- Catalytic Enantioselective Conjugate Addition of Stereodefined Di- and Trisubstituted Alkenylaluminum Compounds to Acyclic Enones
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Catalytic enantioselective conjugate addition (ECA) reactions with readily accessible and stereochemically defined E-, Z-, di- and trisubstituted alkenyl aluminum compounds are disclosed. Transformations are promoted by various NHC-copper catalysts (NHC=N-heterocyclic carbene), which are derived from enantiomerically pure sulfonate imidazolinium salts. The desired products were obtained in up to 89% yield and >99:1 e.r.; the alkenyl moiety was transferred with complete retention of its stereochemical identity in all instances. The scope and limitations of the approach, key mechanistic attributes, and representative functionalization are presented as well. (Figure presented.).
- McGrath, Kevin P.,Hubbell, Aran K.,Zhou, Yuebiao,Santos, Damián Padín,Torker, Sebastian,Romiti, Filippo,Hoveyda, Amir H.
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supporting information
p. 370 - 375
(2019/12/24)
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- Dehydrozingerone Inspired Discovery of Potential Broad-Spectrum Fungicidal Agents as Ergosterol Biosynthesis Inhibitors
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A series of dehydrozingerone derivatives were synthesized, and their fungicidal activities and action mechanism against Colletotrichum musae were evaluated. The bioassay result showed that most compounds exhibited excellent fungicidal activity in vitro at 50 μg mL-1. Compounds 13, 16, 18, 19, and 27 exhibited broad-spectrum fungicidal activity; especially, compounds 19 and 27 were found to have more potent fungicidal activity than azoxystrobin. The EC50 values of compounds 19 and 27 against Rhizoctonia solani were 0.943 and 0.161 μg mL-1 respectively. Moreover, compound 27 exhibited significant in vitro bactericidal activity against Xanthomonas oryzae pv. oryzae, with an EC50 value of 11.386 μg mL-1, and its curative effect (49.64%) and protection effect (51.74%) on rice bacterial blight disease was equivalent to that of zhongshengmycin (42.90%, 40.80% respectively). Compound 27 could also effectively control gray mold (87.10%, 200 μg mL-1) and rice sheath blight (100%, 200 μg mL-1 82.89%, 100 μg mL-1) in vivo. Preliminary action mechanism study showed that compound 27 mainly acted on the cell membrane and significantly inhibited ergosterol biosynthesis in Colletotrichum musae.
- Song, Xiangmin,Zhu, Xinyue,Li, Ting,Liang, Cai,Zhang, Meng,Shao, Yu,Tao, Jun,Sun, Ranfeng
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p. 11354 - 11363
(2019/10/16)
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- An access to α, β-unsaturated ketones via dual cooperative catalysis
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A dual cooperative organocatalytic approach for the synthesis of α, β-unsaturated ketones is described. This one pot transformation is realized via a domino Knoevenagel-Michael-retro Michael reaction sequence. Various aliphatic ketones reacted smoothly with aromatic as well as aliphatic aldehydes in presence catalytic amount of Meldrum's acid and bifunctional amine. The highlights of this protocol are the easy availability of catalysts, high selectivity, and functional group tolerance. The reaction proved to highly E-selective with no side products emanating from self-condensation, unlike the base-mediated reactions.
- Syamala, Lakshmi V.R. Babu,Khopade, Tushar M.,Warghude, Prakash K.,Bhat, Ramakrishna G.
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supporting information
p. 88 - 91
(2018/12/05)
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- Copper-catalyzed retro-aldol reaction of β-hydroxy ketones or nitriles with aldehydes: Chemo- and stereoselective access to (E)-enones and (E)-acrylonitriles
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A copper-catalyzed transfer aldol type reaction of β-hydroxy ketones or nitriles with aldehydes is reported, which enables chemo- and stereoselective access to (E)-α,β-unsaturated ketones and (E)-acrylonitriles. A key step of the in situ copper(i)-promoted retro-aldol reaction of β-hydroxy ketones or nitriles is proposed to generate a reactive Cu(i) enolate or cyanomethyl intermediate, which undergoes ensuing aldol condensation with aldehydes to deliver the products. This reaction uses 1.2 mol% Cu(IPr)Cl (IPr denotes 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) as the catalyst in the presence of 6.0 mol% NaOtBu cocatalyst at room temperature or 70 °C. A range of aryl and heteroaryl aldehydes as well as acrylaldehydes are compatible with many useful functional groups being tolerated. Under the mild and weakly basic conditions, competitive Cannizzaro-type reaction of benzaldehydes and side reactions of base-sensitive functional groups can be effectively suppressed, which show synthetic advantages of this reaction compared to classic aldol reactions. The synthetic potential of this reaction is further demonstrated by the one-step synthesis of biologically active quinolines and 1,8-naphthyridine in excellent yields (up to 91%). Finally, a full catalytic cycle for this reaction has been constructed using DFT computational studies in the context of a retro-aldol/aldol two-stage mechanism. A rather flat reaction energy profile is found indicating that both stages are kinetically facile, which is consistent with the mild reaction conditions.
