- Thermally stable homogeneous catalysts for alkane dehydrogenation
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Thermostability is conditio sine qua non (a necessity) if organometallic compounds are used in the homogeneous catalysis of endothermic processes such as the dehydrogenation of alkanes to alkenes and hydrogen (see scheme). This thermostability and other requirements for such a catalyst are fulfilled by the anthraphos iridium(III)dihydride complex 1.
- Haenel, Matthias W.,Oevers, Stephan,Angermund, Klaus,Kaska, William C.,Fan, Hua-Jun,Hall, Michael B.
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Read Online
- Studies on partial hydrogenation of 1,5,9-cyclo-dodecatriene towards cyclo-dodecene
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The selective hydrogenation of 1,5,9-cis,trans,trans-cyclo-dodecatriene (1,5,9-ctt-CDT) towards cyclo-dodecene (CDE) depends strongly on the pressure of hydrogen, respectively the hydrogenation rate. High yields of CDE (>90%) can only be reached at extremely low hydrogen pressure. In order to elucidate this exceptional reaction performance the course of reaction has been studied for a wide range of hydrogen pressure, 0.01>pH2>2.5MPa, taking into consideration data of other research groups. The CDT hydrogenations were discontinuously carried out in liquid phase on Pd/Al2O3 at T = 353 K. The resulting hypothesis of this study is that the very low reaction rate at low pH2 is necessary in order to realize a dense surface coverage of 1,5,9-CDT and 1,5-cyclo-dodecadiene (CDD) isomers where these molecules show adsorption on Pd via two double bonds so that readsorption of formed CDE and subsequent hydrogenation to cyclo-dodecane (CDA) is hardly possible. On the whole this new hypothesis on the reaction course of CDT hydrogenation gives a sound and fully consistent view on this rather complicated reaction.
- Gaube,David,Sanchayan,Wuchter,Klein
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Read Online
- Direct and Unified Access to Carbon Radicals from Aliphatic Alcohols by Cost-Efficient Titanium-Mediated Homolytic C?OH Bond Cleavage
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Low-valent Ti-mediated homolytic C?O bond cleavage offers unified access to carbon radicals from ubiquitous non-activated tertiary, secondary, and even primary alcohols. In contrast to the representative Ti reagents, which were ineffective for this purpos
- Suga, Takuya,Takahashi, Yuuki,Miki, Chinatsu,Ukaji, Yutaka
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- Method for Preparing Cyclododecene and Synthesis Device Therefor
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A method for preparing cyclododecene and a synthesis device therefor, of the present invention, remarkably increase the conversion ratio of cyclododecatriene and selectivity of cyclododecene, can minimize the costs required for equipment and processing, are practical, reduce processing time, and are industrially advantageous to mass production in comparison with a conventional method and device.
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Paragraph 0082-0119
(2021/03/13)
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- Hydrogenation of 1,5,9-Cyclododecatriene in a Three-Phase System in the Presence of Nickel Nanoparticles Supported on NаX Zeolite
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The hydrogenation of 1,5,9-cyclododecatriene in the presence of nanostructured Ni catalysts, supported with NaX zeolite, in a flow-through reactor at atmospheric hydrogen pressure was investigated. Nickel nanoparticles on the support surface were prepared by chemical reduction of the precursor (NiCl2) with NaBH4 and NH2NH2. The effect exerted on the yield of hydrogenation products by the nominal residence time of the gas phase in the reaction zone and by the process temperature was considered, and the catalyst operation life was analyzed. The catalysts showed high activity and allowed preparation of cyclododecane in ~100% yield at a process temperature of up to 160°С.
- Nebykov,Popov, Yu. V.,Mokhov,Shcherbakova,Zotov, Yu. L.
