- Stable vapor-phase catalytic conversion of pinacolone into 2,3-dimethyl-1,3-butadiene
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In the vapor-phase synthesis of 2,3-dimethyl-1,3-butadiene from pinacolone over modified alumina catalysts, it was found that alumina modified with transition metals such as Co stabilized the conversion of pinacolone and produced 2,3- dimethyl-1,3-butadiene selectively under hydrogen flow conditions, whereas the catalytic activity of pure alumina was seriously deteriorated irrespective of its high initial activity.
- Sato, Satoshi,Sato, Natsumi,Yamada, Yasuhiro
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- NICKEL-CATALYZED ULLMANN-TYPE COUPLING OF ALKENYL HALIDES WITH ZINC POWDER
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Convenient procedure for an Ullmann-type coupling of alkenyl halides using zinc powder, nickel(II) chloride, and potassium iodide and/or thiourea is presented.One double bond in the produced diene retained the configuration of a starting material, while partial cis-trans isomerization was observed in the second one.
- Takagi, Kentaro,Hayama, Naomi
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- Oxidative bond formation and reductive bond cleavage at main group metal centers: Reactivity of five-valence-electron MX2 radicals
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Monomeric five-valence-electron bis(boryl) complexes of gallium, indium, and thallium undergo oxidative M-C bond formation with 2,3-dimethylbutadiene, in a manner consistent with both the redox properties expected for MII species and with metal
- Protchenko, Andrey V.,Dange, Deepak,Blake, Matthew P.,Schwarz, Andrew D.,Jones, Cameron,Mountford, Philip,Aldridge, Simon
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- Control of Polymorphisms and Functions in All-Inorganic Ionic Crystals Based on Polyaluminum Hydroxide and Polyoxometalates
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Two kinds of polymorphs of all-inorganic ionic crystals were obtained by the combination of oppositely charged molecular ions (macroions) with Td symmetry, Keggin-type polyaluminum hydroxide [?-Al13O4(OH)24(H2O)12]7+ (Al13) and polyoxometalates (POMs) [α-CoW12O40]6- (POM6), [α-1,2,3-SiVV3W9O40]7- (POM7), or [α-1,2,3-SiVIVVV2W9O40]8- (POM8) in aqueous solutions. The needle-type crystals were grown by dissolution-recrystallization of the precipitates, which formed immediately by combining Al13 and POMs. On the other hand, the plate-type crystals were grown by adding inorganic salts (e.g., NaCl) into the aqueous solution containing the needle-type crystals: Dissolution of the needle-type crystals occurred followed by precipitation of the plate-type crystals, which is the more insoluble and stable polymorph with larger numbers of hydrogen bonds between the constituent ions. The plate-type crystals possess one-dimensional channels with large apertures (ca. 12 ? × 6 ?) and showed high activities as heterogeneous solid acid catalysts in pinacol rearrangement.
- Mizuno, Kosuke,Mura, Takuto,Uchida, Sayaka
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- CYCLOADDITION REACTIONS OF 2,3-DIDEHYDROTHIOPHENE GENERATED BY FLOW VACUUM THERMOLYSIS OF THIOPHENE-2,3-DICARBOXYLIC ANHYDRIDE
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Flow vacuum thermolysis (FVT) of thiophene-2,3-di-carboxylic anhydride (2) in the presence of 2,3-dimethylbutadiene (6) gives, in addition to 5,6-dimethylthianaphthene (9), small quantities of a dihydrodimethylthianaphthene (12) and another dimethylthianaphthene (13) which is probably also formed by dehydrogenation of 12 with chloranil.The partial structures of these minor products are consistent with their being formed by a -cycloaddition between 6 and an intermediate aryne, 2,3-didehydrothiophene (1), followed by a rearrangement of the resulting adduct 11 and dehydrogenation.FVT of 2 in the presence of 2,5- (17b) or 3,4-dimethylthiophene (17c) also gave a mixture of the dimethylthianaphthenes (18, 22, 23) which can be rationalized as arising by a - and two -cycloadditions of the aryne 1 to the thiophenes 17 with subsequent desulfurization.The lack of equilibration of the products 18, 22, and 23 was demonstrated and their origin as a function of the structure and reactivity of the aryne 1 discussed.
- Reinecke, Manfred G.,Newsom, James G.,Almqvist, Anders
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- A smarter approach to catalysts by design: Combining surface organometallic chemistry on oxide and metal gives selective catalysts for dehydrogenation of 2,3-dimethylbutane
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2,3-dimethylbutane is selectively converted into 2,3-dimethylbutenes at 500 °C under hydrogen or at 390 °C under nitrogen in the presence of bimetallic catalysts Pt-Sn/Li-Al2O3. The high stability of the catalyst along the reaction is obtained by selective modification of the Pt/Li-Al2O3 catalyst using Surface Organometallic Chemistry (SOMC).
- Rouge, Pascal,Garron, Anthony,Norsic, Sébastien,Larabi, Cherif,Merle, Nicolas,Delevoye, Laurent,Gauvin, Regis M.,Szeto, Kai C.,Taoufik, Mostafa
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- Fast kinetics studies of the Lewis acid-base complexation of transient stannylenes with σ- And π-donors in solution
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The Lewis acid-base complexation chemistry of dimethyl- and diphenylstannylene (SnMe2 and SnPh2, respectively) in hexanes solution has been studied by laser photolysis methods. Complexation of the two stannylenes with a series of nine O-, S-, and N-donors (including cyclic and acyclic dialkyl ethers and sulfides, a primary, secondary, and tertiary amine, ethyl acetate and acetone), two alkenes, and an alkyne proceeds rapidly and reversibly to generate the corresponding stannylene-donor Lewis pairs, which have been detected in each case by time-resolved UV-vis absorption spectroscopy. The complexes exhibit UV-vis absorption maxima in the range of λmax ~ 310-405 nm depending on the donor and substitution at tin. Bimolecular rate constants for complexation (kC), which could be determined for 14 of the 24 Lewis pairs that were studied, were found to fall within a factor of four of the diffusional limit in all cases, with SnMe2 showing consistently higher reactivity than SnPh2. Equilibrium constants for complexation (KC) could be measured for all but one of the stannylene-π- and O-donor pairs, the values corresponding to (gas phase) binding free energies in the range of +1.1 to -3.9 kcal mol-1. Comparison of the experimental equilibrium constants for complexation of SnMe2 and SnPh2 with methanol and diethyl ether to those measured previously for the homologous silylenes and germylenes indicates that Lewis acidity decreases in the order SiR2 > SnR2 > GeR2 for both the dimethyl- and diphenyltetrylene series, the diphenyl derivatives exhibiting significantly stronger Lewis acidity in all three cases. The experimental trends in the binding energies and UV-vis spectra of the complexes are reproduced well by density functional theory (DFT) calculations, which have been carried out at the (TD)ωB97XD/def2-TZVP level of theory. The experimental data also show evidence of a reaction between tetramethyldistannene (Me2SnSnMe2, 4a) and amine donors, which is suggested to afford the corresponding amine-stabilized stannylidenestannylene structure. The mechanistic proposal is supported by DFT calculations of the complexation of 4a and SnMe2 with model O-, S- and N-donors.
