- Fluorescence measurement of 3,5-dimethoxyphenol radical cation generated by pulse radiolysis in 1,2-dichloroethane
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Radical cation of 3,5-dimethoxyphenol in the excited state generated in 1,2-dichloroethane solution by the tandem irradiation of 28-MeV electron and 532-nm laser pulses emitted fluorescence around 600-750 nm with a quantum yield of 2.0 × 10-3.
- Ichinose, Nobuyuki,Tojo, Sachiko,Majima, Tetsuro
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Read Online
- Oxygen-Free Regioselective Biocatalytic Demethylation of Methyl-phenyl Ethers via Methyltransfer Employing Veratrol- O-demethylase
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The cleavage of aryl methyl ethers is a common reaction in chemistry requiring rather harsh conditions; consequently, it is prone to undesired reactions and lacks regioselectivity. Nevertheless, O-demethylation of aryl methyl ethers is a tool to valorize natural and pharmaceutical compounds by deprotecting reactive hydroxyl moieties. Various oxidative enzymes are known to catalyze this reaction at the expense of molecular oxygen, which may lead in the case of phenols/catechols to undesired side reactions (e.g., oxidation, polymerization). Here an oxygen-independent demethylation via methyl transfer is presented employing a cobalamin-dependent veratrol-O-demethylase (vdmB). The biocatalytic demethylation transforms a variety of aryl methyl ethers with two functional methoxy moieties either in 1,2-position or in 1,3-position. Biocatalytic reactions enabled, for instance, the regioselective monodemethylation of substituted 3,4-dimethoxy phenol as well as the monodemethylation of 1,3,5-trimethoxybenzene. The methyltransferase vdmB was also successfully applied for the regioselective demethylation of natural compounds such as papaverine and rac-yatein. The approach presented here represents an alternative to chemical and enzymatic demethylation concepts and allows performing regioselective demethylation in the absence of oxygen under mild conditions, representing a valuable extension of the synthetic repertoire to modify pharmaceuticals and diversify natural products.
- Grimm, Christopher,Lazzarotto, Mattia,Pompei, Simona,Schichler, Johanna,Richter, Nina,Farnberger, Judith E.,Fuchs, Michael,Kroutil, Wolfgang
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p. 10375 - 10380
(2020/10/02)
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- Low-Temperature Catalytic Hydrogenolysis of Guaiacol to Phenol over Al-Doped SBA-15 Supported Ni Catalysts
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Selective hydrogenolysis of aromatic carbon-oxygen (Caryl?O) bonds is a key strategy for the generation of aromatic chemicals from lignin. However, this process is usually operated at high temperatures and pressures over hydrogenation catalysts, resulting in a low selectivity for aromatics and an extra consumption of hydrogen. Here, a series of Al-doped SBA-15 mesoporous materials with different Si/Al molar ratios (Al-SBA-15) were prepared via a post-synthesis method using NaAlO2 as the Al source, and then Al-SBA-15 supported Ni catalysts (Ni/Al-SBA-15) were prepared by a deposition-precipitation method using urea as the hydrolysis reagent. The prepared supports and catalysts were extensively characterized using various techniques such as XRD, N2 adsorption/desorption, TEM, 27Al NMR, NH3-TPD, XPS, H2-TPR, and pyridine-FT-IR, and the catalysts were evaluated in the hydrogenolysis of the Caryl?O bond in guaiacol and lignin derived compounds under mild conditions. The effects of the Si/Al ratio in catalyst and reaction parameters on guaiacol conversion and product distribution were investigated in detail, associated with solvent effect. The incorporation of Al into the framework of SBA-15 can improve the Lewis acidity and the dispersion of the supported Ni particles and yet modulate the metal-support interactions, which are propitious to the hydrogenolysis of the Caryl?O bond in guaiacol. The catalyst Ni/Al-SBA-15 with a Si/Al molar ratio of 10 shows the best performance with a guaiacol conversion of 87.4 % and a phenol selectivity of 76.9 % under the mild conditions conducted, because of its proper acidity, suitable metal-support interactions, and high dispersion of the active species. The present study would stimulate research and development in multi-functional catalysts for the generation of valuable chemicals from biomass.
- Wang, Qiuyue,Chen, Yufang,Yang, Guanheng,Deng, Ping,Lu, Xinqing,Ma, Rui,Fu, Yanghe,Zhu, Weidong
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p. 4930 - 4938
(2020/08/26)
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- Rongalite-promoted metal-free aerobic ipso-hydroxylation of arylboronic acids under sunlight: DFT mechanistic studies
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A novel rongalite-promoted metal-free aerobic ipso-hydroxylation of arylboronic acids has been developed. This method employs low-cost rongalite as a radical initiator and O2 as a green oxidizing agent for ipso-hydroxylation. This protocol is compatible with a wide variety of functional groups with good to excellent yields at room temperature. Furthermore, mechanistic insight into the role of superoxide radical anions in C-B cleavage has also been provided based on DFT studies.
