- A Self-Assembled Molecular Cage for Substrate-Selective Epoxidation Reactions in Aqueous Media
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Encapsulation of a manganese porphyrin in a self-assembled molecular cage allows catalytic epoxidation of various substrates in 1:1 water/acetonitrile mixtures. The cage acts as a phase-transfer catalyst and creates a protective environment for the catalyst improving the stability. The encapsulated catalyst also allows discrimination between styrene derivatives of various sizes. In a direct competition experiment, the selectivity of the epoxidation reaction could be inverted with respect to a benchmark catalyst.
- Kuijpers, Petrus F.,Otte, Matthias,Dürr, Maximilian,Ivanovi?-Burmazovi?, Ivana,Reek, Joost N. H.,De Bruin, Bas
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p. 3106 - 3112
(2016/07/06)
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- Making Fe(BPBP)-catalyzed C-H and CC oxidations more affordable
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The limited availability of catalytic reaction components may represent a major hurdle for the practical application of many catalytic procedures in organic synthesis. In this work, we demonstrate that the mixture of isomeric iron complexes [Fe(OTf)2(mix-BPBP)] (mix-1), composed of Λ-α-[Fe(OTf)2(S,S-BPBP)] (S,S-1), Δ-α- [Fe(OTf)2(R,R-BPBP)] (R,R-1) and Δ/Λ-β-[Fe(OTf) 2(R,S-BPBP)] (R,S-1), is a practical catalyst for the preparative oxidation of various aliphatic compounds including model hydrocarbons and optically pure natural products using hydrogen peroxide as an oxidant. Among the species present in mix-1, S,S-1 and R,R-1 are catalytically active, act independently and represent ca. 75% of mix-1. The remaining 25% of mix-1 is represented by mesomeric R,S-1 which nominally plays a spectator role in both C-H and C=C bond oxidation reactions. Overall, this mixture of iron complexes displays the same catalytic profile as its enantiopure components that have been previously used separately in sp3 C-H oxidations. In contrast to them, mix-1 is readily available on a multi-gram scale via two high yielding steps from crude dl/meso-2,2′-bipyrrolidine. Next to its use in C-H oxidation, mix-1 is active in chemospecific epoxidation reactions, which has allowed us to develop a practical catalytic protocol for the synthesis of epoxides.
- Yazerski, Vital A.,Spannring, Peter,Gatineau, David,Woerde, Charlotte H.M.,Wieclawska, Sara M.,Lutz, Martin,Kleijn, Henk,Klein Gebbink, Robertus J.M.
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supporting information
p. 2062 - 2070
(2014/03/21)
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- Cyclopropenone catalyzed substitution of alcohols with mesylate ion
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The cyclopropenone catalyzed nucleophilic substitution of alcohols by methanesulfonate ion with inversion of configuration is described. This work provides an alternative to the Mitsunobu reaction that avoids the use of azodicarboxylates and generation of hydrazine and phosphine oxide byproducts. This transformation is shown to be compatible with a range of functionality. A cyclopropenone scavenge strategy is demonstrated to aid purification.
- Nacsa, Eric D.,Lambert, Tristan H.
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supporting information
p. 38 - 41
(2013/03/28)
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- Epoxidation of olefins by β-bromoalkoxydimethylsulfonium ylides
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Olefins can be converted to their respective epoxides in a one-pot procedure by dissolving the olefin in anhydrous DMSO, adding NBS to the reaction mixture to generate a β-bromoalkoxydimethylsulfonium ylide, and then adding DBU to the reaction mixture. A large variety of alkenes were successfully epoxi-dized with yields largely dependent on the structure of the alkene. Most importantly, the facial selectivity of this one-pot process is the opposite of that observed when using traditional epoxidizing reagents. Electron-poor alkenes are not epoxidized under these conditions.
