- Products, rates, and mechanism of the gas-phase condensation of phenoxy radicals between 500-840 K
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Phenols are demonstrated precursors of 'dioxins' - polychlorinated dibenzo-p-dioxins (DDs) and dibenzofurans (DFs) - in thermal processes, especially incineration. Heterogeneous catalysis, depending on conditions, can play an important role, but mere gas-phase combination of phenolic entities to ultimately DD and/or DF is always possible. The present paper addresses the fundamental role of phenol itself. Phenol has long been known to give DF upon pyrolysis and in similar thermal reactions. In the liquid phase under oxidative conditions it yields five condensation products (A-E); this clearly occurs through the dimerization of two phenoxy (PhO) radicals, followed by enolisation/rearomatisation. Our study shows that in the gas phase, at the lower T end, such dimers are also formed, but still with very little DF. That DF, indeed, is almost the only condensation product at elevated temperatures is substantiated by thermochemical-kinetic analysis (favouring the pathway of ortho-C/ortho-C combination of two PhO radicals), as well as by results obtained with two plausible intermediates, viz. 2,2'- dihydroxybiphenyl (A) and 2-phenoxyphenol (C). Mechanisms for the requisite enolisation and dehydration steps leading to DF are discussed.
- Wiater, Izabela,Born, Jan G. P.,Louw, Robert
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- THE ROLE OF STEREOELECTRONIC FACTORS IN THE OXIDATION OF PHENOLS
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The oxidative coupling of both 3,5-dimethylphenol and phenol leads to the ortho-ortho and ortho-para coupled products as the predominant C-C dimers: stereoelectronic factors determine the preferred mode of approach of the phenoxyl radicals.
- Armstrong, David R.,Breckenridge, Robin J.,Cameron, Colin,Nonhebel, Derek C.,Pauson, Peter L.,Perkins, Peter G.
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- Synthesis of the spirocyclic cyclohexadienone ring system of the schiarisanrins.
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[structure: see text] Studies on the synthesis of the spirocyclic cyclohexadienone ring system 2 of the schiarisanrin family of natural products 1 are described and were based on the Lewis acid-promoted C-alkylation of the corresponding phenolic precursor.
- Coleman,Guernon,Roland
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- CuO grafted triazine functionalized covalent organic framework as an efficient catalyst for C-C homo coupling reaction
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Designing of low cost catalytic system for new C-C bond formation reactions is very challenging in synthetic organic chemistry. Herein, we report a new copper oxide immobilized covalent organic framework (COF) material CuII-TRIPTA by grafting of CuO nanoparticles at the surface of a nitrogen rich porous COF material TRIPTA. TRIPTA has been synthesized through the extended Schiff base reaction between 2,4,6-triformylphloroglucinol and 1,3,5-tris-(4-aminophenyl) triazine. The COF as well as CuO loaded materials are characterized by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), N2 adsorption-desorption, Fourier transform infrared spectroscopy (FT-IR), thermogravimetry (TG) and EPR spectroscopic analyses. CuII-TRIPTA material has been successfully applied as heterogeneous nanocatalyst for the C-C homo-coupling reaction of phenylboronic acids to synthesise wide range of biaryl compounds under mild and eco-friendly conditions (60 °C, methanol solvent). Remarkably high specific surface area of CuII-TRIPTA (583 m2 g?1) and highly accessible catalytic sites in the 2D-hexagonal COF nano-architecture potentially makes it excellent catalyst in the C-C bond formation reaction, which is evident from the high TON of the catalyst in this reaction. The catalyst was recollected and reused till 6th cycles without any noticeable change of its catalytic activity, suggesting its high catalytic efficiency in this C-C bond formation reaction.
- Das, Sabuj Kanti,Krishna Chandra, Bijan,Molla, Rostam A.,Sengupta, Manideepa,Islam, Sk. Manirul,Majee, Adinath,Bhaumik, Asim
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- Photochemistry of Dibenzo-1,4-dioxin: Formation of 2,2'-Biphenylquinone as an Observable Intermediate
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Photolysis of dibenzo-1,4-dioxin 1, which is parent ring system of the well-known environmental contaminant 'dioxin' an 2,3,7,8-tetramethyldibenzo-1,4-dioxin 2, in aqueous solution results in an novel intramolecular rearrangement, giving rise to intermedi
- Guan, Bing,Wan, Peter
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- Photochemical rearrangement of chlorinated dibenzo-p-dioxins. Regioselective carbon-oxygen bond homolysis from the singlet excited state, and carbon-chlorine bond homolysis from the triplet excited state
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UV light irradiation of 1-chloro-, 2-chloro-, 1,2-dichloro-, 2,3-dichloro-, and 2,7-dichlorodibenzo-p-dioxin in methanol leads to regioselective homolysis of carbon-oxygen bond from the singlet excited state to undergo rearrangement into chlorinated 2,2′-biphenols. On the contrary, reaction from the triplet excited state of chlorinated dioxins results in selective formation of dechlorinated congeners without altering the dioxin skeleton. Copyright
- Kobayashi, Takanori,Shimada, Jun-Ichi,Kitahara, Chieko,Haga, Naoki
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- Small Molecule NF-κB Inhibitors as Immune Potentiators for Enhancement of Vaccine Adjuvants
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Adjuvants are added to vaccines to enhance the immune response and provide increased protection against disease. In the last decade, hundreds of synthetic immune adjuvants have been created, but many induce undesirable levels of proinflammatory cytokines including TNF-α and IL-6. Here we present small molecule NF-κB inhibitors that can be used in combination with an immune adjuvant to both decrease markers associated with poor tolerability and improve the protective response of vaccination. Additionally, we synthesize a library of honokiol derivatives identifying several promising candidates for use in vaccine formulations.
