- Enantioselective Synthesis of Chromenes via a Palladium-Catalyzed Asymmetric Redox-Relay Heck Reaction
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A palladium-catalyzed asymmetric redox-relay Heck reaction of 4H-chromenes and arylboronic acids has been successfully developed. The reaction proceeded in moderate to good yields with good to high enantioselectivities. The resulting product is an advanced intermediate of bio-active compound BW683C.
- Jiang, Ze-Zhen,Gao, Ang,Li, Hao,Chen, Di,Ding, Chang-Hua,Xu, Bin,Hou, Xue-Long
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p. 3119 - 3122
(2017/12/04)
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- Protecting group-free use of alcohols as carbon electrophiles in atom efficient aluminium triflate-catalysed dehydrative nucleophilic displacement reactions
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Benzylic and allylic alcohols are rendered electrophilic without chemical modification by the use of aluminium triflate as catalyst. The reaction succeeds with alcohol, thiol, carbon and nitrogen nucleophiles. When phenols are employed as nucleophiles, C-alkylation ensues. An advanced application of the method is demonstrated in the synthesis of 2H-chromenes and their N and S analogues.
- Cullen, Adam,Muller, Alfred J.,Williams, D. Bradley G.
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p. 42168 - 42171
(2017/09/11)
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- Transition-Metal-Free Cross-Coupling of Indium Organometallics with Chromene and Isochroman Acetals Mediated by BF3·OEt2
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A transition-metal-free coupling of triorganoindium reagents with benzopyranyl acetals mediated by a Lewis acid has been developed. The reaction of R3In with chromene and isochroman acetals in the presence of BF3·OEt2 afforded 2-substituted chromenes and 1-substituted isochromans, respectively, in good yields. The reactions proceed with a variety of triorganoindium reagents (aryl, heteroaryl, alkynyl, alkenyl, alkyl) using only 50 mol % of the organometallic, thus demonstrating the efficiency of these species. Preliminary mechanistic studies indicate the formation of an oxocarbenium ion intermediate in the presence of the Lewis acid.
- Gil-Negrete, José M.,Sestelo, José Pérez,Sarandeses, Luis A.
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supporting information
p. 4316 - 4319
(2016/10/12)
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- Dioxomolybdenum Complexes as Excellent Catalysts for the Deoxygenation of Aryl Ketones to Aryl Alkenes
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This work describes a new methodology for the selective deoxygenation of aryl ketones to the corresponding aryl alkenes catalyzed by dioxomolybdenum complexes using silanes as reducing agents. The best results were obtained with the system PhSiH3/MoO2Cl2(H2O)2 (5-10 mol %), which was very efficient for the deoxygenation of a large variety of aryl ketones to alkenes in excellent yields. This new methodology has the advantages of using an inexpensive, environmentally friendly, easily prepared, and air-stable catalyst in ether solution.
- Fernandes, Tiago A.,Fernandes, Ana C.
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p. 3503 - 3507
(2015/11/10)
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- Catalytic Enantioselective Synthesis of 2-Aryl Chromenes and Related Phosphoramidite Ligands and Catalyst Compounds
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Methods to access 2-aryl chromene compounds via an asymmetric catalytic process.
- -
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Paragraph 0021
(2015/11/24)
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- Intramolecular etherification and polyene cyclization of π-Activated Alcohols Promoted by Hot Water
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Hot water, acting as a mildly acidic catalyst, efficiently promoted intramolecular direct nucleophilic substitution reactions of unsaturated alcohols with heteroatom or carbon nucleophiles. In a mixed solvent of water and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), polyene cyclizations using allylic alcohols as initiators gave the desired cyclized products, and in neat HFIP, a tricyclization reaction gave a tetracyclic product in 51% chemical yield.