- Duffy, Ian R.,Leigh, William J.
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- Isomeric effects on the acidity of Al13Keggin clusters in porous ionic crystals
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We demonstrate a facile synthesis method of a porous ionic crystal (PIC) composed of the little-known δ-Keggin-type cationic polyoxoaluminum cluster ([δ-Al13O4(OH)24(H2O)12]7+, δ-Al13) with an oppositely-charged polyoxometalate, which enabled us to investigate the activity as a solid acid. The δ-Al13based PIC exhibited much higher activity in pinacol rearrangement, a typical acid-catalyzed reaction, than the PIC based on the well-known and thermodynamically stable rotational isomer (ε-Al13). This work is a rare example of rotational isomers of polyoxoaluminum clusters exhibiting remarkably different catalytic activities.
- Ogiwara, Naoki,Tamai, Nanako,Uchida, Sayaka,Weng, Zhewei,Yan, Li-Kai,Zhao, Congcong,Zhou, Wei
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- 1,1-Dimetallagermacyclopent-3-enes: Precursors to Transition Metal Substituted Germylenes (Germanediyls)
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Transition metal substituted germylenes have been generated by pyrolysis of 1,1-dimetallagermacyclopent-3-enes and by the metathesis reaction between GeI2 and -(Cp = C5H5).
- Lei, Deqing,Hampden Smith, Mark J.
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- Nickel-catalyzed reductive 1,3-diene formation from the cross-coupling of vinyl bromides
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Facile construction of 1,3-dienes building upon cross-electrophile coupling of two open-chain vinyl halides is disclosed in this work, showing moderate chemoselectivities between the terminal bromoalkenes and internal vinyl bromides. The present method is mild and tolerates a range of functional groups and can be applied to the total synthesis of a tobacco fragrance solanone.
- Sha, Yunfei,Liu, Jiandong,Wang, Liang,Liang, Demin,Wu, Da,Gong, Hegui
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supporting information
p. 4887 - 4890
(2021/06/16)
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- 9,10-anthraquinone derivative and preparation method and application thereof
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The invention discloses a 9,10-anthraquinone derivative. The 9,10-anthraquinone derivative is prepared through the following method that (1), a compound A1 and a constant boiling inorganic acid solution are subjected to a dehydration reaction to obtain a compound B1, a compound A2 and inorganic acid are subjected to a dehydration reaction, and a compound B2 is obtained; (2), 1,4-benzoquinone, the compound B1 and the compound B2 are subjected to addition polymerization in an organic medium, and the 9,10-anthraquinone derivative is obtained. The provided 9,10-anthraquinone derivative provides diversified choices for direct application of an anthraquinone derivative in the field of organic electroluminescence, dyes and medicine, and also provides a new intermediate raw material for further synthesizing the high performance and high application value anthraquinone derivative; the synthesis method is simple, the reaction condition is mild, the source of the reaction raw materials is convenient, the cost is low, the types of an organic solvent is less, and the purity and yield of the obtained product are high.
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Paragraph 0067; 0069; 0070; 0080-0083
(2019/10/08)
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- A method of preparing 1,2,4,5-benzenetetracarboxylic acid or trimellitic acid from pinacol
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The invention relates to a method of preparing 1,2,4,5-benzenetetracarboxylic acid or trimellitic acid from pinacol. The method includes a first step of selectively dehydrating the pinacol in an acid/ionic liquid catalytic system to generate 2,-3-dimethyl-1,3-butadiene; a second step of subjecting the 2,-3-dimethyl-1,3-butadiene and maleate or acrylate to a D-A cycloaddition/dehydrogenation tandemreaction to generate an aromatic ring product; and a third step of subjecting the aromatic ring product to hydrolysis and oxidation to prepare the 1,2,4,5-benzenetetracarboxylic acid or the trimellitic acid. The catalytic system adopted in the method is green, and can be recycled. The raw material is a biomass-based platform chemical, and is cheap and easily available. All reaction processes aresimple. The pinacol dehydration reaction, the dehydrogenation reaction of a D-A product and an oxidation reaction are high in activity and selectivity. The novel method for preparing the 1,2,4,5-benzenetetracarboxylic acid and the trimellitic acid which are fine chemicals from the pinacol that is a lignocelluloses based platform chemical is provided by the invention.
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Paragraph 0055-0060
(2018/04/01)
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- Methods for preparing benzene-ring-containing compounds from pinacol
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The invention relates to methods for preparing durene, 1,2,3-trimethylbenzene, o-xylene, pyromellitic acid and trimellitic acid from pinacol. Durene, 1,2,3-trimethylbenzene and o-xylene are prepared through three steps of reaction, and pyromellitic acid and trimellitic acid are prepared through four steps of reaction. A catalytic system used in the invention is green and environment-friendly, andcan be recycled. The raw materials of method, i.e., pinacol, crotonaldehyde, acrolein and crotonate can all be derived from biomass, and are cheap and easily available. All the reaction processes aresimple and are high in activity and selectivity in the dehydration of pinacol and the dehydrogenation, decarbonylation and oxidation of D-A products. The invention provides novel methods for preparingfine chemicals including durene, 1,2,3-trimethylbenzene, o-xylene, pyromellitic acid and trimellitic acid from lignocellulose-based platform chemicals.
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Paragraph 0042; 0043; 0044; 0046; 0047
(2018/08/04)
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- Sustainable production of pyromellitic acid with pinacol and diethyl maleate
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Herein, we report an unprecedented and sustainable route to synthesize pyromellitic acid (PMA), a monomer of polyimide, with pinacol and diethyl maleate which can be derived from lignocellulose. Analogously, a sustainable route to trimellitic acid (TMA) was also developed using pinacol and acrylate as the feedstocks.
- Hu, Yancheng,Li, Ning,Li, Guangyi,Wang, Aiqin,Cong, Yu,Wang, Xiaodong,Zhang, Tao
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supporting information
p. 1663 - 1667
(2017/06/05)
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- Solid Acid-Catalyzed Dehydration of Pinacol Derivatives in Ionic Liquid: Simple and Efficient Access to Branched 1,3-Dienes
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The selective dehydration of pinacol derivatives to branched 1,3-dienes is extremely challenging because of the predominance of pinacol rearrangement. Herein, we successfully achieve this goal by employing a recyclable solid acid/ionic liquid catalyst system. The dehydration of alkyl- and cycloalkyl-derived diols in an Amberlyst-15/[Emim]Cl system afforded the corresponding 1,3-dienes in good yields, while a Nafion/[Emim]Cl system was demonstrated to be a better catalyst system for the dehydration of aryl-substituted substrates. Our protocol features straightforward and simple access to branched 1,3-dienes, high chemoselectivity, a recyclable catalyst system, a facile separation of dienes just by decantation, and a broad substrate scope.