- Golla, Sivaparwathi,Poshala, Soumya,Pawar, Ravinder,Kokatla, Hari Prasad
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supporting information
(2019/12/27)
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- Bimetallic photoredox catalysis: Visible light-promoted aerobic hydroxylation of arylboronic acids with a dirhodium(ii) catalyst
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We report the use of a rhodium(II) dimer in visible light photoredox catalysis for the aerobic oxidation of arylboronic acids to phenols under mild conditions. Spectroscopic and computational studies indicate that the catalyst Rh2(bpy)2(OAc)4 (1) undergoes metal-metal to ligand charge transfer upon visible light irradiation, which is responsible for catalytic activity. Further reactivity studies demonstrate that 1 is a general photoredox catalyst for diverse oxidation reactions.
- Campbell, Michael G.,Chuang, Gary Jing,Liu, Ming-Lun,Miura-Stempel, Emily,Tu, Jing-Wen,Yang, Hsiang-Ming
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p. 2040 - 2047
(2020/03/13)
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- Rhodium-terpyridine catalyzed redox-neutral depolymerization of lignin in water
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Simple rhodium terpyridine complexes were found to be suitable catalysts for the redox neutral cleavage of lignin in water. Apart from cleaving lignin model compounds into ketones and phenols, the catalytic system could also be applied to depolymerize dioxasolv lignin and lignocellulose, affording aromatic ketones as the major monomer products. The (hemi)cellulose components in the lignocellulose sample remain almost intact during lignin depolymerization, providing an example of a "lignin-first" process under mild conditions. Mechanistic studies suggest that the reaction proceeds via a rhodium catalyzed hydrogen autotransfer process.
- Liu, Yuxuan,Li, Changzhi,Miao, Wang,Tang, Weijun,Xue, Dong,Xiao, Jianliang,Zhang, Tao,Wang, Chao
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supporting information
p. 33 - 38
(2020/01/13)
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- SYNTHESIS OF MORIN AND MORIN DERIVATIVES
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The invention relates to a method for directly producing morin derivatives and high-purity morin of formula (I). The invention also relates to morin derivatives and high-purity morin that can be obtained using the claimed method.
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Paragraph 0031; 0033
(2020/11/24)
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- Visible light induced redox neutral fragmentation of 1,2-diol derivatives
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A homogeneous, redox-neutral photo fragmentation of diol derivatives was developed. Under photo/hydrogen atom transfer (HAT) dual catalysis, diol derivatives such as lignin model compounds and diol monoesters undergo selective β C(sp3)-O bond cleavage to afford ketones, phenols and acids effectively.
- Chen, Kang,Schwarz, Johanna,Karl, Tobias A.,Chatterjee, Anamitra,K?nig, Burkhard
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p. 13144 - 13147
(2019/11/11)
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- Mild Redox-Neutral Depolymerization of Lignin with a Binuclear Rh Complex in Water
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A mild redox-neutral lignin depolymerization system featuring a water-soluble binuclear Rh complex has been developed. The catalytic system could be successfully applied to the depolymerization of a lignin-like polymer, alkaline lignin, as well as raw lignocellulose samples to produce aromatic ketones, providing a homogeneous catalytic system for "lignin-first" biorefinery in water. Mechanistic studies on the model substrate suggest that the reaction proceeds via a metal-catalyzed dehydrogenation step to afford a carbonyl intermediate, followed by C-O bond cleavage to afford ketone and phenol products. Deuterium labeling study shows that the hydrogen used for cleavage of the C-O bond originates from the alcohol moiety in the substrate.
- Liu, Yuxuan,Li, Changzhi,Miao, Wang,Tang, Weijun,Xue, Dong,Li, Chaoqun,Zhang, Bo,Xiao, Jianliang,Wang, Aiqin,Zhang, Tao,Wang, Chao
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p. 4441 - 4447
(2019/05/14)
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- Cobalt Nanoparticles Embedded in N-Doped Porous Carbon Derived from Bimetallic Zeolitic Imidazolate Frameworks for One-Pot Selective Oxidative Depolymerization of Lignin
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Cobalt nanoparticles embedded in N-doped porous carbon (Co@CN) were prepared by the pyrolysis of bimetallic zeolitic imidazolate frameworks (BMZIFs) based on ZIF-8 and ZIF-67. The catalyst shows excellent catalytic efficiency in one-pot selective oxidative cleavage of different linkages like β-O-4, a-O-4 and β-1 in organosolv lignin and lignin model compounds in the presence of oxygen (ambient pressure) under mild conditions (383 K). Compared with traditional supported catalyst, the catalyst gives a highly hollow structure, which favored the adsorption of substrates and oxygen. The uniform cobalt nanoparticles surrounded by N-doped graphitic structures and the strong electron transfer from graphitic nitrogen to Co NPs make it hard to be oxidized prior to use and higher catalytic reactivity. Moreover, the catalyst can be easily recovered by magnetic force after the reaction, and reused after reduction for five times without an obvious change in yields.
