- SYN REGIOSELECTIVITY OF THE HYDROPEROXIDATION OF CYCLO-ALKENES WITH SINGLET OXYGEN
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The regioselectivity of hydroperoxidation of 1-alkylcycloalkenes is rationalized in terms of the formation of a zwitterionic peroxide.
- Jefford, Charles W.,Rimbault, Christian G.
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- Demystifying Cp2Ti(H)Cl and Its Enigmatic Role in the Reactions of Epoxides with Cp2TiCl
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The role of Cp2Ti(H)Cl in the reactions of Cp2TiCl with trisubstituted epoxides has been investigated in a combined experimental and computational study. Although Cp2Ti(H)Cl has generally been regarded as a robust species, its decomposition to Cp2TiCl and molecular hydrogen was found to be exothermic (ΔG = -11 kcal/mol when the effects of THF solvation are considered). In laboratory studies, Cp2Ti(H)Cl was generated using the reaction of 1,2-epoxy-1-methylcyclohexane with Cp2TiCl as a model. Rapid evolution of hydrogen gas was demonstrated, indicating that Cp2Ti(H)Cl is indeed a thermally unstable molecule, which undergoes intermolecular reductive elimination of hydrogen under the reaction conditions. The stoichiometry of the reaction (Cp2TiCl:epoxide = 1:1) and the quantity of hydrogen produced (1 mol per 2 mol of epoxide) is consistent with this assertion. The diminished yield of allylic alcohol from these reactions under the conditions of protic versus aprotic catalysis can be understood in terms of the predominant titanium(III) present in solution. Under the conditions of protic catalysis, Cp2TiCl complexes with collidine hydrochloride and the titanium(III) center is less available for "cross-disproportionation" with carbon-centered radicals; this leads to byproducts from radical capture by hydrogen atom transfer, resulting in a saturated alcohol.
- Gordon, Jonathan,Hildebrandt, Sven,Dewese, Kendra R.,Klare, Sven,Gans?uer, Andreas,Rajanbabu,Nugent, William A.
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- Oxygen Quenching of Electronically Excited Hexanuclear Molybdenum and Tungsten Halide Clusters
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Quenching of the electronically excited Y6(2-) (M = Mo(II), W(II), X,Y = Cl,Br,I) ions by molecular oxygen has been investigated.Stern- Volmer analysis of emission intensity and lifetime data reveals that the rate constants for oxygen quenching of the Y6(2-) ions are similar (kqobs = 8.1(37) * 1E7 M-1 s-1) with the exception of the Y6(2-) clusters, which exhibit significantly greater quenching rates (kqobs = 2.1(5) * 1E9 M-1 s-1).Photosensitized oxidation of 1-methylcyclohexene and 1,2-dimethylcyclohexene by all Y6(2-) clusters yields products expected for the reaction of the olefins with singlet oxygen.No evidence of radical autooxidation products were detected.However, the measured quantum yields for the photooxidation of 2,3-diphenyl-p-dioxene by only the Y6(2-) (M = no W; X = no I) clusters are in agreement with the values calculated from a kinetic scheme involving the exclusive production of singlet oxygen by direct energy transfer; observed quantum yields of Y6(2-) -photosensitized reactions are not consistent with this scheme.One explanation for the enhanced oxygen quenching rates of the Y6(2-) excited states (Y6(2-)(excit)) and anomalous observed quantum yields is the contribution of an electron-transfer pathway to the quenching reaction.Transient absorption spectra for the reaction between W6I14(2-)(excit.) and oxygen, however, do not display transients attributable to electron-transfer products.Accordingly, we ascribe the enhanced quenching rate of Y6(2-)(excit.) by oxygen to greater adiabaticity of the energy-transfer reactions of these ions as compared to their homologous cluster counterparts.The absence of an electron-transfer contribution to the Y6(2-)-cluster photosensitized production of 1O2 (Y6(2-)(excit.) + O2 -> Y6(1-) + O2(1-) -> Y6(2-) + 1O2) parallels the results observed for the photosensitized production of 1O2 by RuL3(2+) (L = plypyridyl) systems, which also produce singlet oxygen exclusively by energy transfer despite the existence of potential electron-transfer pathway.
