- Singlet oxygen generation from H2O2/MoO42-: Peroxidation of hydrophobic substrates in pure organic solvents
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Seventeen organic solvents are screened as reaction media to conduct the molybdate-catalyzed disproportionation of hydrogen peroxide into singlet molecular oxygen, 1O2 (1Δg). The solvents are investigated by resorting to the detection of the infra-red luminescence of 1O2 at 1270 nm. Preparative peroxidations of representative substrates are carried out in the most efficient ones. The latter are protic and polar and constitute a simpler alternative to the well suited but more intricate microemulsion systems for the peroxidation of hydrophobic substrates with chemically generated 1O2.
- Nardello, Véronique,Bogaert, Stéphane,Alsters, Paul L,Aubry, Jean-Marie
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- Practical oxidative dearomatization of phenols with sodium hypochlorite pentahydrate
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A highly efficient and practical oxidative dearomatization of phenols using sodium hypochlorite pentahydrate as an inexpensive, strong oxidant is reported for the first time. The oxidation reactions proceeded very rapidly in the presence of water to give the desired products in excellent yields, and sodium chloride and water were the only by-products derived from the oxidant.
- Uyanik, Muhammet,Sasakura, Niiha,Kuwahata, Mitsuyoshi,Ejima, Yasukazu,Ishihara, Kazuaki
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- PhSeBr mediated hydroxylative oxidative dearomatization of naphthols-an open air facile one-pot synthesis of ketols
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A new methodology for oxidative-dearomatization of planar phenols is described. An economic, viable one-pot metal free protocol for direct conversion of naphthols to α-ketols is reported. Naphthols were found to undergo facile unprecedented oxidative dearomatization with regioselective hydroxylation with phenyl selenyl bromide in open air conditions. Quaternary stereocenters were developed along with formation of sterically demanding α- and γ-ketols with high yields. Functional group tolerance like esters is revealed. A thorough study of the stereoelectronic demands of the unusual oxy-selenium reactive intermediate involved in dearomatization of 1- and 2-naphthols is carried out. 4-Hydroxy cyclohexadieneone and cyclohexadieneone aryl ethers were generated from dialkyl-phenols under similar reaction conditions providing direct evidence of the mechanical postulate. The first instance of the phenoxy-selenium interaction leading to facile dearomatization of arenes is highlighted in this manuscript.
- Sarkar, Debayan,Ghosh, Manoj Kumar,Rout, Nilendri,Giri, Santanab
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- Tandem dienone photorearrangement-cycloaddition for the rapid generation of molecular complexity
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A tandem dienone photorearrangement-cycloaddition (DPC) reaction of novel cyclohexadienone substrates tethered with various 2π and 4π reaction partners resulted in the formation of polycyclic, bridged frameworks. In particular, use of alkynyl ether-tether
- Bos, Pieter H.,Antalek, Mitchell T.,Porco, John A.,Stephenson, Corey R. J.
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- Singlet Oxygen Generation from a Water-Soluble Hypervalent Iodine(V) Reagent AIBX and H2O2: An Access to Artemisinin
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Herein, we report an efficient method for the chemical generation of 1O2 by treatment of H2O2 with AIBX, a highly water-soluble, bench-stable, recyclable hypervalent iodine(V) reagent developed by our group. The generation of 1O2 was confirmed by the following results: (1) capture of 1O2 with the sodium salt of anthracene-9,10-bis(ethanesulfonate) produced the corresponding endoperoxide and (2) TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) produced by the oxidation of 2,2,6,6-tetramethylpiperidine with 1O2 generated using the AIBX/H2O2 system was detected by electron spin resonance spectroscopy. To illustrate the potential utility of this method for organic synthesis, we used the AIBX/H2O2 system to perform typical reactions of 1O2: [2 + 2]/[4 + 2] cycloadditions, Schenck ene reactions, and heteroatom oxidation reactions, which afforded the corresponding products in high yields. Moreover, we used the method to synthesize the antimalarial drug artemisinin. Finally, we demonstrated that AIBX could be regenerated after the reaction by means of a workup involving extraction and removal of water to obtain a precursor of AIBX, which could then be re-oxidized.
