- Chromium-Catalyzed Production of Diols From Olefins
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Processes for converting an olefin reactant into a diol compound are disclosed, and these processes include the steps of contacting the olefin reactant and a supported chromium catalyst comprising chromium in a hexavalent oxidation state to reduce at least a portion of the supported chromium catalyst to form a reduced chromium catalyst, and hydrolyzing the reduced chromium catalyst to form a reaction product comprising the diol compound. While being contacted, the olefin reactant and the supported chromium catalyst can be irradiated with a light beam at a wavelength in the UV-visible spectrum. Optionally, these processes can further comprise a step of calcining at least a portion of the reduced chromium catalyst to regenerate the supported chromium catalyst.
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Paragraph 0111
(2021/03/19)
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- Ambruticins: tetrahydropyran ring formation and total synthesis
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The ambruticins are a family of polyketide natural products which exhibit potent antifungal activity. Gene knockout experiments are in accord with the proposal that the tetrahydropyran ring of the ambruticins is formedviathe AmbJ catalysed epoxidation of the unsaturated 3,5-dihydroxy acid, ambruticin J, followed by regioselective cyclisation to ambruticin F. Herein, a convergent approach to the total synthesis of ambruticin J is described as well as model studies involving epoxidation and cyclisations of unsaturated hydroxy esters to give tetrahydropyrans and tetrahydrofurans. The total synthesis involves preparation of three key fragments which were unitedviaa Suzuki-Miyaura cross-coupling and Julia-Kocienski olefination to generate the required carbon framework. Global deprotection to a triol and selective oxidation of the primary alcohol gave, after hydrolysis of the lactone, ambruticin J.
- Bowen, James I.,Crump, Matthew P.,Wang, Luoyi,Willis, Christine L.
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supporting information
p. 6210 - 6215
(2021/07/28)
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- Mechanistic Insight into Palladium-Catalyzed Cycloisomerization: A Combined Experimental and Theoretical Study
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The cycloisomerization of enynes catalyzed by Pd(OAc)2 and bis-benzylidene ethylenediamine (bbeda) is a landmark methodology in transition-metal-catalyzed cycloisomerization. However, the mechanistic pathway by which this reaction proceeds has remained unclear for several decades. Here we describe mechanistic investigations into this reaction using enynamides, which deliver azacycles with high regio- and stereocontrol. Extensive 1H NMR spectroscopic studies and isotope effects support a palladium(II) hydride-mediated pathway and reveal crucial roles of bbeda, water, and the precise nature of the Pd(OAc)2 pre-catalyst. Computational studies support these mechanistic findings and lead to a clear picture of the origins of the high stereocontrol that can be achieved in this transformation, as well as suggesting a novel mechanism by which hydrometalation proceeds.
- Mekareeya, Aroonroj,Walker, P. Ross,Couce-Rios, Almudena,Campbell, Craig D.,Steven, Alan,Paton, Robert S.,Anderson, Edward A.
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supporting information
p. 10104 - 10114
(2017/08/03)
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- Stereoselective synthesis of conjugated trienols from allylic alcohols and 1-iodo-1,3-dienes
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The stereoselective synthesis of conjugated trienes has been achieved from allylic alcohols and 1-iodo-1,3-dienes using Pd(OAc)2/AgOAc.
- Brandt, Damien,Bellosta, Veronique,Cossy, Janine
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supporting information
p. 5594 - 5597,4
(2012/12/12)
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- Asymmetric syntheses of 8-oxabicyclo[3,2,1]octanes: A cationic cascade cyclization
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High octane: A novel and practical syntheses of 8-oxabicyclo[3.2.1]octanes using a cationic cascade cyclization reaction has been developed (see scheme; TIPS=triisopropylsilyl). The diastereomer of the cyclization product isolated depends upon whether the acetal or aldehyde substrate is used. Copyright
- Li, Bin,Zhao, Yu-Jun,Lai, Yin-Chang,Loh, Teck-Peng
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supporting information; experimental part
p. 8041 - 8045
(2012/09/05)
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- Cross-metathesis reactions of homoallyl methyl malonates with sterically hindered allylic esters
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The methyl malonate esters of 3-buten-1-ol and 2-methyl-3-buten-1-ol can be coupled efficiently to different methallylic esters in the presence of the second-generation Grubbs catalyst to yield trisubstituted olefins by the cross-metathesis reaction. Product selectivity and yields depend on the relative amounts of reagents and to a minor extent on the methallylic ester functional group. Alkyl substituents at either the allylic or the geminal positions significantly affect the product yields and the E/Z stereoselectivity. The cross-metathesis reactions of homoallyl malonates with allylic esters featuring a variety of alkyl substituents at the vinylic and/or allylic positions afford trisubstituted olefins. Copyright
- Barile, Fabio,Bassetti, Mauro,D'Annibale, Andrea,Gerometta, Renzo,Palazzi, Michele
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experimental part
p. 6519 - 6526
(2011/12/05)
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- Copper catalyzed asymmetric synthesis of chiral allylic esters
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The complex derived from Taniaphos ligand 4 and CuBr?Me2S catalyzes the asymmetric addition of Grignard reagents to 3-bromopropenyl esters 1 to provide allylic esters 2 in high yields and high chemio-, regio-, and enantioselectivities. The work demonstrates that allylic asymmetric alkylation (AAA) can be done on substrates bearing a heteroatom at the γ-position. The method is a practical route to chiral, nonracemic allylic alcohols. The use of functionalized substrates 1 or Grignard reagents leads to more complex products 2, which can be further manipulated as demonstrated in conversion to (S)-5-ethyl-2(5H)-furanone 6 and (S)-benzoic acid-cyclopent-2-enyl ester 7. Copyright
- Geurts, Koen,Fletcher, Stephen P.,Feringa, Ben L.
