- Enantioselective Dihydroxylation of Alkenes Catalyzed by 1,4-Bis(9-O-dihydroquinidinyl)phthalazine-Modified Binaphthyl–Osmium Nanoparticles
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A series of unprecedented binaphthyl–osmium nanoparticles (OsNPs) with chiral modifiers were applied in the heterogeneous asymmetric dihydroxylation of alkenes. A remarkable size effect of the OsNPs, depending on the density of the covalent organic shells, on the reactivity and enantioselectivity of the dihydroxylation reaction was revealed. Successful recycling of the OsNPs was also demonstrated and high reaction efficiency and enantioselectivity were maintained.
- Zhu, Jie,Sun, Xiao-Tao,Wang, Xiao-Dong,Wu, Lei
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Read Online
- A soluble block copolymer-supported bis-cinchona alkaloid ligand for the asymmetric dihydroxylation of olefins
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A soluble block copolymer-supported ligand was prepared via polycondensation of a bis-cinchona alkaloid derivative, polyethylene glycol, and terephthaloyl chloride. Its application in the asymmetric dihydroxylation of olefins delivered very good enantioselectivity.
- Kuang, Yong-Qing,Zhang, Sheng-Yong,Wei, Ling-Ling
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Read Online
- A simple and effective soluble polymer-bound ligand for the asymmetric dihydroxylation of olefins: DHQD-PHAL-OPEG-OMe
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The synthesis of a novel soluble polymer-bound ligand DHQD-PHAL-OPEG-OMe and its application in the catalytic asymmetric dihydroxylation (AD) reaction are described. 1,4-Dichlorophthalazine was used as the coupling reagent to connect dihydroquinidine and polyethylene glycol monomethyl ether (MW = 5000, Fluka) while providing an aromatic group at the 9-O-position of dihydroquinidine. Enantiomeric excesses for trans-disubstituted olefins in the AD reaction, with K3Fe(CN)6 as secondary oxidant, are up to 98%.
- Kuang, Yong-Qing,Zhang, Sheng-Yong,Wei, Ling-Ling
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Read Online
- Catalytic asymmetric dihydroxylation of olefins using polysulfone-based novel microencapsulated osmium tetroxide
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A polysulfone based novel polymer-supported osmium catalyst has been developed. The catalyst was prepared from commercially available polysulfone, based on a microencapsulation technique and was employed in the asymmetric dihydroxylation of various olefins using (DHQD)2PHAL as the chiral ligand and NMO as the co-oxidant in H2O-acetone-CH3CN (1:1:1). The catalyst was recovered by simple filtration and was reused to obtain excellent yields with good enantioselectivity up to five times.
- Malla Reddy,Srinivasulu,Venkat Reddy,Narasimhulu,Venkateswarlu
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Read Online
- Multipolymer-supported substrate and ligand approach to the sharpless asymmetric dihydroxylation
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The correct combination of soluble and insoluble polymers allows a multipolymer reaction in which the substrate trans-cinnamate and the chiral ligand are bound to different polymer supports. The reactions (shown schematically on the right) proceed with 98
- Han,Janda
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Read Online
- Total Synthesis of Aetheramide A
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The first total synthesis of the highly potent anti-HIV natural product aetheramide A was accomplished in 18 steps from four equally complex building blocks. The synthesis established the unknown configuration at C26 and used a configurationally labile β-ketoester moiety for the self-adjustment of the configuration at a methyl branch. The pivotal macrolactamization was achieved by trapping a thermally generated acylketene which was derived from its corresponding dioxinone.
- Gerstmann, Lisa,Kalesse, Markus
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- RAS INHIBITORS
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The disclosure features macrocyclic compounds, and pharmaceutical compositions and protein complexes thereof, capable of inhibiting Ras proteins, and their uses in the treatment of cancers.
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Paragraph 1288-1289
(2021/05/07)
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- COVALENT RAS INHIBITORS AND USES THEREOF
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The disclosure features compounds, or pharmaceutically acceptable salts thereof, alone and in combination with other therapeutic agents, pharmaceutical compositions, and protein conjugates thereof, capable of modulating biological processes including Ras, and their uses in the treatment of cancers.
