- Divergent synthesis of flavones and flavanones from 2′-hydroxydihydrochalconesviapalladium(ii)-catalyzed oxidative cyclization
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Divergent and versatile synthetic routes to flavones and flavanonesviaefficient Pd(ii) catalysis are disclosed. These Pd(ii) catalyses expediently provide a variety of flavones and flavanones from 2′-hydroxydihydrochalcones as common intermediates, depending on oxidants and additives,viadiscriminate oxidative cyclization sequences involving dehydrogenation, respectively, in a highly atom-economic manner.
- Son, Seung Hwan,Cho, Yang Yil,Yoo, Hyung-Seok,Lee, Soo Jin,Kim, Young Min,Jang, Hyu Jeong,Kim, Dong Hwan,Shin, Jeong-Won,Kim, Nam-Jung
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p. 14000 - 14006
(2021/04/22)
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- Flavanone-based fluorophores with aggregation-induced emission enhancement characteristics for mitochondria-imaging and zebrafish-imaging
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Fluorophores with aggregation-induced emission enhancement (AIEE) characteristics applied in bioimaging have attracted more and more attention in recent years. In this work, a series of flavanone compounds with AIEE characteristics was developed and applied to fluorescence imaging of mitochondria and zebrafish. The compounds were readily prepared by the thermal dehydration of chalcone that was obtained by the reaction of o-hydroxyacetophenone and benzaldehyde. Two of these compounds showed significant AIEE characteristics by fluorescence performance experiments, including optical spectra, fluorescence spectra, fluorescence quantum yield (?F), fluorescence lifetime, and scanning electron microscopy (SEM). Compared with traditional organic fluorescent dyes, these compounds have high fluorescence emission and high fluorescence quantum yield in solid or aggregated state, which overcomes the shortcoming of aggregation-caused quenching (ACQ). More importantly, the two compounds exhibited low cytotoxicity and good cytocompatibility in A549 lung cells at the experimental concentration range and they specifically targeted mitochondria, which make it of great potential use in mitochondria labeling. In addition, they were embryonic membrane permeable and had different affinities for different tissues and organs of zebrafish, but mainly distributed in the digestive system, providing a basis for the application of such compounds in bioimaging. These AIEE compounds with superior properties could be of great potential use in mitochondria imaging and other in vivo studies.
- He, Feng,Li, Na,Liu, Liyan,Luo, Huiqing,Wang, Huaqiao,Yang, Depo
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- Synthesis of Flavanones via Palladium(II)-Catalyzed One-Pot β-Arylation of Chromanones with Arylboronic Acids
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A total of 47 flavanones were expediently synthesized via one-pot β-arylation of chromanones, a class of simple ketones possessing chemically unactivated β sites, with arylboronic acids via tandem palladium(II) catalysis. This reaction provides a novel route to various flavanones, including natural products such as naringenin trimethyl ether, in yields up to 92percent.
- Cho, Yang Yil,Jang, Hyu Jeong,Kim, Dong Hwan,Kim, Nam Yong,Kim, Nam-Jung,Kim, Young Min,Lee, Soo Jin,Lee, Yong Sup,Park, Boyoung Y.,Son, Seung Hwan,Yoo, Hyung-Seok
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p. 10012 - 10023
(2019/08/30)
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- Discovery of a Prenylated Flavonol Derivative as a Pin1 Inhibitor to Suppress Hepatocellular Carcinoma by Modulating MicroRNA Biogenesis
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Peptidyl-prolyl cis-trans isomerase Pin1 plays a crucial role in the development of human cancers. Recently, we have disclosed that Pin1 regulates the biogenesis of miRNA, which is aberrantly expressed in HCC and promotes HCC progression, indicating the therapeutic role of Pin1 in HCC therapy. Here, 7-(benzyloxy)-3,5-dihydroxy-2-(4-methoxyphenyl)-8-(3-methylbut-2-en-1-yl)-4H-chromen-4-one (AF-39) was identified as a novel Pin1 inhibitor. Biochemical tests indicate that AF-39 potently inhibits Pin1 activity with an IC50 values of 1.008 μm, and also displays high selectivity for Pin1 among peptidyl prolyl isomerases. Furthermore, AF-39 significantly suppresses cell proliferation of HCC cells in a dose- and time-dependent manner. Mechanistically, AF-39 regulates the subcellular distribution of XPO5 and increases miRNAs biogenesis in HCC cells. This work provides a promising lead compound for HCC treatment, highlighting the therapeutic potential of miRNA-based therapy against human cancer.