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p. 15572 - 15573
(2007/10/03)
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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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- Liquid-phase isomerization of saturated and unsaturated epoxides
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The liquid-phase isomerization of a variety of epoxides was studied using a complex catalyst system based on magnesium bromide and dimethylformamide. The data obtained elucidate the mechanism of the liquid-phase isomerization and show the range of oxygen-containing compounds which can be prepared through this reaction.
- Mel'nik,Khvatova,Moskvichev,Srednev,Egorova
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p. 167 - 169
(2007/10/03)
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- Formal total synthesis of (+)-methynolide
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A formal total synthesis of (+)-methynolide was achieved in 23 steps highlighted by a crotylboration, a ring-closing metathesis, a Sharpless kinetic resolution of an allylic alcohol and a Takai reaction.
- Cossy, Janine,Bauer, David,Bellosta, Véronique
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p. 5909 - 5922
(2007/10/03)
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- Stereoselective intramolecular acylation of y'-benzoyloxyphosphine oxides with an internal chlorotrimethylsilane trap: Isolation of silylated tetrahedral intermediates
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The kinetic products of the intramolecular acylation of y'-benzoyloxyphosphine oxides were revealed by conducting the reaction in the presence of an internal trapping agent. A high level of stereocontrol over the formation of both ' : ' the stereogenic centre a to phosphorus and the hemiacetal centre was observed. The stereochemistry of the products was determined by X-ray crystallography and 'H NMR and the stereoselectivity of the reaction is explained in terms of the known structure and configurational instability of lithiated phosphine oxides. The Royal Society of Chemistry 1999.
- Feeder, Neu,Hutton, Gordon,Nelson, Adam,Warren, Stuart
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p. 3413 - 3424
(2007/10/03)
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- Analytical Applications of Raman Spectroscopy in Organic Chemistry: Influence of the Position, Stereochemistry and Substitution Pattern of the Double Bond on the ν(C=C) and ν(sp2CH) Stretching Bands in the Raman Spectra of Alkenyl Methyl Ethers
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The Raman spectra of 29 alkenyl methyl ethers, CnH(2n-1)OCH3, of diverse structure containing up to seven carbon atoms are reported and discussed. All these spectra contain a strong band in the region 1640-1680 cm-1 associated with the stretching vibration of the C=C double bond. Reliable correlations are found between the wavenumber of this band and the position, stereochemistry and substitution pattern of the double bond the band is at higher wavenumber for ethers containing a di- or tri-substituted bond than for those with a monosubstituted bond and at higher wavenumber for trans than cis-stereoisomers. One or more bands in the range 2995-3080 cm-1 associated with the stretching vibration(s) of the sp2C-H bond(s) are also evident in the spectra of most of the ethers, but these bands are sometimes obscured by the stronger bands corresponding to stretching vibrations of the sp3C-H bonds at slightly lower wavenumber (generally below ca. 2950 cm-1). Correlations involving the number and position(s) of these band provide confirmatory evidence on the substitution pattern and stereochemistry of the C=C group. Unequivocal assignment of the symmetric and asymmetric C-H stretching vibrations of the important terminal C=CH2 entity is possible on the basis of these studies; these conclusions are supported by analysis of the Raman spectrum of the deuterium labelled ether CD2=CH(CH2)3OCH3.
- Bowen, Richard D.,Edwards, Howell G. M.,Farwell, Dennis W.,Rusike, Irene,Saunders, Darren M.
