- A Facile Enzyme Assisted Route to (R)- and (S)-t-Butyloxirane and related β-Amino Alcohols - Catalysts for the Enantioselective Addition of Dialkylzinc Reagents to Aldehydes
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(R) and (S)-t-butyloxirane have been prepared in high enantiomeric purity from racemic t-butyloxirane (+/-)-3 by an enzymatic route. (S)-3 has been used for the preparation of the chiral β-amino alcohols (R)- and (S)-1,2, which are catalysts for the enantioselective addition of dialkylzinc reagents to aldehydes.
- Chadha, A.,Goergens, U.,Schneider, M. P.
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Read Online
- Remote Amino Acid Recognition Enables Effective Hydrogen Peroxide Activation at a Manganese Oxidation Catalyst
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Precise delivery of a proton plays a key role in O2 activation at iron oxygenases, enabling the crucial O?O cleavage step that generates the oxidizing high-valent metal–oxo species. Such a proton is delivered by acidic residues that may either
- Costas, Miquel,Olivo, Giorgio,Vicens, Laia
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supporting information
(2021/12/27)
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- An Amphiphilic (salen)Co Complex – Utilizing Hydrophobic Interactions to Enhance the Efficiency of a Cooperative Catalyst
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An amphiphilic (salen)Co(III) complex is presented that accelerates the hydrolytic kinetic resolution (HKR) of epoxides almost 10 times faster than catalysts from commercially available sources. This was achieved by introducing hydrophobic chains that increase the rate of reaction in one of two ways – by enhancing cooperativity under homogeneous conditions, and increasing the interfacial area under biphasic reaction conditions. While numerous strategies have been employed to increase the efficiency of cooperative catalysts, the utilization of hydrophobic interactions is scarce. With the recent upsurge in green chemistry methods that conduct reactions ‘on water’ and at the oil-water interface, the introduction of hydrophobic interactions has potential to become a general strategy for enhancing the catalytic efficiency of cooperative catalytic systems. (Figure presented.).
- Solís-Mu?ana, Pablo,Salam, Joanne,Ren, Chloe Z.-J.,Carr, Bronte,Whitten, Andrew E.,Warr, Gregory G.,Chen, Jack L.-Y.
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supporting information
p. 3207 - 3213
(2021/06/01)
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- Aromatic Donor-Acceptor Interaction-Based Co(III)-salen Self-Assemblies and Their Applications in Asymmetric Ring Opening of Epoxides
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Aromatic donor-acceptor interaction as the driving force to assemble cooperative catalysts is described. Pyrene/naphthalenediimide functionalized Co(III)-salen complexes self-assembled into bimetallic catalysts through aromatic donor-acceptor interactions and showed high catalytic activity and selectivity in the asymmetric ring opening of various epoxides. Control experiments, nuclear magnetic resonance (NMR) spectroscopy titrations, mass spectrometry measurement, and X-ray crystal structure analysis confirmed that the catalysts assembled based on the aromatic donor-acceptor interaction, which can be a valuable noncovalent interaction in supramolecular catalyst development.
- Liang, Jian,Soucie, Luke N.,Blechschmidt, Daniel R.,Yoder, Aaron,Gustafson, Addie,Liu, Yu
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supporting information
p. 513 - 518
(2019/01/14)
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- OXYSTEROLS AND METHODS OF USE THEREOF
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Compounds are provided according to Formula (I): and pharmaceutically acceptable salts thereof, and pharmaceutical compositions thereof; wherein R2, R3, R4, R5, and and R6 are as defined herein. Compounds of the present invention are contemplated useful for the prevention and treatment of a variety of conditions.
