- Selective production of bio-based: Para -xylene over an FeOx -modified Pd/Al2O3catalyst
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para-Xylene (PX) is a basic building block of polyethylene terephthalate, which is currently produced from petroleum resources. Developing a renewable route to PX is highly desirable to address both economic and environmental concerns. Several attempts used noble metal catalysts, e.g. Pd/Al2O3, to synthesize PX from biomass-derived 4-methyl-3-cyclohexene-1-carboxaldehyde (4-MCHCA), but suffered from a severe decarbonylation reaction, resulting in toluene as the main product. In this paper, we report an FeOx modification strategy to suppress the decarbonylation reaction on a Pd/Al2O3 catalyst, leading to a drastic shift in selectivity towards PX with a yield up to 81percent via a cascade dehydroaromatization-hydrodeoxygenation (DHA-HDO) pathway. Characterization and control experiments revealed that the electron density of Pd sites decreased in an FeOx-modified Pd/Al2O3 catalyst compared to Pd/Al2O3, thus tuning the preferential adsorption mode of the substrate from η2-(C,O), the key transition state of the decarbonylation reaction, to the η1-(O) mode that favors the hydrodeoxygenation process. Notably, this designed catalyst is highly stable and is readily applicable in the selective synthesis of a broad range of desired aromatic chemicals via the same DHA-HDO pathway from cyclohex-3-enecarbaldehyde derivatives. Overall, this work develops a controllable catalyst modification strategy that tailors an efficient catalyst for petroleum-independent bio-PX synthesis.
- Fu, Zaihui,Li, Changzhi,Meng, Qingwei,Pan, Xiaoli,Xiao, Yuxue,Zhang, Chao
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supporting information
p. 4341 - 4349
(2020/07/14)
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- Cobalt-catalyzed oxidative esterification of allylic/benzylic C(sp3)–H bonds
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A protocol for the cobalt-catalyzed oxidative esterification of allylic/benzylic C(sp3)–H bonds with carboxylic acids was developed in this work. Mechanistic studies revealed that C(sp3)–H bond activation in the hydrocarbon was the turnover-limiting step and the in-situ formed [Co(III)]Ot-Bu did not engage in hydrogen atom abstraction (HAA) of a C–H bond. This protocol was successfully incorporated into a synthetic pathway to β-damascenone that avoided the use of NBS.
- Ren, Tian-Lu,Xu, Bao-Hua,Mahmood, Sajid,Sun, Ming-Xue,Zhang, Suo-Jiang
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supporting information
p. 2943 - 2948
(2017/04/26)
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- Microwave-assisted hydrothermal synthesis of NiSx and their promotional effect for the hydrodeoxygenation of p-cresol on MoS2
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NiSx were synthesized by microwave assisted hydrothermal method using nickel nitrate and thiourea as precursor materials. Their phase compositions were controlled by adjusting the reaction temperature and pH value. In the hydrodeoxygenation (HDO) of p-cresol on MoS2, adding NiSx enhanced the conversion but had no effect on the product distribution. NiS2 phase exhibited higher promotional effect than NiS and Ni3S4 phases. The HDO reaction mechanism for p-cresol on NiSx + MoS2 could be well explained by the Remote Control model through a migration of spillover hydrogen.
- Wang, Weiyan,Wu, Kui,Li, Lu,Tan, Song,Zhu, Guohua,Li, Wensong,He, Zhiqiang,Yang, Yunquan
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- Highly selective catalytic conversion of phenols to aromatic hydrocarbons on CoS2/MoS2 synthesized using a two step hydrothermal method
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CoS2/MoS2 catalysts were prepared using a two-step hydrothermal procedure for the first time, i.e., MoS2 was synthesized and then CoS2 was prepared and deposited on the surface of the MoS2. The characterization results presented that CoS2 and MoS2 are separated in the resultant catalysts and the surface area of CoS2/MoS2 was much higher than that of Co-Mo-S prepared using a one step method. In the hydrodeoxygenation (HDO) of p-cresol, the presence of CoS2 enhanced the conversion, but excessive CoS2 on the surface of the MoS2 reduced its activity. With an appropriate amount of CoS2, the catalyst presented an unprecedented HDO activity and direct deoxygenation (DDO) selectivity: 98% deoxygenation degree with a selectivity of 99% toluene at 250 °C for 1 h. This CoS2/MoS2 catalyst also exhibited high DDO activity for other phenolic monomers, which minimized hydrogen consumption and improved the economic efficiency.
- Wang, Weiyan,Li, Lu,Wu, Kui,Zhu, Guohua,Tan, Song,Liu, Yan,Yang, Yunquan
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p. 31265 - 31271
(2016/04/08)
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- Dehydrogenation of cycloalkanes at rhodium complexes bearing fluorinated cyclopentadienyl ligands
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The fluorinated cyclopentadienyl complexes [Rh(η5-C5H4CH2CH2C6F13)(CO)2] (2), [Rh(η5-C5H4CH2CH2C8F17)(CO)2] (3), [Rh(η5-C5H4CH2CH2C10F21)(CO)2] (4), [Rh(η5-C5H4CH2CH2CnF2n+1)(CO)(PEt3)] (7: n = 6; 8: n = 8; 9: n = 10) and [Rh(η5-C5H4CH2CH2CnF2n+1)(CO){P(CH2CH2C6F13)3}] (10: n = 8; 11: n = 10) were synthesized and their reactivity was investigated. Compound 3 converts at room temperature into the trinuclear complex [Rh2(η5-C5H4CH2CH2C8F17)2(μ-CO)2Rh(η5-C5H4CH2CH2C8F17)(CO)] (6). The complexes 9 and 11 were employed in dehydrogenation reactions of cycloalkanes in C6F14/hydrocarbon mixtures. Photocatalytic conversions were observed and a turnover number of 16 for the dehydrogenation of cyclooctane with complex 11 was obtained.