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p. 1901 - 1918
(2007/10/03)
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- Total synthesis of (-)-denticulatins A and B using efficient methods of acyclic stereocontrol
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The total synthesis of (-)-denticulatin B (2) was achieved in 9 steps (20% yield), with 70% overall diastereoselectivity, starting from the ethyl ketone (R)-9. Most of the stereochemistry was introduced by substrate-based control. Key steps include the boron-mediated aldol/reduction, 9 → 22, the titanium-mediated aldol-coupling. 26 + 8 → 38, and the directed cyclisation, 35 → 2. Epimerisation at C10 in 35 led to (-)-denticulatin A (1).
- Paterson, Ian,Perkins, Michael V.
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p. 1811 - 1834
(2007/10/03)
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- PHOTOCHEMICAL SYNTHESIS OF THIAZOLYL-THIOPHENE DERIVATIVES
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The synthesis of a new class of compounds deriving from the photochemical coupling between iodothiophene (4, 11, 12 and 13) and thiazole (9 and 10) derivatives is described.The reaction can also be carried out with 5-iodo-2-furancarbaldehyde, 20, with low yields.The compounds 14 - 18 are sensitizers of singlet oxygen in the reaction of 2-methyl-2-pentene, 23, to give the corresponding alcohols 24 and 25.The efficiencies of singlet oxygen formation are in the range 45 - 71percent for the compounds 14, 15 and 17.
- D'Auria, Maurizio,Mico, Antonella De,D'Onofrio, Franco,Piancatelli, Giovanni
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p. 381 - 384
(2007/10/02)
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- NATURAL BITHIOPHENES AS SINGLET OXYGEN SENSITIZERS
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The possibility of using naturally-occurring bithiophenes 4-8 as singlet oxygen photosensitizers has been explored using the reaction of adamantylideneadamantane, 9, and 2-methyl-2-pentene, 11, with singlet oxygen as test reactions.All compounds 4-8 have been found to catalyse the conversions 9 --> 10 and 11 --> 12 + 13.All the reactions are quenched by 1,4-diazabicyclooctane (DABCO).A plot of -1 vs. -1 for different DABCO concentrations showed a common intercept, suggesting that DABCO quenched singlet oxygen generated by light excitation of 4-8.
- D'Auria, Maurizio,D'Onofrio, Franco
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p. 633 - 636
(2007/10/02)
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- Dissociations of Positively Charged Aliphatic Epoxides. I. Structure Elucidation of the η-Cleavage Products
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Dissociative ionization of 1,2-epoxy n-alkanes gives rise to abundant + ions of structure +.This conclusions is drawn from metastable ion analysis and from collosional activation spectra.This fragmentation involves the C-C ring opening and a 1,4-H migration leading to the corresponding enol ether +. precursor of + fragment.The same isomerization scheme applies to 1,2-epoxy methyl substituted alkanes and 2,3-epoxy n-alkanes.
- Bouchoux, Guy,Hoppilliard, Yannik,Jaudon, Pascale
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- THE SYNTHETIC UTILITY OF DIOXYPHOSPHORANES IN ORGANIC SYNTHESIS
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Diethoxytriphenylphosphorane, DTPP, prepared by reaction of triphenylphosphine and diethyl peroxide, is a "hydrolytically active" dioxyphosphorane which promotes mild and efficient cyclodehydration of diols to cyclic ethers in neutral media.Simple 1,2-, 1,4-, and 1,5-diols afford good yields of the cyclic ethers but 1,3-propanediol and 1,6-hexanediol give mainly 3-ethoxy-1-propanol and 6-ethoxy-1-hexanol, respectively, with DTPP.Tri- and tetra-substituted 1,2-diols afford the relatively stable 1,3,2-dioxaphospholanes in the presence of DTPP and the reaction conditions dictate whether epoxides, ketones, or allylic alcohols are obtained.
- Robinson, Philip L.,Kelly, Jeffery W.,Evans, Slayton A.
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- A CONVENIENT "ONE-POT" SYNTHESIS OF EPOXY ALCOHOLS VIA PHOTOOXYGENATION OF OLEFINS IN THE PRESENCE OF TITANIUM(IV) CATALYST
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The ene reaction of singlet oxygen with alkenes in the presence of titanium alkoxides was employed to prepare epoxy alcohols in high diastereoselectivity; enantioselectivity could be achieved by use of diethyl tartrate as chiral auxiliary.
