- Catalytic asymmetric [2+2] cycloaddition between quinones and fulvenes and a subsequent stereoselective isomerization to 2,3-dihydrobenzofurans
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The catalytic enantioselective [2+2] cycloaddition between quinones and fulvenes was achieved, for the first time, by the use of a chiral copper(ii) complex catalyst. The transformation afforded a series of enantiomerically enriched [6,4,5]-tricyclic cyclobutane derivatives in good yields with excellent regio- and stereoselectivities. Furthermore, the [2+2] adducts could be easily converted into formal [3+2] adducts efficiently and stereoselectively.
- Zheng, Haifeng,Xu, Chaoran,Wang, Yan,Kang, Tengfei,Liu, Xiaohua,Lin, Lili,Feng, Xiaoming
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supporting information
p. 6585 - 6588
(2017/07/10)
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- Chiral cobalt(II) complex catalyzed Friedel-Crafts aromatization for the synthesis of axially chiral biaryldiols
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An efficient atroposelective synthesis of axially chiral biaryldiols via asymmetric Friedel-Crafts aromatization between p-quinones and 2-naphthols was developed. A chiral cobalt(ii) complex of N,N′-dioxide enabled the process to generate axially chiral biaryldiols in up to 98% yield and 95% ee. A large range of substituents at different positions of p-quinones and 2-naphthols was tolerable. The configuration of the product and the chiral N,N′-dioxide-Co(ClO4)2 catalyst was identified by X-ray crystal diffraction analysis and a possible catalytic model was suggested.
- Xu, Chaoran,Zheng, Haifeng,Hu, Bowen,Liu, Xiaohua,Lin, Lili,Feng, Xiaoming
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supporting information
p. 9741 - 9744
(2017/09/07)
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- Substituent effects in the oxidation of 2-alkyl-1,4-dialkoxybenzenes with ceric ammonium nitrate
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Increased steric size of alkyl groups and the presence of coordinating atoms on alkoxy groups have both been found to contribute to decreasing yields of diquinones upon reaction of 2-alkyl-1,4-dialkoxybenzenes with CAN. The overall hydrophilicity of the substrates does not appear to be a significant factor in determining the diquinone yield for these reactions.
- Love, Brian E.,Simmons, Alexander L.
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p. 5712 - 5715
(2016/11/29)
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- Effects of reaction conditions on quinone/diquinone product ratios in the oxidation of 1,4-dimethoxybenzene derivatives with ceric ammonium nitrate
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Proper choice of reaction conditions allows formation of either the quinone or corresponding diquinone as the major product upon treatment of 2-alkyl-1,4-dimethoxybenzenes with ceric ammonium nitrate.
- Love, Brian E.,Duffy, Brian C.,Simmons, Alexander L.
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supporting information
p. 1994 - 1997
(2014/04/03)
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- Chemo- and regioselective direct hydroxylation of arenes with hydrogen peroxide catalyzed by a divanadium-substituted phosphotungstate
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Peroxide in, phenol out: The catalyst [-PW10O38V 2(μ-OH)2]3- showed high activity in the hydroxylation of various aromatic compounds with aqueous H2O 2. The system was regioselective, producing para-phenols from monosubstituted benzene derivatives. Furthermore, alkylarenes with reactive side-chain Ca spa 3-H bonds could be chemoselectively hydroxylated without significant formation of side-chain oxygenated products. Copyright
- Kamata, Keigo,Yamaura, Taiyo,Mizuno, Noritaka
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supporting information; scheme or table
p. 7275 - 7278
(2012/08/28)
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- Binuclear iron(III) phthalocyanine(μ-oxodimer)/tetrabutylammonium oxone: A powerful catalytic system for oxidation of hydrocarbons in organic solution
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Binuclear iron(III) phthalocyanine-(μ-oxodimer) complex was tested in catalytic oxygenation reactions of several hydrocarbons using tetrabutylammonium oxone as the oxidant in dichloromethane solution at room temperature. Results of the study demonstrate that this is an extremely powerful catalytic system for oxidative conversion of aromatic hydrocarbons (anthracene, 2-tert- butylanthracene, 2-methylnaphthalene, 9, 10-dihydroanthracene, 1,2,3,4-tetrahydronaphthalene, indane, ethylbenzene, toluene, and benzene) to the respective p-quinones in high yields in 5-30 min. Under these conditions, adamantane is oxidized with 71% conversion after 10 min affording a mixture of 1 -adamantanol, 2-adamantanone, 1-hydroxy-2-adamantanone, and 4-protoadamantanone.
- Neu, Heather M.,Zhdankin, Viktor V.,Nemykin, Victor N.