- Majetich, George,Shimkus, Joel,Li, Yang
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supporting information; experimental part
p. 6830 - 6834
(2011/03/18)
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- Synthesis, crystal structure, and catalytic properties of novel dioxidomolybdenum(VI) complexes with tridentate schiff base ligands in the biomimetic and highly selective oxygenation of alkenes and sulfides
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Four novel dioxidomolybdenum(VI) complexes [MoO2(L x)(CH3OH)] have been synthesized, using 2[(E)-(2-hydroxy-2-phenylethylimino)methyl]phenol derivatives as tridentate ONO donor Schiff base ligands (H2Lx) and MoO 2(acac)2. A monoclinic space group was determined by X-ray crystallography from single-crystal data of a sample of these new complexes. The epoxidation of alkenes by using tert-butyl hydroperoxide and oxidation of sulfides to sulfoxides by urea hydrogen peroxide were efficiently enhanced with excellent selectivity under the catalytic influence these new MoVI complexes. The high efficiency and relative stability of the catalysts have been observed, by turnover numbers and UV/Vis investigations. The electron-poor and bulky ligands promoted the effectiveness of the catalysts. 2010 Wiley-VCH Verlag GmbH & Co. KGaA.
- Rezaeifard, Abdolreza,Sheikhshoaie, Iran,Monadi, Maz,Stoeckli-Evans, Helen
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experimental part
p. 799 - 806
(2010/07/04)
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- Olefin-dependent discrimination between two nonheme HO-Fev=O tautomeric species in catalytic H2O2 epoxidations
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A study was conducted to demonstrate olefin-dependent discrimination of two nonheme HO-Fev=O tautomeric species in catalytic H2O 2 epoxidations. Mechanistic studies were carried out under the condition of excess of olefin to minimize over-oxidation reactions and all reactions for the study were carried out under a N2 atmosphere to prevent auto-oxidation process due to presence of O2. It was observed that the diol/epoxide (D/E) ration for these reaction was dependent on the specific olefin and ranged from 3/2 (cyclooctene) to 6/1 (1-octene). The oxidation of cyclooctene using H218O2 revealed that only 28% of the oxygen atoms in the epoxide derived from H 2O2. Mechanistic results suggested that HO-Fe v=O oxidant need to be labeled before its reaction with substrates.
- Company, Anna,Feng, Yan,Gueell, Mireia,Ribas, Xavi,Luis, Josep M.,Que Jr., Lawrence,Costas, Miquel
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supporting information; experimental part
p. 3359 - 3362
(2009/12/06)
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- Efficient and selective peracetic acid epoxidation catalyzed by a robust manganese catalyst
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(Chemical Equation Presented) A manganese catalyst containing a tetradentate ligand derived from triazacyclononane exhibits high catalytic activity in epoxidation reactions using peracetic acid as oxidant. The system exhibits broad substrate scope and requires small (0.1-0.15 mol %) catalyst loading. The catalyst is remarkably selective toward aliphatic cis-olefins. Mechanistic studies point toward an electrophilic oxidant delivering the oxygen atom in a concerted step.