- Jackson, Julie A.,Turro, Claudia,Newsham, Mark D.,Nocera, Daniel G.
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- Photoassisted Oxygenation of Olefins: An Exchanged Zeolite as a Heterogenous Photosensitizer
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Ru(bpy)3(2+) exchanged into zeolite Y acts as an effective, heterogeneous singlet oxygen sensitizer.The photogenerated singlet oxygen freely diffuses to solution where it reacts with normal selectivity.The photocatalyst has high catalytic turnover, and it
- Pettit, Thomas L.,Fox, Marye Anne
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- CHOLINE METABOLISM INHIBITORS
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The present disclosure relates to compounds, compositions and methods for inhibiting choline metabolism, e.g., conversion of choline to trimethylamine. Disclosed herein are compounds, compositions, and methods for inhibiting choline metabolism, e.g., conversion of choline to TMA. Also disclosed herein are compounds, methods and compositions for inhibiting choline metabolism by gut microbiota resulting in reduction in the formation of trimethylamine (TMA) and trimethylamine N-oxide (TMAO).
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Page/Page column 50; 104
(2020/07/05)
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- Combining Photo-Organo Redox- and Enzyme Catalysis Facilitates Asymmetric C-H Bond Functionalization
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In this study, we combined photo-organo redox catalysis and biocatalysis to achieve asymmetric C–H bond functionalization of simple alkane starting materials. The photo-organo catalyst anthraquinone sulfate (SAS) was employed to oxyfunctionalise alkanes to aldehydes and ketones. We coupled this light-driven reaction with asymmetric enzymatic functionalisations to yield chiral hydroxynitriles, amines, acyloins and α-chiral ketones with up to 99 % ee. In addition, we demonstrate functional group interconversion to alcohols, esters and carboxylic acids. The transformations can be performed as concurrent tandem reactions. We identified the degradation of substrates and inhibition of the biocatalysts as limiting factors affecting compatibility, due to reactive oxygen species generated in the photocatalytic step. These incompatibilities were addressed by reaction engineering, such as applying a two-phase system or temporal and spatial separation of the catalysts. Using a selection of eleven starting alkanes, one photo-organo catalyst and 8 diverse biocatalysts, we synthesized 26 products and report for the model compounds benzoin and mandelonitrile > 97 % ee at gram scale.
- Zhang, Wuyuan,Fueyo, Elena Fernandez,Hollmann, Frank,Martin, Laura Leemans,Pesic, Milja,Wardenga, Rainer,H?hne, Matthias,Schmidt, Sandy
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supporting information
p. 80 - 84
(2019/01/04)
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- Bimetallic Radical Redox-Relay Catalysis for the Isomerization of Epoxides to Allylic Alcohols
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Organic radicals are generally short-lived intermediates with exceptionally high reactivity. Strategically, achieving synthetically useful transformations mediated by organic radicals requires both efficient initiation and selective termination events. Here, we report a new catalytic strategy, namely, bimetallic radical redox-relay, in the regio- and stereoselective rearrangement of epoxides to allylic alcohols. This approach exploits the rich redox chemistry of Ti and Co complexes and merges reductive epoxide ring opening (initiation) with hydrogen atom transfer (termination). Critically, upon effecting key bond-forming and -breaking events, Ti and Co catalysts undergo proton transfer/electron transfer with one another to achieve turnover, thus constituting a truly synergistic dual catalytic system.
- Ye, Ke-Yin,Mccallum, Terry,Lin, Song
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supporting information
(2019/06/24)
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- Palladium-Catalyzed Carbocyclizations of Unactivated Alkyl Bromides with Alkenes Involving Auto-tandem Catalysis
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The development of a general catalytic system for the palladium-catalyzed carbocyclization of unactivated alkyl bromides with alkenes is described. This approach uses a commercially available bisphosphine ligand and avoids the use of carbon monoxide atmosphere present in prior studies involving alkyl iodides. Detailed mechanistic studies of the transformation are performed, which are consistent with auto-tandem catalysis involving atom-transfer radical cyclization followed by catalytic dehydrohalogenation. These studies also suggest that reactions involving alkyl iodides may proceed through a metal-initiated, rather than metal-catalyzed, radical chain process.
