- Nb(salan)-catalyzed asymmetric epoxidation of allylic alcohols with hydrogen peroxide
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(Chemical Presented) Bridging the catalyst: The dimeric complex [(m-oxo){Nb(salan)}2] catalyzes asymmetric epoxidation of allylic alcohols by hydrogen peroxide to give epoxy alcohols with good to high enantioselectivities irrespective of the olefin geometry (see scheme).
- Egami, Hiromichi,Katsuki, Tsutomu
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Read Online
- Vanadium-catalyzed asymmetric epoxidation of allylic alcohols mediated by (+)-norcamphor-derived hydroperoxide
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A protocol for the asymmetric epoxidation of allylic alcohols has been established that employs VO(acac)2 as catalyst, the commercial achiral hydroxamic acid, N-hydroxy-N-phenyl-benzamide, and optically pure (+)-norcamphor-derived hydroperoxide
- Lattanzi, Alessandra,Piccirillo, Sandro,Scettri, Arrigo
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Read Online
- Design, synthesis and antitumor activity evaluation of Chrysamide B derivatives
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Marine natural products derived from special or extreme environment provide an important source for the development of anti-tumor drugs due to their special skeletons and functional groups. In this study, based on our previous work on the total synthesis and structure revision of the novel marine natural product Chrysamide B, a group of its derivatives were designed, synthesized, and subsequently of which the anti-cancer activity, structure-activity relationships and cellular mechanism were explored for the first time. Compared with Chrysamide B, better anti-cancer performance of some derivatives against five human cancer cell lines (SGC-7901, MGC-803, HepG2, HCT-116, MCF-7) was observed, especially for compound b-9 on MGC-803 and SGC-7901 cells with the IC 50 values of 7.88 ± 0.81 and 10.08 ± 1.08 μM, respectively. Subsequently, cellular mechanism study suggested that compound b-9 treatment could inhibit the cellular proliferation, reduce the migration and invasion ability of cells, and induce mitochondrial-dependent apoptosis in gastric cancer MGC-803 and SGC-7901 cells. Furthermore, the mitochondrial-dependent apoptosis induced by compound b-9 is related with the JAK2/STAT3/Bcl-2 signaling pathway. To conclude, our results offer a new structure for the discovery of anti-tumor lead compounds from marine natural products.
- Zhu, Longqing,Li, Junfang,Fan, Xiaohong,Hu, Xiaoling,Chen, Jinhong,Liu, Yonghong,Hao, Xiangyong,Shi, Tao,Wang, Zhen,Zhao, Quanyi
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- Discovery of a novel inhibitor of nitric oxide production with potential therapeutic effect on acute inflammation
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Inflammation as a host's excessive immune response to stimulation, is involved in the development of numerous diseases. To discover novel anti-inflammatory agents and based on our previous synthetic work on marine natural product Chrysamide B, it and a series of derivatives were synthesized and evaluated for their anti-inflammatory activity on inhibition of LPS-induced NO production. Then the preliminary structure–activity relationships were conducted. Among them, Chrysamide B is the most potent anti-inflammatory agent with low cytotoxicity and strong inhibition on the production of NO (IC50 = 0.010 μM) and the activity of iNOS (IC50 = 0.082 μM) in LPS-stimulated RAW 264.7 cells. Primary studies suggested that the mechanism of action may be that it interfered the formation of active dimeric iNOS but not affected transcription and translation. Furthermore, its good performance of anti-inflammatory effect on LPS-induced multiple inflammatory cytokines production, carrageenan-induced paw edema, and endotoxin-induced septic mice, was observed. We believe that these findings would provide an idea for the further modification and research of these analogs in the future.
- Zhu, Long-Qing,Fan, Xiao-Hong,Li, Jun-Fang,Chen, Jin-Hong,Liang, Yan,Hu, Xiao-Ling,Ma, Shu-Meng,Hao, Xiang-Yong,Shi, Tao,Wang, Zhen
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- Chrysamide B derivative with anti-tumor activity and preparation and application of Chrysamide B derivative
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The invention belongs to the field of medicinal chemistry, and particularly relates to a marine natural product Chrysamide B and a derivative thereof. The marine natural product Chrysamide B comprisesstereoisomers or pharmaceutically acceptable salts, solvates and prodrugs of the marine natural product Chrysamide B, general formulas are shown in a formula (I), a formula (II) and a formula (III).The invention also provides preparation and application of the compound. The compound has an anti-cancer effect; the compound has good inhibitory activity on digestive system cancers, leukemia, livertumors, non-small cell lung cancers, cervical cancers, breast cancers and the like and has the effects of inducing tumor cell apoptosis, activating apoptosis protein expression, retarding cycle, inhibiting proliferation and the like and is a potential antitumor drug.
