A correlation was found between the Δδ(2H) values and rate constants kDA, which indicates a direct translation of Lewis acidity into reactivity of the Lewis acid–CBS complexes. Unexpectedly, a significant deviation was found for SnCl4as Lewis acid. The SnCl4–CBS adduct was much more reactive than the Δδ(2H) values predicted and gave similar reaction rates to those observed for the prominent AlBr3–CBS adduct. To rationalize these results, quantum mechanical calculations were performed. The frontier molecular orbital approach was applied and a good correlation between the LUMO energies of the Lewis acid–CBS–naphthoquinone adducts and kDAcould be found. For the SnCl4–CBS–naphthoquinone adduct an unusual distortion was observed leading to an enhanced Lewis acidity. Energy decomposition analysis with natural orbitals for chemical valence (EDA-NOCV) calculations revealed the relevant interactions and activation mode of SnCl4as Lewis acid in Diels–Alder reactions.
- N?dling, Alexander R.,M?ckel, Robert,Tonner, Ralf,Hilt, Gerhard
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p. 13171 - 13180
(2016/09/09)
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- Difluorotris(pentafluoroethyl)phosphorane - A highly active catalyst for Diels-Alder reaction
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Difluorotris(pentafluoroethyl)phosphorane, (C2F5)3PF2, was found to catalyze Diels-Alder reactions of α,β-unsaturated ketones or aldehydes with conjugated dienes or cyclodienes providing the cycloaddition products in high yields. Only a small quantity of this catalyst is required to complete the Diels-Alder reaction. The developed protocol is more convenient than the procedures reported in the literature. Several cyclohexene, naphthalene and norbornene derivatives were obtained in moderate to good yields.
- Bittner, Bozena,Koppe, Karsten,Bilir, Vural,Frank, Walter,Willner, Helge,Ignatev, Nikolai
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supporting information
p. 50 - 60
(2015/03/05)
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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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- 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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- Enantioselective catalytic diels-alder reactions with enones as dienophiles
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The aqua complexes (SM,RC)-[(η5-C 5Me5)M(PROPHOS)(H2O)][SbF6] 2 [PROPHOS = (R)-propane-1,2-diylbis(diphenylphosphane); M = Rh (1), Ir (2)] are active catalysts for the asymmetric Diels-Alder reaction between ketones and dienes. At low temperatures, enantioselectivities of up to 89% ee are achieved. The intermediate Lewis acid-dienophile complexes (S M,RC)-[(η5-C5Me 5)M(PROPHOS)(MVK)][SbF6]2 (MVK = methyl vinyl ketone; M = Rh (3), Ir (4)) and (SIr,RC)- [(η5-C5Me5)Ir(PROPHOS)(EVK)][SbF 6]2 (EVK = ethyl vinyl ketone (5)) have been isolated and characterized by analytical and spectroscopic means, including the determination of the crystal structure of the iridium complexes 4 and 5 by X-ray diffractometric methods. Structural parameters indicate that the dispositions of the coordinated dienophiles are controlled by the CH/π attractive interactions established between a phenyl group of the PROPHOS ligand and the α-vinyl proton of the ketones. Proton NMR parameters indicate that these interactions are maintained in solution. From these data, the stereoselectivity of the catalytic reaction is discussed.
- Carmona, Daniel,Viguri, Fernando,Asenjo, Ainara,Lahoz, Fernando J.,García-Ordu?a, Pilar,Oro, Luis A.