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p. 110 - 115
(2021/03/18)
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- METHOD FOR MANUFACTURING CYCLODODECANONE AND APPARATUS FOR MANUFACTURING THE SAME
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A method for manufacturing cyclododecanone according to the present invention has an effect of having a significantly high conversion rate of cyclododecene and selectivity of cyclododecanone, can minimize the cost used for equipment and processes, is practical, and has an advantageous effect on industrial mass production compared to the prior art by significantly reducing a reaction residence time and a required reaction volume of a reactor.COPYRIGHT KIPO 2019
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Paragraph 0082-0083
(2020/05/14)
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- Process for producing laurolactam and its synthesis apparatus
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A method for manufacturing laurolactam and a synthesis apparatus thereof according to the present invention have a remarkably high conversion rate of raw materials and selectivity of a target compound, have an effect of synthesizing the target compound with a high yield and high purity, can minimize costs used for equipment and processes, are practical, and have an advantage of being more simplified compared to the prior art.COPYRIGHT KIPO 2019
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Paragraph 0082-0084
(2020/05/14)
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- Colloid and Nanosized Catalysts in Organic Synthesis: XIX.1 Influence of the Support Nature on Hydrogenation Catalysis of Cyclic Olefins by Nickel Nanoparticles
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Gas-phase hydrogenation of cycloalkenes in the presence of nickel nanoparticles supported on Ceokar-2, BAU-A activated carbon, alumina, and NaX zeolite proceeds at 140–240°C and atmospheric pressure of hydrogen. The conversion and selectivity depend on the type of support and on the hydrogen excess.
- Popov, Yu. V.,Mokhov,Nebykov,Shcherbakova,Dontsova
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- A long-tethered (P-B-P)-pincer ligand: Synthesis, complexation, and application to catalytic dehydrogenation of alkanes
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A new long-tethered boron-containing (P-B-P)-pincer ligand 8 has been synthesized. Complexation of 8 with [Ir(coe)2Cl]2 (coe = cyclooctene) resulted in (P-B-P)(hydrido)chloroiridium complex (P-B-P)Ir(H)Cl 9. Subsequent reaction with nBuLi led to the formation of dihydride complex (P-B-P)Ir(H)210. Both complexes were found to be moderately active for the catalytic dehydrogenation of alkanes.
- Kwan, Enrique Huang,Kawai, Yasushi Jack,Kamakura, Sei,Yamashita, Makoto
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p. 15931 - 15941
(2016/10/22)
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- 2,2,6,6-Tetramethylpiperidinium triflate (TMPT): a highly selective and self-separated catalyst for esterification
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An eco-friendly and readily accessible 2,2,6,6-tetramethylpiperidinium triflate was found as highly-selective and self-separated catalyst for esterification under solvent-free condition. The X-ray crystallography revealed that it formed a ‘hydrophobic wall’ which could effectively eliminate the generated water from the reactive sites. Moreover, it could precipitate from the reaction system with excellent recovery ratio (>99%) and be reused for ten times without any significant loss of activity.
- Gao, Lan,Liu, Taoping,Tao, Xiaochun,Huang, Yongmin
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p. 4905 - 4909
(2016/10/24)
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- Colloidal and nanosized catalysts in organic synthesis: XV. Gas-phase hydrogenation of alkenes catalyzed by supported nickel nanoparticles
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Gas-phase hydrogenation of alkenes and their derivatives, catalyzed by nickel nanoparticles supported on zeolite or silica gel support occurs at 150–250°С and an atmospheric hydrogen pressure and results in a high conversion. The selectivity of the hydrogenation depends on the amount of hydrogen: at a low diene (triene)–hydrogen ratio, selective hydrogenation of one multiple bond in the substrate is possible.
- Popov, Yu. V.,Mokhov,Nebykov,Latyshova,Panov,Dontsova,Shirkhanyan,Shcherbakova
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p. 2589 - 2593
(2017/03/22)
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- The Retro-Hydroformylation Reaction
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Hydroformylation, a reaction that adds carbon monoxide and dihydrogen across an unsaturated carbon-carbon multiple bond, has been widely employed in the chemical industry since its discovery in 1938. In contrast, the reverse reaction, retro-hydroformylation, has seldom been studied. The retro-hydroformylation reaction of an aldehyde into an alkene and synthesis gas (a mixture of carbon monoxide and dihydrogen) in the presence of a cyclopentadienyl iridium catalyst is now reported. Aliphatic aldehydes were converted into the corresponding alkenes in up to 91 % yield with concomitant release of carbon monoxide and dihydrogen. Mechanistic control experiments indicated that the reaction proceeds by retro-hydroformylation and not by a sequential decarbonylation-dehydrogenation or dehydrogenation-decarbonylation process.