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Paragraph 00402
(2018/05/16)
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- Azidolysis of epoxides catalysed by the halohydrin dehalogenase from Arthrobacter sp. AD2 and a mutant with enhanced enantioselectivity: an (S)-selective HHDH
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Halohydrin dehalogenase from Arthrobacter sp. AD2 catalysed azidolysis of epoxides with high regioselectivity and low to moderate (S)-enantioselectivity (E?=?1–16). Mutation of the asparagine 178 to alanine (N178A) showed increased enantioselectivity towards styrene oxide derivatives and glycidyl ethers. Conversion of aromatic epoxides was catalysed by HheA-N178A with complete enantioselectivity, however the regioselectivity was reduced. As a result of the enzyme-catalysed reaction, enantiomerically pure (S)-β-azido alcohols and (R)-α-azido alcohols (ee???99%) were obtained.
- Mikleu?evi?, Ana,Primo?i?, Ines,Hrenar, Tomica,Salopek-Sondi, Branka,Tang, Lixia,Elenkov, Maja Majeri?
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p. 930 - 935
(2016/09/13)
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- Epoxidation of alkenes catalyzed by some molybdenum(0) and molybdenum(IV) complexes
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Catalytic epoxidations of styrene, cyclohexene, 1-octene, and 3,3-dimethyl-1-butene have been explored utilizing a variety of molybdenum(0) and molybdenum(IV) complexes as precatalysts and tert-butylhydroperoxide (TBHP) as oxidant. The catalytic activities of the complexes MoCl4(CH3CN)2, Mo(CO)3(PTA)3 (PTA = 1,3,5-triaza-7-phosphaadamantane), Mo(CO)3(Mes), and a molybdenum(IV) calix[4]arene salt, [Et3NH][Mo{tBuC4}Cl(CH3CN)] have been investigated. The progress of reactions was monitored with reference to an internal standard by means of 1H NMR spectroscopy. Most of the complexes were found to be effective precatalysts with low catalyst loadings, giving rise to good to excellent conversion of alkenes and yield of the epoxides with the formation of minimal amount of corresponding diol and other side products. The catalytic reactions were found to be most efficient between 100 and 110 °C in minimal solvent or without added solvent.
- Acharya, Sitaram,Hanna, Tracy A.
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p. 113 - 123
(2016/02/18)
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- Total synthesis of the macrocyclic n -methyl enamides palmyrolide a and 2 s -sanctolide a
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Full details of the total syntheses of the initially reported and revised structures of the neuroprotective agent palmyrolide A are reported. The key macrocyclization step was achieved using a sequential ring-closing metathesis/olefin isomerization reaction. Furthermore, the total synthesis of the related macrolide (2S)-sanctolide A is reported. The synthesis used key elements from the synthesis of palmyrolide A, including the RCM/olefin isomerization sequence. The synthetic work described herein serves to facilitate the assignment of stereochemistry of the natural product sanctolide A and demonstrates the utility of this approach for the synthesis of macrocyclic tertiary enamide natural products.
- Wadsworth, Andrew D.,Furkert, Daniel P.,Brimble, Margaret A.
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p. 11179 - 11193
(2015/01/08)
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- Experimental investigation of the low temperature oxidation of the five isomers of hexane
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The low-temperature oxidation of the five hexane isomers (n-hexane, 2-methyl-pentane, 3-methyl-pentane, 2,2-dimethylbutane, and 2,3-dimethylbutane) was studied in a jet-stirred reactor (JSR) at atmospheric pressure under stoichiometric conditions between 550 and 1000 K. The evolution of reactant and product mole fraction profiles were recorded as a function of the temperature using two analytical methods: gas chromatography and synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). Experimental data obtained with both methods were in good agreement for the five fuels. These data were used to compare the reactivity and the nature of the reaction products and their distribution. At low temperature (below 800 K), n-hexane was the most reactive isomer. The two methyl-pentane isomers have about the same reactivity, which was lower than that of n-hexane. 2,2-Dimethylbutane was less reactive than the two methyl-pentane isomers, and 2,3-dimethylbutane was the least reactive isomer. These observations are in good agreement with research octane numbers given in the literature. Cyclic ethers with rings including 3, 4, 5, and 6 atoms have been identified and quantified for the five fuels. While the cyclic ether distribution was notably more detailed than in other literature of JSR studies of branched alkane oxidation, some oxiranes were missing among the cyclic ethers expected from methyl-pentanes. Using SVUV-PIMS, the formation of C 2-C3 monocarboxylic acids, ketohydroperoxides, and species with two carbonyl groups have also been observed, supporting their possible formation from branched reactants. This is in line with what was previously experimentally demonstrated from linear fuels. Possible structures and ways of decomposition of the most probable ketohydroperoxides were discussed. Above 800 K, all five isomers have about the same reactivity, with a larger formation from branched alkanes of some unsaturated species, such as allene and propyne, which are known to be soot precursors.
