- B regioselective and chemoselective biotransformation of 2′-hydroxychalcone derivatives by marine-derived fungi
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Eight fungal strains (Penicillium raistrickii CBMAI 931, Cladosporium sp. CBMAI 1237, Aspergillus sydowii CBMAI 935, Penicillium oxalicum CBMAI 1996, Penicillium citrinum CBMAI 1186, Mucor racemosus CBMAI 847, Westerdykella sp. CBMAI 1679, and Aspergillus sclerotiorum CBMAI 849) mediated the biotransformation of the 2′-hydroxychalcone 1a. The main products obtained were from hydrogenation, hydroxylation, and cyclization reactions. Penicillium raistrickii CBMAI 931 catalyzed the chemoselective reduction of 1a to produce 2′-hydroxydihydrochalcone 2a (72%) in 7 days of incubation in phosphate buffer (pH 7). Aspergillus sydowii CBMAI 935 promoted the hydroxylation of 1a to yield 2′,4-dihydroxy-dihydrochalcone 5a (c = 42%) in 7 days of incubation in phosphate buffer (pH 8). The reaction using P. citrinum CBMAI 1186 and M. racemosus CBMAI 847 presented main cyclization products in phosphate buffer (pH 8), but the reactions with these fungi did not present enantioselectivity. Marine-derived fungi were effective and versatile biocatalysts for biotransformation of the 2′-hydroxychalcones yielding different products according to the conditions and microorganism used.
- Nitschke, Marcia,Porto, André Luiz Meleiro,de Matos, Iara Lisboa
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- Stereoselective reduction of flavanones by marine-derived fungi
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Biotransformation is an alternative with great potential to modify the structures of natural and synthetic flavonoids. Therefore, the bioreduction of synthetic halogenated flavanones employing marine-derived fungi was described, aiming the synthesis of flavan-4-ols 3a-g with high enantiomeric excesses (ee) of both cis- and trans-diastereoisomers (up to >99% ee). Ten strains were screened for reduction of flavanone 2a in liquid medium and in phosphate buffer solution. The most selective strains Cladosporium sp. CBMAI 1237 and Acremonium sp. CBMAI1676 were employed for reduction of flavanones 2a-g. The fungus Cladosporium sp. CBMAI 1237 presented yields of 72–87% with 0–64% ee cis and 0–30% ee trans with diastereoisomeric ratio (dr) from 52:48 to 64:36 (cis:trans). Whereas Acremonium sp. CBMAI 1676 resulted in 31% yield with 77–99% ee of the cis and 95–99% ee of the trans-diastereoisomers 3a-g with a dr from 54:46 to 96:4 (cis:trans). To our knowledge, this is the first report of the brominated flavon-4-ols 3e and 3f. The use of fungi, with emphasis for these marine-derived strains, is an interesting approach for enantioselective reduction of halogenated flavanones. Therefore, this strategy can be explored to obtain enantioenriched compounds with biological activities.
- Birolli, Willian G.,Nitschke, Marcia,Porto, André Luiz M.,Santos, Darlisson de A.,de Matos, Iara L.
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- Transfer Hydrogenation of Flavanones and ortho-Hydroxychalcones to 1,3-Diarylpropanols Catalyzed by CNN Pincer Ruthenium Complexes
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The transfer hydrogenation of flavanones and ortho-hydroxychalcones catalyzed by ruthenium pincer complexes RuCl(CNNPh)(disphosphine) has allowed the synthesis of ortho-hydroxy 1,3-diarypropanols in 80–88 % yield, under mild reaction conditions and short reaction times (1 h) in 2-propanol. The amount of the co-catalyst NaOiPr has been found crucial for the selective reduction of flavanones to ortho-hydroxy 1,3-diarypropanols vs. flavan-4-ols. Preliminary results show that with pincer catalysts bearing (S,R)-Josiphos, flavanone is reduced to the corresponding (S)-alcohol in moderate conversion (36 %) and up to 92 % ee.
- Soto, Martín,Gotor-Fernández, Vicente,Rodríguez-Solla, Humberto,Baratta, Walter
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p. 2152 - 2157
(2021/03/03)
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- Organocatalytic Approach for Assembling Flavanones via a Cascade 1,4-Conjugate Addition/oxa-Michael Addition between Propargylamines with Water
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A DBU-catalyzed one-pot cascade reaction of propargylamines and water for the synthesis of flavanones has been developed. This process proceeds via a sequence of 1,4-conjugate addition of water to alkynyl o-quinone methide (o-AQM), followed by the alkyne-allene isomerization and subsequent intramolecular oxa-Michael addition. This strategy provides a convenient method for accessing a broad range of flavanones in good to excellent yields with good functional-group tolerance, in particular, the reactive halo functional groups.
