- Cationic [5+2] cycloaddition reactions promoted by trimethylsilyl triflate in highly polar media
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Trimethylsilyl triflate is an effective reagent in 3.0 M lithium perchlorate-ethyl acetate for promoting cationic [5+2] cycloaddition reactions.
- Collins, Jon L.,Grieco, Paul A.,Walker, John K.
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Read Online
- Reaction of Alkenes with Unstable Cations Electrogenerated from Phenols
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Reactions of several alkenes with the unstable cations electrogenerated fron 3,4-dimethoxy-6-methylphenol as well as from p-methoxyphenol have been carried out, resulting in C-C bond formation to give the corresponding 1:1 adducts.
- Shizuri, Yoshikazu,Nakamura, Kensuke,Yamamura, Shosuke
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Read Online
- Organophotocatalytic Aerobic Oxygenation of Phenols in a Visible-Light Continuous-Flow Photoreactor
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A mild photocatalytic phenol oxygenation enabled by a continuous-flow photoreactor using visible light and pressurized air is described herein. Products for wide-ranging applications, including the synthesis of vitamins, were obtained in high yields by precisely controlling principal process parameters. The reactor design permits low organophotocatalyst loadings to generate singlet oxygen. It is anticipated that the efficient aerobic phenol oxygenation to benzoquinones and p-quinols contributes to sustainable synthesis.
- Wellauer, Jo?l,Miladinov, Dragan,Buchholz, Thomas,Schütz, Jan,Stemmler, René T.,Medlock, Jonathan A.,Bonrath, Werner,Sparr, Christof
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supporting information
p. 9748 - 9752
(2021/05/27)
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- Polyoxometalate-based supramolecular porous frameworks with dual-active centers towards highly efficient synthesis of functionalized: P -benzoquinones
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Selective oxidation of substituted phenols is an ideal method for preparing functionalized p-benzoquinones (p-BQs), which serve as versatile raw materials for the synthesis of a variety of biologically active compounds. Herein, two new polyoxometalate-based supramolecular porous frameworks, K3(H2O)4[Cu(tza)2(H2O)]2[Cu(Htza)2(H2O)2][BW12O40]·6H2O (1) and H3K3(H2O)3[Cu(Htza)2(H2O)]3[SiW12O44]·14H2O (2) (Htza = tetrazol-1-ylacetic acid), were synthesized and structurally characterized by elemental analysis, infrared spectroscopy, thermal analysis, UV-vis diffuse reflectance spectroscopy, and single-crystal X-ray and powder diffraction. The single-crystal X-ray diffraction analysis indicates that both compounds possess unique petal-like twelve-nucleated Cu-organic units composed of triangular and hexagonal metal-organic loops. In 1, the Cu-organic units are isolated and [BW12O40]5- polyoxoanions are sandwiched between staggered adjacent triangular channels in the structure. However in 2, the Cu-organic units extend into a two-dimensional layered structure, and the [SiW12O44]12- polyoxoanions occupy the larger hexagonal channels in the stacked structure. Both compounds as heterogeneous catalysts can catalyze the selective oxidation of substituted phenols to high value-added p-BQs under mild conditions (60 °C) with TBHP as the oxidant, particularly in the oxidation of 2,3,6-trimethylphenol to 2,3,5-trimethyl-p-benzoquinone (TMBQ, key intermediate in vitamin E production). Within 8-10 min, the yield of TMBQ is close to 100%, and oxidant utilization efficiency is up to 94.2% for 1 and 90.9% for 2. The turnover frequencies of 1 and 2 are as high as 5000 and 4000 h-1, respectively. No obvious decrease in the yield of TMBQ was observed after five cycles, which indicates the excellent sustainability of both compounds. Our study of the catalytic mechanism suggests that there is a two-site synergetic effect: (i) the copper ion acts as the catalytic site of the homolytic radical pathway; and (ii) the polyoxoanion acts as the active center of the heterolytic oxygen atom transfer pathway. This journal is
- An, Haiyan,Chang, Shenzhen,Chen, Yanhong,Huang, Yaohui,Luo, Huiyun,Zhu, Qingshan
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p. 8591 - 8603
(2021/11/17)
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- Regiodivergent oxidation of alkoxyarenes by hypervalent iodine/oxone system
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We have found that the combination of Oxone with an organoiodine compound, i.e., 2-iodobenzoic acid (2-IB), selectively yields p-quinones from monomethoxyarenes under mild conditions. In this reaction system, an organoiodine compound is immediately oxidized by Oxone to generate cyclic hypervalent iodine (III) species in situ, which serves as the specific mediator for the selective p-quinone synthesis, preventing o-quinone formation.