- Wang, Zhandong,Herbinet, Olivier,Cheng, Zhanjun,Husson, Benoit,Fournet, Rene,Qi, Fei,Battin-Leclerc, Frederique
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p. 5573 - 5594
(2014/08/18)
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- A flexible synthesis of C33-C39 polyketide region of apratoxin: Synthesis of natural and unnatural analogues
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A flexible synthesis sequence toward the synthesis of the polyketide region of apratoxin has been developed. The common step of the synthesis is a crotylation reaction. Stereospecific aldolisation, sulfate ring opening or Jacobsen HKR is also highlighted. This synthetic scheme led to the synthesis of several analogues. These examples raise the possibility of synthesising numerous analogues of this portion of apratoxins. Then, together with our supported strategy to synthesise the oxazoline analogue of apratoxin A, this paper opens the possibility to provide easily oxoapratoxin analogues for future SAR studies of this potent antitumoral compound.
- Gilles, Arnaud,Martinez, Jean,Cavelier, Florine
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scheme or table
p. 437 - 440
(2012/03/22)
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- NEW CHIRAL SALEN CATALYSTS AND METHODS FOR THE PREPARATION OF CHIRAL COMPOUNDS FROM RACEMIC EPOXIDES BY USING THEM
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The present invention relates to new chiral salen catalysts and the preparation method of chiral compounds from racemic epoxides using the same. More specifically, it relates to new chiral salen catalysts that have high catalytic activity due to new molecular structures and have no or little racemization of the generated target chiral compounds even after the reaction is completed and can be also reused without catalyst regeneration treatment, and its economical preparation method to mass manufacture chiral compounds of high optical purity, which can be used as raw materials for chiral food additives, chiral drugs, or chiral crop protection agents, etc., using the new chiral salen catalysts.
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Page/Page column 39
(2009/01/24)
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- Highly diastereoselective synthesis of orthoquinone monoketals through λ13-iodane-mediated oxidative dearomatization of phenols
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(Chemical Equation Presented) Versatile chiral substrates for asymmetric synthesis are formed through the spiroketalization of phenols with a chiral substituted ethanol unit O-tethered to the ortho position upon treatment with PhI-(OAc)2 (see example; TFE = 2,2,2-tri-fluoroethanol). Intermediates with a six-membered iodine(III)-containing ring (the natural localized molecular orbitals associated with the I-C6 bond are shown) undergo ligand coupling to give the spiroketals.
- Pouysegu, Laurent,Chassaing, Stefan,Dejugnac, Delphine,Lamidey, Anne-Marie,Miqueu, Karinne,Sotiropoulos, Jean-Marc,Quideau, Stephane
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supporting information; experimental part
p. 3552 - 3555
(2009/02/07)
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- Ring-expanding olefin metathesis: A route to highly active unsymmetrical macrocyclic oligomeric co-salen catalysts for the hydrolytic kinetic resolution of epoxides
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In the presence of the third generation Grubbs catalyst, the ring-expanding olefin metathesis of a monocyclooct-4-en-1-yl functionalized salen ligand and the corresponding Co(II)(salen) complex at low monomer concentrations results in the exclusive formation of macrocyclic oligomeric structures with the salen moieties being attached in an unsymmetrical, flexible, pendent manner. The TOF-MALDI mass spectrometry reveals that the resulting macrocyclic oligomers consist predominantly of dimeric to tetrameric species, with detectable traces of higher homologues up to a decamer. Upon activation under aerobic and acidic conditions, these Co(salen) macrocycles exhibit extremely high reactivities and selectivities in the hydrolytic kinetic resolution (HKR) of a variety of racemic terminal epoxides under neat conditions with very low catalyst loadings. The excellent catalytic properties can be explained in terms of the new catalyst's appealing structural features, namely, the flexible oligomer backbone, the unsymmetrical pendent immobilization motif of the catalytic sites, and the high local concentration of Co(salen) species resulting from the macrocyclic framework. This ring-expanding olefin metathesis is suggested to be a simple way to prepare tethered metal complexes that are endowed with key features - (i) a high local concentration of metal complexes and (ii) a flexible, single point of attachment to the support - that facilitate rapid and efficient catalysis when a bimetallic transition state is required.
