- Isomerization of 2-Methyl-4,5-dihydrofuran. Studies with a Single-Pulse Shock Tube
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The isomerization of 2-methyl-4,5-dihydrofuran was studied behind reflected shock waves in a pressurized driver single-pulse shock tube over the temperature range 805-1030 K and densities of approximately ca 3*10-5 mol/cm3.Two isomerization products, acetylcyclopropane and 3-penten-2-one, are obtained in the isomerization.Acetylcyclopropane is formed in an irreversible process from 2-methyl-4,5-dihydrofuran.It further isomerizes, at higher temperatures, to cis- and trans-3-penten-2-one.At high temperatures where the conversion of 2-methyl-4,5-dihydrofuran is high, the main source for 3-penten-2-one is acetylcyclopropane.At lower temperatures 3-penten-2-one is formed mainly by a direct isomerization of 2-methyl-4,5-dihydrofuran.A small concentration of decomposition products, mainly methane and ethane, are also found in shock mixtures of 2-methyl-4,5-dihydrofuran, particularly at high temperatures.The Arrhenius relations for the tree aforementioned processes are as follows: 2-methyl-4,5-dihydrofuran -> acetylcyclopropane, k1=1015.4 exp(-56.8*103/RT) s-1; 2-methyl-4,5-dihydrofuran -> 3-penten 2-one, k2=1015.7 exp(-63.6*103/RT) s-1; acetylcyclopropane -> 3-penten-2-one, k3=1014.4 exp(-58.3*103/RT) s-1, where R is expressed in units of cal/(K mol).
- Lifshitz, Assa,Laskin, Alexander
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- Catalytic isomerization of allylic alcohols by (η6-p-cymene) -ruthenium(II) complexes in organic and aqueous media: New recyclable and highly efficient catalysts in water containing ammonium-functionalized ligands
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The water-soluble complexes [RuCl2(η6-p-cymene) {κ-(P)-PPh3-n(OCH2CH2NMe 3)n}][SbF6]n [n = 1 (4a), 2 (4b) or 3 (4c)] have been prepared from the neutral precursors [RuCl2(η 6-p-cymene){κ-(P)-PPh3-n(OCH2CH 2NMe2)n}] [n = 1 (2a), 2 (2b) or 3 (2c)] and MeI via quaternization of the nitrogen atom of the terminal aminoalkyl groups, and subsequent counteranion exchange by the treatment with AgSbF6. Complexes 2a-c and 4a-c have proven to be highly active catalysts for isomerization of allylic alcohols in THF and aqueous media, respectively. Moreover, the water-soluble catalysts 4a-c can be reused after a simple extraction process at the end of the reaction. In particular, 4c presents a remarkable capability to be recycled, being active during 10 successive runs.
- Crochet, Pascale,Diez, Josefina,Fernandez-Zumel, Mariano A.,Gimeno, Jose
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- A catalytic asymmetric bioorganic route to enantioenriched tetrahydro- and dihydropyranones
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A conceptually novel approach to hetero Diels-Alder adducts of carbonyl compounds is described using as the key steps an antibody-mediated kinetic resolution of hydroxyenones followed by a ring-closure process. Various β-hydroxyenones proved to be very good substrates for antibodies 84G3- and 93F3-catalyzed retro-aldol reactions, allowing the preparation of highly enantiomerically enriched (up to 99% ee) precursors of pyranones. An attractive feature of this methodology is the possibility to convert these acyclicenantioenriched β-hydroxyenones into tetrahydropyranones by a conventional Michael-type addition procedure or into the corresponding dihydropyranones using an alternative palladium-catalyzed oxidative ring closure. For the palladium-mediated cyclization, a biphasic system has been implemented that allows the direct preparation of enantiopure dihydropyranones from the corresponding racemic aldol precursors using a sequential antibody-resolution/palladium-cyclization strategy, without isolation of the intermediate enantioenriched hydroxyenones. This bioorganic route is best applied to the preparation of hetero Diels-Alder adducts otherwise derived from less nucleophilic dienes and unactivated dienophiles.
- Baker-Glenn, Charles,Hodnett, Neil,Reiter, Maud,Ropp, Sandrine,Ancliff, Rachael,Gouverneur, Veronique
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p. 1481 - 1486
(2007/10/03)
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- Biocatalytic oxidative kinetic resolution of sec-alcohols: Stereocontrol through substrate-modification
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Whole lyophilised cells of Rhodococcus ruber DSM 44541 were employed for the oxidative kinetic resolution of sec-alcohols using acetone as hydrogen acceptor. The enantioselectivity of this process could be controlled effectively by introducing C-C multiple bonds into substrates, which were inefficiently recognised, in particular short-chain (ω-1)-alcohols and (ω-2)-analogs. Thus, the enantioselectivities of rac-2-pentanol (E=16.8) and rac-3-octanol (E=13.3) were significantly improved by introducing a C=C bond adjacent to the alcohol moiety to give racemic (E)-pent-3-en-2-ol and 4-(E)-octen-3-ol, which were resolved with excellent selectivities (E >100 and 50, respectively). In addition, it was found that high stereodifferentiation between the E- and Z-configured double bonds occurred, as the corresponding (Z)-isomers were not converted. Similar selectivity-enhancing effects were observed with acetylenic analogs.
