- Competitive catalytic hydrogenation in unsaturated hydrocarbon systems with sterically hindered double bonds
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A competitive hydrogenation of unsaturated hydrocarbons (α-methylstyrene, cyclohexene, 1-methyl-cyclohex-1-ene, 1-tert-butylcyclohex-1-ene and 3-terr-butylcyclohex-1-ene) in binary and ternary systems with palladium-, platinum- and rhodium-supported catal
- Kacer, Petr,Laate, Leiv,Cerveny, Libor
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Read Online
- Aromatic compound hydrogenation and hydrodeoxygenation method and application thereof
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The invention belongs to the technical field of medicines, and discloses an aromatic compound hydrogenation and hydrodeoxygenation method under mild conditions and application of the method in hydrogenation and hydrodeoxygenation reactions of the aromatic compounds and related mixtures. Specifically, the method comprises the following steps: contacting the aromatic compound or a mixture containing the aromatic compound with a catalyst and hydrogen with proper pressure in a solvent under a proper temperature condition, and reacting the hydrogen, the solvent and the aromatic compound under the action of the catalyst to obtain a corresponding hydrogenation product or/and a hydrodeoxygenation product without an oxygen-containing substituent group. The invention also discloses specific implementation conditions of the method and an aromatic compound structure type applicable to the method. The hydrogenation and hydrodeoxygenation reaction method used in the invention has the advantages of mild reaction conditions, high hydrodeoxygenation efficiency, wide substrate applicability, convenient post-treatment, and good laboratory and industrial application prospects.
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Paragraph 0094-0096; 0098; 0100-0104
(2021/05/29)
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- Light-Promoted Transfer of an Iridium Hydride in Alkyl Ether Cleavage
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A catalytic, light-promoted hydrosilylative cleavage reaction of alkyl ethers is reported. Initial studies are consistent with a mechanism involving heterolytic silane activation followed by delivery of a photohydride equivalent to a silyloxonium ion generated in situ. The catalyst resting state is a mixture of Cp*Ir(ppy)H (ppy = 2-phenylpyridine-κC,N) and a related hydride-bridged dimer. Trends in selectivity in substrate reduction are consistent with nonradical mechanisms for C-O bond scission. Irradiation of Cp*Ir(ppy)H with blue light is found to increase the rate of hydride delivery to an oxonium ion in a stoichiometric test. A comparable rate enhancement is found in carbonyl hydrosilylation catalysis, which operates through a related mechanism also involving Cp*Ir(ppy)H as the resting state.
- Fast, Caleb D.,Schley, Nathan D.
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supporting information
p. 3291 - 3297
(2021/10/12)
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- Organophotoredox/palladium dual catalytic decarboxylative Csp3-Csp3coupling of carboxylic acids and π-electrophiles
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A dual catalytic decarboxylative allylation and benzylation method for the construction of new C(sp3)-C(sp3) bonds between readily available carboxylic acids and functionally diverse carbonate electrophiles has been developed. The new process is mild, operationally simple, and has greatly improved upon the efficiency and generality of previous methodology. In addition, new insights into the reaction mechanism have been realized and provide further understanding of the harnessed reactivity.
- Cartwright, Kaitie C.,Tunge, Jon A.
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p. 8167 - 8175
(2020/09/09)
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- Iterative Preparation of Platinum Nanoparticles in an Amphiphilic Polymer Matrix: Regulation of Catalytic Activity in Hydrogenation
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We demonstrate that iteration of the seeded preparation of platinum nanoparticles dispersed in an amphiphilic polystyrene-poly(ethylene glycol) resin (ARP-Pt) regulates their catalytic activity in the hydrogenation of aromatic compounds in water. The catalytic activity of the fifth generation of ARP-Pt [G5] prepared through four iterations of the seeded preparation was far superior to that of the initial ARP-Pt [G1] in the hydrogenation of aromatic compounds in water.
- Hamasaka, Go,Osako, Takao,Srisa, Jakkrit,Torii, Kaoru,Uozumi, Yasuhiro
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supporting information
p. 147 - 152
(2020/01/23)
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- Selectivity and Mechanism of Iridium-Catalyzed Cyclohexyl Methyl Ether Cleavage
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Cationic bis(phosphine)iridium complexes are found to catalyze the cleavage of cyclohexyl methyl ethers by triethylsilane. Selectivity for C-O cleavage is determined by the relative rates of SN2 demethylation versus SN1 demethoxylation, with the axial or equatorial disposition of the silyloxonium ion intermediate acting as an important contributing factor. Modulation of the electron-donor power of the supporting phosphine ligands enables a switch in selectivity from demethylation of equatorial methyl ethers to 2° demethoxylation. Applications of these accessible catalysts to the selective demethoxylation of the 3α-methoxy group of cholic acid derivatives is demonstrated, including a switch in observed selectivity controlled by 7α-substitution. The resting state of the catalyst has been characterized for two phosphine derivatives, demonstrating that the observed switch in C-O cleavage selectivity likely results from electronic factors rather than from a major perturbation of the catalyst structure.
- Fast, Caleb D.,Jones, Caleb A. H.,Schley, Nathan D.
