- Single-Site Cobalt-Catalyst Ligated with Pyridylimine-Functionalized Metal-Organic Frameworks for Arene and Benzylic Borylation
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We report a highly active single-site heterogeneous cobalt-catalyst based on a porous and robust pyridylimine-functionalized metal-organic frameworks (pyrim-MOF) for chemoselective borylation of arene and benzylic C-H bonds. The pyrim-MOF having UiO-68 topology, constructed from zirconium-cluster secondary building units and pyridylimine-functionalized dicarboxylate bridging linkers, was metalated with CoCl2 followed by treatment of NaEt3BH to give the cobalt-functionalized MOF-catalyst (pyrim-MOF-Co). Pyrim-MOF-Co has a broad substrate scope, allowing the C-H borylation of halogen-, alkoxy-, alkyl-substituted arenes as well as heterocyclic ring systems using B2pin2 or HBpin (pin = pinacolate) as the borylating agent to afford the corresponding arene- or alkyl-boronate esters in good yields. Pyrim-MOF-Co gave a turnover number (TON) of up to 2500 and could be recycled and reused at least 9 times. Pyrim-MOF-Co was also significantly more robust and active than its homogeneous control, highlighting the beneficial effect of active-site isolation within the MOF framework that prevents intermolecular decomposition. The experimental and computational studies suggested (pyrim?-)CoI(THF) as the active catalytic species within the MOF, which undergoes a mechanistic pathway of oxidative addition, turnover limiting σ-bond metathesis, followed by reductive elimination to afford the boronate ester.
- Akhtar, Naved,Antil, Neha,Balendra,Begum, Wahida,Kumar, Ajay,Manna, Kuntal,Newar, Rajashree,Shukla, Sakshi
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- The efficient and selective biocatalytic oxidation of norisoprenoid and aromatic substrates by CYP101B1 from Novosphingobium aromaticivorans DSM12444
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CYP101B1 from Novosphingobium aromaticivorans DSM12444 is a homologue of CYP101A1 (P450cam) from Pseudomonas putida and the CYP101D1, CYP101D2 and CYP101C1 enzymes from the same bacterium. CYP101B1 binds norisoprenoids more tightly than camphor and efficiently hydroxylates substrates in combination with ferredoxin reductase, ArR, and [2Fe-2S] ferredoxin, Arx, electron transfer partners. The norisoprenoids, α-ionone and β-damascone are both oxidised by CYP101B1 with high product formation activity, >500 min-1. α-Ionone oxidation occurred regioselectively at the allylic C3 position while β-damascone was hydroxylated predominantly at C3, 86%, with the main competing minor product arising from oxidation at the allylic C4 position (11%). When incorporated into a whole-cell oxidation system, with ArR and Arx, CYP101B1 is also capable of oxidising the aromatic compound indole. Other aromatic molecules including phenylcyclohexane and p-cymene were tested and both were hydroxylated by CYP101B1. Phenylcyclohexane was selectively oxidised to trans-4-phenylcyclohexanol while p-cymene was hydroxylated at the benzylic carbons to yield a mixture of isopropylbenzyl alcohol and p-α,α-trimethylbenzylalcohol. Trans-4-Phenylcyclohexanol was formed with a product formation rate of 141 min-1 and was five times more active than the oxidation of p-cymene. This journal is
- Hall, Emma A.,Bell, Stephen G.
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- Ruthenium(III)-catalysed Hydrogen Peroxide Oxidation of Alkyl Aromatic Compounds under Phase-Transfer Conditions
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The side chain of alkyl aromatic derivatives is oxidized to aldehydes, ketones, or alcohols by hydrogen peroxide in the presence of a ruthenium(III) salt and a quaternary ammonium phase-transfer catalyst.
- Barak, Gabriela,Sasson, Yoel
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- Allylic oxidation of cyclic alkenes with molecular oxygen and tert-butyl hydroperoxide over copper-manganese oxides
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Abstract: An efficient and mild method for the allylic oxidation of cyclic alkenes employing molecular oxygen and tert-butyl hydroperoxide as the oxidant, copper-manganese oxides as heterogeneous catalyst under ambient temperature is proposed. The catalyst, which was prepared by co-precipitation and characterized, was evaluated oxidation of isolongifolene as a typical mode substrate. The catalyst showed a good catalytic activity and remained nearly the same after four cycles. The scope of the reaction was investigated with a variety of cyclic alkenes compounds. Graphical abstract: [Figure not available: see fulltext.]
- Zhang, Wu,Wei, Qiuyu,Lan, Lingling,Wu, Aiqun,Yin, Xiuju,Shen, Liqun
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- Structure and C-S bond cleavage in aryl 1-methyl-1-arylethyl sulfide radical cations
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Steady state and laser flash photolysis (LFP) of a series of p-X-cumyl phenyl sulfides (4-X-C6H4C(CH3) 2SC6H5: 1, X = Br; 2, X = H; 3, X = CH 3; 4, X = OCH3) and p-X-cumyl p-methoxyphenyl sulfides (4-X-C6H4C(CH3)2SC6H 4OCH3: 5, X = H; 6, X = CH3; 7, X = OCH 3) has been carried out in the presence of N-methoxy phenanthridinium hexafluorophosphate (MeOP+PF6-) under nitrogen in MeCN. Steady state photolysis showed the formation of products deriving from the C-S bond cleavage in the radical cations 1+?-7 +? (2-aryl-2-propanols and diaryl disulfides). Formation of 1+?-7+? was also demonstrated by LFP experiments evidencing the absorption bands of the radical cations 1+?- 3+? (λmax = 530 nm) and 5+?- 7+? (λmax = 570 nm) mainly localized in the arylsulfenyl group and radical cation 4+? (λ max = 410, 700 nm) probably mainly localized in the cumyl ring. The radical cations decayed by first-order kinetics with a process attributable to the C-S bond cleavage. On the basis of DFT calculations it has been suggested that the conformations most suitable for C-S bond cleavage in 1 +?-4+? and 7+? are characterized by having the C-S bond almost collinear with the π system of the cumyl ring and by a significant charge and spin delocalization from the ArS ring to the cumyl ring. Such a delocalization is probably at the origin of the observation that the rates of C-S bond cleavage result in very little sensitivity to changes in the C-S bond dissociation free energy (BDFE). A quite large reorganization energy value (λ = 43.7 kcal mol-1) has been calculated for the C-S bond scission reaction in the radical cation. This value is much larger than that (λ = 12 kcal mol-1) found for the C-C bond cleavage in bicumyl radical cations, a reaction that also leads to cumyl carbocations.