- Hu, Yancheng,Li, Ning,Li, Guangyi,Wang, Aiqin,Cong, Yu,Wang, Xiaodong,Zhang, Tao
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p. 2576 - 2582
(2017/05/31)
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- Sustainable Production of o-Xylene from Biomass-Derived Pinacol and Acrolein
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o-Xylene (OX) is a large-volume commodity chemical that is conventionally produced from fossil fuels. In this study, an efficient and sustainable two-step route is used to produce OX from biomass-derived pinacol and acrolein. In the first step, the phosphotungstic acid (HPW)-catalyzed pinacol dehydration in 1-ethyl-3-methylimidazolium chloride ([emim]Cl) selectively affords 2,3-dimethylbutadiene. The high selectivity of this reaction can be ascribed to the H-bonding interaction between Cl? and the hydroxy group of pinacol. The stabilization of the carbocation intermediate by the surrounding anion Cl? may be another reason for the high selectivity. Notably, the good reusability of the HPW/[emim]Cl system can reduce the waste output and production cost. In the second step, OX is selectively produced by a Diels–Alder reaction of 2,3-dimethylbutadiene and acrolein, followed by a Pd/C-catalyzed decarbonylation/aromatization cascade in a one-pot fashion. The sustainable two-step process efficiently produces renewable OX in 79 % overall yield. Analogously, biomass-derived crotonaldehyde and pinacol can also serve as the feedstocks for the production of 1,2,4-trimethylbenzene.
- Hu, Yancheng,Li, Ning,Li, Guangyi,Wang, Aiqin,Cong, Yu,Wang, Xiaodong,Zhang, Tao
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p. 2880 - 2885
(2017/07/25)
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- Tetrabutylphosphonium Bromide Catalyzed Dehydration of Diols to Dienes and Its Application in the Biobased Production of Butadiene
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We report the use of the ionic liquid tetrabutylphosphonium bromide as a solvent and catalyst for dehydration of diols to conjugated dienes. This system combines stability, high reaction rates, and easy product separation. A reaction mechanism for the model compound 1,2-hexanediol is proposed and experimentally corroborated. This particular mechanism allows for the selective formation of conjugated dienes, in contrast with purely acidic catalysis. Next, the reaction is also performed on various other diols. As a first application, we assessed the biobased production of 1,3-butadiene. With 1,4-butanediol as the starting material, a 94% yield of butadiene was reached at 100% conversion.
- Stalpaert, Maxime,Cirujano, Francisco G.,De Vos, Dirk E.
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p. 5802 - 5809
(2017/09/15)
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- Novel Phospholium-Type Cationic Surfactants: Synthesis, Aggregation Properties and Antimicrobial Activity
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A series of novel phospholium amphiphilic compounds with straight alkyl chains with different numbers of carbon atoms (12, 14, 15, 16, 17, 18) were synthesized. The quaternary phosphorus, phosphonium cation, is incorporated into a five-membered heterocyclic ring. Their physicochemical properties were investigated by measurements of surface tension, conductivity and dynamic light scattering. The critical micelle concentration (cM), the surface tension value at the cM (γcmc), the surface area at the surface saturation per head group (Acmc), the ionization degree of micelle (α), the free energy of micellization (ΔG°mic), and hydrodynamic diameter (dh) were determined. Antimicrobial activity was tested against bacteria and yeast. The structure–activity relationship was determined.
- Luká?, Milo?,Devínsky, Ferdinand,Pisár?ik, Martin,Papapetropoulou, Aspasia,Bukovsky, Marián,Horváth, Branislav
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p. 159 - 171
(2017/01/14)
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- Allylic C–H Activation of Olefins by a TpMe2IrIII Compound
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The IrIIIcompound [TpMe2Ir(C6H5)2(N2)] (1) [TpMe2= hydridotris(3,5-dimethylpyrazolyl)borate] reacts with 1-hexene, propene, α-methylstyrene, and 2,3-dimethylbutadiene to yield organometallic products that derive from allylic C–H activations (complexes 3 from 1-hexene, 2 from propene, 5 from α-methylstyrene, and 7, 8, and 9 from 2,3-dimethylbutadiene), in all cases along with organic products formed in catalytic (Ir-induced) dehydrogenative coupling of benzene (the solvent of the reaction) and the corresponding olefin, with the latter also acting as the hydrogen scavenger in each case. Differently, complex 1 reacts with (E)-β-methylstyrene and cyclohexadiene to yield complex 2 and the known (η4-cyclohexadiene)IrIderivative 6, respectively. Finally, compound 1 reacts under mild conditions with cyclopentadiene and methylcyclopentadiene with the generation of phenyl derivatives 11 and 12 in which the corresponding cyclopentadienyl ligand adopts the η5coordination and forces the TpMe2ligand to coordinate in the κ2mode.
- Cristóbal, Crispín,Santos, Laura L.,Gutiérrez-González, Rubén,álvarez, Eleuterio,Paneque, Margarita,Poveda, Manuel L.
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p. 2534 - 2542
(2016/07/06)
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- Direct Detection, Dimerization, and Chemical Trapping of Dimethyl- and Diphenylstannylene from Photolysis of Stannacyclopent-3-enes in Solution
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Dimethyl- and diphenylstannylene (SnMe2 and SnPh2, respectively) have been successfully detected and characterized in solution. The stannylenes were generated by photolysis of 1,1,3-trimethyl-4-phenyl- (2) and 3,4-dimethyl-1,1-diphenylstannacyclopent-3-ene (3), respectively, which have been shown to extrude the species cleanly and in high (0.6 2SnCl2) as the stannylene substrate. Laser flash photolysis of 2 and 3 in deoxygenated hexanes affords promptly formed transient absorptions assigned to SnMe2 (λmax = 500 nm; ε500 = 1800 ± 600 M-1 cm-1) and SnPh2 (λmax = 290, 505 nm; ε500 = 2500 ± 600 M-1 cm-1), respectively, which decay with absolute second-order rate constants within a factor of 2 of the diffusional limit in both cases. The decay of the stannylenes is accompanied by the growth of new transient absorptions ascribable to the corresponding dimers, the structures of which are assigned with the aid of DFT and time-dependent (TD) DFT calculations at the (TD)ωB97XD/6-31+G(d,p)C,H,O-LANL2DZdpSn level of theory. Dimerization of SnMe2 affords a species exhibiting λmax = 465 nm, which is assigned to the expected Sn=Sn doubly bonded dimer, tetramethyldistannene (Me2Sn=SnMe2, 16a), in agreement with earlier work. In contrast, the spectrum of the dimer formed from SnPh2 exhibits strong absorptions in the 280-380 nm range and a very weak absorption at 650 nm, on the basis of which it is assigned to phenyl(triphenylstannyl)stannylene (17b). The calculations suggest that 17b is formed via ultrafast rearrangement of a novel phenyl-bridged stannylidenestannylene intermediate (20), which can be formed either directly by "endo" dimerization of SnPh2 or by isomerization of the "exo" dimer, tetraphenyldistannene (16b); the predicted barriers for these rearrangements are consistent with the experimental finding that the observed product is formed at close to the diffusion-controlled rate. Absolute rate and equilibrium constants are reported for the reactions of SnMe2 and SnPh2 with Me2SnCl2 and methanol (MeOH), respectively, in hexanes at 25 °C.