- Sun, Kangkang,Chen, Shujie,Zhang, Jiawei,Lu, Guo-Ping,Cai, Chun
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p. 1264 - 1271
(2019/02/01)
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- Chemical Synthesis Enables Structural Reengineering of Aglaroxin C Leading to Inhibition Bias for Hepatitis C Viral Infection
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As a unique rocaglate (flavagline) natural product, aglaroxin C displays intriguing biological activity by inhibiting hepatitis C viral entry. To further elucidate structure-activity relationships and diversify the pyrimidinone scaffold, we report a concise synthesis of aglaroxin C utilizing a highly regioselective pyrimidinone condensation. We have prepared more than 40 aglaroxin C analogues utilizing various amidine condensation partners. Through biological evaluation of analogues, we have discovered two lead compounds, CMLD012043 and CMLD012044, which show preferential bias for the inhibition of hepatitis C viral entry vs translation inhibition. Overall, the study demonstrates the power of chemical synthesis to produce natural product variants with both target inhibition bias and improved therapeutic indexes.
- Zhang, Wenhan,Liu, Shufeng,Maiga, Rayelle I.,Pelletier, Jerry,Brown, Lauren E.,Wang, Tony T.,Porco, John A.
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p. 1312 - 1323
(2019/01/21)
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- Selective Catalytic Methylation of Phloroglucinol with Dimethyl Carbonate in the Presence of Heterogeneous Acids
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A facile process for the methylation of phloroglucinol using environmentally friendly dimethyl carbonate as methylating agent and solvent is described. Widely available and inexpensive solid acids have been used as catalysts to promote this transformation. H-Y zeolite proved particularly selective for monomethylation, hence it has been used for the convenient preparation of methoxyresorcinol (MR), with only limited co-production of dimethoxyphenol (DMP). Conversely, the use of tungstosilicic acid on silica easily afforded DMP in excellent isolated yield.
- Lui, Matthew Y.,Noè, Marco,Masters, Anthony F.,Maschmeyer, Thomas
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p. 6249 - 6255
(2018/12/11)
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- Method for catalyzing oxidative cracking of lignin by heterogeneous cobalt
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The invention discloses a method for catalyzing oxidative cracking of lignin by a heterogeneous cobalt. The method adopts a porous carbon-nitrogen-loaded cobalt nano-material as a catalyst, and oxidative cracking of beta-O-4, alpha-O-4 and beta-1 lignin template compounds and solvent type lignin is carried out under the action of the catalyst with methanol as a solvent and oxygen as an oxidant inorder to obtain phenol, methyl benzoate and other small molecule compounds. The heterogeneous cobalt catalyst adopted in the invention realizes a wide application range of a substrate, is suitable forthe oxidative cracking of the beta-O-4, alpha-O-4 and beta-1 lignin template compounds and solvent type lignin, realizes high yield of a product and no polymerization of the product, and can be simply recovered through magnetic force after the reaction ends.
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Paragraph 0024; 0025; 0026
(2018/11/26)
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- The selective hydrogenolysis of C-O bonds in lignin model compounds by Pd-Ni bimetallic nanoparticles in ionic liquids
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β-O-4 and α-O-4 linkages can be selectively cleaved by Pd-Ni bimetallic nanoparticles in ionic liquids using hydrogen gas as the hydrogen donor under ambient pressure and neutral conditions. No hydrogenation of the benzene ring takes place in the catalytic system. An obvious improvement in activity is found compared with single nickel and palladium catalysts based on the results of experiments and characterization. After the reaction, the catalytic system still remains in the reactor by simple extraction, which can be reused without further treatment.
- Sun, Kang-Kang,Lu, Guo-Ping,Zhang, Jia-Wei,Cai, Chun
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p. 11884 - 11889
(2017/09/18)
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- Copper-Catalyzed Hydroxylation of (Hetero)aryl Halides under Mild Conditions
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The combination of Cu(acac)2 and N,N′-bis(4-hydroxyl-2,6-dimethylphenyl)oxalamide (BHMPO) provides a powerful catalytic system for hydroxylation of (hetero)aryl halides. A wide range of (hetero)aryl chlorides bearing either electron-donating or -withdrawing groups proceeded well at 130 °C, delivering the corresponding phenols and hydroxylated heteroarenes in good to excellent yields. When more reactive (hetero)aryl bromides and iodides were employed, the hydroxylation reactions completed at relatively low temperatures (80 and 60 °C, respectively) at low catalytic loadings (0.5 mol % Cu).
- Xia, Shanghua,Gan, Lu,Wang, Kailiang,Li, Zheng,Ma, Dawei
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supporting information
p. 13493 - 13496
(2016/10/31)
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- NEW LIPOPHENOL COMPOUNDS AND USES THEREOF
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The present invention relates to a compound of formula (I) wherein: - i is 0 or 1; j is 0 or 1; k is 0 or 1; - R1 and R2 are in particular H, (C1-C12)alkyl, or a group of formula C(O)R; - R is a, linear or branched, alkyl radical, comprising at least 19 carbon atoms; - R3 is H and k=0 when j=1; or, when j=0, R3 is -C(O)R or -L-C(O)R; - L, U and L" are linkers; wherein, when j=0, at least one of the groups R1; R2 and R3 comprises a radical R.