- Zheng, Yuanyuan,Pu, Wenchen,Li, Jiao,Shen, Xianyan,Zhou, Qiang,Fan, Xin,Yang, Sheng-Yong,Yu, Yamei,Chen, Qiang,Wang, Chun,Wu, Xin,Peng, Yong
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supporting information
p. 130 - 134
(2018/11/30)
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- Synthesis and evaluation of neuroprotective selenoflavanones
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The physicochemical properties and antioxidant activity of a molecule could be improved by the substitution of an oxygen atom in a molecule with selenium. We synthesized selenoflavanones and flavanones to evaluate their neuroprotective effects. The selenoflavanones showed improved physicochemical properties, suggestive of the ability to pass through the blood-brain barrier (BBB). They showed in vitro antioxidant effects against hydrogen peroxide, and did not result in severe cytotoxicity. Moreover, infarction volumes in a transient ischemia mouse model were significantly reduced by the selenoflavanone treatments.
- Choi, Yong-Sung,Kim, Dong-Myung,Kim, Yoon-Jung,Yang, Sai,Lee, Kyung-Tae,Ryu, Jong Hoon,Jeong, Jin-Hyun
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p. 29574 - 29582
(2015/12/23)
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- Rhodium/chiral diene-catalyzed asymmetric 1,4-addition of arylboronic acids to chromones: A highly enantioselective pathway for accessing chiral flavanones
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Chromone has been noted to be one of the most challenging substrates in the asymmetric 1,4-addi-tion of α,β-unsaturated carbonyl compounds. By employing the rhodium complex associated with a chiral diene ligand, (R,R)-Ph-bod, the 1,4-addition of a variety of aryl-boronic acids was realized to give high yields of the corresponding flavanones with excellent enantioselectivities (≥97% ee, 99% ee for most substrates). Ring-opening side products, which would lead to erosion of product enantioselectivity, were not observed under the stated reaction conditions.
- He, Qijie,Wang, Jun,So, Chau Ming,Hayashi, Tamio,Bian, Zhaoxiang
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supporting information
p. 540 - 543
(2015/05/05)
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- CuO nanoparticles as an efficient catalyst for the synthesis of flavanones
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CuO nanoparticle was found to be an efficient catalyst for the synthesis of flavanones derivatives from the reactions between 2-hydroxyacetophenones and aromatic aldehydes at room temperature. The protocol offers advantages in terms of higher yields, short reaction times, and mild reaction conditions, with reusability of the catalyst. The structures of the synthesized substituted flavanones were confirmed by their Melting point, FT-IR,1 HNMR,13 CNMR and mass spectral analysis.
- Ahmady, Amanollah Zarei,Keshavarz, Mosadegh,Kardani, Maryam,Mohtasham, Neda
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p. 1841 - 1846
(2016/01/25)
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- Mild and efficient one-pot synthesis of diverse flavanone derivatives via an organocatalyzed Mannich-type reaction
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A facile ethylenediamine diacetate (EDDA)-catalyzed one-pot synthesis of biologically interesting flavanone derivatives from 2-hydroxyacetophenones, aromatic aldehydes, and aniline via a Mannich-type reaction is described. This synthetic method provides a rapid access to biologically interesting flavanone derivatives. To demonstrate this method, several biologically interesting natural products bearing a flavanone moiety were synthesized as racemates.
- Vuppalapati, Srinivasu V. N.,Xia, Likai,Edayadulla, Naushad,Lee, Yong Rok
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p. 465 - 474
(2014/03/21)
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- Impact of mono- and disubstitution on the colorimetric dynamic covalent switching chalcone/flavanone scaffold
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The effect of aryl substitution on various aspects of the interconversion of ortho-hydroxychalcones and flavanones has been studied using multiple spectroscopic techniques. Derivatization of the core scaffold predictably alters the midpoint pH of this equilibration process suggesting its viability for application as a functional colorimetric molecular switch.
- Muller, Brian M.,Mai, Jesse,Yocum, Reid A.,Adler, Marc J.
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supporting information
p. 5108 - 5114
(2014/07/08)
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- Palladium-catalyzed asymmetric conjugate addition of arylboronic acids to heterocyclic acceptors
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Flava Flavanone: Asymmetric conjugate additions to chromones and 4-quinolones are reported utilizing a single catalyst system formed in situ from Pd(OCOCF3)2 and (S)-tBuPyOX. Notably, these reactions are performed in wet solvent under ambient atmosphere, and employ readily available arylboronic acids as the nucleophile, thus providing ready access to these asymmetric heterocycles (see scheme).