- Hu, Ze-Nan,Shen, Hui-Jie,Zhang, Chi
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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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p. 9748 - 9752
(2021/05/27)
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- Reductive Aromatization of Quinols with B2pin2 as Deoxidizing Agent
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We have demonstrated B2pin2 as superior deoxidizing agent for the reductive deoxygenation of quinol derivatives under basic conditions. A wide range of highly functionalized phenols were obtained in good yields including a complex drug molecule, which revealed the high functional group tolerance of this protocol.
- Liu, Bin,Xu, Yin,Luo, Zhibin,Xie, Jimin
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supporting information
p. 1022 - 1024
(2020/03/19)
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- “Dark” Singlet Oxygen Made Easy
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An operationally simple continuous flow generator of “dark” singlet oxygen has been developed. The singlet oxygen was efficiently reacted with several chemical traps to give the corresponding oxygenated products in high yields. The developed “dark” singlet oxygen generator has been successfully applied in the synthesis of the antimalarial drug artemisinin.
- Elsherbini, Mohamed,Allemann, Rudolf K.,Wirth, Thomas
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supporting information
p. 12486 - 12490
(2019/08/26)
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- Site-selective Oxidative Dearomatization of Phenols and Naphthols into ortho-Quinols or Epoxy ortho-Quinols using Oxone as the Source of Dimethyldioxirane
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A novel reactivity of dimethyldioxirane, generated in situ from Oxone and acetone, with substituted phenols and naphthols is reported. This methodology allowed the synthesis of ortho-quinols or epoxy ortho-quinols from a site-selective oxidative dearomatization process, with good yields under very mild conditions. A short total synthesis of natural product lacinilene C methyl ether is also described using this process as the key step. (Figure presented.).
- Cabrera-Afonso, María J.,Carre?o, M. Carmen,Urbano, Antonio
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supporting information
(2019/08/21)
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- An Enzymatic Route to α-Tocopherol Synthons: Aromatic Hydroxylation of Pseudocumene and Mesitylene with P450 BM3
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Aromatic hydroxylation of pseudocumene (1 a) and mesitylene (1 b) with P450 BM3 yields key phenolic building blocks for α-tocopherol synthesis. The P450 BM3 wild-type (WT) catalyzed selective aromatic hydroxylation of 1 b (94 %), whereas 1 a was hydroxylated to a large extent on benzylic positions (46–64 %). Site-saturation mutagenesis generated a new P450 BM3 mutant, herein named “variant M3” (R47S, Y51W, A330F, I401M), with significantly increased coupling efficiency (3- to 8-fold) and activity (75- to 230-fold) for the conversion of 1 a and 1 b. Additional π–π interactions introduced by mutation A330F improved not only productivity and coupling efficiency, but also selectivity toward aromatic hydroxylation of 1 a (61 to 75 %). Under continuous nicotinamide adenine dinucleotide phosphate recycling, the novel P450 BM3 variant M3 was able to produce the key tocopherol precursor trimethylhydroquinone (3 a; 35 % selectivity; 0.18 mg mL?1) directly from 1 a. In the case of 1 b, overoxidation leads to dearomatization and the formation of a valuable p-quinol synthon that can directly serve as an educt for the synthesis of 3 a. Detailed product pattern analysis, substrate docking, and mechanistic considerations support the hypothesis that 1 a binds in an inverted orientation in the active site of P450 BM3 WT, relative to P450 BM3 variant M3, to allow this change in chemoselectivity. This study provides an enzymatic route to key phenolic synthons for α-tocopherols and the first catalytic and mechanistic insights into direct aromatic hydroxylation and dearomatization of trimethylbenzenes with O2.