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p. 6450 - 6456
(2020/07/13)
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- Stereoselective Aromatic Ring Hydrogenation over Supported Rhodium Catalysts in Supercritical Carbon Dioxide Solvent
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The combination of supported rhodium metal catalysts and supercritical carbon dioxide solvent was effective for the stereoselective ring hydrogenations of aromatic compounds at low temperature. Higher solubility of hydrogen in supercritical carbon dioxide provides higher concentration of hydrogen on the rhodium surface, but lower that of the intermediate on rhodium surface, which suppresses the flipping of surface intermediate, leading to higher catalyst activities and cis selectivities to the corresponding ring-hydrogenated products as compared with those in organic solvents.
- Shirai,Hiyoshi,Rode
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p. 1926 - 1934
(2019/01/05)
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- Effect of the Crystallographic Phase of Ruthenium Nanosponges on Arene and Substituted-Arene Hydrogenation Activity
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Identifying crystal structure sensitivity of a catalyst for a particular reaction is an important issue in heterogeneous catalysis. In this context, the activity of different phases of ruthenium catalysts for benzene hydrogenation has not yet been investigated. The synthesis of hcp and fcc phases of ruthenium nanosponges by chemical reduction method has been described. Reduction of ruthenium chloride using ammonia borane (AB) and tert-butylamine borane (TBAB) as reducing agents gave ruthenium nanosponge in its hcp phase. On the other hand, reduction using sodium borohydride (SB) afforded ruthenium nanosponge in its fcc phase. The as prepared hcp ruthenium nanosponge was found to be catalytically more active compared to the as prepared fcc ruthenium nanosponge for hydrogenation of benzene. The hcp ruthenium nanosponge was found to be thermally stable and recyclable over several cycles. This self-supported hcp ruthenium nanosponge shows excellent catalytic activity towards hydrogenation of various substituted benzenes. Moreover, the ruthenium nanosponge catalyst was found to bring about selective hydrogenation of aromatic cores of phenols and aryl ethers to the respective alicyclic products without hydrogenolysis of the C?O bond.
- Ghosh, Sourav,Jagirdar, Balaji R.
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p. 3086 - 3095
(2018/05/29)
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- Polysilane-Immobilized Rh-Pt Bimetallic Nanoparticles as Powerful Arene Hydrogenation Catalysts: Synthesis, Reactions under Batch and Flow Conditions and Reaction Mechanism
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Hydrogenation of arenes is an important reaction not only for hydrogen storage and transport but also for the synthesis of functional molecules such as pharmaceuticals and biologically active compounds. Here, we describe the development of heterogeneous Rh-Pt bimetallic nanoparticle catalysts for the hydrogenation of arenes with inexpensive polysilane as support. The catalysts could be used in both batch and continuous-flow systems with high performance under mild conditions and showed wide substrate generality. In the continuous-flow system, the product could be obtained by simply passing the substrate and 1 atm H2 through a column packed with the catalyst. Remarkably, much higher catalytic performance was observed in the flow system than in the batch system, and extremely strong durability under continuous-flow conditions was demonstrated (>50 days continuous run; turnover number >3.4 × 105). Furthermore, details of the reaction mechanisms and the origin of different kinetics in batch and flow were studied, and the obtained knowledge was applied to develop completely selective arene hydrogenation of compounds containing two aromatic rings toward the synthesis of an active pharmaceutical ingredient.
- Miyamura, Hiroyuki,Suzuki, Aya,Yasukawa, Tomohiro,Kobayashi, Shu
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supporting information
p. 11325 - 11334
(2018/09/06)
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- Upgrading of aromatic compounds in bio-oil over ultrathin graphene encapsulated Ru nanoparticles
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Fast pyrolysis of biomass for bio-oil production is a direct route to renewable liquid fuels, but raw bio-oil must be upgraded in order to remove easily polymerized compounds (such as phenols and furfurals). Herein, a synthesis strategy for graphene encapsulated Ru nanoparticles (NPs) on carbon sheets (denoted as Ru@G-CS) and their excellent performance for the upgrading of raw bio-oil were reported. Ru@G-CS composites were prepared via the direct pyrolysis of mixed glucose, melamine and RuCl3 at varied temperatures (500-800 °C). Characterization indicated that very fine Ru NPs (2.5 ± 1.0 nm) that were encapsulated within 1-2 layered N-doped graphene were fabricated on N-doped carbon sheets (CS) in Ru@G-CS-700 (pyrolysis at 700 °C). And the Ru@G-CS-700 composite was highly active and stable for hydrogenation of unstable components in bio-oil (31 samples including phenols, furfurals and aromatics) even in aqueous media under mild conditions. This work provides a new protocol to the utilization of biomass, especially for the upgrading of bio-oil.
- Shi, Juanjuan,Zhao, Mengsi,Wang, Yingyu,Fu, Jie,Lu, Xiuyang,Hou, Zhaoyin
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supporting information
p. 5842 - 5848
(2016/05/24)
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- Selective hydrogenolysis of phenols and phenyl ethers to arenes through direct C-O cleavage over ruthenium-tungsten bifunctional catalysts
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Direct hydrogenolysis of the aromatic Csp2-O bonds in both phenols and phenyl ethers to form arenes selectively is a core enabling technology that can expand greatly the scope of chemical manufacture from biomass. However, conventional hydrogenolysis of phenols typically led to aromatic ring saturation instead of the cleavage of the Csp2-O bonds. Herein, we report a recyclable Ru-WOx bifunctional catalyst that showed high catalytic activities for the hydrogenolysis of a wide range of phenols and phenyl ethers, including dimeric lignin model compounds and the primitive phenols separated from pyrolysis lignin, to form arenes selectively in water. Preliminary mechanistic studies supported that the reactions occurred via a direct cleavage of the Csp2-O bonds and the concerted effects of the hydrogenating Ru sites and the Lewis acidic W sites are the key to such an unusual reactivity.