- Moser, Brittany A.,Escalante-Buendia, Yoseline,Steinhardt, Rachel C.,Rosenberger, Matthew G.,Cassaidy, Britteny J.,Naorem, Nihesh,Chon, Alfred C.,Nguyen, Minh H.,Tran, Ngoctran T.,Esser-Kahn, Aaron P.
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- Phenol conversion and dimeric intermediates in horseradish peroxidase-catalyzed phenol removal from water
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Phenol was removed from water by horseradish peroxidase-catalyzed polymerization. Five dimeric and one trimeric products from the reaction were identified in the aqueous solution. A peroxidase inactivation model for the reaction in the presence of poly(et
- Jian Yu,Taylor,Huixian Zou,Biswas,Bewtra
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- SECOND-ORDER COMBINATION REACTION OF PHENOXYL RADICALS
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Phenoxy radicals, when produced pulse radiolytically at concentrations > 1E-4 M, combine in second-order processes to give 2,2'-, 2,4', and 4,4'-dihydroxybiphenyl as the predominant products.The ratios of these products observed under a variety of conditi
- Ye, Mingyu,Schuler, Robert H.
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- Dendrimer-encapsulated Pd nanoparticles as aqueous, room-temperature catalysts for the Stille reaction
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We report that dendrimer-encapsulated Pd nanoparticles having a diameter of ~1.7 nm are effective and general catalysts for coupling aryl halides to organostannanes (the Stille reaction) under mild conditions. The significant results of this study are that the Stille reaction is catalyzed by dendrimer-encapsulated Pd nanoparticles in very good yield, in aqueous solution at 23 °C, and using only 0.100 atom % of Pd as catalyst.
- Garcia-Martinez, Joaquin C.,Lezutekong, Raphael,Crooks, Richard M.
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- Ir-Catalyzed Ligand-Free Directed C-H Borylation of Arenes and Pharmaceuticals: Detailed Mechanistic Understanding
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An efficient method for Ir-catalyzed ligand free ortho borylation of arenes (such as, 2-phenoxypyridines, 2-anilinopyridines, benzylamines, benzylpiperazines, benzylmorpholines, benzylpyrrolidine, benzylpiperidines, benzylazepanes, α-amino acid derivatives, aminophenylethane derivatives, and other important scaffolds) and pharmaceuticals has been developed. The reaction underwent via an interesting mechanistic pathway, as revealed by the detailed mechanistic investigations by using kinetic isotope studies and DFT calculations. The catalytic cycle is found to involve the intermediacy of an Ir-boryl complex where the substrate C-H activation is the turnover determining step, intriguingly without any appreciable primary KIE. The method displays a broad range of substrate scope and functional group tolerance. Numerous late-stage borylation of various important molecules and drugs were achieved using this developed strategy. The borylated compounds were further converted into more valuable functionalities. Moreover, utilizing the benefit of the B-N intramolecular interaction of the mono borylated compounds, an operationally simple method has been developed for the selective diborylation of 2-phenoxypyridines and numerous functionalized arenes. Furthermore, the synthetic utility has been showcased with the removal of the pyridyl directing group from the borylated product to achieve ortho borylated phenol along with the ipso-borylation for the preparation of 1,2-diborylated benzene.
- Mahamudul Hassan, Mirja Md,Mondal, Biplab,Singh, Sukriti,Haldar, Chabush,Chaturvedi, Jagriti,Bisht, Ranjana,Sunoj, Raghavan B.,Chattopadhyay, Buddhadeb
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supporting information
p. 4360 - 4375
(2022/03/16)
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- A mild and practical method for deprotection of aryl methyl/benzyl/allyl ethers with HPPh2andtBuOK
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A general method for the demethylation, debenzylation, and deallylation of aryl ethers using HPPh2andtBuOK is reported. The reaction features mild and metal-free reaction conditions, broad substrate scope, good functional group compatibility, and high chemical selectivity towards aryl ethers over aliphatic structures. Notably, this approach is competent to selectively deprotect the allyl or benzyl group, making it a general and practical method in organic synthesis.