- Holder, Jeffrey C.,Marziale, Alexander N.,Gatti, Michele,Mao, Bin,Stoltz, Brian M.
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supporting information
p. 74 - 77
(2013/02/25)
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- Highly efficient and green synthesis of flavanones and tetrahydroquinolones
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Highly efficient and green catalytic conversion of 2′-hydroxy and 2′-amino chalcones to flavanones and tetrahydroquinolones is reported herein. 2′-Hydroxy and 2′-amino chalcones can be almost completely converted to flavanones and tetrahydroquinolones in just 2 min in the presence of piperidine and KOH under room temperature. Liquiritigenin is also efficiently synthesized under similar conditions.
- Zheng, Xuxu,Jiang, Heyan,Xie, Jingjing,Yin, Zhongyi,Zhang, Haidong
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p. 1023 - 1029
(2013/03/13)
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- An efficient and facile synthesis of flavanones catalyzed by N-methylimidazole
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The use of N-methylimidazole as an efficient catalyst for the cyclization of 2'-hydroxychalcones to the corresponding flavanones in DMSO was investigated. The scope of this process was studied and various flavanones were obtained exclusively in good yields. Copyright
- Wang, Peng,Yang, Jiabin,Cai, Jin,Sun, Chunlong,Li, Lushen,Ji, Min
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p. 917 - 920
(2013/08/23)
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- Ferrocenyl flavonoid-induced morphological modifications of endothelial cells and cytotoxicity against B16 murine melanoma cells
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With the aim of improving the cytotoxic and vascular disrupting activities of flavonoids, several classes of ferrocenyl-modified flavonoids were prepared and tested on cancer and endothelial cells. Three ten-member series of ferrocenyl flavonoids: chalcones ((E)-1-(R-2′-hydroxyphenyl)-3- ferrocenylprop-2-en-1-ones), aurones ((Z)-R-2-(ferrocenylidene)benzofuran-3- ones) and flavones (R-2-ferrocenyl-chromen-4-ones) were synthesized by recently reported methods. Three ferrocenyl flavonols (R-3-hydroxy-2-ferrocenyl-chromen- 4-ones) and four ferrocenyl flavanones (3-ferrocenylmethylidenyl-R-2- phenylchroman-4-ones) were also obtained. All compounds were evaluated for their cytotoxic effects on a cancer cell line (B16 murine melanoma) and for their morphological effects on endothelial cells (EAhy 926). Some interesting structure-activity relationships were disclosed: of all the compounds, the halogen-substituted aurones showed the best cytotoxic activity, with IC 50 values ranging between 12 and 18 μM. Ferrocenyl flavonols and ferrocenyl flavanones with substitution in the 3-position (-OH and C-Fc respectively) were not active against cancer or endothelial cells. Some of the ferrocenyl flavones caused the endothelial cells to adopt a round shape ("rounding up") at submicromolar concentrations, which can be predictive of vascular disrupting activity. The most morphologically active flavones showed only moderate cytotoxicity against cancer cells, indicating that they may primarily act as antivascular agents.
- Monserrat, Jean-Philippe,Tiwari, Keshri Nath,Quentin, Lionel,Pigeon, Pascal,Jaouen, Gérard,Vessières, Anne,Chabot, Guy G.,Hillard, Elizabeth A.
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- Synthetic approach to flavanones and flavones via ligand-free palladium(ii)-catalyzed conjugate addition of arylboronic acids to chromones
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The remarkable catalytic effects of Fe(OTf)3 in the context of the Pd(ii)-catalyzed conjugate addition of arylboronic acids to chromones were observed to yield a variety of flavanones under mild conditions. The addition of catalytic amounts of DDQ and KNO2 to the reactions exclusively yielded flavone analogs. The reaction scope for the transformation was fairly broad, affording good yields of a wide range of flavanones and flavones, which are privileged structures in many biologically active compounds.
- Kim, Donghee,Ham, Kyungrok,Hong, Sungwoo
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experimental part
p. 7305 - 7312
(2012/09/22)
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- Solution phase photocyclisation reaction of 2-hydroxychalcones to 4-flavanones
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The photochemical cyclisation of 2-hydroxychalcones leading to the synthesis of 4-flavanones in solution phase has been investigated. The formation of photoproducts has been explained on the basis of excited state intramolecular proton transfer (ESIPT) and the cyclisation efficiency of the chalcones has been found to depend upon the electron density on the phenolic oxygen as well as on the carbonyl group. This synthesis of flavanones by photoirradiation is an eco-friendly route with comparative yield to those of thermal methods. Although the molecular skeletons of these substrates is amenable to cis-trans isomerisations and cycloadditions but no photoproducts corresponding to these reactions have been realized.
