- Understanding "on-water" catalysis of organic reactions. Effects of H+ and Li+ ions in the aqueous phase and nonreacting competitor H-bond acceptors in the organic phase: On H2O versus on D2O for Huisgen cycloadditions
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For a typical Huisgen cycloaddition, carried out on water, the behavior of water molecules at the oil-water interface depended on the properties of the reactants. With weakly basic reactants, a small quantity of added H+ (HClO4, 0.0001-0.01 M) present in the aqueous phase had negligible effects, but larger quantities of H+ (HClO4, 0.1-3.0 M) increased the catalytic effect and caused protons to cross the water-organic interface and affect the products. Added Li+ ions (LiClO4, 0.1-3.0 M) had no effect for on-water reactions but enhanced the rates and endo products for in-water reactions. For these cycloaddition reactions, the product endo:exo ratios, when compared to those in organic solvents, can be used to distinguish between the on-water and in-water modes. Comparisons of organic reactions on H2O and on D2O indicate that on-water catalysis ranges from weak to strong trans-phase H-bonding for reactants with basic pKa a > ca. 2 (pKa of conjugate acid). Water shows a chameleon-type response to organic molecules at hydrophobic surfaces.
- Butler, Richard N.,Coyne, Anthony G.
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- Water and organic synthesis: A focus on the in-water and on-water border. Reversal of the in-water breslow hydrophobic enhancement of the normal endo -effect on crossing to on-water conditions for huisgen cycloadditions with increasingly insoluble organic liquid and solid 2π-dipolarophiles
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Measurements of the endo/exo product ratios for Huisgen cycloadditions with a series of vinyl ketones, alkyl acrylates, and substituted styrenes as dipolarophiles with phthalazinium and pyridazinium dicyanomethanide 1,3-dipoles in acetonitrile and water show that as the reactions change from in-water (large hydrophobic enhancement of endo-products) to on-water, the hydrophobic enhancement of the endo-products is reduced and partially reversed (relative to acetonitrile). An expected increase of the endo-effect with increasing hydrophobic character of the dipolarophile is overcome by decreasing water solubility causing changeover to on-water conditions. On-water reactions do not show increased cycloaddition endo-effects (relative to organic solvents) as do in-water reactions.
- Butler, Richard N.,Coyne, Anthony G.,Cunningham, William J.,Moloney, Eamon M.
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- Cu(I)-Catalyzed Highly Enantioselective [3 + 3] Cycloaddition between Two Different 1,3-Dipoles, Phthalazinium Dicyanomethanides and Iminoester-Derived Azomethine Ylides
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(Chemical Equation Presented). The Cu(I)-catalyzed highly enantioselective [3 + 3] cycloaddition between two different 1,3-dipoles, phthalazinium dicyanomethanides and iminoester-derived azomethine ylides, has been achieved under mild reaction conditions, providing novel chiral heterocyclic compounds, 2,3,4,11b-tetrahydro-1H-pyrazino[2,1-a]phthalazine derivatives, in high yields with excellent diastereo- and enantioselectivies (up to 99% yield, 99% ee, >20:1 dr).
- Yuan, Chunhao,Liu, Honglei,Gao, Zhenzhen,Zhou, Leijie,Feng, Yalin,Xiao, Yumei,Guo, Hongchao
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supporting information
p. 26 - 29
(2015/07/28)
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- Sc(OTf)3-Catalyzed [3 + 3] Cycloaddition of Cyclopropane 1,1-Diesters with Phthalazinium Dicyanomethanides
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The Sc(OTf)3-catalyzed diastereoselective [3 + 3] cycloaddition of phthalazinium dicyanomethanides with cyclopropane 1,1-diesters proceeded smoothly under mild reaction conditions, affording a variety of 3,4-dihydro-1H-pyrido[2,1-a]phthalazine derivatives in up to 99% yields with excellent diastereoselectivities.
