Resolution of sulfoxides

II. METHODS FOR OBTAINING OPTICALLY ACTIVE SULFOXIDES A, Resolution of Sulfoxides... 

Asymmetric oxidation of sulfides and kinetic resolution of sulfoxides... 

ASYMMETRIC OXIDATION OF SULFIDES AND KINETIC RESOLUTION OF SULFOXIDES... 

A different approach to the resolution of sulfoxides was recently reported by MikcJajczyk and Drabowicz (35). It takes advantage of the fact that sulfoxides as well as other sulfinyl compounds ry easily form inclusion complexes with 3-cyclodextrin. Since -cycl dextrin (the host) is chiral, its inclusion complexes with racemic guest substances are mixtures of diastereomeis that can be formed in unequal amounts. In this way a series of alkyl phenyl, alkyl p-tolyl, and alkyl benzyl sulfoxides has been resolved. However, the optical... 

Uemura and coworkers utilized (R)-binaphthol 85 as chiral ligand in place of DET in association with Ti(IV)/TBHP, which not only mediated the oxidation of sulfides to (R)-configurated sulfoxides, but also promoted the kinetic resolution of sulfoxides (equation 50). In this latter process the two enantiomers of the sulfoxide are oxidized to sulfone by the chiral reagent at different rates, with decrease of the chemical yield, but increase of the ee values. Interestingly, the presence of ortho-nilro groups on the binaphthol ligand lead to the reversal of enantioselectivity with formation of the (5 )-configurated sulfoxide. Non-racemic amino triols and simple 1,2-diols have been successfully used as chiral mediators. 

Sulfoxides 8 are resolved by 1 only if they have rather short alkyl chains (8d and 8e), whereas for those with longer alkyl moieties, the binaphthol 7 is the better guest. In general, 7 is very suitable for the resolution of sulfoxides and sulfoximines (10a and 10b). 

The asymmetric oxidation of thioethers as well as kinetic resolution of sulfoxides with 30% H2O2 catalyzed by a stable, recyclable and commercially avialable solid WO3 catalyst provides a simple and effective procedure for the preparation of chiral sulfoxides in good enantimeric purity. The procedure is very easy to perform. 

Resolution of Sulfoxides. Although it can be considered as the resolution of an unique type of carboxylic acid, some racemic sulfoxides containing carboxyhc acids have been resolved via diastereomeric crystalline complexes with brucine (eq 11). ... 

Davis, F. A., Billmers, J. M. Chemistry of oxaziridines. 5. Kinetic resolution of sulfoxides using chiral 2-sulfonyloxaziridines. J. Org. Chem. 

Kinetic resolutions. A chiral alcohol is obtained on. selective removal of one enantiomer by acetylation using a chiral analog 1 of DMAP, or by oxidation based on hydrogen transfer to acetone mediated by a Ru complex 2. Benzylic secondary alcohols are resolved by selective pivaloylation with optically activeA-pivaloyl-4-t-butylthiazolidine-2-thione. A kinetic resolution of sulfoxides is based on asymmetric oxidation with (i-PrO)4Ti-cumyl hydroperoxide in the presence of a tartrate ester. Kinetic resolution of 1,3-diarylallenes is realized by selective oxidation with NaClO catalyzed by a chiral (salen)manganese(III) complex, whereas asymmetric hydrolysis of terminal epoxides with the aid of a chiral (salen)cobalt(II) catalyst solves the problem of their accessibility. 

An example of a QSERR study is by Carotti [39]. It involves the resolution of sulfoxides, 20, on a it-acid CSP containing (S,S)-N,N -(3,5-dinitrobenzoyl)-frans-1,2-diaminocyclohexane (DACH-DNB), 19a. After establishing capacity factors, k s and k R for the first and second eluted enantiomers, respectively, as well as determining the separation factors, a, the authors began their computational studies. They used a variety of electronic descriptors for the analytes including electrophilic superdelocalizabilities (S omo) and nucleophilic superdelocalizabilities of various key analyte atoms... 

Sulfides can usually be selectively oxidised to sulfoxides without (too much) over-oxidation to the corresponding sulfones. However, the conversion of sulfoxides into sulfones can be achieved under relatively mild catalytic conditions, if required. Uemura has demonstrated a kinetic resolution of sulfoxides by catalysed oxidation. For example, the oxidation of racemic phenyhnethylsulfoxide (5.152)... 

Scheme 2.64 Resolution of sulfoxide esters by Pseudomonas sp. lipase...

Bryliakov, K. and Talsi, E. (2008). Titanium-Salan-Catalyzed Asymmetric Oxidation of Sulfides and Kinetic Resolution of Sulfoxides with H2O2 as the Oxidant, Eur. J. Org. Chem., 19, pp. 3369-3376. 

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