- Kusumoto, Shuhei,Tatsuki, Toshiumi,Nozaki, Kyoko
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supporting information
p. 8458 - 8461
(2015/11/27)
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- TRANSITION METAL CATALYSTS FOR C-O HYDROGENOLYSIS AND HYDRODEOXYGENATION
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Phosphoranimide-metal catalysts and their role in C—O bond hydrogenolysis and hydrodeoxygenation (HDO) are disclosed. The catalysts comprise of first row transition metals such as nickel, cobalt and iron. The catalysts have a metal to anionic phosphoranimide ratio of 1:1 and catalyze C—O bond hydrogenolyses of a range of oxygen-containing organic compounds under lower temperature and pressure conditions than those commonly used in industrial hydrodeoxygenation.
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Paragraph 0153; 0154
(2014/07/08)
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- The carbon material functionalized with NH2+ and SO3H groups catalyzed esterification with high activity and selectivity
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A novel carbon-based solid acid was conveniently prepared by heating a mixture of d-glucose, p-toluenesulfonic acid and diphenylammonium tosylate. Its structure was measured by XRD, FT-IR, XPS, 13C MAS NMR and EA to illustrate that the carbon material has been functionalized with NH2+ and SO3H groups and has a strong "hydrophobic effect". It can be used to catalyze the esterification reaction of carboxylic acids with equimolar amounts of sterically demanding and acid-sensitive alcohols with high reactivity (yield up to 90%) and selectivity (up to 95%) in heptane at 80 °C. It could be easily recovered and reused more than ten times without loss of activity.
- Zhan, Shaoqi,Tao, Xiaochun,Cai, Liangzhen,Liu, Xiaohui,Liu, Taoping
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supporting information
p. 4649 - 4653
(2015/02/19)
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- Sulfonated polypyrene (S-PPR) as efficient catalyst for esterification of carboxylic acids with equimolar amounts of alcohols without removing water
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Sulfonated polypyrene (S-PPR) efficiently catalyzed the reactions between carboxylic acids and equimolar amounts of alcohols with and without heptane to give the corresponding esters in good to excellent yields. Esterification was carried out at 110 °C without removing water. Transesterification of carboxylic esters with a slight excess of alcohols smoothly proceeded without heptane to give the corresponding esters in good yields. For these reactions, S-PPR was recycled without significant loss of activities.
- Tanemura, Kiyoshi,Suzuki, Tsuneo
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p. 1972 - 1975
(2013/04/23)
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- Hydroacetoxylation of olefins with acetic acid genetated in situ from vinyl acetate in the presence of ruthenium complexes
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Ruthenium complexes catalyze the decomposition of vinyl acetate releasing the acetic acid and its subsequent addition to linear and cyclic olefins.
- Khusnutdinov,Shchadneva,Khisamova,Dzhemilev
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body text
p. 155 - 160
(2011/05/03)
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- Mixed disproportionation versus radical trapping in titanocene(III)-promoted epoxide openings
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The formation of either deoxygenation products or allylic alcohols from epoxides is observed when these substrates are treated with Cp2TiCl under anhydrous conditions. It seems that processes via trisubstituted radicals give allylic alcohols whereas processes via disubstituted radicals may give deoxygenation products or allylic alcohols depending on the structure of the original epoxide. This method allows a controlled access to these functional groups, providing a useful tool in organic synthesis. A mechanistic discussion for these transformations is reported.