- Liebau, Frank,Braun, Thomas,Braun, Beatrice
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p. 192 - 200
(2015/10/28)
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- Synthesis of Ni-P-B amorphous nanoparticles with uniform size as a potential hydrodeoxygenation catalyst
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An Ni-P-B amorphous nano-catalyst was synthesized using a facile chemical reduction method. The amorphous degree was enhanced and the transferred electron decreased with an increase of P content in Ni-P-B. In the hydrodeoxygenation (HDO) of p-cresol, the conversion using Ni-P-B was high up to 98.9% with a selectivity of 6.5% for toluene and a deoxygenation degree of 96.8% at 498 K.
- Wang, Weiyan,Liu, Pengli,Wu, Kui,Zhang, Kun,Li, Lu,Qiao, Zhiqiang,Yang, Yunquan
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supporting information
p. 813 - 816
(2015/02/19)
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- Preparation of Ni-Mo-S catalysts by hydrothermal method and their hydrodeoxygenation properties
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Unsupported Ni-Mo-S catalysts with different Ni/(Ni + Mo) molar ratio were prepared by hydrothermal method using ammonium heptamolybdate and thiocarbamide as materials. The resultant catalysts were characterized by X-ray diffraction, nitrogen physisorption and transmission electron microscopy, and their activities were measured using the hydrodeoxygenation (HDO) of p-cresol as a probe reaction. The addition of Ni promoter caused a reduction in the surface area. The peaks attributed to NiS2 on catalyst surface became noticeable as the Ni content increased in the catalyst. The catalyst with an optimal Ni/(Ni + Mo) molar ratio (0.3) exhibited the highest activity (99.8% deoxgenation degree at 300 °C and 4.0 MPa hydrogen pressure for 6 h). The HDO of p-cresol on these prepared Ni-Mo-S catalysts proceeded with two parallel routes: hydrogenation-dehydration (HYD) and direct deoxygenation (DDO), and HYD/DDO closely related to the Ni/(Ni + Mo) molar ratio in the catalyst, the HDO reaction temperature and H2 pressure. The comparison of Ni-Mo-S with MoS2-NiS2 (prepared by two hydrothermal method) and MoS2 + NiS2 (prepared by physically mixing separately MoS2 and NiS2) indicated that the high HDO activity of Ni promoted MoS2 catalyst was attributed to the synergistic effect of MoS2 and NiS2 rather than the formation of Ni-Mo-S phase, which could be well explained by the remote control model.
- Wang, Weiyan,Li, Lu,Wu, Kui,Zhang, Kun,Jie, Jia,Yang, Yunquan
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- SDBS-assisted hydrothermal synthesis of flower-like Ni-Mo-S catalysts and their enhanced hydrodeoxygenation activity
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Ni-Mo-S catalysts were prepared by sodium dodecyl benzene sulfonate (SDBS) assisted hydrothermal synthesis. The presence of SDBS increased the NiS2 crystallite size, enlarged the interlayer distance of MoS2 plane and formed loose flo
- Wang, Weiyan,Tan, Song,Zhu, Guohua,Wu, Kui,Tan, Liang,Li, Yingze,Yang, Yunquan
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p. 94040 - 94045
(2015/11/17)
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- Synthesis of piperylene and toluene via transfer dehydrogenation of pentane and pentene
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The highly thermally stable anthraphos-based iridium pincer complex ( iPr4Anthraphos)Ir(C2H4) 3, was shown to catalyze transfer dehydrogenation of pentene and pentane using various olefins as acceptors in the temperature range of 160-250 C. Using pentene itself as an acceptor, disproportionation of pentene to pentane and pentadiene was observed, but yields of (E)- and (Z)-1,3-pentadienes (piperylenes) were limited to ~25% as a result of a self-Diels-Alder reaction of the 1,3-dienes to produce isomeric mixtures of the C10 dimers. Using propylene as the acceptor, higher yields of piperylenes were obtained (~40%), but self-Diels-Alder adducts were again observed along with low fractions of propylene/pentadiene Diels-Alder adducts. Using ethylene as the acceptor, the pentadienes produced via hydrogen transfer undergo an in situ Diels-Alder reaction with ethylene to produce 3-methylcyclohexene (along with toluene from further dehydrogenation) in good yields (65%). 3-Methylcylohexene was quantitatively dehydrogenated to toluene over a heterogeneous Pd/C catalyst.
- Kundu, Sabuj,Lyons, Thomas W.,Brookhart, Maurice
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p. 1768 - 1773
(2013/09/02)
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- Enantioselective synthesis of chiral sulfones by ir-catalyzed asymmetric hydrogenation: A facile approach to the preparation of chiral allylic and homoallylic compounds
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A highly efficient and enantioselective Ir-catalyzed hydrogenation of unsaturated sulfones was developed. Chiral cyclic and acyclic sulfones were produced in excellent enantioselectivities (up to 98% ee). Coupled with the Ramberg-Baecklund rearrangement, this reaction offers a novel route to chiral allylic and homoallylic compounds in excellent enantioselectivities (up to 97% ee) and high yields (up to 94%).