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experimental part
p. 4551 - 4557
(2012/08/08)
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- (1R)-(+)-camphor and acetone derived α′-hydroxy enones in asymmetric diels-alder reaction: Catalytic activation by Lewis and bronsted acids, substrate scope, applications in syntheses, and mechanistic studies
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Chemical Equation Presented The Diels-Alder reaction constitutes one of the most powerful and convergent C-C bond-forming transformations and continues to be the privileged route to access cyclohexene substructures, which are widespread within natural products and bioactive constituents. Over the recent years, asymmetric catalytic Diels-Alder methodologies have experienced a tremendous advance, but still inherently difficult diene-dienophile combinations prevail, such as those involving dienes less reactive than cyclopentadiene or dienophiles like β-substituted acrylates and equivalents. Here the main features of a'-hydroxy enones as reaction partners of the Diels-Alder reaction are shown, with especial focus on their potentials and limitations in solving the above difficult cases. α'-Hydroxy enones are able to bind reversibly to both Lewis acids and Bronsted acids, forming 1,4-coordinated species that are shown to efficiently engage in these inherently difficult Diels-Alder reactions. On these bases, a convenient control of the reaction stereocontrol can be achieved using a camphor-derived chiral α'-hydroxy enone model (substrate-controlled asymmetric induction) and either Lewis acid or Bronsted acid catalysis. Complementing this approach, highly enantio- and diastereoselective Diels-Alder reactions can also be carried out by using simple achiral α'-hydroxy enones in combination with Evans' chiral Cu(II)BOX complexes (catalyst-controlled asymmetric induction). Of importance, α'-hydroxy enones showed improved reactivity profiles and levels of stereoselectivity (endo/exo and facial selectivity) as compared with other prototypical dienophiles in the reactions involving dienes less reactive than cyclopentadiene. A rationale of some of these results is provided based on both kinetic experiments and quantum calculations. Thus, kinetic measurements of Bronsted acid promoted Diels-Alder reactions of α'-hydroxy enones show a first-order rate with respect to both enone and Bronsted acid promoter. Quantum calculations also support this trend and provide a rational explanation of the observed stereochemical outcome of the reactions. Finally, these fundamental studies are complemented with applications in natural products synthesis. More specifically, a nonracemic synthesis of (-)-nicolaioidesin C is described wherein a Brαnsted acid catalyzed Diels-Alder reaction involving a α'-hydroxy enone substrate is the key step toward the hitherto challenging tri substituted cyclohexene subunit.
- Banuelos, Patrcia,Garcia, Jesus M.,Gomez-Bengpa, Enrique,Herrero, Ada,Odriozola, Jose M.,Oiarbide, Mikel,Palomo, Claudio,Razkin, Jesus
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supporting information; experimental part
p. 1458 - 1473
(2010/06/11)
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- Impact of carbon dioxide pressurization on liquid phase organic reactions: A case study on Heck and Diels-Alder reactions
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Heck coupling reactions of methyl acrylate with various aryl bromides have been investigated using a Pd/TPP catalyst in toluene under pressurized CO 2 conditions up to 13 MPa. Although CO2 is not a reactant, the pressurization of the reaction liquid phase with CO2 has positive and negative impacts on the rate of Heck coupling depending on the structures of the substrates examined. In the case of either 2-bromoacetophenone or 2-bromocinnamate, the conversion has a maximum at a CO2 pressure of about 3 MPa; for the former, it is much larger by a factor of 3 compared with that under ambient pressure. For 2-bromobenzene, in contrast, the conversion is minimized at a similar CO2 pressure, being half compared with that at ambient pressure. In the other substrates, including the other isomers of these three aryl bromides, the conversion simply decreases or does not change so much with the CO2 pressure. To examine the factors responsible for the effects of CO2 pressurization, the phase behavior and the molecular interactions with dense phase CO2 have also been studied by visual observation and in situ high pressure FT-IR spectroscopy. In addition, impact of CO2 pressurization was also studied for the Diels-Alder reactions of isoprene with a few dienophiles like methyl acrylate, methyl vinyl ketone, and acrolein in the same solvent, toluene, but a heterogeneous silica-alumina catalyst was used (the reaction system was liquid-solid biphasic). When the CO2 pressure is raised, the conversion monotonously decreases for the three dienophiles; however, the product selectivity changes with the pressure, in particular for acrolein. The FT-IR spectroscopic measurements suggest that its reactivity is altered by interactions with CO2 molecules under pressurized conditions.