- Baciocchi, Enrico,Bettoni, Marta,Del Giacco, Tiziana,Lanzalunga, Osvaldo,Mazzonna, Marco,Mencarelli, Paolo
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- Linear Free Energy Relationship Studies of the Dimethyldioxirane C-H Bond Insertion Reaction
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The relative rates of reaction of a series of p-substituted cumenes with dimethyldioxirane have been studied.The products are the corresponding cumyl alcohols.Treatment of the rate data with the Hammett substituent constants reveals that the insertion reaction is an electrophilic process with ρ = -2.76.Similar tretment of the data with the Brown-Okamoto substituent constants gives ρ+ = -1.61.The second-order rate constants for the reaction of a series of substituted adamantanes with dimethyldioxirane were also determined.Again, the products are the corresponding adamantanols.The rate constants were correlated with several types of substituent constants.The best correlations were obtained with the Taft ?* and ?I constants which gave ρ* = -1.08 and ρI = -2.39, respectively.Thus, the insertion reaction in this aliphatic system is also electrophilic.
- Murray, Robert W.,Gu, Hong
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- To Rebound or...Rebound? Evidence for the "alternative Rebound" mechanism in Ca'H Oxidations by the systems nonheme Mn Complex/H2O2/carboxylic acid
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In this work, it has been shown that aliphatic Ca'H oxidations by bioinspired catalyst systems Mn aminopyridine complex/H2O2/carboxylic acid in acetonitrile afford predominantly a mixture of the corresponding alcohol and the ester. The alcohol/ester ratio is higher for catalysts bearing electron-donating groups at the aminopyridine core. Isotopic labeling studies witness that the oxygen atom of the alcohol originates from the H2O2molecule, while the ester oxygen comes exclusively from the acid. Oxidation of ethylbenzene in the presence of acetic acid affords enantiomerically enriched 1-phenylethanol and 1-phenyl acetate, with close enantioselectivities and the same sign of absolute chirality. Experimental data and density functional theory calculations provide evidence in favor of the rate-limiting benzylic H atom abstraction by the high-spin (S = 1) [LMnV(O)OAc]2+active species followed by competitive OH/OC(O)R rebound. This mechanism has been unprecedented for Ca'H oxidations catalyzed by bioinspired Mn complexes. The trends governing the alcohol/ester ratios have been rationalized in terms of steric properties of the catalyst, acid, and substrate. copy; 2021 American Chemical Society.
- Ottenbacher, Roman V.,Bryliakova, Anna A.,Shashkov, Mikhail V.,Talsi, Evgenii P.,Bryliakov, Konstantin P.
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p. 5517 - 5524
(2021/05/31)
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- Palladium-Aminopyridine Catalyzed C?H Oxygenation: Probing the Nature of Metal Based Oxidant
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A mechanistic study of direct selective oxidation of benzylic C(sp3)?H groups with peracetic acid, catalyzed by palladium complexes with tripodal amino-tris(pyriylmethyl) ligands, is presented. The oxidation of arylalkanes having secondary and tertiary benzylic C?H groups, predominantly yields, depending on the substrate and conditions, either the corresponding ketones or alcohols. One of the three 2-pyriylmethyl moieties, which is pending in the starting catalyst, apparently, facilitates the active species formation and takes part in stabilization of the high-valent Pd center in the active species, occupying the axial coordination site of palladium. The catalytic, as well as isotopic labeling experiments, in combination with ESI-MS data and DFT calculations, point out palladium oxyl species as possible catalytically active sites, operating essentially via C?H abstraction/oxygen rebound pathway. For the ketones formation, O?H abstraction/в-scission mechanism has been proposed.
- Lubov, Dmitry P.,Bryliakova, Anna A.,Samsonenko, Denis G.,Sheven, Dmitriy G.,Talsi, Evgenii P.,Bryliakov, Konstantin P.
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p. 5109 - 5120
(2021/11/10)
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- Method for synthesizing tertiary alcohol by catalytically oxidizing benzyl tertiary C-H bonds of aromatic hydrocarbon through metalloporphyrin
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The invention discloses a method for synthesizing tertiary alcohol by catalytically oxidizing benzyl tertiary C-H bonds of aromatic hydrocarbon through metalloporphyrin. The method comprises the following steps: dispersing metalloporphyrin (1*10-1%, mol/mol) into aromatic hydrocarbon; sealing the reaction system, heating to 40-120 DEG C while stirring, introducing an oxidant (0.10-1.0 MPa), keeping the set temperature and pressure, carrying out reactions for 3.0-24.0 hours under stirring, and carrying out after-treatment on the reaction solution to obtain the product aromatic benzyl tertiary alcohol. The method has the advantages of shortest conversion path, highest atom economy, lower reaction temperature, lower environmental influence and the like, and the selectivity of aromatic benzyl tertiary alcohol is high. In addition, the content of aromatic hydrocarbon hydroperoxide is low, and the safety coefficient is high. The invention provides an efficient, feasible and safe method for synthesizing aromatic benzyl tertiary alcohol through selective catalytic oxidation of benzyl tertiary C-H bonds of aromatic hydrocarbon.
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Paragraph 0072-0073
(2020/09/30)
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- Efficient and selective oxidation of tertiary benzylic C[sbnd]H bonds with O2 catalyzed by metalloporphyrins under mild and solvent-free conditions
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The direct and efficient oxidation of tertiary benzylic C[sbnd]H bonds to alcohols with O2 was accomplished in the presence of metalloporphyrins as catalysts under solvent-free and additive-free conditions. Based on effective inhibition on the unselective autoxidation and deep oxidation, systematical investigation on the effects of porphyrin ligands and metal centers, and apparent kinetics study, the oxidation system employing porphyrin manganese(II) (T(2,3,6-triCl)PPMn) with bulkier substituents as catalyst, was regarded as the most promising and efficient one. For the typical substrate, the conversion of cumene could reach up to 57.6% with the selectivity of 70.5% toward alcohol, both of them being higher than the current documents under similar conditions. The superiority of T(2,3,6-triCl)PPMn was mainly attributed to its bulkier substituent groups preventing metalloporphyrins from oxidative degradation, its planar structure favoring the interaction between central metal with reactants, and the high efficiency of Mn(II) in the catalytic transformation of hydroperoxides to alcohols.