- Garcia-Bosch, Isaac,Company, Anna,Fontrodona, Xavier,Ribas, Xavi,Costas, Miquel
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supporting information; experimental part
p. 2095 - 2098
(2009/07/04)
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- Non-heme iron complexes for stereoselective oxidation: Tuning of the selectivity in dihydroxylation using different solvents
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A new class of functional models for non-heme iron-based dioxygenases, including [(N3Py-Me)Fe(CH3CN)2](ClO4) 2 and [(N3Py-Bn)Fe(CH3CN)2](ClO 4)2 {N3Py-Me = [di(2-pyridyl)methyl]methyl(2-pyridyl) methylamine; N3Py-Bn = [di(2-pyridyl)methyl]benzyl(2-pyridyl)methylamine}, is presented here. NMR, UV and X-ray analyses revealed that six-coordinate low-spin FeII complexes with the pyridine N-atoms and the tertiary amine functionality of the ligand bound to Fe are formed. The two remaining coordination sites located cis to each other are occupied by labile CH 3CN groups that are easily exchanged by other ligands. We demonstrate that the reactivity and stereoselectivity of the complexes investigated depend on the choice of the solvent. The complexes have been examined as catalysts for the oxidation of both alkanes and olefins in CH3CN. In this solvent alkanes are oxidized to alcohols and ketones and olefins to the corresponding cis-epoxides and cis-diols. In acetone as solvent a different reactivity pattern was found, with, as the most striking example, the trans-dihydroxylation of cis-olefins. 18O-labeling studies in CH3CN establish incorporation of 18O from H218O2 and H218O in both the epoxide and the diol implicating an HO-FeV=18O active intermediate originating from an H 218O-FeIIIOOH species. These results are in full agreement with mechanistic schemes derived for other dioxygenase model systems. Based on labeling studies in acetone an additional oxidation mechanism is proposed for this solvent, in which the solvent acetone is involved. This is the first example of a catalyst that can give cis- or trans-dihydroxylation products, just by changing the solvent. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
- Klopstra, Marten,Roelfes, Gerard,Hage, Ronald,Kellogg, Richard M.,Feringa, Ben L.
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p. 846 - 856
(2007/10/03)
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- Polyfluorinated quaternary ammonium salts of polyoxometalate anions: Fluorous biphasic oxidation catalysis with and without fluorous solvents
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[Matrix presented] Polyfluorinated quaternary ammonium cations, [CF 3(CF2)7(CH2)3] 3CH3N+ (RFN+), were synthesized and used as countercations for the [WZnM2(H 2O)2(ZnW9O34)2] 12- (M = Mn(II), Zn(II)) polyoxometalate. The (RFN +)12[WZnM2(H20)2 (ZnW9O34)2] compounds were fluorous biphasic catalysts for alcohol and alkenol oxidation, and alkene epoxidation with aqueous hydrogen peroxide. Reaction protocols with or without a fluorous solvent were tested. The catalytic activity and selectivity was affected by both the hydrophobicity of the solvent and the substrate.
- Maayan, Galia,Fish, Richard H.,Neumann, Ronny
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p. 3547 - 3550
(2007/10/03)
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- Manganese-catalyzed epoxidations of alkenes in bicarbonate solutions
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This paper describes a method, discovered and refined by parallel screening, for the epoxidation of alkenes. It uses hydrogen peroxide as the terminal oxidant, is promoted by catalytic amounts (1.0-0.1 mol %) of manganese(2+) salts, and must be performed using at least catalytic amounts of bicarbonate buffer. Peroxymonocarbonate, HCO4-, forms in the reaction, but without manganese, minimal epoxidation activity is observed in the solvents used for this research, that is, DMF and tBUOH. More than 30 d-block and f-block transition metal salts were screened for epoxidation activity under similar conditions, but the best catalyst found was MnSO4. EPR studies show that Mn2+ is initially consumed in the catalytic reaction but is regenerated toward the end of the process when presumably the hydrogen peroxide is spent. A variety of aryl-substituted, cyclic, and trialkyl-substituted alkenes were epoxidized under these conditions using 10 equiv of hydrogen peroxide, but monoalkyl-alkenes were not. To improve the substrate scope, and to increase the efficiency of hydrogen peroxide consumption, 68 diverse compounds were screened to find additives that would enhance the rate of the epoxidation reaction relative to a competing disproportionation of hydrogen peroxide. Successful additives were 6 mol % sodium acetate in the tBUOH system and 4 mol % salicylic acid in the DMF system. These additives enhanced the rate of the desired epoxidation reaction by 2-3 times. Reactions performed in the presence of these additives require less hydrogen peroxide and shorter reaction times, and they enhance the yields obtained from less reactive alkene substrates. Possible mechanisms for the reaction are discussed.