- Dennig, Alexander,Weingartner, Alexandra Maria,Kardashliev, Tsvetan,Müller, Christina Andrea,Tassano, Erika,Schürmann, Martin,Ruff, Anna Jo?lle,Schwaneberg, Ulrich
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p. 17981 - 17991
(2017/11/29)
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- CsOH catalyzed aerobic oxidative synthesis of p-quinols from multi-alkyl phenols under mild conditions
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p-Quinols are ubiquitous structural motifs of various natural products and pharmaceutical compounds, and versatile building blocks in synthetic chemistry. The reported methods for the synthesis of p-quinol require stoichiometric amounts of oxidants. Molecular oxygen is considered as an ideal oxidant due to its natural, inexpensive, and environmentally friendly characteristics. During the ongoing research of C-H bond hydroxylation, we found that multi-alkyl phenols could react with molecular oxygen under mild conditions. Herein, we describe an efficient oxidative de-aromatization of multi-alkyl phenols to p-quinols. 1 atm of molecular oxygen was used as the oxidant. Many multi-alkyl phenols could react smoothly at room temperature. Isotopic labeling experiment was also performed, and the result proved that the oxygen atom in the produced hydroxyl group is from molecular oxygen.
- Liang, Yu-Feng,Wu, Kai,Liu, Zhiqing,Wang, Xiaoyang,Liang, Yujie,Liu, Chenjiang,Jiao, Ning
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p. 1334 - 1339
(2015/03/18)
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- Reactivity of hydroxy- and aquo(hydroxy)-λ3-iodane-crown ether complexes
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We have designed a series of hydroxy(aryl)-λ3-iodane-[18] crown-6 complexes, prepared from the corresponding iodosylbenzene derivatives and superacids in the presence of [18]crown-6, and have investigated their reactivities in aqueous media. These activated iodosylbenzene monomers are all non-hygroscopic shelf-storable reagents, but they maintain high oxidizing ability in water. The complexes are effective for the oxidation of phenols, sulfides, olefins, silyl enol ethers, and alkyl(trifluoro)borates under mild conditions. Furthermore, hydroxy-λ3-iodane-[18]crown-6 complexes serve as efficient progenitors for the synthesis of diaryl-, vinyl-, and alkynyl-λ3-iodanes in water. Other less polar organic solvents, such as methanol, acetonitrile, and dichloromethane, are also usable in some cases. Aqua-friendly iodosylbenzene equivalents: Hydroxy- and aquo(hydroxy)-λ3-iodane-[18]crown-6 complexes (see graphic), readily prepared from commercial PhI(OAc)2 or PhIO, serve as excellent oxygen atom donors toward olefins, phenols, sulfides, and alkyl(trifluoro)borates. They also serve as progenitors for diaryl-, vinyl-, and alkynyl-λ3-iodane-[18]crown-6 complexes. These reactions can be carried out in aqueous media under mild reaction conditions.
- Miyamoto, Kazunori,Yokota, Yukie,Suefuji, Takashi,Yamaguchi, Kentaro,Ozawa, Tomoyuki,Ochiai, Masahito
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supporting information
p. 5447 - 5453
(2014/05/20)
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- Highly efficient method for synthesis of benzoquinones using hypervalent iodine(iii) reagent and sodium bisulfate
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A rapid, one-step, novel approach for the conversion of benzamides into benzoquinones using (diacetoxyiodo)benzene(III) and sodium bisulfate has been developed in aqueous acetonitrile at room temperature. The developed protocol is applicable to several types of substituted benzamide derivatives to get the corresponding benzoquinone products. The developed methodology offers mild reaction condition, short reaction time, and moderate to excellent yields. This is one of the most simple and environmentally benign protocols for synthesis of benzamide derivatives.
- Sasane, Kulbhushan A.,Telvekar, Vikas N.