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Page/Page column 151
(2021/06/04)
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- Asymmetric Total Syntheses of Aetheramides and Their Stereoisomers: Stereochemical Assignment of Aetheramides
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The concise total syntheses of the potent HIV inhibitors aetheramides A and B (IC50 values of 15 and 18 nM), as well as three pairs of their stereoisomers, were achieved, which allowed the complete stereochemical assignment of aetheramides for the first time. With a longest linear sequence of 15 steps, the convergent, fully stereocontrolled route provided aetheramides A and B in 5.3% and 3.6% yields, respectively. The synthetic strategy features efficient Stille coupling for macrocyclization, asymmetric aldol reactions to establish the ambiguous stereochemistries at C-17 and C-26, and implementation of mild conditions to avoid the epimerization of the sensitive polyketide moiety and the migration of the labile lactone.
- Qi, Na,Allu, Srinivasa Rao,Wang, Zhanlong,Liu, Qiang,Guo, Jian,He, Yun
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supporting information
p. 4718 - 4721
(2016/09/28)
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- Highly Enantioselective Iron-Catalyzed cis-Dihydroxylation of Alkenes with Hydrogen Peroxide Oxidant via an FeIII-OOH Reactive Intermediate
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The development of environmentally benign catalysts for highly enantioselective asymmetric cis-dihydroxylation (AD) of alkenes with broad substrate scope remains a challenge. By employing [FeII(L)(OTf)2] (L=N,N′-dimethyl-N,N′-bis(2-methyl-8-quinolyl)-cyclohexane-1,2-diamine) as a catalyst, cis-diols in up to 99.8 % ee with 85 % isolated yield have been achieved in AD of alkenes with H2O2as an oxidant and alkenes in a limiting amount. This “[FeII(L)(OTf)2]+H2O2” method is applicable to both (E)-alkenes and terminal alkenes (24 examples >80 % ee, up to 1 g scale). Mechanistic studies, including18O-labeling, UV/Vis, EPR, ESI-MS analyses, and DFT calculations lend evidence for the involvement of chiral FeIII-OOH active species in enantioselective formation of the two C?O bonds.
- Zang, Chao,Liu, Yungen,Xu, Zhen-Jiang,Tse, Chun-Wai,Guan, Xiangguo,Wei, Jinhu,Huang, Jie-Sheng,Che, Chi-Ming
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supporting information
p. 10253 - 10257
(2016/08/24)
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- Osmium on chelate resin: Nonvolatile catalyst for the synthesis of DIOLS from alkenes
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Osmium tetraoxide (OsO4) was immobilized on a commercially available chelate resin DIAION CR11 (CR11) just by simply immersing it in a methanol solution of OsO4 at room temperature. The resulting purple solid, 5% Os/CR11, indicated no volatility, and effectively catalyzed the oxidation of various alkenes to the corresponding diols.
- Monguchi, Yasunari,Wakayama, Fumika,Takada, Hitoshi,Sawama, Yoshinari,Sajiki, Hironao
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supporting information
p. 700 - 704
(2015/03/14)
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- Highly enantioselective synthesis of anti aryl β-hydroxy α-amino esters via DKR transfer hydrogenation
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An efficient preparation of highly enantiomerically enriched aryl β-hydroxy α-amino esters via dynamic kinetic resolution (DKR), asymmetric transfer hydrogenation of α-amino β-keto esters is described. The anti β-hydroxyl α-amino esters were obtained both in high yields and high diasteroselectivity. The observed high anti selectivity is inconsistent with the previous results in literature. The absolute stereochemistry of the aryl β-hydroxy α-amino esters was unambiguously confirmed via chemical derivatization as well as Vibrational Circular Dichroism (VCD) techniques.
