- Intramolecular Diels-Alder reactions of brominated masked o-benzoquinones. A detour method to synthesize highly functionalized oxatricyclic [m.3.1.0] ring systems from 2-methoxyphenols
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Intramolecular Diels-Alder (IMDA) reactions of masked o-benzoquinones (MOBs) 5a-d to 7a-d and 17a-d to 19a-d generated in situ from 2-methoxyphenols 2-4 and 14-16, respectively, in the presence of alkenols 1a-d, resulting in highly functionalized oxatricyclic [m.3.1.0] ring systems are described. The MOBs 5a-d to 7a-d underwent the IMDA reactions to furnish the adducts 8a-d, 10a-d, and 12a-d (direct method) in poor yields with the concomitant formation of considerable amounts of unexpected byproducts 9a-d, 11a-d, and 13a-d, respectively. To avoid the formation of byproducts and to improve the yields of the desired cycloadducts, a detour method comprising sequential bromination of 2-methoxyphenols 2-4, tandem oxidative acetalization-Diels-Alder reaction, and debromination has been developed. The oxidation of bromophenols 14-16 in the presence of alkenols 1a-d produced the corresponding MOBs 17a-d to 19a-d, which underwent cycloaddition to afford the cycloadducts 20a-d to 22a-d, respectively, as sole products in good to high yields in a highly regio- and stereoselective manner. Treatment of the bromoadducts 20a-d to 22a-d with tributylammonium formate-palladium reagent produced the corresponding debrominated products 8a-d, 10a-d, and 12a-d in high to excellent yields. In general, the latter oxatricycles were obtained in higher overall yields via the detour method than those via the direct method.
- Lin, Ken-Ching,Shen, Yi-Ling,Rao, N. S. Kameswara,Liao, Chun-Chen
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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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- PHOTOOXIDATION OF PHENOLIC COMPOUNDS
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The present invention relates to the photooxidation of phenolic compounds to the respective quinoid compounds using methylene blue as photosensitizer in a solvent mixture of water and alcohols using light of the high wavelength range of the visible spectrum.
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Page/Page column 17-18
(2021/11/26)
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- 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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- 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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- En Route to D-Ring Inverted Phorbol Esters
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Phorbol esters are long regarded as tumor promotors, due to protein kinase C (PKC) activation, but more recently higher oxidized natural derivatives have been shown to display antitumor activity. Given the synthetic difficulty, systematic non-natural syst
- Chow, Sharon,Krainz, Tanja,Bernhardt, Paul V.,Williams, Craig M.
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p. 8761 - 8764
(2019/11/03)
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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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- 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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- Ethynylbenzenoid metabolites of Antrodia camphorata: Synthesis and inhibition of TNF expression
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An improved synthesis of the anti-inflammatory natural product antrocamphin A (2), involving a key Castro-Stephens reaction, is presented, along with the first total synthesis of its congener antrocamphin B (3). Approaches towards the more complex co-meta
- Buccini, Marco,Punch, Kathryn A.,Kaskow, Belinda,Flematti, Gavin R.,Skelton, Brian W.,Abraham, Lawrence J.,Piggott, Matthew J.
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p. 1100 - 1113
(2014/02/14)
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- First total synthesis of antrocamphin A and its analogs as anti-inflammatory and anti-platelet aggregation agents
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Naturally occurring antrocamphin A (1) is a potent anti-inflammatory compound from the edible fungus Antrodia camphorata (Taiwanofungus camphoratus), whose wild fruiting body is used as a valuable folk medicine in Taiwan. This study is the first total syn
- Lee, Chia-Lin,Huang, Chi-Huan,Wang, Hui-Chun,Chuang, Da-Wei,Wu, Ming-Jung,Wang, Sheng-Yang,Hwang, Tsong-Long,Wu, Chin-Chung,Chen, Yeh-Long,Chang, Fang-Rong,Wu, Yang-Chang
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supporting information; experimental part
p. 70 - 73
(2011/02/23)
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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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- 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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- Isolation, Synthesis, Structure-Activity Relationships of Bioactive Benzoquinones from Miconia lepidota from the Suriname Rainforest
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Bioactivity-directed fractionation of an EtOAc extract from the leaves of Miconia lepidota afforded the two benzoquinones 2-methoxy-6-heptyl-1,4-benzoquinone (1) and 2-methoxy-6-pentyl-1,4-benzoquinone (primin) (2). This is the first reported isolation of
- Gunatilaka, A. A. Leslie,Berger, John M.,Evans, Randy,Miller, James S.,Wisse, Jan H.,Neddermann, Kim M.,Bursuker, Isia,Kingston, David G. I.