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- Recoverable polystyrene-supported catalysts for Sharpless allylic alcohols epoxidations
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In this work, new heterogeneous catalysts intended for enantioselective Sharpless epoxidation were prepared. The catalysts are based on Ti(IV) complexes of cross-linked swellable spherical copolymer beads of styrene with ethyl-(4-vinylbenzyl)-L-tartrate, or with ethyl-(2R,3R)-2,3-dihydroxy-4-oxo-5-(4-vinylphenyl)pentanoate. These catalysts were tested in epoxidation of cinnamyl alcohols. High conversion (up to 99%) and high enantioselectivity (up to 99% ee) were achieved in the case of catalysts based on copolymers of styrene with ethyl-(4-vinylbenzyl)-L-tartrate (5, 20, 50%). Unfortunately, the copolymers lost their enantioselectivity due to the leaching of L-tartrate, caused by alcoholysis of ester bond. This problem has been overcome by replacing the ester bond by a stable keto bond. The prepared catalyst based on the copolymer of styrene with ethyl-(2R,3R)-2,3-dihydroxy-4-oxo-5-(4-vinylphenyl)pentanoate (20%) achieved a similarly high conversion and enantioselectivity as in the previous case (up to 99%, up to 99% ee) and was successfully recycled.
- Bartá?ek, Jan,Drabina, Pavel,Váňa, Ji?í,Sedlák, Milo?
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p. 123 - 132
(2019/02/27)
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- Tungsten-catalyzed asymmetric epoxidation of allylic and homoallylic alcohols with hydrogen peroxide
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A simple, efficient, and environmentally friendly asymmetric epoxidation of primary, secondary, tertiary allylic, and homoallylic alcohols has been accomplished. This process was promoted by a tungsten-bishydroxamic acid complex at room temperature with the use of aqueous 30% H2O2 as oxidant, yielding the products in 84-98% ee.
- Wang, Chuan,Yamamoto, Hisashi
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supporting information
p. 1222 - 1225
(2014/02/14)
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- Tungsten-catalyzed regio- and enantioselective aminolysis of trans-2,3-epoxy alcohols: An entry to virtually enantiopure amino alcohols
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The first catalytic enantioselective aminolysis of trans-2,3-epoxy alcohols has been accomplished. This stereo-specific ring-opening process was efficiently promoted by a tungsten/bis(hydroxamic acid) catalytic system, furnishing various anti-3-amino-1,2-diols with excellent regiocontrol and high enantioselectivities (up to 95% ee). Moreover, virtually enantiopure 3-amino-1,2-diols could be obtained by the sequential combination of two reactions that both involve the use of a chiral catalyst.
- Wang, Chuan,Yamamoto, Hisashi
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supporting information
p. 13920 - 13923
(2015/02/05)
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- The cinchona primary amine-catalyzed asymmetric epoxidation and hydroperoxidation of α,β-unsaturated carbonyl compounds with hydrogen peroxide
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Using cinchona alkaloid-derived primary amines as catalysts and aqueous hydrogen peroxide as the oxidant, we have developed highly enantioselective Weitz-Scheffer-type epoxidation and hydroperoxidation reactions of α,β-unsaturated carbonyl compounds (up to 99.5:0.5 er). In this article, we present our full studies on this family of reactions, employing acyclic enones, 5-15-membered cyclic enones, and α-branched enals as substrates. In addition to an expanded scope, synthetic applications of the products are presented. We also report detailed mechanistic investigations of the catalytic intermediates, structure-activity relationships of the cinchona amine catalyst, and rationalization of the absolute stereoselectivity by NMR spectroscopic studies and DFT calculations.
- Lifchits, Olga,Mahlau, Manuel,Reisinger, Corinna M.,Lee, Anna,Fares, Christophe,Polyak, Iakov,Gopakumar, Gopinadhanpillai,Thiel, Walter,List, Benjamin
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p. 6677 - 6693
(2013/06/05)
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- Sulfonylcarbamate as a versatile and unique hydroxy-protecting group: A protecting group stable under severe conditions and labile under mild conditions
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The sulfonylcarbamate group is a unique hydroxyl protecting group. In contrast to typical acyl protecting groups, the sulfonylcarbamate group is stable under harsh basic conditions, while showing labile behavior under mild basic conditions. Its compatibility with other hydroxyl protecting groups and application to carbohydrate chemistry is demonstrated.