- Venning, Alexander R. O.,Kwiatkowski, Megan R.,Roque Pe?a, Joan E.,Lainhart, Brendan C.,Guruparan, Akil A.,Alexanian, Erik J.
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supporting information
p. 11595 - 11600
(2017/08/30)
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- Copper-catalysed conjugate addition of grignard reagents to 2-methylcyclopentenone and sequential enolate alkylation
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The copper/Rev-JosiPhos-catalysed asymmetric conjugate addition of Grignard reagents to 2-methylcyclopentenone (1) provides 2,3-disubstituted cyclopentanones in high yields and enantioselectivities, and good diastereoselectivities. Reaction of the in situ
- Calvo, Beatriz C.,Madduri, Ashoka V. R.,Harutyunyan, Syuzanna R.,Minnaard, Adriaan J.
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p. 2061 - 2069
(2014/07/07)
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- Improved robustness of heterogeneous Fe-non-heme oxidation catalysts: A catalytic and EPR study
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There is currently a rarity in production and in-depth catalytic study of heterogeneous non-heme Fe catalysts. Herein, two heterogeneous catalysts have been synthesized by covalent grafting of non-heme Fe-complexes, DPEIFe IIICl and HFEIFeIIICl, on SiO2. The catalytic performance of the obtained DPEIFeIII@SiO2 and HFEIFe III@SiO2 materials has been systematically studied for catalytic oxidation of cyclohexene. The catalytic data show that the present non-heme Fe catalysts are functional and can achieve higher activity compared to other non-heme Fe reported so far in the literature. Importantly, the heterogeneneous catalysts show a remarkable robustness and improved oxidative stability vs. the homogeneous ones. Studies by UV-vis and EPR reveal a common mechanistic pattern: CH3CN interacts with the Fe-atom promoting the formation of a Low-Spin (S = 1/2) intermediate, in the presence of H 2O2, probably a FeIII-OOH hydroperoxide. The role of radical intermediates was investigated in detail by spin-trapping techniques. Finally, taking into account the nature of oxidation products, a consistent catalytic mechanism, valid for both homogeneous and heterogeneous catalysts, is discussed.
- Bilis,Stathi,Mavrogiorgou,Deligiannakis,Louloudi
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p. 376 - 389
(2014/01/06)
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- Operation of the boomerang mechanism in olefin metathesis reactions promoted by the second-generation Hoveyda catalyst
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A long-standing question in olefin metathesis centers on whether the release-return (boomerang) mechanism contributes to the productivity of Hoveyda-class catalysts. According to this mechanism, a molecule of o-isopropoxystyrene (A) is liberated during catalyst initiation, but recaptures the active catalyst following metathesis. The relevance of this pathway for the second-generation Hoveyda catalyst HII was assessed in metathesis of 1,1-and 1,2-disubstituted olefins. Crossover studies with 13C-labeled A*, as well as competition experiments involving ring-closing or cross metathesis (RCM, CM) in the presence of A (equimolar with HII) indicated rapid reuptake of styrenyl ether. The crossover studies indicated highly efficient catalyst initiation, with the entire catalyst charge being activated before metathesis was complete. In a comparative study involving CM of anethole with methyl acrylate, sustained activity was shown for HII, whereas the second-generation Grubbs catalyst GII was rapidly deactivated. These data demonstrate that the release-return mechanism is indeed operative for HII in these demanding metathesis reactions, and that facile shuttling from a protected recapture cycle into the productive metathesis cycle contributes to the superior performance of HII relative to GII.
- Bates, Jennifer M.,Lummiss, Justin A. M.,Bailey, Gwendolyn A.,Fogg, Deryn E.