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supporting information
p. 468 - 473
(2014/01/23)
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- PROCESS FOR THE OXIDATION OF MESITOL
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The invention relates to a process for the oxidation of mesitol with singlet oxygen, which is re- leased from hydrogen peroxide, this release taking place in the presence of a bismuth com- pound as catalyst. In the process, 2,4,6-trimethylquinol is formed
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Page/Page column 14-19
(2012/08/28)
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- Regioselective and stereoselective cyclizations of cyclohexadienones tethered to active methylene groups
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The cyclization of 2,5-cyclohexadienones tethered to activated methylene groups was studied. The substitution around the cyclohexadienone ring serves to regioselectively direct these cyclizations based primarily on electronic effects. In the case of brominated substrates, these reactions proceed to give highly unusual electron-deficient tricyclic cyclopropanes. By using a Cinchona alkaloid-based phase-transfer catalyst, prochiral cyclohexadienones can be desymmetrized with moderate stereoselectivity.
- Tello-Aburto, Rodolfo,Kalstabakken, Kyle A.,Volp, Kelly A.,Harned, Andrew M.
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supporting information; experimental part
p. 7849 - 7859
(2011/12/04)
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- Desymmetrization of 4-hydroxy-2,5-cyclohexadienones by radical cyclization: Synthesis of optically pure γ-lactones
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Optically pure γ-lactones fused onto a cyclohexenone are available by a radical-based method for desymmetrizing 4-hydroxy-2,5-cyclohexadienones.
- Sunasee, Rajesh,Clive, Derrick L. J.
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supporting information; experimental part
p. 701 - 703
(2010/06/12)
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- Hypervalent iodine oxidation of phenol derivatives using a catalytic amount of 4-iodophenoxyacetic acid and Oxone as a co-oxidant
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Reaction of p-substituted phenols 2 with a catalytic amount of 4-iodophenoxyacetic acid (1) and Oxone as a co-oxidant in tetrahydrofuran (THF) or 1,4-dioxane-water gave the corresponding p-quinols 3 in excellent yields. Reaction of p-dialkoxyarenes 4 in 2,2,2-trifluoroethanol- water gave the corresponding p-quinones 5 in excellent yield without purification. These reactions provide efficient and practical methods for the preparation of p-quinols and p-quinones from p-substituted phenols and p-dialkoxyarenes, respectively. This quinone synthesis was applied to synthesis of blattellaquinone (13), the sex pheromone of the German cockroach Blattella germanica.
- Yakura, Takayuki,Omoto, Masanori,Yamauchi,Tian, Yuan,Ozono, Ayaka
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experimental part
p. 5833 - 5840
(2010/09/11)
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- Hofmann rearrangement of carboxamides mediated by hypervalent iodine species generated in situ from iodobenzene and oxone: Reaction scope and limitations
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Alkylcarboxamides can be converted to the respective amines by Hofmann rearrangement using hypervalent iodine species generated in situ from PhI and Oxone in aqueous acetonitrile. On the basis of this reaction, a convenient experimental procedure for the preparation of alkylcarbamates using Oxone as the oxidant in the presence of iodobenzene in methanol has been developed. An efficient method for direct conversion of substituted benzamides to the respective quinone derivatives by treatment with Oxone and iodobenzene in aqueous acetonitrile has also been found.
- Zagulyaeva, Aleksandra A.,Banek, Christopher T.,Yusubov, Mekhman S.,Zhdankin, Viktor V.
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supporting information; experimental part
p. 4644 - 4647
(2010/12/19)
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- Efficient synthesis of p-quinols using catalytic hypervalent iodine oxidation of 4-arylphenols with 4-iodophenoxyacetic acid and oxone
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Efficient synthesis of p-quinols (2) using catalytic hypervalent iodine oxidation of 4-arylphenols (1) with 4-iodophenoxyacetic acid (3) and Oxone was developed. Reaction of 1 with a catalytic amount of 3 in the presence of Oxone as a co-oxidant in tetrahydrofuran or 1,4-dioxane-water gave the corresponding 2 in excellent yields.