- Huang, Yao-Bing,Yan, Long,Chen, Meng-Yuan,Guo, Qing-Xiang,Fu, Yao
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p. 3010 - 3017
(2015/05/27)
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- Efficient and Practical Arene Hydrogenation by Heterogeneous Catalysts under Mild Conditions
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An efficient and practical arene hydrogenation procedure based on the use of heterogeneous platinum group catalysts has been developed. Rh/C is the most effective catalyst for the hydrogenation of the aromatic ring, which can be conducted in iPrOH under neutral conditions and at ordinary to medium H 2 pressures (10 atm). A variety of arenes such as alkylbenzenes, benzoic acids, pyridines, furans, are hydrogenated to the corresponding cyclohexyl and heterocyclic compounds in good to excellet yields. The use of Ru/C, less expensive than Rh/C, affords an effective and practical method for the hydrogenation of arenes including phenols. Both catalysts can be reused several times after simple filtration without any significant loss of catalytic activity.
- Maegawa, Tomohiro,Akashi, Akira,Yaguchi, Kiichiro,Iwasaki, Yohei,Shigetsura, Masahiro,Monguchi, Yasunari,Sajiki, Hironao
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experimental part
p. 6953 - 6963
(2010/02/28)
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- Toluates: unexpectedly versatile reagents
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The mechanism of the monoelectronic reduction of aromatic esters has been investigated. The unexpected synthetic utility of the toluate moiety in the deoxygenation of alcohols and the allylation of ketones is also reported. Finally, the use of aromatic esters as robust, though easily removable, protecting groups is depicted.
- Lam, Kevin,Markó, István E.
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experimental part
p. 10930 - 10940
(2010/02/28)
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- Using toluates as simple and versatile radical precursors
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(Chemical Equation Presented) The viability of the toluate moiety as a radical precursor has been examined by studying deoxygenation and cyclization reactions.
- Lam, Kevin,Marko, Istvan E.
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scheme or table
p. 2773 - 2776
(2009/05/30)
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- Nanoheterogeneous catalytic hydrogenation of arenes: Evaluation of the surfactant-stabilized aqueous ruthenium(O) colloidal suspension
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The hydrogenation of various aromatic compounds by a surfactant-stabilized aqueous ruthenium(O) colloidal suspension was investigated. The nanocatalysts in the size range of 2.5-3.5 nm were synthesized by reducing ruthenium trichloride salt with sodium borohydride and were stabilized by the highly water soluble N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl)ammonium chloride salt according to our classical approach. The efficient catalytic reactions were performed at room temperature and under hydrogen pressure. The effect of the stirring, namely magnetic stir bar or gas projection impeller, was also studied. A comparison with an analogous rhodium nanocatalyst is described.
- Nowicki, Audrey,Boulaire, Virginie Le,Roucoux, Alain
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p. 2326 - 2330
(2008/09/18)
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- Stereoselective hydrogenation of tert-butylphenols over charcoal-supported rhodium catalyst in supercritical carbon dioxide solvent
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Hydrogenation of 2-, 3-, and 4-tert-butylphenols was studied over a charcoal-supported rhodium catalyst in supercritical carbon dioxide (scCO2) solvent, and the results were compared with those in organic solvents. In the hydrogenation of 4-ter
- Hiyoshi, Norihito,Rode, Chandrashekhar V.,Sato, Osamu,Tetsuka, Hiroyuki,Shirai, Masayuki
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- A mild and facile method for complete hydrogenation of aromatic nuclei in water
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A mild and complete hydrogenation of aromatic rings catalyzed by heterogeneous 10% Rh/C proceeds at 80 °C in water under 5 atm of H 2 pressure. This method is applicable to the hydrogenation of various carbon and heteroaromatic compounds such as alkylbenzenes, biphenyls, pyridines and furans. Georg Thieme Verlag Stuttgart.
- Maegawa, Tomohiro,Akashi, Akira,Sajiki, Hironao
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p. 1440 - 1442
(2007/10/03)
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- Reduction of alkyl and vinyl sulfonates using the CuCl2· 2H2O-Li-DTBB(cat.) system
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The reduction of a series of alkyl mesylates, dimesylates and triflates to the corresponding hydrocarbons was efficiently performed using a reducing system composed of CuCl2·2H2O, an excess of lithium sand and a catalytic amount (5 mol%) of 4,4′-di-tert-butylbiphenyl (DTBB), in tetrahydrofuran at room temperature. The process was also applied to enol and dienol triflates affording alkenes and dienes, respectively. The use of the deuterated copper salt CuCl2·2D2O allowed the simple preparation of the corresponding deuterated products.