- Lane, Benjamin S.,Vogt, Matthew,DeRose, Victoria J.,Burgess, Kevin
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p. 11946 - 11954
(2007/10/03)
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- Efficient epoxidation of alkenes with aqueous hydrogen peroxide catalyzed by methyltrioxorhenium and 3-cyanopyridine
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The epoxidation of alkenes with 30% aqueous hydrogen peroxide is catalyzed efficiently by methyltrioxorhenium (MTO) in the presence of pyridine additives. The addition of 1-10 mol % of 3-cyanopyridine increases the system's efficiency for terminal and trans-disubstituted alkenes resulting in high isolated yields of the corresponding epoxides. The system allows for epoxidation of alkenes with various functional groups. Alkenes leading to acid-sensitive products are efficiently epoxidized using a mixture of pyridine and 3-cyanopyridine as additives. This method is operationally very simple and uses an environmentally benign oxidant. The effects of different pyridine additives on the alkene conversion and the catalyst lifetime are discussed.
- Adolfsson,Coperet,Chiang,Yudin
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p. 8651 - 8658
(2007/10/03)
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- A novel epoxidation reaction of olefins using a combination of chloramine-M, benzaldehyde, and benzyltriethylammonium chloride
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A combination of Chloramine-M (CH3SO2NClNa), benzaldehyde, and benzyltriethylammonium chloride (BTEAC) was found to epoxidize a wide range of olefins. While epoxidation of trans-olefins provided exclusively trans- epoxides, cis-olefins (cis-stilbene, cis-β-methylstyrene, and 4-cis-octene) gave trans-epoxides as major products. Good to excellent diastereoselectivities were obtained for epoxidation of two substituted cyclohexenes. Chloramine-T was found to give a slower reaction than Chloramine-M. cis-N-Sulfonyloxaziridine D is proposed to be the epoxidizing agent in this novel epoxidation reaction on the basis of the mechanistic studies.
- Yang, Dan,Zhang, Chi,Wang, Xue-Chao
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p. 4039 - 4043
(2007/10/03)
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- The dinuclear manganese complex Mn2O(OAc)2(TPTN) as a catalyst for epoxidations with hydrogen peroxide
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In acetone and at ambient temperature, the dinuclear manganese complex of TPTN is able to catalyse the oxidation of several alkenes to the corresponding epoxides with high turnovers numbers (up to 900) using H2O2 as oxidant.
- Brinksma, Jelle,Hage, Ronald,Kerschner, Judith,Feringa, Ben L.
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p. 537 - 538
(2007/10/03)
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- Stereochemical analysis of deuterated alkyl chains by MS/MS
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Vicinally deuterated sec-alkyl phenyl ethers, CH3(CH2)(m)CH(OPh)CHD(CH2)(n)CH3, display significant differences in mass spectra between threo and erythro stereoisomers. MS/MS experiments, in which parent ions of a single mass are selected and their fragmentation patterns subsequently measured, show that alkene expulsion represents virtually the only decomposition pathway. Two types of MS/MS experiment are reported: mass- analyzed ion kinetic energy (MIKE) spectroscopy of metastable ions and collisionally activated decomposition (CAD) of stable ions. The expulsion of a deuterated alkene from a monodeuterated precursor yields ionized phenol, PhOH·+ (m/z 94). The expulsion of an undeuterated alkene yields PhOD·+ (m/z 95). Without exception, the ratios (PhOD·+/PhOH·+) from precursors in the threo series have values greater than their diastereomers in the erythro series. The ratio of ratios, r = PhOD·+/PhOH·+ for the threo divided by PhOD·+/PhOH·+ for the erythro, has a value of 1.2 for the 2- phenoxy-3-deuteriobutanes and larger values for all of the higher homologues up through the monodeuterated phenoxyoctanes (m + n = 4). The highest degree of stereoselectivity, r = 5.8, is measured for 3-phenoxy-4-deuteriohexane. Experiments with multiply deuterated analogues show that alkene elimination is highly regioselective, unlike the corresponding decompositions of ionized sec-alcohols or their acetates. The fact that a large fraction of ionized sec-alkyl phenyl ethers undergo stereospecific syn-elimination means that mass spectrometry has a useful capacity to distinguish one isotopically labeled diastereomer from another.