- Kamboj, Ramesh C.,Berar, Surinder,Berar, Urmila,Gupta, Satish C.
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p. 879 - 885
(2012/04/04)
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- Synthesis of flavanones by use of anhydrous potassium carbonate as an inexpensive, safe, and efficient basic catalyst
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Anhydrous potassium carbonate has been utilized as an inexpensive, safe, and efficient basic catalyst for the synthesis of flavanones starting either from 2′-hydroxychalcones or from 2′-hydroxyacetophenones. In both the cases the favored reaction condition was either refluxing in a solvent with added catalyst or microwave irradiation on the catalyst.
- Mondal, Rina,Gupta, Arpita Das,Mallik, Asok K.
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experimental part
p. 5020 - 5024
(2011/10/19)
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- A new series of flavones, thioflavones, and flavanones as selective monoamine oxidase-B inhibitors
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A new series of synthetic flavones, thioflavones, and flavanones has been synthesized and evaluated as potential inhibitors of monoamine oxidase isoforms (MAO-A and -B). The most active series is the flavanone one with higher selective inhibitory activity against MAO-B. Some of these flavanones (mainly the most effective) have been separated and tested as single enantiomers. In order to investigate the MAOs recognition of the most active and selective compounds, a molecular modeling study has been performed using available Protein Data Bank (PDB) structures as receptor models for docking experiments.
- Chimenti, Franco,Fioravanti, Rossella,Bolasco, Adriana,Chimenti, Paola,Secci, Daniela,Rossi, Francesca,Yá?ez, Matilde,Orallo, Francisco,Ortuso, Francesco,Alcaro, Stefano,Cirilli, Roberto,Ferretti, Rosella,Sanna, M. Luisa
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experimental part
p. 1273 - 1279
(2010/04/24)
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- Catalytic enantioselective synthesis of flavanones and chromanones
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The enantioselective synthesis of flavanones and chromanones is described. Bifunctional thiourea catalysts promote an asymmetric oxo-conjugate addition to a β-ketoester alkylidene in high yields with excellent enantioselectivity (80-94% ee) for aryl and alkyl substrates. Decarboxylation of the β-ketoester proceeds smoothly in a one-pot procedure to afford the enantioenriched flavanones and chromanones. Copyright
- Biddle, Margaret M.,Lin, Michael,Scheidt, Karl A.
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p. 3830 - 3831
(2008/02/04)
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- Synthesis of oxygen heterocycles
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A generalised scheme for the synthesis of flavones, flavonones and chromones involving 3-acyl-γ-pyrone intermediates has been developed. Convenient synthesis of other oxygen heterocycles using similar procedure have been outlined.
- Ganguly,Mahata,Biswas
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p. 1347 - 1349
(2007/10/03)
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- Synthesis of flavanones using nanocrystalline MgO
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The design and development of a truly nano heterogeneous catalyst for the Claisen-Schmidt condensation (CSC) of benzaldehydes with 2-hydroxyacetophenone to yield substituted chalcones followed by isomerization to afford flavanones with excellent yields and selectivity is described.
- Choudary,Ranganath,Yadav, Jagajit,Lakshmi Kantam
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p. 1369 - 1371
(2007/10/03)
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- New synthesis of flavanones catalyzed by L-proline
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L-Proline is utilized as an efficient organocatalyst for the synthesis of substituted flavanones and chalcones in good yields. The efficiency of the catalyst was proved with a variety of substrates ranging from electron-deficient to electron-rich aryl aldehydes and 2-hydroxyacetophenones.
- Chandrasekhar,Vijeender,Venkatram Reddy
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p. 6991 - 6993
(2007/10/03)
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- Highly diastereoselective Michael reaction under solvent-free conditions using microwaves: Conjugate addition of flavanone to its chalcone precursor
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Microwave-assisted reaction of 2′-hydroxychalcones in the presence of DBU resulted in the formation of hitherto unknown dimers by conjugate addition of the intermediate cyclic ketone to the starting enone.