- Yakura, Takayuki,Omoto, Masanori
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body text
p. 643 - 645
(2009/12/24)
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- Oxidative de-aromatization of para-alkyl phenols into para-peroxyquinols and para-quinols mediated by oxone as a source of singlet oxygen
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(Chemical Equation Presented) Easy does it: Easily handled and environmentally safe oxone generates singlet oxygen which effects the simple and selective oxidative de-aromatization of para-alkyl phenols 1 into para-peroxyquinols 2 under very mild conditions with good to excellent yields. A one-pot access to para-quinols 3 from 1 is also possible after treatment of the crude reaction mixture with sodium thiosulfate.
- Carreno, M. Carmen,Gonzalez-Lopez, Marcos,Urbano, Antonio
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p. 2737 - 2741
(2007/10/03)
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- Bromide-assisted oxidation of substituted phenols with hydrogen peroxide to the corresponding p-quinol and p-quinol ethers over WO4 2--exchanged layered double hydroxides
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A simple and efficient one-pot synthesis of p-quinols and their ethers occurs over tungstate-exchanged layered double hydroxides (WO4 2--LDHs), which catalyze the bromide-assisted oxidation of substituted phenols to the corresponding 4-alkoxy- and 4-hydroxycyclohexa-2,5- dienones in high yields (see scheme).
- Sels,De Vos,Jacobs
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p. 310 - 313
(2007/10/03)
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- Isolation, Characterization, and Reaction of Activated Iodosylbenzene Monomer Hydroxy(phenyl)iodonium Ion with Hypervalent Bonding: Supramolecular Complex PhI+OH·18-Crown-6 with Secondary I...O Interactions
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The isolation, characterization, and reaction of the active species hydroxy(phenyl)iodonium ion with hypervalent bonding are reported. Reaction of iodosylbenzene with HBF4-Me2O in the presence of equimolar 18-crown-6 in dichloromethane afforded the hydroxy-λ3-iodane complex PhI(OH)BF4·18-crown-6 as stable yellow prisms. X-ray structure analysis indicated that both the close contacts between the iodine(III) and the three adjacent oxygen atoms of 18-crown-6, and the hydrogen bonding OH...O(crown ether) will be responsible for the increased stability of the complex as compared to the uncomplexed PhI(OH)BF4. The crown ether complex is highly reactive and serves as a versatile oxidant even in water: thus, the complex undergoes oxidative transformations of a variety of functional groups such as olefins, alkynes, enones, silyl enol ethers, sulfides, and phenols under mild conditions. Copyright
- Ochiai, Masahito,Miyamoto, Kazunori,Shiro, Motoo,Ozawa, Tomoyuki,Yamaguchi, Kentaro
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p. 13006 - 13007
(2007/10/05)
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- Reactivity and selectivity of aryloxylium ions
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The reactivity and selectivity of aryloxylium ions in acetonitrile-water mixtures are described. The 4-bromo-2,4,6-trialkylcyclohexa-2,5-dienones used as substrates were synthesised by electrophilic bromination in yields of 60% (3 R = Me) and 52% (7 R = B
- Hegarty, Anthony F.,Keogh, Joseph P.
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p. 758 - 762
(2007/10/03)
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- Oxidative demethylation of 4-methylphenols to 1,4-benzoquinones with hydrogen peroxide, catalyzed by K10 montmorillonite
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2,4,6-Trimethylphenol and pentamethylphenol react with hydrogen peroxide in the presence of K10 montmorillonite (22°C, CCl4, 2 h) to afford, respectively, 2,6-dimethyl-1,4-benzoquinone and 2,3,5,6-tetramethyl-1,4-benzoquinone. 2,6-Di-tert-butyl-4-methylphenol and 4-methylphenol do not react under the same conditions. The mechanism of this reaction is discussed.