- Pan, Wenjing,Li, Chenchen,Zhu, Haoyin,Li, Fangfang,Li, Tao,Zhao, Wanxiang
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p. 7633 - 7640
(2021/09/22)
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- Conversion method of dibenzo[c,e][1,2]oxathiane-6-oxide compound
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The invention relates to the technical field of organic chemistry, in particular to a conversion method of a dibenzo[c,e][1,2]xathiane-6-oxide compound. According to the specific scheme, the dibenzo[c,e][1,2]oxathiane-6-oxide compound is taken as a raw material, heated in a polar or deuterated solution under an alkaline condition, or in the presence of a metal reagent the dibenzo[c,e][1,2]oxathiane-6-oxide compound is desulfurized, or widely used in the field of organic chemistry and pharmaceutical chemistry. The conversion method has the advantages of mild reaction conditions, high yield, good reaction universality, simple operation and the like.
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- Preparation method of 2,2'-dihydroxybiphenyl
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The invention relates to a preparation method of 2,2'-dihydroxybiphenyl. Through the preparation method, the problems of cumbersome operation, high production cost, low yield and pollution to the environment of an existing method can be solved effectively
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Paragraph 0012-0018
(2019/10/01)
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- Dimerization of Aromatic Compounds Using Palladium-Carbon-Catalyzed Suzuki-Miyaura Cross-Coupling by One-Pot Synthesis
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The aromatic dimers play a significant role in many aspects. Herein, we report a simple palladium-carbon catalyst that is highly effective for the dimerization of brominated aromatic compounds under mild conditions using abundant brominated aromatic compounds, bis(pinacolate)diboron and potassium acetate by a 'one-pot' method. This process, which we believe proceeds via a Suzuki-Miyaura cross-coupling reaction mechanism, allows access to a variety of aromatic compounds under mild reaction conditions and has a good functional group tolerance with moderate to high yields.
- Du, Fangyu,Zhou, Qifan,Liu, Dongdong,Fang, Ting,Shi, Yajie,Du, Yang,Chen, Guoliang
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supporting information
p. 779 - 784
(2018/02/09)
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- Rhodium-Catalyzed 2-Arylphenol-Derived Six-Membered Silacyclization: Straightforward Access toward Dibenzooxasilines and Silicon-Containing Planar Chiral Metallocenes
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The C/Si switch strategy has been regarded as a useful and efficient strategy for the discovery of drugs and materials. Thus, development of a methodology to access diverse silacycles is of great significance and in great demand. Among these, C-H bond silylation provides a powerful and straightforward synthetic method to form diverse silacycles in an atom- and step-economical fashion. However, C-H bond silylation has not been used to access any six-membered silicon-bridged π-conjugated scaffolds and enantioselective six-membered C-H silylation has never been presented. Herein, we successfully accessed diverse six-membered π-conjugated dibenzooxasilines via C-H bond silylation and investigated their photophysical properties. Furthermore, we realized enantioselective six-membered C-H siylation to directly afford planar chiral metallocene oxasilolanes with high ee (up to 95% ee). We also demonstrated the synthetic usefulness of dibenzooxasilines and planar chiral metallocene-fused benzooxasilolines as valuable synthetic intermediates via diverse additional transformations. Moreover, six-membered silicon-bridged ladder π-conjugated systems were designed and rapidly constructed by using our methods. The isomerization and silicon effects on molecular geometries and photophysical properties were also evaluated in detail.
- Zhao, Wen-Tao,Lu, Zhuo-Qun,Zheng, Hanliang,Xue, Xiao-Song,Zhao, Dongbing
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p. 7997 - 8005
(2018/08/01)
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- Au-Pd bimetallic nanoparticles supported on a high nitrogen-rich ordered mesoporous carbon as an efficient catalyst for room temperature Ullmann coupling of aryl chlorides in aqueous media
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An ionic liquid derived highly nitrogen-rich mesoporous carbon supported Au-Pd alloy was found to be an efficient and recyclable catalyst for the Ullmann coupling reaction of various aryl chlorides at room temperature in aqueous media.
- Karimi, Babak,Barzegar, Hossein,Vali, Hojatollah
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p. 7155 - 7158
(2018/07/05)
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- Ionic composite of palladium(II)/iron bis(dicarbollide) for catalytic oxidative carbonylation in the formation of diphenyl carbonate
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The carborane-based sandwich iron complex, [n-Bu4N]{Fe(3,3′)-[1,2-(PPh2)2-1,2-C2B9H9]2}, was synthesized in 53.1% yield. A catalyst composite of PdAc2/[n-Bu4N]{Fe(3,3′)-[1,2-(PPh2)2-1,2-C2B9H9]2} was found to be highly active for the oxidative carbonylation of phenol, with the formation of diphenyl carbonate (DPC). A DPC yield of 46% and a turnover number (TON) of 511 were achieved in 4 h using the composite at 110 °C. For comparison, the reaction was also investigated using catalyst composites of PdAc2/Mn(acac)3, PdAc2/Fe(acac)3, PdAc2/Co(acac)3 and PdAc2/Ce(acac)3 (acac = acetylacetone) under the same conditions of temperature and pressure. The DPC yield was determined by gas chromatography with flame ionization detector (GC-FID). All new products were characterized by elemental analysis, and by 1H, 13C, 11B and 31P NMR and FT-IR spectroscopy.
