- Target analysis of α-alkylidene-γ-butyrolactones in uropathogenic E. coli
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α-Alkylidene-γ-butyrolactones are quite common in nature and exhibit a broad spectrum of biological activities. We therefore synthesized a small library of xanthatine inspired α-alkylidene-γ-butyrolactones to screen non-pathogenic and uropathogenic E. col
- Kunzmann, Martin H.,Sieber, Stephan A.
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Read Online
- On the addition of .OH radicals to the ipso positions of alkyl-substituted aromatics: Production of 4-hydroxy-4-methyl-2,5-cyclohexadien-1-one in the radiolytic oxidation of p-cresol
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4-Hydroxy-4-methyl-2,5-cyclohexadien-1-one has been conclusively identified by its 1H and 13C NMR spectra as a significant initial product in the radiolysis of aqueous solutions of p-cresol. This product is formed as the result of ox
- Schuler, Robert H.,Albarran, Guadalupe,Zajicek, Jaroslav,George,Fessenden, Richard W.,Carmichael, Ian
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Read Online
- Substrate-Selectivity in Catalytic Photooxygenation Processes Using a Quinine-BODIPY System
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Substrate selectivity by means of synthetic catalysts remains a challenging topic in chemistry. Here, a catalytic system combining an iodo-BODIPY photosensitizer and quinine was evaluated in the competitive photooxygenation of non-hydrogen and hydrogen-bond-donor substrates. The ability of quinine to activate hydrogen-bond-donor substrates towards photooxygenation was reported and the results were benchmarked with photooxygenation experiments in the absence of quinine.
- Coeffard, Vincent,Fischer, Jér?me,Nun, Pierrick,Serier-Brault, Hélène
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Read Online
- Quinone Alkylation Using Organocadmium Reagents: A General Synthesis of Quinols
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Reactions of p-benzoquinone with organocadmium reagents yield quinols, the result of quinone carbonyl monoalkylation. The reactions proceed in good yield and are devoid of bisaddition and hydroquinone byproducts. Quinone alkylations using this method show
- Aponick, Aaron,McKinley, Jason D.,Raber, Jeffrey C.,Wigal, Carl T.
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Read Online
- Reactions of p-Quinols with Aldehydes and Imines: Stereoselective Access to Polyheterobicyclic and Tricyclic Systems
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Dihydrobenzo[1,3]dioxolanones, tetrahydrobenzo[d]oxazolones and heterotricyclic derivatives have been stereoselectively synthesized from p-quinols upon reaction with aldehydes or benzaldimines under basic catalysis. Reactions occurred in an experimentally
- García-García, Carolina,Redondo, María C.,Ribagorda, María,Carre?o, M. Carmen
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Read Online
- Redox-neutral functionalization of α-Csp3-H bonds of secondary cyclic amines: a highly atom-economical strategy forN-arylation/formal cross-dehydrogenative couplings
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An efficient redox-neutral method has been developed for α-Csp3-H functionalization of secondary cyclic aminesviaconcurrentN-arylation/formal cross dehydrogenation coupling (CDC) with sp2-C-H and sp3-C-H bonds of arenes an
- Husen, Saddam,Jha, Priyankar,Kumar, Ravindra
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supporting information
p. 2950 - 2955
(2021/05/05)
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- Multigram Synthesis of Trioxanes Enabled by a Supercritical CO2Integrated Flow Process
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Photochemical synthesis of highly reactive hydroperoxides and their conversion into useful products, such as 1,2,4-trioxanes, are of wide interest for synthetic organic chemistry and pharmaceutical manufacturing particularly because of their relevance as potential antimalarial and anticancer treatment drugs, for example, Artemisinin. One class of antimalarial drugs is based on 1,2,4-trioxane scaffolds although production of such compounds on a gram scale is challenging due to their instability in oxidizable solvents. Furthermore, current methods employ either solid oxidants, which make continuous processing problematic, or molecular oxygen, requiring long reaction times of up to 48 h. Here, we report a new multigram continuous approach using a custom-built high-pressure sapphire photoreactor to synthesize trioxanes via the dearomatization of para-substituted phenols by photogenerated singlet oxygen in supercritical CO2. CO2 also facilitates mixing with O2 and has lower viscosity, thereby improving penetration into the pores of the solid acid catalyst used for the formation of trioxanes. We show the capabilities of a 5.2 mL reactor to scale up the reaction to 67 g/day. This synthetic approach provides a platform to rapidly access high-value compounds under flow conditions, with high atom efficiencies, excellent yields, short reaction times, and without the need for isolation of hazardous intermediates.