- Fujita,Tanaka,Akiyama,Asai,Hao,Zhao,Arai
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experimental part
p. 1615 - 1625
(2009/07/01)
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- Ruthenium-lewis acid catalyzed asymmetric diels-alder reactions between dienes and α,β-unsaturated ketones
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The complex [Ru(Cp)(R,R-BIPHOP-F)(acetone)][SbF6],(R,R)-1a. was used as catalyst for asymmetric Diels-Alder reactions between dienes (cyclopentadiene, methylcyclopentadienc, isoprene, 2,3-dimethylbutadiene) and α,β-unsaturated ketones (methyl vinyl ketone (MVK). ethyl vinyl ketone, divinyl ketone, α-bromovinyl methyl ketone and α-chlorovinyl methyl ketone). The cycloaddition products were obtained in yields of 50-_90% and with enantioselectivities up to 96% ee. Ethyl vinyl ketone, divinyl ketone and the halogenated vinyl ketones worked best and their reactions with acyclic dienes consistently provided products with >90% ee. α-Chlorovinyl methyl ketone performed better than α-bromovinyl methyl ketone. The reaction also provided a [4.3.1]bicyclic ring system in 95% ee through an intramolecular cycloaddition reaction. Crystal structure determinations of [Ru(Cp)((S,S)-BIPHOP-F)(mvk)]-[SbF6], (S,S)-1b, and [Ru(Cp)((R,R)-Me4BIPHOP-F)(acrolein)][SbF6], (R,R)-2b, provided the basis for a rationalization of the asymmetric induction.
- Rickerby, Jenny,Vallet, Martial,Bernardinelli, Gerald,Viton, Florian,Kuendig, E. Peter
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p. 3354 - 3368
(2008/03/27)
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- Secondary organic aerosol from limona ketone: Insights into terpene ozonolysis via synthesis of key intermediates
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Limona ketone was synthesized to explore the secondary organic aerosol (SOA) formation mechanism from limonene ozonolysis and also to test group-additivity concepts describing the volatility distribution of ozonolysis products from similar precursors. Limona ketone SOA production is indistinguishable from α-pinene, confirming the expected similarity. However, limona ketone SOA production is significantly less intense than limonene SOA production. The very low vapor pressure of limonene ozonolysis products is consistent with full oxidation of both double bonds in limonene and furthermore with production of products other than ketones after oxidation of the exo double bond in limonene. Mass-balance constraints confirm that ketone products from exo double-bond ozonolysis have a minimal contribution to the ultimate product yield. These results serve as the foundation for an emerging framework to describe the effect on volatility of successive generations of organic compounds in the atmosphere. the Owner Societies.
- Donahue, Neil M.,Tischuk, Joshua E.,Marquis, Bryce J.,Huff Hartz, Kara E.
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p. 2991 - 2998
(2008/09/18)
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- Liquid-phase noncatalytic oxidation of monoterpenoids with nitrous oxide
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A series of monoterpenoids differing in the number of double bonds and the pattern of their substitution were tested in the liquid-phase noncatalytic oxidation with nitrous oxide (N2O). The structure of olefins has a significant effect on the oxidation route. In the case of terpenoids containing 1,1-disubstituted double bond, nor-carbonyl compounds are formed with high selectivity.
- Romanenko,Starokon',Panov,Tkacheva
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p. 1239 - 1243
(2008/09/17)
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- Regioselective alkene carbon-carbon bond cleavage to aldehydes and chemoselective alcohol oxidation of allylic alcohols with hydrogen peroxide catalyzed by [cis-Ru(II)(dmp)2(H2O)2] 2+ (dmp = 2,9-dimethylphenanthroline)
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(Chemical Equation Presented) [cis-Ru(II)(dmp)2(H 2O)2]2+ (dmp = 2,9-dimethylphenanthroline) was found to be a selective oxidation catalyst using hydrogen peroxide as oxidant. Thus, primary alkenes were very efficiently oxidized via direct carbon-carbon bond cleavage to the corresponding aldehydes as an alternative to ozonolysis. Secondary alkenes were much less reactive, leading to regioselective oxidation of substrates such as 4-vinylcyclohexene and 7-methyl-1,6-octadiene at the terminal position. Primary allylic alcohols were chemoselectively oxidized to the corresponding allylic aldehydes, e.g., geraniol to citral.