- Biying, Algin Oh,Yuanting, Karen Tang,Hosmane, Narayan S.,Zhu, Yinghuai
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supporting information
p. 195 - 200
(2017/09/30)
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- Effects of water and alcohols on the polymerization of furan during its acid-catalyzed conversion into benzofuran
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Furan, an important product from catalytic pyrolysis of biomass, has the potential to be further converted into value-added chemicals or biofuels. This study investigated the conversion of furan into benzofuran over a Br?nsted acid catalyst (Amberlyst 70) at 140-190°C in various solvents. With water as the solvent, furan could barely make its way to benzofuran as its polymerization dominated. With methanol as the solvent, the polymerization of furan was suppressed and benzofuran formation was enhanced substantially. This is because in methanol, the reactive intermediates (i.e., aldehydes) were stabilized and their involvement in polymerization reactions was suppressed. Other alcohols showed similar effects on suppressing polymerization. In dimethyl sulfoxide (DMSO), the polymerization of furan was also effectively suppressed. However, furan was not converted to benzofuran but to levulinic acid via a distinct reaction route.
- Hu, Xun,Jiang, Shengjuan,Kadarwati, Sri,Dong, Dehua,Li, Chun-Zhu
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p. 40489 - 40501
(2016/05/24)
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- Synthesis of 2,2′-biphenols through direct C(sp2)-H hydroxylation of [1,1′-biphenyl]-2-ols
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A novel synthesis of diversely substituted 2,2′-biphenols through Pd(ii)-catalyzed, tBuOOH-oxidized, and hydroxyl-directed C(sp2)-H hydroxylation of [1,1′-biphenyl]-2-ols has been developed. Notably, this finding is distinct from previous reports in which [1,1′-biphenyl]-2-ols underwent an intramolecular C-H activation and C-O bond formation to afford dibenzofurans under the promotion of Pd(ii) but in the absence of tBuOOH.
- Duan, Shitao,Xu, Yuanshuang,Zhang, Xinying,Fan, Xuesen
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p. 10529 - 10532
(2016/09/02)
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- 3-Hydroxypyrimidine-2,4-diones as Selective Active Site Inhibitors of HIV Reverse Transcriptase-Associated RNase H: Design, Synthesis, and Biochemical Evaluations
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Human immunodeficiency virus (HIV) reverse transcriptase (RT) associated ribonuclease H (RNase H) remains an unvalidated antiviral target. A major challenge of specifically targeting HIV RNase H arises from the general lack of selectivity over RT polymerase (pol) and integrase (IN) strand transfer (ST) inhibitions. We report herein the synthesis and biochemical evaluations of three novel 3-hydroxypyrimidine-2,4-dione (HPD) subtypes carefully designed to achieve selective RNase H inhibition. Biochemical studies showed the two subtypes with an N-1 methyl group (9 and 10) inhibited RNase H in low micromolar range without siginificantly inhibiting RT polymerase, whereas the N-1 unsubstituted subtype 11 inhibited RNase H in submicromolar range and RT polymerase in low micromolar range. Subtype 11 also exhibited substantially reduced inhibition in the HIV-1 INST assay and no significant cytotoxicity in the cell viability assay, suggesting that it may be amenable to further structure-activity relationship (SAR) for identifying RNase H inhibitors with antiviral activity.
- Tang, Jing,Liu, Feng,Nagy, Eva,Miller, Lena,Kirby, Karen A.,Wilson, Daniel J.,Wu, Bulan,Sarafianos, Stefan G.,Parniak, Michael A.,Wang, Zhengqiang
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p. 2648 - 2659
(2016/04/10)
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- Suzuki-Miyaura coupling of halophenols and phenol boronic acids: Systematic investigation of positional isomer effects and conclusions for the synthesis of phytoalexins from pyrinae
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The Suzuki-Miyaura couplings of o-, m-, and p-halophenols with o-, m-, and p-phenol boronic acids were investigated for all combinations under standardized conditions, using Pd/C as a heterogeneous catalyst and water as a solvent. In the case of iodophenols, conventional heating was used, while for bromophenols significantly better results could be obtained using microwave irradiation. This systematic study revealed that 2,4′-biphenol is particularly difficult to access, irrespective of the starting materials used, but that these difficulties can be overcome by using different additives. The conclusions drawn from this investigation allowed us to identify conditions for the protecting group-free or minimized total synthesis of biaryl-type phytoalexins. These compounds possess antibacterial activity and are produced by fruit trees as a response to microbial infection.