- Radivoy, Gabriel,Alonso, Francisco,Moglie, Yanina,Vitale, Cristian,Yus, Miguel
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p. 3859 - 3864
(2007/10/03)
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- Radical deoxygenation of hydroxyl groups via phosphites
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A highly efficient, two-step sequence method for the deoxygenation of hydroxyl groups has been developed. The method involves the preparation of the 2-(2-iodophenyl)ethyl methyl phosphite derivative of an alcohol using methyl dichlorophosphite and 2-(2-iodophenyl)ethanol. Treatment of the phosphite intermediate with (n-Bu)3SnH/AIBN in refluxing benzene cleanly produces the deoxygenation product of the original alcohol. Copyright
- Zhang, Liming,Koreeda, Masato
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p. 13190 - 13191
(2007/10/03)
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- Alkylation of alkenes: Ethylaluminum sesquichloride-mediated hydro-alkyl additions with alkyl chloroformates and di-tert-butylpyrocarbonate
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A general method for the hydro-alkyl addition to the nonactivated C=C double bond of alkenes using alkyl chloroformates (primary, secondary), 12, and di-tert-butylpyrocarbonate, 52, mediated by ethylaluminum sesquichloride (Et3Al2Cl3) has been developed. Reaction of 12 and 52, respectively, with Et3Al2Cl3 gives an alkyl cation which is added to the alkene; hydride transfer to the adduct carbenium ion or, if applicable, 1,2-H shift followed by hydride transfer from Et3Al2Cl3 to the rearranged adduct carbenium ion gives the saturated addition product. The reaction has been applied to 1-alkenes, 2-methyl-1-alkenes, internal double bonds, and to three cyclic alkenes. Special interest has been focused on alkylations of unsaturated fatty compounds, such as oleic acid (2), which are important renewable feedstocks. 2-Methylalkanes, 3-methylalkanes, 2,4-dimethylalkanes, 2,3-dimethylalkanes, 2,2,4-trimethylalkanes, cyclohexylalkanes, and carboxylic acids and esters with the respective branched alkyl chain have been synthesized with good to moderate yields.
- Biermann, Ursula,Metzger, Juergen O.
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p. 10319 - 10330
(2007/10/03)
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- Gas-phase hydrogenation of 4-tert-butylphenol over Pt/SiO2
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Gas-phase hydrogenation of 4-tert-butylphenol (4-TBP) over 1% Pt/SiO 2 to cis and trans 4-tert-butylcyclohexanol (4-TBCHOL), via the intermediate 4-tert-butylcyclohexanone, was studied in a differential reactor at atmospheric pressure and at temperatures between 127 and 227°C. The formation of by-products due to hydrogenolysis played an important role in the reaction at temperatures over 200°C. The rates of 4-t-butylcyclohexanol and 4-t-butylcyclohexanone formation passed through a maximum at 187°C. The catalyst deactivation was also considerable. Being thermodynamically more stable the trans form of the alcohols isomers is produced in separate experiments by epimerization in the presence of hydrogen as an astoichiometric compound. The reaction network for the reaction is proposed.
- Kalantar, Ahmad,Backman, Henrik,Carucci, Jose H.,Salmi, Tapio,Murzin, Dmitry Yu.
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- A highly selective arene hydrogenation catalyst that operates in ionic liquid
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The synthesis and structural characterization of [Ru(η6-p-cymene)(η2-TRIPHOS)Cl][PF6] is described. The complex is a highly active, homogeneous arene hydrogenation catalyst that is selective toward the hydrogenation of aromatic rings in preference to alkenes, as demonstrated by the hydrogenation of allylbenzene to allylcyclohexane. The catalyst operates in both dichloromethane and ionic liquids and undergoes no decomposition in the latter solvent. Copyright
- Boxwell, Clive J.,Dyson, Paul J.,Ellis, David J.,Welton, Thomas
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p. 9334 - 9335
(2007/10/03)
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- Reduction of sulfonates and aromatic compounds with the NiCl2 · 2H2O- Li-arene (cat.) combination
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A series of alkyl mesylates, dimesylates and alkyl or aryl triflates have been reduced to the corresponding hydrocarbons with nickel(II) chloride dihydrate, an excess of lithium powder and a catalytic amount of DTBB (10 mol%) in THF at room temperature. This methodology applied to enol triflates allowed the preparation of olefins or alkanes depending on the amount of the Ni(II) salt used. The reduction of different aromatic or heteroaromatic compounds under the above mentioned conditions leads to the partial or total reduction of the starting materials, the process being a reasonable alternative to the well-known Birch reaction. The use of the deuterium oxide- containing nickel(lI) salt allows the simple preparation of deuterated products.
- Radivoy, Gabriel,Alonso, Francisco,Yus, Miguel
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p. 14479 - 14490
(2007/10/03)
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- Reduction of thiols with LiAlD4: A mechanistic study
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Reduction of thiols with LiAlD4, in refluxing dioxane, leads to alkane products that contain only about 60% deuterium. Current work strongly suggests that dioxane is the source of hydrogen incorporation in the product, probably via transfer from an intermediate thioalkoxy-aluminate species.
- Smith, Michael B.,Wolinsky, Joseph
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p. 1431 - 1433
(2007/10/03)
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- One-Step Deoxygenation of Alcohols into Alkanes by a 'Double Electrolysis' in the Presence of a Phosphine
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Deoxygenation of primary and secondary alcohols was effectively achieved in one-step by constant current electrolysis of a mixture of a phosphine, an alcohol, and Et4NBr in CH3CN with one compartment cell at room temperature under N2 atmosphere.