- Manabe, Shino,Yamaguchi, Masanori,Ito, Yukishige
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supporting information
p. 8332 - 8334
(2013/09/23)
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- Nanosheet-enhanced enantioselectivity in the vanadium-catalyzed asymmetric epoxidation of allylic alcohols
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The use of suitable chiral ligands is an efficient means of producing highly enantioselective transition-metal catalysts. Herein, we report a facile, economic, and effective strategy for the design of chiral ligands that demonstrate enhanced enantioselectivity and catalytic efficacy. Our simple strategy employs naturally occurring or synthetic inorganic nanosheets as huge and rigid planar substituents for, but not limited to, naturally available α-amino-acid ligands; these ligands were successfully used in the vanadium-catalyzed asymmetric epoxidation of allylic alcohols. The crucial role of the inorganic nanosheets as planar substituents in improving the enantioselectivity of the reaction was clearly revealed by relating the observed enantiomeric excess with the distribution of the catalytic centers and the accessibility of the substrate molecules to the catalytic sites. DFT calculations indicated that the LDH layer improved the enantioselectivity by influencing the formation and stability of the catalytic transition states, both in terms of steric resistance and H-bonding interactions. Handy tricks for asymmetric catalysis: The inorganic layer serves as a huge and rigid planar substituent to effectively enhance the enantioselectivity in the vanadium-catalyzed asymmetric epoxidation of allylic alcohols. Copyright
- Zhao, Li-Wei,Shi, Hui-Min,Wang, Jiu-Zhao,He, Jing
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experimental part
p. 9911 - 9918
(2012/09/10)
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- Highly enantioselective and efficient asymmetric epoxidation catalysts: Inorganic nanosheets modified with α-amino acids as ligands
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Layered catalyst: The attachment of α-amino acid ligands to inorganic nanosheets for use as ligands to vanadium, resulted in a catalyst that enhanced the enantioselectivity of the epoxidation of allylic alcohols (see picture). The catalyst can be colloidized, allowing for the catalytic reactions to be carried out under pseudo-homogeneous reaction conditions and also the catalysts to be directly recycled by simple liquid/liquid separation. Copyright
- Wang, Jiuzhao,Zhao, Liwei,Shi, Huimin,He, Jing
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supporting information; experimental part
p. 9171 - 9176
(2011/11/05)
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- Oxidation catalysis of Nb(salan) complexes: Asymmetric epoxidation of allylic alcohols using aqueous hydrogen peroxide as an oxidant
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Several optically active Nb(salan) complexes were synthesized, and their oxidation catalysis was examined. A dimeric μ-oxo Nb(salan) complex that was prepared from Nb(OiPr)5 and a salan ligand was found to catalyze the asymmetric epoxidation of allylic alcohols using a urea-hydrogen peroxide adduct as an oxidant with good enantioselectivity. However, subsequent studies of the time course of this epoxidation and of the relationship between the ee of the ligand and the ee of the product indicated that the μ-oxo dimer dissociates into a monomeric species prior to epoxidation. Moreover, monomeric Nb(salan) complexes prepared in situ from Nb(OiPr)5 and salan ligands followed by water treatment were found to catalyze the epoxidation of allylic alcohols better using aqueous hydrogen peroxide in CHCl3/brine or toluene/brine solution with high enantioselectivity ranging from 83 to 95% ee, except for the reaction of cinnamyl alcohol that showed a moderate ee of 74%. This is the first example of the highly enantioselective epoxidation of allylic alcohols using aqueous hydrogen peroxide as an oxidant.