- Schmidt, Bernd,Riemer, Martin
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p. 4104 - 4118
(2014/05/20)
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- The acetal concept: Regioselective access to ortho,ortho-diphenols via dibenzo-1,3-dioxepines
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Traditional methods are ill-suited for the synthesis of ortho,ortho-biphenols, a structural motif found in many polyphenolic natural products, as well as synthetically useful compounds such as the chiral ligands binol, vapol, and vanol. The new route consists of a radical-based reaction of an acetal-tethered biphenyl ether substrate and subsequent hydrolytic cleavage of the dibenzo-1,3-dioxepine intermediate. Copyright
- Masters, Kye-Simeon,Br?se, Stefan
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p. 866 - 869
(2013/02/26)
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- Tethering for selective synthesis of 2,2′-biphenols: The acetal method
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2,2'-Biphenols are a large and diverse group of compounds with exceptional properties both as ligands and bioactive agents. Traditional methods for their synthesis by oxidative dimerisation are often problematic and lead to mixtures of ortho- and para-connected regioisomers. To compound these issues, an intermolecular dimerisation strategy is often inappropriate for the synthesis of heterodimers. The 'acetal method' provides a solution for these problems: stepwise tethering of two monomeric phenols enables heterodimer synthesis, enforces ortho regioselectivity and allows relatively facile and selective intramolecular reactions to take place. The resulting dibenzo[1,3]dioxepines have been analysed by quantum chemical calculations to obtain information about the activation barrier for ring flip between the enantiomers. Hydrolytic removal of the dioxepine acetal unit revealed the 2,2′-biphenol target. All tied up! Oxidative dimerisation of phenols often results in regioisomeric mixtures. One solution is the use of an acetal tether to impart ortho reactivity to the hydroxyarenes in a 1:1 ratio. Cyclisation forms dibenzo[1,3]dioxepine intermediates, then cleavage of the acetal linker delivers the unmasked biphenol (see scheme). Copyright
- Masters, Kye-Simeon,Bihlmeier, Angela,Klopper, Wim,Braese, Stefan
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p. 17827 - 17835
(2014/01/17)
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- 2,2′-biphenols via protecting group-free thermal or microwave-accelerated suzuki-miyaura coupling in water
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User-friendly protocols for the protecting group-free synthesis of 2,2′-biphenols via Suzuki-Miyaura coupling of o-halophenols and o-boronophenol are presented. The reactions proceed in water in the presence of simple additives such as K2CO3, KOH, KF, or TBAF and with commercially available Pd/C as precatalyst. Expensive or laboriously synthesized ligands or other additives are not required. In the case of bromophenols, efficient rate acceleration and short reaction times were accomplished by microwave irradiation.
- Schmidt, Bernd,Riemer, Martin,Karras, Manfred
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p. 8680 - 8688
(2013/09/24)
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- Facile synthesis of 2-arylphenols via palladium-catalyzed cross-coupling of aryl iodides with 6-diazo-2-cyclohexenones
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2-Arylphenols were conveniently synthesized from aryl iodides and 6-diazo-2-cyclohexenones, in moderate to excellent yields, via tandem Pd-catalyzed cross-coupling/aromatization. The preliminary results for the corresponding enantioselective version showe
- Yang, Ke,Zhang, Jun,Li, Yun,Cheng, Bin,Zhao, Liang,Zhai, Hongbin
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supporting information
p. 808 - 811
(2013/03/28)
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- Active-alkali metal-promoted reductive cleavage of chlorinated phenols
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We investigated the degradation of chlorinated phenols under reductive electron transfer reaction conditions. Although Li and Na metal proved useless, activated forms of these metals, either their soluble naphthalene radical anions or 1,2-diarylethane dianions, promoted the degradation of the starting materials to various extents. Additionally, efficient dehalogenation of the sodium salts of several mono-, di-, and tri-chlorophenols was obtained by their reduction with an excess of Na metal and a catalytic amount of naphthalene. Springer-Verlag 2012.
- Azzena, Ugo,Dettori, Giovanna,Pisano, Luisa,Pittalis, Mario,Mangano, Giuseppe,Petretto, Giacomo,Pintore, Giorgio
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experimental part
p. 601 - 605
(2012/07/28)
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- A mild and efficient method for the selective deprotection of silyl ethers using KF in the presence of tetraethylene glycol
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A mild and efficient protocol for the deprotection of silyl ethers using KF in tetraethylene glycol is reported. A wide range of alcoholic silyl ethers can be selectively cleaved in high yield in the presence of certain acid- and base-labile functional groups. Moreover, the phenolic silyl ethers were cleaved exclusively, without affecting the alcoholic silyl ethers, at room temperature. The Royal Society of Chemistry 2011.
- Yan, Hailong,Oh, Joong-Suk,Song, Choong Eui
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supporting information; experimental part
p. 8119 - 8121
(2012/01/04)
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- Synthesis of unsymmetrical o-biphenols and o-binaphthols via silicon-tethered Pd-catalyzed C-H arylation
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A mild, practical, and efficient method for the synthesis of unsymmetrical o-biphenols (including o-phenol-naphthols and o-binaphthols) has been developed. Unsymmetrical bis-aryloxy silanes, which were readily prepared in a semi-one-pot fashion, underwent the Pd-catalyzed intramolecular arylation followed by a routine TBAF desilylation step to furnish valuable unsymmetrical biphenols without necessity of isolation of seven-membered intermediates. The excellent functional group tolerance allows for synthesis of a variety of functionalized o-biphenols and o-binaphthols from easily available staring materials.