- Zheng, Xiaolai,Jones, Christopher W.,Weck, Marcus
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p. 1105 - 1112
(2007/10/03)
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- Hydrolytic kinetic resolution of epoxides catalyzed by chromium(III)-endo, endo-2,5-diaminonorbornane-salen [Cr(III)-DIANANE-salen] complexes. Improved activity, low catalyst loading
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The hydrolytic kinetic resolution (HKR) of terminal epoxides, using chiral chromium(III)-salen catalysts based on DIANANE (endo,endo-2,5-diaminonorbornane) , was studied. A broad substrate scope was found for the chromium(III)-DIANANE catalysts, and very low loadings (down to 0.05 mol%) were needed to achieve high enantiomeric purities of both the remaining epoxides and the product diols (up to >99% ee). Besides monosubstituted epoxides, 2-methyl-2-n-pentyloxirane, which is an example for 2,2-disubstituted epoxides, could be ring-opened in an asymmetric fashion with water in the presence of an electronically tuned chromium-(III)-DIANANE complex.
- Berkessel, Albrecht,Ertuerk, Erkan
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p. 2619 - 2625
(2007/10/03)
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- Mechanistic Investigation Leads to a Synthetic Improvement in the Hydrolytic Kinetic Resolution of Terminal Epoxides
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The mechanism of the hydrolytic kinetic resolution (HKR) of terminal epoxides was investigated by kinetic analysis using reaction calorimetry. The chiral (salen)Co-X complex (X = OAc, OTs, Cl) undergoes irreversible conversion to (salen)Co-OH during the course of the HKR and thus serves as both precatalyst and cocatalyst in a cooperative bimetallic catalytic mechanism. This insight led to the identification of more active catalysts for the HKR of synthetically useful terminal epoxides. Copyright
- Nielsen, Lars P. C.,Stevenson, Christian P.,Blackmond, Donna G.,Jacobsen, Eric N.
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p. 1360 - 1362
(2007/10/03)
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- Highly selective hydrolytic kinetic resolution of terminal epoxides catalyzed by chiral (salen)CoIII complexes. Practical synthesis of enantioenriched terminal epoxides and 1,2-diols
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The hydrolytic kinetic resolution (HKR) of terminal epoxides catalyzed by chiral (salen)CoIII complex 1·OAc affords both recovered unreacted epoxide and 1,2-diol product in highly enantioenriched form. As such, the HKR provides general access to useful, highly enantioenriched chiral building blocks that are otherwise difficult to access, from inexpensive racemic materials. The reaction has several appealing features from a practical standpoint, including the use of H2O as a reactant and low loadings (0.2-2.0 mol %) of a recyclable, commercially available catalyst. In addition, the HKR displays extraordinary scope, as a wide assortment of sterically and electronically varied epoxides can be resolved to ≥ 99% ee. The corresponding 1,2-diols were produced in good-to-high enantiomeric excess using 0.45 equiv of H2O. Useful and general protocols are provided for the isolation of highly enantioenriched epoxides and diols, as well as for catalyst recovery and recycling. Selectivity factors (krel) were determined for the HKR reactions by measuring the product ee at ca. 20% conversion. In nearly all cases, krel values for the HKR exceed 50, and in several cases are well in excess of 200.
- Schaus, Scott E.,Brandes, Bridget D.,Larrow, Jay F.,Tokunaga, Makoto,Hansen, Karl B.,Gould, Alexandra E.,Furrow, Michael E.,Jacobsen, Eric N.