- Wu, Lingqiao,Abreu, Bruna L.,Blake, Alexander J.,Taylor, Laurence J.,Lewis, William,Argent, Stephen P.,Poliakoff, Martyn,Boufroura, Hamza,George, Michael W.
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supporting information
p. 1873 - 1881
(2021/07/21)
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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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- Phosphine-Catalyzed Cascade Michael Addition/[4+2] Cycloaddition Reaction of Allenoates and 2-Arylidene-1,3-indanediones
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The phosphine-catalyzed cascade Michael addition/[4+2] cycloaddition reaction of tetrahydrobenzofuranone-derived allenoates and 2-arylidene-1,3-indanediones has been reported, affording spirocyclic 1,3-indanedione derivatives in moderate to high yields wi
- Shi, Wangyu,Mao, Biming,Xu, Jiaqing,Wang, Qijun,Wang, Wei,Wu, Yongjun,Li, Xuefeng,Guo, Hongchao
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supporting information
p. 2675 - 2680
(2020/03/26)
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- Site-selective 1,3-double functionalization of arenes using: Para -quinol, C-N, and C-C/C-P three-component coupling
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A catalytic and site-selective approach has been demonstrated for dual functionalization of arenes via cross-coupling reactions of p-quinols with amines and isocyanides/phosphites. The strategy enables the production of a series of 3-amino-benzamides and
- Husen, Saddam,Chauhan, Anil,Kumar, Ravindra
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supporting information
p. 1119 - 1124
(2020/03/11)
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- Synthesis, characterisation, and reactivity of novel pseudocyclic hypervalent iodine reagents with heteroaryl carbonyl substituents
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Two new hypervalent iodine reagents containing furan and thiophene moieties in addition to a carbonyl group in the vicinity of the iodine atom were synthesised and characterised. The X-ray analysis of both compounds revealed a strong intramolecular contact between the carbonyl oxygen and the hypervalent iodine atom with tosylate as a counter ion. The two reagents showed a broad range of synthetic applications and proved to be versatile oxidizing agents.
- Qurban, Jihan,Elsherbini, Mohamed,Alharbi, Haifa,Wirth, Thomas
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supporting information
p. 7998 - 8000
(2019/07/12)
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- Multicatalytic dearomatization of phenols into epoxyquinols: Via a photooxygenation process
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A multicatalytic photooxygenation of substituted phenols in the presence of rose bengal and cesium carbonate under green LED light is reported. This transformation enabled the introduction of both atoms of singlet oxygen and led to the one-pot synthesis o
- Péault, Louis,Nun, Pierrick,Le Grognec, Erwan,Coeffard, Vincent
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supporting information
p. 7398 - 7401
(2019/06/27)
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- N-Heterocycle-Stabilized Iodanes: From Structure to Reactivity
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Pseudocyclic aryl-λ3-iodanes are superior reagents for a variety of oxidative transformations due to a well-balanced relation between stability, solubility and reactivity. Their properties are substantially influenced by a dative interaction between a Lewis base, in general the oxygen atom of a carboxylic acid or an amide, and the central hypervalent iodine atom. This work presents the first systematic investigation of pseudocyclic N-heterocycle-stabilized iodanes (NHIs). The synthesis of these throughout shelf-stable solids is robust and can be achieved on a large scale. Their reactivity is highly tunable, depending on the stabilizing heterocycle. Solid state structures of selected derivatives are reported and their reactivity in a model oxygen transfer reaction is compared. Further derivatization reactions to N-heterocycle-stabilized pseudocyclic diaryliodonium salts and cyclic iodoso species are presented as well.
- Boelke, Andreas,Lork, Enno,Nachtsheim, Boris J.
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supporting information
p. 18653 - 18657
(2018/11/23)
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- Nitrogen-Bridged, Natural Product Like Octahydrobenzofurans and Octahydroindoles: Scope and Mechanism of Bridge-Forming Reductive Amination via Caged Heteroadamantanes
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The biological significance of sp3-rich synthetic scaffolds with natural product like features yet distinct global frameworks is being increasingly recognized in medicinal chemistry and biochemistry. Taking inspiration from the vast array of bi
- Wales, Steven. M.,Adcock, Holly V.,Lewis, William,Hamza, Daniel,Moody, Christopher J.