- Zhou, Taigang,Peters, Byron,Maldonado, Matias F.,Govender, Thavendran,Andersson, Pher G.
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p. 13592 - 13595
(2012/10/08)
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- Copper-catalyzed asymmetric allylic alkylation of racemic cyclic substrates: Application of dynamic kinetic asymmetric transformation (DYKAT)
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The copper-catalyzed asymmetric allylic alkylation (AAA) is of great interest in organic synthesis. This reaction was extensively studied using a broad range of substrates, ligands and organometallic reagents. However, the use of racemic substrates was still limited. Although some processes of kinetic resolution are reported in the literature, no examples of quantitative deracemization are described as is the case for the Pd-catalyzed allylic alkylation. We present here a full account of our investigations through the development of the first example of such a process in copper-catalyzed AAA. High enantioselectivities (up to 99% ee), scope of the reaction and mechanistic considerations are reported herein.
- Langlois, Jean-Baptiste,Alexakis, Alexandre
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supporting information; scheme or table
p. 447 - 457
(2010/06/13)
-
- Synthesis and examination of antimicrobial properties of aminomethylated derivatives C6-C7 of alicyclic diols
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Synthesis of C6-C7 alicyclic diols was studied by a catalytic oxidation of cyclohexene, norbornene and their methyl derivatives in the presence of heterogenized molybdenum-containing catalysts. By a triple condensation of the diols with formaldehyde and secondary amines a synthesis of their aminomethylated derivatives with various substituents at nitrogen atom was examined. Antimicrobial properties of the synthesized amino alcohols in M-10 oil as additives with fungicidal and bactericidal activities were studied.
- Alimardanov,Sadygov,Suleimanova,Dzhafarova,Abdullaeva,Babaev
-
body text
p. 1255 - 1262
(2009/12/08)
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- Transformations of β-alkylcyclohexane hydrocarbons on modified pentasils with participation of methanol and oxidants
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The reactions of dehydroalkylation of methylcyclohexane, ethylcyclohexane, and methylcyclohexene isomers and toluene alkylation with methanol on platinum-and gallium-modified pentasil in the presence of an O 2-CO2 mixture was studied. Optimum conditions were found for the one-step dehydroalkylation of methylcyclohexane on the ring. Under these conditions, the degree of conversion of methylcyclohexane and methylcyclohexene isomers into xylene isomers is above that of toluene alkylation to afford xylene. According to the discussed reaction mechanism, the dehydroalkylation of cyclohexane hydrocarbons on Pt, Ga-pentasil involves both the steps of formation of unsaturated intermediates and toluene in status nascendi. Nauka/Interperiodica 2006.
- Alimardanov,Velieva,Dadasheva,Rustamov
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p. 353 - 361
(2008/04/18)
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- The diagnostic substrate bicyclohexane reveals a radical mechanism for bacterial cytochrome P450 in whole cells
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(Figure Presented) On home ground: The reaction mechanisms of bacterial alkane-oxidizing cytochrome P450s were determined in their native environment using a novel diagnostic substrate probe, bicyclohexane, in whole cells and cell-free extracts (see picture). Purified P450cam also oxidizes bicyclohexane. Clear evidence for a substrate-based radical with a lifetime of 75-250 ps was obtained.
- Austin, Rachel N.,Deng, Dayi,Jiang, Yongying,Luddy, Kate,Van Beilen, Jan B.,Ortiz De Montellano, Paul R.,Groves, John T.
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p. 8192 - 8194
(2008/02/08)
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- Dehydroalkylation of methylcyclohexane by methanol on modified zeolites: Kinetic features and reaction mechanism
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The reaction of methylcyclohexane dehydroalkylation by methanol on modified forms of mordenite and pentasil was studied. The kinetic features of the process in the presence of HNa-pentasil modified by gallium and iron oxides and phosphorus were investigated. A kinetic model that fairly well describes the process at 430-570°C is suggested. The reaction mechanism is considered, which involves the dehydroalkylation of methylcyclohexane by methanol via the intermediate dehydrogenation of both hydrocarbons and alcohol and the subsequent interaction of the unsaturated compounds formed with formaldehyde adsorbed on the catalyst surface. Copyright
- Alimardanov,Velieva,Suleimanova,Tairova,Sh Sadygova
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- A cyclopropyl-homoallyl rearrangement accompanying the borane-mediated reduction of tosylhydrazones
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The Wolff-Kishner reduction of strained cyclopropyl ketones 9-oxo-2,8-didehydronoradamantane (1) and 5-oxo-2,4-didehydrobrendane (5) proceeds without rearrangement, while the borane-mediated reduction of the corresponding tosylhydrazones 1a and 5a affords the rearranged products tricyclo[4.2.1.03.8]non-4-ene (3) and 4-brendene (7), respectively. Rearrangement also occurs during the reduction of the less-strained tosylhydrazones 8a and 10a derived from cyclopropyl methyl ketone (8) and bicyclo[4.1.0]heptan-2-one (10). The results obtained in experiments with deuterated reagents support a concerted mechanism of diazene decomposition/cyclopropyl-homoallyl rearrangement. This rearrangement offers a great possibility for the preparation of new polycyclic molecules and, moreover, is a convenient method for regiospecific isotopic labeling using deuterated reagents. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.
