- Titanium-Catalyzed, Asymmetric Sulfoxidation of Alkyl Aryl Sulfides with Optically Active Hydroperoxides
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The Ti-catalyzed, asymmetric oxidation of alkyl aryl sulfides by enantiomerically pure hydroperoxides (ee >99%) has been examined. Enantioselectivities with ee values up to ca. 80% were achieved for the oxygen transfer from (S)-(-)-1-phenylethyl hydroperoxide 2a to methyl phenyl and methyl p-tolyl sulfide 1a in CCl4 as solvent, but with much overoxidation to the corresponding sulfone 4. Detailed mechanistic studies showed that the enantioselectivity of the sulfide 1a oxidation results from a combination of a rather low (ee values >20%) asymmetric induction in the sulfoxidation and an effective kinetic resolution (ee values ca. 80% at 85% sulfide conversion) of the sulfoxide 3a by enantioselective oxidation to the sulfone 4a. The overoxidation (loss of chemoselectivity) is due to sulfoxide coordination to the Ti metal to generate a template in which the oxygen atom is intramolecularly transferred from the bound and activated, optically active hydroperoxide to the ligated sulfoxide in a stereocontrolled manner.
- Adam, Waldemar,Korb, Marion N.,Roschmann, Konrad J.,Saha-Moeller, Chantu R.
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Read Online
- Chiral Ligands in Hypervalent Iodine Compounds: Synthesis and Structures of Binaphthyl-Based λ3-Iodanes
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Several novel binaphthyl-based chiral hypervalent iodine(III) reagents have been prepared and structurally analysed. Various asymmetric oxidative reactions were applied to evaluate the reactivities and stereoselectivities of those reagents. Moderate to excellent yields were observed; however, very low stereoselectivities were obtained. NMR experiments indicated that these reagents are very easily hydrolysed in either chloroform or DMSO solvents leading to the limited stereoselectivities. It is concluded that the use of chiral ligands is an unsuccessful way to prepare efficient stereoselective iodine(III) reagents.
- Zhang, Huaiyuan,Cormanich, Rodrigo A.,Wirth, Thomas
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supporting information
(2021/12/22)
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- Identification of MsrA homologues for the preparation of (R)-sulfoxides at high substrate concentrations
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Here we report a methionine sulfoxide reductase A (MsrA) homologue with extremely high substrate tolerance and a wide substrate scope for the biocatalytic preparation of enantiopure sulfoxides. This MsrA homologue which was obtained from Pseudomonas alcaliphila (named paMsrA) showed good activity and enantioselectivity towards a series of aryl methyl/ethyl sulfoxides 1a-1k, with electron-withdrawing or electron-donating substituents at the aromatic ring. Chiral sulfoxides in the R configuration were prepared with approximately 50% of yield and up to 99% enantiomeric excess through the asymmetric reductive resolution of racemic sulfoxide catalyzed by the recombinant paMsrA protein. More importantly, kinetic resolution has been successfully accomplished with high enantioselectivity (E > 200) at initial substrate concentrations up to 320 mM (approximately 45 g L-1), which represents a great improvement in the aspect of the substrate concentration for the biocatalytic preparation of chiral sulfoxides.
- Yang, Jiawei,Wen, Yuanmei,Peng, Liaotian,Chan, Yu,Cheng, Xiaoling,Chen, Yongzheng
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p. 3381 - 3388
(2019/04/01)
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- HPLC enantioseparation on a homochiral MOF-silica composite as a novel chiral stationary phase
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The last frontier in the development of chiral stationary phases for chromatographic enantioseparation involves homochiral metal-organic frameworks (MOFs). Using enantiopure (R)-2,2′-dihydroxy-1,1′-binaphthalene-6,6′-dicarboxylic acid as a starting material, we prepared three homochiral MOFs that were further used as chiral stationary phases for high-performance liquid chromatography to separate the enantiomers of various kinds of racemic sulfoxides, sec-alcohols, β-lactams, benzoins, flavanones and epoxides. The experimental results showed excellent performances for enantioseparation, and highlighted that enantioseparation on homochiral MOF columns is practical.