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Page/Page column 39
(2015/11/10)
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- INTERMOLECULAR C-H SILYLATION OF UNACTIVATED ARENES
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Reaction mixtures for silvlating arene substrates and methods of using such reaction mixtures to silyiate the arene substrates are provided. Exemplary reaction mixtures include the arene substrate, a liganded metal catalyst, a hydrogen acceptor and an organic solvent. The reaction conditions allow for diverse substituents on the arene substrate.
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- Synthesis and evaluation of polyunsaturated fatty acid-phenol conjugates as anti-carbonyl-stress lipophenols
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Carbonyl and oxidative stress play a substantial role in various neurodegenerative diseases such as Alzheimer's Disease, Parkinsonism, and Age-related Macular Degeneration (AMD). In retinal pathologies, both mechanisms are involved in the transformation of all-trans-retinal (AtR, reactive aldehyde) into bis-retinoid A2E. Since an accumulation of AtR and A2E contributes to photoreceptor apoptosis, we designed and synthesized a series of O-alkylated resorcinol derivatives featuring enhanced anti-carbonyl-stress properties. Additionally, these phenolic structures are linked to a polyunsaturated fatty acid such as docosahexaenoic acid (C22:6 n-3; DHA) or to a lysophosphatidylcholine-DHA conjugate, in order to specifically increase their bioavailability, and thus, to target the retina. Selective syntheses of phloroglucinol-DHA, resveratrol-DHA, and phloroglucinol-DHA-PC (PC = phosphatidylcholine) conjugates using silyl protecting group strategies are presented, along with results of testing that demonstrate their ability to lower AtR toxicity in ARPE-19 cell lines. In order to use resorcinol derivatives to fight against the carbonyl-stress mechanism observed in retina pathologies, new lipophenol conjugates were synthesized with the aim of increasing bioavailability and reaching retina tissue. Strategies to link polyunsaturated fatty acids to polyphenol backbones are presented, along with the results of testing against retinal pigment epithelial cell lines. Copyright
- Crauste, Celine,Vigor, Claire,Brabet, Philippe,Picq, Madeleine,Lagarde, Michel,Hamel, Christian,Durand, Thierry,Vercauteren, Joseph
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p. 4548 - 4561
(2014/08/05)
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- Acceleration of the Dakin reaction by trifluoroacetic acid
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An acceleration of the Dakin reaction caused by addition of trifluoroacetic acid is described. The modified protocol converts aromatic aldehydes to the corresponding phenols within 4 hours at room temperature by means of hydrogen peroxide in acidic medium. This acceleration is attributed to the stability of hydrogen peroxide in an acidic medium. This modified protocol provides alternative and easy access to important phenolic precursors that have been used in the synthesis of various natural products.
- Natu, Arun D.,Burde, Ameya S.,Limaye, Rohan A.,Paradkar, Madhusudan V.
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p. 381 - 382
(2014/07/08)
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- Copper(ii)-catalyzed C-O coupling of aryl bromides with aliphatic diols: Synthesis of ethers, phenols, and benzo-fused cyclic ethers
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A highly efficient copper-catalyzed C-O cross-coupling reaction between aryl bromides and aliphatic diols has been developed employing a cheaper, more efficient, and easily removable copper(ii) catalyst. A broad range of aryl bromides were coupled with aliphatic diols of different lengths using 5 mol% CuCl2 and 3 equivalents of K2CO3 in the absence of any other ligands or solvents to afford the corresponding hydroxyalkyl aryl ethers in good to excellent yields. In this newly developed protocol, aliphatic diols have multilateral functions as coupling reactants, ligands, and solvents. The resulting hydroxyalkyl aryl ethers were further readily converted into the corresponding phenols, presenting a valuable alternative way to phenols from aryl bromides. Furthermore, it was demonstrated that they are useful intermediates for more advanced molecules such as benzofurans and benzo-fused cyclic ethers. This journal is
- Liu, Yajun,Park, Se Kyung,Xiao, Yan,Chae, Junghyun
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p. 4747 - 4753
(2014/06/24)
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- Rhodium-catalyzed intermolecular C-H silylation of arenes with high steric regiocontrol
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Regioselective C-H functionalization of arenes has widespread applications in synthetic chemistry. The regioselectivity of these reactions is often controlled by directing groups or steric hindrance ortho to a potential reaction site. Here, we report a catalytic intermolecular C-H silylation of unactivated arenes that manifests very high regioselectivity through steric effects of substituents meta to a potential site of reactivity. The silyl moiety can be further functionalized under mild conditions but is also inert toward many common organic transformations, rendering the silylarene products useful building blocks. The remote steric effect that we observe results from the steric properties of both the rhodium catalyst and the silane.