- Kragol, Goran,Benko, Iva,Muharemspahic, Jasmina,Mlinaric-Majerski, Kata
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p. 2622 - 2625
(2007/10/03)
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- Stereochemistry of hydrodenitrogenation: The mechanism of elimination of the amino group from cyclohexylamines over sulfided Ni-Mo/γ-Al2O3 catalysts
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HDS and HDN are among the most significant catalytic processes in the petroleum industry, because during these processes sulfur and nitrogen are removed in the form of H2S and ammonia from oil fractions. The HDN of cyclohexylamine and of the diastereomers of 2-methylcyclohexylamine and 2,6-dimethylcyclohexylamine was studied at 200°-350°C and 50 bar over a sulfided Ni-Mo/γ-Al2O3 catalyst. The rate of HDN of alkyl-substituted cyclohexylamines over sulfided Ni-Mo catalysts depended on the number of β hydrogen atoms and on their stereochemical relation to the amino group. Isomerization of olefinic products and the amines prevented meaningful mechanistic studies at 350°C. The cis diastereomers reacted faster than the trans diastereomers, because they allowed for an anti geometric relationship in the chair conformation between the amino group and a hydrogen atom on a β carbon atom. The syn elimination occurred to a considerable extent at higher temperatures in molecules that were unable to undergo anti elimination. The activation energy of anti elimination was lower than that of syn elimination, and the activation energy of anti elimination involving a hydrogen atom attached to a tertiary β carbon atom was lower than that involving a hydrogen atom attached to secondary β carbon atom.
- Prins,Ranade,Rota,Ranade
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p. 389 - 399
(2007/10/03)
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- Steric and electronic effects in the diastereoselective catalytic epoxidation of cyclic allylic alcohols with methyltrioxorhenium (MTO)
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The steric effects of allylic substituents in the epoxidations with methyltrioxorhenium/urea/hydrogen peroxide adduct (MTO/UHP) have been assessed for a series of 3-alkyl-substituted cyclohexenes. The trans selectivity increases with the size of the substituent and the diastereoselectivities follow an excellent linear correlation with the steric substituent constants of Taft (E(s)) or Charton (v). Good cis selectivity is observed in the epoxidation of the cyclic allylic alcohols 2-cyclopentenol and 2-cyclohexenol due to a hydroxy-directing effect through hydrogen bonding; however, for 2-cycloheptenol and 2-cyclooctenol hydrogen bonding is ineffective and steric interactions cause a higher trans selectivity. The conformationally fixed cis- and trans-5-tert-butyl-2-cyclohexenols serve as suitable substrates for gauging the dihedral angle of the transition states for the oxygen transfer in these epoxidations. Thus, the MTO/UHP oxidant favours a quasi-equatorial arrangement of the hydroxy group for effective hydrogen bonding (hydroxy-group directivity), in analogy to m- chloroperbenzoic acid (m-CPBA) and dimethyldioxirane (DMD), and a dihedral angle of ca. 130°is suggested.
- Adam, Waldemar,Mitchell, Catherine M.,Saha-Moeller, Chantu R.
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p. 785 - 790
(2007/10/03)
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- Structure and Thermal Decomposition of Some 5-(Cyclohexyloxy)thianthreniumyl Perchlorates
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Five sets of cis- and trans-substituted cyclohexanols were used for reaction with thianthrene cation radical perchlorate, namely, cis- and trans-cyclohexane-1,2-diol, cis- and trans-2-methyl-, 3-methyl-, and 4-methylcyclohexanol, and cis,cis- and trans,trans-3,5-dimethylcyclohexanol. Reaction in CH2-Cl2 solution and precipitation with ether gave the corresponding crystalline 5-(cyclohexyloxy)-thianthreniumyl perchlorate salts. The configuration of each salt in CDCl3 was shown by 1H and 13C NMR spectroscopy to correspond with the configuration of the cyclohexanol from which it was made. X-ray Ortep diagrams of four of the salts confirmed the structure deduced from NMR spectroscopy. In the NMR, inequivalence of the 1H and 13C signals from the thianthreniumyl 4-and 6-, 1- and 9-, 2- and 8-, and 3- and 7-positions was found when the 1′-position of the cyclohexyl ring was stereogenic. In the four Ortep diagrams, the orientation of the S-O bond was psuedoaxial. Thermal decomposition of the salts made from the monosubstituted cyclohexanols at 100°C in CH3CN solution gave products consistent with the assigned structures.
- Zhao, Wenyi,Shine, Henry J.,Whittlesey, Bruce R.
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p. 8693 - 8701
(2007/10/03)
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- Carbenes in constrained systems. 4. Encapsulation of an asymmetric diazirine: Reactivity of 2-methylcyclohexanylidene
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2-Methylcyclohexanylidene was generated from the corresponding diazirine within the cavities of α-, β- and γ-cyclodextrin by photolysis in the solid state. To surmise how these constrained systems affect the residing carbene's selectivity, a comparison with conventional reaction methods was made.