- Morizur,Taphanel,Mayer, Philip S.,Morton, Thomas Hellman
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p. 381 - 387
(2007/10/03)
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- Epoxidation of alkenes using dioxygen in the presence of an alcohol catalyzed by N-hydroxyphthalimide and hexafluoroacetone without any metal catalyst
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A new approach for the epoxidation of alkenes using O2 without any metal catalyst was developed; a variety of alkenes were epoxidized in a regio- and stereoselective manner with O2 in the presence of benzhydrol catalyzed by N-hydroxyphthalimide and hexafluoroacetone.
- Iwahama, Takahiro,Sakaguchi, Satoshi,Ishii, Yasutaka
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p. 727 - 728
(2007/10/03)
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- Reactions of Microwave-Generated O(3P) Atoms with Unsaturated Hydrocarbons
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The reactions of neat olefins or solutions of olefins in acetone at low temperature with oxygen atoms were examined. O(3P) atoms were produced by microwave irradiation of He/O2 mixtures, followed by contact of the plasma with the fluid at low pressure and temperature. Addition of oxygen atoms to olefins results in skeletal rearrangements involving hydrogen and alkyl migration reactions and ring rearrangements of the intermediate oxygen adducts in competition with epoxide formation. While epoxide formation predominates for simple olefins such as 1- and 4-octene with minor yields of rearrangement products, for highly substituted or strained olefins, such as norbornadiene, skeletal rearrangement dominates following oxygen atom addition. When oxidation of norbornadiene is carried out in the presence of a radical inhibitor to suppress secondary oxidation leading to benzene, the novel ring-rearrangement product, bicyclo[3.2,31.0]hex- 3-ene-endo-6-carboxaldehyde, is produced from norbornadiene in significant yields.
- Tanner,Kandanarachchi,Das,Brausen,Vo,Camaioni,Franz
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p. 4587 - 4593
(2007/10/03)
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- Photodeoxygenation of dibenzothiophene sulfoxide: Evidence for a unimolecular S-O cleavage mechanism
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Photolysis of dibenzothiophene sulfoxide results in the formation of dibenzothiophene and oxidized solvent. Though quantum yields are low, chemical yields of the sulfide are quite high. Yields of the oxidized solvents can also be high. Typical products are phenol from benzene, cyclohexanol, and cyclohexene from cyclohexane and 2-cyclohexenol and epoxycyclohexane from cyclohexene. A number of experiments designed to elucidate the mechanism of the hydroxylation were carried out, including measurements of quantum yields as a function of concentration, solvent, quenchers, and excitation wavelength. These data are inconsistent with a mechanism involving a sulfoxide dimer, which also does not properly account for the solvent oxidations. It is suggested hbat the active oxidizing agent may be atomic oxygen O(3P) or a closely related noncovalent complex, based on the nature of the oxidation chemistry, comparison to known rate constants for O(3P) reactivity, and the quantum yield data.
- Gregory, Daniel D.,Wan, Zehong,Jenks, William S.
-
-
- Studies on Polyoxo- and Polyperoxo-metalates. Part 1. Tetrameric Heteropolyperoxotungstates and Heteropolyperoxomolybdates
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New heteropolyperoxometalates of the type R34> (3+) (en = ethane-1,2-diamine); X = P or As; M = Mo or W> have been characterized by IR, Raman and where appropriate 31P NMR spectroscopy.Epoxidation of cyclic and linear alkenes by these species with H2O2 as co-oxidant has been studied; 4>(3-) was found to be the most effective.The oxidation of alcohols by 4>(3-) with H2O2 has been investigated.
- Dengel, Andrew C.,Griffith, William P.,Parkin, Bernardeta C.