- Chen, Cheng,Hartwig, John F.
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p. 853 - 857
(2014/03/21)
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- Hydroxyphosphinylation reaction of 3-cyclopropylideneprop-2-en-1-ones via C-P σ-bond cleavage
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An unexpected hydroxyphosphinylation of 3-cyclopropylideneprop-2-en-1-ones with phosphines has been observed. This method provides a unique regio- and stereoselective synthesis of highly functionalized 1-dialkylphinyl-3-oxo-(1Z)- alkenyl cyclopropanols with important potentials. The reaction displays an unusual mechanistic feature - a highly selective cleavage of C-P σ bonds in phosphines.
- Miao, Maozhong,Cao, Jian,Huang, Xian,Wu, Luling
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p. 5999 - 6007
(2013/07/26)
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- Selective methylation of phloroglucinol in the presence of a glycoluril clip
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Methylation of phloroglucinol was performed using dimethyl sulfate as the methylating agent in the presence and absence of a glycoluril clip. The results showed that the yield of the di-methylated product decreased significantly in the presence of a glycoluril clip (host), due to the formation of a host-guest complex between the clip and phloroglucinol. Also, the reaction was conducted with different quantities (mol %) of the host.
- Rezaei-Seresht, Esmail,Maleki, Behrooz,Amiri-Moghaddam, Zeinab,Taghizadeh, Sara
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p. 3855 - 3857
(2013/07/25)
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- Mechanochemical degradation of lignin and wood by solvent-free grinding in a reactive medium
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A mechanochemical approach for the cleavage of β-O-4-linkages in lignin is reported. The method is transition metal- and solvent-free, requires only inexpensive reagents, and tolerates the presence of water and standard reagent impurities.
- Kleine, Tillmann,Buendia, Julien,Bolm, Carsten
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p. 160 - 166
(2013/02/23)
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- Iridium-catalyzed C-H activation/borylation/oxidation for the preparation of bis-protected phloroglucinol derivatives
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The preparation of bis-protected phloroglucinol derivatives from a range of protected resorcinol substrates is presented. Functionalization was achieved via a two-step, one-pot iridium-catalyzed C-H activation/borylation/oxidation protocol. Our system gave high conversions to the arylboronic esters and good yields of the desired phenols following subsequent oxidation. A range of common protecting group categories was studied including alkyl, silyl, ether and ester.
- Marshall, Laura J.,Cable, Karl M.,Botting, Nigel P.
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experimental part
p. 2690 - 2692
(2010/07/04)
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- Synthesis of dimethyl ether of marsupsin
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Total synthesis of the dimethyl ether of marsupsin, in seven steps starting from phloroglucinol, is described.
- Srikrishna,Mathews
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scheme or table
p. 383 - 385
(2009/12/24)
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- 2-(Diethylamino)ethanethiol, a new reagent for the odorless deprotection of aromatic methyl ethers
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A new reagent for the deprotection of aromatic methyl ethers, 2-(diethylamino)ethanethiol, is reported. This compound, commercially available as its HCl salt, affords the corresponding phenols in good to excellent yields on a wide variety of substrates. A clear advantage of this method over the use of more common thiols, such as ethanethiol, is the easy extraction of both the deprotecting reagent and the byproduct 2-(diethylamino)ethyl methyl sulfide into the aqueous phase by quenching with dilute acid, which allows an essentially odorless workup.
- Magano, Javier,Chen, Michael H.,Clark, Jerry D.,Nussbaumer, Thomas
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p. 7103 - 7105
(2007/10/03)
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- Sulfur-substituted α-alkyl phenethylamines as selective and reversible MAO-A inhibitors: Biological activities, CoMFA analysis, and active site modeling
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A series of phenethylamine derivatives with various ring substituents and with or without N-methyl and/or C-α methyl or ethyl groups was synthesized and assayed for their ability reversibly to inhibit monoamine oxidase A (MAO-A) and monoamine oxidase B (MAO-B). Several compounds showed potent and selective MAO-A inhibitory activity (IC50 in the submicromolar range) but none showed appreciable activity toward MAO-B. A three-dimensional quantitative structure-activity relationship study for MAO-A inhibition was performed on the series using comparative molecular field analysis (CoMFA). The resulting model gave a cross-validated q2 of 0.72 and showed that in this series of compounds steric properties of the substituents were more important than electrostatic effects. Molecular modeling based on the recently published crystal structure of inhibitor-bound MAO-A provided detailed evidence for specific interactions of the ligands with the enzyme, supported by previous references and consistent with results from the CoMFA. On the basis of these results, structural determinants for selectivity of substituted amphetamines for MAO-A are discussed.
- Gallardo-Godoy, Alejandra,Fierro, Angélica,McLean, Thomas H.,Castillo, Mariano,Cassels, Bruce K.,Reyes-Parada, Miguel,Nichols, David E.