- Hu, Meng-Yun,Liu, Lei,Qi, Bei,She, Yuan-Bin,Shen, Hai-Min,Ye, Hong-Liang
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- Method for selectively oxidizing cumene compounds
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The invention relates to a method for selectively oxidizing cumene compounds, and the method comprises the following steps: placing cumene compounds shown in a formula (I), an iron porphyrin catalyst,an oxidant and a dispersant into a ball milling tank, sealing the ball milling tank, performing ball milling for 3 to 24 hours at a rotating speed of 100 to 800 rpm at room temperature, stopping ballmilling once every 1 to 3 hours in the ball milling process, discharging gases in the ball milling tank, finishing the reaction, and performing post-treatment on a reaction mixture to obtain product2-phenyl-2-propanol compound shown in a formula (II); according to the invention, the oxidation conversion of the cumene and derivatives thereof is realized through solid-phase ball milling, the reaction mode is novel, the operation is convenient, and the energy consumption is low; the method needs no organic solvent, thus effectively avoiding the use of toxic and harmful organic solvents and being green and environment-friendly; has low peroxide content and high safety factor, and high 2-phenyl-2-propanol and derivative selectivity and meets the social requirements of the current green chemical process, environmental compatibility chemical process and biological compatibility chemical process.
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Paragraph 0095; 0096
(2019/11/21)
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- Heterologous expression of geraniol dehydrogenase for identifying the metabolic pathways involved in the biotransformation of citral by Acinetobacter sp. Tol 5
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The biotransformation of citral, an industrially important monoterpenoid, has been extensively studied using many microbial biocatalysts. However, the metabolic pathways involved in its biotransformation are still unclear, because citral is a mixture of the trans-isomer geranial and the cis-isomer neral. Here, we applied the heterologous expression of geoA, a gene encoding geraniol dehydrogenase that specifically converts geraniol to geranial and nerol to neral, to identify the metabolic pathways involved in the biotransformation of citral. Acinetobacter sp. Tol 5 was employed in order to demonstrate the utility of this methodology. Tol 5 transformed citral to (1R,3R,4R)-1-methyl-4-(1-methylethenyl)-1,3-cyclohexanediol and geranic acid. Biotransformation of citral precursors (geraniol and nerol) by Tol 5 transformant cells expressing geoA revealed that these compounds were transformed specifically from geranial. Our methodology is expected to facilitate a better understanding of the metabolic pathways involved in the biotransformation of substrates that are unstable and include geometric isomers.
- Usami, Atsushi,Ishikawa, Masahito,Hori, Katsutoshi
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p. 2012 - 2020
(2018/11/06)
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- Selective reaction of benzyl alcohols with HI gas: Iodination, reduction, and indane ring formations
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Reactions of benzyl alcohols with HI in solvent-free conditions were examined. Three types of reactions (iodination, reduction, and ring formation) occurred depending on the degree of crowding around the benzyl position and the benzylic stabilization of substrates. Results also showed that the ring formation to give indanes proceeded efficiently when HI was used, and that compounds with electron-rich aromatic rings gave indane derivatives in good yields.
- Matsumoto, Shoji,Naito, Masafumi,Oseki, Takehisa,Akazome, Motohiro,Otani, Yasuhiko
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p. 7254 - 7259
(2017/11/24)
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- The Oxidation of Hydrophobic Aromatic Substrates by Using a Variant of the P450 Monooxygenase CYP101B1
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The cytochrome P450 monooxygenase CYP101B1, from a Novosphingobium bacterium is able to bind and oxidise aromatic substrates but at a lower activity and efficiency than norisoprenoids and monoterpenoid esters. Histidine 85 of CYP101B1 aligns with tyrosine 96 of CYP101A1, which, in the latter enzyme forms the only hydrophilic interaction with its substrate, camphor. The histidine residue of CYP101B1 was mutated to phenylalanine with the aim of improving the activity of the enzyme for hydrophobic substrates. The H85F mutant lowered the binding affinity and activity of the enzyme for β-ionone and altered the oxidation selectivity. This variant also showed enhanced affinity and activity towards alkylbenzenes, styrenes and methylnaphthalenes. For example the rate of product formation for acenaphthene oxidation was improved sixfold to 245 nmol per nmol CYP per min. Certain disubstituted naphthalenes and substrates, such as phenylcyclohexane and biphenyls, were oxidised with lower activity by the H85F variant. Variants at H85 (A and G) designed to introduce additional space into the active site so as to accommodate these larger substrates did not improve the oxidation activity. As the H85F mutant of CYP101B1 improved the oxidation of hydrophobic substrates, this residue is likely to be in the substrate binding pocket or the access channel of the enzyme. The side chain of the histidine might interact with the carbonyl groups of the favoured norisoprenoid substrates of CYP101B1.
- Sarkar, Md. Raihan,Lee, Joel H. Z.,Bell, Stephen G.
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p. 2119 - 2128
(2017/10/12)
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- From DNA to catalysis: A thymine-acetate ligated non-heme iron(III) catalyst for oxidative activation of aliphatic C-H bonds
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A non-heme, iron(iii)/THA(thymine-1-acetate) catalyst together with H2O2 as an oxidant is efficient in oxidative C-H activation of alkanes. Although having a higher preference for tertiary C-H bonds, the catalyst also oxidizes aliphatic secondary C-H bonds into carbonyl compounds with good to excellent conversions. Based on the site selectivity of the catalyst and our mechanistic studies the reaction proceeds via an Fe-oxo species without long lived carbon centered radicals.
- Al-Hunaiti, Afnan,R?is?nen, Minn?,Repo, Timo
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p. 2043 - 2046
(2016/02/05)
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- Synthesis of Terephthalic Acid by p-Cymene Oxidation using Oxygen: Toward a More Sustainable Production of Bio-Polyethylene Terephthalate
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The synthesis of terephthalic acid from biomass remains an unsolved challenge. In this study, we conducted the selective oxidation of p-cymene (synthesized from biodegradable terpenes, limonene, or eucalyptol) into terephthalic acid over a Mn–Fe mixed-oxide heterogeneous catalyst. The impact of various process parameters (oxidant, temperature, reaction time, catalyst amount, oxygen pressure) on the selectivity to terephthalic acid was evaluated, and some mechanistic aspects were elucidated. An unprecedented synthesis of biobased terephthalic acid (51 % yield) in the presence of O2 is reported.
- Nea?u, Florentina,Culic?, Geanina,Florea, Mihaela,Parvulescu, Vasile I.,Cavani, Fabrizio
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p. 3102 - 3112
(2016/11/17)
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- Compounds of the menthane series. Synthesis of unsaturated primary alcohols with the o- and p-menthane skeletons
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Precursors to terpene alcohols of the o- and p-menthane series (o-cimen-7-ol and o- and p-cimen-9-ols) were synthesized, and their reduction with lithium in ethylenediamine was studied. The reduction of o- and p-cimen-9-ols in the presence of isopropyl alcohol selectively afforded the corresponding 1,4-dihydro derivatives. Under analogous conditions, o-cimen-7-ol was converted into a mixture of unsaturated hydrocarbons. The reduction with lithium in ethylenediamine in the absence of isopropyl alcohol in all cases gave mixtures of menthene alcohols.