- Egami, Hiromichi,Oguma, Takuya,Katsuki, Tsutomu
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scheme or table
p. 5886 - 5895
(2010/07/05)
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- Modification of chiral dimethyl tartrate through transesterification: Immobilization on POSS and enantioselectivity reversal in sharpless asymmetric epoxidation
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Modification of dimethyl tartrate has been investigated through transesterification with aminoalcohols to provide reactive functionalities for the covalent bonding of chiral tartrate to polyhedral oligomeric silsesquioxanes. The transesterification of dimethyl tartrate has been widely studied using different catalytic systems and reaction conditions. Through the proper selection of both the catalytic system and the reaction conditions, it is possible to achieve monosubstituted or bis-substituted tartrate derivatives as sole products. All the intermediate chiral tartrate-derived ligands were successfully used in the homogeneous enantioselective epoxidation of allylic alcohols providing moderate enantiomeric excess over the products. Attached amine groups have been used to support the modified tartrate ligands on to a haloaryl-functionalized silsesquioxane moiety. This final chiral tartrate ligand displays reverse enantioselectivity in the asymmetric epoxidation of allylic alcohols with regard to the starting dimethyl tartrate ligand, both molecules having the same chiral sign. However, the POSS-containing ligand can be easily recovered in almost quantitative yield and reused in asymmetric epoxidation reactions. In addition, recovered silsesquioxane-pendant ligand, though displaying decreasing catalytic activity in recycling epoxidation tests, showed very stable enantioselective behavior.
- Garcia, Rafael A.,Van Grieken, Rafael,Iglesias, Jose,Sherrington, David C.,Gibson, Colin L.
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experimental part
p. 675 - 683
(2010/09/14)
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- Vanadium-catalyzed asymmetric epoxidation of allylic alcohols in water
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Asymmetric V-catalyzed epoxidation of allylic alcohols can be carried out in water with chiral ligands, which incorporate sulfonamide and hydroxamic acid fragments. Furthermore, the reaction, notorious for its ligand-deceleration effect, in water turned into the ligand-accelerated process. By using this aqueous protocol, a range of allylic alcohols were epoxidized with up to 94% ee.
- Malkov, Andrei V.,Czemerys, Louise,Malyshev, Denis A.
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supporting information; experimental part
p. 3350 - 3355
(2009/09/26)
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- Synthesis of new chiral ketones from d-glucose derivatives and their use in the enantioselective epoxidation of arylalkenes
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A new backbone model for a chiral carbohydrate-derived ketone for asymmetric epoxldatlon is presented. The oxo function is sited in a seven-membered ring fused to the sugar moety. The synthesized compound is an effective chirality-transfer agent in dioxirane-mediated epoxidation, giving ees of up to 74%.
- Vega-Perez, Jose Manuel,Holm, Margarita Vega,Luisa Martinez,Blanco, Eugenia,Iglesias-Guerra, Fernando
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experimental part
p. 6009 - 6018
(2010/03/03)
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- Prompt determination of absolute configuration for epoxy alcohols via exciton chirality protocol
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A microscale protocol for determination of absolute configurations of 2,3-epoxy alcohols is described. 2,3-Disubstituted (cis and trans), 2,2-disubstituted, 2,2,3-trisubstituted, and 2,3,3-trisubstituted epoxy alcohols rendered prominent ECCD signals upon complexing with a Lewis acidic porphyrin tweezer and consequently provide straightforward assignment of chirality for epoxy alcohols. This method proved to be rapid, simple, sensitive, and reliable for the class of molecules listed above. Copyright
- Li, Xiaoyong,Borhan, Babak
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supporting information; experimental part
p. 16126 - 16127
(2009/05/09)
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- Enantioselective epoxidation of allylic alcohols by a chiral complex of vanadium: An effective controller system and a rational mechanistic model
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(Chemical Equation Presented) Bishydroxamic acid derivatives are used as ligands for a vanadium catalyst in the preparation of epoxy alcohols (see scheme). The methodology uses aqueous tert-butyl hydroperoxide (TBHP) as an achiral oxidant, low catalyst loading, low reaction temperatures (0°C to room temperature), and simple workup procedures. The reaction is applied to the kinetic resolution of a secondary allylic alcohol and the preparation of small epoxy alcohols. R1, R2, R3: alkyl, aryl, H.
- Zhang, Wei,Basak, Arindrajit,Kosugi, Yuji,Hoshino, Yujiro,Yamamoto, Hisashi
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p. 4389 - 4391
(2007/10/03)
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- Amino acid-derived hydroxamic acids as chiral ligands in the vanadium catalysed epoxidation
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New sulfonamide-derived hydroxamic acids 7-11 have been developed as chiral ligands for the V-catalysed asymmetric epoxidation, showing high reactivity at subzero temperatures and moderate to good enantioselectivity. The strong accelerating effect exhibited by the ligands of this type can be attributed to the sulfonamide functionality. A range of cinnamyl type allylic alcohols were epoxidised with up to 74% ee. The Royal Society of Chemistry 2005.