- Duffy, Ian R.,Leigh, William J.
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p. 5029 - 5044
(2015/11/09)
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- A transition-metal-free Heck-type reaction between alkenes and alkyl iodides enabled by light in water
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A transition-metal-free coupling protocol between various alkenes and non-activated alkyl iodides has been developed by using photoenergy in water for the first time. Under UV irradiation and basic aqueous conditions, various alkenes efficiently couple with a wide range of non-activated alkyl iodides. A tentative mechanism, which involves an atom transfer radical addition process, for the coupling is proposed.
- Liu, Wenbo,Li, Lu,Chen, Zhengwang,Li, Chao-Jun
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supporting information
p. 6170 - 6174
(2015/06/08)
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- New extraction procedure for protonated polyoxometalates prepared in aqueous-organic solution and characterisation of their catalytic ability
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Although POMs prepared in aqueous-organic solutions have been reported to exhibit interesting chemical properties and may be efficient catalysts, they could not be isolated in their protonated form using the normal extraction method. In this study, a new procedure of isolating protonated POMs, [S 2VxM18-xO62](4+x)- and [AsVxM12-xO40](3+x)- (M = Mo, W; x = 0-2), which were prepared in an aqueous-organic mixed solution, was developed by modifying and optimising the extraction conditions. Isolated protonated POMs were characterised using IR and Raman spectroscopy, and their acidity was measured using a Hammett indicator. The acidity of H4S 2W18O62, H5S2VW 17O62, H4S2Mo18O 62, and H3As2W18O62 was stronger than that of H3PW12O40. Their catalytic ability was investigated in multiple types of organic reactions, including pinacol rearrangement, acetal formation with benzaldehyde and ethylene glycol, and the Friedel-Crafts acylation of anisole with ethyl pyruvate. They exhibited greater catalytic ability than commercially available POMs such as H3PM12O40 and H4SiM 12O40 (M = Mo, W).
- Ueda, Tadaharu,Yamashita, Keisuke,Onda, Ayumu
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p. 181 - 187
(2014/11/08)
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- 2-PHENYL-5-HETEROCYCLYL-TETRAHYDRO-2H-PYRAN-3-AMINE COMPOUNDS FOR USE IN THE TREATMENT OF DIABETES AND ITS ASSOCIATED DISORDERS
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The present invention relates to novel compounds of the general formula (I) their tautomeric forms, their enantiomers, their diastereoisomers, their pharmaceutically accepted salts, or pro-drugs thereof, which are useful for the treatment or prevention of diabetes mellitus (DM), obesity and other metabolic disorders. The invention also relates to process for the manufacture of said compounds, and pharmaceutical compositions containing them and their use.
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Page/Page column 29; 30
(2014/05/07)
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- High-yielding synthesis of β-octaalkyl-meso-(bromophenyl)-substituted porphyrins and X-ray study of axial complexes of their zinc complexes with THF and 1,4-dioxane
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New 5-(4-bromophenyl)-3,7,12,13,17,18-hexamethyl-2,8-dipentyl- and 5,15-bis(4-bromophenyl)-2,8,12,18-tetramethyl-2,8,12,18-tetrapentylporphyrins (H2P-1 and H2P-2) and their zinc metal complexes (ZnP-1 and ZnP-2, respectively) were sy
- Mikhalitsyna, Elena A.,Tyurin, Vladimir S.,Nefedov, Sergey E.,Syrbu, Sergey A.,Semeikin, Aleksandr S.,Koifman, Oskar I.,Beletskaya, Irina P.
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p. 5979 - 5990
(2013/02/26)
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- Replacing conventional carbon nucleophiles with electrophiles: Nickel-catalyzed reductive alkylation of aryl bromides and chlorides
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A general method is presented for the synthesis of alkylated arenes by the chemoselective combination of two electrophilic carbons. Under the optimized conditions, a variety of aryl and vinyl bromides are reductively coupled with alkyl bromides in high yields. Under similar conditions, activated aryl chlorides can also be coupled with bromoalkanes. The protocols are highly functional-group tolerant (-OH, -NHTs, -OAc, -OTs, -OTf, -COMe, -NHBoc, -NHCbz, -CN, -SO2Me), and the reactions are assembled on the benchtop with no special precautions to exclude air or moisture. The reaction displays different chemoselectivity than conventional cross-coupling reactions, such as the Suzuki-Miyaura, Stille, and Hiyama-Denmark reactions. Substrates bearing both an electrophilic and nucleophilic carbon result in selective coupling at the electrophilic carbon (R-X) and no reaction at the nucleophilic carbon (R-[M]) for organoboron (-Bpin), organotin (-SnMe3), and organosilicon (-SiMe2OH) containing organic halides (X-R-[M]). A Hammett study showed a linear correlation of σ and σ(-) parameters with the relative rate of reaction of substituted aryl bromides with bromoalkanes. The small ρ values for these correlations (1.2-1.7) indicate that oxidative addition of the bromoarene is not the turnover-frequency determining step. The rate of reaction has a positive dependence on the concentration of alkyl bromide and catalyst, no dependence upon the amount of zinc (reducing agent), and an inverse dependence upon aryl halide concentration. These results and studies with an organic reductant (TDAE) argue against the intermediacy of organozinc reagents.
- Everson, Daniel A.,Jones, Brittany A.,Weix, Daniel J.
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supporting information; experimental part
p. 6146 - 6159
(2012/05/07)
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- Pinacol-type rearrangement catalyzed by Zr-incorporated SBA-15
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Highly ordered zirconium-incorporated SBA-15 materials, designated as Zr-SBA-15, with Zr/Si ratios up to 10.8 mol% were one-pot synthesized in a self-generated acidic environment. Zr was incorporated into the SBA-15 framework as isolated Zr species, and it also formed superficial zirconia clusters with two or more Zr centers on the pore walls when the Zr/Si ratio was higher than 3 mol%. The acid amounts of Zr-SBA-15 materials increased linearly with Zr loading, but the acidities were lower than those of commercially available HY and ZSM-5 zeolites. However, when used as the catalysts in liquid phase pinacol-type rearrangement, one-pot synthesized Zr-SBA-15 materials, especially those with superficial zirconia clusters, were the most efficient catalysts. The pinacolone yield of 2.7 g/g catal h and selectivity of 81% were achieved in 1 h over Zr-SBA-15 with a Zr/Si ratio of 10.8 mol%. Moreover, Zr-SBA-15 was also efficient in catalyzing the rearrangement of bulky 2,3-pinanediol to yield camphor as the major product through hydrogen migration.