- Zhang, Feng-Zhi,Tian, Yan,Li, Guo-Xing,Qu, Jin
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p. 1107 - 1115
(2015/01/30)
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- Glycerol as an efficient medium for the Petasis borono-mannich reaction
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The multicomponent Petasis borono-Mannich (PBM) reaction is a useful tool for the preparation of complex molecules in a single step from boronic acids, aldehydes/ketones, and amines. Here, we describe the use of glycerol in the PBM reaction of salicylalde
- Rosholm, Tomi,Gois, Pedro M. P.,Franzen, Robert,Candeias, Nuno R.
-
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- Lewis and Bronsted acid cocatalyzed reductive deoxyallenylation of propargylic alcohols with 2-nitrobenzenesulfonylhydrazide
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Reductive deoxyallenylation of sterically hindered tertiary propargylic alcohols was realized on reaction with 2-nitrobenzenesulfonylhydrazide (NBSH) by the combined use of Lewis and Bronsted acid catalysts. This method features a broad substrate scope, m
- Liu, Zhaohong,Liao, Peiqiu,Bi, Xihe
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p. 17277 - 17281
(2015/02/05)
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- Structurally diverse α-substituted benzopyran synthesis through a practical metal-free C(sp3)-H functionalization
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A trityl ion-mediated practical C-H functionalization of a variety of benzopyrans with a wide range of nucleophiles (organoboranes and C-H molecules) at ambient temperature has been disclosed. The metal-free reaction has an excellent functional group tole
- Chen, Wenfang,Xie, Zhiyu,Zheng, Hongbo,Lou, Hongxiang,Liu, Lei
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supporting information
p. 5988 - 5991
(2015/01/08)
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- Palladium-catalyzed coupling of N-tosylhydrazones and β-bromostyrene derivatives: New approach to 2H-chromenes
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2H-Chromene is an important structural motif that exists in natural products and non-natural compounds possessing interesting biological activities. In this investigation, a highly efficient approach toward 2H-chromenes has been developed based on palladium-catalyzed coupling of N-tosylhydrazones and β-bromostyrenes. The mechanism of this reaction is proposed that involves the formation of vinyl palladium by carbene migratory insertion and the intramolecular nucleophilic substitution. This journal is
- Xia, Yamu,Xia, Ying,Zhang, Yan,Wang, Jianbo
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supporting information
p. 9333 - 9336
(2014/12/11)
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- Metalloradical approach to 2H -chromenes
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Cobalt(III)-carbene radicals, generated through metalloradical activation of salicyl N-tosylhydrazones by cobalt(II) complexes of porphyrins, readily undergo radical addition to terminal alkynes to produce salicyl-vinyl radical intermediates. Subsequent hydrogen atom transfer (HAT) from the hydroxy group of the salicyl moiety to the vinyl radical leads to the formation of 2H-chromenes. The Co(II)-catalyzed process can tolerate various substitution patterns and produces the corresponding 2H-chromene products in good isolated yields. EPR spectroscopy and radical-trapping experiments with TEMPO are in agreement with the proposed radical mechanism. DFT calculations reveal the formation of the salicyl-vinyl radical intermediate by a metalloradical-mediated process. Unexpectedly, subsequent HAT from the hydroxy moiety to the vinyl radical leads to formation of an o-quinone methide intermediate, which dissociates spontaneously from the cobalt center and easily undergoes an endocyclic, sigmatropic ring-closing reaction to form the final 2H-chromene product.
- Paul, Nanda D.,Mandal, Sutanuva,Otte, Matthias,Cui, Xin,Zhang, X. Peter,De Bruin, Bas
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p. 1090 - 1096
(2014/02/14)
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- An unexpected rearrangement-hydration reaction sequence of 2H-chromenes to dihydrochalcones under catalysis of HAuCl4
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2-Aryl-2H-chromenes in aqueous DCM medium under catalysis of HAuCl 4 are converted into 3-(2-hydroxyaryl)-1-arylpropan-1-ones through hydration-rearrangement reaction sequence in very good yield. The key step probably involves the [1,5] hydride shift followed by the hydrolysis under the reaction condition. The notable advantages of this method are operational simplicity and ease of isolation of products and also provide a pathway to convert the chalcone into DHCs with the transposition of carbonyl group. 2012 Elsevier Ltd. All rights reserved.