- Malkov, Andrei V.,Bourhani, Zainaba,Kocovsky, Pavel
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p. 3194 - 3200
(2007/10/03)
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- Catalytic asymmetric epoxidation
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The present invention relates to the synthesis of chiral epoxides via a catalytic asymmetric oxidation of olefins. Additionally, the methodology provides a method of asymmetrically oxidizing sulfides and phosphines. This asymmetric oxidation employs a catalyst system composed of a metal and a chiral bishydroxamic acid ligand, which, in the presence of a stoichiometric oxidation reagent, serves to asymmetrically oxidize a variety of substrates.
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Page/Page column 17
(2010/02/12)
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- Control of enantioselectivity through a hydrogen-bonded template in the vanadium(V)-catalyzed epoxidation of allylic alcohols by optically active hydroperoxides
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The vanadium(V)-catalyzed asymmetric epoxidation of primary allylic alcohols by the optically active TADDOL-derived hydroperoxide as the asymmetric controller provides the corresponding (R)-epoxides in up to 72% ee. From this mechanistic study we conclude
- Adam, Waldemar,Beck, Albert K.,Pichota, Arkadius,Saha-Moeller, Chantu R.,Seebach, Dieter,Vogl, Nadine,Zhang, Rui
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p. 1355 - 1361
(2007/10/03)
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- Chiral hydroperoxides as oxygen source in the catalytic stereoselective epoxidation of allylic alcohols by sandwich-type polyoxometalates: Control of enantioselectivity through a metal-coordinated template
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The epoxidation of allylic alcohols is shown to be efficiently and selectively catalyzed by the oxidatively resistant sandwich-type polyoxometalates, POMs, namely [WZnM2(ZnW9O 34)2]q- [M = OV(IV), Mn(II), Ru(III), Fe(III), Pd(II), Pt(II), Zn(II); q = 10-12], with organic hydroperoxides as oxygen source. Conspicuous is the fact that the nature of the transition metal M in the central ring of polyoxometalate affects significantly the reactivity, chemoselectivity, regioselectivity, and stereoselectivity of the allylic alcohol epoxidation. For the first time, it is demonstrated that the oxovanadium(IV)-substituted POM, namely [ZnW(VO)2(ZnW 9O34)2]12-, is a highly chemoselective, regioselective, and also stereoselective catalyst for the clean epoxidation of allylic alcohols. A high enantioselectivity (er values up to 95:5) has been achieved with [ZnW(VO)2(ZnW9O 34)2]12- and the sterically demanding TADOOL-derived hydroperoxide TADOOH as regenerative chiral oxygen source. Thus, a POM-catalyzed asymmetric epoxidation of excellent catalytic efficiency (up to 42 000 TON) has been made available for the development of sustainable oxidation processes. The high reactivity and selectivity of this unprecedented oxygen-transfer process are mechanistically rationalized in terms of a peroxy-type vanadium(V) template.
- Adam, Waldemar,Alsters, Paul L.,Neumann, Ronny,Saha-Moeller, Chantu R.,Seebach, Dieter,Beck, Albert K.,Zhang, Rui
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p. 8222 - 8231
(2007/10/03)
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- Highly efficient catalytic asymmetric epoxidation of allylic alcohols by an oxovanadium-substituted polyoxometalate with a regenerative TADDOL-derived hydroperoxide
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(Matrix presented) The oxovanadium(IV) sandwich-type POM catalyzes the chemo-, regio-, and stereoselective epoxidation of allylic alcohols by chiral hydroperoxides with very high catalytic efficiency (up to 42 000 TON), a potentially valuable oxidation for the development of sustainable processes. By using the sterically demanding, TADDOL-derived hydroperoxide TADOOH as the chiral oxygen source, enantiomeric ratios (er) of up to 95:5 have been achieved.
- Adam, Waldemar,Alsters, Paul L.,Neumann, Ronny,Saha-Moeller, Chantu R.,Seebach, Dieter,Zhang, Rui
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p. 725 - 728
(2007/10/03)
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- Catalytic asymmetric epoxidation of allylic alcohols using a renewable hydroperoxide
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Sharpless modified asymmetric epoxidation of allylic alcohols can be successfully performed using an easily accessible and renewable tertiary furyl hydroperoxide in the presence 20 mol% of the chiral Ti(O-i-Pr)4/L-DIPT/MS 4 ? system.