- Fedorov,Fedorova,Sheverdov,Pavlov,Eremkin
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p. 806 - 812
(2016/07/30)
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- DICARBOXYLIC ACID MONOMERS AND METHODS OF MAKING AND USING THE SAME
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Disclosed herein are phenylindane dicarboxylic acid (PIDA) monomers, polymer compositions comprising the PIDA monomers, and methods of preparing PIDA monomers. This abstract is intended as a scanning tool for purposes of searching in the particular art and is not intended to be limiting of the present disclosure.
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Paragraph 0304
(2015/12/07)
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- Mechanism of Selective C-H Hydroxylation Mediated by Manganese Aminopyridine Enzyme Models
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The mechanism of selective oxidation of aliphatic C-H groups with H2O2 in the presence of aminopyridine Mn complexes, modeling the reactivities of natural oxygenases of the cytochrome P450 superfamily, has been examined. The oxygenation of C-H groups proceeds via hydrogen atom abstraction by the electrophilic metal site; the logarithm of C-H oxidation rates correlates linearly with bond dissociation energies for homolytic C-H bond cleavage. Hammett correlations and stereospecificity studies reflect the formation of a short-lived electron-deficient radical intermediate. Isotopic labeling studies confirm the incorporation of 18O from added H218O, thus providing so far lacking evidence for the oxomanganese(V)-mediated oxidation mechanism. (Figure Presented).
- Ottenbacher, Roman V.,Talsi, Evgenii P.,Bryliakov, Konstantin P.
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- C-S bond cleavage in aromatic sulfide radical cations
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The results of our recent studies of the structural effects on the C-S bond fragmentation process of aromatic sulfur radical cations are reported.
- Lanzalunga, Osvaldo
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p. 322 - 330
(2013/07/25)
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- Visible-light photosensitized oxidation of α-terpinene using novel silica-supported sensitizers: Photooxygenation vs. photodehydrogenation
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Three silica-immobilized organic photocatalysts, based on rose bengal (RB), antraquinone-2-carboxylic acid (ANT-COOH) and a new cyanoanthracene derivative (DBTP-COOH), were prepared and characterized. Their efficiency for the photooxidation of α-terpinene was compared to that of their soluble counterparts. In solution, the three sensitizers showed high quantum yield of singlet oxygen production. Significant autooxidation to p-cymene occurred in the absence of catalyst while the mechanism of the sensitized reaction strongly depended on sensitizer structure. With DBTP and RB materials, ascaridole was rapidly produced by singlet oxygen addition. In contrast, ANT-based sensitizers favored photodehydrogenation to p-cymene through an electron-transfer step inducing a radical chain reaction, followed by further p-cymene oxidation upon prolonged irradiation. The highest efficiency and selectivity were obtained for photooxygenation with DBTP-based materials, and for photodehydrogenation with ANT-based materials, these properties make them attractive for future applications as immobilized photocatalyst in solar synthesis, waste treatment, and microflow reactors.
- Ronzani, Filippo,Costarramone, Nathalie,Blanc, Sylvie,Benabbou, Abdelhamid Khalil,Bechec, Mickael Le,Pigot, Thierry,Oelgemoeller, Michael,Lacombe, Sylvie
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p. 164 - 174
(2013/07/05)
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- ANTIVIRAL DRUGS FOR TREATMENT OF ARENA VIRUS INFECTION
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Compounds, methods and pharmaceutical compositions for treating viral infections, by administering certain compounds in therapeutically effective amounts are disclosed. Methods for preparing the compounds and methods of using the compounds and pharmaceutical compositions thereof are also disclosed. In particular, the treatment and prophylaxis of viral infections such as caused by the Arenavirus family such as Lassa fever, Argentine hemorrhagic fever, Bolivian hemorrhagic fever, and Venezuelan hemorrhagic fever
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Paragraph 0000192; 0000194
(2013/08/28)
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- An efficient and mild oxidation of α-isophorone to ketoisophorone catalyzed by N-hydroxyphthalimide and copper chloride
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N-hydroxyphthalimide (NHPI) and copper chloride (CuCl2) were first utilized for aerobic oxidation of α-isophorone (α-IP) to ketoisophorone (KIP) and the effects of co-catalysts, temperature, reaction time, solvent, amount of CuCl2 and pressure of oxygen were investigated extensively. NHPI/CuCl2 turned out to be highly efficient to this oxidation with up to 91.3% conversion and 81.0% selectivity under mild conditions. And various hydrocarbons including benzylic compounds, cycloalkene and its derivatives were also oxidized smoothly under optimized conditions. Moreover, the possible reaction mechanism was proposed and verified by FT-IR spectra.
- Chen, Lihua,Tang, Ruiren,Li, Zhongying,Liang, Shan
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experimental part
p. 459 - 463
(2012/05/20)
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- Lipase-mediated resolution of substituted 2-aryl-propanols: Application to the enantioselective synthesis of phenolic sesquiterpenes
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A comprehensive study of the lipase-mediated resolution of substituted 2-aryl-propanols is reported. The latter alcohols were submitted to the irreversible acetylation catalyzed either by PPL, CRL, or lipase PS. The enantioselectivity of these transformations was dependent on the type of lipase used. The type of substituents and particularly their position on the aromatic ring strongly affected the selectivity of the reaction. The experiments described prove that PPL is the more versatile lipase catalyzing the acetylation with an enantiomeric ratio (E) value that ranges from 1 up to 144, depending on the substrate used. Conversely, the same transformations were catalyzed by CRL and lipase PS with an enantiomeric ratio value, which is always less than 5. The remarkable behavior of PPL was exploited in the large scale resolution of some substituted 2-aryl-propanols whose enantiomeric forms are relevant building blocks in the enantioselective synthesis of phenolic sesquiterpenes. By these means, the synthesis of (S)-turmeronol B and the formal syntheses of (R)-curcumene, (R)-curcuphenol, (R)-xanthorrhizol, and (R)-curcuhydroquinone were accomplished.