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supporting information
p. 4696 - 4704
(2018/09/14)
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- Bio-inspired Domino oxa-Michael/Diels–Alder/oxa-Michael Dimerization of para-Quinols
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A bio-inspired, pyrrolidine-mediated, dimerization of para-quinols has been developed. It represents one of the most complex, yet general, dimerization reactions ever disclosed, selectively forming four new bonds, four new rings, and eight new contiguous stereogenic centres. The para-quinol starting materials are easily handled, bench-stable compounds, accessed in just one step from aromatic feedstocks. The reaction can be scaled up to give grams of polycyclic material, primed for further elaboration.
- Green, Nicholas J.,Connolly, Catherine A.,Rietdijk, Koen P. W.,Nichol, Gary S.,Duarte, Fernanda,Lawrence, Andrew L.
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supporting information
p. 6198 - 6202
(2018/05/30)
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- Torsional steering as friend and foe: development of a synthetic route to the briarane diterpenoid stereotetrad
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Two synthetic routes to the briarane stereotetrad have been investigated. The first route employed a boron aldol reaction to establish the stereogenic all-carbon quaternary carbon (C1). In this case, it was found that torsional steering in the transition
- Moon, Nicholas G.,Harned, Andrew M.
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p. 1876 - 1888
(2017/03/09)
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- Phosphazene-catalyzed desymmetrization of cyclohexadienones by dithiane addition
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We report a desymmetrization of cyclohexadienones by intramolecular conjugate addition of a tethered dithiane nucleophile. Mild reaction conditions allow the formation of diversely functionalized fused bicyclic lactones. The products participate in facially selective additions from the convex surface, leading to allylic alcohol derivatives.
- Horwitz, Matthew A.,Massolo, Elisabetta,Johnson, Jeffrey S.
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supporting information
p. 762 - 767
(2017/06/21)
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- Phosphine-Catalyzed [4 + 2] Annulation of Allenoate with Sulfamate-Derived Cyclic Imines: A Reaction Mode Involving γ′-Carbon of α-Substituted Allenoate
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A phosphine-catalyzed [4 + 2] cycloaddition of cyclic α-substituted allenoates with sulfamate-derived cyclic imines has been reported. Using dibenzylphenylphosphine as the nucleophilic catalyst, the reaction worked efficiently to yield various fused multicyclic heterocyclic compounds in high yields with excellent diastereoselectivities. It undergoes a new reaction mode involving γ′-carbon of α-substituted allenoate.
- Mao, Biming,Shi, Wangyu,Liao, Jianning,Liu, Honglei,Zhang, Cheng,Guo, Hongchao
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supporting information
p. 6340 - 6343
(2017/12/08)
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- Preparation, structure, and versatile reactivity of pseudocyclic benziodoxole triflate, new hypervalent iodine reagent
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A new pseudocyclic triflate derivative of benziodoxole (IBA-OTf) was prepared and characterized by X-ray analysis. This highly electrophilic reagent readily reacts with various organic substrates to give the corresponding products in good yields. Furthermore, IBA-OTf can be used as a catalyst with m-chloroperoxybenzoic acid as the terminal oxidant. This journal is
- Yoshimura, Akira,Nguyen, Khiem C.,Klasen, Scott C.,Saito, Akio,Nemykin, Victor N.,Zhdankin, Viktor V.
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supporting information
p. 7835 - 7838
(2015/05/13)
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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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- Cu-catalyzed asymmetric borylative cyclization of cyclohexadienone- containing 1,6-enynes
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The first Cu-catalyzed asymmetric borylative cyclization of cyclohexadienone-containing 1,6-enynes is achieved through a tandem process: selective β-borylation of propargylic ether and subsequent conjugate addition to cyclohexadienone. The reaction proceeds with excellent regioselectivity and enantioselectivity to afford an optically pure cis-hydrobenzofuran framework bearing alkenylboronate and enone substructures. Furthermore, the resulting bicyclic products could be converted to bridged and tricyclic ring structures. This method extends the realm of Cu-catalyzed asymmetric tandem reactions using bis(pinacolato)diboron (B2pin 2).