- Liu, Zhuqing,Shultz, C.Scott,Sherwood, Candice A.,Krska, Shane,Dormer, Peter G.,Desmond, Richard,Lee, Claire,Sherer, Edward C.,Shpungin, Joseph,Cuff, James,Xu, Feng
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scheme or table
p. 1685 - 1688
(2011/05/05)
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- Synthesis of amino thiols and isocysteines via regioselective ring opening of sulfamidates with tetrathiomolybdate
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Herein we present a simple and highly efficient method for the synthesis of β and γ-amino thiols via regioselective ring opening of sulfamidates with tetrathiomolybdate 1. The generality of this methodology has been shown by synthesizing carbohydrate deri
- Nasir Baig,Phani Kumar,Mannuthodikayil, Jamsad,Chandrasekaran, Srinivasan
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scheme or table
p. 3111 - 3118
(2011/05/17)
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- Sequential reactions with Grubbs catalyst and ad-mix-α//βusing pdms thimbles
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Incompatible Grubbs catalyst and an osmium dihydroxylation catalyst were site-isolated from each other using polydimethylsiloxane thimbles. The Grubbs catalyst was added to the interior of the thimbles, and AD-mix-α//β was added to the exterior. Organic substrates readily fluxed through the walls of the thimbles and reacted with each catalyst. A series of cascade reactions were developed including those with intermediates possessing low boiling points or that were foul smelling.
- Mwangi, Martin T.,Schulz, Michael D.,Bowden, Ned B.
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supporting information; experimental part
p. 33 - 36
(2009/08/08)
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- Methanesulfonamide: A cosolvent and a general acid catalyst in sharpless asymmetric dihydroxylations
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To obtain information about the effect that methanesulfonamide has in the hydrolysis step in Sharpless asymmetric dihydroxylation, a series of aliphatic and conjugated aromatic olefins were dihydroxylated with and without methanesulfonamide. The hypothesis in this study was that methanesulfonamide is a cosolvent that aids in the transfer of the hydroxide ions from the water phase to the organic phase. A plot of t90% versus the computational partition coefficient clog P of the intermediate osmate ester of nonterminal aliphatic olefins revealed that the polarity of the intermediate osmate ester has a significant effect on the reaction time and methanesulfonamide effect. The more polar the intermediate osmate ester, the faster is the reaction without methanesulfonamide and the smaller the accelerating methanesulfonamide effect. Methanesulfonamide had no accelerating effect in the asymmetric dihydroxylation of short chain terminal aliphatic olefins as a result of easier accessibility of terminal osmate ester groups to the water phase. A cosolvent hypothesis was found not to be valid in asymmetric dihydroxylations of conjugated aromatic olefins. In the reaction conditions used in Sharpless asymmetric dihydroxylation, weakly acidic methanesulfonamide was found to be a general acid catalyst that protonates the intermediate osmate esters of conjugated aromatic olefins in the hydrolysis step.
- Junttila, Mikko H.,Hormi, Osmo O.E.
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experimental part
p. 3038 - 3047
(2009/08/08)
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- Stereoselectivity of an ω-transaminase-mediated amination of 1,3-dihydroxy-1-phenylpropane-2-one
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The stereoselectivity of a recently isolated ω-transaminase from Chromobacterium violaceum in the amination of 1,3-dihydroxy-1-phenylpropan-2-one has been determined. The enzyme is not enantioselective towards a racemic mixture of 1,3-dihydroxy-1-phenylpr
- Smithies, Kirsty,Smith, Mark E.B.,Kaulmann, Ursula,Galman, James L.,Ward, John M.,Hailes, Helen C.
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scheme or table
p. 570 - 574
(2009/09/05)
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- Structure-activity relationship (SAR) studies of 3-(2-amino-ethyl)-5-(4-ethoxy-benzylidene)-thiazolidine-2,4-dione: Development of potential substrate-specific ERK1/2 inhibitors
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A series of analogs of 3-(2-amino-ethyl)-5-(4-ethoxy-benzylidene)-thiazolidine-2,4-dione, a putative substrate-specific ERK1/2 inhibitor, were synthesized and biologically characterized in human leukemia U937 cells to define its pharmacophore. It was disc
- Li, Qianbin,Al-Ayoubi, Adnan,Guo, Tailiang,Zheng, Hui,Sarkar, Aurijit,Nguyen, Tri,Eblen, Scott T.,Grant, Steven,Kellogg, Glen E.,Zhang, Shijun
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scheme or table
p. 6042 - 6046
(2010/05/18)
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- Gelozymes in organic synthesis. Part IV: Resolution of glycidate esters with crude Mung bean (Phaseolus radiatus) epoxide hydrolase immobilized in gelatin matrix
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A crude extract of Mung bean meal (Phaseolus radiatus) possessing epoxide hydrolase activity immobilized in gelatin gel (gelozyme) is employed in the stereoselective epoxide ring opening of glycidate esters. Thus, ethyl trans-(±)-3-phenyl glycidate 1a and methyl trans-(±)-3-(4-methoxyphenyl) glycidate 1b gave (2S,3R)-glycidate esters (ee >99% and 45% yield) with gelatin immobilized enzyme in diisopropyl ether. The corresponding (2R,3S)-enantiomer of 1a was hydrolyzed by an epoxide hydrolase to predominantly give the anti-product, ethyl (2R,3R)-2,3-dihydroxy-3-phenylpropanoate, with a diastereomeric excess of 78% and ee 94% (40%). A small amount (5%) of racemic syn-product was also obtained as a result of the spontaneous hydrolysis. In the case of 1b, the hydrolysis product was racemic due to high reactivity of the glycidate toward water.