- Maeda, Hatsuo,Maki, Toshihide,Eguchi, Kaoru,Koide, Takashi,Ohmori, Hidenobu
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p. 4129 - 4132
(2007/10/02)
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- Radical Cations of Cyclohexanes Alkyl-substituted on One Carbon: An ESR Study of the Jahn-Teller Distorted HOMO of Cyclohexane
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Cation radicals of cyclohexanes alkyl-substituted on one carbon have been stabilized in perfluoromethylcyclohexane and other halocarbon matrices at 4.2 K and studied by means of ESR spectroscopy.It was found that all have an electronic ground state resembling the 2Ag state of the cyclohexane cation, one of the possible states following a Jahn-Teller distortion of the D3d cyclohexane chair structure.The cations can be classified into two groups depending on the substituted alkyl group.To the first group belong the cations with a methyl group or a primary carbon (ethyl, n-propyl or isobutyl group) attached to the ring.The disubstituted cyclohexane cations of 1,1-dimethylcyclohexane and 1-methyl-1-ethylcyclohexane were also found to have a similar structure.The ESR spectra are characterized by a 1:2:1 three-line pattern with the hyperfine (hf) splitting due to two magnetically equivalent equatorial ring hydrogens.The magnitude of the splitting was found to depend on the size and number of substituents, ranging from 74 G (methylcyclohexane.+) to 55 G (isobutylcyclohexane.+).An additional doublet, 17-34 G, due to a hydrogen on the substituent could be detected in certain cases.Such hydrogens are axial with one of the elongated C-C bonds in the ring structure which contains a relatively large fraction of the unpaired electron.It follows that the substituents are located asymmetrically with respect to an ag-like SOMO in the ring.In the second group a secondary or tertiary carbon connects the substituent to the ring, such as an isopropyl or tert-butyl group.The largest hf splittings are ca. 30 G in magnitude, due to certain hydrogens on the substituent which are axial with respect to the cyclohexyl bond.It follows that an ag-like SOMO in the ring here is symmetrically arranged with respect to the position of the substituent.Hyperconjugation is the dominating mechanism for the spin transfer in all cations reported in this study.
- Shiotani, Masaru,Lindgren, Mikael,Ohta, Nobuaki,Ichikawa, Takahisa
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p. 711 - 719
(2007/10/02)
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- Lithium Aluminum Hydride Reduction of N-Aziridinylimines to Hydrocarbons
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The hydride reduction of ketone and aldehyde N-aziridinylimines is reported.Unlike most other hydrazone reductions, the reaction proceeds at room temperature under non-acidic conditions, providing an unusually mild carbonyl-to-methylene conversion.
- Leone, Christina L.,Chamberlin, A. Richard
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p. 1691 - 1694
(2007/10/02)
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- New Desulfurizations by Nickel-Containing Complex Reducing Agents
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Desulfurizations of saturated aliphatic or aromatic sulfoxides or sulfones are efficiently performed with nickel complex reducing agents (NiCRA's).The complete desulfurization of dithioketals can be effected in high yields with these reagents, while their half-desulfurization is efficiently achieved with 2,2'-bipyridine-modified nickel complex reducing agents (NiCRA-bpy).The desulfurization of vinyl thioethers, sulfoxides, and sulfones have been shown to be chemoselective, leaving the C-C double bond intact.The desulfurization of (E)-PhSO2(CH3)C=CHPh to cis-CH3CH=CHPh with NiCRA in the presence of quinoline is 95percent enantioselective.
- Becker, Sandrine,Fort, Yves,Caubere, Paul
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p. 6194 - 6198
(2007/10/02)
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- Stereochemical Aspects of Oxirane Ring Opening. Heterogeneous Catalytic Deuterolysis of cis and trans-1,2-Epoxy-4-t-butylcyclohexanes
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2H NMR analysis of deuterolyzed products from cis- and trans-1,2-epoxy-4-t-butylcyclohexane indicated that the cleavage of the oxirane C-O bond proceeds with inversion of configuration over noble metal catalysts except for Ru, while with retention over Co
- Ishiyama, Jun-ichi,Yashima, Hiroaki,Matsuo, Hironobu,Senda, Yasuhisa,Imaizumi, Shin,et al.
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p. 989 - 992
(2007/10/02)
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- Phenyl Selenoesters as Effective Precursors of Acyl Radicals for Use in Intermolecular Alkene Addition Reactions
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The scope of the use of phenyl selenoesters as effective precursors to acyl radicals for use in intermolecular olefin addition reactions is detailed.
- Boger, Dale L.,Mathvink, Robert J.
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p. 1777 - 1779
(2007/10/02)
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- ACTIVATION OF REDUCING AGENTS. SODIUM HYDRIDE CONTAINING COMPLEX REDUCING AGENTS 26. -- NEW EFFICIENT DESULFURIZING NICKEL CONTAINING REAGENTS
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It is shown that nickel containing Complex Reducing Agents NaH-RONa-NiX2 as such or in the presence of ligands are very efficient in desulfurizing organic compounds such as sulfur containing heteroaromatic substrates, aryl thioethers, dithioketals, sulfoxides or sulfones.
- Becker, S.,Fort, Y.,Vanderesse, R.,Caubere, P.