- Liu, Ping,Fukui, Yuki,Tian, Ping,He, Zhi-Tao,Sun, Cai-Yun,Wu, Nuo-Yi,Lin, Guo-Qiang
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p. 11700 - 11703
(2013/09/02)
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- Facile synthesis of α-methylidene-γ-butyrolactones: Intramolecular Rauhut-Currier reaction promoted by chiral acid-base organocatalysts
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The acid-base organocatalyzed intramolecular Rauhut-Currier (RC) reaction of the dienone enolates has been developed. The enantioselective RC process produces the highly functionalized α-methylidene-γ-butyrolactones as a single diastereomer with up to 98% ee.
- Takizawa, Shinobu,Nguyen, Tue Minh-Nhat,Grossmann, André,Suzuki, Michitaka,Enders, Dieter,Sasai, Hiroaki
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p. 1202 - 1209
(2013/02/23)
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- Exploring Morita-Baylis-Hillman reactions of p-quinols
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[Chemical equation presented] The Morita Baylis Hillman reaction of p-methylquinols with activated aromatic aldehydes has been studied. Depending on the reaction conditions (solvent and additives), three different products were formed. A mono or double Mo
- Redondo, Maria C.,Ribagorda, Maria,Carreno, M. Carmen
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scheme or table
p. 568 - 571
(2010/05/19)
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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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- Oxidation of 4-arylphenol trimethylsilyl ethers to p-arylquinols using hypervalent iodine(III) reagents
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An efficient synthesis of p-arylquinols by the oxidation of 4-arylphenol trimethylsilyl ethers with phenyliodine(III) diacetate (PIDA) is reported. This protocol greatly improved the yield of p-quinol by minimizing oligomer side products compared to the o
- Felpin, Fran?ois-Xavier
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p. 409 - 412
(2008/02/04)
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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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- The hydrolysis of 4-acyloxy-4-substituted-2,5-cyclohexadienones: Limitations of aryloxenium ion chemistry
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The title compounds serve as potential precursors to aryloxenium ions, often proposed, but primarily uncharacterized intermediates in phenol oxidations. The uncatalyzed and acid-catalyzed decomposition of 4-acetoxy-4-phenyl-2,5-cyclohexadienone, 2a, generates the quinol, 3a. 18O-Labeling studies performed in 16O-H2O, and monitored by LC/MS and1 13C NMR spectroscopy that can detect 18O-induced chemical shifts on 13C resonances, show that 3a was generated in both the uncatalyzed and acid-catalyzed reactions by C alkyl-O bond cleavage consistent with formation of an aryloxenium ion. Trapping with N3- and Br- confirms that both uncatalyzed and acid-catalyzed decompositions occur by rate-limiting ionization to form the 4-biphenylyloxenium ion, 1a. This ion has a shorter lifetime in H2O than the corresponding nitrenium ion, 7a (12 ns for 1a, 300 ns for 7a at 30 °C). Similar analyses of the product, 3b, of acid- and base-catalyzed decomposition of 4-acetoxy-4-methyl-2,5-cyclohexadienone, 2b, in 18O-H2O show that these reactions are ester hydrolyses that proceed by Cacyl-O bond cleavage processes not involving the p-tolyloxenium ion, 1b. Uncatalyzed decomposition of the more reactive 4-dichloroacetoxy-4-methyl-2,5-cyclohexadienone, 2b′, is also an ester hydrolysis, but 2b′ undergoes a kinetically second-order reaction with N3- that generates an oxenium ion-like substitution product by an apparent SN2′ mechanism. Estimates based on the lifetimes of 1a, 7a, and the p-tolylnitrenium ion, 7b, and the calculated relative stabilities of these ions toward hydration indicate that the aqueous solution lifetime of 1b is ca. 3-5 ps. Simple 4-alkyl substituted aryloxenium ions are apparently not stable enough in aqueous solution to be competitively trapped by nonsolvent nucleophiles.
- Novak, Michael,Glover, Stephen A.
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p. 8090 - 8097
(2007/10/03)
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- Oxidation of phenols with chlorine dioxide
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The oxidation of different phenols, viz., phenol, 3-methylphenol, 4-methylphenol, 4-tert-butylphenol, 2-cyclohexylphenol, 2,6-di-tert-butyl-4- methylphenol, and 2,4-dichlorophenol, with chlorine dioxide in acetonitrile was studied spectrophotometrically. The reaction rate is described by a second-order equation w = k[PhOH]? [ClO2]. The rate constants were measured and activation parameters of oxidation were determined in a temperature interval of 10-60°C. A dependence of the reaction rate constant on the phenol structure was found. The oxidation products were identified, and their yields were established.