- Liu, Honglei,Yuan, Chunhao,Wu, Yang,Xiao, Yumei,Guo, Hongchao
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supporting information
p. 4220 - 4223
(2015/09/15)
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- Effect of electron-withdrawing substituents on the epoxide ring: An experimental and theoretical electron density analysis of a series of epoxide derivatives
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A series of acceptor-substituted epoxide derivatives is scrutinized by means of experimental and theoretical electron-density investigations. Due to the possibility of nucleophilic ring-opening, the epoxide ring is not only a very useful functional group in organic synthesis, but acceptor-substituted epoxides are valuable building blocks for the design of protease inhibitors. Therefore, the electron-density analysis in this work focuses on two main aspects that can contribute to rational drug design: (i) the quantification of the electron-withdrawing substituent effects on the epoxide ring and (ii) the intermolecular interactions involving the epoxide ring in combination with different substituents. It can be shown that the electron-withdrawing properties of the substituents cause an elongation of the C-C bonds in the epoxide rings and the loss of electron density can be measured by an analysis of critical points, atomic charges, and the source function. The different strengths of the substituents are reflected in these properties. Covalent and electrostatic contributions to the intermolecular interactions and thus the lattice energies are depicted on different molecular surfaces.(Figure Presented)
- Grabowsky, Simon,Schirmeister, Tanja,Paulmann, Carsten,Pfeuffer, Thomas,Luger, Peter
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experimental part
p. 1305 - 1318
(2011/04/23)
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- The first, general, highly efficient method for preparing tetrasubstituted epoxides using HOF·CH3CN
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Tetrasubstituted epoxides, and especially electron-depleted ones, generally are difficult to prepare. HOF·CH3CN complex, probably the best oxygen transfer agent known today, epoxidizes tetrasubstituted alkenes at 0 °C in a matter of minutes or less in excellent yields. HOF·CH3CN complex is very easy to prepare by bubbling diluted fluorine (commercial) through aqueous acetonitrile. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.
- Rozen, Shlomo,Golan, Elizabeth
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p. 1915 - 1917
(2007/10/03)
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- Dioxygen ligand transfer from platinum to molybdenum. Isolation of a highly reactive molybdenum(VI) oxoperoxo dimer
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The reaction of Pt(O2)(PPh3)2 with Mo(O)2(mesityl)2 (mesityl = 2,4,6-Me3C6H2) in pyridine results in the transfer of the dioxygen ligand from platinum to molybdenum giving, in the presence of PPh4Cl, a molybdenum peroxo compound 1 in which all the organic moieties have been lost.This compound epoxidizes tetracyanoethylene at a rate estimated at 104 greater than the known oxodiperoxomolybdenum complex 2.Furthermore, 1 exhibits a high selectivity for electron-poor olefins (TCNE/cyclooctene = 103).Elemental analysis, IR and 17O NMR indicate that 1 is the tetraphenylphosphonium salt of an oxoperoxomolybdenum(VI) dimer. - Keywords: dioxygen transfer; platinum peroxo; molybdenum oxoperoxo; epoxidation
- Arzoumanian, Henri,Sanchez, Jose,Strukul, Giorgio,Zennaro, Roberto
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p. 1119 - 1122
(2007/10/03)
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- KINETIC STUDY ON PYROLYTIC ELIMINATION OF ETHYLPHENYLSULFONIUM DICYANOMETHYLIDE
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Ethyl(Substituted phenyl)sulfonium dicyanomethylides (1) were prepared and pyrolyzed in sealed tubes in benzene.The rate for pyrolysis of the substrate was correlated in a good first-order kinetic equation (γ = 0.999). The rate constant was 11.4 * 10-4 s-1 at 150 deg C.Pyrolysis of (1) was found to proceed about 3 times faster than that of ethylphenylsulfonium bis(methoxycarbonyl)methylide (2).Activation parameters calculated from the Arrhenius equation were as follows: ΔH(excit.) = 128 (KJ/mol), ΔS(excit.) = 1.7 J/K/mol (150 deg C, γ = 0.999), in which the magnitude of activation enthalpy was almost the same as that of (2), while the activation entropy was considerably larger compared with that of ethyl phenyl sulfoxide (-75.1 J/K/mol).Thus, the S-Cα bond of (1) was found to be looser in the transition state.The reactivities of sulfonium ylides, sulfoxides and sulfilimines estimate the magnitude of the activation entropies of the substrates.Substituent effect on the phenyl group afforded a positive Hammet ρ-value (ρ = 0.42, γ = 0.996) vs. ?-values. From these results, it was suggested that pyrolysis of sulfonium ylides proceeds via essentially concerted intramolecular cis-elimination in which the transition state is E1-like. Key words: pyrolysis; elimination; mechanism; kinetics; sulfonium ylide.