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p. 1307 - 1315
(2007/10/03)
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- A novel preparation of 3,3-dimethylbutyraldehyde via isomerization of 3,3-dimethyl-1-butene epoxide
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3,3-Dimethylbutyraldehyde is prepared in a highly economical manner by regioselective isomerization of the title epoxide in the presence of LiTMP.
- Katritzky, Alan R.,Fang, Yunfeng,Prakash, Indra
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p. 635 - 636
(2007/10/03)
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- Method for preparing 3, 3-dimethybutyraldehyde
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A method is disclosed for preparing 3,3-dimethylbutyraldehyde by using silica gel to isomerize 3,3-dimethyl-1,2-epoxybutane, which in turn may be prepared by oxidation of dimethylbutene. Also disclosed is a method for oxidizing dimethylbutene with dimethyldioxirane to form 3,3-dimethyl-1,2-epoxybutane. The methods provide an economical means of preparing 3,3-dimethylbutyraldehyde.
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- Method for preparing 3,3-dimethylbutyraldehyde
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A method is disclosed for preparing 3,3-dimethylbutyraldehyde by isomerization of 3,3-dimethylepoxybutane with a basic lithium salt which in turn may be prepared by oxidation of dimethylbutane. The method provides an economical means of preparing 3,3-dimethylbutyraldehyde.
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- Synthesis and catalytic epoxidation activity of terpene-derived D4-symmetric metalloporphyrins
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We report here a flexible synthesis of chiral, D4-symmetric porphyrins from cyclic ketone starting materials. Two porphyrins have been synthesized from the terpene 1-R-(+)-nopinone, obviating the need to perform a resolution. The chloromanganese derivative of one of these porphyrins is a good catalyst for the epoxidation of terminal alkenes, providing epoxides with e.e.'s of 70% with high turnover numbers. A predictive model for oxygen atom transfer in the chiral pocket is discussed.
- Barry, John F.,Campbell, Lara,Smith, Dudley W.,Kodadek, Thomas
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p. 7753 - 7776
(2007/10/03)
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- Kinetics and mechanism of the epoxidation of alkyl-substituted alkenes by hydrogen peroxide, catalyzed by methylrhenium trioxide
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Epoxidations of alkyl-substituted alkenes, with hydrogen peroxide as the oxygen source, are catalyzed by CH3ReO3 (MTO). The kinetics of 28 such reactions were studied in 1:1 CH3CN-H2O at pH 1 and in methanol. To accommodate the different requirements of these reactions, 1H-NMR, spectrophotometric, and thermometric techniques were used to acquire kinetic data. High concentrations of hydrogen peroxide were used, so that diperoxorhenium complex CH3Re(O)(η2-O2)2(H 2O), B, was the only predominant and reactive form of the catalyst. The reactions between B and the alkenes are about 1 order of magnitude more rapid in the semiaqueous solvent than in methanol. The various trends in reactivity are medium-independent. The rate constants for B with the aliphatic alkenes correlate closely with the number of alkyl groups on the olefinic carbons. The reactions become markedly slower when electron-attracting groups, such as halo, hydroxy, cyano, and carbonyl, are present. The rate constants for catalytic epoxidations with B and those reported for the stoichiometric reactions of dimethyldioxirane show very similar trends in reactivity. These findings suggest a concerted mechanism in which the electron-rich double bond of the alkene attacks a peroxidic oxygen of B. These data, combined with those reported for the epoxidation of styrene (a term intended to include related molecules with ring and/or aliphatic substituents) by B and by the monoperoxo derivative of MTO, suggest that all of the rhenium-catalyzed epoxidations occur by a common mechanism. The geometry of the system at the transition state can be inferred from these data, which suggest a spiro arrangement.
- Al-Ajlouni, Ahmad M.,Espenson, James H.