- Bushmelev,Genaev,Shubin
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- A Simple and Efficient Procedure for the Preparation of p-Quinols by Hypervalent Iodine Oxidation of Phenols and Phenol Tripropylsilyl Ethers
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Oxidation of para-substituted phenols with benzene (BTIB) in aqueous acetonitrile at 0 deg C gives p-quinols in moderate to good yields; higher yields are obtained when tripropylsilyl ethers of phenols are used.
- McKillop, Alexander,McLaren, Lee,Taylor, Richard J. K.
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p. 2047 - 2048
(2007/10/02)
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- Process for the preparation of 4-hydroxy-2,4,6-trimethyl-2,5-cyclohexadienone
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4-Hydroxy-2,4,6-trimethyl-2,5-cyclohexadienone is prepared by oxidation of 2,4,6-trimethylphenol with a manganese derivative of valency greater than 2 in an aqueous acidic medium.
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- Process for the preparation of 4-hydroxy-2,4,6-trimethyl-2,5-cyclohexadienone
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4-Hydroxy-2,4,6-trimethyl-2,5-cyclohexadienone is made by chlorinating 2,4,6-trimethylphenol with chlorine in an organic solvent in the absence of base while the hydrogen chloride formed is removed as it is formed by physical means and hydrolyzing the reaction mixture with water optionally in the presence of an inorganic base.
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- Process for the preparation of 4-hydroxy-2,4,6-trimethyl-2,5-cyclohexadienone
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4-Hydroxy-2,4,6-trimethyl-2,5-cyclohexadienone is prepared by treatment of 2,4,6-trimethylphenol with a halogenation agent and water in the presence of an organic solvent which is inert to the halogenation agent.
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- Process for producing 4-hydroxy-2,4,6-trimethylcyclohexa-2,5-diene-1-one
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A process for the preparation of 4-hydroxy-2,4,6-trimethylcyclohexa-2,5-diene-1-one from 2,4,6-trimethylphenol is disclosed, comprising reacting 2,4,6-trimethylphenol with an aqueous solution or suspension of hypohalogenous acid or salt thereof in an aqueous medium or mixed medium of water and specific organic solvents. This process enables to prepare 4-hydroxy-2,4,6-trimethylcyclohexa-2,5-diene-1-one, which is a precursor for 2,3,5-trimethylhydroquinone, a starting material for the preparation of vitamin E, by a simplified operation, safely and at high yields.
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- PHOTOINDUCED ELECTRON TRANSFER OXIDATION - 1. 9,10-DICYANOANTHRACENE-SENSITIZED PHOTOOXIDATION OF HINDERED PHENOLS.
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9,10-Dicyanoanthracene (DCA)-sensitized photooxidation reactions of hindered phenols and catechols (I) proceed via the initial electron transfer from 1 to **1DCA. 4-Hydroperoxy-2,5-cyclohexadien-1-ones and 4-hydroxy-2,5-cyclohexadien-1-ones are obtained from 2,4,6-trialkyl-substituted phenols, and an o-benzoquinone and furanone derivatives are afforded from 3,5-di-t-butylcatechol.
- Futamura,Yamazaki,Ohta,Kamiya
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p. 3852 - 3855
(2007/10/02)
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- Selective Reactions of Carbanions with p-Quinones. The Aggregate Model
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Additions of carbanions to unsymmetrical p-quinones can be achieved at either carbonyl carbon by a judicious choice of reaction conditions.
- Liotta, Dennis,Saindane, Manohar,Barnum, Christopher
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p. 3369 - 3370
(2007/10/02)
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- Novel process for preparation of 4-hydroxy-2,4,6-trimethyl-2,5-cyclohexadiene-1-one
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A process for preparing 4-hydroxy-2,4,6-trimethyl-2,5-cyclohexadiene-1-one comprising reacting 2,4,6-trimethyl phenol with molecular oxygen or a molecular oxygen-containing gas. The product (also called mesitylquinol) is an intermediate useful as a raw material for the synthesis of a variety of industrial chemicals such as a drugs, dyestuffs, and pigments.
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