- Maiti, Gourhari,Kayal, Utpal,Karmakar, Rajiv,Bhattacharya, Rudraksha N.
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p. 6321 - 6325,5
(2012/12/12)
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- A facile synthesis of 2h-chromenes and 9-functionalized phenanthrenes through reactions between α,β-unsaturated compounds and arynes
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Facile syntheses of 2H-chromenes or 9-functionalized phenanthrenes under mild conditions in moderate to good yields have been developed. They each involve annulations of arynes with α,β-unsaturated compounds bearing different electron-withdrawing groups (EWGs). Depending on the natures of the different EWGs, the reactions proceed by different pathways: enals react with arynes through a tandem [2+2] cycloaddition/thermal electrocyclic ring-opening/6e-electrocyclization sequence to afford 2H-chromenes, whereas acyl-/ethoxycarbonyl-/cyano-substituted styrenes undergo Diels-Alder reactions with arynes followed by aromatization to afford 9-functionalized phenanthrenes. The scope, limitations, regioselectivities and mechanisms have been studied and are discussed in detail. Depending on the natures of different EWGs in α,β-unsaturated compounds, the reactions between arynes and α,β-unsaturated compounds proceed by different tandem pathways to afford either 2H-chromenes or 9-functionalized phenanthrenes in a selective manner, which is of potential pharmaceutical interest.
- Zhang, Tiexin,Huang, Xian,Wu, Luling
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experimental part
p. 3507 - 3519
(2012/07/30)
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- Nickel-catalyzed cross-coupling of chromene acetals and boronic acids
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A modular and highly efficient protocol for the synthesis of 2-aryl- and heteroaryl-2H-chromenes is described. Under base-free conditions, readily accessible 2-ethoxy-2H-chromenes undergo Csp3-O activation and C sp3-C bond formation in the presence of an inexpensive nickel catalyst and boronic acids. This new strategy enables broad access to 2-substituted-2H-chromenes and has been applied to the late-stage incorporation of complex molecules, including the pharmaceuticals loratidine and indomethacin methyl ester.
- Graham, Thomas J. A.,Doyle, Abigail G.
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supporting information; experimental part
p. 1616 - 1619
(2012/06/05)
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- Water as the reaction medium for multicomponent reactions based on boronic acids
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Water is a suitable medium for the Petasis-borono-Mannich multicomponent reaction. Salicylaldehyde, glyoxalic acid, glycoaldehyde and glyoxal were reacted with several boronic acids and different amines affording alkylaminophenols, 2H-chromenes, α-amino a
- Candeias, Nuno R.,Cal, Pedro M.S.D.,André, Vania,Duarte, M. Teresa,Veiros, Luís F.,Gois, Pedro M.P.
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scheme or table
p. 2736 - 2745
(2010/05/17)
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- Water: A suitable medium for the Petasis borono-Mannioh reaction
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Water was used as the solvent in the Petasis borono-Mannich reaction. With the use of salicylaldehyde, secondary amines and boronic acids, several alkylaminophenols were obtained in considerably high yields in water. By using the same methodology, 2H-chro
- Candeias, Nunc R.,Veiros, Luis F.,Afonso, Carlos A. M.,Gois, Pedro M. P.
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experimental part
p. 1859 - 1863
(2009/08/17)
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- Synthesis of 2-substituted 2H-chromenes using potassium vinyltrifluoroborates
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2H-Chromenes were synthesized from salicylaldehyde using potassium vinylic borates in the presence of secondary amines. We synthesized these 2H-chromene derivatives as a part of an ongoing project to develop inhibitors for TGF-β receptors. Potassium vinyl
- Liu, Fei,Evans, Todd,Das, Bhaskar C.