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p. 2963 - 2966
(2007/10/02)
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- Studies on the Mechanism of Transition-Metal-Assisted Sodium Borohydride and Lithium Aluminium Hydride Reductions
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Studies on the course of transition-metal-assisted NaBH4 and LiAlH4 reductions of (1) nitriles, (2) alkenes, and (3) alkyl halides are described. (1) The kinetics of benzonitrile (PhCN) reduction indicate that at high nitrile:catalyst ratios, the rate of reduction is independent of PhCN concentrations.Furthermore, the rate of PhCN reduction exhibits a first-order dependence on NaBH4 concentration, as measured over a fourfold range of BH4(1-) concentration and several half-lives of PhCN.Moreover, when PhCN was reduced with equimolar mixtures of NaBH4 and NaBD4, a significant primary kinetic isotope effect was observed.Rapid complexation of PhCN to be boride surface apparently activates the nitrile group toward rate-determining hydride addition from dissolved, uncoordinated NaBH4. (2) The selective reduction of alkenes by NaBH4-CoCl2 is attributed to adventitious heterogeneous catalytic hydrogenation. (3) The combination of LiAlH4 with CoCl2 forms a black precipitate of cobalt aluminide (CoAl) which was isolated, analyzed by atomic absorption spectroscopy, and shown to play an essential catalytic role in the reduction of alkyl halides.Labeling experiments demonstrate stereochemical randomization by a heterogeneous process involving solvent as the hydrogen donor and LiAlH4 as a co-reductant.A radical mechanism involving halide atom transfer or oxidative addition to the aluminide is proposed.
- Osby, John O.,Heinzman, Stephen W.,Ganem, Bruce
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- A RADICAL DEOXIGENATION OF SECONDARY ALCOHOLS TO HYDROCARBONS BY USE OF TRIBUTYLTIN HYDRIDE
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Secondary alcohols 1 reacted with 2,2'-dibenzothiazolyldisulfide in the presence of tributylphosphine to give corresponding sulfides 2 in good yields.Sulfides 2 were subsequently desulfurized to hydrocarbons 3 with tributyltin hydride in radical conditions.
- Watanabe, Yoshihiko,Araki, Takumi,Ueno, Yoshio,Endo, Takeshi
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p. 5385 - 5388
(2007/10/02)
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- MECHANISMS OF FREE-RADICAL REACTIONS. XVII. STEREOSELECTIVITY OF THE FREE-RADICAL ABSTRACTION OF A HALOGEN ATOM FROM 4-tert-BUTYLCYCLOHEXYL HALIDES AND 2-NORBORNYL HALIDES
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The free-radical reduction of cis- and trans-4-tert-butylcyclohexyl halides and also of exo- and endo-2-chloronorbornanes by the trialkyl hydrides of group IVB elements was studied by the method of competing reactions.For the derivatives of cyclohexane the reactivity of the axial C-Hlg bond is 2-4 times higher than the reactivity of the equatorial bond.In the case of halogenonorbornanes the abstraction of the exo-halogen atom takes place at a higher rate.The stereoselectivity of the reaction increases in the transition from the bromides to the chlorides.The nature of the changes in the stereoselectivity with variation in the structure of the reagents and in the nature of the halogen atom agrees well with theories about the torsional interactions arising in the transition state.
- Dneprovskii, A. S.,Pertsikov, B. Z.
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p. 222 - 227
(2007/10/02)
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- Reactions of tert-Butyllithium with α,ω-Dihaloalkanes. Evidence for Single-Electron-Transfer-Mediated Metal-Halogen Interchange Involving Alkyl Radical-Halide Ion Adducts
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The reactions of tert-butyllithium (t-BuLi) with primary α-iodo-ω-haloalkanes and α,ω-dibromoalkanes have been investigated in experiments conducted at -23 deg C in n-pentane-diethyl ether (3:2 by volume) solution.It has been found that production of an α-lithio-ω-haloalkane (1) by metal-halogen interchange at one end of a 1,3-, 1,4-, or 1,5-dihalide results in intramolecular coupling to give cycloalkanes in high yield.As the chain length of the dihalide is increased beyond five carbon atoms the production of an α,ω-dilithio species by interchange at bothends of the dihalide ceases to be excluded by cyclization of 1 and a precipitous drop in the yield of cycloalkane was found to occur in reactions of 1,6-diiodoalkanes with t-BuLi.Metal-halogen interchange was the exclusive process observed in reactions of α,ω-dihalides with t-BuLi provided at least one halogen of the substrate was an iodine.By contrast, similar treatment of α,ω-dibromoalkane provided only minor amounts of product attributable to metal-halogen interchange.Under conditions that provide an essentially quantitative yield of carboxylic product from reductive cyclization of 1 generated from 1,5-diiodo-3,3-dimethylpentane, the corresponding 1,5-dibromide was converted to a mixture composed of cycloalkane, products from Wurtz-type coupling with t-BuLi, and quantities of parent alkane from formal reduction of the dihalide.The mechanism of the metal-halogen interchange was further probed by using 6-halo-1-hexene substrates.Observation of cyclized product from the reaction of t-BuLi with 6-bromo- and 6-iodo-1-hexene demonstrated that the interchange between t-BuLi and primary alkyl bromides and iodides occurs predominantly via single-electron-tranfer (SET) process.Incorporation of alkyl radical-halide ion adducts with halogen dependent lifetimes as intermediates following SET from alkyllithium to alkyl halide serves to explain the disparate behavior of alkyl bromides and iodides when treated with t-BuLi.A unifield SET-mediated mechanism for metal-halogen interchange and Wurtz coupling is presented.
- Bailey, William F.,Gagnier, Paul R.,Patricia, Jeffrey J.
