Titanium‐Catalyzed Tandem Sulfoxidation‐Kinetic Resolution Process: A Convenient Method for Higher Enantioselectivities and Yields of Chiral Sulfoxide

Jia, Xian; Li, Xingshu; Xu, Lijin; Li, Yue‐Ming; Shi, Qian; Au‐Yeung, Terry T.‐L.; Yip, Chiu Wing; Yao, Xin‐Sheng; Chan, Albert S. C.

doi:10.1002/adsc.200404018

Cited by 58 publications

(27 citation statements)

References 34 publications

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“…[34] The process developed by Uemura and co-workers [33,35] has been exploited by Scettri and co-workers (using furyl hydroperoxides as the oxidant) [36] and more recently by Chan and co-workers (using tertbutylhydroperoxide as the oxidant). [37] Specifically, Chan and co-workers described a process in which an initial oxidation at 0 8C (at which temperature the enantioselectivity is optimum) and then at 25 8C (where the kinetic resolution is most efficient) allowed the isolation of sulfoxides in reasonable yields and excellent ee values (65 % and 99.9 % ee in the case of methyl para-tolyl sulfoxide, the best so far published). [37] However, it appears that no significant kinetic resolution in the oxidation of sulfoxides has so far been reported in studies in which chiral vanadium(iv)-Schiff base complexes were used.…”

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confidence: 96%

“…[37] Specifically, Chan and co-workers described a process in which an initial oxidation at 0 8C (at which temperature the enantioselectivity is optimum) and then at 25 8C (where the kinetic resolution is most efficient) allowed the isolation of sulfoxides in reasonable yields and excellent ee values (65 % and 99.9 % ee in the case of methyl para-tolyl sulfoxide, the best so far published). [37] However, it appears that no significant kinetic resolution in the oxidation of sulfoxides has so far been reported in studies in which chiral vanadium(iv)-Schiff base complexes were used. Nevertheless, such an effect has been reported in the case of vanadium-salan systems (selectivity factor S = 7.3 for the resolution of methyl phenyl sulfoxide) when larger amounts of catalyst (5 mol %) were used.…”

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confidence: 96%

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Vanadium‐Catalyzed Sulfur Oxidation/Kinetic Resolution in the Synthesis of Enantiomerically Pure Alkyl Aryl Sulfoxides

2005

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Chiral sulfoxides are an important class of compounds that find increasing use as chiral auxiliaries in asymmetric synthesis. [1,2] Current interest also reflects the existence of products with biological properties containing a sulfinyl group with a defined configuration. [3] Several methods for the asymmetric oxidation of prochiral sulfides have been reported, including the use of chiral oxidants, such as chiral oxaziridines, [4] chiral hydroperoxides, [5] and enzymes. [6,7] The majority of investigations have concentrated on the use of chiral metal complexes [1,3,[8][9][10][11] following the initial reports by Kagan and co-workers [12,13] and Modena and co-workers [14] on the use of variously modified Sharpless reagents for this reaction.One of the most widely studied metal-based systems has been that discovered by Bolm and Bienewald, [15,16] who employed a combination of Schiff bases 1 derived from chiral amino alcohols and [VO(acac) 2 ] (1.0 mol %; acac = acetylacetanoate), with aqueous hydrogen peroxide as the oxidant, in a two-phase system using dichloromethane as the solvent at 20 8C (Scheme 1). The advantages of the system developed by Bolm et al. include high activity, the very simple reaction conditions, and the use of hydrogen peroxide as the oxidant. The only drawback associated with the initial ligands tested was that the levels of enantiomeric excess were good, rather than excellent. Other research groups sought to optimize the system, by variation of the aromatic aldehyde, [17][18][19] the amino alcohol, [20] and the manner of addition of hydrogen peroxide, [21] and in many cases it is striking that the best outcome was usually obtained when the reaction was conducted in dichloromethane at 0 8C. A very nice application of the system developed by Bolm et al. was the asymmetric oxidation of ditert-butyl disulfide, reported by Ellman and co-workers, [22] who have since reported the results of spectroscopic studies with a view to understanding the nature of the active catalytic species better.[23] The nature of the active species is still not completely established, but while spectroscopic studies indicate the presence of a vanadium(v)oxomonoperoxo species, [24] recent calculations suggest that the active species may be a vanadium(v)oxohydroperoxide. [25] Recently, the use of analogous salan ligands has been reported to give high levels of enantioselectivity (95 % ee) in the oxidation of methyl phenyl sulfide, but lower levels of enantioselectivity were observed with other substrates. [26] Anson and co-workers screened a variety of chiral Schiff base ligands, and found that the 3,5-diiodo ligand (S)-2, in combination with [VO(acac) 2 ] gave excellent results in the catalytic asymmetric sulfoxidation of alkyl aryl sulfides with hydrogen peroxide, again in dichloromethane at 0 8C.[27] For example, methyl phenyl sulfide was oxidized to (S)-methyl phenyl sulfoxide (81 %, 90 % ee). Recently, Bolm and coworkers reported that a combination of this ligand with iron is also very effective for the asymmetric ox...