- Serra, Stefano
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experimental part
p. 619 - 628
(2011/07/08)
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- Dynamic path bifurcation in the Beckmann reaction: Support from kinetic analyses
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The reactions of oximes to amides, known as the Beckmann rearrangement, may undergo fragmentation to form carbocations + nitriles when the migrating groups have reasonable stability as cations. The reactions of oxime sulfonates of 1-substituted-phenyl-2-propanone derivatives (7-X) and related substrates (8-X, 9a-X) in aqueous CH3CN gave both rearrangement products (amides) and fragmentation products (alcohols), the ratio of which depends on the system; the reactions of 7-X gave amides predominantly, whereas 9a-X yielded alcohols as the major product. The logk-logk plots between the systems gave excellent linear correlations with slopes of near unity. The results support the occurrence of path bifurcation after the rate-determining TS of the Beckmann rearrangement/fragmentation reaction, which has previously been proposed on the basis of molecular dynamics simulations. It was concluded that path-bifurcation phenomenon could be more common than thought and that a reactivity-selectivity argument based on the traditional TS theory may not always be applicable even to a well-known textbook organic reaction.
- Yamamoto, Yutaro,Hasegawa, Hiroto,Yamataka, Hiroshi
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p. 4652 - 4660
(2011/07/29)
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- Aqueous phase C-H bond oxidation reaction of arylalkanes catalyzed by a water-soluble cationic Ru(III) complex [(pymox-Me2) 2RuCl2]+BF4-
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The cationic complex [(pymox-Me2)RuCl2] -BF4- was found to be a highly effective catalyst for the C-H bond oxidation reaction of arylalkanes in water. For example, the treatment of ethylbenzene (1.0 mmol) with t-BuOOH (3.0 mmol) and 1.0 mol % of the Ru catalyst in water (3 mL) cleanly produced PhCOCH3 at room temperature. Both a large kinetic isotope effect (kH/k D) 14) and a relatively large Hammett value (ρ) -1.1) suggest a solvent-caged oxygen rebounding mechanism via a Ru(IV)-oxo intermediate species.
- Yi, Chae S.,Kwon, Ki-Hyeok,Lee, Do W.
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supporting information; experimental part
p. 1567 - 1569
(2009/08/07)
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- Evolved CYP102A1 (P450BM3) variants oxidise a range of non-natural substrates and offer new selectivity options
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The evolution of CYP102A1 variants with enhanced activity and altered specificity characteristics. The Royal Society of Chemistry.
- Whitehouse, Christopher J. C.,Bell, Stephen G.,Tufton, Henry G.,Kenny, Richard J. P.,Ogilvie, Lydia C. I.,Wong, Luet-Lok
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p. 966 - 968
(2008/09/21)
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- Desaturation of alkylbenzenes by cytochrome P450BM3 (CYP102A1)
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A study was conducted to investigate the desaturation of alkylbenezenes by cytochrome P450BM3 (CYP102A1). It was observed during the study that oxidation of alkylbenzenes with CYP102A1 involves a gamut of P450 activity types that are terminal, sub-terminal benzylic and aromatic hydroxylation; terminal and sub-terminal desaturation; and epoxidation of the olefins. It was also found that the desaturation of cumene by CYP102A1 is sensitive to α-deuteration and insensitive to β-deuteration. Intramolecular deuterium isotope study revealed that the first abstraction in the desaturation of valproic acid and ezlopitant by microsomal P450s take place from activated carbon atoms. The increased β-hydroxylation percentages show that the β-carbon lies closer to the ferryl oxygen in the KT5.
- Whitehouse, Christopher J.C.,Bell, Stephen G.,Wong, Luet-Lok
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supporting information; scheme or table
p. 10905 - 10908
(2009/11/30)
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- Improved preparative route toward 3-arylcyclopropenes
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A convenient preparative protocol for the synthesis of various 3-arylcyclopropenes in a multigram scale is disclosed. Optimization of the reaction conditions and isolation procedures allowed for significant improvement of the chemical yields of these strained products. The described protocol was used for efficient preparation of a series of 3-methyl-3-arylcyclopropenes possessing different substituents in the aromatic ring. The effect of substitution in the aryl group on the stability of 3-arylcyclopropenes, as well as the corresponding precursors, is discussed.
- Sherrill, William M.,Kim, Ryan,Rubin, Michael
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p. 8610 - 8617
(2008/12/21)
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- Kinetics and mechanism of acid catalysed hydration of α- methylstyrenes
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Twelve para-substituted α-methylstyrenes with substituents H, CH 3, CF3, CH3O, CH3S, F, Cl, Br, CH3CO, CH3SO2, CN a NO2 were synthesised; additionally, the acid catalysed hydration kinetics of these compounds were measured in sulfuric acid in a concentration range c from 0.017 to 9.58 mol l-1, at 25.0°C. The observed rate constants obtained were used to construct the kinetic acidity function and calculate the catalytic rate constants. Based on the evaluation of the acidity function kinetic dependence on acid medium concentration, and the substituent effects of acid catalysed hydration of α-methylstyrenes on the catalytic rate constants, the mechanism of acid catalysed hydration was verified. The mechanism involves the addition of a proton to the double bond of α-methylstyrene in the rate-limiting reaction step denoted as A-SE2. No evident difference was found between the effects of the acid medium on the acid catalysed hydration of styrenes and α-methylstyrenes, which indicates very similar activity coefficients of the reactants, and of the transition state of both substrates. The substituent effects evaluation shows that the rate-limiting step of the reaction consists in the addition of a proton to the substrate. The carbocation formation in the transition state of this reaction step proceeds roughly half-way compared with the extent of the carbocation formation by cumyl chloride hydrolysis. The obtained carbocation is in particular stabilised by the substituents with +M effect, while the influence of the substituents with -M and I effects is significantly smaller.
- Pytela, Oldrich,Trlida, Bronislav
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p. 1025 - 1036
(2008/09/19)
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- Optically active nitrile oxides: synthesis and 1,3-dipolar cycloaddition reactions
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Baker's yeast-promoted reduction of the C{double bond, long}C bond in 2-aryl-1-nitropropenes gave the corresponding optically active (R)-2-aryl-1-nitropropanes of high enantiomeric purity (ee >90%). They were next converted with the aid of the Mukaiyama and Hoshino method into the optically active nitrile oxides, which were made to react in situ with ethyl propiolate, methylvinyl ketone and (R)-1-phenyl-2-(phenylsulfonyl)ethyl acrylate to yield the appropriate, enantiomerically enriched, isoxazoles or 4,5-dihydroisoxazoles as diastereomeric mixtures, respectively.