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p. 2407 - 2419
(2007/10/03)
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- Atropo-enantioselective total synthesis of knipholone and related antiplasmodial phenylanthraquinones
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The "lactone concept" has been efficiently employed for the first atropo-enantioselective synthesis of knipholone and related natural phenylanthraquinones. Besides the regio- and stereoselective construction of the biaryl axis, another important step was the "synthetically late" introduction of the C-acetyl group, either by a Friedel-Crafts type acetylation or by an ortho-selective Fries rearrangement first tested on simplified model systems and subsequently applied to the highly atroposelective preparation of the natural products and of simplified analogs thereof for biotesting. The synthetic availability of these natural biaryls, their precursors, and their unnatural analogs permitted a broader investigation of the antiplasmodial activities of these interesting biaryls.
- Bringmann, Gerhard,Menche, Dirk,Kraus, Juergen,Muehlbacher, Joerg,Peters, Karl,Peters, Eva-Maria,Brun, Reto,Bezabih, Merhatibeb,Abegaz, Berhanu M.
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p. 5595 - 5610
(2007/10/03)
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- Iodothyronine Deiodinase Mimics. Deiodination of o,o'-Diiodophenols by Selenium and Tellurium Reagents
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To better understand, and in the extension mimic, the action of the three selenium-containing iodothyronine deiodinases, o,o'-diiodophenols were reacted under acidic conditions with sodium hydrogen telluride, benzenetellurol, sodium hydrogen selenide, or benzeneselenol and under basic conditions with the corresponding deprotonated reagents. Sodium hydrogen telluride was found to selectively remove one iodine from a variety of 4-substituted o,o'-diiodophenols, including a protected form of thyroxine (T4). Thus, it mimics the D1 variety of the iodothyronine deiodinases. Sodium telluride was a more reactive deiodinating agent toward o,o'-diiodophenols, often causing removal of both halogens. Benzenetellurol and sodium benzenetellurolate sometimes showed useful selectivity for monodeiodination. However, the products were often contaminated by small amounts of organotellurium compounds. Sodium hydrogen selenide, sodium selenide, benzeneselenol, and sodium benzeneselenolate were essentially unreactive toward o,o'-diiodophenols. To gain more insight into thyroxine inner-ring deiodination, substituted 2,6-diiodophenyl methyl ethers were treated with some of the chalcogen reagents. Reactivity and selectivity for monodeiodination varied considerably depending on the substituents attached to the aromatic nucleus. In general, it was possible to find reagents that could bring about the selective mono- or dideiodination of these substrates.
- Vasil'ev, Andrei A.,Engman, Lars
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p. 3911 - 3917
(2007/10/03)
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- Oligomeric flavanoids. Part 25. Cleavage of the acetal functionality in A-type proanthocyanidins
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The hepta-O-methyl ethers 3 and 4 of procyanidin A-1 1 and A-2 2 are subject to facile cleavage of the acetal functionality with sodium cyanoboranuide in trifluoroacetic acid at 0°C. This straight forward chemical method permits the unambiguous establishment of the absolute configuration of the DEF-flavanyl unit and the D-ring carbon and oxygen atoms that are involved in the double linkage of the A-class proanthocyanidins.
- Steynberg, Petrus J.,Cronje, Annemarie,Steynberg, Jan P.,Bezuidenhoudt, Barend C.B.,Brandt, E. Vincent,Ferreira, Daneel
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p. 2591 - 2598
(2007/10/03)
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- Benzopyranones, processes for their preparation and their use
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Described are 2H-1-benzopyran-2-ones (coumarin derivates) of general formula (I), STR1 wherein R1 is a hydroxyl group, a lower-alkoxy group, a cycloalkoxy group with 4 to 6 C-atoms or the alkyl- or arylsulphonyloxy group R6 --SO2 O--; R2 and R3, independently of each other, are hydrogen atoms, hydroxyl groups, lower-alkoxy groups or cycloalkoxy groups with 4 to 6 C-atoms; R4 is a hydrogen atom, a lower-alkyl group with 1 to 4 C-atoms or a phenyl group; Y is a nitrogen atom, a CH group or a COH group; R5 is a phenyl, naphtyl, pyridinyl or pyrimidinyl group which may optionally be substituted by one or two C1 -C5 alkyl groups, by one or two halogen atoms, by a halogen and C1 -C5 alkyl together, by perfluoroalkyl with 1 to 3 C-atoms, by C1 -C5 alkoxy, by hydroxy, by methylenedioxy or by nitro; R6 is a lower-alkyl group, a cycloalkyl group with 4 to 6 C-atoms or a phenyl group which may optionally be substituted by one or two C1 -C5 alkyl groups, by one or two halogen atoms, or by perfluoroalkyl with 1 to 3 C-atoms; and n=1 to 4; plus their addition compounds with physiologically tolerated acids. Also described are methods of preparing these compounds, novel intermediates in their preparation and methods of preparing such intermediates. The novel coumarin derivatives described possess a neuroprotective and psychopharmacological action. The invention also concerns pharmaceuticals containing these compounds.