- He, Xinwei,He, Xinwei,Xie, Mengqing,Li, Ruxue,Choy, Pui Ying,Tang, Qiang,Shang, Yongjia,Kwong, Fuk Yee
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p. 4306 - 4310
(2020/06/05)
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- Oxygen mediated highly efficient cobalt(ii) porphyrin-catalyzed reduction of functional chromones: experimental and computational studies
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The highly efficient oxygen mediated reduction of functional chromones with sodium borohydride (NaBH4) catalyzed by cobalt(ii) porphyrins afforded biologically active chroman-4-ols as the reduction products in 80-98% yields. Oxygen assists in the formation of hydridocobalt(iii) porphyrin as a key intermediate, which releases hydride rapidly to reduce the chromones. Additionally, the correlation between quantum calculation results of the catalysts' conversions, yields, times and logarithms of the rate constants for the oxygen assisted reduction reaction was studied. The mechanism of the reaction was also justified by establishing a quantitative relationship between the rate constant, the α-HOMO orbital of the catalytic complex and the stabilization energy of the complex with oxygen.
- Poonam,Kumari, Pratibha,Grishina, Maria,Potemkin, Vladimir,Verma, Abhishek,Rathi, Brijesh
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p. 5228 - 5238
(2019/03/29)
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- Cyclopentadienyl-ruthenium(II) complexes as efficient catalysts for the reduction of carbonyl compounds
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This work reports the reduction of a large variety of aldehydes and ketones with the system PhSiH3/[CpRu(PPh3)2Cl] in good to excellent yields and high chemoselectivity. The catalyst [CpRu(PPh3)2Cl] can be used in at least 12 catalytic cycles with excellent catalytic activity and several substrates were reduced under solvent free conditions.
- Cabrita, Ivania R.,Florindo, Pedro R.,Fernandes, Ana C.
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p. 1511 - 1516
(2017/02/18)
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- Enantioselective reduction of flavanone and oxidation of cis- and trans-flavan-4-ol by selected yeast cultures
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This research investigated stereochemistry of reduction of racemic flavanone and a concurrent competitive process of oxidation, taking place in cultures of live yeast strains. The results obtained gave us information about capability of tested biocatalysts for enantioselective (with respect to both substrate and product) reduction of flavanone and for enantioselective oxidation of the resulting cis- and trans-flavan-4-ols. As a result of our experiments we obtained (2S,4S)-cis-flavan-4-ol with 43% of conversion and 96% of enantiomeric excess, and (2R,4S)-trans-flavan-4-ol with 41% of conversion and ee > 99% in the culture of Rhodotorula rubra; (2S,4S)-cis-flavan-4-ol (43%, ee = 96%) along with (2R,4R)-cis-flavan-4-ol (44%, ee = 61%) in the culture of Zygosaccharomyces bailii KCh 907. Additionally, some of the tested strains demonstrated an excellent capability for enantioselective oxidation of (±)-cis-flavan-4-ol and (±)-trans-flavan-4-ol, obtained by chemical synthesis. A one-day biotransformation in the culture of Candida parapsilosis KCh 909 afforded (S)-flavanone (ee = 93%) as 49% of the reaction mixture and 49% of unreacted (2R,4R)-cis-flavan-4-ol with ee = 97%. Racemic trans-flavan-4-ol was effectively oxidized in the culture of Yarrowia lipolytica KCh 71 - after a three-day biotransformation the reaction mixture contained 52% of (R)-flavanone (ee = 85%) and 48% of (2R,4S)-trans-flavan-4-ol with a high enantiomeric excess (ee = 93%).
- Janeczko, Tomasz,Dymarska, Monika,Siepka, Monika,Gni?ka, Rados?aw,Le?niak, Agnieszka,Pop?oński, Jaros?aw,Kostrzewa-Sus?ow, Edyta
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- Synthesis, enantiomeric separation and docking studies of spiropiperidine analogues as ligands of the nociceptin/orphanin FQ receptor
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A series of triazospirodecanone derivatives were synthesized as potential NOP ligands. 8-(Chroman-4-yl)-1-phenyl-1,3,8-triazaspiro[4.5]decan-4-one (4) and its 5-fluoro analogue (18) proved to be active as agonists with EC50 values in the submicromolar range. Single enantiomers of compound 4 were separated and tested as NOP agonists; the eutomer R-(+)-4 showed a pEC 50 of 7.34. Finally docking studies were performed on the NOP receptor to identify the most significant stereospecific interactions.