- Ganiev,Ganieva,Kabal'nova
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p. 2281 - 2284
(2007/10/03)
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- Generation and trapping of the 4-biphenylyloxenium ion by water and azide: Comparisons with the 4-biphenylylnitrenium ion
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Generation of the 4-biphenylyloxenium ion, 1a, from hydrolysis of 4-acetoxy-4-phenyl-2,5-cyclohexadienone, 2a, is demonstrated by common ion rate depression and azide trapping. The ion is less selective with a shorter lifetime (12 ns at 30 °C) in aqueous
- Novak, Michael,Glover, Stephen A.
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p. 7748 - 7749
(2007/10/03)
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- Stereoselective synthesis of heterocyclic cage compounds by domino conjugate additions
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Heterocyclic cage compounds have been stereoselectively synthesized from enantiopure [(S)R]-[(p-tolylsulfinyl)methyl]-p-quinols or their amine analogues and 2-(trimethylsilyloxy)furan in the presence of Bu4NF. The method is particularly valuable not only because of the stereochemical control but also because the reactions occur in an experimentally simple one-pot procedure through a domino sequence of three consecutive conjugate additions. The intermediate 1,4-adducts could be isolated when the reaction was carried out in the presence of BF3·OEt2.
- Carreno, M. Carmen,Garcia Luzon, Carmen,Ribagorda, Maria
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p. 208 - 216
(2007/10/03)
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- New cyclohexadienone derivatives: Preparation and chiral discrimination in high-pressure diels - Alder cycloadditions
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A wide range of cyclohexadienones has been synthesised in order to study their reactivity and their regio- and stereoselectivity with the enantiopure diene 1 under high-pressure conditions. Computational investigations were used to point out some paramete
- Tran-Huu-Dau, Marie-Elise,Wartchow, Rudolf,Winterfeldt, Ekkehard,Wong, Yung-Sing
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p. 2349 - 2369
(2007/10/03)
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- A novel m-CPBA oxidation: p-quinols and epoxyquinols from phenols
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Steroidal quinols were obtained on large scale in 50-57% yield, together with syn-epoxyquinols. The reaction conditions can be adjusted to afford only the corresponding steroidal epoxyquinol in 51-54% yield.
- Solaja, Bogdan A.,Milic, Dragana R.,Gasic, Miroslav J.
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p. 3765 - 3768
(2007/10/03)
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- π-Facial selectivity in nucleophilic additions to 4,4-disubstituted dienones: Experimental support for electrostatic control
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The 4,4-disubstituted cyclohexadienones 5-10 and 32 were prepared by hypervalent iodine oxidation of the corresponding phenols. Our study of the facial selectivity in nucleophilic carbonyl additions provided experimental evidence for dominant dipolar cont
- Wipf, Peter,Kim, Yuntae
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p. 11678 - 11688
(2007/10/02)
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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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- BIOGENESIS-LIKE TRANSFORMATION OF SALIDROSIDE TO RENGYOL AND ITS RELATED CYCLOHEXYLETANOIDS OF FORSYTHIA SUSPENSA
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Photooxygenation of salidroside (8) in methanol in presence of Rose Bengal afforded cornoside (9), which, on high pressure hydrogenation with 5percent palladium on activated carbon, yielded rengyoside B (6).Reduction of 6 with sodium borohydride gave rengyoside A(5) stereoselectively.By enzymatic hydrolysis, 9, 6 and 5 furnished rengyolone (4), rengyoxide (3) and rengyol (1), respectively. Similerly, p-hydroxyphenylethanol (10), the aglycone part of salidroside (8), was oxygenated photochemically to a dienone alcohol, which cyclized spontaneously to rengyolone (4).Hallerone (17) was obtained by the photooxygenation of p-hydroxyphenylethyl acetate (10b).Thus the plausible biosynthetic routes from salidroside (8) to rengyol (1) and the related natural cyclohexylethanoids were simulated chemically.