- Devi, Avala Vedamayee,Lahari, Challa,Swarnalatha, Lakshmi,Fadnavis
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p. 1139 - 1144
(2008/09/20)
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- Catalytic Asymmetric Dihydroxylation of Olefins Using a Recoverable and Reusable Ligand
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A free bis-cinchona alkaloid derivative ligand was prepared by a simple synthetic manipulation. With ligand/olefin mole ratio of 1%, the asymmetric dihydroxylation reactions of six olefins proceeded smoothly to give the chiral vicinal diols in high chemical yields and optical yields. The ligand itself could be recovered quantitatively by a simple operation and reused five times without loss of enantioselectivity.
- Wang, Qiao Feng,Sun, Xiao Li,Zhang, Sheng Yong,Qin, Xiang Yang,Zhao, Yan
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- Supported ruthenium nanoparticle catalyst for cis -dihydroxylation and oxidative cleavage of alkenes
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The present invention relates to the use of nanosized metal particles (e.g., ruthenium) grafted on inert solid support for oxidation of alkenes. The supported metal catalyst can effect cis-dihydroxylation and oxidative cleavage of alkenes to give the respective cis-diols and carbonyl products.
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Page/Page column 3-4
(2008/06/13)
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- Alkene cis-dihydroxylation by [(Me3tacn)(CF3CO 2)RuVIO2]CIO4 (Me3tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane): Structural characterization of [3 + 2] cycloadducts and kinetic studies
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cis-Dioxoruthenium(VI) complex [(Me3tacn)(CF3CO 2)RuVIO2]CIO4 (1, Me3tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane) reacted with alkenes in aqueous tert-butyl alcohol to afford cis-1,2-diols in excellent yields under ambient conditions. When the reactions of 1 with alkenes were conducted in acetonitrile, oxidative C=C cleavage reaction prevailed giving carbonyl products in >90% yields without any cis-diol formation. The alkene cis-dihydroxylation and C=C cleavage reactions proceed via the formation of a [3 + 2] cycloadduct between 1 and alkenes, analogous to the related reactions with alkynes [Che et al. J. Am. Chem. Soc. 2000, 122, 11380], With cyclooctene and trans-β-methylstyrene as substrates, the Ru(III) cycloadducts [(Me3tacn)(CF 3CO2)RuIIIO(H)CH(CH2) 6HCO]CIO4 (4a) and [(Me3tacn)(CF 3CO2)RuIIIO(H)-PhCHCH(CH3)O]CIO 4 (4b) were isolated and structurally characterized by X-ray crystal analyses. The kinetics of the reactions of 1 with a series of p-substituted styrenes has been studied in acetonitrile by stopped-flow spectrophotometry. The second-order rate constants varied by 14-fold despite an overall span of 1.3 V for the one-electron oxidation potentials of alkenes. Secondary kinetic isotope effect (KIE) was observed for the oxidation of β-d2-styrene (kH/kD = 0.83 ± 0.04) and α-deuteriostyrene (kH/kD = 0.96 ± 0.03), which, together with the stereoselectivity of cis-alkene oxidation by 1, is in favor of a concerted mechanism.