- Tanaka, Koichi,Muraoka, Toshihide,Otubo, Yasuhiro,Takahashi, Hiroki,Ohnishi, Atsushi
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p. 21293 - 21301
(2016/03/08)
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- Efficient HPLC enantiomer separation using a pillared homochiral metal-organic framework as a novel chiral stationary phase
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HPLC enantioseparation of racemates using novel pillared homochiral metal-organic framework-silica composite as chiral stationary phase has been successfully demonstrated.
- Tanaka, Koichi,Hotta, Naoki,Nagase, Shohei,Yoza, Kenji
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supporting information
p. 4891 - 4894
(2016/07/06)
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- Enantioselective sulfoxidation reaction catalyzed by a G-quadruplex DNA metalloenzyme
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Enantioselective sulfoxidation reaction is achieved for the first time by a DNA metalloenzyme assembled with the human telomeric G-quadruplex DNA and Cu(ii)-4,4′-bimethyl-2,2′-bipyridine complex, and the mixed G-quadruplex architectures are responsible for the catalytic enantioselectivity and activity.
- Cheng, Mingpan,Li, Yinghao,Zhou, Jun,Jia, Guoqing,Lu, Sheng-Mei,Yang, Yan,Li, Can
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p. 9644 - 9647
(2016/08/04)
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- Method for preparing chiral sulfoxide through catalysis of asymmetric oxidation of thioether
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The invention provides a method for preparing chiral sulfoxide. According to the method, in a mixed solvent, thioether is used as a substrate, a complex produced by chiral tetradentate organic ligand and a metal manganese compound in situ is used as a cat
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Paragraph 0058; 0059; 0060; 0061; 0062
(2016/10/10)
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- Enantioselective oxidation of sulfides with H2O2 catalyzed by a pre-formed manganese complex
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A facile and environmentally friendly method is presented for the asymmetric oxidation of sulfides with H2O2, utilizing a pre-formed manganese complex. Just in the presence of a low catalytic amount of carboxylic acid (CA), a variety of sulfide substrates, including aryl alkyl, aryl benzyl and cyclic sulfides, reacted to form chiral sulfoxides in high yields (up to 95%) and excellent enantioselectivities (>99% ee) under mild conditions. Moreover, the practical utility of the method has been demonstrated by the synthesis of esomeprazole and albendazole sulfoxide (ABZO).
- Dai, Wen,Li, Guosong,Wang, Lianyue,Chen, Bo,Shang, Sensen,Lv, Ying,Gao, Shuang
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p. 46545 - 46554
(2014/12/10)
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- Titanium-salan-catalyzed asymmetric sulfoxidations with H2O 2: Design of more versatile catalysts
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Titanium-salan complexes with 3,3'-diphenyl substituents in the salicylidene rings of the salan ligand are efficient sulfoxidation catalysts, capable of catalyzing the asymmetric oxidation of bulky aryl benzyl sulfides with H2O2 with good to high enantioselectivities. In this paper, substituent effects on titanium-salan-catalyzed enantioselective oxidation of sulfides to sulfoxides have been systematically investigated. Titanium-salan catalysts with halogen substituents at the 5,5'-positions (3,3'-H2dihydrogen substituted) have been found to catalyze the oxidation of both bulky aryl benzyl sulfides and small alkyl phenyl sulfides with good to high enantioselectivities. Kinetic data witness a direct attack of the sulfide to the electrophilic active oxygen species; a consistent reaction mechanism is proposed. Copyright 2013 John Wiley & Sons, Ltd. Titanium-salan complexes with halogen substituents at the 5,5'-positions are versatile catalysts for the oxidation of both bulky aryl benzyl sulfides and small alkyl phenyl sulfides, demonstrating good to high chemoselectivity (up to 92 %) and enantioselectivity (up to 93 % ee). Copyright
- Talsi, Evgenii P.,Bryliakov, Konstantin P.
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p. 239 - 244
(2013/06/04)
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- Chiral microporous Ti(salan)-based metal-organic frameworks for asymmetric sulfoxidation
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Chiral porous metal-metallosalan frameworks are constructed from an unsymmetrical chiral pyridinecarboxylate ligand derived from Ti(salan) and are shown to be heterogeneous catalysts for asymmetric oxidation of thioethers to sulfoxides.