- Rosenberg,Kam,Brinker
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p. 3235 - 3238
(2007/10/03)
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- Reaction of thianthrene cation radical with alcohols: Cyclohexanols
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Cyclohexanol (1), 4-methylcyclohexanol (2), 4-tert-butylcyclohexanol (3), cis-2-methyl- (4) and trans-2-methylcyclohexanol (5) reacted cleanly with thianthrene cation radical perchlorate (Th·+ClO4-) in the presence of 2,6-di-tert-butyl-4-methylpyridine (DTBMP). The alcohols were converted quantitatively into cyclohexenes, while Th·+ was converted quantitatively into thianthrene (Th) and thianthrene 5-oxide (ThO). The oxygen atom of ThO came from the alcohol, as was demonstrated with the use of [18O]cyclohexanol.
- Shine, Henry J.,Yueh, Wang
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p. 6583 - 6586
(2007/10/02)
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- Hydrogen Transfer Reactions, 19. - The Catalysis of Hydrogen Transfer and 1,5-H Shift by Rhodium(III) Chloride in Homogeneous Organic Systems
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In homogeneous solution, partly in the presence of a phase-transfer catalyst, rhodium(III) chloride catalyzes the disproportionation of 1,3-cyclohexadiene and to a lesser extent 1,5-H shifts.In the start phase the catalyst is reduced to the active monovalent state.In these catalytic systems the dehydrogenation proceeds stereoselectively. - This was shown by tracer experiments and isotopes effects using deuterated 1,3-cyclohexadienes 1a-d, which were synthesized with high isotopomeric purity.Key Words: Rhodium chloride / Hydrogen transfer / Deuterated 1,3-cyclohexadienes / Isotope effects
- Wehage, Hubert,Heesing, Albert
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p. 209 - 215
(2007/10/02)
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- Hydroboration. 86. Convenient Conversion of Aldehydes and Ketones into the Corresponding Alkenes via Hydroboration of their Enamines. A Remarkably Simple Synthesis of Either (Z)- or (E)-Alkenes
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Aldehydes and ketones are converted into the corresponding alkenes via hydroboration of their enamines.Hydroboration of aldehyde enamines by 9-borabicyclononane (9-BBN), followed by methanolysis, affords the corresponding terminal alkenes in 75-90percent yields.Unsaturated aldehyde enamines produce the corresponding dienes under these conditions.Enamines derived from substituted cyclic ketones and heterocyclic ketones are readily accommodated in this reaction to afford the corresponding alkenes in very good yields.The synthesis of pure (Z)- or (E)-alkenes is readily achieved from the same acyclic ketone enamine by modification of the hydroboration-elimination procedure: (A) hydroboration by 9-BBN followed by methanolysis or (B) hydroboration by borane methyl sulfide (BMS) followed by methanolysis and hydrogen peroxide oxidation.Mechanistic rationale is provided.
- Singaram, Bakthan,Rangaishenvi, Milind V.,Brown, Herbert C.,Goralski, Christian G.,Hasha, Dennis L.
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p. 1543 - 1549
(2007/10/02)
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- Microwave-Induced Reactions of Organic Substrates in the Cage of Zeolites
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Microwave irradiation of compounds 1, 7, 15, 19, 23, and 24 adsorbed on Y zeolites has been studied.The reaction rate of the corresponding rearrangement, dehydrogenation and dehydration is dramatically enhanced as compared with reactions under thermal conditions.
- Ipaktschi, Junes,Brueck, Matthias
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p. 1591 - 1593
(2007/10/02)
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- A NEW FORM OF THE REDUCTION OF BENZENE AND ITS ALKYL-SUBSTITUTRD DERIVATIVES TO 1,4-DIHYDRO DERIVATIVES IN THE LITHIUM-ISOPROPYL ALCOHOL-ETHYLENEDIAMINE SYSTEM
-
A new method, convenient and effective for preparative purposes, is proposed for the reduction of benzene, toluene, and o-cymene in the lithium-isopropyl alcohol-ethylenediamine system.It is based on reaction at 85-95 deg C with arene, alcohol, diamine, and metal in molar equivalent ratios of 1:4-6:0.25-0.5:2-3.
- Bazyl'chik, V. V.,Fedorov, P. I.,Odinokov, V. N.
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p. 1668 - 1670
(2007/10/02)
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- Photochemical Dehydrogenation of Alkanes Catalyzed by trans-Carbonylchlorobis(trimethylphosphine)rhodium: Aspects of Selectivity and Mechanism
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The photochemical dehydrogenation of alkanes is catalyzed in solution by trans-Rh(PMe3)2(CO)Cl with high efficiency; quantum yields up to 0.10 and turnover numbers as high as 5000 are achieved with cyclooctane as substrate.The intramolecular regioselectivity of the reaction is investigated with methyl-, ethyl-, and isopropylcyclohexane.In competition experiments, cyclooctane is found to be 17 times as reactive as cyclohexane; under carbon monoxide atmosphere, the selectivity is enhanced to a factor of 130.A kinetic isotope effect, kH/kD=5.3, is found for thedehydrogenation of C6H12/C6D12.Both intra- and intermolecular selectivities are consistent with a pathway involving a reversible C-H oxidative addition followed by a β-hydrogen elimination. trans-Rh(PMe3)2(CO)Cl is demonstrated to be the only significant photoactive species in solution.The dehydrogenation reaction is quenched by carbon monoxide with Stern-Volmer kinetics.On the basis of these results, a mechanism is proposed in which the enrgy needed to drive these thermodynamically unfavorable dehydrogenations is obtained only from Rh-CO bond photolysis.