- Lattanzi, Alessandra,Iannece, Patrizia,Scettri, Arrigo
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p. 5629 - 5631
(2007/10/03)
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- Influence of hydroperoxides on the enantioselectivity of metal-catalyzed asymmetric Baeyer-Villiger oxidation and epoxidation with chiral ligands
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Chiral hydroperoxides have a significant influence on the enantioselectivity of the metal-catalyzed asymmetric Baeyer-Villiger oxidation of cyclic ketones and the epoxidation of allylic alcohols, when chiral ligands are employed. If both the ligand and th
- Bolm, Carsten,Beckmann, Oliver,Kuehn, Toralf,Palazzi, Chiara,Adam, Waldemar,Rao, Paraselli Bheema,Saha-Moeller, Chantu R.
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p. 2441 - 2446
(2007/10/03)
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- Asymmetric epoxidation of allylic alcohols using vanadium complexes of (N)-hydroxy-[2.2]paracyclophane-4-carboxylic Amides
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Vanadium complexes of (N)-hydroxy-[2.2]paracyclophane-4-carboxylic amides 3 are catalysts for the asymmetric epoxidation of allylic alcohols with tert-butyl hydroperoxide as terminal oxidant. Up to 71% ee have been obtained with 3c bearing an adamantyl-su
- Bolm, Carsten,Kühn, Toralf
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p. 899 - 901
(2007/10/03)
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- Design of optically active hydroxamic acids as ligands in vanadium- catalyzed asymmetric epoxidation
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New optically active hydroxamic acids bearing a 1,1'-binaphthyl group were prepared as ligands in a vanadium-catalyzed asymmetric epoxidation. The feature of these hydroxamic acids is a sterically hindered ligand. The asymmetric epoxidation with good selectivity and reactivity can be established by using VO(O-i-Pr)3 (5 mol%) and a small excess amount of ligand (7.5 mol%) with triphenylmethyl hydroperoxide (TrOOH) in toluene at - 20 °C. Disubstituted allyl alcohols were epoxidized more rapidly than mono- or tri-substituted allyl alcohols, and were obtained in good to high enantioselectivities (48 - 94%ee). The transition state based on X-ray crystal structure of 1e is discussed.
- Hoshino, Yujiro,Murase, Noriaki,Oishi, Masataka,Yamamoto, Hisashi
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p. 1653 - 1658
(2007/10/03)
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- A pH Study on the Chiral Ketone Catalyzed Asymmetric Epoxidation of Hydroxyalkenes
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A detailed study shows that the chiral ketone catalyzed asymmetric epoxidations of hydroxyalkenes are highly pH dependent. The lower enantioselectivity obtained at low pH is attributed to the substantial contribution of the direct epoxidation by Oxone. At high pH the epoxidation mediated by chiral ketone out-competes the racemic epoxidation, leading to higher enantioselectivity. The effective substrates include allylic alcohol, homoallylic alcohol, and bishomoallylic alcohol. In most cases, over 90% ee was obtained.
- Wang, Zhi-Xian,Shi, Yian
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p. 3099 - 3104
(2007/10/03)
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- A divergent approach to the myriaporones and tedanolide: Enantioselective preparation of the common intermediate
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The tedanolide and myriaporone classes of natural products represent interesting targets for synthesis because of their structural similarity and biological activity. The asymmetric preparation of a potential common intermediate in the total synthesis of each of these targets is presented. The key step, a Zr-mediated allylation, allows for the efficient preparation of the hydroxypropionate structural unit.
- Taylor, Richard E.,Ciavarri, Jeffrey P.,Hearn, Brian R.
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p. 9361 - 9364
(2007/10/03)
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- The diastereoselective epoxidation of olefins in supercritical carbon dioxide
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Allylic alcohols are epoxidized with tert-butyl hydroperoxide in the presence of a vanadyl salen oxo-transfer catalyst in supercritical CO2. The metal catalyst was prepared in a simple two step, Schiff base reaction to form the salen ligand, followed by complexation to the vanadyl group. The epoxidation reactions are clean and give both high yields and good diastereoselectivity.
- Haas, Geoffrey R.,Kolis, Joseph W.