- Zhu, Chengfeng,Chen, Xu,Yang, Zhiwei,Du, Xia,Liu, Yan,Cui, Yong
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p. 7120 - 7122
(2013/08/23)
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- PROCESS FOR THE ASYMMETRIC OXIDATION OF ORGANIC COMPOUNDS WITH PEROXIDES IN THE PRESENCE OF A CHIRAL ACID CATALYST
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The present invention relates to a process for the asymmetric oxidation of nucleophilic organic compounds, particularly metal-free, with peroxide compounds in the presence of a chiral Bronsted acid catalyst. In one detail, the present invention relates to a process for enantioselective sulfoxidation of thiocompounds with peroxide compounds in the presence of a chiral imidodiphosphate catalyst. In another detail, the present invention relates to a process for enantioselective sulfoxidation of thiocompounds with peroxide compounds in the presence of a chiral phosphoric acid catalyst.
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Page/Page column 19-23
(2013/07/25)
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- Supramolecular assembly of chiral polyoxometalate complexes for asymmetric catalytic oxidation of thioethers
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In this paper, a chiral amphiphilic cation with two stereocenters has been employed to encapsulate a well-known catalytically activated sandwich-type polyoxometalate, Na12[WZn3(H2O) 2(ZnW9O34)2], through electrostatic interaction. The prepared chiral organic cation-encapsulated polyoxometalate complexes were found to self-aggregate into spherical supramolecular assemblies with a diameter of ca. 100 nm in the reaction solution. These assemblies, serving as microreactors, exhibited an efficient asymmetric catalytic activity for the oxidation of sulfide with up to 72% enantiomeric excess. The coverage density of chiral organic cations enwrapped on the polyoxometalate surface was proved to have an important influence on the enantioselectivity. Detailed kinetic study of the catalytic process showed that the enantioselectivity of sulfide oxidation was derived from the combination of an ineffective asymmetric sulfoxidation and an effective kinetic resolution of the sulfoxide. The present research strategically offers an understanding for the direct and efficient construction of polyoxometalate based supramolecular catalysts for asymmetric reactions through controlling the surface microenvironment.
- Wang, Yizhan,Li, Haolong,Qi, Wei,Yang, Yang,Yan, Yi,Li, Bao,Wu, Lixin
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p. 9181 - 9188
(2013/01/13)
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- Activation of H2O2 by chiral confined Bronsted acids: A highly enantioselective catalytic sulfoxidation
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Confined chiral Bronsted acids are shown to catalyze asymmetric oxidations of sulfides to sulfoxides with hydrogen peroxide. The wide generality and high enantioselectivity of the developed method compare even to the best metal-based systems and suggest utility in other asymmetric oxidations.
- Liao, Saihu,Coric, Ilija,Wang, Qinggang,List, Benjamin
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supporting information; experimental part
p. 10765 - 10768
(2012/08/28)
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- Catalytic enantioselective oxidation of bulky alkyl aryl thioethers with H2O2 over titanium-salan catalysts
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A simple and efficient catalytic procedure for the oxidation of bulky (preferably aryl benzyl substituted) thioethers with hydrogen peroxide in good to high yields and enantioselectivities (up to 98.5%ee) is reported. The high optical yields are achieved in a tandem stereoconvergent enantioselective oxidation and kinetic resolution process. A reasonable balance between the sulfoxide yield and enantioselectivity could be found by varying the concentration and temperature. An improved synthesis of the titanium-salan catalysts for the preparation of a more stereoselective catalyst is reported.
- Bryliakov, Konstantin P.,Talsi, Evgenii P.
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experimental part
p. 4693 - 4698
(2011/10/03)
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- Organocatalytic asymmetric synthesis of sulfoxides from sulfenic acid anions mediated by a cinchona -derived phase-transfer reagent
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Preliminary results concerning a conceptually novel route to chiral sulfoxides based on the asymmetric alkylation of sulfenate salts with alkyl halides mediated by a chiral phase-transfer catalyst are described. As a representative example, o-anisyl methyl sulfoxide was produced in 96% yield and with an enantiomeric excess of 58% using commercial cinchonidinium derivative 2a.