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p. 1578 - 1581
(2008/09/18)
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- Intramolecular nucleophilic capture of radical cations by tethered hydroxy functions
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A range of systems bearing hydroxy functions tethered to the molecular framework gives rise to a family of interesting radical cations, 5{radical dot}+-11{radical dot}+, upon electron transfer to photo-excited cyanoaromatics. Geraniol (5), nerol (6), citronellol (7), chrysanthemol (8), homochrysanthemol (9), trans-1-o-hydroxyphenyl-2-phenylcyclopropane (10), and endo-5-hydroxymethylnorbornene (11), generate a series of mono-, bi-, or tricyclic ethers via a series of four- to seven-membered transition states. Two of the radical cations, 5{radical dot}+ and 6{radical dot}+, undergo tandem cyclizations where 1,5- and/or 1,6-C-C cyclizations precede nucleophilic capture.
- Roth, Heinz D.,Herbertz, Torsten,Sauers, Ronald R.,Weng, Hengxin
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p. 6471 - 6489
(2007/10/03)
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- A structure-activity study for the inhibition of metalloproteinase-9 activity and gene expression by analogues of gallocatechin-3-gallate
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Catechins are able to modulate the gelatinolytic activity of matrix metalloproteinase-9 (MMP-9) by reducing its release from macrophages. Gallocatechins decrease MMP-9 secretion by lowering MMP-9 promoter activity and mRNA levels. The effect appears to be dependent on some structural and stereochemical requirements. In this study, the relationship between chemical structure and activity was studied by testing the effect of analogues of (±)-gallocatechin-3-gallate (±)-GCG, selectively deprived of hydroxyl groups, on MMP-9 activity, transcription, and secretion. Our results indicate that (±)-GCG and (±)-catechin-3-gallate are characterized by a substitution pattern compatible with direct inhibition of MMP-9 activity. Conversely, when transcription was the target, (±)-trans-3-flavanol-3- benzoate, lacking all the hydroxyl groups, was the most effective both in lowering MMP-9 promoter activity and consequently protein secretion, and in inhibiting nuclear-factor-κB-driven transcription. Our results suggest that the structural requirements for enzyme inhibition are different from those necessary for targeting gene expression. Birkhaeuser Verlag, 2005.
- Dell'Agli,Bellosta,Rizzi,Galli,Canavesi,Rota,Parente,Bosisio,Romeo
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p. 2896 - 2903
(2007/10/03)
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- Synthesis of 2H-chromenes in ionic liquid solvents
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Vinylboronic acids react with o-hydroxyaryl aldehydes in room temperature ionic liquids in the presence of secondary amines to generate 2H-chromenes.
- Kabalka, George W.,Venkataiah, Bollu,Das, Bhaskar C.
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p. 2194 - 2196
(2007/10/03)
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- Palladium(0)-catalyzed synthesis of 2-phenyl-2H-chromene
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2-Phenyl-2H-chromene is obtained in quite good yield starting from 3-[(2-tert-butyldimethylsilyl)oxyphenyl]prop-2-enal. Condensation of this aldehyde with phenyl magnesium bromide, followed by the acetylation of the alcohol obtained, and then intramolecular cyclization in the presence of a palladium catalyst gave the phenylchromene in an overall 34% yield.
- Labrosse,Lhoste,Sinou
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p. 3667 - 3674
(2007/10/03)
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- Stereoselective reductive opening of 2,3-benzofuran - A two-step synthesis of 2H-chromenes including deoxycordiachromene
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The reaction of 2,3-benzofuran (1) with lithium and a catalytic amount of 4,4′-di-tert-butylbiphenyl (TDBB, 5 mol %) in THF at 0 °C leads to the stereoselective ring opening of the heterocycle, yielding the (Z)-organolithium derivatives (2) which, by reaction with different electrophiles [H2O, D2O, tBuCHO, PhCHO, Ph(CH2)2CHO, Me2CO, nPrCOMe, PhCOMe, (CH2)4CO] at -78 °C and final hydrolysis with water, give the expected (Z)-products 3. Cyclisation of the products obtained by reaction with carbonyl compounds under acidic conditions affords the expected substituted 2H-chromenes 4, including deoxycordiachromene 4j.