- Justicia, José,Jiménez, Tania,Morcillo, Sara P.,Cuerva, Juan M.,Oltra, J. Enrique
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experimental part
p. 10837 - 10841
(2010/02/28)
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- Lewis acid-promoted electron transfer deoxygenation of epoxides, sulfoxides, and amine N-oxides: the role of low-valent niobium complexes from NbCl5 and Zn
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A mild and operationally simple deoxygenation of epoxides, sulfoxides, and amine N-oxides is described using a sub-stoichiometric amount of low-valent niobium complexes generated in situ from commercially available NbCl5 and zinc dust. The deoxygenation proceeds by a reductive cleavage of polarized O-C/O-N/O-S bonds through a single electron transfer from zinc metal to the niobium-substrate complex due to the high oxophilic nature of the niobium species. The presence of adjacent radical-stabilizing groups is beneficial to epoxide substrates; however the similar prerequisite does not apply to sulfoxides and amine N-oxides, where a broad range of substrates are efficiently deoxygenated in excellent yields.
- Oh, Kyungsoo,Knabe, William Eric
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experimental part
p. 2966 - 2974
(2009/05/30)
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- Bimetallic Ru-Sn nanoparticle catalysts for the solvent-free selective hydrogenation of 1,5,9-cyclododecatriene to cyclododecene
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(Figure Presented) Tin(n)y catalysts: Bimetallic RuSn supported nanoparticle catalysts (see picture; Ru green, Sn blue, O red), prepared from the carbonyl-cluster precursors [Ru4 (μ4-SnPh) 2(μ-SnPh2)4-x(CO)12-x] (x = 0, 2, 3, 4) are shown to be active catalysts for the highly selective hydrogenation of 1,5,9-cyclododecatriene to cyclododecene under mild conditions.
- Adams, Richard D.,Boswell, Erin M.,Captain, Burjor,Hungria, Ana B.,Midgley, Paul A.,Raja, Robert,Thomas, John Meurig
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p. 8182 - 8185
(2008/09/18)
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- One-pot synthesis of substituted styrenes from vicinal dibromoalkanes and arylboronic acids
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Dehydrobromination of vicinal dibromoalkanes in systems comprising 1,2-dimethoxy-ethane, N-butyl-N′-methylimidazolium tetrafluoroborate (or tetrabutylammonium bromide), and a base with subsequent palladium-catalyzed cross-coupling of the thus formed bromoalkenes with arylboronic acids furnished substituted styrenes. Springer Science+Business Media, Inc. 2007.
- Tikhonov,Vasil'ev,Chirskaya,Struchkova,Merkulova,Zlotin
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p. 122 - 129
(2008/02/08)
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- An efficient method for chlorination of alcohols using PPh3/Cl3CCONH2
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A new and convenient method for the chlorination of alcohols utilizing PPh3/Cl3CCONH2 is addressed. Various alcohols could smoothly be converted into their corresponding alkyl chlorides in high yield under mild conditions with short reaction times. A mechanism is disclosed with the evidence of inversion of configuration of the analogous alkyl chloride derived from R-(-)-2-octanol.
- Pluempanupat, Wanchai,Chavasiri, Warinthorn
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p. 6821 - 6823
(2007/10/03)
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- Rapid conversion of hindered arylsulfonates to alkyl chlorides with retention of configuration
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Arylsulfonates of hindered secondary alcohols are converted to the corresponding alkyl chlorides very rapidly and in good yields in the presence of titanium tetrachloride at low temperatures. These reactions proceed with exclusive retention of configuration.
- Lepore, Salvatore D.,Bhunia, Anjan K.,Mondal, Deboprosad,Cohn, Pamela C.,Lefkowitz, Craig
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p. 3285 - 3286
(2007/10/03)
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- METHOD FOR PRODUCING ESTER AND ESTERIFICATION CATALYST
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A process for producing an ester includes the step of allowing a carboxylic acid to react with an alcohol, wherein an ammonium sulfonate is used as an esterification catalyst, the ammonium sulfonate being composed of an ammonium cation having a basic skeleton represented by formula (1) (wherein n represents 1 or 2) in which hydrogen atoms in the benzene rings and hydrogen atoms bonded to bridge carbon may be substituted), and a sulfonic acid anion represented by RSO 3 - (wherein R represents an arene, a perfluoroalkane having 1 to 8 carbon atoms, or a bulky alkane).