- Zagozda, Marcin,Plenkiewicz, Jan
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p. 1457 - 1464
(2008/02/11)
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- A new synthetic method for methyl ketones from carboxylic acids using metallic strontium and methyl iodide
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Carboxylic acids reacted with metallic strontium and methyl iodide to give methyl ketones preferentially in moderate to good yields. Copyright
- Miyoshi, Norikazu,Matsuo, Tsuyoshi,Asaoka, Masashi,Matsui, Aki,Wada, Makoto
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- The ritter reaction under truly catalytic bronsted acid conditions
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Simple organic acids like 2,4-dinitrobenzenesulfonic acid (DNBSA) catalyze the Ritter reaction of secondary benzylic alcohols giving rise to the corresponding N-benzylacetamides in usually high yields. Reactions can be conducted without exclusion of oxygen and without the need of dry solvents. With tertiary α,α-dimethylbenzylic alcohols a different pathway involving a formal dimerization reaction takes place under the acid-catalytic conditions used. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
- Sanz, Roberto,Martinez, Alberto,Guilarte, Veronica,Alvarez-Gutierrez, Julia M.,Rodriguez, Felix
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p. 4642 - 4645
(2008/03/12)
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- Formation of trans-verbenol and verbenone from α-pinene catalysed by immobilised Picea abies cells
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Both enantiomers and the raceinate of α-pinene were transformed by Picea abies cells immobilised on alginate. The main products were cis- and trans-verbenol, the later being further transformed to verbenone. The enantiomeric purity of each product more or less corresponded to that of the substrate. Transformation by free cells was faster than that by the immobilised cells. The ratio of products differed to some extent between the transformation by tree and immobilised cells.
- Vanek, Tomas,Halik, Jan,Vankova, Radmila,Valterova, Irena
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p. 321 - 325
(2007/10/03)
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- Carbocation-forming reactions in ionic liquids
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A number of trifluoroacetates, mesylates, and triflates have been studied in ionic liquids. Several lines of evidence indicate that all of these substrates react via ionization to give carbocationic intermediates. For example, cumyl trifluoroacetates give mainly the elimination products, but the Hammett ρ+ value of -3.74 is consistent with a carbocationic process. The analogous exo-2-phenyl-endo-3-deutero-endo-bicyclo-[2.2.1]hept-2-yl trifluoroacetate gives an elimination where loss of the exo-hydrogen occurs from a cationic intermediate. 1-Adamantyl mesylate and 2-adamantyl triflate react to give simple substitution products derived from capture of 1- and 2-adamantyl carbocations by the residual water in the ionic liquid. The triflate derivative of pivaloin, trans-2-phenylcyclopropylcarbinyl mesylate, 2,2-dimethoxycyclobutyl triflate, the mesylate derivative of diethyl (phenylhydroxymethyl)-thiophosphonate, and Z-1-phenyl-5-trimethylsilyl-3-penten- 1-yl trifluoroacetate all give products derived carbocation rearrangements (kΔ processes), anti-7-Norbornenyl mesylate gives products with complete retention of configuration, indicative of involvement of the delocalized 7-norbornenyl cation. 1,6-Methano[10]annulen-11-yl triflate reacts in [BMIM][NTf2] to give 1,6-methano[10]annulen-11-ol, along with naphthalene, an oxidized product derived from loss of trifluoromethanesulfinate ion. Analogous loss of CF3SO2- can be seen in reaction of PhCH(CF3)OTf. Ionic liquids are therefore viable solvents for formation of carbocationic intermediates via kc and k Δ processes.
- Creary, Xavier,Willis, Elizabeth D.,Gagnon, Madeleine
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p. 18114 - 18120
(2007/10/03)
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- Indium(III) bromide-catalyzed chemioselective dimerization of vinylarenes
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Indium(III) bromide catalyzes the dimerization of α-substituted vinylarenes. Chemioselectivity towards open chain or cyclic dimers depends on the nature of the substituent at the aryl group of the vinylarene.
- Peppe, Clovis,Lang, Ernesto Schulz,De Andrade, Fabiano Molinos,De Castro, Liérson Borges
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p. 1723 - 1726
(2007/10/03)
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- Formation mechanism of p-methylacetophenone from citral via a tert-alkoxy radical intermediate
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The aim of this study was to clarify the formation mechanism of a potent off-odorant, p-methylacetophenone, from citral under acidic aqueous conditions. An acidic aqueous solution (pH 3.0) containing 10 mg/L of citral was stored at 40 °C for 2 weeks. Among the compounds detected in the stored citral solution, 4-(2-hydroxy-2-propyl)benzaldehyde was identified for the first time as a degradation product from citral. The formation of p-methylacetophenone and 4-(2-hydroxy-2-propyl)-benzaldehyde behaved the same when antioxidants were added to the citral solution. In addition, both compounds were formed by the Fe2+-induced decomposition of 8-hydroperoxy-p-cymene, another compound identified in the stored citral solution. These results suggested that both p-methylacetophenone and 4-(2-hydroxy-2-propyl)benzaldehyde can be formed via the same radical intermediate [p-CH3C6H 4C(CH3)2O.] that can be derived from the O-O bond homolysis of 8-hydroperoxy-p-cymene. On the other hand, the degradation of 8-hydroperoxy-p-cymene without Fe2+ under acidic aqueous conditions did not yield p-methylacetophenone and 4-(2-hydroxy-2-propyl) benzaldehyde, but the degradation of citral without Fe2+ did. Therefore, other than the decomposition of 8-hydroperoxy-p-cymene, a mechanism to generate the tert-alkoxy radical intermediate was proposed for the formation of p-methylacetophenone and 4-(2-hydroxy-2-propyl)benzaldehyde in the citral solution.
- Ueno, Toshio,Masuda, Hideki,Ho, Chi-Tang
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p. 5677 - 5684
(2007/10/03)
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- Photo- and radiation-chemical production of radical cations of methylbenzenes and benzyl alcohols and their reactivity in aqueous solution
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Radical cations of methylated benzenes and benzyl alcohols were generated by photoionization and by reaction SO4·- in aqueous solution. The photoionization requires two 248 nm photons. The lifetimes with the oxidant SO4 and absorption spectra of the radical cations produced were determined by time-resolved conductance and optical detection, and the reaction products were measured by GC. As expected, the radical cation lifetimes increase strongly with increasing number of additional methyl groups, and so does the ratio of deprotonation from a methyl or hydroxymethyl group vs. addition (of water) to a ring position. In the case of toluene the radical cation appears to have a chemical lifetime τ of 10-100 ps ≤ τ ≤ 20 ns, i.e., longer than it takes for an ion pair to separate into the free (solvated) ions, and it reacts predominantly by addition of water to the ring rather than by deprotonation from the methyl group. A further observation is that, as compared to methoxylated analogues, the methylated benzyl alcohol radical cations are much more reactive, such that OH-induction of side-chain fragmentation, as often required with methoxylated benzyl alcohol-type radical cations, is not necessary.