- Battisti, Umberto M.,Corrado, Sandra,Sorbi, Claudia,Cornia, Andrea,Tait, Annalisa,Malfacini, Davide,Cerlesi, Maria Camilla,Calò, Girolamo,Brasili, Livio
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p. 973 - 983
(2014/07/08)
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- Enantioselective reduction of flavanone and oxidation of cis- and trans-flavan-4-ol by selected yeast cultures
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This research investigated stereochemistry of reduction of racemic flavanone and a concurrent competitive process of oxidation, taking place in cultures of live yeast strains. The results obtained gave us information about capability of tested biocatalysts for enantioselective (with respect to both substrate and product) reduction of flavanone and for enantioselective oxidation of the resulting cis- and trans-flavan-4-ols. As a result of our experiments we obtained (2S,4S)-cis-flavan-4-ol with 43% of conversion and 96% of enantiomeric excess, and (2R,4S)-trans-flavan-4-ol with 41% of conversion and ee > 99% in the culture of Rhodotorula rubra; (2S,4S)-cis-flavan-4-ol (43%, ee = 96%) along with (2R,4R)-cis-flavan-4-ol (44%, ee = 61%) in the culture of Zygosaccharomyces bailii KCh 907. Additionally, some of the tested strains demonstrated an excellent capability for enantioselective oxidation of (±)-cis-flavan-4-ol and (±)-trans-flavan-4-ol, obtained by chemical synthesis. A one-day biotransformation in the culture of Candida parapsilosis KCh 909 afforded (S)-flavanone (ee = 93%) as 49% of the reaction mixture and 49% of unreacted (2R,4R)-cis-flavan-4-ol with ee = 97%. Racemic trans-flavan-4-ol was effectively oxidized in the culture of Yarrowia lipolytica KCh 71 - after a three-day biotransformation the reaction mixture contained 52% of (R)-flavanone (ee = 85%) and 48% of (2R,4S)-trans-flavan-4-ol with a high enantiomeric excess (ee = 93%).
- Janeczko, Tomasz,Dymarska, Monika,Siepka, Monika,Gni?ka, Rados?aw,Les?niak, Agnieszka,Pop?oński, Jaros?aw,Kostrzewa-Sus?ow, Edyta
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- Ruthenium-NHC-catalyzed asymmetric hydrogenation of flavones and chromones: General access to enantiomerically enriched flavanones, flavanols, chromanones, and chromanols
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Two to four! Readily available flavones and chromones were efficiently converted into four valuable chiral classes of O-heterocycles - flavanones, chromanones, flavanols, and chromanols - by means of an enantioselective Ru/NHC-catalyzed hydrogenation process (see scheme; NHC=N-heterocyclic carbene, PCC=pyridinium chlorochromate). Copyright
- Zhao, Dongbing,Beiring, Bernhard,Glorius, Frank
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p. 8454 - 8458
(2013/09/02)
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- Design and synthesis of novel diphenacoum-derived, conformation-restricted vitamin K 2,3-epoxide reductase inhibitors
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Two novel diphenacoum-derived analogues 5 and 6 are designed, synthesized and tested as potential vitamin K 2,3-epoxide reductase (VKOR) inhibitors. The inhibition studies indicated that 5 is a potent VKOR inhibitor, which confirmed that the replacement of the tetrahydronaphthalene on diphenacoum to a chroman functionality does not have a major impact on inhibition potency. The conformation-restricted compound 6 is a moderate inhibitor which may serve as a lead compound for further study of the mode of action of coumarin-type anticoagulants at the molecular level.
