- ELECTROCHEMICAL TRANSFORMATIONS OF 2'-HYDROXYCHALCONES INTO FLAVANOIDS
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2'-Hydroxychalcones are cyclized to flavanones, and flavone, or flavonol, by electrochemically generated tris-(4-bromophenyl)amine cation radical as homogeneous electron-transfer agent.
- Sanicanin, Zivko,Tabakovic, Ibro
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- Attrition-enhanced deracemization and absolute asymmetric synthesis of flavanones from prochiral precursors
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Seven racemic 5,7-dimethoxyflavanones afforded conglomerate crystals upon recrystallization from a solvent. Three methodologies were investigated to achieve asymmetric transformation based on dynamic crystallization of the chiral conglomerate system. The first was chiral symmetry breaking of racemic flavanones by attrition-enhanced deracemization. Continuous suspension of racemic flavanones in a small amount of propanol in the presence of a base (1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)) and glass beads promoted chiral symmetry breaking and converted the flavanones to crystals of (+)- or (-)-enantiomers with 78 to 99% ee. The second method involved cyclization of the intermediate aldol product to give optically active flavanone with 90% ee involving a reversible oxa-Michael addition reaction with attrition-enhanced deracemization. The third was a reaction starting from prochiral 2-hydroxy-4,6-dimethoxyacetophenone and 2-naphthaldehyde under basic conditions, which gave the corresponding flavanone in 89% ee.
- Kasashima, Yoshio,Mino, Takashi,Sakamoto, Masami,Shimizu, Waku,Uemura, Naohiro,Yoshida, Yasushi
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p. 5676 - 5681
(2020/10/13)
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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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- Synthesis of isoflavones containing naturally occurring substitution pattern by oxidative rearrangement of respective flavanones using thallium(III) p-tosylate
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Claisen condensation of substituted 2′-hydroxyacetophenones 1a-c with aromatic aldehydes affords respective substituted 2′-hydroxychalcones 2a-n which on base catalyzed cyclization in pyridine:methanol:water (1:1:1) give respective flavanones 3a-n. The oxidative rearrangement of flavanones with thallium(III) p-tosylate furnishes respective isoflavones 4a-n in overall 62-72% yields starting from 1. The present methodology has been successfully applied for the synthesis of naturally occurring isoflavones such as di-O-methyldaidzein 4a, cabruvin 4b, pseudobabtigenin methylether 4d, 5,7-dimethoxyisoflavone 4f, 5,7,4′-trimethoxyisoflavone 4g, derrustone 4i, 7,8,3′,4′- tetramethoxyisoflavone 41, purpuranin-A 4m and 7,8,3′,4′,5′- pentamethoxyisoflavone 4n and thus the first synthesis of 4n is reported.
- Singh, Om V.,Muthukrishnan,Sunderavadivelu
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p. 2575 - 2581
(2007/10/03)
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- A new and efficient Baeyer-Villiger rearrangement of flavanone derivatives by the methyltrioxorhenium/H2O2 catalytic system
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The catalytic Baeyer-Villiger rearrangement of flavanones is described by the use of the homogeneous methyltrioxorhenium (MTO)/H2O2 system. In these experimental conditions 3,4-dihydro-4-phenyl-1,5-benzodioxepin-2-ones and previously
- Bernini, Roberta,Mincione, Enrico,Cortese, Manuela,Aliotta, Giovanni,Oliva, Anna,Saladino, Raffaele
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p. 5401 - 5404
(2007/10/03)
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- Synthesis of a Typical Chalkone and a Flavanone of Wyethia glabra
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The constitution of a new chalkone as 2',4',6'-trihydroxy-4-methoxychalkone (1), isolated from Wyethia glabra has now been confirmed by its synthesis using 2'-hydroxy-4',6'-dibenzoyloxy-4-methoxychalkone (1a) as an essential intermediate.The structure of another compound as 5,3',4'-trihydroxy-7-methoxyflavanone (2) (eriodictyol-7-methyl ether) isolated from the same source, has also been confirmed by its synthesis using vanillin as the starting material.
- Babber, Sunanda,Chandra, S.,Aggarwal, Anil K.
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p. 797 - 798
(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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