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p. 3969 - 3976
(2007/10/03)
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- Alkene Epoxidation catalysed by Camphor-derived β-Ketophosphonate Complexes of Molybdenum(VI)
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New β-ketophosphonates (L) have been prepared from (R)- or (S)-camphor with various substituents on the phosphorus atom and reacted with to form complexes .These complexes have been used to give highly active catalysts for epoxidation of alkenes by t-BuOOH.Very fast initial rates (ca. 400 catalyst turnovers in the first minute) gave way to much slower rates because the hemi-labile β-ketophosphonate is displaced by a diol ligand.In the presence of molecular sieves, the fast initial stage of the reaction is extended and for styrene, which gives low conversions followed by degradation in the absence of molecular sieves, styrene oxide can be formed with 98percent conversion and 94percent selectivity.It is demonstrated that both the t-BuOOH and the catalyst bind to the molecular sieves, the latter with loss of the β-ketophosphonate ligand.
- Clarke, Russell,Gahagan, Michael,Mackie, Raymond K.,Foster, Douglas F.,Cole-Hamilton, David J.,et al.
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p. 1221 - 1226
(2007/10/02)
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- Asymmetric microbial hydrolysis of epoxides
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Kinetic resolution of 2-mono- and 2,2-disubstituted epoxides was accomplished using epoxide hydrolases from bacterial and fungal origin by employing lyophilized whole microbial cells. In all cases investigated, the biocatalytic hydrolysis was shown to proceed with retention of configuration at the stereogenic center leading to 1,2-diols and remaining epoxides. The selectivity of the reaction was dependent on the substrate structure and the strain used with E-values ranging from low or moderate (with 2-monosubstituted epoxides) to excellent (E >100, with 2,2-disubstituted oxiranes).
- Mischitz,Kroutil,Wandel,Faber
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p. 1261 - 1272
(2007/10/03)
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- Early transition metal alkoxide complexes bearing homochiral trialkanolamine ligands
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Enantiomerically pure trialkanolamines of the formula N(CH2CHROH)3, where R = methyl (3a), cyclohexyl (3b), teri-butyl (3c), or phenyl (3d), are readily synthesized by the reaction of ammonia with 3 equiv of an enantiopure epoxide. Trialkanolamines 3a-d replace n-propanol in tri-n-propyl vanadate to afford corresponding complexes 4a-d of the formula LV=O, where L is the deprotonated trialkanolamine. Similarly, (S,S,S)-triisopropanolamine 3a reacts with Ti(OiPr)4 to produce monomeric LTi(OiPr), 7a, which upon treatment with acetyl chloride gives the chloro complex LTiCl, 7b. The later group 5 ethoxides react with 3a to produce LM(OEt)2 (M = Nb, Ta). Partial hydrolysis of the Nb and Ta derivatives produces tetrameric μ-oxo-bridged structures which retain the trialkanolamine ligands. In all complexes the transition metal resides in a highly asymmetric environment, suggesting that this class of complexes may find use in the field of asymmetric catalysis. The X-ray crystal structures of complexes 4c and 7b are reported.
- Nugent, William A.,Harlow, Richard L.
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p. 6142 - 6148
(2007/10/02)
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- A CATALYTIC ENANTIOSELECTIVE SYNTHESIS OF CHIRAL MONOSUBSTITUTED OXIRANES
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A new catalytic enentioselective synthesis of monosubstituted oxiranes has been developed from achiral trichloromethyl ketones by (a) enentioselective carbonyl reduction, (b) selective bis-dechlorination and (c) base-induced ring closure of the resulting chlorohydrins.
- Corey, E. J.,Helal, Christopher J.
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p. 5227 - 5230
(2007/10/02)
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- Kinetic Resolution of Racemic β-Hydroxy Amines by Enantioselective N-Oxide Formation
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Kinetic resolution of racemic β-hydroxy amines with a t-butyl substituent was attained in high optical yield by asymmetric oxidation.