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Page/Page column 5-6; 14; 20
(2008/06/13)
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- Bulky diarylammonium arenesulfonates as mild and extremely active dehydrative ester condensation catalysts
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More environmentally benign alternatives to current chemical processes, especially large-scale, fundamental reactions like ester condensations, are highly desirable for many reactions. Bulky diarylammonium pentafluorobenzenesulfonates and tosylates serve as extremely active dehydration catalysts for the ester condensation reaction of carboxylic acids with equimolar amounts of sterically demanding alcohols and acid-sensitive alcohols. Typically, the esterification reaction is performed in heptane by heating at 80°C in the presence of 1 mol% of the catalyst without removing water. Esterification with primary alcohols proceeds without solvents even at room temperature. Furthermore, 4-(N-mesitylamino)polystyrene resin-bound pentafluorobenzenesulfonate can be recycled more than 10 times without a loss of activity.
- Sakakura, Akira,Nakagawa, Shoko,Ishihara, Kazuaki
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p. 422 - 433
(2007/10/03)
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- METHOD OF FLUORINATION
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A method of fluorination comprising reacting monosaccharides, oligosaccharides, polysaccharides, composite saccharides formed by bonding of these saccharides with proteins and lipids and saccharides having polyalcohols, aldehydes, ketones and acids of the polyalcohols, and derivatives and condensates of these compounds with a fluorinating agent represented by general formula (I) thermally or under irradiation with microwave or an electromagnetic wave having a wavelength around the microwave region. In accordance with the method, the fluorination at a selected position can be conducted safely at a temperature in the range of 150 to 200°C where the reaction is difficult in accordance with conventional methods. The above method comprising the irradiation with microwave or an electromagnetic wave having a wavelength around the microwave region can be applied to substrates other than saccharides. When a complex compound comprising HF and a base is reacted under irradiation with microwave, fluorination at a specific position which is difficult in accordance with conventional methods proceeds highly selectively, efficiently in a short time and safely.
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Page/Page column 14
(2008/06/13)
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- Conversion of alkyl halides into alcohols via formyloxylation reaction with DMF catalyzed by silver salts
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The transformation of alkyl halides into alcohols via a two-step process based on the reaction with DMF catalyzed by Ag(I) salts followed by acid or basic hydrolysis of the intermediate formate ester has been evaluated. The results show that a large variety of primary and some secondary alkyl halides can be transformed efficiently into the corresponding alcohols, making this alkyl halide to alcohol interconversion a valuable alternative to the existing procedures, particularly in molecules with labile functional groups that are generally involved in multistep synthesis. Georg Thieme Verlag Stuttgart.
- Abad, Antonio,Agullo, Consuelo,Cunat, Ana C.,Navarro, Ismael
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p. 3355 - 3361
(2007/10/03)
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- A mild and efficient protocol for the conversion of carboxylic acids to olefins by a catalytic decarbonylative elimination reaction
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A new method for the conversion of aliphatic carboxylic acids to olefins under unprecedented mild conditions is disclosed, wherein the carboxylic acids are converted in situ with pivalic anhydride to the mixed anhydrides, which regioselectively add to a PdCl2-DPE-Phos catalyst. At a temperature of only 110°C, smooth decarbonylation and β-hydride elimination occur, and the corresponding olefins along with CO, CO2 and pivalic acid are liberated.
- Goossen, Lukas J.,Rodriguez, Nuria
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p. 724 - 725
(2007/10/03)
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- Selective hydrogenation of cyclododecatriene to cyclododecene
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A method for the production of cyclododecene (CDEN) by selective gas-phase hydrogenation of cyclododecatriene (CDT) and/or cyclododecadiene (CDD) involves using a solid-bed reactor in which the bed number (Bo) is more than 100 (Bo = product of average flow rate and length of flow tube divided by axial diffusion coefficient).