- Kogan, Vladimir,Quintal, Miriam M.,Neumann, Ronny
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p. 5039 - 5042
(2007/10/03)
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- Design and synthesis of endoperoxide antimalarial prodrug models
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A masked combination chemotherapy which relies on the embedding of a number of active components, in a latent form, within a single endoperoxidic chemical entity is the aim of the research presented. The approach is illustrated by means of purposely designed bicyclic endoperoxide prodrug prototypes 1 and subsequently validated through the study of model compounds 2 (Ar= Ph, p-FC 6H4, p-ClC6H4.
- O'Neill, Paul M.,Stocks, Paul A.,Pugh, Matthew D.,Araujo, Nuna C.,Korshin, Edward E.,Bickley, Jamie F.,Ward, Stephen A.,Bray, Patrick G.,Pasini, Erica,Davies, Jill,Verissimo, Edite,Bachi, Mario D.
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p. 4193 - 4197
(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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- 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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- Isotope ratio analysis by HRGC-MS of monoterpene hydrocarbons from citrus essential oils
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The isotope ratio of monoterpene hydrocarbons in citrus essential oils of different origins was measured by ordinary high-resolution gas chromatography-mass spectrometry (HRGC-MS). The isotope ratio (Ir) was determined by the ratio of the isotope peak intensity (m/z 137) to the molecular mass peak intensity (m/z 136) of the monoterpene hydrocarbons. The accuracy of Ir was examined by measuring monoterpene hydrocarbon standards and 13C-labeled compounds. The isotope fingerprints based on the values of monoterpene hydrocarbons from lemon, lime and yuzu essential oils were determined. These citrus essential oils were also discriminated by a principal component analysis of their Ir data. The characteristic vectors showed that α-terpinene, β-pinene and β-phellandrene were important components for distinguishing between the citrus species. It is suggested that this technique will be applicable to evaluate the quality, genuineness and origin of citrus fruits and their products.
- Satake, Atsushi,Une, Akitoshi,Ueno, Takao,Ukeda, Hiroyuki,Sawamura, Masayoshi
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p. 599 - 604
(2007/10/03)
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- α′-hydroxy Enones as Achiral Templates for Lewis Acid-Catalyzed Enantioselective Diels - Alder Reactions
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α′-Hydroxy enones react with dienes in the presence of (S,S)-[Cu(tBu-box)](OTf)2 or (S,S)-[Cu(tBu-box)](SbF6)2 (2 to 10 mol %) to afford the corresponding Diels?Alder adducts in high yield and selectivity. Isomeric ratios (regioselectivity, endo/exo or cis/trans) of up to >99:1 and ee values of up to >99% are obtained. Significantly, difficult dienes such as isoprene, 2,3-dimethyl butadiene and piperylene behave satisfactorily. Subsequent oxidative cleavage of the ketol in the resulting cycloadducts by treatment with cerium ammonium nitrate (CAN) yields the corresponding enantiopure carboxylic acids. Alternatively, carbonyl addition and subsequent diol cleavage with CAN produces the corresponding ketone adducts. Copyright
- Palomo, Claudio,Oiarbide, Mikel,Garcia, Jesus M.,Gonzalez, Alberto,Arceo, Elena
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p. 13942 - 13943
(2007/10/03)
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- A chiral acrylate equivalent for metal-free Diels-Alder reactions: endo-2-acryloylisoborneol
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The principle of metal-free activation of enones toward the Diels-Alder reaction with dienes is demonstrated by exploiting the capability of Bronsted acids to activate α′-hydroxyenones through hydrogen bonding. The diastereoselective application of such a principle is nicely realized by using a newly designed family of camphor-based chiral enones, which upon catalytic action of either trifluoroacetic or triflic acid lead to the corresponding cycloadducts with high chemical and stereochemical efficiency. Copyright