- Gelat, Fabien,Jayashankaran, Jayadevan,Lohier, Jean-Francois,Gaumont, Annie-Claude,Perrio, Stephane
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p. 3170 - 3173
(2011/08/06)
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- Planar chiral flavinium salts - Prospective catalysts for enantioselective sulfoxidation reactions
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A novel planar chiral flavinium salt, 3-benzyl-5-ethyl-10-(8- phenylnaphthalen-1-yl)isoalloxazinium perchlorate (2b), which bears a phenyl cap that covers one side of the isoalloxazinium skeleton plane, has been prepared as a potential catalyst for the enantioselective H2O2 oxidation of sulfides. The rate of H2O2 oxidation of sulfides in the presence of racemic 2b is comparable to that of the reaction catalysed by 5-ethyl-3,10-dimethylisoalloxazinium perchlorate, which indicates that the bulky shielding substituent does not influence the catalytic activity of the flavinium unit. The turnover frequency for the oxidation of thioanisole with hydrogen peroxide with 2b is 870 h-1. The enantiomerically pure salts (+)-2b and (-)-2b were prepared from the pure enantiomers (+)-3b and (-)-3b of 3-benzyl-10-(8-phenylnaphthalen-1-yl)isoalloxazine (3b) obtained by HPLC separation of racemic 3b on a chiral stationary phase. The enantiomerically pure salts (+)-2b and (-)-2b catalyse the H2O2 oxidation of para-substituted thioanisoles with enantiomeric excesses of 34-44%. The highest enantioselectivity (54% ee) was observed in the oxidation of methyl naphthyl sulfide.
- Jurok, Radek,Cibulka, Radek,Dvorakova, Hana,Hampl, Frantisek,Hodacova, Jana
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experimental part
p. 5217 - 5224
(2010/11/02)
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- Titanium-salan-catalyzed asymmetric oxidation of sulfides and kinetic resolution of sulfoxides with H2O2 as the oxidant
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Asymmetric oxidation of sufides to sulfoxides by aqueous hydrogen peroxide with catalysis by titanium-salan complexes is presented. Optically active sulfoxides have been obtained with good to high enantioselectivities (up to 97% ee) by a tandem enantioselective oxidation and kinetic resolution procedure, the catalyst performing over 500 turnovers with no loss of enantioselectivity. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Bryliakov, Konstantin P.,Talsi, Evgenii P.
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scheme or table
p. 3369 - 3376
(2009/04/07)
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- Artificial metalloenzyme for enantioselective sulfoxidation based on vanadyl-loaded streptavidin
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Nature's catalysts are specifically evolved to carry out efficient and selective reactions. Recent developments in biotechnology have allowed the rapid optimization of existing enzymes for enantioselective processes. However, the ex nihilo creation of catalytic activity from a noncatalytic protein scaffold remains very challenging. Herein, we describe the creation of an artificial enzyme upon incorporation of a vanadyl ion into the biotin-binding pocket of streptavidin, a protein devoid of catalytic activity. The resulting artificial metalloenzyme catalyzes the enantioselective oxidation of prochiral sulfides with good enantioselectivities both for dialkyl and alkyl-aryl substrates (up to 93% enantiomeric excess). Electron paragmagnetic resonance spectroscopy, chemical modification, and mutagenesis studies suggest that the vanadyl ion is located within the biotin-binding pocket and interacts only via second coordination sphere contacts with streptavidin.
- Pordea, Anca,Creusa, Marc,Panek, Jaroslaw,Duboc, Carole,Mathis, Deborah,Novic, Marjana,Ward, Thomas R.
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experimental part
p. 8085 - 8088
(2009/02/01)
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- Development and application of versatile bis-hydroxamic acids for catalytic asymmetric oxidation
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In this article, we describe the development and preliminary results of our new designed C2-symmetric bis-hydroxamic acid (BHA) ligands and the application of the new ligands for vanadium-catalyzed asymmetric epoxidation of allylic alcohols as well as homoallylic alcohols. From this success we demonstrate the versatile nature of BHA in the molybdenum catalyzed asymmetric oxidation of unfunctionalized olefins and sulfides.