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scheme or table
p. 6545 - 6548
(2011/02/22)
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- Selective activation of C-H bonds on the ring of ethylbenzene catalyzed by several diperoxovanadate complexes
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The competitive oxidation of the C-H bonds on the aromatic ring and side-chain of ethylbenzene (EB) with hydrogen peroxide is investigated over four diperoxovanadate catalysts, that is, K3[VO(O2) 2(ox)] (bpV(ox)), K2
- Liu, Qiuyuan,Zhu, Liangfang,Li, Li,Guo, Bin,Hu, Xiaoke,Hu, Changwei
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experimental part
p. 71 - 77
(2011/01/08)
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- Synthesis of 2-substituted quinones, vitamin K3, and vitamin K1 from p-cresol. BF3·OEt2-catalyzed methyl migration of 4-tert-butyldioxycyclohexadienones
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BF3·OEt2-catalyzed methyl group migration of 4-methyl-4-tert-butyldioxycyclohexadienone, which is obtained by ruthenium-catalyzed oxidation of p-cresol with tert-butyl hydroperoxide, in hexafluoro-2-propanol/toluene gave toluquinone efficiently. The reaction can be applied to the regio-selective short-step syntheses of vitamin K3 and vitamin K1 from p-cresol.
- Murahashi, Shun-Ichi,Fujii, Akiko,Inubushi, Yasutaka,Komiya, Naruyoshi
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scheme or table
p. 2339 - 2341
(2010/05/19)
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- Electrophysiological and behavioral activity of secondary metabolites in the confused flour beetle, tribolium confusum
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Several previous studies have addressed pheromone communication in various flour beetles (Coleoptera: Tenebrionidae), including the confused flour beetle, Tribolium confusum (du Val). Different stereoisomers of 4,8-dimethyldecanal (DMD) were reported as the only components of an aggregation pheromone, but the behavioral activity of DMD is low. In the present study, additional previously reported secondary metabolites (benzoquinones and hydrocarbons) were tested for electrophysiological activity (EAG) with both sexes of T. confusum. Two benzoquinones and three monoenic hydrocarbons elicited significant EAG activity from both male and female antennae. There was an elevated male EAG response (vs. the females) to two out of the three hydrocarbons and for both quinones. The EAG-active compounds were subsequently investigated for behavioral activity in a walking bioassay. Benzoquinones are considered toxic and have been assigned a function as alarm substances in flour beetles, but we found that methyl-1, 4-benzoquinone in intermediate concentrations was attractive to both male and female beetles and could therefore act as an aggregation pheromone component. Males were also attracted to ethyl-1,4-benzoquinone. The corresponding hydroquinones, presumed precursors of the benzoquinones, did not elicit any electrophysiological response and were not tested for behavioral activity. The unsaturated hydrocarbons (1-tetradecene, 1-pentadecene, and 1-hexadecene) elicited significant EAG responses from both male and female antennae and were also attractive in the behavioral assay. Our results show that several beetle-produced compounds, in addition to 4,8-dimethyldecanal, may be part of a complex pheromone system in flour beetles and play a role in mediating aggregation in T. confusum.
- Verheggen,Ryne,Olsson,Arnaud,Lognay,Hoegberg,Persson,Haubruge,Loefstedt
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p. 525 - 539
(2008/09/17)
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- Acid-induced rearrangement reactions of reduced benzoquinone cyclopentadiene cycloadducts
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Several Diels-Alder adducts between benzoquinones and cyclopentadiene were reduced to the corresponding diols 7a-c and 11. Treatment of these diols with strong acid triggered a skeletal rearrangement reaction resulting in compounds 8a-c and 12 that contain a 4,8-methanoazulene substructure. In addition, a dyotropic-like rearrangement of the tetracyclic lactone 13 to the spirolactone 18 was observed. Five of the structures were supported by X-ray analysis.
- Eipert, Martin,Maichle-Moessmer, Caecilia,Maier, Martin E.
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p. 8692 - 8695
(2007/10/03)
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- Kinetics of oxidation of hydroquinones by molecular oxygen. Effect of superoxide dismutase
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The kinetics of the autoxidation of sixteen hydroquinones (QH2) (substituted 1,4-hydroquinones and 1,4-dihydroxynaphthalenes as well as 9,10-dihydroxyphenanthrene) were studied using the Clark electrode technique in aqueous solution, pH 7.40, at 37°C both with and without added superoxide dismutase (SOD). QH2 oxidation occurs typically with a self-acceleration. A maximum rate of oxidation, RMAX, was found to be the most indicative parameter characterizing QH2 oxidizability. A kinetic scheme of QH2 autoxidation was developed; computer simulations carried out on the basis of this scheme reproduce the main kinetic features of the studied process. QH2 autoxidation is suggested to be a free-radical chain process with semiquinone (Q-) and superoxide (O2-) as chain-carrying species. The oxidation is initiated by reaction (1) Q + QH2→2Q- + 2H+. The addition of SOD results in two main effects: shifting the equilibrium (2) Q- + O2?Q + O2- (K2) to the right and suppressing reaction (3) QH2 + O2-→Q- + H2O2. The net effect of SOD depends basically on K2. When K2 2 > 0.1, the more SOD inhibits the oxidation, the higher K2. The concentration of SOD causing the 50%-effect on RMAX ([SOD]50), both inhibitory and stimulatory, decreases dramatically when K2 increases. At [SOD] ? [SOD]50 the rate of QH2 autoxidation is definitively determined by the rate of reaction (1). For the majority of QH2, [SOD]50 is significantly less than the physiological values of [SOD] and thus QH2 autoxidation in biological environment is expected to occur in the above kinetically simple mode.