- Palomo, Claudio,Oiarbide, Mikel,Garcia, Jesus M.,Gonzalez, Alberto,Lecumberri, Ainara,Linden, Anthony
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p. 10288 - 10289
(2007/10/03)
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- Unexpected catalyzed C=C bond cleavage by molecular oxygen promoted by a thiyl radical
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Olefin oxidation with molecular oxygen, promoted by a transition metal catalyst and a thiophenol, involved C=C bond cleavage into the corresponding carbonyl derivatives. This new reaction proceeds under one atmosphere of oxygen, at room temperature, in the presence of an excess of thiophenol and a catalyst such as MnL2 3a or VC1L2 3c. It was applied to aromatic and aliphatic olefins, as well as to functionalized or unfunctionalized acyclic compounds, providing the corresponding ketones and aldehydes in up to 98% yield. The synthetic interest of this catalytic oxidation was illustrated by a one-step preparation of the fragrance (-)-4-acetyl-1-methylcyclohexene 7e in 73% isolated yield. The C=C bond cleavage probably results from a catalyzed decomposition of the β-hydroperoxysulfide intermediate 12 that is formed by the radical addition of thiophenol to the olefin in the presence of oxygen. Although an excess of the thiophenol was used, it was transformed into the disulfide which could then be reduced without purification in 83% overall yield, thereby allowing for recycling. In addition, the C=C bond cleavage under oxygen could be promoted by catalytic quantities of the thiyl radical, generated by photolysis of the disulfide; thus, in the presence of 0.1 equiv of bis(4-chlorophenyl) disulfide 4b and 5% of the manganese complex 3a, trans-methylstilbene 1b gave, under radiation, benzaldehyde 6a and acetophenone 7a in up to 95% yield. This new reaction offers an alternative to the classical C=C bond cleavage procedures, and further developments in the fields of bioinorganic and environmental chemistry are likely.
- Baucherel,Uziel,Juge
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p. 4504 - 4510
(2007/10/03)
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- Phosphonium tosylates as solvents for the Diels-Alder reaction
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Phosphonium tosylates have been investigated as solvents for the Diels-Alder reactions of isoprene with methyl acrylate, but-3-en-2-one and acrylonitrile. The reactions with oxygen-containing dienophiles showed high regioselectivity.
- Ludley, Petra,Karodia, Nazira
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p. 2011 - 2014
(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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- Carboxylic acids in secondary aerosols from oxidation of cyclic monoterpenes by ozone
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A series of smog chamber experiments have been conducted in which five cyclic monoterpenes were oxidized by ozone. The evolved secondary aerosol was analyzed by GC-MS and HPLC-MS for nonvolatile polar oxidation products with emphasis on the identification of carboxylic acids. Three classes of compounds were determined at concentration levels corresponding to low percentage molar yields: i.e. dicarboxylic acids, oxocarboxylic acids, and hydroxyketocarboxylic acids. Carboxylic acids are highly polar and have lower vapor pressures than their corresponding aldehydes and may thus play an important role in secondary organic aerosol formation processes. The most abundant carboxylic acids were the following: cis-pinic acid AB1 (cis-3- carboxy-2,2-dimethylcyclobutylethanoic acid) from α-and β-pinene; cis- pinonic acid A3 (cis-3-acetyl-2,2-dimethylcyclobutylethanoic acid) and cis- 10-hydroxypinonic acid AB6 (cis-2,2-dimethyl-3- hydroxyacetylcyclobutylethanoic acid) from α-pinene and β-pinene; cis-3- caric acid C1 (cis-2,2-dimethyl-1,3-cyclopropyldiethanoic acid), cis-3- caronic acid C3 (2,2-dimethyl-3-(2-oxopropyl)cyclopropanylethanoic acid), and cis-10-hydroxy-3-caronic acid C6 (cis-2,2-dimethyl-3-(hydroxy-2- oxopropyl)cyclopropanylethanoic acid) from 3-carene; cis-sabinic acid S1 (cis-2-carboxy-1-isopropylcyclopropylethanoic acid) from sabinene; limonic acid L1 (3-isopropenylhexanedioic acid), limononic acid L3 (3-isopropenyl-6- oxo-heptanoic acid), 7-hydroxylimononic acid L6 (3-isopropenyl-7-hydroxy-6- oxoheptanoic acid), and 7-hydroxylimononic acid L6' (7-hydroxy-3-isopropenyl- 6-oxoheptanoic acid) from limonene. A series of smog chamber experiments have been conducted in which five cyclic monoterpenes were oxidized by ozone. The evolved secondary aerosol was analyzed by GC-MS and HPLC-MS for nonvolatile polar oxidation products with emphasis on the identification of carboxylic acids. Three classes of compounds were determined at concentration levels corresponding to low percentage molar yields: i.e. dicarboxylic acids, oxocarboxylic acids, and hydroxyketocarboxylic acids. Carboxylic acids are highly polar and have lower vapor pressures than their corresponding aldehydes and may thus play an important role in secondary organic aerosol formation processes. The most abundant carboxylic acids were the following: cis-pinic acid AB1 (cis-3-carboxy-2,2-dimethylcyclobutylethanoic acid) from α- and β-pinene; cis-pinonic acid A3 (cis-3-acetyl-2,2-dimethylcyclobutylethanoic acid) and cis-10-hydroxypinonic acid AB6 (cis-2,2-dimethyl-3-hydroxyacetylcyclobutyl-ethanoic acid) from α-pinene and β-pinene; cis-3-caric acid C1 (cis-2,2-dimethyl-1,3-cyclopropyldiethanoic acid), cis-3-caronic acid C3 (2,2-dimethyl-3-(2-oxopropyl)cyclopropanylethanoic acid), and cis-10-hydroxy-3-caronic acid C6 (cis-2,2-dimethyl-3-(hydroxy-2-oxopropyl)cyclopropanyl-ethanoic acid) from 3-carene; cis-sabinic acid S1 (cis-2-carboxy-1-isopropylcyclopropylethanoic acid) from sabinene; limonic acid L1 (3-isopropenylhexanedioic acid), limononic acid L3 (3-isopropenyl-6-oxo-heptanoic acid), 7-hydroxy-limononic acid L6 (3-isopropenyl-7-hydroxy-6-oxoheptanoic acid), and 7-hydroxylimononic acid L6′ (7-hydroxy-3-isopropenyl-6-oxoheptanoic acid) from limonene.
- Glasius, Marianne,Lahaniati, Maria,Calogirou, Aggelos,Di Bella, Dario,Jensen, Niels R.,Hjorth, Jens,Kotzias, Dimitrios,Larsen, Bo R.
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p. 1001 - 1010
(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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- 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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- Silica-Promoted Diels-Alder Reactions in Carbon Dioxide from Gaseous to Supercritical Conditions
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Amorphous fumed silica (SiO2) was shown to increase yields and selectivities of several Diels-Alder reactions in gaseous and supercritical CO2. Pressure effects on the Diels-Alder reaction were explored using methyl vinyl ketone and penta-1,3-diene at 80°C. The selectivity of the reaction was not affected by pressure/ density. As pressure was increased, the yield decreased. At the reaction temperature, adsorption isotherms at various pressures were obtained for the reactants and the Diels-Alder adduct. As expected when pressure is increased, the ratio of the amount of reactants adsorbed to the amount of reactants in the fluid phase decreases, thus causing the yield to decrease. The Langmuir adsorption model fit the adsorption data. The Langmuir equilibrium partitioning constants all decreased with increasing pressure. The effect of temperature on adsorption was experimentally determined and traditional heats of adsorption were calculated. However, since supercritical CO2 is a highly compressible fluid, it is logical to examine the effect of temperature at constant density. In this case, entropies of adsorption were obtained. The thermodynamic properties that influence the real enthalpy and entropy of adsorption were derived. Methods of doping the silica and improving yields and selectivities were also explored.
- Weinstein, Randy D.,Renslo, Adam R.,Danheiser, Rick L.,Tester, Jefferson W.