- Russo-Caia, Claudia,Steenken, Steen
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p. 1478 - 1485
(2007/10/03)
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- Spectral properties and absolute rate constants for β-scission of ring-substituted cumyloxyl radicals. A laser flash photolysis study
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A laser flash photolysis study of the spectral properties and β-scission reactions of a series of ring-substituted cumyloxyl radicals has been carried out. All cumyloxyl radicals display a broad absorption band in the visible region of the spectrum, which decays on the microsecond time scale, leading to a strong increase in absorption in the UV region of the spectrum, which is attributed to the corresponding acetophenone formed after β-scission of the cumyloxyl radicals. The position of the visible absorption band is red-shifted by the presence of electron-donating ring substituents, while a blue-shift is observed in the presence of electron-withdrawing ring substituents, suggesting that + R ring substituents promote charge separation in the excited cumyloxyl radical through stabilization of the partial positive charge on the aromatic ring of an incipient radical zwitterion. Along this line, an excellent Hammett-type correlation between the experimentally measured energies at the visible absorption maxima of the cumyloxyl radicals and σ+ substituent constants is obtained. A red-shift is also observed on going from MeCN to MeCN/H2O for all cumyloxyl radicals, pointing toward a specific effect of water. The ring substitution does not influence to a significant extent the rate constants for β-scission of the cumyloxyl radicals, which varies between 7.1 × 105 and 1.1 × 106 s-1, a result that suggests that cumyloxyl radical β-scission is not governed by the stability of the resulting acetophenone. Finally, κβ increases on going from MeCN to the more polar MeCN/H2O 1:1 for all cumyloxyl radicals, an observation that reflects the increased stabilization of the transition state for β-scission through increased solvation of the incipient acetophenone product.
- Baciocchi, Enrico,Bietti, Massimo,Salamone, Michela,Steenken, Steen
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p. 2266 - 2270
(2007/10/03)
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- Vilsmeier-Haack reaction of tertiary alcohols: Formation of functionalised pyridines and naphthyridines
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Vilsmeier-Haack reaction of 2-arylpropan-2-ols proceeds with multiple iminoalkylations leading to the formation of conjugated iminium salts which on ammonium acetate-induced cyclisation afford 4-arylnicotinaldehydes in good yields. Tertiary alcohols derived from aliphatic or alicyclic ketones by the addition of methyl Grignard are converted into substituted pyridines and naphthyridines by the action of Vilsmeier's reagent in N,N-dimethylformamide followed by nucleophile-assisted cyclisation in the presence of ammonium acetate.
- Thomas,Asokan
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p. 2583 - 2587
(2007/10/03)
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- Base-catalysed rearrangement of terpinolene oxide
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Terpinolene oxide, a tetrasubstituted spiro epoxide has been found to get rearranged over KO'Bu in DMSO to give p-cymenol in high yields.
- Pasha,Nagaraja
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p. 1172 - 1173
(2007/10/03)
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- Ozone-mediated nitration of bicumene and derivatives with nitrogen dioxide. Preferential mesolytic bond cleavage over nuclear nitration in evidence for the electron transfer nature of the kyodai-nitration of arenes
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The ozone-mediated reaction of bicumene and some derivatives 1 with nitrogen dioxide in dichloromethane at low twmperatures resulted in the facile cleavage of the central C-C bond to give the corresponding benzyl nitrate and its descendants 4-6. mesolytic bond cleavage occured almost exclusively over nuclear substitution at temperatures as low as -20 deg C, especially at low concentration (2 x 10-3 mol dm-3).This result may be rationalized in terms of initial electron transfer between the aromatic substrate and nitrogen trioxide in situ to form the aromatic radical cation, which then undergoes C-C bond scission at the benzylic position.In contrast, bibenzyl 2a is simply nitrated on the aromatic ring under similar conditions, giving the expected nitration products 7 and 8a-c along with a small amount of benzaldehyde 9.Results obtained from semi-empirical calculations and cyclic voltammetry are also in accord with the electron transfer nature of the reaction.The C-Si bond fission of benzyltrimethylsilane, C-C bond fragmentation of cyclic acetals of aromatic carbonyl compounds as well as side-chain reactions of toluene and derivatives, have all previously been observed under certain conditions of the kyodai-nitration and can be understood on a similar basis as described above.The possible involment of electron transfer processes in aromatic nitration with acetyl nitrate has also been suggested.
- Suzuki, Hitomi,Mori, Tadashi
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p. 1265 - 1274
(2007/10/03)
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- Metal cation-exchanged montmorillonite(Mn+-mont)-catalysed carbonyl-ene reactions
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Metal cation-exchanged montmorillonite (Mn+-mont) works in acetonitrile at 80°C as a Lewis acid catalyst for the intermolecular carbonyl-ene reaction of α-methylstyrenes with paraformaldehyde to give the corresponding homoallylic alcohols, Zr4+-mont being the most effective of the many Mn+-mont catalysts examined. Similarly, the catalyst is also useful for the highly stereoselective intramolecular cyclization of citronellals to afford isopulegols, the reaction being much faster. Regeneration of the catalyst is confirmed for Zr4+-mont, which can be effectively recycled at least five times.
- Tateiwa, Jun-Ichi,Kimura, Akihiro,Takasuka, Masaaki,Uemura, Sakae
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p. 2169 - 2174
(2007/10/03)
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- Catalytic Oxidation of (+)-3-Carene with Oxygen
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Liquid-phase oxidation of (+)-3-carene in the presence of catalysts with active additives (pyridine, amines, and amines) has been studied.
- Tolstikov, G. A.,Galin, F. Z.,Ignatyuk, V. K.,Kashina, Yu. A.,Galkin, E. G.
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p. 1044 - 1046
(2007/10/03)
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- Base-catalysed rearrangement of p-menth-1-en-4(8)-oxide
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p-Menth-1-en-4(8)-oxide (1), a tetrasubstituted spiro epoxide is normally resistant towards bases but under forcing condition with AIP rearranges to p-mentha-1,8-dien-4-ol (2).On the other hand, with t-BuOK, p-mentha-1,3-dien-8-ol (3) and p-mentha-1,4-dien-8-ol (4) are formed as the major products.These compounds readily get oxidised to p-cymen-8-ol (5), as seen in the reaction of 1 with N-LiEDA.