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- A New Approach to the Synthesis of Cortical Steroids
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A new bondset for cortical steroid synthesis is developed from the dual concepts of convergent assembly and multiple construction. A short synthesis on this bondset is presented in which the final bond construction by electrocyclization took an unwanted c
- Shih, Ing-Lung,Hendrickson, James B.
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p. 133 - 140
(2007/10/03)
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- Regioselective synthesis of substituted pterocarpans and pterocarpenes. Lewis acid Ti(IV) promoted formal (3 + 2) cycloaddition reactions
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A synthesis of novel pterocarpans (8a-3, 10a-c and 11a-e) and pterocarpenes (7a-d and 9a-c) has been carried out. This method involves the Lewis acid Ti(IV) promoted formal (3 + 2) cycloaddition reaction of 2-alkoxy-1,4-benzoquinones (6a-c) with appropriately substituted 2H-chromenes (1a-b, 2a-b and 5) at -78°C.
- Murugesh,Subburaj,Trivedi
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p. 2217 - 2228
(2007/10/03)
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- DNA cleavage by Di- and trihydroxyalkylbenzenes. Characterization of products and the roles of O2, Cu(II), and alkali
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Several 5-alkyl-1,3-dihydroxybenzene (5-alkylresorcinol, 1) and 6-alkyl-1,2,4-trihydroxybenzene (2) derivatives were prepared and used to study the mechanism by which such compounds effect Cu(II)-dependent DNA strand scission. Comparison of the methyl, n-pentyl, n-undecyl, and n-hexadecyl derivatives in each structural series indicated that the efficiency of DNA cleavage increased with increasing length of the alkyl substituent. DNA cleavage by the 5-alkylresorcinols appears to involve initial oxygenation of the benzene nucleus, a process that occurs readily at alkaline pH in the presence of Cu2+ and O2. The resulting trihydroxylated benzenes mediate DNA cleavage in a reaction dependent on the presence of both Cu2+ and O2. The mechanism appears to involve reduction of Cu2+ by the trihydroxybenzene moiety in 2, with subsequent formation of reactive oxygen species. The ability of catalase and dimethyl sulfoxide to suppress DNA strand scission is consistent with the intermediacy of H2O2 and ?OH in the DNA strand scission process.
- Singh, Udai S.,Scannell, Ralph T.,An, Haoyun,Carter, Barbara J.,Hecht, Sidney M.
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p. 12691 - 12699
(2007/10/03)
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- Stereospecific Lewis Acid-Promoted Reactions of Styrenyl Systems with 2-Alkoxy-(6-alkyl)-1,4-benzoquinones: Scope, Limitations, and Synthetic Applications
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Titanium(IV)-promoted reactions of various (E)-1-propenylbenzenes with 2-methoxy- and 2-methoxy-6-methyl-1,4-benzoquinones produce trans 2-aryl-6-methoxy-3-(and 4-di)methyl-2,3-dihydro-5-benzofuranols (10-12), rel-(1S,6R,7R,8R)-3-methoxy-8-aryl-7-(and 1-di)methylbicyclooct-3-ene-2,5-diones (2 + 2 cycloadducts, 13-15) and/or rel-(1R,5R,6R,7R)-7-aryl-3-hydroxy-6-(and 4)-methylbicyclooct-3-ene-2,8-diones (5 + 2 cycloadducts, 16/17).In many cases, each of the three products can be obtained selectively in good yield by control of reaction conditions and/or by choice of substituents on the quinone or the propenylbenzene.The dihydrobenzofurans are formed stereoselectively, whereas the formation of the bicyclo systems are stereospecific processes.Thus, reactions of (Z)-1-propenylbenzenes afford rel-(1R,6S,7R,8R)-8-aryl-3-methoxy-7-methylbicyclooct-3-ene-2,5-diones (24, 25).No bicyclosystems are found in reactions of the (Z)-propenylbenzenes.The products all apparently result from a thermally allowed 2? + 4? (2 + 5) cycloaddition of the propenylbenzene with a 2-methoxy-4-oxo-2,5-cyclohexadienyl carbocation intermediate (26) formed by coordination of the Ti(IV) to the C-1 carbonyl oxygen of the quinone.In the cycloaddition, the aryl ring of the propenylbenzene occupies an endo position with respect to the pentadienyl carbocation moiety of 26 and the bicyclo carbocation product of the cycloaddition (28/29) either undergoes dealkylation or rearrangement to yield the observed products.Treatment of the bicylo systems with protic acid effects their rearrangement to the dihydrobenzofuranols.Reactions of 2-propenylbenzenes and arylcycloalkenes with the quinones regioselectively give dihydrobenzofuranols 43-45 and 49-54, respectively; a 2 + 2 cycloadduct is found in low yield in only one case.The 7-aryl-3-hydroxy-6-methylbicyclooct-3-ene-2,8-diones are produced exclusively in reactions of 2-((4-methoxybenzyl)oxy)-1,4-benzoquinones with various propenylbenzenes.Application of these reactions to the synthesis of (+/-)-obtusafuran, (+/-)-liliflol-B, (+/-)-kadsurenone, and (+/-) denudatin are reported.
