- Flexible C2-symmetric bis-sulfoxides as ligands in enantioselective 1,4-addition of boronic acids to electron-deficient alkenes
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The application of acyclic C2-symmetric chelating bis-sulfoxide ligands in the Rh(I)-catalyzed enantioselective 1,4-addition of boronic acids to electron-deficient alkenes is reported. Among the acyclic ethane-bridged bis-sulfoxides tested, the
- Khiar, Noureddine,Salvador, Alvaro,Valdivia, Victoria,Chelouan, Ahmed,Alcudia, Ana,Alvarez, Eleuterio,Fernandez, Inmaculada
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p. 6510 - 6521
(2013/07/26)
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- Sequential deracemization of sulfoxides via whole-cell resolution and heterogeneous oxidation
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A new concept for the synthesis of asymmetric sulfoxides exploiting sequential deracemization of racemic (rac) sulfoxides using a two-stage protocol had been developed. Enantio-pure sulfoxide was obtained using Escherichia coli (E. coli) cells to catalyze the reduction of (R)-sulfoxide to the thioether, and then using a heterogeneous Ta2O5-SiO2 catalyst for catalyzing the oxidation of the ethers to the rac-sulfoxide. The performance of E. coli depended on the strain and the conditions under which the bacteria growth was carried out (e.g. source of carbon, presence of vitamins, and concentration of dimethyl sulfoxide, DMSO). Under optimized conditions, the E. coli cells performed the rac-sulfoxide resolution for different sufoxides leading to the best enantiomeric excess (ee) of around 62% (S)-MTSO (methyl tolyl sulfoxide) with 49% conversion of the rac-MTSO. The sequential deracemization process applied for rac-MTSO was cyclically performed leading to 97.5% ee of (S)-sulfoxide and a 56% yield in (S)-sulfoxide after three deracemization cycles of rac-MTSO.
- Tudorache, Madalina,Nica, Simona,Bartha, Emerich,Lupan, Iulia,Parvulescu, Vasile I.
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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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- Photopromoted Ru-catalyzed asymmetric aerobic sulfide oxidation and epoxidation using water as a proton transfer mediator
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Ru(NO)-salen complexes were found to catalyze asymmetric aerobic oxygen atom transfer reactions such as sulfide oxidation and epoxidation in the presence of water under visible light irradiation at room temperature. Oxidation of sulfides including alkyl aryl sulfides and 2-substituted 1,3-dithianes using complex 2 as the catalyst proceeded with moderate to high enantioselectivity of up to 98% ee, and epoxidation of conjugated olefins using complex 3 as the catalyst proceeded with good to high enantioselectivity of 76-92% ee. Unlike biological oxygen atom transfer reactions that need a proton and electron transfer system, this aerobic oxygen atom transfer reaction requires neither such a system nor a sacrificial reductant. Although the mechanism of this oxidation has not been completely clarified, some experimental results support the notion that an aqua ligand coordinated with the ruthenium ion serves as a proton transfer agent for the oxygen activation process, and it is recycled and used as the proton transfer mediator during the process. Thus, we have achieved catalytic asymmetric oxygen atom transfer reaction using molecular oxygen that can be carried out under ambient conditions.
- Tanaka, Haruna,Nishikawa, Hiroaki,Uchida, Tatsuya,Katsuki, Tsutomu
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supporting information; experimental part
p. 12034 - 12041
(2010/11/04)
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- Highly enantioselective oxidation of sulfides to sulfoxides by a new oxaziridinium salt
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The new oxaziridinium salt 5 (R2 = TBDPS) is an effective reagent for the highly enantioselective oxidation of sulfides to sulfoxides with up to >99% ee and good yields. As such, it represents a new valuable nonmetallic alternative to the existing methods for asymmetric sulfoxidation.
- Del Rio,Wang,Achab,Bohe
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p. 2265 - 2268
(2008/02/04)
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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 General and Expeditious One-Pot Synthesis of Sulfoxides in High Optical Purity from Norephedrine-Derived Sulfamidites
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A general and simple procedure for preparing any kind of enantiomerically enriched sulfoxide starting from norephedrine-derived N-benzyloxycarbonylsulfamidite 3a is reported. After one-pot reaction of 3a with RMgX, HBF4, and R'MgX, a variety of sulfoxides 6 are obtained in ee usually higher than 93% and isolated yields ranging between 50 and 78%. The obtained configuration is tunable by simply electing the order of the addition of the reagents.
- Ruano, Jose L. Garcia,Alemparte, Carlos,Aranda, M. Teresa,Zarzuelo, Maria M.
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- Dynamic kinetic transformation of sulfinyl chlorides: Synthesis of enantiomerically pure C2-symmetric bis-sulfoxides
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Two modular and highly convergent approaches for the synthesis of both isomers of a large number of optically pure C2-symmetric bis-sulfoxides have been developed, and their scope and limitations have been assessed. The first one uses as intermediate diastereomerically pure C2-symmetric bis-sulfinate esters 6(Ss,Ss) and 6(Rs,Rs), obtained by dynamic kinetic resolution of ethane-1,2-bis-sulfinyl chloride 5. A single inducer of chirality, the glucose-derived DAG (diacetone-D-glucose) 1 is used for the enantioselective synthesis of both diastereomerically pure C2-symmetric bis-sulfinate esters, thanks to the opposite stereodirecting effect of pyridine and iPr2NEt used to catalyze the reaction. The second approach is based on the copper-catalyzed oxidative coupling of optically pure lithiomethyl sulfoxides. Both isomers of a large number of methyl sulfoxides can be obtained in a convergent manner using (Rs)- and (Ss)-DAG methanesulfinate esters 8Rs and 8Ss. Methanesulfinates 8Rs and 8Ss are also obtained in an enantioselective way by a dynamic kinetic resolution of methane sulfinyl chloride 24. The final bis-sulfoxides are obtained with enhanced enantioselectivities compared to the corresponding monomers, as a result of the Horeau effect which is operating in both approaches. A model based on the formation of pentacoordinated sulfur intermediate is proposed. This model can explain the dynamic kinetic resolution observed via Berry pseudorotations, without the commonly accepted in situ racemization of the starting material. The usefulness of the approaches is demonstrated by the preparation of complexes of Pd(II) and Ru(II) bearing bidentated chiral sulfoxides as ligands.
- Khiar, Noureddine,Araujo, Cristina S.,Alcudia, Felipe,Fernandez, Inmaculada
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p. 345 - 356
(2007/10/03)
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