- Yus, Miguel,Foubelo, Francisco,Ferrandez, Jose V.
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p. 2809 - 2813
(2007/10/03)
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- 2H-chromenes from salicylaldehydes by a catalytic petasis reaction
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(Matrix presented) The Petasis condensation of vinylic or aromatic boronic acids, aromatic aldehydes, and amines is assisted by a hydroxy group adjacent to the aldehyde moiety. The products derived from salicylaldehydes and vinylboronic acids undergo cycl
- Wang, Qian,Finn
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p. 4063 - 4065
(2007/10/03)
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- Time-Resolved Absorption Studies on the Photochromic Process of 2H-Benzopyrans in the Picosecond to Submillisecond Time Domain
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Picosecond to submillisecond photochromic reactions of 2,4-diphenyl-2H-benzopyran and 2,2,4-triphenyl-2H-benzopyran have been investigated by time-resolved absorption spectroscopy. The C-O bond cleavage of the benzopyrans (closed forms) occurs via the first excited singlet state within 2 ps to produce vibrationally excited open forms in the ground electronic state. In the subnanosecond to submillisecond time domain, several decay components with almost the same spectral profiles are observed. These components are assigned to respective stereoisomers with respect to two double bonds and one single bond of the open enone forms. From the pump-laser power dependencies of the yields of the open forms, it is suggested that the photocleavage gives at first only the open forms revertible to the closed form by a single-bond rotation, and that the photoexcitation of the first generated open forms gives rise to other open forms which need a double-bond rotation for reversion to the closed form. The photochromic reactions of a series of 2H-benzopyrans bearing substituents on the pyran ring have also been studied using nanosecond time-resolved absorption spectroscopy. The size of a substituent in the 4-position fairly affects the rate constants of the thermal reversion of the open form to the closed form.
- Kodama, Yoichi,Nakabayashi, Takakazu,Segawa, Katsunori,Hattori, Emi,Sakuragl, Masako,Nlshi, Nobuyuki,Sakuragi, Hirochika
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p. 11478 - 11485
(2007/10/03)
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- A NOVEL SYNTHESIS OF FLAV-3-ENES BY CLAISEN REARRANGEMENT
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1-Arylprop-2-ynyl aryl ethers (6) undergo a facile Claisen rearrangement in N,N-diethylaniline/o-dichlorobenzene to give flav-3-enes in good yields.
- Subramanian, Rajaram Sankara,Balasubramanian, Kalpattu Kuppusamy
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p. 6797 - 6800
(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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- 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)
-
- Synthesis of 4-Substituted Flavans from 4α-Halogenoflavans
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The reactions of flavan-4α- or -4β-ols unsubstituted in ring A with phosphorus or similar halides give 4α-halogenoflavans which react with a variety of nucleophiles (phenolate ions, thiophenolate ions, amines, and alcohols) yielding the corresponding 4-su
- Brown, Ben R.,Guffogg, Stephen,Kahn, Michael L.,Smart, John W.,Stuart, Ian A.
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p. 1825 - 1829
(2007/10/02)
-
- Reactions of Flav-2-enes and Flav-2-en-4-ones (Flavones)
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Flav-2-enes, flavones, and 3-alkyl ethers of flavonols add alcohols and carboxylic acids in the presence of N-bromosuccinimide to give 2-alkoxy- and 2-acyloxy-3-bromoflavans which provide routes to cis-3-bromoflavans by reduction and to 3,4-diols by elimination and reaction with osmium tetraoxide.The 2-acyloxyflavans react with alcohols yielding 2-alkoxyflavans.Flavonols react with N-bromosuccinimide and alcohols to give bromine-free hemiacetals, the known 2,3-dialkoxy-3-hydroxyflavanones.
- Bird, T. Geoffrey C.,Brown, Ben R.,Stuart, Ian A.,Tyrrell, William R.
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p. 1831 - 1846
(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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