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p. 2387 - 2394
(2014/07/21)
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- Intramolecular carbonickelation of alkenes
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The efficiency of the intramolecular carbonickelation of substituted allylic ethers and amines has been studied to evaluate the influence of the groups borne by the double bond on this cyclization. The results show that when this reaction takes place, it affords only the 5-exo-trig cyclization products, viz. dihydrobenzofurans or indoles. Depending on the tethered heteroatom (O or N), the outcome of the cyclization differs. While allylic ethers are relatively poor substrates that undergo a side elimination and need an intracyclic double bond to proceed, allylic amines react well and afford indoline and indole derivatives. Finally, the synthesis of the trinuclear ACE core of a morphine-like skeleton was achieved by using NiBr2bipy catalysis.
- Lhermet, Rudy,Durandetti, Muriel,Maddaluno, Jacques
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supporting information
p. 710 - 716
(2013/06/05)
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- Stereo- and regioselectivity in the P450-catalyzed oxidative tandem difunctionalization of 1-methylcyclohexene
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The selective partial oxidation of small non-functionalized molecules using biocatalysis based on P450 monooxygenases is known to be difficult due to the expected poor regio- and stereoselectivity, but in this study it was nevertheless attempted. 1-Methyl
- Roiban, Gheorghe-Doru,Agudo, Rubén,Reetz, Manfred T.
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p. 5306 - 5311
(2013/07/05)
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- Highly ordered mesoporous zirconia-polyoxometalate nanocomposite materials for catalytic oxidation of alkenes
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A series of well-ordered mesoporous ZrO2-based heteropoly acid nanocomposite frameworks has been prepared through a surfactant-assisted sol-gel copolymerization route. The pore walls of these materials consist of nanocrystalline tetragonal ZrO2 and Keggin-type 12-phosphomolybdic acid (PMA) components with different PMA loadings, i.e. 12, 22 and 37 wt%. Small angle X-ray scattering, high-resolution TEM and N2 physisorption measurements indicated mesoporous property in hexagonal p6mm symmetry with large internal BET surface areas and narrow-sized pores. The incorporated PMA clusters preserve intact their Keggin structure into the mesoporous frameworks according to EDX, FT-IR and diffuse-reflectance UV/vis/NIR spectroscopy. The obtained ZrO2-PMA nanocomposites demonstrated great application potential in oxidative catalysis, exhibiting exceptional stability and catalytic activity in oxidation of alkenes using hydrogen peroxide as oxidant. The Royal Society of Chemistry 2011.
- Armatas, Gerasimos S.,Bilis, Georgios,Louloudi, Maria
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experimental part
p. 2997 - 3005
(2011/10/05)
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- Glycol-modified molybdate catalysts for efficient singlet oxygen generation from hydrogen peroxide
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Pretreatment of molybdate-exchanged layered double hydroxides in polyalcohols such as ethylene glycol affords heterogeneous catalysts showing largely improved oxidant efficiency compared to the unmodified materials. The Royal Society of Chemistry.
- Wahlen, Joos,De Vos, Dirk,Jary, Walther,Alsters, Paul,Jacobs, Pierre
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p. 2333 - 2335
(2008/02/11)
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- Confined space-controlled hydroperoxidation of trisubstituted alkenes adsorbed on pentasil zeolites
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Photosensitized oxidation of trialkylalkenes 2-methyl-2-pentene (1), 1-methylcyclohexene (2), trans-3-methyl-2-pentene (3), cis-3-methyl-2-pentene (4), and 2-methyl-2-butene (5) included in the internal framework of Na-ZSM-5 zeolites was investigated. The zeolite samples having adsorbed the alkenes were suspended in isooctane, and the sensitizer, tetraphenylporphyrin (TPP), was dissolved in the solution. Singlet oxygen produced in the solution diffused into the internal framework of the zeolites and reacted with alkenes. For all the substrates studied, the ene-type allylic hydroperoxides were obtained in a highly regioselective manner. The regiochemistry for 1-4 in favor of the allylic hydrogen abstraction from the largest substituents is in contrast to their photooxidation within the dye-supported zeolite Na-Y, where the secondary hydroperoxides are preferentially produced. The tight confinement of the alkenes within the narrow channels of the ZSM-5 zeolites is likely to be responsible for this selectivity.