- Yip, Wing-Ping,Yu, Wing-Yiu,Zhu, Nianyong,Che, Chi-Ming
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p. 14239 - 14249
(2007/10/03)
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- Ruthenium nanoparticles supported on hydroxyapatite as an efficient and recyclable catalyst for cis-dihydroxylation and oxidative cleavage of alkenes
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Impregnation of hydroxyapatite with colloidal ruthenium results in the formation of a catalyst that effects cis-dihydroxylation and oxidative cleavage of alkenes to their respective cis-1,2-diols and carbonyl products in good to excellent yields (see scheme). The supported ruthenium catalyst can be easily recycled and reused for consecutive reaction runs without significant deterioration of the catalytic activities. R1, R2 = H, alkyl, aryl.
- Ho, Chi-Ming,Yu, Wing-Yiu,Che, Chi-Ming
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p. 3303 - 3307
(2007/10/03)
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- Electronic effects in olefin oxidation by imidoosmium(VIII) compounds
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Imido osmium(VIII) complexes are versatile oxidants for C-C double bond functionalisation. Despite their structural similarity with OsO4 their reactivity cannot always be compared with this seminal reagent. Detailed investigations including kinetic competition experiments are presented that uncover the electronic and steric preferences of osmium imido complexes. The different behaviour of OsO4 and its imido derivatives towards tertiary amines and diamines is clarified. Hammett correlation studies reveal that the reactivity spectrum of the respective oxidants ranges from a strongly electrophilic behaviour in the case of OsO4 to a rather nucleophilic character as encountered for OsO(NtBu)3. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
- Muniz, Kilian
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p. 2243 - 2252
(2007/10/03)
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- Polysiloxane-bound ligand accelerated catalysis: A modular approach to heterogeneous and homogeneous macromolecular asymmetric dihydroxylation ligands
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Polysiloxane acts as a modular scaffold for macromolecular reagent development. Two separate components were covalently integrated into one material, one constituent provided reagent functionality, the other modulated solubility. In particular cinchona alkaloid based ligands used in the osmium tetroxide catalyzed asymmetric dihydroxylation (AD) reaction were covalently attached to commercially available polysiloxane. To enhance the reactivity of these polymeric ligands, multifunctional reagents were designed to include both the cinchona alkaloid and an alkoxyethylester solubilizing moiety providing random co-polymers. While the mono-functional materials led to heterogeneous conditions, the bifunctional polymers resulted in homogeneous reaction mixtures. Although both reagent types provided diol products with excellent yield and selectivity (>99% ee in nearly quantitative yield) the homogeneous analog has nearly twice the reactivity. Every repeat unit in the heterogeneous material was functionalized along the polysiloxane backbone while approximately half of these sites contained ligand in the homogeneous version. This approach led to macromolecular catalysts with high loadings of ligand and therefore materials with very low equivalent weights. Although these polymers are highly loaded they do maintain reactivity on a par with their free ligand counterpart. Using straightforward purification techniques (i.e. precipitation, simple filtration, or ultrafiltration) these polymeric ligands were easily separated from diol product and reused multiple times. Polysiloxane is a viable support for the catalysis of AD reactions and may provide a generally useful backbone for other catalytic systems.
- DeClue, Michael S.,Siegel, Jay S.
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p. 2287 - 2298
(2007/10/03)
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- Direct catalytic asymmetric aldol-type reaction of aldehydes with ethyl diazoacetate
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(Matrix presented) The direct aldol-type condensation of aldehydes with ethyl diazoacetate catalyzed by the chiral complex of BINOL derivatives-Zr(OtBu)4 gave β-hydroxy α-diazo carbonyl compounds with moderate enantioselectivities (5
- Yao, Wengang,Wang, Jianbo
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p. 1527 - 1530
(2007/10/03)
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- Osmium tetroxide in poly(ethylene glycol) (PEG): A recyclable reaction medium for rapid asymmetric dihydroxylation under Sharpless conditions
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PEG (400) has been used as a recyclable and rapid reaction medium for the asymmetric dihydroxylation of olefins; Sharpless ligand is efficiently recovered and recycled with good enantioselectivity.