- Zhang, Song-Lin,Deng, Zhu-Qin
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p. 7282 - 7294
(2016/08/05)
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- Organocatalyzed Asymmetric Conjugate Addition of Heteroaryl and Aryl Trifluoroborates: A Synthetic Strategy for Discoipyrrole D
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Bis-heteroaryl or bis-aryl stereocenters were formed by an organocatalytic enantioselective conjugate addition using the respective trifluoroborate salts as nucleophiles. Control studies suggested that fluoride dissociation is necessary in the anhydrous conditions. This strategy is applicable to the synthesis of discoipyrrole D, an inhibitor of BR5 fibroblast migration.
- Shih, Jiun-Le,Nguyen, Thien S.,May, Jeremy A.
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supporting information
p. 9931 - 9935
(2015/08/19)
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- Synthesis of 2-aryl-substituted chromans by intramolecular C-O bond formation
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A synthetic route for the preparation of 2-aryl-substituted chromans from commercially available starting materials and utilizing either a palladium- or copper-catalyzed intramolecular cyclization of aryl bromides is described. Chromans with stereocontrol at C-2 can thus be obtained via a palladium-catalyzed asymmetric allylic etherification procedure utilizing a chiral indole-phosphine oxazoline (IndPHOX) ligand. Georg Thieme Verlag Stuttgart · New York.
- Wang, Yu,Franzén, Robert
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supporting information; experimental part
p. 925 - 929
(2012/06/15)
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- Anomalous Z-isomer content in Wittig reaction products from keto-stabilised ylides with ortho-heteroatom substituted benzaldehydes
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Wittig reaction products of keto-stabilised ylides with ortho-substituted benzaldehydes are found to show significantly higher than expected Z-alkene content (up to 50%) compared to analogous reactions of the same ylides with benzaldehyde itself. A cooperative effect is seen whereby the unusual Z-content is further augmented if the ylide bears greater steric bulk in the α′-position. These results are consistent with our previous observations on reactions of all ylide types with aldehydes bearing a β-heteroatom. Significantly, the cooperative effect, previously seen only with semi-stabilised ylides, has now been extended to stabilised ylides. Both the anomalous increase in Z-content and the cooperative effect can be rationalised within the [2+2] cycloaddition mechanism of the Wittig reaction.
- Byrne, Peter A.,Higham, Lee J.,McGovern, Pádraic,Gilheany, Declan G.
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p. 6701 - 6704
(2013/01/15)
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- Chromatography-free wittig reactions using a bifunctional polymeric reagent
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The first example of a polystyrene bearing two distinct reagent groups has been prepared. This phosphine and amine functionalized material was used in one-pot Wittig reactions with an aldehyde and either an α-halo-ester, -ketone, or -amide. Due to the heterogeneous nature of the polymer, the desired alkene product of these reactions could be isolated in excellent yield in essentially pure form after only filtration and solvent removal.
- Leung, Peter Shu-Wai,Teng, Yan,Toy, Patrick H.
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supporting information; experimental part
p. 4996 - 4999
(2010/12/25)
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- Substituted 3-phenylpropenoates and related analogs: Electron ionization mass spectral fragmentation and density functional theory calculations
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Analysis of ethyl 3-(2-chlorophenyl)propenoate by electron ionization mass spectrometry showed the distinct loss of an ortho chlorine. To characterize the structural requisites for the observed mass fragmentation, a series of 30 halogen-substituted 3-phenylpropenoate-related structures were examined. All ester-containing alkene derivatives exhibited loss of the distinctive chlorine from the 2-position of the phenyl ring. Analogous derivatives with the halogen (chlorine or bromine) in the para position did not evidence selective halogen loss. Results demonstrated that substituted 3-phenylpropenoates and their analogs fragment via the formation of a previously reported benzopyrylium intermediate. To understand the correlation between the intramolecular radical substitution and the abundance and selectivity of the chlorine (or other halogen) displacement, density functional theory calculations were performed to determine the charge on the principal cation involved in the chlorine loss (in the ortho, meta, and para positions), the charge for the neutral radical (noncation), the excess alpha-electron density on the relevant atom and the energy to form the cation from the neutral atom (ionization energy). Results showed that the selectivity and extent of halogen displacement correlated highly to the electrophilicity of the radical cation as well as the neutral radical. These data further support the proposed fragmentation mechanism involving intramolecular radical elimination. Copyright
- Wheelock,Colvin,Sanborn,Hammock
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scheme or table
p. 1053 - 1062
(2009/07/04)
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- 2-Amino-quinazolin-5-ones
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2-Amino-quinazolin-5-one compounds, stereoisomers, tautomers, pharmaceutically acceptable salts, and prodrugs thereof; compositions that include a pharmaceutically acceptable carrier and one or more of the 2-amino-quinazolin-5-one compounds, either alone or in combination with at least one additional therapeutic agent. Methods of using the 2-amino-quinazolin-5-one compounds, either alone or in combination with at least one additional therapeutic agent, in the prophylaxis or treatment of cell proliferative diseases.
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Page/Page column 20
(2010/11/25)
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- Combined Suzuki coupling - Wittig olefination reaction in aqueous medium
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Bromoarene carbaldehydes and bromoheteroarene carbaldehydes underwent a one-pot Suzuki cross coupling and Wittig olefination in aqueous medium to give compounds with extended π-systems.
- Yamamoto, Kyoko,Watanabe, Masataka,Ideta, Kyoko,Mataka, Shuntaro,Thiemann, Thies
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p. 1299 - 1307
(2008/02/08)
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