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p. 2098 - 2107
(2007/10/02)
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- PHOTOREDUCTION DES ESTERS CARBOXYLIQUES DANS L'HEXAMETHYLPHOSPHORTRIAMIDE (HMPT)
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Use of HMPT as solvent in photochemistry allows efficient photoreductions.Alkyl esters and especially non absorbing alkyl acetates are photoreduced in excellent yields into alkanes.In the latter case, a protonating agent is necessary.Numerous examples illustrate the generality and convenience of the reaction.This photoreduction involves an electron transfer from HMPT to ester.
- Portella, C.,Deshayes, H.,Pete, J. P.,Scholler, D.
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p. 3635 - 3644
(2007/10/02)
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- Stereoelectronic Effects in Hydrogen-atom Transfer Reactions of Substituted Cyclohexyl Radicals
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Thermolysis of the peroxyoxalates (1)-(7) and the diacyl peroxides (8)-(11) in cyclohexane at 100 deg C gives cycloalkenes and cycloalkanes by hydrogen-atom transfer reactions of the initially formed conformationally biased 4-t-butyl-, 4-t-butyl-cis,cis-2,6-dimethyl-, 4-t-butyl-cis,trans-2,6-dimethyl-, 4-t-butyl-cis-2-methyl-, 4-t-butyl-trans-2-methyl-, and 5-t-butyl-cis-2-methylcyclohexyl radicals (12)-(17).The composition of the product mixtures indicates that transfer of axial β-hydrogen atoms occurs more rapidly than does transfer of equatorial β-hydrogen atoms.These results support the hypothesis that homolytic fission of a C-H bond is favoured when it lies chlose to the plane of an adjacent semi-occupied orbital.
- Beckwith, Athelstan L. J.,Easton, Christopher J.
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p. 661 - 668
(2007/10/02)
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- Ionization Energies and Entropies of Cycloalkanes. Kinetics of Free Energy Controlled Charge-Transfer Reactions.
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Enthalpies and entropies of ionization (ΔH0ion and ΔS0ion) of alkylcyclohexanes, as well as cycloheptane, cyclooctane, and trans-Decalin, have been determined by charge-transfer equilibrium measurements.Values of ΔHion, in units of kcal mol-1 (or eV), range from 229.6 (9.96) for cycloheptane to 210.7 (9.14) for trans-Decalin.A major effect of alkyl substitution is observed following substitution at a site α to a tertiary hydrogen atom (as from methylcyclohexane to 1,2-dimethylcyclohexane), or following replacement of a tertiary hydrogen atom (as from methylcyclohexane to 1,1-dimethylcyclohexane).In both cases, ΔH0 ion decreases by ca. 5 kcal mol-1.Entropies of ionization are near zero for alkylcyclohexanes but range up to 5 cal deg-1 mol-1 for nonsubstituted cycloalkanes (cyclooctane).The charge-transfer reactions involving the cycloalkanes are shown to be fast processes; i.e., the sum of the reaction efficiencies (r=k/kcollision) of the forward and reverse processes is near unity.The efficiencies of these processes appear to be determined uniquely by the overall free energy change (or equilibrium constant K).Specifically, the reaction efficiencies are defined, within a factor of 2 by the relation r=K/(1+K), which can be justified by using transition-state theory applied to the decomposition of a collision complex over surfaces lacking energy barriers.These reactions are defined as intrinsically fast processes in that they are slowed only by the overall reaction thermochemistry and not by any properties or reactions of the intermediate complex.
- Sieck, L. Wayne,Mautner, Michael
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p. 3646 - 3650
(2007/10/02)
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- VERSATILE POLYMER-BOUND RHODIUM CATALYSTS. FACILE HYDROGENATION OF AROMATIC COMPOUNDS IN THE LIQUID PHASE
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Immobilized complexes prepared from 2 (nbd=norbornadiene) and phosphinated polydiacetylene or silica are efficient catalysts for the hydrogenation of arenes under mild conditions.However, the homologous catalyst supported on a phosphinated polystyrene is not active.
- Okano, Tamon,Tsukiyama, Katsunori,Konishi, Hisatoshi,Kiji, Jitsuo
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p. 603 - 606
(2007/10/02)
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- Catalytic Hydrogenation of Aromatic Hydrocarbons. Stereochemical Definition of the Catalytic Cycle for η3-C3H5Co(P(OCH3)3)3
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The η3-C3H5Co(P(OCH3)3)3-catalyzed hydrogenations with D2of a series of unsaturated organic molecules, including cyclohexenes, cyclohexadienes, and arenes, have been investigated.Complete cis stereoselectivity was observed in the addition of deuterium to the unsaturated ring systems.When alkyl-substituted arenes were reduced with D2, the hydrogen atoms in the alkyl chains underwent H-D exchange as long as each successive carbon atom in the chain possessed at least one hydrogen atom.Hence, extensive H-D exchange occured in n-alkyl side chains while the tert-butyl side chain was deuterium free.When alkyl-substituted arenes were hydrogenated in the presence of olefins such as 1-hexene, a variety of isomeric alkylcyclohexenes and alkenylcyclohexanes were observed.The relative concentrations of these isomeric species provided information about the relative stabilities of the (olefin)cobalt species in the catalytic cycle.Further mechanistic information was obtained from other competitive reactions, i.e., hydrogenation reactions involving equimolar quantities of two different unsaturated molecules.The proposed initiation steps of the catalytic cycle have been revised on the basis of a study of η3-C8H13Co(P(OCH3)3)3 as a catalyst precursor.The cyclooctenyl-cobalt bond was cleaved by hydrogen early in the reaction, leaving the highly coordinately unsaturated hydride, HCo(P(OCH3)3)2, which is probably the true catalytic species.