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Page column 8
(2008/06/13)
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- (E)-Cycloalkenes and (E,E)-cycloalkadienes by ring closing diyne- or enyne-yne metathesis/semi-reduction
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A concise, practical and stereoselective entry into macrocyclic (E)-alkenes is outlined comprising a sequence of ring closing alkyne metathesis (RCAM), trans-selective hydrosilylation of the resulting cycloalkynes catalyzed by [Cp*Ru(MeCN)3]PF6, and a protodesilylation of the ensuing vinylsilanes with AgF in aq. THF/MeOH. Moreover, the first examples of intramolecular enyne-yne metathesis reactions catalyzed by the Schrock alkylidyne complex (tBuO)3WCCMe3 are reported; the resulting cyclic enynes can be converted along similar lines into the corresponding (E,E)-configured 1,3-dienes in good overall yields. Cycloalkyne 4 and the (E)-configured cyclic olefins 6 and 21 were characterized by X-ray crystallography.
- Lacombe, Fabrice,Radkowski, Karin,Seidel, Günter,Fürstner, Alois
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p. 7315 - 7324
(2007/10/03)
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- A facile route to olefins from vic-diols via cyclic sulfates with triphenylphosphine and iodine
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Treatment of cyclic sulfates of vic-diols with triphenylphosphine and iodine offers the corresponding olefins in high yields at room temperature. Both cyclic sulfates of d,l-hydrobenzoin and meso-hydrobenzoin give trans- stilbene.
- Jang, Doo Ok,Joo, Yung Hyup,Cho, Dae Hyan
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p. 2379 - 2386
(2007/10/03)
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- Fluorination of secondary and primary alcohols by thermal decomposition of electrochemically generated alkoxy triphenylphosphonium tetrafluoroborates
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Replacement of hydroxyl groups in secondary and primary alcohols (1) with a fluorine atom arising from tetrafluoroborate anion has been performed by the electrochemical formation of alkoxy triphenylphosphonium tetrafluoroborates (2) from 1, followed by their thermal decomposition. The procedure is quite simple, involving: (1) constant-current electrolysis of a mixture of 1, Ph3P, and Ph3PH·BF4 in CH2Cl2 in an undivided cell; (2) refluxing a tetrahydrofuran or dioxane solution of the residue afforded by evaporation of the solvent in vacuo after the electrolysis. Cyclic secondary alcohols such as 3β-hydroxy steroids and 2-adamantanol are transformed into the corresponding fluorides in satisfactory yields when the geometry of the leaving group in 2 is suitable for the substitution or an elimination process for 2 to give an alkene is stereochemically forbidden. The fluorination of steroidal alcohols and 4-phenyl-1-cyclohexanol proceeded with complete inversion, demonstrating that a fluorine atom from the tetrafluoroborate anion attacks from the side opposite to the phosphonium moiety in 2 via an SN2 mechanism rather than an SN1 mechanism. The fluorination of acyclic secondary and primary alcohols was performed by the present method in reasonable yields, although the reaction for the latter required more forcing conditions, such as refluxing in dioxane.
- Maeda, Hatsuo,Koide, Takashi,Matsumoto, Sayaka,Ohmori, Hidenobu
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p. 1480 - 1483
(2007/10/03)
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- OXIDATIVE SUBSTITUTION OF PhTe AND PhSe MOIETIES IN ALKYL PHENYL TELLURIDES AND SELENIDES LEADING TO ESTERS AND ALCOHOLS
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Oxidation of alkyl phenyl tellurides and/or selenides with sodium periodate (NaIO4) in aqueous acetic acid or with metachloroperbenzoic acid (MCPBA) in N,N-dimethylformamide or N,N-dimethylacetamide affords a mixture of the corresponding alkyl esters (acetates or formates) and/or alcohols in 20-94percent yield under mild conditions (at 20-80 deg C for 0.5-24 h).
- Hirai, Yasuyuki,Ohe, Kouichi,Toshimitsu, Akio,Uemura, Sakae
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p. 173 - 176
(2007/10/02)
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- Nucleophilic Reactions of Acetals, Alkyl Sulfonates, and Oxiranes with Diisobutylaluminum Benzenetellurolate
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Diisobutylaluminum benzenetellurolate was proved to be an effective nucleophilic reagent toward acetals, alkyl sulfonates, and oxiranes to give the corresponding tellurides.These reactions showed the characteristics of an SN2 type.When the substitution reactions were sterically hindered, olefins and allylic alcohols were obtained from alkyl sulfonates and oxiranes, respectively.