- Chandrasekhar,Narsihmulu,Sultana, S. Shameem,Reddy, N. Ramakrishna
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p. 1716 - 1717
(2007/10/03)
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- Stereoselective and regioselective reaction of cyclic ortho esters with phenols
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Cyclic ortho esters undergo stereoselective and regioselective reaction with phenols when treated with BF3·OEt2 at low temperatures. Attack of the phenol on the ortho ester occurs at an open carbon para to electron-donating groups on the phenol ("C-addition") or at the phenolic hydroxyl group ("O-addition") depending on the nature of the cation formed from reaction of the ortho ester and BF3·OEt2. Products resulting from O-addition undergo reversion to a mixture of starting phenol, C-addition product, and O-addition product if treated with BF3·OEt2 at room temperature, but C-addition products are stable under the same conditions. X-ray structural analysis of the C-addition compound indicates that its stereochemistry is opposite to that observed in reaction of similar ortho esters with chloride from TMSCl. However, the stereochemistry of the reaction can be rationalized by the ability of the ortho ester to isomerize via an intermediate benzylic cation and examination of the preferred trajectory of attack of the nucleophile on the intermediate oxonium ion.
- Bozell,Miller,Hames,Loveless
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p. 3084 - 3089
(2007/10/03)
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- Solvent effect on ruthenium catalyzed dihydroxylation
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The effect of different solvents on flash dihydroxylation is compared and for the first time, the replacement of ethyl acetate with acetone was shown to give a successful, catalytic cis-dihydroxylation of the alkene moiety in cholesteryl acetate and the ruthenium catalytic cycle could be maintained by methanesulfonamide in the absence of acetonitrile.
- Shing, Tony K. M.,Tam, Eric K. W.
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p. 2179 - 2180
(2007/10/03)
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- Asymmetric syntheses of chiral allylic alcohols
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Chiral allylic alcohols 2 can easily be obtained by elimination from iodo ketals 10. These are available from natural sources, or by application of the asymmetric Sharpless dihydroxylation to vinylogous esters 6, subsequent reduction, halogenation and elimination. This protocol allows the synthesis of highly functionalized allylic alcohols, which can be used in asymmetric Claisen rearrangements.
- Schneider, Christiane,Kazmaier, Uli
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p. 1314 - 1320
(2007/10/03)
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- Biotransformations with baker's yeast: pH effects on diastereoselectivity during α-hydroxy-β-ketoester reductions and carbon-carbon bond cleavages
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Baker's yeast mediated reduction of α-substituted-β-ketoesters lead to reduction of the carbonyl group with high enantiospecificity and diastereoselectivity at low pH (4.0-5.0, e.e. >99%, d.e. >90%) but cleavage of the C-C bond is observed at higher pH >8.0). Similar carbon-carbon bond cleavages are observed in the reactions of α-acetamido-β-ketoesters and acetamidocinnamic acid.
- Fadnavis,Kumara Vadivel,Bhalerao
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p. 2355 - 2359
(2007/10/03)
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- Rhutenium-Catalyzed cis-Dihydroxylation of Alkenes: Scope and Limitations
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Oxidative ruthenium catalysis (0.07 molequiv RuCl3*(H2O)3, 1.5 molequiv NaIO4, EtOAc/CH3CN/H2O 3:3:1), beyond the usual C-C bond cleavage to give dicarbonyls, have been shown to syn-dihydroxylate a wide range of alkenes (except for strained bicyclic alkenes, sterically hindered trisubstituted alkenes, and most tetrasubstituted alkenes) to give vicinal diols rapidly (within minutes) and efficiently.The minor products are the usual oxidative fission products, namely, ketones and aldehydes or carboxylic acids, and sometimes ketols.Longer reaction times lower the yields of most diols, probably owing to oxidative glycol cleavage.Reactions with substrates containing one or more electron-withdrawing groups in conjugation with or adjacent to the alkene moiety are generally slower but give better yields.The diastereoselectivity of the present "flash" dihydroxylation, anti to the existing α-stereogenic center, with cycloalkenes is excellent whereas that with acyclic alkenes is moderate to poor.Sodium metaperiodate is still the best co-oxidant for the catalytic reaction.Aqueous acetonitrile (approximately 86percent) as an alternative solvent system was found to give better yields of 1,2-diols than the original solvent system in some cases. - Keywords: alkenes, catalysis, dihydroxylations, electrophilicity, ruthenium compounds.