- Chen, Ding-Uei,Kuo, Pei-Yu,Yang, Ding-Yah
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p. 2665 - 2668
(2007/10/03)
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- A Reinvestigation of the Meerwein-Ponndorf-Verley Reduction: A Highly Efficient Variation Using Zirconium Catalysts
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A new variation of the Meerwein-Ponndorf-Verley reduction based on mechanistic considerations is presented.Under optimized conditions 1-(4-dimethylaminophenyl)ethanol was used as the reducing alcohol (2-4 equiv.), Zr(O-tBu)4 as the catalyst (0.2 equiv.), and toluene or cyclohexane as the solvent.Aldehydes and ketones (if not extremely sterically hindered) were reduced to the corresponding alcohols at room temperature mostly within 2-4 h in essentially quantitative yield. α,β-Unsaturated carbonyl compounds cleanly react in a 1,2-mode to afford the corresponding allylic alcohols. - Key Words: Reductions / Meerwein-Ponndorf-Verley reaction / Catalysis / Zirconium tetra-tert-butoxide / β-Hydride shift / Kinetics
- Knauer, Birgit,Krohn, Karsten
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p. 677 - 684
(2007/10/02)
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- The Diastereoselectivity of Zirconium Alkoxide Catalysed Meerwein-Ponndorf-Varley Reductions
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The new variation of the Meerwein-Ponndorf-Verley reduction using 1-ethanol (6) or 1-tetralol (12) (3 equiv.) as the reducting alcohols and Zr(OtBu)4 as the catalyst (0.2 equiv.) is kinetically controlled and highly stereoselective.Preferential axial attack is achieved with the sterically less bulky alcohol 6 in the case of 4-tert-butyl- and 3-methylcyclohexanones (1a -> 96percent axial and 3a -> 93percent axial attack).The combination tetralol (12)/Zr(OtBu)4 behaves as a very bulky reducting agent, and the thermodynamically less stable alcohols 2c (80percent) and 4c (92 - 96percent) are formed preferentially in the reduction of 2a and 4b.The fused bicyclic systems 1-methyl-2-tetralone (14a) and flavanone (15a) and the steroids 16a-18a are reduced with high stereoselectivity to the corresponding cis alcohols 14b and 15b and the β-alcohols 16b-18b.The stereochemical outcome is in agreement with the Felkin-Ahn model. - Key Words: Reduction / Meerwein-Ponndorf-Verley reduction / Catalysis / Zirconium tetra-tert-butoxide / Stereochemistry / Diastereoselectivity / Felkin-Ahn model
- Krohn, Karsten,Knauer, Birgit
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p. 1347 - 1352
(2007/10/02)
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- REDUCTION OF 2'-HYDROXY CHALCONES UNDER PHASE TRANSFER CATALYSIS - A NEW METHOD FOR THE SYNTHESIS OF FLAVAN-4-OLS
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Reduction of 2'-hydroxy chalcones uner phase transfer catalysis conditions is discussed.The products are identified as 2,4-cis-flavan-4-ols.
- Jyotsna, D.,Rao, A. V. Subba
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p. 1009 - 1014
(2007/10/02)
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- STEREOSELECTIVITY AT BENZYLIC CARBON. FLAVANOIDS-V. SYNTHESIS OF TRANS-4-ACETAMIDOFLAVANS
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Some reactions of 4-substituted flavans have been studied. 4-Chloro/bromo derivatives react under neutral conditions with phthalimide and acetonitrile leading to displacement of axial halogen by nitrogen with inversion.In contrast, irrespective of the ste
- Hirwe, A.,Marathe, K. G.,Mohorkar, S. S.,Ramdas, K.,Singh, C. B.
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p. 1539 - 1546
(2007/10/02)
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- Carbon-13 NMR Spectral Investigations: Part 13 - Yb(fod)3-induced Carbon-13 NMR Shift Studies on Some Benzopyrone Derivatives
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The Yb(fod)3-induced shifts have been utilized for the definitive carbon-13 signal assignments for chromone, chromanone, chroman-4-ol, flavone, flavanone and flavan-4-ol derivatives, leading to the revision of several earlier reported assignments.The carbon-13 signal displacement associated with acetylation and trichloroacetylcarbamate formation have also been discussed.
- Agrawal, Pawan K.
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p. 1228 - 1230
(2007/10/02)
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- DEOXYGENATION OF ALDEHYDES AND KETONES WITH SODIUM CYANOBOROHYDRIDE
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Treatment of hydroxy-substituted aromatic aldehydes and ketones with sodium cyanoborohydride yields the corresponding methylene compounds under conditions which favor intermediate carbonium ion formation.
- Elliger, Carl A.