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Vanadium‐Catalyzed Sulfur Oxidation/Kinetic Resolution in the Synthesis of Enantiomerically Pure Alkyl Aryl Sulfoxides

2005

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“…[4b,8] Recently Chan developed a one-pot, titanium-catalyzed tandem sulfoxidation and kinetic resolution process, which proceeded at different temperatures and gave extremely high ee values and acceptable yields of chiral sulfoxides. [9] Katsuki found that 10% sulfone was observed in the case of methyl p-nitrophenyl sulfide as substrate during vanadium-catalyzed sulfoxidation;…”

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confidence: 99%

Vanadium‐Catalyzed Enantioselective Sulfoxidation and Concomitant, Highly Efficient Kinetic Resolution Provide High Enantioselectivity and Acceptable Yields of Sulfoxides

Zeng

Wang

et al. 2005

Adv Synth Catal

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Simple, inexpensive, preformed vanadiumSchiff base complexes were facilely prepared and used in enantioselective sulfoxidation. Both the amount of aqueous H 2 O 2 and reaction time greatly influenced the ee values and yields of chiral sulfoxides. High enantioselectivities (up to 99% ee) and reasonable yields ( > 40%) for various chiral sulfoxides were achieved by combining enantioselective sulfoxidation and appropriate concomitant kinetic resolution.

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“…Although a number of approaches using catalytic Ti-complexes of chiral diols have been described in the literature, [19][20][21][22][23][24] many of these cannot be considered truly catalytic, either because they employ only substoichiometric amounts of Ti and diol (up to 0.4 equiv) 21 or give good enantioselectivity not in the enantioselective sulfide oxidation process, but mainly thanks to a kinetic resolution process 25 determined by a concomitant enantioselective overoxidation of the sulfoxide to sulfone. 19,23,[26][27][28][29][30][31][32] In the latter case, although the ee's of sulfoxides are high, this goal is reached with significant reduction of chemical yields, which often do not exceed 50%. Some years ago we described a real catalytical oxidation of sulfides in which the use of 5% mol of a catalyst formed in situ by reacting Ti(i-PrO) 4 , enantiopure 1,2-diphenylethan-1,2-diol (1a), and water gave the optically active sulfoxide in good to high ee's avoiding the overoxidation of sulfoxide to sulfone and kinetic resolution.…”

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confidence: 95%

Enantioselective oxidation of sulfides catalyzed by titanium complexes of 1,2‐diarylethane‐1,2‐diols: Effect of the aryl substitution

et al. 2008

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The effects of the substitution on the aryl moiety on the asymmetric oxidation of sulfides mediated by Ti-complexes of chiral 1,2-diarylethane-1,2-diols were investigated. The substitution of the aryl ring of the diol with both EWG and EDG substituents generally decreased the enantioselectivity with respect to the use of unsubstituted 1,2-diphenylethane-1,2-diol (1a). Only in the presence of 1,2-di(4-t-butyl)phenyl-1,2-diol (1g) were higher ee's obtained with aryl methyl and aryl benzyl sulfides affording ee's up to 90 and 99%, respectively. Lower ee's were achieved with larger naphthyl and aryl alkyl sulfides. Contrary to the other Ti-alcoholates used in the oxidation of sulfides, the Ti-complex of diol 1g was soluble in hexane, allowing us to perform the process with high enantioselectivity in this solvent, with great environmental advantages over the commonly used chlorinated solvents.

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Titanium‐Catalyzed Tandem Sulfoxidation‐Kinetic Resolution Process: A Convenient Method for Higher Enantioselectivities and Yields of Chiral Sulfoxide

Cited by 58 publications

References 34 publications

Vanadium‐Catalyzed Sulfur Oxidation/Kinetic Resolution in the Synthesis of Enantiomerically Pure Alkyl Aryl Sulfoxides

Vanadium‐Catalyzed Sulfur Oxidation/Kinetic Resolution in the Synthesis of Enantiomerically Pure Alkyl Aryl Sulfoxides

Vanadium‐Catalyzed Enantioselective Sulfoxidation and Concomitant, Highly Efficient Kinetic Resolution Provide High Enantioselectivity and Acceptable Yields of Sulfoxides

Enantioselective oxidation of sulfides catalyzed by titanium complexes of 1,2‐diarylethane‐1,2‐diols: Effect of the aryl substitution

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