- Barlan, Allan U.,Zhang, Wei,Yamamoto, Hisashi
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p. 6075 - 6087
(2008/02/03)
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- Efficient soluble polymer-supported tartrate/Ti catalyst for asymmetric oxidation of prochiral sulfides
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A group of soluble polymer-supported chiral tartrate ligands was prepared by liquid-phase synthesis with ligand diversity strategy. Moderate to excellent chemical yields and enantiomeric excesses were obtained by using soluble polymer-supported tartrate ester in asymmetric oxidation of prochiral sulfides using Ti(O-i-Pr)4/cumyl hydroperoxide, and the workup was greatly simplified. The influence of substituent in chiral tartrate ligands on the enantioselectivities of the reaction was disclosed.
- Gao, Jinshan,Guo, Hongchao,Liu, Shangzhong,Wang, Min
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p. 8453 - 8455
(2008/03/13)
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- Enantioselective sulfoxidation and kinetic resolution combined protocol mediated by a functionalized (S)-norcamphor-based hydroperoxide/titanium(IV) isopropoxide system
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A functionalized tertiary furyl hydroperoxide derived from (S)-norcamphor has been easily synthesized in good yield and in a highly diastereoselective manner. Good to high enantioselectivities (up to 99% ee) and acceptable to good yields (up to 86%) were achieved for the sulfoxides, by tandem stereoconvergent asymmetric sulfoxidation and kinetic resolution when using the novel hydroperoxide s oxygen donor and chirality source in the presence of catalytic loadings of titanium(IV) isopropoxide as the catalyst.
- Lattanzi, Alessandra,Piccirillo, Sandro,Scettri, Arrigo
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p. 357 - 363
(2008/02/07)
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- Catalytic enantioselective oxidation of sulfides and disulfides by a chiral complex of bis-hydroxamic acid and molybdenum
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A chiral bis-hydroxamic acid (BHA)-molybdenum complex was used for the catalytic asymmetric oxidation of sulfides and disulfides utilizing one equivalent of alkyl peroxide with yields up to 83% and ee up to 86%. An extension of our methodology combines the asymmetric oxidation with kinetic resolution providing excellent enantioselectivity (ee 92-99%).
- Basak, Arindrajit,Barlan, Allan U.,Yamamoto, Hisashi
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p. 508 - 511
(2007/10/03)
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- Oxidative kinetic resolution of alkyl aryl sulfoxides
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Kinetic resolution is observed in the oxidation of racemic alkyl aryl sulfoxides using a combination of VO(acac)2 and ligand 1 in chloroform at 0 °C, conditions previously described for asymmetric oxidation of prochiral sulfides. Kinetic resolution is also observed in toluene as the solvent, although higher temperatures are required. Georg Thieme Verlag Stuttgart.
- Mohammadpoor-Baltork, Iraj,Hill, Mathias,Caggiano, Lorenzo,Jackson, Richard F. W.
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p. 3540 - 3544
(2007/10/03)
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- 4-Hydroxyacetophenone monooxygenase from Pseudomonas fluorescens ACB as an oxidative biocatalyst in the synthesis of optically active sulfoxides
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Recombinant 4-hydroxyacetophenone monooxygenase (HAPMO) from Pseudomonas fluorescens ACB has been tested as a catalyst in sulfoxidation reactions on a set of aromatic sulfides. With a few exceptions, excellent enantioselectivities in the synthesis of chiral phenyl and benzyl sulfoxides were achieved. The bacterial Baeyer-Villiger monooxygenase was also shown to accept racemic sulfoxides, a prochiral diketone and an organoboron compound as substrates. This study demonstrates the great biocatalytic potential of this novel oxidative enzyme.
- De Gonzalo, Gonzalo,Torres Pazmino, Daniel E.,Ottolina, Gianluca,Fraaije, Marco W.,Carrea, Giacomo
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p. 130 - 135
(2007/10/03)
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- Investigations on the iron-catalyzed asymmetric sulfide oxidation
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The development of an enantioselective sulfide oxidation involving a chiral iron catalyst and aqueous hydrogen peroxide as oxidant is described. In the presence of a simple carboxylic acid, or a carboxylate salt, the reaction affords sulfoxides with remarkable enantioselectivities (up to 96% ee) in moderate to good yields. The influence of the structure of the additive on the reaction outcome is reported. In the sulfoxide-to-sulfone oxidation a kinetic resolution (with s = 4.8) occurs, which, however, plays only a negligible role in the overall enantioselective process. Furthermore, a positive nonlinear relationship between the ee of the product and that of the catalyst has been found. On the basis of these observations, a possible catalyst structure is proposed.