- Chen, Yu-Zhe,Wu, Li-Zhu,Zhang, Li-Ping,Tung, Chen-Ho
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p. 4676 - 4681
(2007/10/03)
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- Efficient photocatalytic oxidation of cycloalkenes by dihydroxo(tetraphenylporphyrinato)-antimony supported on silica gel under visible light irradiation
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In order to develop a photocatalyst operating under visible light irradiation, silica gel-supported dihydroxo(tetraphenylporphyrinato)antimony (V) complex, [SbTPP(OH)2]+/SiO2, was prepared. The photocatalytic oxidation of cycloalkenes with oxygen molecule was performed on [SbTPP(OH)2]+/SiO2 particles under irradiation of fluorescent light. The photocatalytic oxidation of cycloalkenes gave the corresponding cis-1,2-epoxycycloalkane, 2-cycloalkene-1-ol, and trans-1,2-cycloalkanediol.
- Shiragami, Tsutomu,Makise, Ryu-Ichi,Inokuchi, Yousuke,Matsumoto, Jin,Inoue, Haruo,Yasuda, Masahide
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p. 736 - 737
(2007/10/03)
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- Efficient palladium-catalyzed nucleophilic addition of triorganoindium reagents to carbocyclic derivatives
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Palladium (0)-catalyzed allylic substitution reactions employing triorganoindium reagents have been investigated. In situ generated vinyl- and arylindiums react with substituted and unsubstituted cyclohex-2-enyl esters in the presence of 1-3 mol % Pd2(dba)3 to produce vinyl- or arylcyclohexenes in moderate to excellent yields. The stereoselectivity of this process was also examined, and evidence is presented that the reaction proceeds with inversion of stereochemical configuration.
- Baker, Lucas,Minehan, Thomas
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p. 3957 - 3960
(2007/10/03)
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- (2-hydroxy)ethyl-thioureas useful as modulators of alpha2B adrenergic receptors
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Compounds of formula (i) and of formula (ii) wherein the symbols have the meaning disclosed in the specification, specifically or selectively modulate α2B and/or α2C adrenergic receptors in preference over α2A adrenergic receptors, and as such are useful for alleviating chronic pain and allodynia and have no or only minimal cardivascular and/or sedatory activity.
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- Synthetic studies towards (+)-Dihydroampullicin. Michael addition of N-Boc-2-(tert-butyldimethylsiloxy)-3-methyl-pyrrole to α-methylene lactones
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The Michael addition of N-(tert-butoxycarbonyl)-2-(tert-butyldimethylsiloxy)-3-methyl-pyrrole (4) to several α-methylene lactones catalyzed by fluoride ions yielded the corresponding homologated products (26-30) with good yields. Application of this react
- Marcos,Redero,Bermejo
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p. 8451 - 8455
(2007/10/03)
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- Efficient and recyclable monomeric and dendritic Ru-based metathesis catalysts
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Several highly active, recoverable and recyclable Ru-based metathesis catalysts are presented. The crystal structure of Ru complex 5, beating a 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene and styrenyl ether ligand is disclosed. The heterocyclic ligand significantly enhances the catalytic activity, and the styrenyl ether allows for the easy recovery of the Ru complex. Catalyst 5 promotes ring-closing metathesis (RCM) and the efficient formation of various trisubstituted olefins at ambient temperature in high yield within 2 h; the catalyst is obtained in >95% yield after silica gel chromatography and can be used directly in subsequent reactions. Tetrasubstituted olefins can also be synthesized by RCM reactions catalyzed by 5. In addition, the synthesis and catalytic activities of two dendritic and recyclable Ru-based complexes are disclosed (32 and 33). Examples involving catalytic ring-closing, ring-opening, and cross metatheses are presented where, unlike monomer 5, dendritic 33 can be readily recovered.
- Garber, Steven B.,Kingsbury, Jason S.,Gray, Brian L.,Hoveyda, Amir H.