- Endo, Katsuya,Seya, Kazuhiko,Hikino, Hiroshi
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p. 3673 - 3682
(2007/10/02)
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- The Addition of Organolithium Reagents to Quinone Silyl Methyl Monoketals. A Useful Expedient in the Synthesis of p-Quinols Having Acid-Sensitive Groups
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Acid hydrolyses of dimethyl ketals 4-alkyl- and 4-aryl-4-hydroxy-2,5-cyclohexadienones having an acid-sensitive functionality often afford low or no yields of the respective 4-substituted 4-hydroxy-2,5-cyclohexadienones (p-quinols).However, addition of me
- Stern, Alan J.,Swenton, John S.
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p. 2465 - 2468
(2007/10/02)
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- Quinol Epoxides from p-Cresol and Estrone by Photooxygenation and Titanium(IV)- or Vanadium(V)-Catalyzed Oxygen Transfer
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On treatment with Ti(OiPr)4, 4-hydroperoxy-4-methyl-2,5-cyclohexadien-1-one (1) and 10β-hydroperoxy-1,4-estradiene-3,17-dione (3), readily available by photooxygenation of p-cresol and estrone, respectively, were converted to the corresponding epoxyquinol
- Adam, Waldemar,Lupon, Pilar
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- Acid-Catalyzed Hydrolysis of N-Hydroxyacetanilides: Amide Hydrolysis vs N-O Bond Heterolysis
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Although it has been widely assumed that N-hydroxy-N-aryl amides decompose in acidic solution by acid-catalyzed N-O bond heterolysis, we have found that the N-hydroxyacetanilides 1a-e largely decompose by the alternative amide hydrolysis pathway.The immediate products of hydrolysis, the hydroxylamines 2a-e, can be detected by direct or indirect methods, but these materials also decompose via the Bamberger rearrangement under the reaction conditions.Only the p-EtO- and p-MeO-substituted N-hydroxyacetanilides (1a and 1b) exhibit any sign of N-O bond heterolysis, and only as a minor component (ca. 7percent) of the overall hydrolysis.No change in mechanism could be found for 1d in H2SO4 solutions as concentrated as 9 M.The lack of reactivity of 1a-e to N-O bond heterolysis is largely due to unfavorable protonation of the OH group.Protonation of the carbonyl oxygen is favored over the hydroxyl oxygen by ca. 7 orders of magnitude.
- Novak, Michael,Bonham, Gayl A.,Mohler, Linda K.,Peet, Kristine M.
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p. 3903 - 3908
(2007/10/02)
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- Hydrolysis of N-(Sulfonatooxy)-p-acetotoluidide: Solution Chemistry of Models for Carcinogenic Metabolites of Aromatic Amides
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The hydrolysis reactions of the title compound, a model for the carcinogenic metabolites of polycyclic aromatic amides, were investigated over the pH range 1.0-8.0 by UV spectroscopic methods, product analyses, HPLC, and 1H NMR.This compound is unique among the N-(sulfonatooxy)acetanilides that have been studied to date in that over most of the pH range examined it exhibits non-first-order reaction kinetics.Product analyses indicate that, like the other N-(sulfonatooxy)acetanilides, the hydrolysis of this compound involves N-O bond cleavage, and the kinetics of the N-O bond cleavage process are consistent with a mechanism that includes generation of nitrenium ion-sulfate ion pairs.Four transient species, 9-12, were generated in sufficient quantity to be detected during the hydrolysis reaction.On the basis of isolated decomposition products and kinetic and spectral data obtained during the course of the hydrolysis reaction, the intermediate 9 was identified as 4-hydroxy-4-methylcyclohexa-2,5-dien-1-one N-acetylimine, while 10 and 11 were identified as the isomeric cis- and trans-N-acetyl-2-amino-5,6-dihydroxy-5-methylcyclohexa-1,3-dienes.These species are analogous to materials isolated by Gassman and Granrud from the methanolysis reactions of the methanesulfonate ester of N-hydroxy-p-acetotoluidide.The fourth intermediate, 12, has been tentatively identified as 4-(sulfonatooxy)-4-methylcyclohexa-2,5-dien-1-one.The pH dependence of the hydrolysis reactions of 9 and 10 have also been thoroughly investigated.Both are subject to acid catalysis of hydrolysis and give rise to a number of products.
- Novak, Michael,Roy, Ajit K.
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p. 571 - 580
(2007/10/02)
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- THE FLUORIDE ION EFFECT IN THE REACTIONS OF SINGLET OXYGEN WITH ENOLS
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The fluoride ion effect in the reaction of enolic systems with singlet oxygen has been investigated. β-Dicarbonyl compounds yielded 1,2,3-tricarbonyl derivatives, some of which underwent further hydration, whereas α-diketones suffered oxidative decarboxylation to give open-chain aldehydo-acids or keto-acids.