- Maguire, John A.,Boese, William T.,Goldman, Alan S.
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p. 7088 - 7093
(2007/10/02)
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- Use of high pressure in the reduction of organic chlorides with tri-n-butyltin hydride
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The use of the high pressure technique enables reduction of organic halides by tri-n-butyltin hydride to be carried out in the absence of a catalyst or free radical initiator.It leads to a better conservation of the structure of the starting material during the reduction.In the case of some unsaturated halides, a new chemoselectivity has been observed in favour of the addition of the hydride on the carbon-carbon double bond.
- Rahm, A.,Amardeil, R.,Degueil-Castaing, M.
-
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- Cyclic Ether Formation in Superacid Media
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The formation of ethers in superacids by interaction of a primary hydroxy group with a carbocation centre has been investigated by a study of cyclisation of suitable substrates, mainly 1-(2-hydroxyethyl)cyclohexanols to give hydrobenzofurans.Cyclisation traps thermodynamically stable ionic species, with rates of reaction dependent upon the size of the ether ring formed.Three- and four-membered ether rings were not formed, five-membered ether rings formed readily, the reaction being comparable in rate with a 1,2-methyl shift.Six-membered rings formed a little less readily and seven-membered rings less readily still, though a yield of 34 percent from a suitable substrate has been recorded.An unexpected feature of the reactions was their stereospecificity; in one case, this is believed to result from a methyl shift concerted with attack of the primary hydroxy group, the reaction proceeding through hindered transition state, in which methyl loss, probably as CH3+, competes with a 1,2-methyl shift.
- Carr, Graham,Whittaker, David
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p. 359 - 366
(2007/10/02)
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- Platinacyclobutane chemistry: Cis-disubstituted platinacyclobutane complex from bicyclo[4.1.0] heptane
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The methodology for the preparation, isolation, and characterization of platinacyclobutanes from cis-disubstituted cyclopropane derivatives is established. In this case the metallacyclobutane was successfully prepared and characterized from bicyclo[4.1.0]
- Parsons,Jennings
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p. 1435 - 1437
(2008/10/08)
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- Selective Catalytic Dehydrogenation of Alkanes to Alkenes
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Linear and cyclic alkanes can be selectively dehydrogenated to the corresponding alkenes both thermally and photochemically (254 nm) with iridium complexes as catalysts.In the photochemical case, a sacrificial hydrogen acceptor is not required and H2 is evolved directly.Preferential initial formation of the least stable alkene (e.g., methylenecyclohexane from methylcyclohexane) is explained by attack at unhindered C-H bonds by an oxidative addition to the metal.A subsequent β-elimination gives the alkene.A key feature of the catalyst, 2-O2CCF3)(PR3)2> (4), is that the chelating acetate group can open up to allow β-elimination to take place in the alkyl hydride intermediate 2-O2CCF3)(PR3)2>.Prolonged reaction times lead to progressive isomerization of the alkene to give the thermodynamic product (e.g., 1-methylcyclohexene from methylcyclohexane).Up to 32 turnovers of dehydrogenation are seen.Deactivation of the catalyst takes place by P-C hydrogenolysis of the PAr3 ligand in the thermal case; the rise in the amount of ArH formed parallels the fall-off in activity of the catalyst.P-C cleavage does not take place in the photochemical system (R = cyclohexyl).A reversiblecyclometalation of the catalyst 4a (R = p-FC6H4) is observed after removal of the hydride ligands with t-BuCH=CH2.In the presence of C6H6, a C-H oxidative addition product, 2-O2CCF3)(PR3)2>, is formed instead (kH/kD = 4.5) and can be isolated from the reaction mixtures; This supports the oxidative addition pathway proposed for the alkanes.Equilibrium constants for the reaction of 4a with alkenes to give 1-O2CCF3)(PR3)2> are reported.
- Burk, Mark J.,Crabtree, Robert H.
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p. 8025 - 8032
(2007/10/02)
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- DEHYDRATION OF ALCOHOLS CATALYZED BY COPPER(II) SULFATE ADSORBED ON SILICA GEL.
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Copper(II) sulfate adsorbed on silica gel efficiently dehydrated secondary and tertiary alcohols under mild conditions to give olefins.The rate of dehydration of tertiary alcohols is much faster than that of secondary alcohols.
- Nishiguchi, Takeshi,Machida, Nakahira,Yamamoto, Etsuko
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p. 4565 - 4568
(2007/10/02)
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- Studies on Hydrogenation by Nickel Complexes. 5. The Selective Hydrogenation of 1,4-Cyclohexadienes to Cyclohexenes Catalyzed by a Nickel Complex
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1,4-Cyclohexadiene was hydrogenated selectively to cyclohexene with a nickel catalyst generated from bis(acetylacetonato)nickel(II), triethyldialuminium trichloride, and triphenylphosphine at 40 deg C under an atmospheric pressure of hydrogen.The hydrogenation of eleven kinds of alkyl-substituted 1,4-cyclohexadienes gave the corresponding cyclohexenes in good yields by the nickel catalyst.The structural factors of the alkyl substituent on the diolefin are shown to affect the hydrogenation rate.The homogeneous nickel catalyst system, in which a nickel hydride complex NiH(PPh3)(AlCl4) is supposed to be an active species, was effective for the selective hydrogenation of the diolefin to the olefin.A plausible pathway involving ?-allylnickel complexes for the hydrogenation is proposed.