- Yoshimura, Toshiaki,Motoyama, Atsushi,Kitada, Tomoko,Tsukurimichi, Eiichi,Simasaki, Choichoiro,Hasegawa, Kiyoshi
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- RADICAL CARBAMOYLATION OF 1,2,3-TRIAZINIUM 2-DICYANOMETHYLIDES
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The nucleophilic radical carbamoylation of 4,6-disubstituted 1,2,3-triazinium 2-dicyanomethylides occurred at their 5-positions followed by the elimination of dicyanomethylene to form 5-substituted 1,2,3-triazines.The reaction did not proceed when parent triazines were adopted as the substrates.
- Nagata, Kazuhiro,Itoh, Takashi,Okada, Mamiko,Takahashi, Hiroyuki,Ohsawa, Akio
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p. 855 - 857
(2007/10/02)
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- A COMBINED AB INITIO AND GAS ELECTRON DIFFRACTION STUDY OF THE MOLECULAR STRUCTURE OF 1,1-DICYANOCYCLOBUTANE
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The molecular structure of 1,1-dicyanocyclobutane was investigated by gas electron diffraction and the results are compared with 4-21G ab initio gradient geometry refinements.In the cyclobutane ring C1-C2 > C2-C3 in contrast to structural trends generally observed for cyclobutyl systems with a single electronegative substituent.The C-CN groups are slightly non-linear, with the CN groups bent away from one another.The structural features observed can be rationalized in terms of a special electronic interaction between the geminal cyano groups, which is also suggested by the 13C NMR spectrum.
- Dakkouri, M.,Ephardt, H.,Siam, K.,Schaefer, L.,Alsenoy, C. van
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p. 123 - 136
(2007/10/02)
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- High-Field Rapid Injection NMR: Observation of Unstable Primary Ozonide Intermediates
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A "rapid injection" NMR system is described for use on a 360-MHz superconducting spectrometer.The major advantages of the high-field sytem over our original system are increased sensitivity, resolution, and rapidity.The technique was used to study the ozonolysis of tetramethylethylene and (briefly) cis-but-2-ene, particularly the decomposition of the corresponding primary ozonides 2 and 4, with half-lives of 0.74 and 0.06 s, respectively, at -92 deg C.It was found that the decomposition of 2 in CD2Cl2 (a) had Δ H(excit) = 39 kJ/mol and Δ S(excit) = 28 J/(molK), (b) was unaffected by the presence of TCNE, but (c) was acid-catalyzed.The effects of substituents, solvent, and acid catalysts on the decomposition of primary ozonides are discussed.
- McGarrity, John F.,Prodolliet, Jacques
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p. 4465 - 4470
(2007/10/02)
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- Photoinduced Reactions. Part 116. The Reaction of Epoxides with Oxygen-transfer Reagents
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A C-C bond cleavage of the epoxide ring to give the corresponding ketone has been achieved by various oxygen-transfer agents such as ozone, ozone or pyridine N-oxide with irradiation, and m-chlorobenzoic acid.The reaction with ozone is interpreted in terms of a perepoxide intermediate.
- Ito, Yoshikatsu,Matsuura, Teruo
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p. 1871 - 1873
(2007/10/02)
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