- Legros, Julien,Bolm, Carsten
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p. 1086 - 1092
(2007/10/03)
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- A re-investigation of Modena's protocol for the asymmetric oxidation of prochiral sulfides
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The reactivity of commercially available or easily accessible hydroperoxides has been conveniently exploited for the achievement of highly efficient and enantioselective catalytic modifications of Modena's protocol for the asymmetric oxidation of sulfides. A notably enhanced enantioselectivity has been obtained by exploiting a concomitant process of stereoconvergent kinetic resolution taking place under catalytic conditions.
- Massa, Antonio,Mazza, Valeria,Scettri, Arrigo
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p. 2271 - 2275
(2007/10/03)
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- Vanadium-catalyzed sulfur oxidation/kinetic resolution in the synthesis of enantiomerically pure alkyl aryl sulfoxides
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(Chemical Equation Presented) The importance of the mix: The use of chloroform as solvent, the ligand (R)-2 and [VO(acac)2] as catalyst, and H2O2 as oxidant promotes the highly enantioselective oxidation of simple alkyl aryl sulfides 1 to give alkyl aryl sulfoxides (R)-3 (see scheme). The success of this process partly derives from an efficient kinetic resolution of the product sulfoxides.
- Drago, Carmelo,Caggiano, Lorenzo,Jackson, Richard F. W.
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p. 7221 - 7223
(2007/10/03)
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- Highly enantioselective iron-catalyzed sulfide oxidation with aqueous hydrogen peroxide under simple reaction conditions
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An attractive alternative to the currently existing methods for the metal-catalyzed oxidation of sulfides to sulfoxides is asymmetric iron-catalyzed oxidation with hydrogen peroxide as the terminal oxidant (see scheme). In the presence of a benzoic acid derivative, this simple process provides sulfoxides with up to 96% ee in moderate to good yields (up to 78%).
- Legros, Julien,Bolm, Carsten
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p. 4225 - 4228
(2007/10/03)
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- Ionic liquids as a new reaction medium for oxidase-peroxidase-catalyzed sulfoxidation
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The possibility of the application of oxidase and peroxidase as catalysts in ionic liquids is demonstrated in the chemo- and stereoselective oxidation of sulfides. The high operational stability of these enzymes in ionic liquids is reported. The substrate
- Okrasa, Krzysztof,Guibe-Jampel, Eryka,Therisod, Michel
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p. 2487 - 2490
(2007/10/03)
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- Vanadium-catalyzed enantioselective sulfoxidation of methyl aryl sulfides with hydrogen peroxide as terminal oxidant
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Chiral vanadium complex prepared in situ from VO(acac)2 and Schiff base 9 was found to be an efficient catalyst for oxidation of various methyl aryl sulfides with hydrogen peroxide as terminal oxidant. For example, oxidation of methyl 2-naphthyl sulfide using a VO(acac)2, 9, and hydrogen peroxide system proceeded with high enantioselectivity of 93% ee as well as acceptable chemical yield.
- Ohta,Shimizu,Kondo,Katsuki
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p. 161 - 163
(2007/10/03)
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- Enantioselective sulfide oxidation with H2O2: A solid phase and array approach for the optimisation of chiral Schiff base-vanadium catalysts
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Two libraries of chiral Schiff base ligands were synthesised and screened in the vanadium-catalysed oxidation of alkyl aryl sulfides with hydrogen peroxide as terminal oxidant. The vanadium-chiral Schiff base complex 10, readily prepared from 3,5-diiodo-salicylaldehyde and (S)-tert-leucinol, was found to be highly enantioselective. Optically active sulfoxides could thus be obtained in good yields with up to 97% ee.
- Pelotier, Béatrice,Anson, Mike S.,Campbell, Ian B.,Macdonald, Simon J. F.,Priem, Ghislaine,Jackson, Richard F. W.
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p. 1055 - 1060
(2007/10/03)
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- Towards a correlation of absolute configuration and chiroptical properties of alkyl aryl sulfoxides: A coupled-oscillator foundation of the empirical Mislow rule?
