Sulfoxides, alkyl phenyl inclusion

Cyclodextrins, toroidal molecules composed of 6, 7 and 8 D-glucose units, are now commercially available at reasonable cost. They form inclusion compounds with a variety of molecules and often differentially include sulfoxide enantiomers29,30. This property has been used to partially resolve some benzyl alkyl, phenyl alkyl and p-tolyl alkyl sulfoxides. The enantiomeric purities after one inclusion process ranged from 1.1 % for t-butyl p-tolyl sulfoxide to 14.5% for benzyl r-butyl sulfoxide. Repeating the process on methyl p-tolyl sulfoxide (10) increased its enantiomeric purity from 8.1% to 11.4% four recrystallizations raised the value to 71.5%. The use of cyclodextrins in asymmetric oxidations is discussed in Section II.C.l and in the resolution of sulfmate esters in Section II.B.l. 

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... 

As mentioned in Section 2, isopropyl phenyl sulfoxide was included in the crystals of 1 with a high enantioselectivity of its (.S )-form. Generally, the inclusion compound of a sulfoxide was prepared by two methods (1) insoluble 1 was simply stirred in the presence of an alkyl phenyl sulfoxide and water (Method A sorption ) and (2) 1 was recrystallized in the presence of the sulfoxide (Method B ... 

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. 

This (Sj-rich methyl phenyl sulfoxide was subjected to the inclusion with the enantiomer (1 ) as summarized in Scheme 1. In this procedure, (.S )-methyl phenyl sulfoxide was obtained with high enantioselectivity. It is noteworthy that racemic methyl phenyl sulfoxide can be recovered from the washings. Thus, two enantiomers of methyl phenyl sulfoxide can be obtained by the use of the dipeptide (1) and its enantiomer (1 ). It should be noted that the present procedure can be applicable to other alkyl phenyl sulfoxides. 

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