- Sasaki, Kazuaki,Mori, Toshiharu,Doi, Yoshitaka,Kawachi, Akinori,Aso, Yoshio,et al.
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p. 415 - 418
(2007/10/02)
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- On the mechanism of deoxygenation of secondary alcohols by tin hydride reduction of methyl xanthates and other thiocarbonyl derivatives
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The room temperature deoxygenation of xanthates and thionocarbonates using (n - Bu) 3Sn-H - Et3B - air has been studied, especially with 119Sn N.M.R. spectroscopy. The orignal conception of tin radical attack on thiocarbonyl is confirmed.
- Barton,Jang,Jaszberenyi Cs.
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p. 3991 - 3994
(2007/10/02)
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- Triethylborane-Induced Hydrodehalogenation of Organic Halides by Tin Hydrides
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The reduction of organic halides with tributyltin hydride in the presence of a catalytic amount of triethylborane has been studied. (1) Alkyl iodides and alkyl bromides reacted easily with tin hydride at -78 deg C to give the corresponding hydrocarbons, while alkyl chlorides were sluggish to react and recovered unchanged. (2) The reduction of alkenyl halides such as 1-deuterio-1-iodo-1-dodecene and 1-iodo-1-triethylsilyl-1-dodecene proceeded nonstereospecifically. (3) The reduction of aryl halides with n-Bu3SnH-Et3B system was not so effective as the reduction of alkyl halides and alkenyl halides.Whereas aryl iodides were reduced at room temperature with n-Bu3SnH, aryl bromides hardly reacted with n-Bu3SnH even at 80 deg C.
- Miura, Katsukiyo,Ichinose, Yoshifumi,Nozaki, Kyoko,Fugami, Keigo,Oshima, Koichiro,Utimoto, Kiitiro
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p. 143 - 147
(2007/10/02)
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- Preparation of Alkylchromium Reagents by Reduction of Alkyl Halides with Chromium(II) Chloride under Cobalt Catalysis
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Alkyl halides and tosylates are reduced with CrCl2 in the presence of a catalytic amount of vitamin B12 or cobalt phthalocyanine to give alkylchromium reagents, which add to aldehydes without affecting the coexisting ketone or ester groups.
- Takai, Kazuhiko,Nitta, Kenji,Fujimura, Osamu,Utimoto, Kiitiro
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p. 4732 - 4734
(2007/10/02)
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- Dehydration of Alcohols Catalysed by Metallic Sulphates Supported on Silica Gel
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Many metallic sulphates and hydrogen sulphates supported on silica gel efficiently catalyse dehydration of secondary and tertiary alcohols under mild conditions.The sulphates of CeIV, TiIV, and FeIII were most active.Silica gel was essential for the efficient dehydration in each case.The dehydration catalysed by Fe2(SO4)3, CuSO4, and NaHSO4 on silica gel was studied in detail.The order of the reactivity of alcohols was tertiary > secondary > primary.The dehydration activity of methanesulphonic acid was also enhanced (ca. 14 times at 90 deg C) by the presence of silica gel.Some mechanistic investigations were carried out.
- Nishiguchi, Takeshi,Kamio, Chizuko
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p. 707 - 710
(2007/10/02)
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- EPOXIDES AS ALKENE PROTECTING GROUPS. A MILD AND EFFICIENT DEOXYGENATION
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Dimethyl diazomalonate smoothly deoxygenates epoxides to alkenes with rhodium(II) acetate catalysis.
- Martin, Michael G.,Ganem, Bruce
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p. 251 - 254
(2007/10/02)
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- A New Stereospecific trans-Elimination of 2-Alkoxy- and 2-Cycloalkoxytropones to Alkenes and Cycloalkenes: the first Verification of the s8? + a2? + s2?> Process
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Solutions of 2-alkoxy- and 2-cycloalkoxy-tropones were heated to give alkenes and cycloalkenes respectively, without skeletal rearrangement, in good yields; deuterium labelling studies confirmed a stereospecific trans-elimination, in a s8? + a2? + s2?> mode, with an interesting isotope effect and a large rate retardation.