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p. 2683 - 2688
(2007/10/02)
-
- Dioxiranes. 20. Preparation and properties of some new dioxiranes
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The in situ method for producing dioxiranes has been modified to permit the isolation in ketone solution of some nonvolatile dioxiranes. The dioxiranes have been characterized spectroscopically and, in some cases, by chemical reactions.
- Murray, Robert W.,Singh, Megh,Jeyaraman, Ramasubbu
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p. 1346 - 1351
(2007/10/02)
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- Direct Catalytic Transformation of Olefins into α-Hydroxy Ketones with Hydrogen Peroxide Catalyzed by Peroxotungstophosphate
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Aliphatic olefins were directly converted into α-hydroxy ketones with acidic aqueous hydrogen peroxide in the presence of catalytic amount of peroxytungstophosphate (PCWP) under the biphasic system using chloroform as a solvent.The acidic medium was necessary to open the resulting epoxide to vic-diol which was subsequently oxidized to α-hydroxy ketones.
- Sakata, Yasuyuki,Katayama, Yuji,Ishii, Yasutaka
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p. 671 - 674
(2007/10/02)
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- β-Peroxyalkyl radicals and their role in the generation of epoxides during the autoxidation of alkenes. An example of the interplay of free radical, peroxide and organometallic chemistries
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The systematics of the γ-scission reactions of β-peroxyalkyl radicals to yield epoxides have been extended to include variations in the degree of alkylation at the α- and β-carbon atoms and in the nature of the departing alkoxyl radical.The ratios of geometrically isomeric epoxides so produced have been shown to be dependent upon the steric bulk of the Cα- and Cβ-substituents but rather independent of the nature of the departing alkoxyl radical.The relative importance of 1,5-H atom transfer in β-peroxyalkyl radicals has been considered and some evidence forits occurrence adduced.The relevance of these findings to published data for alkene autoxidation is discussed in terms of two competing pathways, in which, it is suggested, steric factors determine the outcome.
- Courtneidge, John L.,Bush, Melanie
-
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- A New Route to Epoxides and Ketones by m-Chloroperbenzoic Acid Oxidation of β-Hydroxyalkyl Phenyl Selenides and Tellurides
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Treatment of primary (β-hydroxy)alkyl phenyl selenides with m-chloroperbenzoic acid (3-5 mol equiv.) in tetrahydrofuran or methanol gives the corresponding epoxides in high yield. cis-1-Methylene-4-t-butylcyclohexane oxide is obtained stereospecifically from 4-t-butyl-1-(phenylselenomethyl)cyclohexanol prepared by the addition of α-(phenylseleno)methyl anion to 4-t-butylcyclohexanone.On the other hand, similar oxidation of secondary (β-hydroxy)alkyl phenyl selenides affords the unexpected carboxylic acids or their esters.When a phenyl group is present on the carbon bearing the OH moiety in β-hydroxyselenides and tellurides , the oxidation is accompanied by phenyl migration to afford ketones.The reaction can be applied to one-carbon-homologated ring expansion of the benzene-ring-fused cyclic ketones by combining with the addition of an α-(phenylseleno)methyl or α-(phenyltelluro)methyl moiety to the ketones.
- Uemura, Sakae,Ohe, Kouichi,Sugita, Nobuyuki
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p. 1697 - 1703
(2007/10/02)
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- Synenergistic Effect of Lipophilic Carboxylic Acids and Heterocyclic Axial Ligands in Alkene Epoxidation by Hydrogen Peroxide catalysed by Manganese(III) Tetra-aryl Porphyrins
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The rate of alkene epoxidation promoted by 30percent H2O2 and catalysed by MnIIItetra(2,6-dichlorophenyl)porphyrin is strongly enhanced by the addition of lipophilic carboxylic acids and lipophilic imidazole or pyridine axial ligands, in 1-8:1 and 1:1 molar ratios with respect to the porphyrin.