- Chen, Shih-Yuan,Lee, Jyh-Fu,Cheng, Soofin
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scheme or table
p. 196 - 205
(2010/06/12)
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- 1,4,2-Diazaphospholidine-3,5-diones and related compounds: A lecture on unpredictability in catalysis
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1,4,2-diazaphospholidine-3,5-diones and related compounds and unpredictability in catalysis was studied. The five-membered ring species 4 6, which are all readily accessible by the McCormack reaction, optionally with subsequent hydrogenation, were selected for this study. The use of saturated species of type 4 (1-organyl-phospholanes) as catalysts led to a complete reverse in the selectivity of the reaction, in favor of the formation of the isocyanate trimers. Owing to the high activity of the corresponding P-oxides in carbodiimidization reactions, it can be assumed that the findings can be attributed to partial air oxidation of the trivalent phosphorus species applied. The symmetrical species 6, in total contrast to the other two members of the series, do not exhibit any catalytic activity with respect to isocyanates and instead react cleanly with two equivalents of isocyanate to effect the extrusion of 1,3-diene.
- Richter, Frank U.
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supporting information; experimental part
p. 5200 - 5202
(2009/12/24)
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- DEHYDRATION OF ALCOHOLS TO GIVE ALKENES OR ETHERS
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The present invention relates to a process for the dehydration of alcohols, polyalcohols or alcoholates having at least one CH group in the α-position to the alcoholate or alcohol function to give alcenes or ethers, where the dehydration is carried out in ionic liquids of the general formula K+A?.
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Page/Page column 9
(2009/04/24)
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- Nickel-catalyzed carbonylative Negishi cross-coupling reactions
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Catalytic carbonylative Negishi cross-coupling reactions are described. This method readily provides various enones from enol triflates and diorganozinc reagents with catalytic amounts of nickel(II) chloride-4,4′-dimethoxyl-2,2′-bipyridyl under carbon mon
- Wang, Qiaoling,Chen, Chuo
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p. 2916 - 2921
(2008/09/21)
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- Studies of the condensation of sulfones with ketones and aldehydes
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The condensation of ketones or aldehydes with sulfunes was shown to give a variety of products. Condensation of 2-methylcyclohexanone with dimethyl sulfone using potassium t-butoxide as base gave useful yields of 1,2- dimethylenecyclohexane. Under the same conditions, cycloheptanone, 3-methyl-2-butanone, and 2-bulanone were converted to dienes. Remarkably, these reaction conditions converted acetophenone into p-terphenyl (10%) and (E)-1,4-diphenyl-3-penten-1-one (44%). Propiophenone was converted to 2′-methyl-p-terphenyl (61%). Using α-tetralone produced 1-methynaphthalene and naphthalene. No reaction took place with β-tetralone. Using diethyl sulfone with α-tetralone lead to pure naphthalene. Condensation of isobutyraldehyde and dimethyl sulfone using potassium t-butoxide gave isoprene in low yield. Using benzaldehyde and benzyl phenyl sulfone in N,N-dimethylcinnamide gave 1,2-diphenyl-1- phenylsulfonylethylene, N,N-dimethylcinnamide, and a complex condensation product. Only 1,2-diphenyl-1-phenylsulfonylethylene was obtained when the solvent was THF.
- Garst, Michael E.,Dolby, Lloyd J.,Esfandiari, Shervin,Okrent, Rachel A.,Avey, Alfred A.
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p. 553 - 556
(2007/10/03)
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- Allyl, methallyl, prenyl, and methylprenyl ethers as protected alcohols: Their selective cleavage with diphenyldisulfone under neutral conditions
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Diphenyldisulfone is a mild and efficient reagent for selective cleavage of methylprenyl (2,3-dimethylbut-2-en-1-yl), prenyl (3-methylbut-2-en1-yl), and methallyl (2-methylallyl) ethers. These reaction conditions are compatible with the presence of other protecting groups such as acetals, acetates, and allyl, benzyl, and TBDMS ethers. Exposure of 2,3-dimethylbut-2-en-1-yl and 3-methylbut-2-en1-yl ethers to diphenyldisulfone led to the formation of 2,3-dimethylbuta-1,3-diene and isoprene, respectively. 2-Methylallyl ethers undergo isomerization to 2-methylpropenyl ethers, which are easily hydrolyzed into the corresponding free alcohols and isobutyraldehyde.
- Markovic, Dean,Vogel, Pierre
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p. 2693 - 2696
(2007/10/03)
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- Flash vacuum pyrolysis over magnesium. Part 1 - Pyrolysis of benzylic, other aryl/alkyl and aliphatic halides
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Flash vacuum pyrolysis over a bed of freshly sublimed magnesium on glass wool results in efficient coupling of benzyl halides to give the corresponding bibenzyls. Where an ortho halogen substituent is present further dehalogenation gives some dihydroanthracene and anthracene. Efficient coupling is also observed for halomethylnaphthalenes and halodiphenylmethanes while chlorotriphenylmethane gives 4,4′-bis(diphenylmethyl)biphenyl. By using α,α′-dihalo-o-xylenes, benzocyclobutenes are obtained in good yield, while the isomeric α,α′-dihalo-p-xylenes give a range of high thermal stability polymers by polymerisation of the initially formed p-xylylenes. Other haloalkylbenzenes undergo largely dehydrohalogenation where this is possible, in some cases resulting in cyclisation. Deoxygenation is also observed with haloalkyl phenyl ketones to give phenylalkynes as well as other products. With simple alkyl halides there is efficient elimination of HCl or HBr to give alkenes. For aliphatic dihalides this also occurs to give dienes but there is also cyclisation to give cycloalkanes and dehalogenation with hydrogen atom transfer to give alkenes in some cases. For 5-bromopent-1-ene the products are those expected from a radical pathway but for 6-bromohex-1-ene they are clearly not. For 2,2-dichloropropane and 1,1-dichloropropane elimination of HCl occurs but for 1,1-dichlorobutane, -pentane and -hexane partial hydrolysis followed by elimination of HCl gives E, E-, E,Z- and Z,Z- isomers of the dialk-1-enyl ethers and fully assigned 13C NMR data are presented for these. With 6-chlorohex-1-yne and 7-chlorohept-1-yne there is cyclisation to give methylenecycloalkanes and -cycloalkynes. The behaviour of 1,2-dibromocyclohexane and 1,2-dichlorocyclooctane under these conditions is also examined. Various pieces of evidence are presented that suggest that these processes do not involve generation of free gas-phase radicals but rather surface-adsorbed organometallic species.
- Aitken, R. Alan,Hodgson, Philip K.G.,Morrison, John J.,Oyewale, Adebayo O.
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p. 402 - 415
(2007/10/03)
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- Effect of various acids at different concentrations on the pinacol rearrangement
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The formation of side products in the pinacol-pinacolone rearrangement was studied as a function of concentration and strength of various aqueous acids using 1H NMR spectroscopy. In all cases, pinacolone was the principal product and in most cases, its relative yield decreased with respect to 2,3-dimethyl-1,3-butadiene, when the acid concentration was lowered or the corresponding conjugate base was added.