- Sakai, Mutsuji,Hirano, Nobuo,Harada, Fumiya,Sakakibara, Yasumasa,Uchino, Norito
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p. 2923 - 2926
(2007/10/02)
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- Alkylation of Allylic Derivatives. 11. Copper(I)-Catalyzed Cross Coupling of Allylic Carboxylates with Grignard Reagents
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Reactions of allylic carboxylates with Grignard reagents containing catalytic amounts (1-10 mol percent) of cuprous salts give high yields of cross-coupled products.With alkyl Grignard reagents, regiochemistry can be controlled by choice of cuprous salt.With cuprous halides, little regiospecificity is observed.There is a small excess of γ-coupling in unbiased systems such as 5-methyl-2-cyclohexenyl (1), 2-cyclohexenyl (3), and β-phenylallyl (5) carboxylates.With CuCN, complete regiospecificity (exclusive γ-coupling) is observed with all alkyl Grignard reagents in unbiased systems, and with n-butylmagnesium halide >97percent γ-coupling results with α-methyl-γ-phenylallyl pivalate (7-OPiv) which is biased in favour of coupling at the α-position.In sharp contrast to alkyl Grignard reagents, phenyl and vinyl Grignard reagents containing CuCN show no regiospecificity.
- Tseng, Chung Chyi,Paisley, Steven D.,Goering, Harlan L.
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p. 2884 - 2891
(2007/10/02)
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- Reactions of Diethoxytriphenylphosphorane with Diastereoisomeric 3-Methylcyclohexane-1,2-diols. Control of Regioselectivity by Methyl Substitution during Cyclodehydration and Rearrangement of 1,2-Diols
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The diastereoisomeric 3-methylcyclohexane-trans-1,2-diols undergo cyclodehydration with diethoxytriphenylphosphorane (DTPP) to afford the cis- and trans-3-methylcyclohexene oxides.The ratio of cis and trans epoxides is best explained by assuming preferential phosphoranylation of the C1 hydroxyl group followed by " 3-exo-tet " alkoxide displacement of triphenylphosphine oxide.The diastereoisomers of 3-methylcyclohexane-cis-1,2-diol afford stable ? -dioxyphosphoranes when allowed to react with DTPP.These 1,3,2-dioxaphosphoranes were subjected to flash thermolysis ( 300 deg C ) conditions and afforded the isomeric 2- and 3-methylcyclohexanones via a 1,2-hydride shift.
- Robinson, Philip L.,Evans, Slayton A.
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p. 3860 - 3863
(2007/10/02)
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- Hydrogenolysis of Small Cycloalkanes, X. - Catalytic Hydrogenation of Bicycloalkanes
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Dependent on n different products are obtained from bicycloalkanes by hydrogenation on Pt and Pd/C catalysts: from n = 5 onward only methylcycloalkanes of the same ring size; with n = 4 additionally 2-7 percent of cycloheptane is formed; with n = 3 ring enlargement increases to 5-20 percent and with n = 2 cyclopentane is the only product.Mainly butane is formed from bicyclobutane and no intermediate could be detected.Explanations are attempted.The expected products are produced on hydrogenation of methyl-substituted derivatives and spiroalkanes.
- Stahl, Karl-Johannes,Hertzsch, Winfried,Musso, Hans
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p. 1474 - 1484
(2007/10/02)
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- Electrophilic Cleavage of Cyclopropanes. Acetolysis of Bicyclic and Tricyclic Cyclopropanes
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The acetolysis of a series of bicycloalkanes and propellanes has been studied.The effect of ring strain, caused by changing ring size or introducing a trans-ring fusion, on the rate and products of the reaction has been examined.No correlation was found between rates of acetolysis and strain energy relief, but with the exception of propellane, there is a rough correlation with ionization potentials.The degree of polarization of the C-C bonds in the presence of a proton correlates very well with reactivity and is a controlling factor for the acetolysis rates.The importance of the energies of unoccupied orbitals with the appropriate symmetry in controlling electron polarization is shown by the large difference in rate of reaction between - and propellanes.
- Wiberg, Kenneth B.,Kass, Steven R.,Meijere, Armin de,Bishop, K. C.
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p. 1003 - 1007
(2007/10/02)
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- ACTIVATION OF C-H BONDS IN SATURATED HYDROCARBONES. THE SELECTIVE, CATALYTIC FUNCTIONALISATION OF METHYL GROUPS BY MEANS OF A SOLUBLE IRIDIUM POLYHYDRIDE SYSTEM
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The selective, catalytic conversion of methylcyclohexane into methylenecyclohexane at 100 deg C, and of n-hexane into 1-hexene at 45 deg C, has been effected using bis(triisopropylphosphine)iridium pentahydride and an olefin (neohexene) as a hydrogen acceptor; with this system, approximate relative reactivities of C-H bonds in saturated hydrocarbons are: sec-alkyl-H, 1; iso-alkyl-H, 8; n-alkyl-H, >60.