- China, Hideyasu,Tanihara, Kokoro,Sasa, Hirotaka,Kikushima, Kotaro,Dohi, Toshifumi
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- Oxidation of Electron-Rich Arenes Using HFIP-UHP System
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The straightforward oxidation of electron-rich arenes, namely, phenols, naphthols, and anisole derivatives, under mild reaction conditions, is described by means of the use of an environmentally benign HFIP-UHP system. The corresponding quinones or hydroxylated arenes were obtained in moderate to good yields.
- Llopis, Natalia,Baeza, Alejandro
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p. 6159 - 6164
(2020/05/20)
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- A Catalytic Oxidative Quinone Heterofunctionalization Method: Synthesis of Strongylophorine-26
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The preparation of heteroatom-substituted p-quinones is ideally performed by direct addition of a nucleophile followed by in situ reoxidation. Albeit an appealing strategy, the reactivity of the p-quinone moiety is not easily tamed and no broadly applicable method for heteroatom functionalization exists. Shown herein is that Co(OAc)2 and Mn(OAc)3?2 H2O act as powerful catalysts for oxidative p-quinone functionalization with a collection of O, N, and S nucleophiles, using oxygen as the terminal oxidant. Preliminary mechanistic observations and the first synthesis of the cytotoxic natural product strongylophorine-26 is presented.
- Yu, Wanwan,Hjerrild, Per,Jacobsen, Kristian M.,Tobiesen, Henriette N.,Clemmensen, Line,Poulsen, Thomas B.
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supporting information
p. 9805 - 9809
(2018/07/31)
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- An expedient synthesis of murrayaquinone A via a novel oxidative free radical reaction
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Murrayaquinones A–D is a group of four bioactive carbazole-1,4-dione natural products isolated from the root bark of the plant Murraya eucrestifolia hayata. Murrayaquinone is synthesized in five steps starting from the commercially available 2,4,5-trimeth
- McDonald, Jeffrey W.,Miller, John E.,Kim, Minjee,Velu, Sadanandan E.
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p. 550 - 553
(2018/01/17)
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- Synthesis of coenzyme Q0 through divanadium-catalyzed oxidation of 3,4,5-trimethoxytoluene with hydrogen peroxide
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The selective oxidation of methoxy/methyl-substituted arenes to the corresponding benzoquinones has been first realized using aqueous hydrogen peroxide as a green oxidant, acid tetrabutylammonium salts of the γ-Keggin divanadium-substituted phosphotungstate [γ-PW10O38V2(μ-O)2]5- (I) as a catalyst, and MeCN as a solvent. The presence of the dioxovanadium core in the catalyst is crucial for the catalytic performance. The reaction requires an acid co-catalyst or, alternatively, a highly protonated form of I can be prepared and employed. The industrially relevant oxidation of 3,4,5-trimethoxytoluene gives 2,3-dimethoxy-5-methyl-1,4-benzoquinone (ubiquinone 0 or coenzyme Q0, the key intermediate for coenzyme Q10 and other essential biologically active compounds) with 73% selectivity at 76% arene conversion. The catalyst retains its structure under turnover conditions and can be easily recycled and reused without significant loss of activity and selectivity.
- Zalomaeva, Olga V.,Evtushok, Vasilii Yu.,Maksimov, Gennadii M.,Maksimovskaya, Raisa I.,Kholdeeva, Oxana A.
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p. 5202 - 5209
(2017/04/27)
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- Dimethyl carbonate: an environmentally friendly solvent for hydrogen peroxide (H2O2)/methyltrioxorhenium (CH3ReO3, MTO) catalytic oxidations
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Environmentally friendly oxidations of various organic compounds with the hydrogen peroxide (H2O2)/methyltrioxorhenium (CH3ReO3, MTO) catalytic system have been described in dimethyl carbonate (DMC), a cheap commercially available and benign chemical having interesting solvating properties, low toxicity and high biodegradability. Oxidations proceeded with good conversions and in good yields. Spectrophotometric analysis demonstrated that the [CH3ReO(O-O)2] complex was formed in DMC and that it was stable for several days at room temperature.