- Hayashi, Masahiko,Okamura, Fumie,Toba, Taketo,Oguni, Nobuki,Sharpless, K. Barry
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p. 547 - 548
(2007/10/02)
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- A High Activity Molybdenum containing Epoxidation Catalyst and its Use in Regioselective Epoxidation of Polybutadiene
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MoO2Cl2 is a highly active catalyst for the epoxidation of alkenes by ButOOH; for polybutadiene containing cis-1,4-, trans-1,4-, and 1,2-polymerised units, very high selectivity to the backbone double bonds is observed.
- Gahagan, Michael,Iraqi, Ahmed,Cupertino, Domenico C.,Mackie, Raymond K.,Cole-Hamilton, David J.
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p. 1688 - 1690
(2007/10/02)
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- Method for the isomerization of oxiranes
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The method for the isomerization of oxiranes of the general formula: STR1 wherein R1 and R3 are hydrogen; R2 is alkyl or alkylene groups of 3 to 26 carbon atoms or the phenyl group which may also be substituted, and R4 is hydrogen or alkyl from 1 to 26 carbon atoms and in which the carbon atoms of the epoxy ring can also form components of a cyclic system, wherein as a catalyst there is used alkali iodide and a polyethyleneglycol with an average mol mass of 400 to 10,000 with a boiling point, preferably above the boiling point of the carbonyl compounds that are formed.
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- Catalytic Asymmetric Cyclization of Some Bromohydrins with Chiral Cobalt Complex
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Asymmetric cyclization of a variety of bromohydrins with base was examined in the presence of an optically active cobalt(salen) type complex.Optically active oxiranes of modest optical purities were obtained. erythro-3-Bromo-2-butanol and threo-3-bromo-2-butanol were cyclized similarly, and only trans-2,3-dimethyloxirane and cis-2,3-dimethyloxirane were obtained, respectively, indicating that the cyclization of bromohydrin proceeds by complete SN2 type reaction.
- Takeichi, Tsutomu,Takakura, Teruo,Ishimori, Michihiro,Tsuruta, Teiji
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p. 603 - 605
(2007/10/02)
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- Diastereoselectivity in the Diels-Alder Reactions of Thioaldehydes
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The Diels-Alder reaction of thioaldehydes with cyclopentadiene occurs with a preference for the endo isomer.The highest selectivity is observed for thioaldehydes RCHS where R is a bulky group such as tert-butyl or isopropyl.Thioaldehydes having α-alkoxy, acetoxy, or siloxy substituents also react with useful endo selectivity.Secondary orbital overlap is a small factor in these reactions since α-oxo thioaldehydes react with relatively low endo selectivity.Steric effects are primarily responsible for the endo preferences observed.The Diels-Alder reactions of chiral α-oxygen substituted thioaldehydes also occur with useful thioformyl face selectivity.A Cornforth transition state 5 is most likely for the selectivity observed for α-alkoxy or acetoxy thioaldehydes, but the α-hydroxy analogue 23 reacts with the opposite facial preference.The highest face selectivity is obtained with the acetonide of thioglyceraldehyde, generated by photolysis of the phenacyl sulfide 15b.
- Vedejs, E.,Stults, J. S.,Wilde, R. G.
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p. 5452 - 5460
(2007/10/02)
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- Synthesis and Insecticidal Activity of Oxazaphospholidines, Oxathiaphospholanes, and Thiazaphospholidines
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Fifty-five new five-membered cyclic organophosphorus compounds including oazaphospholidines, thiazaphospholidines, and oxathiaphospholanes were synthesized, which have substituents at 4- or/and 5-positions besides at the 2-position.The thiazaphospholidines showed the highest insecticidal activity followed by oxathiaphospholanes and oxazaphospholidines.The position preference of substituents in insecticidal activity was most obvious in the oxazaphospholidines.It was preferable for insecticidal activity to have the substituent near the more basic atom: the 4-position for thiazaphospholidine and oxazaphospholidine, the 5-position for oxathiaphospholane, with the exception of 4- or 5-phenyl oxazaphospholidine.
