- An efficient regioselective bromination protocol of activated coumarins using 2,4,4,6-tetrabromo-2,5-cyclohexadienone
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2,4,4,6-Tetrabromo-2,5-cyclohexadienone mediated bromination of a wide assortment of activated coumarins in acetonitrile has been accomplished with high regioselectivity and good to excellent yields. The selectivity and efficiency of bromination were found to be markedly dependent on electronic factors, particularly degree of electron withdrawal from electron-releasing 7-oxygenated substituents to the C-3 position of the α-pyrone moiety by vinylogous resonance and the presence of nucleophilic additives such as water and tetra-n-butylammonium bromide in the reaction medium. The sole by-product of the reaction was converted back to the reagent by oxidation with KBr-KBrO 3, which was recycled three times without significant loss of efficiency.
- Ganguly, Nemai C.,Nayek, Subhasis,Chandra, Sumanta
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- Copper(II) halides adsorbed on alumina as halogenating reagent for coumarins
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Coumarin and its derivatives have been halogenated selectively at C-3 position with copper(II) halides adsorbed on neutral alumina and halobenzene.
- Thapliyal,Singh,Khanna
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- A Copper Halide Promoted Regioselective Halogenation of Coumarins Using N-Halosuccinimide as Halide Source
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A safe, convenient, and regioselective synthesis of 3-halo coumarins using a metal halide (CuX 2 alone or with ZnX 2) promoted halogenation with N -halosuccinimide (NXS) as halide source is reported. The synthesis involved the steady in situ generation of highly reactive positive halogen (X +) by the coordination of copper or zinc with the N -halosuccinimide and subsequent electrophilic aromatic substitution of the electron-deficient coumarins. This procedure works well also for the halogenation of less electron-rich naphthoquinones, flavones, and methoxypsoralen in moderate to quantitative yields. This protocol features simple experimental conditions using readily available inexpensive reagents and provides a convenient approach to the chlorination or bromination of some useful heteroaromatic compounds.
- Su, Jinling,Zhang, Yan,Chen, Mingren,Li, Weiming,Qin, Xuewei,Xie, Yanping,Qin, Lixiao,Huang, Shihua,Zhang, Min
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supporting information
p. 630 - 634
(2019/03/08)
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- 3-arylcoumarin derivatives manifest anti-proliferative activity through Hsp90 inhibition
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The potential therapeutic benefits associated with Hsp90 modulation for the treatment of cancer and neurodegenerative diseases highlight the importance of identifying novel Hsp90 scaffolds. KU-398, a novobiocin analogue, and silybin were recently identified as new Hsp90 inhibitors. Consequently, a library of 3-arylcoumarin derivatives that incorporated the structural features of KU-398 and silybin was designed, synthesized, and evaluated against two breast cancer cell lines. Western blot analysis confirmed that the resulting 3-arylcoumarin hybrids target the Hsp90 protein folding machinery.
- Zhao, Huiping,Yan, Bin,Peterson, Laura B.,Blagg, Brian S. J.
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p. 327 - 331
(2012/05/20)
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- Dioxane dibromide mediated bromination of substituted coumarins under solvent-free conditions
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An efficient solvent-free protocol for regioselective bromination of substituted coumarins has been developed by using dioxane dibromide as the solid brominating agent. The efficacy of the solvent-free protocol has been established. The effects of the electronic nature and location of the substituents on the outcome of the reaction have been rationalized with a proposed mechanism.
- Chaudhuri, Subrata Kumar,Roy, Sanchita,Bhar, Sanjay
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supporting information; experimental part
p. 323 - 329
(2012/05/04)
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- Chemo-and regioselective bromination of aromatic compounds in the presence of γ-picolinium bromochromate (γ-PBC)/CH3CN
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Regioselective oxidative bromination of activated aromatic compounds has been studied using γ-Picolinium bromochromate in either CH3COOH or CH3CN is reported. The results obtained revealed excellent yields of monobromo compounds at para-position under thermal condition especially in methyl cyanide.
- Mahmoodi,Yazdanbakhsh,Hassanzadeh
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experimental part
p. 429 - 434
(2012/04/04)
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- Simple catalyst-free regio- and chemoselective monobromination of aromatics using NBS in polyethylene glycol
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NBS in polyethylene glycol has been efficiently utilized for regio- and chemoselective bromination of activated aromatics at room temperature to form the corresponding bromo products in excellent yields. Copyright Taylor & Francis Group, LLC.
- Venkateswarlu, Katta,Suneel, Kanaparthy,Das, Biswanath,Reddy, Kuravallapalli Nagabhushana,Reddy, Thummala Sreenivasulu
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experimental part
p. 215 - 219
(2009/04/07)
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- An efficient, rapid and regioselective nuclear bromination of aromatics and heteroaromatics with NBS using sulfonic-acid-functionalized silica as a heterogeneous recyclable catalyst
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A simple, efficient and rapid method has been developed for high-yielding regioselective nuclear monobromination of aromatic and heteroaromatic compounds using NBS in the presence of sulfonic-acid-functionalized silica at room temperature. The catalyst works under heterogeneous conditions and can be recycled.
- Das, Biswanath,Venkateswarlu, Katta,Krishnaiah, Maddeboina,Holla, Harish
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p. 8693 - 8697
(2007/10/03)
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- Mild regioselective monobromination of activated aromatics and heteroaromatics with N-bromosuccinimide in tetrabutylammonium bromide
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Highly regioselective nuclear bromination of activated aromatic and heteroaromatic compounds has been accomplished using N-bromosuccinimide in tetrabutylammonium bromide. Pre-dominant para-selective monobromination of activated aromatics such as phenols and anilines, rate acceleration of bromination for moderately activated and less reactive substrates on addition of acidic montmorillonite K-10 clay, with or without microwave assistance, are the notable features of this protocol.
- Ganguly, Nemai C.,De, Prithwiraj,Dutta, Sanjoy
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p. 1103 - 1108
(2007/10/03)
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- Microwave induced selective bromination of 1,4-quinones and coumarins
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Microwave irradiation accelerates the bromination of 1,4-quinones and coumarins with (i) bromide adsorbed on neutral alumina in 'dry media' and (ii) with iodine monobromide on acetic acid as compared to the reactions run at room temperature. Bromination takes place selectively at active quinonoid position in 1,4-quinones and at α,β-double bond in coumarins.
- Bansal, Vandana,Kanodia, Saraswati,Thapliyal, Prakash C.,Khanna, Rajinder N.
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p. 887 - 892
(2007/10/03)
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- Nucleophilic 1,2 addition of bromine to electron deficient double bonds by perbromide reagents
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Perbromide compounds prove to be excellent reagents for achieving nucleophilic 1,2 addition of bromine to the double bond of α,β-unsaturated compounds. This reaction proved to be highly selective in eudesmanolides with an electronegative substituent at C-
- Collado, Isidro G.,Galan, Rosario H.,Massanet, Guillermo M.,Alonso, Miguel S.
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p. 6433 - 6440
(2007/10/02)
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- Chemistry of Natural Products, Part 155; A Simple Synthesis of 4-(Herniarine-3-yl)-2-methyl-3-buten-2-ol
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A simple synthesis of 4-(herniarine-3-yl)-2-methyl-3-buten-2-ol from umbelliferone in relatively high yield is described. Key words: Umbelliferone, 3-Bromo-herniarine, Heck Reaction, 4-(Herniarine-3-yl)-2-methyl-3-buten-2-ol
- Reisch, Johannes,Zappel, Johannes
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p. 1801 - 1802
(2007/10/02)
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