- Patonay, Tamás,Varma, Rajender S.,Vass, András,Lévai, Albert,Dudás, József
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p. 1403 - 1406
(2007/10/03)
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- ONE-STEP CONVERSION OF FLAVANONES INTO ISOFLAVANONES: A NEW FACILE BIOMIMETIC SYNTHESIS OF ISOFLAVONES
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One-step chemical conversion of flavanones into isoflavones by use of thallium trinitrate (TTN) is reported, and the mechanism of a 2,3-aryl migration in this reaction is discussed in relation to in vivo rearrangement process of flavanone precursors in the isoflavone biosynthesis.
- Kinoshita, Takeshi,Ichinose, Koji,Sankawa, Ushio
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p. 7355 - 7356
(2007/10/02)
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- Kinetics and Mechanism of the Cyclisation of 2',6'-Dihydroxychalcone and Derivates
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pH-Rate profiles are reported for the cyclisation in water to 5-hydroxyflavanones of 2',6'-dihydroxychalcone (1) and its 4-methoxy (2), 3,4-dimethoxy (3), 3,4,5-trimethoxy (4), 2,4,6-trimethoxy (5), 4-chloro (6), and 3,4,4'-trimethoxy (8) derivates.As for the previously studied 2',6'-dihydroxy-4,4'-dimethoxychalcone (7), rate coefficients are established for acid-catalysed cyclisation of neutral chalcone, for unimolecular cyclisation of the neutral, monoanionic, and dianionic chalcone, and for the base-catalysed reverse ring-opening reaction.Cyclisation of the monoanion of 2',6'-dihydroxychalcone is almost 40 times faster than that of the monoanion of the 2'-hydroxy-6'-methoxyhalcone (10) and is also estimated to be about ten times faster than that of the reactive monoanion of 2',4'-dihydroxychalcone.These are the first calculations of the enhancement of rate of monoanion cyclisation by the 6'-OH group.The effect is only small, and is suggested to arise largely from stabilisation of the transition state for ketonisation by hydrogen bonding to enolate oxygen.Other reactivity differences amongst the chalcone monoanions are also discussed.Enthalpy and entropy of activation data are reported for monoanion cyclisation of (1), (2), and (4)-(6).Rate coefficients for the cyclisation of the chalcone monoanions are almost identical for (1)-(4) and (6) in water but not in deuterium oxide: kinetic hydrogen isotope effect (KIE) values are 3.4 (1), 5.7 (2), 4.9 (3), 3.0 (4), 7.5 (5), 2.9 (6), and 5.0 (8).For chalcones (2) and (7), the KIE values of which are both 5.7, the amounts of H versus D incorporation at the flavanone 3-carbon for monoanion cyclisation in H2O/D2O mixtures were established by mass spectroscopy.This gave product (or 'discrimination') isotope effect (PIE) values of 7.9 for (2) and 3.8 for (7), suggesting for (2) but not (7) an inverse effect contribution to KIE from sources other than rate-limiting proton transfer to carbon.Monoanion cyclisation of (1) in D2O was established by 1H n.m.r. as involving almost equal amounts of anti and syn addition of 2'-O- to the enone double bond.Reactivity differences amongst the chalcones for reactions other than monoanion cyclisation are only briefly considered.
- Miles, Christopher O.,Main, Lyndsay
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p. 1623 - 1632
(2007/10/02)
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- PHOTO-OXIDATIVE CYCLISATION OF 2'-HYDROXYCHALCONES LEADING TO FLAVONES INDUCED BY HETEROCYCLE N-OXIDES: HIGH EFFICIENCY OF PYRIMIDOPTERIDINE N-OXIDE FOR THE PHOTOCHEMICAL DEHYDROGENATION
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Irradiation of 2'-hydroxychalcones (3) with UV-visible light in the presence of heterocycle N-oxides such as pyrimidopteridine N-oxide (I) results in the formation of the corresponding flavones (4) and flavanones (5).The photooxidative cyclisation of (3) induced by (1) to give (4) most efficiently occurred among the heterocycle N-oxides examined and could be reasonably explained by considering an initial single-electron oxidation of (3) by (1) under the photochemical conditions and subsequent intramolecular cyclisation.
- Maki, Yoshifumi,Shimada, Kaoru,Sako, Magoichi,Hirota, Kosaku
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p. 3187 - 3194
(2007/10/02)
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- Synthesis of 2-Benzylidene-3(2H)-benzofuran-3-ones (Aurones) by Oxidation of 2'-Hydroxychalcones with Mercury(II) Acetate
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The reaction of 2'-hydroxychalcones with mercury(II) acetate in acetic acid gives predominantly 2-benzylidene-3(2H)-benzofuran-3-ones (aurones) in 28-62 percent yield accompanied by flavonones in 5-21 percent yield.