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p. 8168 - 8179
(2007/10/03)
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- Asymmetric Ring-Closing Metathesis Catalyzed by Chiral Molybdenum Alkylidene Complexes
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Kinetic resolution was observed in ring-closing metathesis of racemic dienes catalyzed by the newly developed chiral molybdenum alkylidene complexes (R,R)-Mo(CHCMe2Ph)(NAr)(TBEC) 1 (Ar = 2,6-i-Pr2C6H3, TBEC = 2′,2′ ,2″,2″-tetrakis(trifluoromethyl)-1,2-bis(2′-hydroxyethyl) cyclopentane) and (R,R)-Mo(CHCMe2Ph)(NAr)(TBEH) 2 (Ar - 2,6-i-Pr2C6H3, TBEH = 2′,2′,2″,2″-tetrakis(trifluoro- methyl)-1,2-bis(2′-hydroxyethyl)cyclohexane). In the case of a prochiral symmetric triene substrate, optically active cyclized product was formed by catalytic ring-closing metathesis with 1, which opens the possibility of a new version of two-directional synthesis. Although the observed enantiomeric excesses were modest to low, this data demonstrates the feasibility of asymmetric induction by chiral alkylidene catalysts in ring-closing metathesis.
- Fujimura, Osamu,Grubbs, Robert H.
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p. 824 - 832
(2007/10/03)
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- Synthesis of Alkyl Allylic Ethers and 1,3-Dienes by the Reaction of Conjugated Cyclohexenones with Sodium Borohydride-Cerium(III) Chloride in Aliphatic Alcohols
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The reaction of conjugated cyclohexenones 1,3-containing 3-methyl-2-en-1-one moiety with NaBH4/CeCl3*7H2O in primary aliphatic alcohols (MeOH, EtOH, n-PrOH) affords alkyl allylic ethers and 1,3-dienes.In isopropanol or tert-butanol only 1,3-dienes are obtained.Ketones 4-6 containing 2-methyl-2-en-1-one moiety are reduced under the same conditions to the corresponding allylic alcohols irrespective of the alcohol used.Key words: reduction, α,β-unsaturated ketones, allylic alcohols, alkyl allylic ethers, sodium borohydride, cerium(III) chloride
- Uzarewicz, A.,Dresler, R.
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p. 1655 - 1658
(2007/10/03)
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- Preparation of Allylic Acetates from Simple Alkenes by Palladium(II)-Catalyzed Acetoxylation
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The scope and limitations of palladium-catalyzed allylic acetoxylation has been investigated, using benzoquinone-manganese dioxide as the reoxidation system.Unsubstituted cycloalkenes gave good to excellent yields of allylic acetates.Total yields were also good for many substituted cycloalkenes and for linear alkenes, but these substrates generally gave several isomeric acetates.The exploratory mechanistic studies show that the acetoxylation can proceed via both 1,2-acetoxypalladation and η3-allylpalladium complex formation.The keen balance between these processes depends on the structure of the alkene.
- Hansson, Sverker,Heumann, Andreas,Rein, Tobias,Akermark, Bjoern
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p. 975 - 984
(2007/10/02)
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- Palladium-catalyzed allylic acetoxylation: an exploratory study of the influence of added acids
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In order to investigate the possibility of improving the selectivity in palladium-catalyzed acetoxylation of substituted cycloalkenes and linear alkenes, the influence of added strong acids has been studied.It was found that the product selectivity can be increased in some cases, but also that side reactions lower the total yields when trifluoroacetic or stronger acids are used.The improvement of the selectivity may possibly be due to a change in mechanism for the acetoxylation.
- Akermark, Bjoern,Hansson, Sverker,Rein, Tobias,Vagberg, Jan,Heumann, Andreas,Baeckvall, Jan-Erling
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p. 433 - 444
(2007/10/02)
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- Preparation of chiral allylic alcohols using Rhizopus nigricans. Use of the Harada-Nakanishi exciton chirality method for verifying configurational assignments of allylic alcohols
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A series of (R) acyclic and cyclic allylic alcohols was prepared by enantioselective hydrolysis of acetates using Rhizopus nigricans.The configurations of the alcohols formed were established by chemical methods and, in the case of 1,2-benzocyclohepta-1,3
- Ito, Satoru,Kasai, Masaji,Ziffer, Herman,Silverton, J.V.