- Roginsky, Vitaly,Barsukova, Tatyana
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p. 1575 - 1582
(2007/10/03)
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- The kinetics and thermodynamics of quinone-semiquinone-hydroquinone systems under physiological conditions
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The steady-state concentration of semiquinones (Q·-) determined by EPR in the mixtures of eleven alkyl-, methoxy-and chloro-substituted 1,4-benzoquinones as well as 1,4-naphthoquinone (Q) with corresponding hydroquinones (QH2) in aqueous buffer. pH 7.40, was used to calculate a constant for equilibrium (1) Q + QH2?Q·- + Q·- + 2H+ (k1; 2k-1; K1 = k1/2k-1). The rale constants for comproportionation between Q and QH2, k1, were calculated from the combination of K1 determined in this work and 2k-1 reported previously. The Nernst equation was applied to calculate the change in one-electron reduction potential ΔE1 = E(Q/Q·-) - E(Q·-/QH2) in equilibrium (1). The E(Q·-/QH2) values were calculated from ΔE1 and the values of E(Q/Q·-) known from the literature. The correlations between E(Q·-/QH2) and E(Q/Q·-) as well as between ΔE1 (k1) and E(Q/Q·-) are discussed. The values of ΔE1 and k1 are suggested to be the key factors governing the autoxidation of QH2.
- Roginsky, Vitaly A.,Pisarenko, Leonid M.,Bors, Wolf,Michel, Christa
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p. 871 - 876
(2007/10/03)
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- Comparative pulse radiolysis studies of alkyl- and methoxy-substituted semiquinones formed from quinones and hydroquinones
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Absorption spectra and rate constants for the disproportionate of 12 alkyl- and methoxy-substituted semiquinone anion free radicals (Q?-) produced by the one-electron reduction (using CO2?- as a reductant) of 1,4-benzoquinones and 1,4-naphthoquinone (Q) as well the oxidation (using N3? as an oxidant) of the corresponding hydroquinones (QH2) were determined by pulse radiolysis in 50 mM sodium phosphate buffer, pH 7.40 at room temperature. Both spectral and kinetic characteristics of Q?- only moderately depended on whether Q?- was produced from Q or QH2. Spectra of benzosemiquinones display two peaks with maximum at 310-320 nm and ca. 430 nm with the ratio of about 2-2.5. Molar absorption coefficients were determined. Rate constants for Q?- disproportionation (2k1) were correlated with the nature of substituents. While 2k1 was scarcely affected by methyl substitution, Q?- containing isopropyl, tert-butyl and methoxy substituents were visibly more stable than non-substituted and methyl-substituted Q?-.
- Roginsky, Vitaly A.,Pisarenko, Leonid M.,Bors, Wolf,Michel, Christa,Saran, Manfred
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p. 1835 - 1840
(2007/10/03)
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- Oxidation of C2, C3 and Higher Alkanes by a Ruthenium-Oxo System
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Barium ruthenate, BaRuO3(OH)2, when dissolved in TFA-CH2Cl2 containing a few equivalents of 2,2'-bipyridine, generates a highly reactive ruthenium-oxo system that is capable of oxidizing ethane and propane at room temeprature with good yields.
- Lau, Tai-Chu,Mak, Chi-Keung
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p. 943 - 944
(2007/10/02)
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- Reactive dyestuffs
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Triphendioxazine reactive dyestuffs of the general formula STR1 with the substituent definition given in the description, are outstandingly suitable for dyeing and printing materials containing hydroxyl groups or amide groups. They give red dyeings with high wet- and light-fastnesses.
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- STUDIES ON THE TWO-PHASE NITRATION OF SELECTED PHENOLS
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The two phase nitration of several phenols by aqueous acid, sodium nitrate and diethyl ether, yielded as well as the expected nitro-phenols, a benzoquinone.A variable induction period was observed which could be significantly reduced by added sodium nitrite.
- Thompson, Malcolm J.,Zeegers, Petrus J.
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p. 2471 - 2474
(2007/10/02)
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- Triphendioxazine dyestuffs
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Triphendioxazine dyestuffs of the formula STR1 having the substituent meanings specified in the descriptive part, are highly suitable for dyeing and printing hydroxyl- or amido-containing materials, in particular fibre materials, and produce wash-fast dyeings and prints.
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- STUDIES ON QUINONES. XIV. OXIDATIVE DEMETHYLATION OF HYDROQUINONES DIMETHYLETHERS WITH NITRIC ACID- IMPREGNATED MANGANESE DIOXIDE
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The oxidative cleavage of several hydroquinones dimethylethers with nitric acid-impregnated manganese dioxide, in methylene chloride solution at room temperature, gave the corresponding quinones in 76-95percent yield.
- Errazuriz, B.,Tapia, R.,Valderrama, J. A.
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p. 819 - 822
(2007/10/02)
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