- Wasserman, Harry H.,Pickett, James E.
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p. 2155 - 2162
(2007/10/02)
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- Hydrolysis of N-(Pivaloyloxy)-p-acetotoluidide: N-O Bond Cleavage Reactions of a Model Proximate Carcinogen
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The hydrolysis reactions of N-(pivaloyloxy)-p-acetotoluidide (1a), a model for the carcinogenic metabolites of polycyclic aromatic amides, were investigated by a combination of UV spectroscopy, product analyses, and HPLC methods at 70 deg C over the pH range 2.0-8.0.Under these conditions 1a undergoes exclusive N-O bond cleavage to yield products characteristic of processes involving nitrenium ion pairs.In many ways the reactions of 1a in aqueous solution parallel those of the analogous sulfuric acid ester, 1b.However, two unique products, 3-(pivaloyloxy)-4-methylacetanilide (2b) and 4-acetotoluidide (9), which have no analogues in the reactions of 1b under these conditions, were isolated.The first-order rate constant for the decomposition of 1a, which is independent of pH and buffer composition, is (380 +/- 60)-fold less than the corresponding rate constant for 1b under the same conditions.The characteristics of the hydrolysis reaction of 1a are considerably different from those of the N-acetoxy-N-arylacetamides which undergo a considerable amount of acyl transfer under similar conditions.These results indicate that pivalic acid esters may be more appropriate models for the proximate carcinogens derived from N-hydroxy-N-arylacetamides than are the acetic acid estrs if, indeed, nitrenium ions are the ultimate carcinogens.
- Novak, Michael,Roy, Ajit K.
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p. 4884 - 4888
(2007/10/02)
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- KINETIC SUBSTITUENT AND ISOTOPE EFFECTS IN THE ACID-CATALYSED REARRANGEMENT OF N-PHENYLHYDROXYLAMINES. ARE NITRENIUM IONS INVOLVED?
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Acidity-rate profiles have been established for the rearrangement of N-phenylhydroxylamine and its derivatives in aqueous sulphuric acid and also in D2SO4-D2O.The results, particularly the change in the magnitude of the kinetic solvent isotope effect on increasing the acidity, are consistent only with a reaction mechanism involving unimolecular decomposition of the O-protonated species.N-Ethyl substitution has only a very small effect on the overall rate of reaction, whereas the rate constant was increased by ca. 100 by 4-Me substitution.The substituent effects argue against the involvement of a nitrenium ion intermediate but rather suggest that the intermediate is better represented by an imine structure with the positive charge at the 4-position in the aromatic ring.
- Kohnstam, George,Petch, W. Andrew,Williams, D. Lyn H.
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p. 423 - 428
(2007/10/02)
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- A New Keto-alcohol, (-)-Mintlactone, (+)-isoMintlactone and Minor Components in Peppermint Oil
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Eighty-one constituents were newly identified from the oil of Mentha piperita L., including a new keto-alcohol, (-)-mintlactone and (+)-isomintlactone.They were determined by spectral data and syntheses to be 4-hydroxy-4-methyl-2-cyclohexen-1-one (8), (6R
- Takahashi, Katsuhiro,Someya, Taichi,Muraki, Shigeru,Yoshida, Toshio
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p. 1535 - 1544
(2007/10/02)
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- REACTIONS OF ORGANOLITHIUM REAGENTS WITH p-BENZOQUINONES AND CYCLOHEXADIENONS, SYNTHESIS OF 4-ALKYL-4-HYDROXYCYCLOHEXA-2,5-DIEN-1-ONES AND 1,4-DIALKYLCYCLOHEXA-2,5-DIENE-1,4-DIOLS.
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Addition of organolithium reagents to p-benzoquinones in ether gives the corresponding 4-alkyl-4-hydroxycyclohexa-2,5-dien-1-ones.Addition of excess of the reagent to the p-benzoquinones, or to the 4-alkyl-4-hydroxycyclohexa-3,5-dien-1-ones, in tetrahydrofuran, gives the corresponding dialkylcyclohexa-2,5-diene-1,4-diols.
- Fischer, A.,Henderson, N.
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p. 701 - 704
(2007/10/02)
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