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p. 2878 - 2887
(2007/10/03)
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- Isotope effects for lewis acid catalyzed Diels-Alder reactions. The experimental transition state
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2H and 13C kinetic isotope effects were determined for all positions on isoprene in its reactions with methyl vinyl ketone, ethyl acrylate, and acrolein catalyzed by Et2AlCl. The results are taken as supporting a highly asynchronous concerted [4+2] cycloaddition. Comparison of the experimental isotope effects with calculated values supports this conclusion and the accuracy of the calculated transition structure.
- Singleton, Daniel A.,Merrigan, Steven R.,Beno, Brett R.,Houk
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p. 5817 - 5821
(2007/10/03)
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- A cationic palladium(II) complex-catalyzed diels-alder reaction
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A cationic palladium(II) complex, [PdL2(RCN)2](BF4)2, has been found to catalyze the Diels-Alder reaction of α, β-unsaturated carbonyl compounds with dienes, affording the corresponding cycloadducts in good yields. Excellent enanlioselectivity can be achieved in the reaction of N- acryloyloxazolidinone and cyclopentadiene by use of a chiral ligand, BINAP.
- Oi, Shuichi,Kashiwagi, Kenji,Inoue, Yoshio
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p. 6253 - 6256
(2007/10/03)
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- Solvent effects on Diels-Alder reactions. the use of aqueous mixtures of fluorinated alcohols and the study of reactions of acrylonitrile
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Rate, endolexo, regio- and diastereo-facial selectivities of several Diels-Alder reactions were measured in a series of fluorinated alcohol-water mixtures, whose solvophobicity has been determined by means of the solvophobic power (Sp) parameter. Solvophobicity is the main factor influencing the reaction rate, although in some reactions hydrogen bond donating (HBD) ability may also play a role. Both solvophobicity and HBD ability are important to account for changes in endolexo selectivity. HBD ability is the main factor responsible for the changes in regio- and diastereo-facial selectivities, induced by the reaction medium. On the other hand, the kinetic rate constants and endolexo selectivity of the reaction of acrylonitrile with cyclopentadiene, as well as the regioselectivity of the reaction of acrylonitrile with isoprene, have been determined in 23 reaction media. The analysis of the results using empirical solvent parameters show that the reaction rate depends on solvophobic, HBD and dipolarity interactions, whereas endolexo selectivity is influenced by solvophobic and dipolarity interactions, and the regioselectivity only by HBD effects.
- Cativiela, Carlos,Garcia, Jose I.,Gil,Martinez, Rosa M.,Mayoral, Jose A.,Salvatella, Luis,Urieta, Jose S.,Mainar,Abraham, Michael H.
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p. 653 - 660
(2007/10/03)
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- A New Preparation of (1S,2R,4S)-(-)-4-Acetyl-1,2-Epoxy-1-Methylcyclohexane, a Unike Synthon for the Synthesis of the Sex Pheromone of the Southern Green Stinkbug, Nezara viridula (L.)
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A new preparation of (1S,2R,4S)-(-)-4-acetyl-1,2-epoxy-1-methylcyclohexane, a unique synthon for the synthesis of the sex pheromone of the southern green stinkbug, Nezara viridula (L.), is described.The stereoselectve formation of the epoxide ring has been accomplished by intramolecular substitution of a selenone group.
- Ceccherelli, Paolo,Curini, Massimo,Epifano, Francesco,Marcotullio, Maria Carla,Rosati, Ornelio
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p. 315 - 316
(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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- 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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- Diiodosamarium, a Catalyst Precursor for Diels-Alder and Hetero Diels-Alder Reactions.
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SmI2 presents catalytic activity for Diels-Alder reactions between cyclopentadiene or isoprene and various dienophiles, and for hetero Diels-Alder reactions.
