- Deciphering Reactivity and Selectivity Patterns in Aliphatic C-H Bond Oxygenation of Cyclopentane and Cyclohexane Derivatives
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A kinetic, product, and computational study on the reactions of the cumyloxyl radical with monosubstituted cyclopentanes and cyclohexanes has been carried out. HAT rates, site-selectivities for C-H bond oxidation, and DFT computations provide quantitative information and theoretical models to explain the observed patterns. Cyclopentanes functionalize predominantly at C-1, and tertiary C-H bond activation barriers decrease on going from methyl- and tert-butylcyclopentane to phenylcyclopentane, in line with the computed C-H BDEs. With cyclohexanes, the relative importance of HAT from C-1 decreases on going from methyl- and phenylcyclohexane to ethyl-, isopropyl-, and tert-butylcyclohexane. Deactivation is also observed at C-2 with site-selectivity that progressively shifts to C-3 and C-4 with increasing substituent steric bulk. The site-selectivities observed in the corresponding oxidations promoted by ethyl(trifluoromethyl)dioxirane support this mechanistic picture. Comparison of these results with those obtained previously for C-H bond azidation and functionalizations promoted by the PINO radical of phenyl and tert-butylcyclohexane, together with new calculations, provides a mechanistic framework for understanding C-H bond functionalization of cycloalkanes. The nature of the HAT reagent, C-H bond strengths, and torsional effects are important determinants of site-selectivity, with the latter effects that play a major role in the reactions of oxygen-centered HAT reagents with monosubstituted cyclohexanes.
- Martin, Teo,Galeotti, Marco,Salamone, Michela,Liu, Fengjiao,Yu, Yanmin,Duan, Meng,Houk,Bietti, Massimo
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supporting information
p. 9925 - 9937
(2021/06/30)
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- Highly Selective Hydrogenation of Phenols to Cyclohexanone Derivatives Using a Palladium@N-Doped Carbon/SiO2Catalyst
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A new palladium-based heterogeneous material was synthesized by means of immobilization of Pd(OAc)2/1,10-phenanthroline on commercially available SiO2and subsequent pyrolysis at 600 °C for 2 h in air, namely, a Pd@N-doped carbon/SiO2catalyst. The obtained catalyst was studied by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS) techniques, and was effectively applied in the highly selective hydrogenation of phenols to give the corresponding cyclohexanone derivatives with 93-98% yields at 100 °C under 0.4 MPa H2in EtOH. It was demonstrated that introducing nitrogen could effectively promote the Pd dispersion and enhance the electronic interaction of Pd, both of which facilitate the improvement of the catalytic activity and selectivity. The likely reaction pathway was outlined to elucidate the selective hydrogenation mechanism according to experimental results.
- Sheng, Xueru,Wang, Chao,Wang, Wentao
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supporting information
p. 2425 - 2431
(2021/11/16)
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- The Silicon-Hydrogen Exchange Reaction: A Catalytic σ-Bond Metathesis Approach to the Enantioselective Synthesis of Enol Silanes
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The use of chiral enol silanes in fundamental transformations such as Mukaiyama aldol, Michael, and Mannich reactions as well as Saegusa-Ito dehydrogenations has enabled the chemical synthesis of enantiopure natural products and valuable pharmaceuticals. However, accessing these intermediates in high enantiopurity has generally required the use of either stoichiometric chiral precursors or stoichiometric chiral reagents. We now describe a catalytic approach in which strongly acidic and confined imidodiphosphorimidates (IDPi) catalyze highly enantioselective interconversions of ketones and enol silanes. These "silicon-hydrogen exchange reactions"enable access to enantiopure enol silanes via tautomerizing σ-bond metatheses, either in a deprotosilylative desymmetrization of ketones with allyl silanes as the silicon source or in a protodesilylative kinetic resolution of racemic enol silanes with a carboxylic acid as the silyl acceptor.