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p. 574 - 582
(2007/10/02)
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- Anti-Markovnikov Addition of Nucleophiles to a Non-conjugated Olefin via Single Electron Transfer Photochemistry
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Nucleophilic solvent has been added regiospecifically in an anti-Markovnikov manner to a simple non-conjugated olefin, 1-methylcyclohexene, through single electron transfer induced photochemistry using the 1-cyanonaphthalene - biphenyl pair for achieving photooxidation.
- Gassman, Paul G.,Bottorff, Kyle J.
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p. 5449 - 5452
(2007/10/02)
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- Lithium Aluminium Hydride Partially Decomposed with (-)-N-Methylephedrine and 2-Alkylaminopyridine: An Improved Chiral Hydride Useful for the Practical Asymmetric Reduction of Achiral Cyclic Ketones
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The title chiral hydride was found to reduce various achiral cyclic ketons, giving the corresponding optically active cyclic (R)-alcohols in high optical (73-98percent) yields.The development of the improved chiral hydride and some characteristics of the reagent are also described.Keywords - asymmetric reduction; lithium aluminium hydride; (-)-N-methylephedrine; 2-alkylaminopyridine; 2-cyclohexen-1-one; achiral cyclic ketone; optically active cyclic alcohol
- Kawasaki, Motoji,Suzuki, Yasutaka,Terashima, Shiro
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- INFLUENCE OF CYCLODEXTRINS ON THE SODIUM BOROHYDRIDE REDUCTION OF CYCLOHEXENONES
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The sodium borohydride reduction of cyclohexenones in aqueous medium is changed in the presence of cyclodextrins. β-cyclodextrin favours the 1,4-reduction over the 1,2-reduction whereas α-cyclodextrin favours the 1,2-reduction.
- Chenevert, Robert,Chamberland, Daniel
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p. 1117 - 1118
(2007/10/02)
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- SODIUM BOROHYDRIDE REDUCTION OF CYCLOHEXENONES IN THE PRESENCE OF AMYLOSE
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Amylose can alter the regioselectivity of the sodium borohydride reduction of cyclohexenones.Addition of amylose favours the simple carbonyl reduction over the conjugate reduction.
- Chenevert, Robert,Ampleman, Guy
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p. 1489 - 1490
(2007/10/02)
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- DICYANOANTHRACENE SENSITIZED PHOTO-OXYGENATION OF OLEFINS. ELECTRON TRANSFER AND SINGLET OXYGEN MECHANISMS
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Cyanoaromatic sensitizers, in particular 9,10-dicyanoanthracene (DCA), sensitize the photooxygenation of olafins by two distinct mechanisms.In the case of aryl substituted olefins (OL), which react extremely slowly (if at all) with singlet oxygen, the reaction proceeds by way of electron transfer to produce discrete radical ions (DCA-. and OL+.).In the presence of oxygen, this ionic process results, ultimately, in the cleavage of the olefin to carbonyl compounds along with production of some epoxide and other minor byproducts.Aromatic ethers can interfere with this process by reducing the radical cation by electron transfer, resulting in net quenching of the reaction.With simple alkenes the DCA-sensitized reaction takes a different course, producing hydroperoxide products with distributions which are very similar to those obtained with the singlet oxygen ene reaction.Careful study has shown that this reaction does, indeed, proceed by way of singlet oxygen, which is produced by at least two mechanism: (1) enhanced intersystem crossing, in which 1DCA is quenched by interaction with the olefin, leading to a low yield of 3DCA, which subsequently reacts with oxygen to produce singlet oxygen; and (2) direct reaction of 1DCA with oxygen.At limiting high oxygen concentration, this process produces 2 mol of singlet oxygen for each mol of 1DCA quenched; the mechanism involves energy transfer to produce 3DCA and 1 mol of singlet oxygen; the 3DCA reacts again with oxygen to produce a second mol of singlet oxygen.The complex kinetic behaviour of simple olefins in the presence of DCA can be satisfactorily rationalized by these mechanisms.
- Foote, Christopher S.
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p. 2221 - 2228
(2007/10/02)
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- REACTIVITY OF CYCLOALKENES.