- Weghe, Pierre Van de,Collin, Jacqueline
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p. 2545 - 2548
(2007/10/02)
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- Farnesyl-diphosphate synthase. Interplay between substrate topology, stereochemistry, and regiochemistry in electrophilic alkylations
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The absolute stereochemistries of 8-OPP, 9-OPP, and 10-OPP obtained from incubation of bisubstrate analogs 1-OPP and 2-OPP with farnesyl-diphosphate synthase were determined by correlation of ORD spectra with those of synthetic materials. Only one enantiomer was found for each of the enzymatic products. The products from 1-OPP were (S)-8-OPP and (S)-10-OPP, while those from 2-OPP were (R)-8-OPP, (R)-9-OPP, and (R)-10-OPP. Conformational analysis of 1-OPP and 2-OPP, which considers topological limitations imposed by FPP synthase, indicates that the products from the enzymatic reactions are formed from discrete E·S complexes formed from different conformers of the substrates. Overlays of the conformations that give the observed products are consistent with a model where the hydrocarbon moieties occupy a central volume flanked on top and bottom by their diphosphate residues.
- Jo Davisson,Dale Poulter
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p. 1245 - 1260
(2007/10/02)
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- Zeolite and Lewis Acid Catalysis in Diels-Alder Reactions of Isoprene
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The use of zeolites as catalysts in Diels-Alder reactions of isoprene, 2, has been studied.The regioselectivity in zeolite-catalyzed reactions was compared with the regioselectivity of the same reaction using Lewis acid catalysts.The reaction was studied with seven dienophiles: but-3-en-one (1a), 3-bromobut-3-en-2-one (1b), methyl propenoate (1c), cyclohex-2-enone (1d), phenylethene (1e), ethyl propynoate (1f) and propenenitrile (1g).The following catalysts were investigated: zeolites: ZSM-5, mordenite, zeolite Y-152, zeolite Y-45, and zeolite β Lewis acids: aluminum tribromide, aluminum trichloride, antimony pentachloride, antimony triiodide, boron trifuoride-diethyl ether, manganese difluoride and zinc dichloride.The zeolite-catalyzed reactions afforded the Diels-Alder product with the denophiles 1a-1d, but not with the other dienophiles, 1e-1g.The dienophiles which failed to undergo cycloaddition in the presence of zeolites also did so or afforded poor results with the Lewis acid catalysts.With the exception of the reaction of 1b catalyzed by ZSM-5, which afforded a regioisomeric ratio of 13/87, the other zeolite-catalyzed reactions afforded regioisomeric ratios in the range 6/94-0/100 which is similar to that obtained by Lewis acid catalysis.The experimental conditions were studied in detail for two zeolite catalysts (mordenite, zeolite beta) in the reaction of isoprene with 1d.The optimum experimental conditions with respect to yield and selectivity were established by multivariate techniques.In this reaction, zeolite catalysis was found to afford high yields of cis-6-methyl-6(7)-1-octalone.Under Lewis acid catalyzed conditions, this product is rapidly epimerized into the trans isomer.Full experimental details are given for the preparative use of the method.Examples are provided by the reactions with the dienophiles 1a, 1c and 1d catalyzed by zeolite beta.Factors determining the regioselectivity of zeolite-catalyzed Diels-Alder reaction are briefly discussed.
- Eklund, Lars,Axelsson, Anna-Karin,Nordahl, Ake,Carlson, Rolf
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p. 581 - 591
(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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- 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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- Ring enlargement reaction of 2-(1-alkenyl)-1-cyclobutyl ketones. A new method for the preparation of 4-acyl-1-cyclohexenes
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Various 1,2-disubstituted 4-acyl-1-cyclohexenes were obtained by the ethylaluminum dichloride promoted ring enlargement reaction of 2-(1-alkenyl)-1-cyclobutyl ketones prepared by the conjugate addition of 1-alkenylmagnesium bromides With 1-cyclobutenyl ketones.
- Fujiwara, Tooru,Takeda, Takeshi
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p. 6027 - 6030
(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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- CATALYSIS OF DIELS-ALDER REACTIONS BY METALLOPORPHYRINS
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Aluminium (III) tetraphenyl porphyrin chloride (AITPPCl) has been shown to catalyze Diels-Alder reactions of α,β-unsaturated carbonyl compounds in moderate yield.Selectivity based on electronic effects is exhibited which is different from that seen with catalysts such as diethylaluminium chloride.
- Bartley, David W.,Kodadek, Thomas J.
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p. 6303 - 6306
(2007/10/02)
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