- Takeshita, Hitoshi,Mametsuka, Hiroaki
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p. 483 - 484
(2007/10/02)
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- Highly Selective Carbon-Carbon Bond Forming Reactions Mediated by Chromium(II) Reagents
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A low valent chromium reagent is generated from chromium(III) chloride and a half mol of lithium aluminum hydride in tetrahydrofuran.The reagent behaves similarly to anhydrous chromium(II) chloride, which is commercially available, and reduces allylic halides to produce unisolable allylchromium species which add efficiently to aldehydes or ketones with high degree of stereo- and chemoselectivity.Particularly, high threo selectivity is observed in the reaction of aldehydes and 1-bromo-2-butene and is ascribed to a chair-like six-membered transition state.Simple reduction od allylic and benzylic halides produces biallyls and bibenzyls, while gem-dibromocyclopropanes afford the corresponding allenes in excellent yields.
- Hiyama, Tamejiro,Okude, Yoshitaka,Kimura, Keizo,Nozaki, Hitosi
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p. 561 - 568
(2007/10/02)
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- Cob(I)alamin als Katalysator. 6. Mitteilung . Bildung und Fragmentierung von Alkylcobalaminen, ein Gleichgewichtsprozess zwischen nukleophiler Addition und reduktiver Fragmentierung
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Isolated olefines can be saturated using catalytic amounts of cob(I)alamin in aqueous acetic acid; as electron source an excess of zinc dust is added to the solution containing the homogeneous catalyst.During this overall hydrogenation of isolated double bonds intermediate alkylcobalamins are formed (compare e.g.Schemes 2, 4, 5, 7 and 12).Clear evidence is presented that the nucleophilic attack on the isolated double bond is carried out by cob(I)alamin and not by cob(II)alamin also present in the system (see Scheme 3b and 3c).As this catalytic saturation of olefins depends on the pH of the solution, characterized by a slow reaction at pH=7.0 compared to the same reduction in aqueous acetic acid (see Scheme 2, 2 -> 4, and Scheme 3a), it is reasonable to accept the participation of an electrophilic attack by a proton during the generation of alkylcobalamins. - We use the term nucleophilic addition to describe the formation of alkylcobalamins from a proton, an olefin and cob(I)alamin (compare Schemes 4-7 and 12).A special sequence of experiments showed the nucleophilic addition to beregioselective.Preferentially the higher substituted alkylcobalamin revealed to be produced.Therefore, the nucleophilic addition of cob(I)alamin follows the Markownikoff rule (compare chap. 4: formation and fragmentation of β-hydroxyalkylcobalamins).Under the reaction conditions applied the intermediate alkylcobalamins can be present in base-on and base-off forms.They are known to exist as octahedral complexes and might also be stable to some extent as tetragonal-pyramidal species.In addition the base-off forms can partially be protonated at the dimethylbenzimidazole moiety in aqueous acetic acid (compare Scheme 12).From this equilibrium of intermediate alkylcobalamins three modes of decay disclosed to be possible: (i) The reductive fragmentation leading to an olefin, a proton, and cob(I)alamin is the formal retro-reaction of the nucleophilic addition (see Schemes 2, 4 and 6-12).This equilibrium of an associated alkylcobalamin and the corresponding dissociation products revealed to be a fast process compared to the reductive cleavage of the Co, C-bond cited below (s. (iii)). (ii) As the second reaction pattern an oxidative fragmentation producing an olefin, a hydroxy anion (or water, respectively) and cob(III)alamin has been observed (see Schemes 7, 8, 10 and 12). (iii) The slow reductive cleavage of the Co, C-bond, initiated by addition of electrons (see ), was the third reaction path observed (see Schemes 2, 4-8 and 10-12. - The stereochemistry of the three transformations originating from the intermediate alkylcobalamins is unknown up to now.The antiperiplanar pattern of the fragmentation reactions presented in the Schemes has been chosen arbitrarily (see e.g.Scheme 12).
- Fischli, Albert,Mueller, Peter Michael
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p. 529 - 554
(2007/10/02)
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