- Felkin, Hugh,Fillebeen-Khan, Tauqir,Holmes-Smith, Rupert,Yingrui, Lin
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p. 1999 - 2000
(2007/10/02)
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- Thermal and Photochemical Catalytic Dehydrogenation of Alkanes with (R = C6H4F-p and Cyclohexyl)
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(cy = cyclohexyl) catalyses the photochemical dehydrogenation of cyclo-octane both in the presence and absence of a hydrogen-acceptor.
- Burk, Mark J.,Crabtree, Robert H.,McGrath, Dominic V.
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p. 1829 - 1830
(2007/10/02)
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- Protium-deuterium exchange of cyclic and acyclic alkanens in dilute acid medium at elevated temperatures
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A modification of the high temperature - dilute acid (HTDA) method for deuterium labelling of aromatic compounds has been applied to the H-D exchange of a number of cyclic and acyclic alkenes.Cyclopentene, cyclohexene, cyclododecene, and tetramethylethylene have been completely exchanged in excellent yield. 1-Methylcyclopentene and 1-methylcyclohexene have also been perdeuterated and cycloheptene and cyclooctene partially labelled but require spinning band distillation or preparative glpc for separation from rearrangement products.A variety of C5-C8 acyclic alkeneshave also been treated under HTDA conditions.
- Werstiuk, Nick Henry,Timmins, George
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p. 530 - 533
(2007/10/02)
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- Thermolysis of unsymmetrically substituted vinylcyclopropanes. The effect of substituents on the site-selectivity of homo--sigmatropic hydrogen migrations
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Thermolysis of the unsymmetrical vinylcyclopropanes 18-24 reveals a notable substituent effect on the site-selectivity of homo--sigmatropic hydrogen shifts.Rearrangement of 18-20 (OMe substituent) produces only products 25-27, respectively (HA migration).In sharp contrast, thermolysis of 24 (Me3Si substituent) provides exclusively substance 34 (HX migration).Thermolysis of substrates bearing methyl (21, 22) or phenyl (23) groups provide, in each case, mixtures of the two possible products.
- Piers, Edward,Maxwell, Anderson Richard
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p. 2392 - 2395
(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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- The Selective Catalytic Conversion of Cycloalkanes into Cycloalkenes using a Soluble Rhenium Polyhydride System
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Selective catalytic dehydrogenation (up to 9 turnovers) of cycloalkanes CnH2n (n = 6, 7, and 8) to the corresponding cycloalkenes is achieved, under mild conditions (30 - 80 deg C), using dilute (ca. 3 mM) solutions of the bis(phosphine)rhenium heptahydrides (Ar3P)2ReH7 (Ar=p-F-C6H4, Ph, and p-Me-C6H4) in the cycloalkane, with an olefin as the hydrogen acceptor.
- Baudry, Denise,Ephritikhine, Michel,Felkin, Hugh,Holmes-Smith, Rupert
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p. 788 - 789
(2007/10/02)
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- THE CLEMMENSEN REDUCTION OF ENOL ETHERS: CYCLOPROPYL ETHERS FROM MONO- AND DI-METHOXYCYCLOHEXA-1,4-DIENES
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Clemmensen reduction (zinc and hydrogen chloride in dry diethyl ether) of 1-methoxy- and 1,5-dimethoxy-cyclohexa-1,4-diene affords the cyclopropyl ethers, 1-methoxy- and 1,5-dimethoxy-bicyclohexane; in the presence of acetic anhydride, reduction of 6-acetyl-1-methoxy-6-methyl-cyclohexa-1,4-diene leads regiospecifically to 7-acetoxy-1-methoxy-6,7-dimethyl-bicyclohept-4-ene.
- Elphimoff-Felkin, Irene,Sarda, Pierre
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p. 4425 - 4428
(2007/10/02)
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- Metal-Catalyzed Organic Photoreactions. Bond-Cleavage Selectivity and Synthetic Application of the Iron(III) Chloride Catalyzed Photooxidation of Cyclic Olefins
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Photooxidation of olefins in pyridine in the presence of iron(III) chloride produced either α-chloro ketones (type A), gem-dichloro ketones (type B), or α,ω-dichloro ketones (type C), depending upon the substitution pattern of the substrate olefin.The synthetic utility of the type B reaction was demonstrated by the synthesis of some natural products.The synthesis of optically active solanone from D-p-menthene confirmed the D configuration of the natural product.
- Kohda, Akira,Nagayoshi, Kazuo,Maemoto, Kazuo,Sato, Tadashi
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p. 425 - 432
(2007/10/02)
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- Experimental and calculated thermodynamic data for the isomeric methylenecyclohexenes and methylenecyclohexane
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The equilibria in the isomerisation of the methylcyclohexenes and methylenecyclohexane have been investigated in the temperature range of 413 to 523 K. ΔrH and ΔrS have been calculated from the experimental data for the following equilibria: methylenecyclohexane1-methylcyclohexene, 3-methylcyclohexene1-methylcyclohexene and 4-methylcyclohexene1-methylcyclohexene.The resulting values for ΔrH and ΔrS are respectively: 7.3+-1.7, 7.6+-0.5, and 6.7+-0.4 kJ mol-1 and -15.9+-0.3, 1.0+-1.6 and 1.5+-1.4 J mol-1 K-1.These data are compared with values calculated using molecular mechanics.
- Peereboom, M.,Graaf, B. van de,Baas, J.M.A.
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p. 336 - 338
(2007/10/02)
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