- Shing, Tony K. M.,Tam, Eric K. W.,Tai, Vincent W.-F.,Chung, Ivan H. F.,Jiang, Qin
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- The Osmium-Catalyzed Asymmetric Dihydroxylation: A New Ligand Class and a Process Improvement
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Two key improvements in the osmium-catalyzed asymmetric dihydroxylation have led to a simple procedure which is applicable to a wide range of olefins.
- Sharpless, K. Barry,Amberg, Willi,Bennani, Youssef L.,Crispino, Gerard A.,Hartung, Jens,et al.
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p. 2768 - 2771
(2007/10/02)
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- New Ligands Double the Scope of the Catalytic Asymmetric Dihydroxylation of Olefins
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Improved ligands render terminal olefins good substrates for the osmium-catalyzed asymmetric dihydroxylation (ADH) process, and the amounts of chiral ligand and osmium catalyst required diminish dramatically.
- Sharpless, K. Barry,Amberg, Willi,Beller, Matthias,Chen, Hou,Hartung, Jens,et al.
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p. 4585 - 4588
(2007/10/02)
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- Synthesis of O-Protected (R)-2-Hydroxy Aldehyde and Their Hydrocyanation
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The synthesis of O-silyl- and O-benzyl-protected (R)-2-hydroxy aldehydes (R)-6 from (R)-2-hydroxy carboxylic acids (R)-1 is described.While attempts for their diastereoselective hydrocyanation with hydrocyanic acid and (R)-oxynitrilase as catalyst have not been successful, the cyano silylation with trimethylsilyl cyanide occurred diastereoselectively with a ratio of 81:19 preferring the threo form without racemization at C-2 of the 2-hydroxy aldehyde. Key Words : (R)-2-Hydroxy aldehydes, O-protected / Hydrocyanation
- Effenberger, Franz,Hopf, Martin,Ziegler, Thomas,Hudelmayer, Jochen
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p. 1651 - 1659
(2007/10/02)
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- Catalytic Hydroxylation of Olefins by Polymer-Bound Osmium Tetroxide
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Osmium tetroxide, linked to insoluble crosslinked polymers and copolymers bearing tertiary amino functions, has been used in the presence of secondary oxidants, such as hydrogen peroxide, tert-butyl hydroperoxide and trimethylamine N-oxide, to accomplish the catalytic hydroxylation of olefins.The polymeric reagent offers the advantages of easy and safe handling, and simple separation from the reaction medium.Generally good yields of vicinal diols have been obtained.
- Cainelli, Gianfranco,Contento, Michele,Manescalchi, Francesco,Plessi, Laura
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- Kinetics and Mechanism of the Oxidation of Unsaturated Carboxylic Acids by Methyltributylammonium Permanganate in Methylene Chloride Solutions
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The product obtained when permanganate is reduced by unsaturated carboxylic acids under anhydrous conditions is manganese(III).The rate of reaction, which is subject to acid catalysis, exhibits a Hammet ρ value of 1.11 and inverse secondary isotope effects (kH/kD = 0.96-0.98) when the hydrogens on the double bond are replaced by deuterium.The involvement of a free-radical process is indicated by the formation of polymer during the oxidation of acrylic and methacrylic acids.The reaction is believed to be initiated by formation of an organometallic complex in which the double bond is a η2 ligand on manganese.Rearrangement of this complex results in the formation of a reactive manganate(V) cyclic diester, which undergoes a rapid (free-radical) reduction to manganese(III).
- Perez-Benito, Joaquin F.,Lee, Donald G.
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p. 3239 - 3243
(2007/10/02)
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- Spiro Asymmetric Induction. 3. Synthesis of Optically Pure Syn or Anti α,β-Dihydroxy Esters by the Aldol Condensation of Chiral Glycolate Enolates
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The diastereoselectivity of the aldol condensation of the chiral glycolate enolates 1 and 2 is metaltunable, providing either syn or anti adducts 3-6.Ethanolysis of these adducts then provides any stereoisomer of the α,β-dihydroxy esters 7-10 in optically
- Pearson, William H.,Cheng, Minn-Chang
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p. 3176 - 3178
(2007/10/02)
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