- Zhou, Hui,Bae, Han Yong,Leutzsch, Markus,Kennemur, Jennifer L.,Bécart, Diane,List, Benjamin
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supporting information
p. 13695 - 13700
(2020/08/24)
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- Continuous Synthesis of Aryl Amines from Phenols Utilizing Integrated Packed-Bed Flow Systems
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Aryl amines are important pharmaceutical intermediates among other numerous applications. Herein, an environmentally benign route and novel approach to aryl amine synthesis using dehydrative amination of phenols with amines and styrene under continuous-flow conditions was developed. Inexpensive and readily available phenols were efficiently converted into the corresponding aryl amines, with small amounts of easily removable co-products (i.e., H2O and alkanes), in multistep continuous-flow reactors in the presence of heterogeneous Pd catalysts. The high product selectivity and functional-group tolerance of this method allowed aryl amines with diverse functional groups to be selectively obtained in high yields over a continuous operation time of one week.
- Ichitsuka, Tomohiro,Kobayashi, Shū,Koumura, Nagatoshi,Sato, Kazuhiko,Takahashi, Ikko
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supporting information
p. 15891 - 15896
(2020/07/13)
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- Aliphatic C-H Bond Oxidation with Hydrogen Peroxide Catalyzed by Manganese Complexes: Directing Selectivity through Torsional Effects
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Substituted N-cyclohexyl amides undergo aliphatic C-H bond oxidation with H2O2 catalyzed by manganese complexes. The reactions are directed by torsional effects leading to site-selective oxidation of cis-1,4-, trans-1,3-, and cis-1,2-cyclohexanediamides. The corresponding diastereoisomers are unreactive under the same conditions. Competitive oxidation of cis-trans mixtures of 4-substituted N-cyclohexylamides leads to quantitative conversion of the cis-isomers, allowing isolation and successive conversion of the trans-isomers into densely functionalized oxidation products with excellent site selectivity and good enantioselectivity.
- Milan, Michela,Bietti, Massimo,Costas, Miquel
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supporting information
p. 2720 - 2723
(2018/05/22)
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- Ductile Pd-Catalysed Hydrodearomatization of Phenol-Containing Bio-Oils Into Either Ketones or Alcohols using PMHS and H2O as Hydrogen Source
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A series of phenolic bio-oil components were selectively hydrodearomatized by palladium on carbon into the corresponding ketones or alcohols in excellent yields using polymethylhydrosiloxane and water as reducing agent. The selectivity of the reaction was governed by the water concentration where selectivity to alcohol was favoured at higher water concentrations. As phenolic bio-oil examples cardanol and beech wood tar creosote were studied as substrate to the developed reaction conditions. Cardanol was hydrodearomatized into 3-pentadecylcyclohexanone in excellent yield. From beech wood tar creosote, a mixture of cyclohexanols was produced. No hydrodeoxygenation occurred, suggesting the applicability of the reported method for the production of ketone-alcohol oil from biomass. (Figure presented.).
- Di Francesco, Davide,Subbotina, Elena,Rautiainen, Sari,Samec, Joseph S. M.
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supporting information
p. 3924 - 3929
(2018/09/14)
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- Construction of Distant Stereocenters by Enantioselective Desymmetrizing Carbonyl-Ene Reaction
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An efficient desymmetrizing carbonyl-ene reaction of 1-substituted 4-methylenecyclohexanes with glyoxal derivatives was thus executed by a chiral N,N′-dioxide/NiII catalyst, providing facile access to cyclohexene derivatives bearing two remote 1,6-related stereocenters. This distal stereocontrol methodology originates from the efficient interaction between the catalyst with enophiles, discrimination of the two chair conformations of olefinic components, and the intrinsic six-membered transition-state structure of ene process.
- Luo, Weiwei,Lin, Lili,Zhang, Yu,Liu, Xiaohua,Feng, Xiaoming
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p. 3374 - 3377
(2017/07/15)
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- Readily Accessible Bulky Iron Catalysts exhibiting Site Selectivity in the Oxidation of Steroidal Substrates
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Bulky iron complexes are described that catalyze the site-selective oxidation of alkyl C-H bonds with hydrogen peroxide under mild conditions. Steric bulk at the iron center is introduced by appending trialkylsilyl groups at the meta-position of the pyridines in tetradentate aminopyridine ligands, and this effect translates into high product yields, an enhanced preferential oxidation of secondary over tertiary C-H bonds, and the ability to perform site-selective oxidation of methylenic sites in terpenoid and steroidal substrates. Unprecedented site selective oxidation at C6 and C12 methylenic sites in steroidal substrates is shown to be governed by the chirality of the catalysts.