- Bernini, Roberta,Mincione, Enrico,Barontini, Maurizio,Crisante, Fernanda,Fabrizi, Giancarlo,Gambacorta, Augusto
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p. 6895 - 6900
(2008/02/10)
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- Convenient oxidation of alkylated phenols and methoxytoluenes to antifungal 1,4-benzoquinones with hydrogen peroxide (H2O2)/methyltrioxorhenium (CH3ReO3) catalytic system in neutral ionic liquid
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Alkylated phenol and methoxytoluene derivatives were catalytically and selectively oxidized to the corresponding 1,4-benzoquinones in good conversions and yields. Reactions were performed with hydrogen peroxide (H2O2)/methyltrioxorhenium (CH3ReO3) in 1-butyl-3-methylimidazolium tetrafluoroborate [bmim]BF4, a neutral ionic liquid. Compounds were tested in vitro for their antifungal activity against the growth of several widespread soil fungi. Some of them were proved to be potent inhibitors of Fusarium sp. than ketoconazole, a commercially available and expensive antifungal agent.
- Bernini, Roberta,Mincione, Enrico,Barontini, Maurizio,Fabrizi, Giancarlo,Pasqualetti, Marcella,Tempesta, Sabrina
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p. 7733 - 7737
(2007/10/03)
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- Synthesis and spectroscopic characterization of [1′-14C]ubiquinone-2, [1′-14C]-5-demethoxy-5-hydroxyubiquinone-2, and [1′-14C]-5-demethoxyubiquinone-2
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[1′-14C]Ubiquinone-2, [1′-14C]-5-demethoxy-5-hydroxyubiquinone-2, and [1′-14C]-5-demethoxyubiquinone-2 have been synthesised from [1-14C]acetic acid. A common feature of these benzoquinones is the isoprenoid chain, and the 14C-label has therefore been incorporated in this isoprenoid. The coupling of the different quinone head groups and the isoprenoid chain is the last step in the total synthesis, to prevent unnecessary loss of the labelled material during synthesis. The products have been characterised by mass spectrometry, 1H NMR and 13C NMR.
- Van Der Klei, Anita,De Jong, Robertus L. P.,Lugtenburg, Johan,Tielens, Aloysius G. M.
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p. 3015 - 3023
(2007/10/03)
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- Selective oxidation of phenol and anisole derivatives to quinones with hydrogen peroxide and polymer-supported methylrhenium trioxide systems
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A convenient and efficient application of heterogeneous poly(4-vinylpyridine)/methyl rhenium trioxide (PVP/MTO) systems for the selective oxidation of substituted phenol and anisole derivatives to benzoquinones is described. Environment friendly, easily available, and low cost H2O2 was used as the oxygen atom donor. All catalysts were stable systems for at least five recycling experiments. In the oxidation of some natural phenols such as cardanol derivatives higher conversion and yields of benzoquinones were observed with respect to MTO in homogeneous phase suggesting a support-mediated molecular recognition process based on hydrogen-bonding interactions.
- Saladino, Raffaele,Neri, Veronica,Mincione, Enrico,Filippone, Paolino
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p. 8493 - 8500
(2007/10/03)
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- Oxidation of marchantin A trimethyl ether and related aromatic compounds with m-chloroperbenzoic acid
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Marchantin A trimethyl ether was subjected to react with m-chloroperbenzoic acid to yield hydroxylated derivatives as well as ring C degraded esters. This reaction was confirmed by application to catechol dimethyl ether and dihydroeugenol dimethyl ether.