- Bleeke, J. R.,Muetterties, E. L.
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p. 556 - 564
(2007/10/02)
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- Mechanism of the Liquid-Phase Catalytic Hydrogenolysis on Palladium/Carbon of Cyclohexene Epoxides
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Heterogeneous catalytic hydrogenolysis of cyclohexene epoxides on 10percent Pd/C was studied in different solvents. The principal products were found to be alcohols, formed by cleavage of one epoxide C-O bond. In addition, simultaneous cleavage of both C-O bonds gave hydrocarbons, and isomerization on the catalyst gave ketones as byproducts. The deuterolysis of cis- and trans-tert-butylcyclohexene epoxides and kinetic studies with cyclohexene epoxides carrying an axial methyl group in position 3 or 5 showed that hydrogenolysis gives preferentially axial alcohols and trans hydrogen addition, after a "roll over" on the catalyst. If one epoxide carbon carries a methyl group, conformational and steric factors come into play. C-O bond cleavage at the more substituted carbon, leading to equatorial alcohols, becomes competitive with preferential formation of axial alcohols, and steric hindrance to molecular reorientation on the catalyst causes cis as well as trans hydrogen addition.
- Accrombessi, Georges C.,Geneste, Patrick,Olive, Jean-Louis,Pavia, Andre A.
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p. 4139 - 4143
(2007/10/02)
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- Solution Thermodynamics Studies. 5. A Thermodynamic Study of Solvent Effects on the Relative Stability of Diastereoisomers. The trans-1,2-Dibromo-4-tert-butylcyclohexane, trans-2,3-Dibromodecalin, and 1-Bromo-4-tert-butylcyclohexane Systems
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Calorimetric measurements of transfer enthalpies associated with acidity-coefficient determinations lead us to a precise description of the solvent influence on the relative stability of the stereoisomers of the title compounds.This solvent influence is i
- Ramos, J. J. Moura,Dumont, L.,Stien, M. L.,Reisse, J.
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p. 4150 - 4154
(2007/10/02)
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- Alkyllithium Reagents from Alkyl Halides and Lithium Radical Anions
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The reaction of alkyl halides with three different lithium radical anions, lithium naphthalene (LiN), lithium di-tert-butylnaphthalene (LiDBN), and lithium di-tert-butylbiphenyl (LiDBB), was studied.The reaction of alkyl halides with an excess of LiN, LiDBN, or LiDBB in THF at -78 deg C leads to a consistently high yield (96-100percent) of reduction products (RH, RLi) with a high degree of formation of RLi (anion trapping 93-95percent) in the case of LiDBB.LiDBN consistently produces high yields of reduction products (89-99percent) with widely variable amounts of anion trapping (21-88percent), while LiN provides variable yields of reduction (39-99percent) and anion trapping (24-65percent).Variation of the concentration of lithium bromide and naphthalene and the ratio of alkyl halide to naphthalene in conjunction with the use of deuterium tracer experiments provided evidence consistent with a competition between metalation of the lithium dihydronaphthalenedicarboxylate by alkyllithium and carbonation of alkyllithium in the carbonation step of the analysis.
- Freeman, Peter K.,Hutchinson, Larry L.
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p. 1924 - 1930
(2007/10/02)
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- ETUDE DU CARACTERE NUCLEOPHILE DES RADICAUX LORS DE LA REACTION DE TRANSFERT SUR LA LIAISON O-O DES PERACIDES
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Peracids RCO3H yield free radicals R. which react either with the peracid or with solvent giving the alcohol ROH and the hydrocarbon RH.The nucleophilic character of the free radicals was modified either by substitution of the carbon bearing the odd electron by inductive groups or by changing the free radical hybridation by the means of blocked structures such as cyclic or bicyclic free radicals.For each R., the measurement of the ratio ROH/RH establishes a reactivity scale for R. with the peracid O-O bond.This reactivity does not depend on free radical stability but depends strongly on nucleophilic character.A primary free radical is less reactive than a secondary one, and is much less reactive than a tertiary one.A bridgehead free radical as the bicycloheptyle-1 does not react with the peracid.These results are interpreted to indicate a transition state with charge transfer (polar effect), the peracid being electrophilic and the free radical nucleophilic; PMO theory is discussed.
- Fossey, Jacques,Lefort, Daniel
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p. 1023 - 1036
(2007/10/02)
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- Bis(triphenylphosphine)copper (I) tetrahydroborate in the reduction of P-toluenesulphonylhydrazones and 2,4,6-triisopropylbenzenesulphonyl hydrazones (trisyl hdyrazones) to alkanes
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Saturated ketones and aldehydes are converted via their p-toluenesulphonyl hydrazones to the corresponding alkanes by treatment with bis(triphenylphosphine) copper (I) tetrahydroborate; trisylhydrazones give moderate yields of alkanes at room temperature on treatment with bis(triphenylphosphine)copper (I) tetrahydroborate.
- Fleet,Harding,Whitcombe
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p. 4031 - 4034
(2007/10/02)
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