- Font, David,Canta, Mercè,Milan, Michela,Cussó, Olaf,Ribas, Xavi,Klein Gebbink, Robertus J. M.,Costas, Miquel
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supporting information
p. 5776 - 5779
(2016/05/09)
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- Highly Selective Hydrogenation of Aromatic Ketones and Phenols Enabled by Cyclic (Amino)(alkyl)carbene Rhodium Complexes
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Air-stable Rh complexes ligated by strongly σ-donating cyclic (amino)(alkyl)carbenes (CAACs) show unique catalytic activity for the selective hydrogenation of aromatic ketones and phenols by reducing the aryl groups. The use of CAAC ligands is essential for achieving high selectivity and conversion. This method is characterized by its good compatibility with unsaturated ketones, esters, carboxylic acids, amides, and amino acids and is scalable without detriment to its efficiency.
- Wei, Yu,Rao, Bin,Cong, Xuefeng,Zeng, Xiaoming
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supporting information
p. 9250 - 9253
(2015/08/11)
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- Selective Hydrogenation of Phenol to Cyclohexanone over Pd-HAP Catalyst in Aqueous Media
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The production of pure cyclohexanone under mild conditions over catalysts with high reactivity, selectivity, compatibility, stability, and low cost is still a great challenge. Here we report a hydroxyapatite-bound palladium catalyst (Pd-HAP) to demonstrate its excellent performance on phenol hydrogenation to cyclohexanone. Based on catalyst characterization, the Pd nanoclusters (≈0.9 nm) are highly dispersed and bound to phosphate in HAP. Only basic active sites on HAP surface are detected. At 25°C and ambient H2 pressure in water, phenol can be 100% converted into cyclohexanone with 100% selectivity. This system shows a universal applicability to temperature, pH, solvent, low H2 purity, and pressure. The catalyst reveals high stability to be recycled without deactivation or morphology change; and Pd nano-clusters barely aggregate even at 400°C. During the reaction, HAP adsorbs phenol, and Pd nanoclusters activate and spillover H2. The mechanism is also investigated, proposed, and verified.
- Xu, Guangyue,Guo, Jianhua,Zhang, Ying,Fu, Yao,Chen, Jinzhu,Ma, Longlong,Guo, Qingxiang
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p. 2485 - 2492
(2015/08/24)
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- Site-selective oxidation of unactivated C sp 3-H bonds with hypervalent iodine(III) reagents
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By design: The site-selective oxidation of unactivated secondary C sp 3-H bonds was accomplished with hypervalent iodine(III) reagents and tert-butyl hydroperoxide (see scheme). The preparation and derivatization of the hypervalent iodine(III) reagent are simple, thus allowing the rational design of these reagents to optimize the site selectivity of the oxidation. Copyright
- Moteki, Shin A.,Usui, Asuka,Zhang, Tiexin,Solorio Alvarado, Cesar R.,Maruoka, Keiji
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supporting information
p. 8657 - 8660
(2013/09/12)
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- Direct selective hydrogenation of phenol and derivatives over polyaniline-functionalized carbon-nanotube-supported palladium
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Cyclohexanone is an industrially important intermediate in the synthesis of materials such as nylon and polyamides, but direct selective hydrogenation of phenol to cyclohexanone under green conditions is a challenge owing to the over-reduction of cyclohexanone to cyclohexanol. A catalyst made of palladium nanoparticles supported on polyaniline-functionalized carbon nanotubes, Pd-PANI/CNT, which was shown to be highly active towards the direct hydrogenation of phenol to cyclohexanone, is reported. Phenol conversion exceeding 99 % was achieved with a cyclohexanone selectivity of >99 % under atmospheric pressure of hydrogen in aqueous media. The generality of the catalyst for this reaction was demonstrated by selective hydrogenation of other hydroxylated aromatic compounds with similar performance, again under green and mild conditions. It is suggested the Pd-N interactions and polymeric stabilization play a key role in the formation of stable and highly dispersed palladium nanoparticles on the conducting composite material PANI/CNT. The results also indicate that the phenol conversion is related presumably to the conductive property of PANI/CNT, whereas the cyclohexanone selectivity is attributed to the nitrogen-containing nature of PANI/CNT. Support group: Direct selective hydrogenation of phenol to cyclohexanone was achieved over a polyaniline (PANI)-functionalized carbon-nanotube (CNT)-supported palladium catalyst under atmospheric hydrogen pressure in aqueous media (see scheme). The results indicate that the phenol conversion is related to the conductive property of composite material PANI/CNT, whereas the cyclohexanone selectivity is attributed to the nitrogen-containing nature of PANI/CNT.