- Tori, Motoo,Sono, Masakazu,Toyota, Masao,Asakawa, Yoshinori
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p. 647 - 650
(2007/10/03)
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- Oxidation of some Disubstituted Anisole Derivatives with Ceric Perchlorate in Perchloric Acid Solution
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The influence of concentration of particular reagents on the kinetics of Ce(IV) reduction by 2,6-dimethyl and 3,5-dimethyl-anisole as well as 2-methoxy-5-methyl- and 4-methoxy-2-methyl-aniline in perchloric acid solution was investigated, establishing the stoichiometry of these processes.Some intermediate products - macromolecular, derivatives of p-benzoquinone and 4,4'-diphenoquinone - were separated and identified.The effects of substituents and the conditions of performed oxidation processes on the kind and yield of the resultant products were considered.Key words: oxidation, anisole derivatives, kinetics
- Leszczynski, L.,Dziegiec, J.
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p. 1855 - 1862
(2007/10/02)
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- THE ESR SPECTRA, STRUCTURE, AND REACTIVITY OF AROMATIC RADICAL-CATIONS IN SUPERACIDS
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The oxidation of aromatic compounds by lead dioxide in superacids based on fluorosulfonic acid at -75 deg C takes place by a one-electron mechanism and leads in many cases to relatively stable radical-cations.The ESR spectra, the isotropic hyperfine coupling constants, data on the reactivity of the radical-cations, and the structures of the final products from their transformations under "long-life" conditions are presented.
- Rudenko, A. P.
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p. 1946 - 1980
(2007/10/03)
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- Regioselective Lewis acid-directed reactions of 2-alkoxy-5-alkyl-1,4-benzoquinones with styrenes: Synthesis of burchellin and guianin neolignans
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Reactions of 2-carbomethoxy-5-methoxy-1,4-benzoquinone with (E)-propenylbenzenes promoted by Ti(IV) regio- and stereoselectively yield trans 2-aryl-4-carbomethoxy-7-methoxy-3-methyl-2,3-dihydro-5-benzofuranols. However, the products found in Lewis acid-promoted reactions of 2-alkoxy-5-alkyl-1,4-benzoquinones with (E)-propenylbenzenes depend on the nature of the Lewis acid. Low-temperature reactions with SnCl4 produce rel-(1R,6S,7S,8R)-4-alkoxy-1-alkyl-7-aryl-8-methylbicyclo[4.2.0]oct-3- ene-2,5-diones 21-23 and products derived from them. Allowing the reactions to warm to room temperature results in rel-(2S,3S,3aR)-3a-alkyl-2-aryl-5-hydroxy-3-methyl-2,3,3a,6-tetrahydro -6-oxobenzofurans as mixtures of keto-enol tautomers 26/27 and 28/29. With Ti(IV) as promoter, the reactions can be made to produce either 21-23 or the regioisomeric rel-(1S,6R,7R,8S)-4-alkoxy-1-alkyl-8-aryl-7-methylbicyclo[4.2.0]oct-3- ene-2,5-diones 18-20. The ratio of the two depends upon the makeup of the Ti(IV) promoter and the substituents on the propenylbenzene. A mechanistic rationale is presented involving regioselective coordination of the different Lewis acids to the quinone. Thus, SnCl4 binds to the C-1 carbonyl and C-2 alkoxy oxygens, forming a complex possessing a 2-alkoxy-5-alkyl-4-oxo-2,5-cyclohexadienyl carbocation moiety (e.g. 30) which undergoes a thermally allowed 4π + 2π (5 + 2) cycloaddition with propenylbenzene to give a bicyclo[3.2.1]octenyl carbocation 31; this cation then rearranges to the observed products. On the other hand, the Ti(IV)-promoted reactions give either bicyclo[3.2.1]octenyl carbocation 31 or 34, depending upon reaction conditions, followed by rearrangement. Cyclobutanes 18-20 undergo protic acid rearrangement to give trans 7-alkoxy-4-alkyl-2-aryl-3-methyl-2,3-dihydro-5-benzofuranols 15-17, whereas cyclobutanes 21-23 yield 5-alkyl-7-aryl-3-hydroxy-6-methylbicyclo[3.2.1]oct-3-ene-2,8-diones 24/25. The reactions provide an efficient and stereoselective route to neolignans of the guianin and burchellin classes.
- Engler,Wei,Letavic,Combrink,Reddy
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p. 6588 - 6599
(2007/10/02)
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- The acid-catalyzed oxidation of methoxybenzenes to p-benzoquinones by dimethyldioxirane
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Methoxybenzenes 1 were oxidized to phenols and/or p-benzoquinones by dimethyldioxirane; in the presence of strong acids, the intermediate phenols were effectively converted to the p-benzoquinones 3.