- Adam, Waldemar,Griesbeck, Axel,Staab, Eugen
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p. 2839 - 2842
(2007/10/02)
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- Diethoxytriphenylphosphorane: A Mild, Regioselective Cyclodehydrating Reagent for Conversion of Diols to Cyclic Ethers. Stereochemistry, Synthetic Utility, and Scope
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Diethoxytriphenylphosphorane, Ph3P(OEt)2, prepared by reaction of triphenylphosphine and diethyl peroxide, is a "hydrolytically active" dioxyphosphorane which promotes mild cyclodehydration (40-110 deg C) of diols to cyclic ethers in neutral media.The regioselectivity in the closure of (S)-(+)-propane-1,2-diol and (R)-(-)-pentane-1,4-diol with Ph3P(OEt)2 is high (81-82 percent) while the cyclodehydration of (S)-(+)-phenylethane-1,2-diol gives racemized (+/-)-styrene oxide.Simple 1,2-, 1,4-, and 1,5-diols afford good yields of the cyclic ethers but 1,3-propanediol and 1,6-hexanediol give mainly 3-ethoxy-1-propanol and 6-ethoxy-1-hexanol, respectively with Ph3P(OEt)2.Tri- and tetra-substituted 1,2-diols afford the relatively stable 1,3,2-dioxaphospholanes (or ?-dioxyphosphoranes) in the presence of Ph3P(OEt)2, and, depending on conditions, the 1,3,2-dioxaphospholanes are selectively converted to epoxides, ketones or allylic alcohols.The carbonyl compounds arise from 1,2-hydride and 1,2-methyl migrations; the allylic alcohols are derived from thermolytic eliminations. trans-1,2-Cyclohexanediols afford essentially quantitative yields (>95 percent) of the cyclohexene oxides while cis-1,2-cyclohexanediol gives the stable 1,3,2-dioxaphospholane with Ph3P(OEt)2 which decomposes under thermal conditions to cyclohexanone (90 percent).Ph3P(OEt)2 is extremely useful for conversion of "sensitive" 1,2-diols to acidic and /or thermally labile epoxides as demonstrated by the quantitative conversion of 9,10-dihydro-trans-9,10-phenanthrenediol to 9,10-dihydrophenanthrene oxide and 2α,10-pinanediol to 2α,10-epoxypinane.
- Robinson, Philip L.,Barry, Carey N.,Kelly, Jeffery W.,Evans, Slayton A.
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p. 5210 - 5219
(2007/10/02)
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- CHEMISTRY OF SINGLET OXYGEN. PART 44: MECHANISM OF PHOTOOXIDATION OF 2,5-DIMETHYLHEXA-2,4-DIENE AND 2-METHYL-2-PENTENE.
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Solvent and temperature effects on the singlet oxygen oxidations of 2,6-dimethyl-2,4-hexadiene (DMHD) and 2-methyl-2-pentene (2M2P) are studied. It is concluded that the initial interaction between 2M2P and **1O//2 (which gives only ene products) and that between DMHD and **1O//2 (which gives ene products, dioxetane, and nonreactive quenching) are identical. It is also suggested that the quenching path for DMHD could involve formation of an intermediate zwitterion or 1,4-biradical, which undergoes intersystem crossing and decays to ground-state oxygen and DMHD.
- Manring,Foote
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p. 4710 - 4717
(2007/10/02)
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- Quenching of Singlet Oxygen by 1,3,5-Triaryl-2-pyrazolines
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The efficient quenching of photochemically generated singlet oxygen by four 1,3,5-triaryl-2-pyrazolines (5-8) and p-(diethylamino)benzaldehyde diphenylhydrazone (9) has been investigated by inhibition of the photosensitized oxygenation of 1,3 diphenylisobenzofuran and 2-methyl-2-pentene. 1-Phenyl-3--5--2-pyrazoline (8) quenches singlet oxygen without any reaction at all, and the quenching rate constant reaches a maximum of 5.8 x 109 M-1 s-1.The quenching ability correlates with the value of their one-electron oxidation potentials (Ep).
- Ando, Wataru,Sato, Rikiya,Yamashita, Masataka,Akasaka, Takeshi,Miyazaki, Hajime
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p. 542 - 546
(2007/10/02)
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- Studies on the Autoxidation of Branched-chain Olefins. I. Autoxidation of 2-Methylalk-1-enes and 2-Methylalk-2-enes
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The products of the autoxidation of 2-methylpent-1-ene, 2-methylpent-2-ene, 2-methylhex-1-ene, 2-methylhex-2-ene, 2,4,4-trimethylpent-1-ene, and 2,4,4-trimethylpent-2-ene were analyzed by gas chromatography.The identification of the products corresponding to the individual peaks was possible by comparison with authentic substances or by preparative gaschromatographic separation and n.m.r.-spectroscopy of the isolated samples.In this way not only the epoxides and the products of the oxidative cleavage of the C=C double bond but also the allylic alcohols formed by LiAlH4-reduction of the oxidation mixtures could be identified and analyzed.From the results the compositions of the original oxidation mixtures were calculated.
- Bilas, W.,Hoebold, W.,Pritzkow, W.
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p. 125 - 141
(2007/10/02)
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