- Huang, Chunhui,Gevorgyan, Vladimir
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supporting information; experimental part
p. 2442 - 2445
(2010/07/10)
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- A new mild deprotecting method for O-benzylsulfonyl phenols and alcohols based on a DTBB-catalyzed lithiation
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A variety of alcohols and phenols, protected as the corresponding benzylsulfonic esters, were efficiently deprotected by selective reductive cleavage of the sulfur-oxygen bond, using an excess of lithium sand and a catalytic amount (5 mol%) of 4,4′-di-tert-butylbiphenyl (DTBB) as electron carrier, in THF at 0° C. This deprotection system was also efficient at -50 °C and was compatible with a wide range of other functional groups. Georg Thieme Verlag Stuttgart.
- Alonso, Francisco,Moglie, Yanina,Vitale, Cristian,Radivoy, Gabriel,Yus, Miguel
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p. 1971 - 1976
(2007/10/03)
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- Polymer electrolyte and process for producing the same
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A polymer electrolyte having, in a main chain, a structural unit represented by the following formula (1):-[Ar1-(SO2-N-(X+)-SO2-Ar2)m-SO2-N-(X+)-SO2-Ar1-O]- wherein Ar1 and Ar2 independently represent a divalent aromatic groups, m represents an integer of 0 to 3, and X+ represents an ion selected from hydrogen ion, an alkali metal ion and ammonium ion, which is excellent in proton conductivity, thermal resistance and strength. The polymer electrolyte is soluble in solvents and has excellent film forming property and recycling efficiency.
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- Ingold-Fischer "Persistent Radical Effect", Solvent Effect, and Metal Salt Oxidation of Carbon-Centered Radicals in the Synthesis of Mixed Peroxides from tert-Butyl Hydroperoxide
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Mixed peroxides are formed from tert-butyl hydroperoxide (TBH), tert-butyl peroxalate (TBP), and a variety of substrates (p-cresol, cyclohexene, styrene, α-methylstyrene, acrylonitrile, 2-methylcyclohexanone). Also, the oxidation of THF in the presence of acrylonitrile under the same conditions gives the mixed peroxide, generated by addition of the tetrahydrofuranyl radical to the double bond and the cross-coupling of the radical adduct with the tert-butylperoxyl radical. Similarly, benzoyl peroxide, TBH, and acrylonitrile give the mixed peroxide by oxidative arylation of the double bond. Paradoxically, TBH acts as effective inhibitor of the polymerization of vinyl monomers (acrylonitrile, styrene). An overall kinetic evaluation suggests that the conditions for the Ingold-Fischer "persistent radical effect", characterized by the simultaneous formation of a persistent and a transient radical, are fulfilled in all cases. The reactions are strongly affected by solvents, which form hydrogen bonds with TBH. Catalytic amounts of Cu(II) and Fe(III) salts influence the selectivity; the possibility that the mixed peroxides can also be generated by metal salt oxidation of carbon-centered radicals is discussed.
- Bravo, Anna,Bjorsvik, Hans-Rene,Fontana, Francesca,Liguori, Lucia,Minisci, Francesco
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p. 3849 - 3857
(2007/10/03)
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- Products of oxidative coupllng of phenol by horseradish peroxidase
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The oxidation and coupling of phenol by horseradish peroxidase in the presence of hydrogen peroxide yielded dimers trimers and higher molecular weight polymers which are mostly insoluble in water, so the products may be removed by centrifugation. However we discovered some products, such as dimers o,o'-biphenol, p,p'-biphenol, o,p'-biphenol, o-phenoxyphenol and p-phenoxyphenol, even though trimer 4-(4-phenoxyphenoxy)phenol were present in the aqueous phase at a very low concentration.
