Sulfoxides chiral recognition

Optical resolution of selenoxides by complexation is more efficient than that of sulfoxides. Although efficiency of the resolution for o- and />-tolyl-substituted sulfo- xides is not good, the efficiency for selenoxides with the same substituent is good. In order to clarify the mechanism of the efficient chiral recognition, X-ray crystal structure of a 1 1 complex of 14b and (-)-126f was studied.52... 

Using a chiral recognition rationale, Plrkle, et fd (10) designed a chiral fluoroalcohollc bonded stationary phase which separates the enantiomers of sulfoxides, lactones, and derivatives of alcohols, amines, amino acids, hydroxy acids, and mercaptans. 

A study on the time course of the enantiomeric excess of the sulfoxide revealed that it was highly dependent on the reaction time. In addition, as the reaction proceeded, the formation of sulfone was observed. With the gradually increasing amounts of sulfone the ee of the sulfoxide was raised. This dependence of the enantiomeric excess on time and sulfone formation indicated that a kinetic resolution process of the newly formed sulfoxide took place. Chiral recognition of the (S)-sulfoxide by the Ti(OiPr)4/(i )-BINOL complex led preferably to consumption of this enantiomer and thereby raised the enantiomeric excess of the fi j-sulfoxide. 

From their QSERR they find solute lipophilicity and steric properties as being responsible for analyte retention (k ) while enantioseparation (a) varied mainly with electronic and steric properties. The main difference between the analytes is that the enantioseparation of the esters is correlated with steric parameters that scale linearly with log a while the sulfoxides scale nonlinearly (parabolic), but this may be due to a computational artifact. The 3D-QSERR derived from field analysis revealed that while superpositioning of field maps for both analytes are not exactly the same, a similar balance of physicochemical forces involved in the chiral recognition process are at play for both sets of analyes. This type of atomistic molecular modeling, then, is a powerful adjunct to the type of modeling described earlier in this chapter and will, no doubt, be used more frequently in future studies. 

Davis et al. used a chiral oxaziridine for the asymmetric oxidation of sulfides to sulfoxides.Oxidation of isopropyl- -tolyl sulfide (427) with oxaziridine 428, for example, gave 60.3% ee (S) of 429 (at -78°C in chloroform).5 0 The absolute configuration of the sulfide is determined by approach of the sulfide to the oxaziridine oxygen, as illustrated by 430. Steric factors appear to be the primarily reason for the chiral recognition. 5 1 In this model, attack by sulfur minimizes the Rl and Rs interactions with the oxaziridine... 

Enantiopure sulfinimines are ammonia imine synthons useful in the asymmetric synthesis of amines and -amino acid derivatives. Sulfinimines unavailable via the Andersen synthesis (R = H) are prepared hy asymmetric oxidation of the sulfenimines, ArS-N=C(R)PhX, with (+)-( ) or (-)-(1) at -20 to 20 °C in CCI4 (eq 8). Crystallization improves the ee to >95%. The sulfoxide chiral recognition model correctly predicts the configuration of the product. 

It should be noted that benzyl methyl sulfoxide was included without the recognition of its chirality (entry 7 in Table 1) [23]. Using single-crystal X-ray analyses... 

It should be noted that benzyl methyl sulfoxide was included without the recognition of their chirality (entry 7 in Table 4).26 By single crystal X-ray analyses of this inclusion compound, it was elucidated that the molecules of 1 form the layer structure similar to the one of the above alkyl phenyl sulfoxide-inclusion crystals, and the sulfoxides are included between these layers. There are two different recognition cavities on the upper side for its S enantiomer and on the lower side for its K enantiomer. The upper side cavity can be illustrated by motif A, and the lower side one by motif B in Figure 16. 

Kielbasirisky et al. (2008) have recently demonstrated the first case of enzymatic recognition of a nitrile with a P chiral snlfnr atom. Nine different commercial nitri-lases were screened using cyanomethyl p-tolyl sulfoxide as substrate all reactions occurred in a mixture of buffer phosphate and a co-solvent was used to dissolve the substrate. Very interestingly, they obtained both the acid and the amide as hydrolysis products with different ee and absolnte confignrations depending on the enzyme used (Table 17.17). 

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