- Roy, Animesh,Gurudutt, K. N.,Rao, Sanjay
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p. 636 - 638
(2007/10/03)
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- A comparison of substituent effects on the stability of α,α-dimethylbenzyl carbocations in aqueous solution and in the gas phase: How significant is nucleophilic solvation?
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Rate and equilibrium constants for conversion of ring-substituted cumyl alcohols in acidic solutions of 50:50 (v/v) trifluoroethanol/water (I = 0.50, NaClO4) to an equilibrium mixture of the corresponding cumyl alcohol, cumyl trifluoroethyl ether, and α-methylstyrene and the fractional yields of cumyl trifluoroethyl ether obtained from partitioning of the cumyl carbocation intermediates of these reactions between capture by water and by trifluoroethanol have been determined. These data and estimates of absolute rate constants for the reaction of ring-substituted cumyl carbocations with water in 50:50 (v/v) trifluoroethanol/water30 have been used to calculate equilibrium constants KR and Kp respectively for conversion of ring-substituted cumyl carbocations to the corresponding cumyl alcohols and α-methylstyrenes and the changes in Gibbs free energy (△Gx)sol for deprotonation of ring-substituted cumyl carbocations by α-methylstyrene. A plot of (△Gx)sol against (△Gx)gas for the corresponding reactions in the gas phase is linear with a slope of 0.70, in contrast to the previously reported unitary slopes of correlations of substituent effects on carbocation stability in solution and in the gas phase. We conclude that there is a modest increase in the stabilization of ring-substituted cumyl carbocations by solvation as their stability is decreased, but that this is much smaller than the change in stabilization by solvation with the changing stability of pyridinium and anilinium ions. The possible relevance of these data to the stabilization of carbocations by nucleophilic solvation is discussed.
- Richard, John P.,Jagannadham, Vandannapu,Amyes, Tina L.,Mishima, Masaaki,Tsuno, Yuho
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p. 6706 - 6712
(2007/10/02)
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- The enantioselective metabolism of p-cymene in rabbits
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p-Cymene (1) was metabolized in rabbits and the following four optically active metabolites, 2-(p-tolyl)-1-propanol (3': R/S = 65:35), 2-(p-tolyl)propanoic acid (5': R/S = 0:100), p-(2-hydroxy-1-methylethyl)benzoic acid (6': R/S = 91:9) and p-(1-carboxyethyl)benzoic acid (8': R/S = 30:70), were isolated in addition to three optically inactive metabolites, 2-(p-tolyl)-2-propanol (2), p-isopropylbenzoic acid (4'), and p-(1-hydroxy-1-methylethyl)benzoic acid (7'). The presumed metabolic pathways of p-cymene in rabbits were confirmed by the administration of the intermediate metabolites (2, 3', 4', and 5'). The enantiomeric ratios of the metabolites, 3' and 6', suggested that ω-hydroxylations of the isopropyl group in 1 and 4' occurred preferentially at the pro-S methyl group. In the metabolism of 1, the S-isomers are predominant in the propanoic acid derivatives, but the R-isomers are rich in the propanol derivatives. It is of interest that the metabolism of 4', however, produced predominantly the corresponding propanol derivative (6'; R/S = 91:9) and propanoic acid derivative (8'; R/S = 80:20) possessing the same R-configuration. Some optically active p-cymene derivatives were also synthesized as standard compounds.
- Matsumoto,Ishida,Yoshida,Terao,Takeda,Asakawa
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p. 1721 - 1726
(2007/10/02)
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- PRODUCTS OF THE CATALYTIC LIQUID-PHASE OXIDATION OF 3-CARENE
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The liquid-phase oxidation of 3-carene in the presence of various catalytic systems has been studied.The possibility has been shown of the directed preparation of 3-carene oxide, of ketones with a carane skeleton and a 7-membered ring, or of aromatic tertiary alcohols.
- Vyglazov, O. G.,Manukov, E. N.,Fedorishcheva, M. N.,Ariko, N. G.,Chuiko, V. A.,Bazhina, G. N.
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p. 283 - 287
(2007/10/02)
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- Radical ions in photochemistry. Carbon-carbon bond cleavage of radical cations in solution: Theory and application
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The cleavage of radical cations of two series of alkanes, 1,1,2-triaryl- and 1,1,2,2-tetraarylalkanes, generated by photoinduced single electron transfer in acetonitrile-methanol, occurs with formation of radical and carbocation fragments. The radical cations of some unsymmetrically substituted alkanes cleave to give all four of the possible products, two hydrocarbons emanating from the radicals and two methyl ethers from the carbocations, in proportion to the oxidation potentials of the two possible radical fragments. There is an excellent linear correlation between the logarithm of the observed ratio of products and that calculated from the reported electrochemically determined oxidation potentials (r = 0.998, 5 points). The proportionality constant (1.27) for this relationship is close to unity which indicates that the product ratio is determined by the relative rates of cleavage in the two possible modes or by equilibration of the radicals and carbocations before separation of the geminate radical carbocation pair and not by equilibration upon reencounter of freely solvated radical and carbocation fragments. The effect of temperature on the relative oxidation potentials of the radicals studied is small and can be neglected when radicals of the same order (i.e., both secondary or both tertiary) and of similar size are compared. The ratio of products obtained upon cleavage of the radical cation at 25 °C can be used to determined standard oxidation potentials of radicals. The oxidation potential of the diphenylmethyl radical (0.350 V vs SCE) has been accepted as the primary standard and the (4-methyl-phenyl)phenylmethyl (0.265 V) and bis(4-methylphenyl)methyl (0.188 V) radicals are established as secondary standards against which the oxidation potentials of other radicals can be measured. Oxidation potentials of several 4-substituted cumyl radicals have been determined by this photochemical method. There is a good (r = 0.987, 5 points) linear correlation between the measured oxidation potentials and the σ+ substituent constants. The reaction constant is appropriately negative and large (p = -6).
- Popielarz,Arnold
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p. 3068 - 3082
(2007/10/02)
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- A SHORT AND EFFICIENT METHOD FOR THE PREPARATION OF α,p-DIMETHYLSTYRENE FROM CITRAL
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Acid catalysed cyclization of citral to give α,p-dimethyl styrene using chloranil as an oxidizing agent is reported.The important aspect of this transformation is the dehydration of intermediate piperitenol followed by dehydrogenation to furnish the target compound in 80.5percent yield.
- Barton, Derek H. R.,Parekh, Shyamal I.
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p. 3353 - 3362
(2007/10/02)
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