- Huixian,Taylor
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p. 1807 - 1817
(2007/10/03)
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- Formation and reactivity of 4-oxocyclohexa-2,5-dienylidene in the photolysis of 4-chlorophenol in aqueous solution at ambient temperature
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Nanosecond laser flash photolysis of an aqueous solution of 4-chlorophenol (λexc = 266 nm) produces, at pulse end, a transient with absorption maxima at 384, 370, and ca. 250 nm; upon addition of an H-donor such as 2-propanol, this spectrum is converted into that of the phenoxyl radical (λmax = 400 and 385 nm), and in presence of O2, it is converted into a transient with a broad absorption band peaking at 460 nm. This reaction behavior can be understood by assuming formation of the carbene, 4-oxocyclohexa-2,5-dienylidene, by elimination of HCl from excited 4-chlorophenol; the pulse end transient spectrum is assigned to this species, while the 460 nm band is assigned to benzoquinone O-oxide formed by addition of O2 to the carbene. Both phenoxyl radical and benzoquinone O-oxide are produced upon photolysis of 4-chlorophenol in neat alkanols as well. On the other hand, photolysis in n-hexane yields the triplet-triplet absorption, which is absent in polar solvents, and no indication of carbene formation. It can be concluded that the primary step of 4-chlorophenol photolysis in aqueous or alcoholic solution is heterolytic C-Cl bond scission; a quantum yield of 0.75 is determined for it in neutral or acid aqueous medium upon excitation at 266 nm. Photolysis of chlorophenolate produces the same transients, but with a markedly lower yield, and, in addition, eaq- and 4-chlorophenoxyl radicals. The proposed reaction mechanism provides a straightforward explanation of the results of photoproduct analysis, published by previous authors as well as contributed in the present work. In particular, formation of p-benzoquinone in the presence of O2 can be accounted for by intermediate formation of benzoquinone O-oxide. Production of 4-oxocyclohexa-2,5-dienylidene with high yield allows, for the first time, extensive investigation of the kinetics and mechanism of the reactions of a carbene in an aqueous environment. In the present work, we have studied (a) the addition reaction with O2 on the one hand and with halides on the other; (b) H abstraction reactions with alkanols; (c) reaction with 4-chlorophenol itself; and (d) reaction with H2O. The rate constants for reaction with O2 (3.5 × 109 M-1 s-1) and with I- (4.6 × 109 M-1 s-1) are close to the diffusion-controlled limit, whereas reactions with Br- (6.8 × 107 M-1 s-1) and Cl- (5 M-1 s-1) are slower. Rate constants for reaction with alkanols follow the pattern known for their reactions with radicals, with values ranging from 5 × 105 M-1 s-1 for tert-butyl alcohol to 1.9 × 107 M-1 s-1 for 2-butanol. All these observations are consistent with the triplet character of the carbene. A rate constant of 1.5 × 103 M-1 s-1 has been determined for reaction with H2O. This reaction is not accompanied by formation of OH radicals; it is concluded that it proceeds by insertion into the O-H bond rather than by O-H cleavage. The exceptional stability of the carbene in aqueous solution is thus mainly attributed to the high barrier for O-H rupture in the water molecule. Additionally, a specific carbene-H2O interaction is revealed by semiempirical calculations, which could contribute to energetic and orientational hindrance of the reaction. Further theoretical results support the interpretation of both spectroscopic and kinetic properties of the carbene.
- Grabner, Gottfried,Richard, Claire,K?hler, Gottfried
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p. 11470 - 11480
(2007/10/02)
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- MECHANISM OF THE REACTION OF OZONE WITH PHENOLS
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An investigation has been carried out into the composition of the products of the O3 reaction with PhOH in different solvents and into the kinetics of their build-up.A scheme is proposed for the reaction in which the first stage, which limits the rate of
- Konstantinova, M. L.,Razumovskii, S. D.,Zaikov, G. E.
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p. 271 - 275
(2007/10/02)
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- KINETICS AND MECHANISM OF THE REACTION OF OZONE WITH PHENOL IN ALKALINE MEDIA
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The kinetics of the reaction of O3 with PhOH in alkaline medium has been studied.The rate of oxidation of phenol by ozone is directly proportional to the concentrations of reactants and increases in a complex manner with increase in alkali content in aque
- Konstantinova, M. L.,Razumovskii, S. D.,Zaikov, G. E.
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p. 266 - 270
(2007/10/02)
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- Photochemical Oxygenation of Phenols by Pyrimidopteridine N-Oxide. Comparative Studies with Pyridazine and Isoalloxazine N-Oxides
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1,3,7,9-Tetrabutylpyrimidopteridine-2,4,6,8(1H,3H,7H,9H)-tetraone 5-oxide 1 transfers its N-oxide oxygen to phenols, i.e., phenol 5, p-cresol 6, L-tyrosine methyl ester 7, and p-hydroxyacetanilide (acetaminophen) 8, under photochemical conditions to give the corresponding dihydric phenols as major products without any accompanying photochemical intramolecular rearrangements of the N-oxide group taking place.This oxygenation is reasonably explained in terms of a photo-induced single electron transfer (SET) followed by oxygen-atom transfer (the SET mechanism) which occurs via the initial formation of a charge-transfer complex between compound 1 and the phenols employed.Comparative experiments with 3,10-dibutylisoalloxazine 5-oxide 3 and 3-methylpyridazine 2-oxide 4 well demonstrate the simplicity and the mechanistic characteristics of the photochemistry of compound 1.
- Sako, Magoichi,Ohara, Seiji,Hirota, Kosaku,Maki, Yoshifumi
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p. 3339 - 3344
(2007/10/02)
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- Polar Effects in the Decomposition of Bis(3-alkoxyaroyl) Peroxides. Synthesis of 8-Alkoxy-6H-dibenzopyran-6-ones
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The reaction of four substituted bis(3-alkoxybenzoyl) peroxides (1b-e) in neat phenols (2a-e) affords mainly 8-alkoxy-6H-dibenzopyran-6-ones (7) and ortho-benzoyloxylation products (4) of the phenol.Diaroyl peroxides without electron-releasing meta substituents afford essentially products 4.A mechanism involving monoelectronic oxidation of the phenol by the peroxide and biaryl coupling by preferential addition of the phenol radical cation to the ortho positions to the alkoxy group of the diaroyl peroxide is suggested.