- Adam,Shimizu
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p. 560 - 562
(2007/10/02)
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- New Synthesis of 2-Alkoxy-5-methyl-1,4-benzoquinones by the Oxidation of 4-Methylcatechol with Copper (II) Chloride in Alcohols
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4-Methylcatechol was oxidized with copper (II) chloride in various alcohols under oxygen to give the corresponding 2-alkoxy-5-methyl-1,4-benzoquinones.
- Takizawa, Yasuomi,Iwasa, Yoshihito,Suzuki, Toshiaki,Miyaji, Hiroyuki
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p. 1863 - 1864
(2007/10/02)
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- Toward the Synthesis of the Taxol C,D Ring System: Photolysis of α-Methoxy Ketones
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Model systems for the synthesis of the C and D rings of taxol are described, involving photolyses of α-methoxy ketones.Cis-fused oxetanols common to taxol are formed along with novel trans-fused oxetanols.Experiments bearing on the selectivity of this process as well as the mechanistic hypothesis are also described.
- Wender, Paul A.,Rawlins, David B.
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p. 7033 - 7048
(2007/10/02)
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- Synthesis and inhibitory activity of bromoquinone derivatives
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2,5 Dibromo-3-methyl-6-isopropyl-1,4-benzoquinone has been reported inhibitory to b6-f and b-c1 complexes [Malkin, R. (1977) Biochim. Biophys. Acta., 501, 552-554]. In this paper, four classes of the analogues are synthesized. They were 5-bromo-3-methyl, 3-bromo-2-methoxy-5-methyl, 2,5-dibromo-3-methyl, and 3,5-dibromo-2-methyl derivatives with the side chain -(CH2)nH of N=5,7,9,11 and 13 at position 6. Dibromo compounds are usually more inhibitory in the mitochondrial ubiquinol cytochrome c reductase; the maximal inhibition was usually with 9 methylene in a functional group.
- Gu, Lianquan,Liu, Cuihua,Xu, Jingxing,King, Tsoo E.
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p. 3199 - 3210
(2007/10/02)
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- Oxidation of Methoxy- and/or Methyl-Substituted Benzenes and Naphthalenes to Quinones and Phenols by H2O2 in HCOOH
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The oxidation of a number of arenes (methoxybenzenes, methylbenzenes, and naphthalenes) to quinones and phenols by H2O2 in HCOOH has been examined.Methoxybenzenes were much more easily oxidized to p-benzoquinones than methylbenzenes (e.g., 1,3,5-trimethoxybenzene was oxidized to 2,6-dimethoxy-p-benzoquinone in a 75percent yield and 1,2,4-trimethylbenzene to 2,3,5-trimethyl-p-benzoquinone in a 16percent yield).Electron-withdrawing substituents, such as nitro, cyano, and chloro groups, lowered the conversion of reactants and changed the product selectivity from quinones to phenols.Methoxybenzonitriles were oxidized to corresponding phenols in a moder ate yield (e.g., 2,6-dimethoxybenzonitrile to 3-hydroxy-2,6-dimethoxybenzonitrile in a 39percent yield and a 64percent selectivity).
- Orita, Hideo,Shimizu, Masao,Hayakawa, Takashi,Takehira, Katsuomi
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p. 1652 - 1657
(2007/10/02)
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- Efficient Preparation of Some Biologically Active Substances from Natural and Nonnatural Aromatic Compounds by m-Chloroperbenzoic Acid Oxidation
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Six naturally occurring aromatic terpenoids and six nonnatural aromatic compounds were oxidized by m-chloroperbenzoic acid in chloroform to give 1,2- and 1,4-quinones or hydroxylated products in which vitamin K1, insecticidal, piscicidal, and antifungal compounds were included.The present method is advantageous for obtaining different types of natural or nonnatural aromatic products having biological activity from the starting aromatic compounds in a one-step reaction.