- Sekizaki, Haruo
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p. 1407 - 1409
(2007/10/02)
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- Cyclodehydrogenation of 2'-Hydroxychalcones with DDQ: A Simple Route for Flavones and Aurones
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The oxidation of 2'-hydroxychalcones with 2,3-dichloro-5,6-dicyano-p-benzoquinone provides a useful synthetic route for flavones and aurones.
- Imafuku, Kimiaki,Honda, Masaaki,McOmie, J. F. W.
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p. 199 - 201
(2007/10/02)
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- PHOTOOXYGENATION REACTIONS OF 4-FLAVANOLS AND BENZYLIC-TYPE ALCOHOLS.
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On irradiation in benzene under oxygen atmosphere cis- and trans-4-flavanols gave flavanones with significant structural effects on the yield: A high cis/trans selectivity and enhancement effect by electron-donating substituents. A series of benzylic-type alcohols showed similar substituent effects. The structure-reactivity relationships were explained in terms of the stereoelectronic requirements for favorable overlapping of intermediates. In order to infer the active oxidant species, the photoreactions were compared with the oxidations by singlet oxygen and superoxide ion. The involvement of superoxide ion or its related species such as electron transfer complex R** plus **. . . . O//2** minus **. was suggested. The effects of additives and solvents were also investigated.
- Suzuki,Yamazaki,Takabe,Morioka,Mizuno,Matsushima
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p. 1870 - 1875
(2007/10/02)
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- Reaction of 2'-Hydroxychalcones with Methylene Iodide: A Novel Formation of 3-Aryl-2,5-dihydro-5-oxo-1-benzoxepins
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2'-Hydroxychalcones (1a-c) bearing a methoxy group at 4'-position react with methylene iodide in the presence of K2CO3 and Me2CO for 38 hr to give besides the corresponding flavanones (2a-c), 3-aryl-2,5-dihydro-5-oxo-1-benzoxepins (3a-c).However, the 2'-hydroxychalcones (1d and 1e), having 4',6'-dimethoxy groups react sluggishly requiring 170 hr and also the product is a mixture of not only the corresponding flavanones (2d,e) and benzoxepinones (3d,e) as above but also of the biscompounds (4a,b) having intermolecular methylenedioxy group.The structures of benzoxepinones (3) have been established by their PMR, 13C-NMR and mass spectral data.Their formation has been rationalised via the formation of cyclopropane ring (5), followed by ring cleavage and H- shift.
- Jain, A. C.,Nayyar, Naresh K.,Sharma, B. N.
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p. 1211 - 1215
(2007/10/02)
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- The Kinetics and Mechanism of the Cyclisation of Some 2'-Hydroxychalcones to Flavanones in Basic Aqueous Solution
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Rate coefficients for the chalcone-flavanone equilibration reaction have been established for some 2'-hydroxychalcones over the pH range (ca. 8-11) in which their 2'-hydroxy-groups undergo ionisation.The chalcones studied were the parent 2'-hydroxychalcone (I) and its following derivatives: 4'-OMe (II), 6'-OMe (III), 4'-OH (IV), 4',6'-Me2 (V), and 5',6'-benzo (VI).Pseudo-first-order rate coefficients (kobs) which, for the reversible reactions concerned, are the sum of the forward and reverse rate coefficients, were fitted to the kinetic form, kobs=kfA+k'fB+k''aOH- in which k and k' are the rate coefficients for the unimolecular cyclisation of neutral and of ionised chalcones respectively (fA and fB are the fractions of total chalcone present in the neutral and ionised forms at the pH concerned) and where k'' is the second-order rate coefficient for the reverse reaction of flavanone which involves hydroxide ion (activity aOH-).Data analysis gave rate coefficients and pKa values for all but chalcone (IV) which has a different kinetic form.A conjugate addition-elimination mechanism is proposed to account for the pH-rate profiles, one of which differs from that previously reported.Possible effects on rate coefficients of non-bonded interactions between 6'-substituents and carbonyl oxygen are briefly considered but the differences between chalcones with and without 6'-substituents are sufficiently small to deter prolonged discussion.There seems to be little serious hindrance of cyclisation for any of the 6'-substituted chalcone anions.
- Old, K. Barry,Main, Lyndsay
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p. 1309 - 1312
(2007/10/02)
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