- Chen, Jinzhu,Zhang, Wei,Chen, Limin,Ma, Longlong,Gao, Hui,Wang, Tiejun
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p. 142 - 148
(2013/04/10)
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- Selective hydrogenation of phenol and derivatives over polymer- functionalized carbon-nanofiber-supported palladium using sodium formate as the hydrogen source
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Selective hydrogenation of phenol to cyclohexanone over a catalyst of polyaniline-functionalized carbon-nanofiber-supported palladium (Pd-PANI/CNF) with sodium formate as the hydrogen source has been studied. Phenol conversion exceeding 99 % was achieved with a cyclohexanone selectivity of >99 % in aqueous media. In an extension to Pd-PANI/CNF, polymers such as polypyrrole (PPY), poly(4-vinylpyridine) (PVP), and poly(1-vinylimidazole) (PVI) were further applied to a catalyst of Pd-polymer/CNF for selective phenol hydrogenation. All of the Pd-polymer/CNF catalysts showed excellent to good performance toward selective phenol hydrogenation. However, Pd-PANI/CNF was considerably more active and selective to afford the desired cyclohexanone than Pd-PPY/CNF, Pd-PVP/CNF, and Pd-PVI/CNF. Moreover, a series of phenol-derived compounds were selectively hydrogenated in high yields under the investigated aqueous conditions. The research highlights an environmentally benign and effective process for the selective reduction of phenol derivatives with sodium formate as an alternative hydrogen source. Source material: Palladium supported on nitrogen-containing-polymer-functionalized carbon nanofibers was used as the catalyst for selective hydrogenation of phenol to cyclohexanone using sodium formate as the hydrogen source in aqueous media (see figure). The hydrogenation involved a hydrogen-transfer reaction pathway with cyclohexanone as the "intermediate". Copyright
- Chen, Aibing,Li, Yonglei,Chen, Jinzhu,Zhao, Guoying,Ma, Longlong,Yu, Yifeng
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p. 1370 - 1378
(2013/12/04)
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- Oxidation of alcohols with hydrogen peroxide in the presence of a new triple-site phosphotungstate
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A new clean catalytic process for the selective oxidation of alcohol to ketones has been studied. The catalytic properties were investigated with aqueous hydrogen peroxide under halide- and organic solvent-free conditions. The results show that triethyl({2, 4, 6-trimethyl-3, 5-bis[(triethylazaniumyl) methyl]phenyl}methyl)azanium (tribromide) based phosphotungstate complex (TBAP) has excellent catalytic ability to the oxidation reaction of alcohol by hydrogen peroxide with high yield. Moreover this catalyst could be easily recovered by simple workup and reused up without any appreciable loss of its activity. ARKAT-USA, Inc.
- He, Ying,Ma, Xiaoyun,Lu, Ming
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p. 187 - 197
(2012/10/29)
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- Kinetic analysis of 4-isopropylphenol hydrogenation over activated carbon-supported rhodium catalysts in supercritical carbon dioxide solvent
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Hydrogenation behavior of 4-isopropylphenol to 4-isopropylcyclohexanol over activated carbon-supported rhodium catalysts in supercritical carbon dioxide (scCO2) at 313 K was studied in a batch reactor and the results were compared with those in 2-propanol. Higher yields of cis-4-isopropylcyclohexanol were obtained in scCO2 than in 2-propanol, and the formation of a byproduct, isopropylcyclohexane, was suppressed in scCO2. The catalyst modification with hydrochloric or phosphoric acid enhanced the yield of cis-4-isopropylcyclohexanol in both scCO2 and 2-propanol solvents. Kinetic analyses of the reaction profiles revealed higher reaction rates in scCO2 than those in 2-propanol for the 4-isopropylcyclohexanol formation both by the direct hydrogenation of 4-isopropylphenol and by the consecutive hydrogenation of 4-isopropylcyclohexanone, and also revealed that the addition of hydrochloric acid increased the consecutive hydrogenation rate of 4-isopropylcyclohexanone to cis-4-isopropylcyclohexanol, which reduced the total reaction time needed for the complete hydrogenation of 4-isopropylphenol to 4-isopropylcyclohexanol. The Royal Society of Chemistry 2012.