- Stampfer, Wolfgang,Kosjek, Birgit,Faber, Kurt,Kroutil, Wolfgang
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p. 275 - 280
(2007/10/03)
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- Oxidation of Diols and Ethers by NaBrO3/NaHSO3 Reagent
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NaBrO3 combined with NaHSO3 was found to be an excellent oxidizing reagent of alcohols, diols, and ethers under mild conditions. A variety of aliphatic and cyclic diols were selectively oxidized with satisfactory yields to the corresponding hydroxy ketones and/or diketones, which are difficult to selectively prepare due to a concomitant formation of cleaved products. For example, 2-hydroxycyclohexanone and 1,2-cyclohexanedione were selectively formed by allowing 1,2-cyclohexanediol to react with NaBrO3/NaHSO3 reagent in a selected solvent. On the other hand, an alkyl ether, such as dioctyl ether, reacted with NaBrO3/NaHSO3, in water at room temperature to give octyl octanoate in 82% yield. The same oxidation at higher temperature (60°C) produced the α-brominated ester, octyl 2-bromooctanoate, which is considered to be formed through an alkenyl alkyl ether as the intermediate. The treatment of 1-ethoxy-l-heptene with NaBrO3/NaHSO3 afforded ethyl 2-bromoheptanoate and 2-bromoheptanoic acid as the major products.
- Sakaguchi, Satoshi,Kikuchi, Daisuke,Ishii, Yasutaka
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p. 2561 - 2566
(2007/10/03)
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- Lewis Acid-Promoted Coupling Reactions of Acid Chlorides with Organoaluminum and Organozinc Reagents
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An efficient synthesis of α,α-unsaturated ketones by the reaction of acid chlorides with trialkyl-aluminum (1/3 mole equiv) in the presence of AlCl3 (1 mol equiv) is described. Dialkylzincs were also useful and are easier to prepare than trialkylaluminum. Reaction of RCOCl with R′AlCl3 or R′2AlCl gave R′COR, without AlCl3, in high yield.
- Arisawa, Mitsuhiro,Torisawa, Yasuhiro,Kawahara, Michiaki,Yamanaka, Masamichi,Nishida, Atsushi,Nakagawa, Masako
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p. 4327 - 4329
(2007/10/03)
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- Transformation of 1,3-, 1,4- and 1,5-diols over perfluorinated resinsulfonic acid (Nafion-H)
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The transformations of 1,3-, 1,4- and 1,5-diols over perfluorinated resinsulfonic acids (Nafion-H) were studied and correlations were examined between the structure of the investigated diols, the possible transformation directions and the catalytic properties of Nafion-H. Comparisons were also made between the catalytic properties of Nafion-H and zeolites. The characteristic transformations of 1,3-diols depend on their structure. 1,3-Propanediol undergoes dehydration via 1,2-elimination and yields oligomers via intermolecular dehydration. 1,3-Diols with an alkyl substituent on the carbon between those bearing the OH groups undergo 1,2-elimination yielding unsaturated alcohols and dienes, and give carbonyl compounds via the loss of water and hydride shifts analogous to the pinacol rearrangement. The strong acidity of Nafion-H and the lack of strong basic sites are advantageous for the latter reaction. 1,3-Diols with two substituents at this position mainly yield fragmentation products. Stereoselective cyclodehydration to the corresponding oxacycloalkanes is the characteristic transformation of 1,4- and 1,5-diols over Nafion-H.
- Bucsi,Molnar,Bartok,Olah
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p. 3319 - 3326
(2007/10/02)
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- Condensation of Propiolactones with Phosphorus Ylides: a Convenient Synthesis of α,β-Ethylenic Ketones
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δ-Hydroxy-β-ketophosphoranes have been obtained by condensation of propiolactones with ylides and afforded α,β-unsaturated ketones on heating.
- Le Roux, Juliette,Le Corre, Maurice
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p. 1464 - 1465
(2007/10/02)
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- Palladium(0)-catalyzed isomerization of α,β-epoxy ketones to β-diketones
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In the presence of catalytic amounts of tetrakis(triphenylphosphine)palladium(0) and 1,2-bis(diphenylphosphino)ethane, α,β-epoxy ketones isomerize to the corresponding β-diketones in high yields.Both open-chain and cyclic substrates can be used.Possible reaction mechanisms are discussed.
- Suzuki, M.,Watanabe, A.,Noyori, R.
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p. 230 - 236
(2007/10/02)
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- VINYL MIGRATION IN THE OXYTHALLATION OF SOME 1,3-DIENES
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The oxythallation of certain 1,3-dienes with thallium (III) nitrate trihydrate in MeOH-CH2Cl2 at 0-20 deg C gave products after vinyl migration .Methyl 1-methylcyclopropyl ketone, obtained in the reaction of 2,3-dimethyl-1,3-butadiene, was presumably derived from a cyclopropylmethyl cation, an intermediate in the vinyl migration.
- Murakami, Masashi,Nishida, Shinya
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p. 997 - 1000
(2007/10/02)
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