- Auricchio, Sergio,Citterio, Attilio,Sebastiano, Roberto
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p. 6312 - 6316
(2007/10/02)
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- Activation of Reducing Agents. Sodium Hydride Containing Complex Reducing Agents. 31. NiCRAL's as Very Efficient Agents in Promoting Homo-Coupling of Aryl Halides
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Homo-coupling of aryl bromides and chlorides is efficiently performed with nickel-containing complex reducing agents NiCRA-bpy.In a number of cases the presence of alkali iodides improves the procedure.Yields are very high and a number of functional groups are resistant.The mechanistic and catalytic aspect of these reactions are discussed.
- Lourak, Mouhsine,Vanderesse, Regis,Fort, Yves,Caubere, Paul
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p. 4840 - 4844
(2007/10/02)
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- Activation of Reducing Agents. Sodium Hydride Containing Complex Reducing Agents. 32. NiCRAL's as Very Efficient Agents in Promoting Cross-Coupling of Aryl Halides
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Nickel-containing complex reducing agents NiCRA-bpy are shown to be the first nickel reagents able to efficiently perform cross-coupling of aryl halides.The presence of KI in the reaction medium generally improves the procedure.The mechanism and influence of the structures of the substrates are discused.
- Lourak, Mouhsine,Vanderesse, Regis,Fort, Yves,Caubere, Paul
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p. 4844 - 4848
(2007/10/02)
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- Oxidativ Coupling of Phenols. Part 6. A Study of the Role of Spin Density Factors on the Product Composition in the Oxidations of 3,5-Dimethylphenol and Phenol
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Oxidations of both 3,5-dimethyphenol and phenol with di-t-butyl peroxide at 140 degC gave as the major product the ortho-ortho-C-C coupled dimer, while oxidations with di-t-butyl peroxyoxalate at room temperature give much more of the ortho-para-C-C dimer.The results are not consistent either with the spin density distribution in the phenoxyl radical intermediates or with steric effects being the major factor which determines the product composition.It is proposed that the two phenoxyl radicals involved in coupling preferentially approach each other in a 'sandwich like' manner with the oxigens in a 1,3-relationship.
- Armstrong, David R.,Cameron, Colin,Nonhebel, Derek C.,Perkins, Peter G.
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p. 563 - 568
(2007/10/02)
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- Acid-Catalyzed Solvolysis of N-Sulfonyl- and N-Acyl-O-arylhydroxylamines. Phenoxenium Ions
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The acid-catalyzed reaction of N-acyl- and N-sulfonyl-O-arylhydroxylamines with benzene proceeded quite smoothly to give 2- and 4-hydroxybiphenyls.The results of product analysis, the orientation of the reaction, and the effects of substituents on the nitrogen atom and on the phenyl ring suggested a mechanism that involves a phenoxenium ion.The phenoxenium ion was trapped by benzene and other various nucleophiles.
- Endo, Yasuyuki,Shudo, Koichi,Okamoto, Toshihiko
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p. 6393 - 6397
(2007/10/02)
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- Hard Acid and Soft Nucleophile System. 2.Demethylation of Methyl Ethers of Alcohol and Phenol with an Aluminum Halide-Thiol System
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Aliphatic and aromatic methyl ethers have been easily cleaved on treatment with a hard acid, aluminum halide, and a soft nucleophile, EtSH, to give parent alcohols and phenols, respectively.With compounds possessing both aliphatic and aromatic methyl ether groups, simultaneous demethylation of both types of ethers occurred.The ethereal carbon-oxygen bond in compounds possessing both ether and ester groups was selectively cleaved under mild conditions by using dichloromethane as a cosolvent.Acetoxyl and N-acetyl groups were shown to be stable to this reagent system, except for easy hydrolysis of aromatic acetoxyl groups under conditions of workup after the reaction.
- Node, Manabu,Nishide, Kiyoharu,Fuji, Kaoru,Fujita, Eiichi
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p. 4275 - 4277
(2007/10/02)
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- Bisfluoran chromogenic compounds, preparation thereof, and pressure-sensitive copy systems employing same
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A substantially colorless bisfluoran chromogenic material having the structural formula STR1 wherein R1 and R2 each represent an alkyl group; X and Y each represent a hydrogen atom, a halogen atom, an hydroxyl group, an alkyl group, a nitro group, an amino group, an acyl group, or a carboalkoxy group; Z represents an oxy radical, a carbonyl group, an alkylene group, an alkylidene group, a sulfonyl group, or a thio radical; and n represents an integer from 0 to 1. The bisfluoran compounds are produced by reacting a 4-dialkylamino-2-hydroxy-2'-carboxybenzophenone with a diphenol wherein the diphenol is unsubstituted in at least one of the positions ortho to an hydroxyl group in each of the phenyl rings. The bisfluorans are used in pressure-sensitive copy systems comprising a support bearing microcapsules containing the bisfluorans, alone, or in combination with other color-forming materials.
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