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- Photogeneration of HF from Fluoromethoxybenzenes in Aqueous Solution
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Photolysis of fluoromethoxybenzenes in aqueous solution results in a clean substitution of fluoride by water, resulting in the generation of HF, the mechanism of which is believed proceed via aryl cations from loss of fluoride ion in the primary photochemical step.
- Zhang, Guangzhong,Wan, Peter
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- Use of the Hammett Correlation and ?+ for Calculation of One-Electron Redox Potentials of Antioxidants
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Spectral, acid-base, and redox properties of methoxyphenoxyl radicals were determined in aqueous solutions by pulse radiolysis.Except for 2,6-dimethoxyphenoxyl, with λmax 7 = 0.58 V vs NHE, whereas the effect of meta substitution was minimal for 3,5-dimethoxyphenol, E7 = 0.85 V, yet this was 0.12 V lower than the measured E7 of 0.97 V for unsubstituted phenol.The reduction potential E7 of methoxyphenoxyl radicals satisfies the Hammett correlation using Brown ?+ substituent constants, as do other monosubstituted phenoxyls if the additivity of ?+ values is assumed and the state of protonation of the substituents is taken into consideration.The derived ?+(CH3O)m value of -0.14, in contrast to reported positive values, indicates the contribution of the methoxy group, even in the meta position, to charge delocalization and resonant stabilization of the phenoxyl radical.The contribution of the ring structure to more negative ?+ values was observed, as expected.Use of the Hammett correlation is suggested for rapid estimation and accurate calculation of the redox potentials of polysubstituted phenolic antioxidants.
- Jovanovic, Slobodan V.,Tosic, Mihajilo,Simic, Michael G.
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p. 10824 - 10827
(2007/10/02)
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- Direct Lithiation of Alkoxyphenols: Metalation vs Demethylation. An Experimental and Theoretical (MNDO) Study
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The direct lithiation of simple alkoxyphenols has been studied both from a theoretical and an experimental viewpoint.Efficient lithiations were achieved by using a 2:1 tBuLi-tBuOLi mixture (LICLIOR) in THF at room temperature.In most cases alkoxy groups are responsible for the regioselectivity observed, although for the case of 2-methoxyphenol both the OMe and OLi groups actually act as ortho-directing groups during lithiation.Demethylation has been shown to be a common side reaction of lithiation of phenolic or nonphenolic alkoxy aromatics.MNDO calculations provide good support for all the experimental observations.Thus, lithiation and demethylation are shown to be competing pathways, the former being kinetically favored whereas the latter leads to the thermodynamically more stable compounds.Calculations also show that the so-called geminal demethylations are more favored processes than the alternative vicinal demethylations.Moreover, MNDO allows the measurement of the extent of agostic activation of the ortho hydrogens with respect to the OMe and OLi groups involved in lithiation.Finally, MNDO nicely predicts the important role of reaction temperature in successful direct lithiation of simple alkoxyphenols.
- Morey, Jeroni,Costa, Antoni,Deya, Pere M.,Suner, Guillem,Saa, Jose M.
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p. 3902 - 3909
(2007/10/02)
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- Bromophloroglucinols and their methyl ethers
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All 16 bromination products of phloroglucinol and its methyl ethers, as well as five bromoresorcinols and three of their dimethyl ethers, were synthesized and analyzed by nuclear magnetic resonance spectroscopy.Two or three equivalents of bromine convert phloroglucinol to di- and tribromophloroglucinol, 5-methoxyresorcinol to the tri- and 2,4-dibromo, 3,5-dimethoxyphenol to the tri- and 2,6-dibromo, and 1,3,5-trimethoxybenzene to the dibromo compound.With one equivalent of bromine, 3,5-dimethoxyphenol reacts preferentially at C-2 while 5-methoxyresorcinol gives both monobromo isomers.Partial debromination with sodium sulfite yields successively 2,4-dibromo- and 2-bromo-5-methoxyresorcinol from the tribromo compound but fails with brominated 3,5-dimethoxyphenol.In the resorcinol series, C-2 is invariably the least reactive position. 4,6-Dibromo-5-methoxyresorcinol and 2,4-dibromo-3,5-dimethoxyphenol are accessible by methylation of dibromophloroglucinol, obtained from 3,5-dibromo-2,4,6-trihydroxybenzoic acid by decarboxylation.In contrast to resorcinol and tribromoresorcinol, the partial bromination of pholoroglucinol and debromination of tribromopholoroglucinol are not selective.The 13Cnmr spectra of bromophloroglucinol methyl ethers show characteristic downfield shifts for methoxy groups orthogonal to the aromatic ring plane.
- Kiehlmann, E.,Lauener, R. W.
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p. 335 - 344
(2007/10/02)
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- Chemical Studies on the Constituents of the Thymelaeaceous Plants.III. Structure of a Novel Spiro Biflavonoid, Daphnodorin C, from Daphne odora THUNB.