- Hiyoshi, Norihito,Sato, Osamu,Yamaguchi, Aritomo,Rode, Chandrashekhar V.,Shirai, Masayuki
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experimental part
p. 633 - 638
(2012/05/04)
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- Synthesis of (1S,4R)-4-isopropyl-1-methyl-2-cyclohexen-1-ol, the aggregation pheromone of the ambrosia beetle Platypus quercivorus, its racemate, (1R,4R)- and (1S,4S)-isomers
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(S)-Perillyl alcohol was converted to (R)-cryptone (91.5-93% ee) in six steps, which was then treated with methyllithium to give (1S,4R)-4-isopropyl-1-methyl-2-cyclohexen-1-ol, the aggregation pheromone of the ambrosia beetle Platypus quercivorus. The racemic pheromone was also prepared by methylation of (±)-cryptone. Both (1R,4R)- and (1S,4S)-isomers (98% ee) of the pheromone were synthesized from the enantiomers of dihydrolimonene oxide.
- Mori, Kenji
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p. 2133 - 2142
(2007/10/03)
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- Highly diastereoselective formation of spirocyclic compounds via 1,5-hydrogen transfer: A total synthesis of (-)-erythrodiene
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(Chemical Equation Presented) A highly stereoselective synthesis of (-)-erythrodiene starting from 4-isopropylcyclohexanone is described. The key reactions are an asymmetric methoxycarbonylation of the starting ketone and a highly diastereoselective radical cascade involving addition of a phenylthiyl radical to a terminal alkyne followed by a 1,5-hydrogen transfer and a 5-exo-cyclization.
- Lachia, Mathilde,Denes, Fabrice,Beaufils, Florent,Renaud, Philippe
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p. 4103 - 4106
(2007/10/03)
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- Vanadium phosphorus oxide as an efficient catalyst for hydrocarbon oxidations using hydrogen peroxide
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Calcined vanadium phosphorus oxide (VPO) prepared by an organic route is found to be an active and effective catalyst for the oxidation of various alkanes such as cyclopentane, cyclohexane, n-hexane, cycloheptane, cyclooctane, cyclodecane and adamantane in acetonitrile solvent using the environmentally benign oxidant, hydrogen peroxide, where the oxidation mechanism is believed to involve a reversible V4+/V5+ redox cycle.
- Pillai, Unnikrishnan R.,Sahle-Demessie, Endalkachew
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p. 525 - 528
(2007/10/03)
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- Copper-catalysed aerobic oxidation of alcohols using fluorous biphasic catalysis
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A copper(I) catalysed and TEMPO mediated fluorous biphasic oxidation of primary, secondary, allylic and benzylic alcohols with oxygen in the presence of a bipyridine ligand bearing perfluorinated ponytails is described. High chemoselectivities are observed in the oxidation of substituted cyclohexanols (substituted axial cyclohexanols react 6-8 times faster than the corresponding equatorial cyclohexanols).
- Ragagnin, Gianna,Betzemeier, Bodo,Quici, Silvio,Knochel, Paul
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p. 3985 - 3991
(2007/10/03)
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- Amidino derivatives useful as nitric oxide synthase inhibitors
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The current invention discloses useful pharmaceutical compositions containing amidino derivative useful as nitric oxide synthase inhibitors.
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- A convenient, efficient method for conjugate reductions using catalytic quantities of Cu(I)
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Exposure of enones and enals to either Bu3SnH or PhSiH3 in the presence of ≤ 5 mol % [(Ph3P)CuH]6 leads to products of 1,4-hydride delivery in good yields.
- Lipshutz, Bruce H.,Keith, John,Papa, Patrick,Vivian, Randall
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p. 4627 - 4630
(2007/10/03)
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- Amidino dervatives useful as nitric oxide synthase inhibitors
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The current invention discloses useful pharmaceutical compositions containing azepine derivatives useful as nitric oxide synthase inhibitors.