- Anelli, Pier Lucio,Banfi, Stefano,Montanari, Fernando,Quici, Silvio
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p. 779 - 780
(2007/10/02)
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- Quaternary Ammonium Tetrakis(diperoxotungsto)phosphates(3-) as a New Class of Catalysts for Efficient Alkene Epoxidation with Hydrogen Peroxide
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The use of quaternary ammonium tetrakis(diperoxotungsto)phosphates(3-) in conjuction with hydrogen peroxide as the primary oxidant in an aqueous/organic biphase system provides an efficient, versatile, and synthetically valuable catalytic method for olefin epoxidation.By this method, a variety of water-insoluble unactivated alkenes, internal or terminal, open-chain or cyclic, isolated or carrying diversified functionalities, were epoxidized in high yields under mild conditions and after relatively short reaction times.
- Venturello, Carlo,D'Aloiso, Rino
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p. 1553 - 1557
(2007/10/02)
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- About the Influence of Pressure on the Catalyzed Liquid-Phase Oxidation of cis- and trans-Oct-4-ene
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The investigation of the influence of pressure on the liquid-phase oxidation of cis- and trans-oct-4-ene shows that the reaction rate increases up to 491 kPa in the non-catalyzed oxidation reaction, but up to 981 kPa in the MoO2(acac)2-catalyzed reaction n-oct-1-ene reacts more slowly than cis- and trans-oct-4-ene as well in the pressure-less reaction as in the oxidation under pressure.In the non-catalyzed oxidation reaction the cis/trans-epoxide ratios don't depend on the pressure, but in the MoO2(acac)2-catalyzed oxidation reaction the cis/trans-epoxide ratios increase with increasing pressure.The optimum of the reaction temperature lies between 110 and 130 deg C.
- Schnurpfeil, D.,Hronec, M.
-
-
- The Catalysis of the Co-Oxidation of cis-Oct-4-ene and n-Butyric Aldehyde
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The co-oxidation of cis-oct-4-ene and butyric aldehyde in the absence of catalysts, or in the presence of molybdenum and Co(acac)3, resp., was studied in dependence on the aldehyde/olefin ratio, on the temperature and other reaction conditions.Under the same conditions, the non-catalyzed co-oxidation converted 50percent, the MoO2(acac)2-catalyzed one 68percent, and the Co(acac)3-catalyzed one 40percent of the reacted olefin into the epoxide.The cis/trans-epoxide ratio in the molybdenum-catalyzed co-oxidation was nearly 2 independent of the aldehyde/olefin ratio.In the non-catalyzed co-oxidation the cis/trans epoxide ratio depends linearly on the aldehyde/olefin ratio (cis/trans E.=0.58+0.90 nAl0/nO0).From these dependences we can conclude that the homolytic mechanism of epoxide formation decreases and the polar mechanism (Prilezaev-reaction) increases with increasing aldehyde/olefin ratio.Optimization of the epoxide yields according to a Box-Hunter experimental plan gave the following reaction conditions to yield 95percent epoxide based on reacted olefin: 70 deg C, ΔnS/nO0 = 0.49, nK0/nO0 = 3.5 E-3, nAl0/nO0 = 0.53.The co-oxidation in the presence of other molybdenum catalysts of the chloro-nitrosyl-complex type and of the carbonyl-complex type as well as the co-oxidation with other aldehydes were studied, too.
- Schnurpfeil, D.,Just, G.,Kraft, F.,Seyrich, A.
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p. 191 - 203
(2007/10/02)
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- About the Catalysis of the Prilezaev Reaction
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It is shown that a catalysis of the Prilezaev reaction exists.We investigated the influence of homogeneous molybdenum catalysts on the epoxidation reaction of olefins with percarboxylic acids kinetically.The second order reaction rate data show that the MoO2(acac)2 catalyzed cyclohexene epoxidation with peracetic acid runs two times faster than the uncatalyzed reaction and the same epoxidation of oct-1-ene runs 15 to 30 times faster.In the same way the reduction af activation parameters in the catalytic reaction proves the catalytic effect.An influence of catalyst concentration and a formation period at the beginning of the catalytic reaction were observed.The influence of the structure of olefin and of the kind of catalyst were investigated and discussed.A formulation of the transition state is given and discussed in relation to the uncatalyzed Prilezaev reaction and to the Halcon reaction.