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p. 1315 - 1324
(2007/10/02)
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- Synthesis of Biflavonoids in which the Flavan Units are linked through Oxygen from C-2 to C-3 or C-4
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Flav-2-enes have been utilised via 2,3-cis-2-acetoxy-3-bromoflavans for the synthesis of C-2-O-C-3- and C-2-O-C-4-linked biflavonoids.For example, 2,3-cis-2-acetoxy-3-bromoflavans react with (+/-)-tetra-O-methylcatechin (18) to give
- Brown, Ben R.,Stuart, Ian A.,Tyrrell, A. William R.
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p. 2563 - 2572
(2007/10/02)
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- Epimerisation of 4-Acetoxyflavans and Flavan-4-ols
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5,7,3',4'-Tetramethoxyflavan-4β-ol reacts at 0 deg C with pyridine, ang a trace of acetic acid to give the 4β-acetoxy derivative but at 90 deg C the 4α-acetoxyflavan is formed.Either acetate when equilibrated with this acetylating agent yields a mixture o
- Attwood, Michael R.,Brown, Ben R.,Pike, William T.
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p. 2229 - 2236
(2007/10/02)
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- Synthesis and Reactions of 4-Aryloxyflavans
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4α-Aryloxyflavans unsubstituted in ring A have been synthesised by the reaction of phenols with flavan-4β-ols in the presence of boron trifluoride in ether.If reaction times are prolonged beyond disappearance of the starting 4β-ols, thermodynamic control leads to 4-arylflavans and the yields of 4-aryloxyflavans are negligible. 4-Arylflavans are the sole products when the catalyst is toluene-p-sulphonic acid.Thermal decomposition of flavan-4-yl phenol carbonate in the presence of phenols affords a synthesis of 4α-aryloxyflavans free from 4-arylflavans.Syntheses of 7-methoxy-4α-aryloxyflavans have not been successful, nor can 4-aryloxyflavan-3-ols be obtained from 3,4-diols by these methods.The 4-aryloxyflavans react rapidly with acids to yield 4-carbocations which can be trapped by a variety of nucleophiles yielding 4α-ols with water, 4α-alkoxyflavans with alcohols, 4α-arylflavans with phenols, and 4α-sulphides with thiols. 2,3-cis-Flav-3-ene epoxide reacts with phenols to give 2,3-cis-3,4-cis-4-aryloxyflavan-3-ols and with sodium salts of phenols to give 2,3-cis-3,4-trans-4-aryloxyflavan-3-ols.The 2,3-trans-epoxide similarly gives the 2,3-trans-4-aryloxyflavan-3-ols.A biflavonoid containing a 4-aryloxy link has been synthesised from the 2,3-trans-epoxide and 7-hydroxyflavan-4-one.A series of 2,3-trans-4'-methoxy-4-aryloxyflavan-3-ols has been synthesised from crude 2,3-trans-4'-methoxyflav-3-ene epoxide.The substitution of a methoxy group into position 7 of the flavonoid A-ring prevented the preparation of the epoxides, but the action of N-bromosuccinimide and sodium acetate in acetic anhydride and acetic acid on 7,4'-dimethoxyflav-3-ene gave 2,3-cis- and 2,3-trans-4-acetoxy-3-bromo-7,4'-dimethoxyflavans, the latter of which was converted by the action of sodium salts of phenols into the expected 4-aryloxyflavan-3-ols. 5,7,3',4'-Tetramethoxyflav-3-ene gave nuclear brominated products even with N-bromosuccinimide; thus, the synthesis of 5,6,3'4'-tetramethoxy-4-aryloxyflavan-3-ols has not been possible by this method.
- Bateman, Graham,Brown, Ben R.,Campbell, John B.,Cotton, Charles A.,Johnson, Philip,et al.
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p. 2903 - 2912
(2007/10/02)
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- A General and Practicable Synthesis of Polycyclic Heteroaromatic Compounds. Part 2. Reaction of Quinone-methides of Pyridones, Pyrimidines, Coumarin, and Benzene with Aromatic Amines in a Novel Synthesis of Polycyclic Heteroaromatic Compounds
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The synthesis of polycyclic heteroaromatic compounds using the reaction of a quinone-methide, generated in situ, with an aromatic amine has been successfully extended using quinone-methides of coumarin and of pyridones.Preliminary studies with the benzenoid quinone-methide (33) have so far proved to give only low yields of the expected acridines.Generation of 'quinone-methides' in which the carbonyl is part of an amide group did not lead to polycyclic heteroaromatic compounds.
- Asherson, Janet L.,Bilgic, Orhan,Young, Douglas W.
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p. 522 - 528
(2007/10/02)
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