- Engler, Thomas A.,Combrink, Keith D.,Letavic, Michael A.,Lynch, Kenneth O.,Ray, James E.
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p. 6567 - 6587
(2007/10/02)
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- Synthesis of Side-Chain-Modified Analogues of the Allergen Primin
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Benzoquinones such as primin (2-methoxy-6-pentyl-1,4-benzoquinone) from Primula obconica HANCE (Primulaceae) are known to be strong sensitizers and thus the source of severe allergic contact dermatitis (cell-mediated type of allergy).In order to determine
- Koenig, Wilfried A.,Faasch, Holger,Heitsch, Holger,Colberg, Cornelia,Hausen, Bjoern M.
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p. 387 - 393
(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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- A New General Synthetic Approach to Diterpenes: Application to Syntheses of (+ -)-Taxodione and (+ -)-Royleanone.
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High-pressure Diels - Alder reactions of 1,3,3-trimethyl-2-vinyl-1-cyclohexenes 3a,b,i with substituted 1,4-benzoquinones afford, in good yield, highly functionalized tricyclic ring systems which are found in many classes of naturally occuring terpenes.Notably, the reactions of 3a are highly regio- and stereoselective.Efficient, formal syntheses of antitumor diterpenes (+ -)-taxodione and (+ -)-royleanone are reported, which demonstrate the practical application of this new strategy for the preparation of varied terpene systems.Of particular interest is that the high-pressure reactions are accelerated by mild Lewis acids and the regio- and stereoselectivity of these reactions is also improved under the combined high-pressure / Lewis acid conditions in comparison to the high-pressure conditions alone.Indeed, in the reaction of 3a with 2-methoxy-5-methyl-1,4-benzoquinone, ZnBr2 is required to effect the Diels-Alder reaction even at 12 kbar, and endo adduct 12c is formed stereoselectively in 90percent yield.In contrast, low-temperature Ti(IV)-catalyzed reactions of diene 3a with methoxy-substituted 1,4-benzoquinones at atmospheric pressure regioselectively produce dihydrobenzofurans 19 and 20, apparently via alkylation of the quinone Ti(IV) complex by the diene followed by the ring closure.
- Engler, Thomas A.,Sampath, Umashanker,Naganathan, Sriram,Velde, David Vander,Takusagawa, Fusao
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p. 5712 - 5727
(2007/10/02)
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- Metalation of Phenols. Synthesis of Benzoquinones by the Oxidative Degradation Approach
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In a effort to explore the potential of so-called oxidative degradation approach for the synthesis of quinones, we have investigated the direct metalation of a number of simple phenols such as o- and p-hydroxybenzyl alcohols, benzyl methyl ethers and N,N-dimethylbenzylamines.Apparently, only those phenolic substrates having available both a coordinating group for chelation and an electron-withdrawing group in a 1,3-relationship are efficiently lithiated, by the action of n-BuLi, in a regioselective manner.Those positions on the aromatic nucleus just flanked by a coordinating, or an acid-base, group could be metalated by action of the t-BuLi/THP system, in favorable cases.
- Saa, Jose M.,Llobera, Antonia,Garcia-Raso, Angel,Costa, Antonio,Deya, Pedro M.
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p. 4263 - 4273
(2007/10/02)
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- Fermy's Salt Promoted Oxidative Degradation of p-Hydroxybenzylamines and p-Hydroxybenzamides. A Novel Approach to p-Quinones
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p-Hydroxybenzylamines and primary p-hydroxybenzamides undergo oxidative degradation by the action of Fermy's salt, thus providing p-benzoquinones in good yields.
- Saa, Jose M.,Llobera, Antonia,Deya, Pedro M.
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p. 771 - 774
(2007/10/02)
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- Quassinoids. 2. A New Approach to the BCD Ring System
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Diels-Alder reaction of 2,6-disubstituted quinones 4 and simple dienes 5 furnished cis adducts 3 in good yields.Basic isomerization provided the trans-decalins 11 which were converted into the lactones 2 which are models of the BCD ring systems of quassin
- Stevens, Robert V.,Angle, Steven R.,Kloc, Ken,Mak, Kok F.,Trueblood, Kenneth N.,Liu, You-Xi
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p. 4347 - 4353
(2007/10/02)
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