- Wu, Shao-Yong,Hirashima, Akinori,Takeya, Ryuko,Eto, Morifusa
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p. 2911 - 2918
(2007/10/02)
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- USING THE COMPARISON OF STERIC VERSUS ELECTRONIC EFFECTS TO INFER MECHANISTIC INFORMATION IN STEPWISE ELECTROPHILIC ADDITION REACTIONS INVOLVING THREE-MEMBERED CYCLIC INTERMEDIATES
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Correlations of IP's versus relative reactivities or formation constants of reactions of alkenes with ArSCl, MeCO3H, Ag(1+), or HgCl2 reveal that complexation reactions show steric dependence, that additions with the first step rate-determining are sterically independent, and that those with the second step rate-determining are sterically dependent.
- Nelson, Donna J.,Soundararajan, Raman
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p. 6207 - 6210
(2007/10/02)
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- Epoxidation by Dimethyldioxirane: Electronic and Steric Effects
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The reaction of dimethyldioxirane (1) with a series of di- and monosubstituted alkenes 2-17 produced the corresponding epoxides in high yield.A kinetic study of the epoxidation of 2-17 by 1 in dried acetone showed the reaction to be of the first order with respect to both alkene and dioxirane.For certain cis/trans-dialkylalkenes, the cis compounds were found to be of ca. 10-fold greater reactivity than the corresponding trans isomers.However, cis/trans pairs of alkenes with phenyl substituents were found to be of similar reactivity.A kinetic study on the reaction of a series of substituted styrenes yielded an excellent LFER with a ρ value of -0.90.Addition of water to dioxirane reactions in acetone increased the observed rates of epoxidation.However, a tertiary allylic alcohol was found to undergo epoxidation slower than expected.The mechanistic implications of the results are discussed.
- Baumstark, A. L.,Vasquez, P. C.
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p. 3437 - 3439
(2007/10/02)
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- Asymmetric Synthesis Using Chirally Modified Borohydrides. Part 3. Enantioselective Reduction of Ketones and Oxime Ethers with Reagents Prepared from Borane and Chiral Amino Alcohols
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The asymmetric reduction of aromatic and aliphatic ketones, halogeno ketones, keto esters, and ketone oxime ethers with reagents prepared from borane and chiral amino alcohols has been investigated.When α,α-diphenyl-β-amino alcohols, such as (2S,3R)-(-)-2-amino-3-methyl-1,1-diphenylpentanol (2d), were used as a chiral auxiliary, very high enantioselectivities (ca. 90percent e.e.) were obtained in the reduction of various ketones and oxime ethers.
- Itsuno, Shinichi,Nakano, Michio,Miyazaki, Koji,Masuda, Hirofumi,Ito, Koichi,et al.
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p. 2039 - 2044
(2007/10/02)
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- Mechanism of Epoxidation of Norbornene with α-Hydroperoxy Diazenes
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Thermolysis of α-hydroperoxy diazenes 1a-1c (Me2C(OOH)N=NR: 1a, R = CH2CF3; 1b, R = CH2CH2OCH3; 1c, R = CH2CH2OC6H5) at 50 deg C in benzene containing norbornene or in neat norbornene affords exo-(2R)-norbornane and exo-norbornene epoxide as major products and exo,exo-(2R)-3-hydroxynorbornane as a minor product.The reaction kinetics and the effects of deuteration of the hydroperoxy function on the distribution of products points to a radical chain process for the hydroalkylation and for the epoxidation.The other major product is formed by a competitive radical chain reaction.
- Osei-Twum, Emmanuel Y.,Warkentin, John
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p. 4725 - 4729
(2007/10/02)
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- The Efficiency of Benzil-Sensitized Photoepoxidation: A Correction
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Photosensitized epoxidation of norbornene by benzil leads to about two epoxide molecules or less per diketone molecule consumed, not the larger numbers previously reported.It is not necessary to postulate a chain mechanism for this epoxidation, although side reactions still complicate the process in many cases.
- Bartlett, Paul D.,Roof, Antonius A.M.,Shimizu, Nobujiro
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p. 3130 - 3131
(2007/10/02)
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- Process for preparing aldehydes from oxirane compounds
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Aldehydes are prepared by reacting an oxirane compound with hydrogen peroxide in the presence of a boron compound.
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