- De Lezaeta, Monica,Sattar, Wajiha,Svoronos, Paris,Karimi, Sasan,Subramaniam, Gopal
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p. 9307 - 9309
(2007/10/03)
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- Syntheses, structures and properties of kinetically stabilized distibenes and dibismuthenes, novel doubly bonded systems between heavier group 15 elements
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The first stable distibene (RSb=SbR) and dibismuthene (RBi=BiR) were successfully synthesized by taking advantage of steric protection using an efficient steric protection group, 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (Tbt). Since it is quite difficult to investigate the reactivities of the distibene (TbtSb=SbTbt) and dibismuthene (TbtBi= BiTbt) in solution due to their extremely low solubility values, similarly overcrowded distibene and dibismuthene, BbtE=EBbt (E = Sb, Bi), with sufficiently high solubility were also synthesized using another bulky substituent, 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl group (Bbt). The crystallographic analysis and spectroscopic studies of these stable dipnictenes led to the systematic comparison of structural parameters and physical properties for all homonuclear doubly bonded systems between heavier group 15 elements. In addition to these experimentally obtained results, theoretical calculations for these doubly bonded systems also revealed the intrinsic character of dipnictenes.
- Sasamori, Takahiro,Arai, Yoshimitsu,Takeda, Nobuhiro,Okazaki, Renji,Furukawa, Yukio,Kimura, Masahiro,Nagase, Shigeru,Tokitoh, Norihiro
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p. 661 - 675
(2007/10/03)
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- Conrotatory photochemical ring opening of alkylcyclobutenes in solution. A test of the hot ground-state mechanism
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Quantum yields for photochemical ring opening of six alkylcyclobutenes have been measured in hexane solution using 228-nm excitation, which selectively populates the lowest π,R(3s) excited singlet states of these molecules and has been shown previously to lead to ring opening with clean conrotatory stereochemistry. The compounds studied in this work - 1,2-dimethylcyclobutene (1), cis- and trans-1,2,3,4-tetramethylcyclobutene (cis- and trans-5), hexamethylcyclobutene (8), and cis- and trans-tricyclo[6.4.0.02,7]dodec-12-ene (cis- and trans-9) - were selected so as to span a broad range in molecular weight and as broad a range as possible in Arrhenius parameters for thermal (ground-state) ring opening. RRKM calculations have been carried out to provide estimates of the rate constants for ground-state ring opening of each of the compounds over a range of thermal energies from 20 00O to 49 000 cm-1. These have been used to estimate upper limits for the quantum yields of ring opening via a hot ground-state mechanism, assuming a value of kdeact = 1011 s-1 for the rate constant for collisional deactivation by the solvent, that internal conversion to the ground state from the lowest Rydberg state occurs with close to unit efficiency, and that ergodic behavior is followed. The calculated quantum yields are significantly lower than the experimental values in all cases but one (1). This suggests that the Rydberg-derived ring opening of alkylcyclobutenes is a true excited-state process and rules out the hot ground-state mechanism for the reaction.
- Cook,Leigh,Walsh
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p. 5188 - 5193
(2007/10/03)
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- The acidity and catalytic activity of supported acidic cesium dodecatungstophosphates studied by MAS NMR, FTIR, and catalytic test reactions
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Acidic cesium salts of dodecatungstophosphoric acid (H3PW) supported on silica and MCM-41 were characterized by multinuclear MAS NMR, FTIR, and catalytic test reactions. 31P-NMR data indicate that the supported samples contain salts of various stoichiometries (Cs3PW and Cs2HPW) and even H3PO4. According to 29Si-NMR data, deposition of the Cs salt does not change the relative amount of various SiOH groups in the case of the silica support. In contrast, when the support is MCM-41, the relative amount of the SiOH groups increases significantly, indicating the breaking of the siloxane bonds resulting from their interaction with H3PW. The 133Cs MAS-NMR spectra also suggest that the CsPW salt interacts more strongly with the MCM-41 support than with SiO2. The results of catalytic studies show that cesium salts of dodecatungstophosphoric acid with low Cs content supported on silica or MCM-41 (Cs1.7H1.3[PW12O40]-on-SiO 2 and Cs1.8H1.2[PW12O40]-on-MCM41) are active, selective, and recyclable catalysts in Friedel-Crafts alkylations (isopropylation, transalkylation), the aromatic ortho-Claisen rearrangement, and the dehydration of pinacol. The specific activity of these catalyst preparations are comparable with that of neat Cs2.6H0.4[PW12O40]. This indicates that the active species are in a well-dispersed form.
- Molnar,Beregszaszi,Fudala,Lentz,Nagy,Konya,Kiricsi
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p. 379 - 386
(2007/10/03)
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- New fused bicyclic cyclotrigermanes from cycloaddition reactions of cyclotrigermene
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The mesityl-substituted cyclotrigermene 1 underwent [2+4] cycloaddition with isoprene and 2,3-dimethyl-1,3-butadiene to yield 1,6,7-trigerma-7-mesitylbicyclo[4.1.0]hept-3-ene derivatives 2, and [2+2] cycloaddition with phenylacetylene to yield 1,4,5-trige
- Fukaya, Norihisa,Ichinohe, Masaaki,Sekiguchi, Akira
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p. 3881 - 3884
(2007/10/03)
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- COMPOUNDS FOR ORGANIC EL ELEMENT AND ORGANIC EL ELEMENT
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An object of the invention is to provide an organic EL device-forming compound and an organic EL device which produce light emission of satisfactory luminance, especially at long wavelength and are durable in that improved light emitting performance lasts for a long time. The object is attained by a compound having a basic skeleton represented by formula (I) and an organic EL device comprising the same. In formula (I), R1to R8each are hydrogen or a substituted or unsubstituted aryl or alkenyl group, with the proviso that at least six of R1to R8are substituted or unsubstituted aryl or alkenyl groups.
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- Stereospecific (Conrotatory) Photochemical Ring Opening of Alkylcyclobutenes in the Gas Phase and in Solution. Ring Opening from the Rydberg Excited State or by Hot Ground State Reaction?
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The photochemistry of 1,2-dimethylcyclobutene and cis- and trans-1,2,3,4-tetramethylcyclobutene has been studied in the gas phase (1 atm; SF6 buffer) and in hydrocarbon solvents with 193-, 214-, and 228-nm light sources. The major products are the isomeric dienes from electrocyclic ring opening and 2-butyne + alkene (ethylene or E-/Z- 2-butene) due to formal [2+2]-cycloreversion. The total yields of dienes relative to 2-butyne are generally higher in the gas phase than in solution but decrease with increasing excitation wavelength under both sets of conditions. In the case of cis-1,2,3,4-tetramethylcyclobutene, 228-nm photolysis results in the stereospecific formation of E,Z-3,4-dimethyl-2,4-hexadiene - the isomer corresponding to ring opening by the thermally allowed (conrotatory) electrocyclic pathway - in both the gas phase and solution. All three diene isomers are obtained upon 228-nm photolysis of trans-1,2,3,4-tetramethylcyclobutene, but control experiments suggest that the thermally allowed isomers (E,E- and Z,Z-3,4-dimethyl-2,3-hexadiene) are probably the primary products in this case as well. The results are consistent with cycloreversion resulting from excitation of the low-lying π,R(3s) singlet state and with ring opening proceeding by at least two different mechanisms depending on excitation wavelength. The first, which dominates at short wavelengths, is thought to involve direct reaction of the second excited singlet (π,π*) state of the cyclobutene. The second mechanism, which dominates at long wavelengths, is proposed to ensue either directly from the lowest energy (Rydberg) state or from upper vibrational levels of the ground state, populated by internal conversion from this excited state.