- Asakawa, Yoshinori,Matsuda, Reiko,Tori, Motoo,Sono, Masakazu
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p. 5453 - 5457
(2007/10/02)
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- ON THE REGIOSELECTIVITY OF THE FREMY'S SALT OXIDATION OF PHENOLS
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A detailed study of the regioselectivity of the Fremy's salt oxidation of phenols, including a series of MNDO calculations of the intermediate phenoxy radicals, has been carried out.The analysis of these results has led us to establish a new rule for the para vs. ortho regioselectivity, namely: "C-4 unsubstituted phenols, as well as phenols substituted at C-4 with easy-to-displace groups, undergo oxidation (or oxidative degradation) by the action of Fremy's salt, thus eventually providing the corresponding p-quinones".A similar rule for the ortho vs. ortho' regioselectivity could not be so precisely formulated since now steric effects play a significant major role.
- Deya, Pedro M.,Dopico, Mercedes,Raso, Angel Garcia,Morey, Jeronimo,Saa, Jose M.
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p. 3523 - 3532
(2007/10/02)
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- Natural Benzofurans. Synthesis of Moracin A and B
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2-(3,5-Dihydroxyphenyl)-4,6-dimethoxybenzofuran (Moracin A) and 2-(3-hydroxy-5-methoxyphenyl)-5-hydroxy-6-methoxybenzofuran (Moracin B), phytoalexins isolated from diseased mulberry have been synthesized by short routes in which the benzofuran heterocyclic system is formed by an intramolecular Wittig reaction.
- Burke, John M.,Stevenson, Robert
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p. 451 - 466
(2007/10/02)
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- A SYNTHESIS OF GYMNOMITROL
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Condensation of 1,2-dimethylcyclopentene 10 with 2-methyl-4,4,5-trimethoxycyclohexa-2,5-dienone 7 in methylene chloride-nitromethane with added stannic chloride gave a mixture of the two diastereomeric bicyclooctanes 13 and 14 by ionic cycloaddition.After selective reduction of the saturated carbonyl group with sodium borohydride, and hydrogenation of the double bond the two epimers 18 and 20 (ratio 3.3:1) were separable by chromatography.Protection of the hydroxy group in 18 with dihydropyran and, reduction of the α-methoxyketone 19 with calcium in liquid ammonia gave ketone 21.Gymnomitrol 1 was then prepared by Wittig olefination followed by deprotection of the hydroxy group.
- Buechi, George,Chu, Ping-Sun
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p. 4509 - 4514
(2007/10/02)
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- A synthesis of gymnomitrol
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Condensation of 1,2 - dimethylcyclopentene 10 with 2 - methyl - 4,4, 5 - trimethoxycyclohexa - 2,5 -dienone 7 in methylene chloride - nitromethane with added stannic chloride gave a mixture of the two diastereo-meric bicyclo[3.2.1]octanes 13 and 14 by ionic [4+2]cycloaddition. After selective reduction of the saturated carbonyl group with sodium borohydride, and hydrogenation of the double bond the two epimers 18 and 20 (ratio 3.3:1) were separable by chromatography. Protection of the hydroxy group in 18 with dihydropyran and, reduction of the α-methoxyketone 19 with calcium in liquid ammonia gave ketone 21. Gymnomitrol 1 was then prepared by Wittig olefination followed by deprotection of the hydroxy group.
- Bchi, George,Chu, Ping-Sun
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p. 4509 - 4513
(2015/01/08)
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- A synthesis of gymnomitrol
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Condensation of 1,2 - dimethylcyclopentene 10 with 2 - methyl - 4,4, 5 - trimethoxycyclohexa - 2,5 -dienone 7 in methylene chloride - nitromethane with added stannic chloride gave a mixture of the two diastereomeric bicycle[3.2.1]octanes 13 and 14 by ionic [4+2]cycloaddition. After selective reduction of the saturated carbonyl group with sodium borohydride, and hydrogenation of the double bond the two epimers 18 and 20 (ratio 3.3:1) were separable by chromatography. Protection of the hydroxy group in 18 with dihydropyran and, reduction of the α-methoxyketone 19 with calcium in liquid ammonia gave ketone 21. Gymnomitrol 1 was then prepared by Wittig olefination followed by deprotection of the hydroxy group.
- Büchi, George,Chu, Ping-Sun
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p. 4509 - 4513
(2014/12/10)
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