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- The Interaction of π orbitals with a carbocation over three σ bonds
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The semi-π analogue of double hyperconjugation ("hyperconjugation/conjugation") has been examined in 4-isopropylidenecyclohexyl mesylate (4-OMs) by comparison with the saturated analogue, trans-4-isopropylcyclohexyl mesylate (5-OMs). The unsaturated substrate reacts in 97% trifluoroethanol only four times faster than the saturated substrate. Raber-Harris plots indicate that both substrates react by ks mechanisms; i.e., solvolysis occurs with solvent assistance rather than carbocation formation. These results are consistent with the absence of a direct, through-bond interaction of the double bond with the reactive center. The absence is caused at least in part by less than ideal overlap of the γ,δ π orbitals with the α,β σ orbitals. In contrast, an electron-rich tin atom attached to the 4-position provides a large rate enhancement and changes the mechanism to carbocation formation through double hyperconjugation.
- Lambert, Joseph B.,Ciro, Sol M.
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p. 1940 - 1945
(2007/10/03)
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- A stereoselective total synthesis of (±)-erythrodiene
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Erythrodiene, a unique spirobicyclic sesquiterpene hydrocarbon from the Caribbean gorgonian coral Erythropodium caribaeorum, has been synthesized from 4-isopropylcyclohexanol in 8-steps and approximately 16% overall yield. The synthesis features a stereoselective intramolecular carbomercuration reaction as the key step.
- Huang, He,Forsyth, Craig J.
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p. 7889 - 7890
(2007/10/02)
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- SPIROJATAMOL, A NEW SKELTTAL SESQUITERPENOID OF NARDOSTACHYS JATAMANSI ROOTS
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A new sesquiterpenoid 1 was isolated from the roots of Nardostachys jatamansi and its structure was established by means of spectroscopic data and chemical evidences.Compound 1 has a novel spiranic sesquiterpenoid skeleton.
- Bagchi, Anjana,Oshima, Yoshiteru,Hikino, Hiroshi
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p. 1523 - 1530
(2007/10/02)
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- Electrocatalytic Hydrogenation Using Precious Metal Microparticles in Redox-Active Polymer Films
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Glassy carbon felt electrodes have been modified by electrodeposition of poly(pyrrole-viologen) films (derived from N,N'-dialkyl-4,4'-bipyridinium salts), followed by electroprecipitation of precious metal (Pt, Pd, Rh, or Ru) microparticles.The resulting electrodes have been proved to be active for the electrocatalytic hydrogenation of conjugated enones (2-cyclohexen-1-one, cryptone, carvone, isophorone), styrene, and benzonitrile in aqueous media (pH 1).Despite low loading of metal catalysts, high electric and product yields and a long term stability of these cathodes have been observed.The influence of the metal loading and the polymer structure on the catalytic efficiency as well as the selectivity obtained according to the metal catalyst used have been studied.Comparision with results previously reported for other catalytic cathodes like Pt/Pt, Pd/C, or Raney nickel electrodes proves the high efficiency of these microparticles within redox polymer film based electrodes.
- Coche, Liliane,Ehui, Bernadette,Limosin, Daniele,Moutet, Jean-Claude
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p. 5905 - 5910
(2007/10/02)
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- ELECTROCATALYSE PAR DES FILMS DE POLYPYRROLES FONCTIONNALISES
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In this paper are rewiewed the possibilities of the utilization of modified electrodes by N-substituted polypyrroles by mediator groups in terms of electrocatalysis.
- Deronzier, Alain
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- ULTRASONICALLY IMPROVED REDUCTIVE PROPERTIES OF AN AQUEOUS Zn-NiCl2 SYSTEM - 1 SELECTIVE REDUCTION OF α,β-UNSATURATED CARBONYL COMPOUNDS
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Conjugate addition of several compounds is obtained with good to excellent yield in an aqueous medium using a reagent constituted by zinc dust and nickel chloride(9-1).Ultrasounds are shown to improve the yields and reaction rates.
- Petrier, Christian,Luche, Jean-Louis
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p. 2347 - 2350
(2007/10/02)
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