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The structure of a novel spiro biflavonoid, daphnodorin C (3), previously isolated from the root and bark of Daphne odora THUNB., was established on the basis of chemical and spectral studies, and confirmed by an X-ray diffraction analysis. Keywords---Dap
- Baba, Kimye,Takeuchi, Kazuo,Doi, Mitsunobu,Kozawa, Mitsugi
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p. 1853 - 1859
(2007/10/02)
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- Process for preparing 3-phenoxy-1-azetidines and carboxamide derivatives
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An improved process is disclosed for preparing 3-phenoxyazetidines which utilizes a phase transfer catalyst to add the phenoxy group to azetidine blocked in the 1-position by a diphenylmethane group and utilizes a stabilizing tertiary amine base to prevent dimerization during hydrogenolysis to remove the blocking group. The crude product containing diphenylmethane may be used without purification to prepare 3-phenoxy-1-azetidinecarboxamides.
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- Boron Trichloride as a Selective Demethylating Agent for Hindered Ethers: a Synthesis of the Phytoalexins α- and β-Pyrufuran, a Synthesis of Tri-O-methylleprolomin and its Demethylation
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Boron trichloride has been found to be an efficient reagent for the selective cleavage of sterically hindered methoxy groups in methoxyarenes.The scope and utility of this reaction are explored with examples drawn from derivatives of benzene, naphtalene, 9,10-dihydrophenanthrene and dibenzofuran.The method is applied to the synthesis of the phytoalexins α- (56) and β-pyrofuran (58) (1,3,4-trimethoxydibenzofuran-2-ol and 1,2,4-trimethoxydibenzofuran-3-ol).A synthesis of tri-O-methylleprolomin (61), a derivative of the unusual lichen metabolite leprolomin (60), is described and its demethylation with boron trichloride is studied.
- Carvalho, Christopher F.,Russo, Albert V.,Sargent, Melvyn V.
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p. 777 - 792
(2007/10/02)
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- Boron Trichloride as a Selective Demethylating Agent for Hindered Ethers
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Boron trichloride has been found to be an efficient reagent for the selective cleavage of sterically hindered methoxy groups in methoxyarenes; the scope and utility of this reaction are explored.
- Carvalho, Christopher F.,Sargent, Melvyn V.
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p. 227 - 229
(2007/10/02)
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- Electro-organic Reactions. Part 18. The Competition between Cleavage at Aryl-Oxygen and at Tetrazol-5-yl-Oxygen Bonds in the Cathodic Reduction of Aryl Tetrazolyl Ethers
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5-Aryloxy-1-phenyltetrazoles are cleaved cathodically in a 2 F mol-1 process.Initial electron transfer is to the tetrazole ring and the compounds cleave predominantly at the tetrazolyl-oxygen bond.An exception is 5-(p-cyanophenoxy)-1-phenyltetrazole which undergoes 1 F mol-1 cleavage to 1-phenyltetrazolone and benzonitrile.Competitive electrolysis of pairs of the tetrazolyl ethers, differently substituted in the aryloxy-ring, allows an estimation of relative rates of cleavage.These rates are found to be roughly related to the pKa values of the corresponding phenols.
- Akbulut, Ural,Toppare, Levent,Utley, James H. P.
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p. 391 - 394
(2007/10/02)
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- SELECTIVE DEALKYLATIONS OF ARYL ALKYL ETHERS AND THIOETHERS BY SODIUM IN HMPA
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The reaction of sodium with bis- and tris(alkoxy)benzenes in HMPA gives selectively the products of monodealkylation.The reaction proceeds through a dianion which fragments into an alkyl and an aryloxy anion.The positional selectivity of this fragmentation is governed by the structure of both the alkyl and aryloxy groups.With bis- and tris(alkoxy)benzenes which for symmetry reasons can afford aryloxy anions having the same basicity, the dealkylation involves exlusively the less substituted alkyl group.On the contrary, in the asymmetric terms, the positional selectivity of the dealkylation process is governed by the basicity of the aryloxy anion.On the basis of these concepts several efficient and synthetically useful reactions have been developed.In most cases the selectivity obtained in the present reactions in different from that observed with other previously developed methods which use sodium methoxide or sodium alkenethiolates in HMPA.It is shown that the appropriate choice of the reagent allows selective dealkylation of the desired alkoxy group of a poly(alkoxy)benzene.The reaction of sodium with bis(alkylthio)benzenes in HMPA gives the bis(mercapto)benzenes.If the reduction is carried out with a solution of sodium in HMPA, the reaction gives instead the products of monodealkylation.This however is not selective.It is suggested that in the case of thioethers the dealkylation products originate from the fragmentation of the radical anions.
- Testaferri, L.,Tiecco, M.,Tingoli, M.,Chianelli, D.,Montanucci, M.
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p. 3687 - 3692
(2007/10/02)
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