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The objective of this work is to investigate the kinetic relationships, to determine the composition of the products, and to elucidate the mechanism of their formation during liquid-phase oxidation of cyclohexene and of isomeric methylcyclohexenes (RH). Experiments show that the main products of oxidation of cyclohexene and of isomeric methylcyclohexenes are mixtures of hydroperoxides, unsaturated alcohols, ketones, and oxides. The isomeric methylcyclohexenes form the following series in order to selectivity of formation of methylcyclohexenols: 3-methylcyclohexene greater than 1-methylcyclohexene greater than 4-methylcyclohexene greater than cyclohexene; the corresponding series for alpha -oxide formation is 1-methylcyclohexene greater than 4-methylcyclohexene greater than 3-methylcyclohexene. A mathematical model of noncatalytic oxidation of cyclohexene has been formulated, and the rate constants of the process have been determined.
- Azhikova,Syroezhko,Proskuryakov
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p. 2133 - 2140
(2007/10/02)
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- CHEMISTRY OF SINGLET OXYGEN. 47. 9,10-DICYANOANTHRACENE-SENSITIZED PHOTOOXYGENATION OF ALKYL-SUBSTITUTED OLEFINS.
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9,10-Dicyanoanthracene (DCA) sensitizes the photooxygenation of 1-methylcyclohexene, 1,2-dimethylcyclohexene, and cholesterol in acetonitrile and benzene. For all three olefins, the products are the same as those formed by reaction with singlet oxygen. Th
- Araki,Dobrowolski,Goyne,Hanson,Zhi Qui Jiang,Lee,Foote
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p. 4570 - 4575
(2007/10/02)
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- THE INFLUENCE OF LITHIUM COMPLEXING AGENTS ON THE REGIOSELECTIVITY OF REDUCTIONS OF SUBSTITUTED 2-CYCLOHEXENONES BY LiAlH4 and LiBH4
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A reversal of regioselectivity of LiAlH4 or LiBH4 reduction of 2-cyclohexenone induced by addition of -cryptand to the reaction medium is accompanied by a rate decrease.In the absence of the cryptand, carbonyl attack predominates (C1:C3=86:14 with LiAlH4 in THF).In the presence of the cryptand, double bond attack is favoured (C1:C3=14:86).This effect is larger with LiAlH4 than with LiBH4.This trend is general in the case of five substituted 2-cyclohexenones.Using 12-crown-4 as a Li+ coordinator, a change in regioselectivity occurs but it is less pronunced than with the cryptand.
- Loupy, Andre,Seyden-Penne, Jacqueline
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p. 1937 - 1942
(2007/10/02)
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- Studies on the Autoxidation of Some Monocyclic Olefins
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The autoxidations of cyclopentene, cyclohexene, cycloheptene, cyclooctene, cycloocta-1,5-diene, 1-methylcyclopentene, 1-methylcyclohexene, 1-methylcycloheptene, 1-methylcyclooctene, methylene cyclopentene, and methylene cyclohexene with pure oxygen under normal pressure were studied.The epoxides formed were determined gaschromatographically.In most cases also the products of allylic oxidation were analyzed and their structures elucidated after reduction to the corresponding allyl alcohols.The portions of high boiling or polymeric products which could not be detected gaschromatographically and also the real yields of epoxides were determined by balance experiments in the presence of inert internal standards.
- Blau, K.,Mueller, U.,Pritzkow, W.,Schmidt-Renner, W.,Sedshaw, Z.
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p. 915 - 932
(2007/10/02)
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- Deamination of N-(6-endo-Methylbicyclohex-6-exo-yl)- and N-(6-endo-Methylbicyclohex-2-en-6-exo-yl)-N-nitrosourea. Attempted Non-photochemical Generation of trans-Cyclohexene Derivatives
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Decomposition of the stereochemically fixed diazonium ions 12 in alkaline methanol affords only 3-substituted 2-methylcyclohexenes 32-36.The corresponding unsaturated diazonium ions 18 gave the products 37-39.Reactions that have been found when generating
- Jendralla, Heiner
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p. 3585 - 3596
(2007/10/02)
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