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The absorption and circular dichroism (CD) data for a series of alkyl aryl sulfoxides 1-16 of known S configuration have been analyzed. The strong bathochromic effect exerted by the nitro group in the para position of the phenyl sulfoxides indicates that the sulfur atom acts as an electron donor moiety towards the phenyl ring. Such behavior requires a significant 2p(C)-3sp3(S) overlap, and therefore the phenyl (and p-substituted phenyl) sulfoxides 1-12, as well as the 2-naphthyl sulfoxides 15 and 16, must assume a conformation which permits such orbital overlap. The steric effect of the peri hydrogen in 1-naphthyl-substituted compounds 13 and 14 does not allow a conformation of this type, and in these compounds the above-mentioned 2p(C) and 3sp3(S) orbitals are positioned in almost orthogonal planes. This conformational difference is clearly shown by the absorption spectra: compounds 1-12, 15, and 16 show the lowest energy σ → σ* transition of the sulfoxide chromophore at approximately 250 nm, indicating the existence of a conjugated S=O chromophore. In contrast, the corresponding absorption in 13 and 14 occurs at about 200 nm, indicating the presence of an isolated S=O chromophore. The CD spectra of 13 and 14 show a negative, couplet-like feature between 250 and 200 nm. This spectral feature can be interpreted in terms of exciton coupling between the allowed σ → σ* transition of the isolated S=O chromophore at 200 nm and the 1B transition of the naphthalene chromophore. In fact, the Harada-Nakanishi rule predicts a negative CD couplet for an S-configured sulfoxide in the conformation found by UV analysis, as found experimentally. The CD spectrum of 13 is quantitatively reproduced by DeVoe coupled-oscillator calculations, strongly implying that a coupled-oscillator mechanism is operative in determining the optical activity of 13 and 14. This approach has also tentatively been extended to the conjugated sulfoxides 1-12, taking into account the coupling of the benzene chromophore 1La transition with the σ → σ* transition of the S=O chromophore. In this case the Harada-Nakanishi rule also predicts a negative CD couplet for the S-configured sulf-oxides, as found experimentally.
- Rosini, Carlo,Donnoli, Maria Irene,Superchi, Stefano
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- Discovery of new solid phase sulfur oxidation catalysts using library screening
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The discovery of a new solid-supported ligand 5 for the catalytic asymmetric oxidation of aryl alkyl sulfides in up to 72% ee using Ti(Oipr)4 and aqueous H2O2 is reported.
- Green,Monti,Jackson,Anson,Macdonald
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p. 2594 - 2595
(2007/10/03)
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- Photophysics and photostereomutation of aryl methyl sulfoxides
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The effect of a methanesulfinyl group on the photophysics of several aromatic chromophores is reported. The spectroscopic singlet and triplet energies are affected only modestly, compared to that parent arenes, but the fluorescence yields fall by at least 1 order of magnitude. Fluorescence lifetimes are short. Fluorescence enhancements are observed on cooling the sulfoxides from room temperature to 77 K. High quantum yields of stereomutation are reduced as the temperature drops. There is not a consistent effect on triplet or phosphorescence yields. It is proposed that these results are consistent with a nonradiative pathway for deactivation of the singlet that results in stereomutation. A modest activation energy of a few kcal/mol is estimated for the photochemical racemization of 1-methanesulfinylpyrene.