- Leigh, William J.,Cook, Bruce H. O.
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p. 5256 - 5263
(2007/10/03)
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- Catalytic hydromagnesation of di- and polymethyl-substituted 1,3-butadienes
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Hydromagnesation of di- and polymethyl-substituted 1,3-butadienes with alkylmagnesium halides in the presence of Ni(PPh3)2Cl2 and NiPy4Cl2 was studied.
- Viktorov,Zubritskii
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p. 1755 - 1765
(2007/10/03)
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- Dehalogenation of organic halides by flash vacuum pyrolysis over magnesium: A versatile synthetic method
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Flash vacuum pyrolysis over magnesium at 600°C results in efficient dehalogenation of a variety of organic halides and provides a preparatively useful method for C-C bond formation and other reactions.
- Aitken, R. Alan,Hodgson, Philip K. G.,Oyewale, Adebayo O.,Morrison, John J.
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p. 1163 - 1164
(2007/10/03)
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- Thermal reaction of (CH3)2C=C(CH3)2 in the presence of di-tert-butyl peroxide; reactions of the radicals ·CH3, (CH3)3C·C(CH3)2 and (CH3)2C=C(CH3)·CH2
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A study of the thermal reaction of (CH3)2C=C(CH3)2 (23DMB2) in the presence of di-t-butyl peroxide (PODBT) at 389-451 K yielded kinetic data on some reactions of the radicals ·CH3, (CH3)3C·C(CH3)2 (1122TMP·) and (CH3)2C=C(CH3) ·CH2 (112TMA·). The ratio of the cross-combination ratios of the radicals o(112TMA·, 122TMP·)/φ(·CH3, 1122TMP·) and the rate constant for H-abstraction from 23DMB2 by ·CH3 relative to that of the recombination reaction, ·CH3 + (CH3)2C=C(CH3)2 → CH4 + (CH3)2C=C(CH3) ·CH2 (4) 2·CH3 → C2H6 (7) have been determined. The values are φ(1122TMP·, 112TMA·)/φ(·CH3, 1122TMP·) = 0.9 ± 0.3 log(k4/k71/2) = (3.74 ± 0.21) - (36.3 ± 2.2)/Θ where Θ = RT ln 10 and the units are dm3/2 mol-1/2 s-1/2 for k4/k71/2, and kJ mol-1 for the energy of activation.
- Koertvelyesi,Seres
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p. 253 - 273
(2007/10/03)
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- Solvent effect in pericyclic reactions. X. The cheletropic reaction
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The effect of the solvent on the cheletropic reaction of 3,4-dimethyl-2,5-dihydrothiophen-1,1-dioxide was kinetically investigated in 14 solvents. The rate constants of the forward reaction as well as those of the reverse process and the corresponding equilibrium constants were found to be linearly correlated with the E(T)(30) solvent polarity parameters. The solvent effect can be interpreted in terms of change of polarity during the activation process. The different response of the forward and reverse process to the increase of solvent polarity pointed out a clear difference between pericyclic reactions characterized by non-specific solvent effects and those whose medium effect is determined by the specific interaction between the FMO of solute and solvent.
- Desimoni,Faita,Garau,Righetti
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p. 6241 - 6248
(2007/10/03)
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- Cyclobutene photochemistry. Steric effects on the photochemical ring opening of alkylcyclobutenes
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Quantum yields for photochemical ring opening and cycloreversion in hydrocarbon solution have been determined for the direct photolysis (214 nm) of six 1,2-dimethylcyclobutene derivatives which contain methyl groups at C3, and C4 in numbers varying from zero to four. As the hydrogens on C3/C4 of the parent compound (1,2-dimethylcyclobutene) are replaced with increasing numbers of methyl groups, the total quantum yield for ring opening increases to a maximum of ~0.3 and then decreases with further methyl substitution. The quantum yields for ring opening (φtotal) of hexamethylcyclobutene and 1,2-dimethylcyclobutene are nearly the same, and the lowest in the series. The maximum occurs with trans-1,2,3,4-tetramethylcyclobutene; φtotal for the cis-isomer is significantly lower, but both yield an approximate 1:1 mixture of formally allowed and forbidden diene isomers. A similar trend is observed in the relative quantum yields for ring opening and cycloreversion throughout the series. The results are interpreted in terms of a combination of bond strength and steric effects on the efficiency of the ring-opening process. Increasing methyl substitution causes an increase in φtotal through the first three members of the series owing to progressive weakening of the C3-C4 bond. Compounds containing cis-dimethyl substitution exhibit substantially reduced quantum yields for ring opening, relative to what would be expected based on bond strength effects alone. This is proposed to be due to steric effects on the efficiency of the process, suggesting that the initial stages of the photochemical ring opening of cyclobutene involve disrotatory motions on the excited singlet state potential energy surface.
- Leigh, William J.,Postigo, J. Alberto
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p. 1688 - 1694
(2007/10/02)
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- Ketone Coupling on Reduced TiO2 (001) Surfaces: Evidence of Pinacol Formation
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Reductive coupling of acetone and acetophenone was investigated in temperature-programmed desorption (TPD) studies on both reduced (Ar(1+)-bombarded) and oxidized TiO2 (001) surfaces.The principal reaction product of either ketone on the reduced surface was a symmetric olefin with twice the carbon number of the reactant. 2,3-Diphenyl-2-butene comprised over 65percent of the volatile carbon-containing species desorbed from the reduced surface following acetophenone adsorption.The main side reactions which yielded products of the same carbon number as the reactants included deoxygenation to form olefins and deoxygenation plus hydrogenation to yield saturated species.The yield of reduction products was greatly diminished on the oxidized TiO2 (001) surface; the yield of 2,3-dimethyl-2-butene, the reductive coupling product of acetone, decreased 10-fold with respect to the yield from the reduced surface.This decrease in activity for reductive coupling is similar in scale to that observed for benzaldehyde coupling on the same surfaces, supporting the conclusion that both ketone and aldehyde coupling reactions occur at ensembles of Ti cations able to undergo a four-electron oxidation.Phenyl groups adjacent to the carbonyl carbon have the greatest effect on the carbonyl coupling reaction, giving significantly higher yield of the coupled olefin product.The observation of a small amount of the pinacol, 2,3-diphenyl-2,3-butanediol, during acetophenone TPD is the first direct evidence that the carbonyl coupling reaction on reduced TiO2 surfaces proceeds through a pinacolate intermediate, as it does for the McMurry reaction carried out in liquid-solid slurries.
- Pierce, Keith G.,Barteau, Mark A.