- Schnurpfeil, D.
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p. 885 - 894
(2007/10/02)
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- About the Formation of trans-Epoxides in the Liquid Phase Oxidation of cis/trans-n-Alkenes Catalyzed by Technetium
-
The liquid-phase oxidation of n-oct-1-ene, cis-oct-4-ene and cis/trans mixtures of oct-4-ene with molecular oxygen in the presence of the technetium complexes 1 to 10 was studied.Low epoxide yields (/=10percent) are characteristic features of the reactions.Pure cis-oct-4-ene and mixtures of cis/trans-oct-4-ene yields in cis/trans-epoxide ratios lower than 0.05.Isomerization reactions and nucleophilic epoxide ring opening reactions are not responsible for the low epoxide yield and the favoured formation of trans-epoxide.Epoxide decomposition by a Tc-catalyzed radical reaction which prefers the cis-epoxide is discussed.
- Rummel, S.,Schnurpfeil, D.
-
-
- The Catalyzed Liquid-Phase Oxidation of cis- and trans-Oct-4-ene
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The influences of MoO2(acac)2, MoO3 and Co(acac)3 on the liquid-phase oxidation of cis- and trans-oct-4-ene at 110 deg C were studied.In the presence of molybdenum catalysts the yield of epoxides and the stereoselectivity of epoxide formation are increased.The results are in good agreement with the hypothesis that molybdenum compounds effect only the stereospecific reaction of the hydroperoxides formed with the starting olefin yielding the corresponding epoxide. The cobaltic complex increases the rate of autoxidation, but has no remarkable influence on the yield of epoxides.In the presence of Co(acac)3 more trans-epoxide is formed from cis-oct-4-ene than in the uncatalyzed reaction.This can be explained by an increase of the lifetime of the intermediate peroxyalkyl radical, effected by complex formation of the radical with a cobalt species.
- Rothe, D.,Schnurpfeil, D.
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p. 596 - 608
(2007/10/02)
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- The Transition Metal Catalyzed Nucleophilic Epoxide Ring Opening Reaction
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The catalytic influence of MoO2(acac)2, Mo(CO)6, MoCl5, WCl6 and TaCl5 on the reaction of 1,2-epoxy-octane with ethanol at 100 deg C in dioxan or chlorobenzene as solvents is proved.Water and hydroperoxides react with a higher rate than alcohols.When changing from primary to secondary and tertiary alcohols a decrease of the reaction rate is observed. 2,3- and 3,4-Epoxyheptane and cis- and trans-4,5-epoxy-octane react more slowly than the corresponding 1,2-epoxides.Epichlorhydrin and methylglycidether react with a lower, cyclohexene oxide, styrene oxide and norbornene oxide react with a higher rate than 1,2-epoxyoctane.The reactivities of the two dicyclopentadiene monoepoxides correspond with the reactivities of the norbornene and cyclopentene oxides.In the molybdenum catalyzed epoxide ring opening reaction an isomer distribution appears in favour of the 1-hydroxy-2-ethoxy-alkane 2.A mechanism in the coordination sphere of the transition metal complex is proposed.
- Lauterbach, G.,Posselt, G.,Schaefer, R.,Schnurpfeil, D.
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p. 101 - 120
(2007/10/02)
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- EPOXIDATION OF OLEFINS BY HYDROGEN PEROXIDE IN THE PRESENCE OF TETRACHLOROACETONE
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1,1,3,3-Tetrachloroacetone, an inexpensive, commercially available material, has been shown to be effective in mediating the hydrogen peroxide oxidation of a variety of olefins to epoxides.The chloroacetone is readily recovered for re-use.
- Stark, Charles J.
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p. 2089 - 2092
(2007/10/02)
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