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p. 5923 - 5926
(2007/10/03)
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- Stereospecific rearrangements of optically active 2-aryl-3-ethenyloxiranes to give optically active β-ethenylbenzeneethanols: Benzyl vs. allyl cations and an efficient synthesis of (s)-ibuprofen
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Rearrangements of aryl- and ethenyl-substituted oxiranes proceed well in the presence of triethylsilane and BF3 to give optically active alcohols, which we have used for a synthesis of (S)-ibuprofen 1. We have also shown that a vinyl group migrates to a benzylic cation faster than a phenyl group migrates to an allyl cation.
- Jung, Michael E.,Anderson, Karen L.
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p. 2605 - 2608
(2007/10/03)
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- A Tellurium Transposition Route to Allylic Alcohols: Overcoming Some Limitations of the Sharpless-Katsuki Asymmetric Epoxidation
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Good yields of enantiomeric allylic alcohols can be obtained in high enantiomeric excess (ee) by combining Sharpless-Katsuki asymmetric epoxidation process (SAE) with tellurium chemistry.The advantages of the tellurium process are as follows: (1) the 50percent yield limitation on the allylic alcohol in the Sharpless kinetic resolution (SKR) can be overcome; (2) allylic tertiary alcohols which are unsatisfactory substrates in the SKR can be obtained in high optical purity; (3) optically active secondary allylic alcohols with tertiary alkyl substituents (e.g. tert-butyl) at C-1 can be obtained in high ee; (4) optically active sterically congested cis secondary alcohols can be obtained in high ee; and (5) the nuisance of the slow SAE of some vinyl carbinols can be avoided.The key step in the reaction sequence is either a stereospecific 1,3-transposition of double bond and alcohol functionalities or an inversion of the alcohol configuration with concomitant deoxygenation of the epoxide function in epoxy alcohols.Trans secondary allylic alcohols can be converted to cis secondary allylic alcohols by way of erythro epoxy alcohols (glycidols); threo glycidyl derivatives are converted to trans secondary allylic alcohols.These transformations are accomplished by the action of telluride ion, generated in situ from the element, on a glycidyl sulfonate ester.Reduction of elemental Te is conveniently done with rongalite (HOCH2SO2Na) in an aqueous medium.This method is satisfactory when Te2- is required to attack at primary carbon site of a glycidyl sulfonate.In cases where Te2- is required to attack a secondary carbon site, reduction of the tellurium must be done with NaBH4 or LiEt3BH.Elemental tellurium is precipitated during the course of the reactions and can be recovered and reused.
- Dittmer, Donald C.,Discordia, Robert P.,Zhang, Yanzhi,Murphy, Christopher K.,Kumar, Archana,et al.
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p. 718 - 731
(2007/10/02)
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- Catalytic Asymmetric Epoxidation and Kinetic Resolution: Modified Procedures Including in Situ Derivatization
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The use of 3A or 4A molecular sieves ( zeoiltes ) substantially increases the scope of the titanium(IV)-catalyzed asymmetric epoxidation of primary allylic alcohols.Whereas without molecular sieves epoxidations employing only 5 to 10 mol percent Ti(O-i-Pr)4 generally led to low conversion or low enantioselectivity, in the presence of molecular sieves such reactions generally led to high conversion (>95percent) and high enantioselectivity (90-95percent ee).The epoxidations of 20 primary allylic alcohols are described.Especially noteworthy are the epoxidations of cinnamyl alcohol, 2-tetradecyl-2-propen-1-ol, allyl alcohol, and crotyl alcohol-compounds which heretofore had been considered difficult substrates for asymmetric epoxidation.In the case of allylic alcohol, the use of cumene hydroperoxide substantially increases both the reaction rate and the conversion, even in the absence of molecular sieves.In general, enantioselectivities are slightly depressed (by 1-5percent ee) relative to reactions employing 50-100 mol percent Ti(O-i-Pr)4.The epoxidation of low molecular weight allylic alcohols is especially facilitated and, in conjuction with in situ derivatization, provides for the synthesis of many epoxy alcohol synthons which were previously difficult to obtain.The kinetic resolution of four secondary allylic alcohols with 10 mol percent Ti(O-i-Pr)4 is also described.The role of molecular sieves in the reaction and the effects of variation in reaction stoichiometry, oxidant, and tartrate are discussed.
- Gao, Yun,Hanson, Robert M.,Klunder, Janice M.,Ko, Soo Y.,Masamune, Hiroko,Sharpless, K. Barry
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p. 5765 - 5780
(2007/10/02)
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