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p. 2405 - 2410
(2007/10/02)
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- Transformation of 1,2-diols over perfluorinated resinsulfonic acids (Nafion-H)
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The transformations of 1,2-diols over perfluorinated resinsulfonic acids (Nafion-H) were studied, and correlations were examined between the structures of the investigated diols, the possible dehydration routes and the catalytic properties of Nafion-H. Comparisons were also made between the catalytic properties of Nafion-H and NaHX zeolite. Because of its stronger acidity, Nafion-H functions at temperatures considerably lower than those for the usual dehydrating catalysts, e.g. the zeolites. As is well established for other solid electrophilic catalysts, the dehydration of 1,2-diols mainly proceeds via the pinacol rearrangement. The lower temperatures and the stronger acidity of Nafion-H strongly favour the pinacol rearrangement versus 1,2-elimination. The reaction conditions are also advantageous for the formation of substituted 1,3-dioxolanes in a secondary condensation step between the unreacted diol and the primarily formed carbonyl compounds. Nafion-H gradually deactivates during long use, but it can be partially reactivated by washing with acetone.
- Bucsi,Bucsi, Imre,Molnar,Molnar, Arpad,Bartok,Bartok, Mihaly,Olah,Olah, George A.
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p. 8195 - 8202
(2007/10/02)
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- Reaktive Arsen-Heterocyclen. III. 3-Arsolene: Synthese und Reaktionen am Arsen
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3-Arsolenes (R=Ph, Me, t-Bu, Cl, R'=H, Me) are readily obtained from zirconocene-butadiene complexes and RAsCl2.Alkylation with methyl iodide gives arsonium salts (R=Ph, Me, t-Bu, R'=H, Me), treatment with sulphur gives sulphides (R=Me, t-Bu), while oxidation with Br2 or SO2Cl2 results in ring cleavage.From chloroarsolene substitution products (R=I, H, SPh, OMe, NMe2) as well as coupling products with As-As, As-O-As, and As-S-As units were synthesized.In addition, a number of arsolene complexes with the metals chromium, molybdenum, tungsten, and ruthenium is described. Key words: Arsolene; Zirconocene; Group 6; Ruthenium; Phosphorus
- Schenk, Wolfdieter A.,Voss, Eckhard
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- Thermal Reaction of the Isopropyl Radical with 2,3-Dimethylbut-2-ene
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The CH3CH(*)CH3 radical (iP*) initiated homogeneous gas-phase thermal reaction of 2,3-dimethylbut-2-ene has been studied at 490-540 K by means of the thermal decomposition of azoisopropane (AIP).The products were identified using gas-chromatography (GC) and gas chromatography-mass spectrometry (GC-MS).The rate constant for the decomposition of AIP: AIP -> 2 CH3CH(*)CH3 + N2 (1) is log(k1/s-1) = (16.36 +/- 0.49) - (201.5 +/- 5.4) kJ mol-1/θ, where θ = RTln 10.The rate constant of the H-abstraction yielding the 1,1,2-trimethylallyl radical (TMA*) relative to the corresponding self-combination was determined for the first time.CH3CH(*)CH3 + (CH3)2C=C(CH3)2 -> C3H8 + (CH3)2C=C(CH3)CH2(*) (2), CH3CH(*)CH3 + CH3CH(*)CH3 -> (CH3)2CHCH(CH3)2 (9) log2/k91/2)/dm3/2 mol-1/2> = (4.99 +/- 0.49) - (57.0 +/- 5.4) kJ mol-1/θ.The TMA* formed in the reaction (2) combines with iP* terminally and non-terminally.The ratio of the rate constants was found to be independent of temperature: k10/k11 = 2.8 +/- 0.1. iP* disproportionates with both iP* and TMA*.The disproportionation-combination ratios determined are Δ (iP*, iP*) = 0.58 +/- 0.06 and Δ (iP*, TMA*) = 0.03 +/- 0.01.
- Koertvelyesi, Tamas,Seres, Laszlo
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p. 2445 - 2450
(2007/10/02)
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- The Kinetics of Pyrolysis of 1,3,3-Trimethylcyclopropene. Evidence for the Involvement of Alkylidene Carbenes in the Thermal Isomerisation of Cyclopropenes
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A low yield of 4-methylpent-2-yne in the gas-phase isomerisation of 1,3,3-trimethylcyclopropene is shown to be more consistent with an alkylidene carbene transient than with a 1,3-biradical intermediate.
- Walsh, Robin,Wolf, Christian,Untiedt, Sven,Meijere, Armin de
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p. 421 - 422
(2007/10/02)
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- SILICON-CONTAINING HETEROCYCLES. LIX. EFFECTS OF SUBSTITUENTS AT SILICON ON THE RETRODIENE DECOMPOSITION OF SILACYCLOPENTENES IN THE GAS PHASE
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The rate of exchange reactions in the silacyclopentene-diene system is determined by the rate of retrodiene decomposition of the heterocycle.The rate constants for the retrodiene decomposition of 1,1-dichloro-, 1,1-difluoro-, and 1,1-dimethyl-1-silacyclo-3-pentene have been measured.Electron-acceptor substituents (Cl and F) at silicon accelerate, and electron-donor substituents (Me) retard the rate of decomposition of silacyclopentenes and exchange reactions.In the gas phase, 2,3-dimethyl-1,3-butadiene adds dichlorosilylene at the double bonds twice as rapidly as does 1,3-butadiene.
- Chernyshev, E. A.,Bykovchenko, V. G.,Komalenkova, N. G.,Kel'man, M. Ya.,Kisileva, T. S.,Shevchenko, O. V.
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p. 143 - 146
(2007/10/02)
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- Novel synthesis of (η3-allyl)platinum(II) complexes from enol triflates and simple olefins and their regiospecific deprotonation
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Reaction of bis(triphenylphosphine)(ethylene)platinum(0) (1) with alkylvinyl triflates 2a-c in ethylene-saturated solutions, exclusively yields the stable cationic (η3-allyl)platinum(II) complexes 5a-c. Solution chemistry establishes that the reaction proceeds through the intermediacy of σ-vinyl complexes 3a-c followed by rate-limiting ethylene migratory insertion. The interaction of 3a with propylene regiospecifically produces η3-allyl complex 6. The σ-vinyl adducts 3b,c were not isolable, but were characterized in situ by NMR spectroscopy. A single-crystal molecular structure determination is reported for 5b. Heating 6 and 5b in the presence of triethylamine at as low as 50 °C in THF cleanly affords 2,3-dimethylbutadiene (16) and 2-methyl-1,3-pentadiene (17), respectively.
- Zhong, Zhandong,Hinkle, Robert J.,Arif, Atta M.,Stang, Peter J.
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p. 6196 - 6202
(2007/10/02)
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- Preparation of conjugated dienes
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A process for the preparation of a compound of general formula STR1 in which R1 represents a hydrogen atom or a methyl group, one of R2 and R3 represents a hydrogen atom and the other of R2 and R3 is the same as R1, which comprises reacting a compound of the general formula with a salt of formic acid in the presence of a catalyst system comprising a palladium salt and a phosphorus compound of general formula in which n is 0,1,2 or 3 and each X independently represents an alkyl, alkenyl, aryl, aralkyl, alkaryl or cycloalkyl group, and recovering the desired compound of formula (I).
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