- Lee,Jenks
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p. 474 - 480
(2007/10/03)
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- Tandem peroxidase-glucose oxidase catalysed enantioselective sulfoxidation of thioanisoles
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The synthesis of chiral sulfoxides from sulfides with high level of chemical conversion and asymmetric induction was discussed. The method used the oxygen transfer propensity of a peroxidase-glucose oxidase bioenzymatic system. The degree of conversion of
- Okrasa, Krzysztof,Guibe-Jampel, Eryka,Therisod, Michel
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p. 1077 - 1079
(2007/10/03)
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- Asymmetric synthesis with the enzyme Coprinus peroxidase: Kinetic resolution of chiral hydroperoxides and enantioselective sulfoxidation
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The enzyme Coprinus peroxidase (CiP) was employed for the kinetic resolution of racemic hydroperoxides 1 and the asymmetric sulfoxidation of prochiral sulfides 4. Eleven hydroperoxides 1a-k were reduced by CiP and guaiacol as reductant under conditions of kinetic resolution with enantioselectivities of up to >98% for the (S)-hydroperoxide 1 and 90% for the (R)-alcohol 2. In the absence of a reductant, the hydroperoxide 1a afforded with CiP enantiomerically enriched hydroperoxide la (ee up to 54%) and alcohol 2a (ee up to 40%), as well as ketone 3a (which is also formed simultaneously in all other reactions) and molecular oxygen. Catalase activity was established for CiP with hydrogen peroxide. When aryl alkyl sulfides 4 were used as oxygen acceptors, three products, sulfoxides 5, alcohols 2, and hydroperoxides 1, were obtained, all in enantiomerically enriched form. The highest ee value (89%) was achieved for the sulfoxide derived from naphthyl methyl sulfide (4f). Thus, CiP may be utilized for the asymmetric synthesis of optically active hydroperoxides 1, alcohols 2, and sulfoxides 5.
- Adam, Waldemar,Mock-Knoblauch, Cordula,Saha-Moeller, Chantu R.
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p. 4834 - 4839
(2007/10/03)
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- Hypervalent Iodine(V)-Induced Asymmetric Oxidation of Sulfides to Sulfoxides Mediated by Reversed Micelles: Novel Nonmetallic Catalytic System
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Although several types of chiral hypervalent iodine reagents have been used for asymmetric induction, all of them have needed more than a stoichiometric amount of chiral reagents and have shown low enantioselectivities. The described new catalytic asymmetric oxidation using a hypervalent iodine(V) reagent, iodoxybenzene (PhIO2), in a cationic reversed micellar system provides the first example of a catalytic asymmetric oxidation of sulfides to sulfoxides in high chemical yield with moderate to good enantioselectivity without the use of any transition-metal catalysts. The solubilization and activation of PhIO2 by adding catalytic amounts of both cetyltrimethylammonium bromide (CTAB) and a chiral tartaric acid derivative were found to be indispensable for the enhancement of chemical and optical yields.
- Tohma, Hirofumi,Takizawa, Shinobu,Watanabe, Hiroaki,Fukuoka, Yuko,Maegawa, Tomohiro,Kita, Yasuyuki
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p. 3519 - 3523
(2007/10/03)
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- Catalytic asymmetric oxidation of aryl sulfides with a Ti/H2O/(R,R)- diphenylethane-1,2-diol complex: A versatile and highly enantioselective oxidation protocol
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A new catalytic procedure for the asymmetric oxidation of aryl alkyl and aryl benzyl sulfides to optically active sulfoxides by hydroperoxides is described. This oxidation of sulfides is mediated by a chiral Ti complex formed in situ by reacting Ti(i-PrO)4, (R,R)-diphenylethane-1,2-diol (1), and water. The conditions of the reaction (stoichiometric composition of the catalyst, temperature, and the presence of additives and solvent) have been determined in order to reach the highest enantioselectivity and avoid the intervention of a kinetic resolution process. The oxidation protocol described herein is quite versatile as the values of chemical yields (60- 73%) and of enantioselectivity (ee 70-80%) achieved for aryl alkyl sulfides are almost independent of the nature of the aryl substituent and of the size of the alkyl group. Notably, aryl benzyl sulfides, which are poor substrates for the Ti/DET catalyzed oxidations, afforded very high ee's (92-99%) with this oxidation system.
- Donnoli, Maria Irene,Superchi, Stefano,Rosini, Carlo
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p. 9392 - 9395
(2007/10/03)
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- Asymmetric Oxidation of Alkyl Aryl Sulfides in Crystalline Cyclodextrin Complexes
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Alkyl aryl sulfides were enantioselectively oxidized in the crystalline cyclodextrin (CD) complexes under various conditions.The oxidation of alkyl phenyl sulfoxides in the β-cyclodextrin (β-CD) complexes resulted in higher chiral induction than that in t
- Sakuraba, Hidetake,Natori, Kazuhiro,Tanaka, Yoshio
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p. 4124 - 4129
(2007/10/02)
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