Chiral sulphur compounds types

The most important class of chiral sulphur compounds is the sulphoxides. As a result of the presence of the lone pair, the stereochemistry at sulphur is pyramidal and molecules of the general type (38) and (39) are opposite enantiomers. The sulphoxides are of considerable importance in asymmetric synthesis (see chapter 5) and, as for the phosphines, are generally obtained in enantiomerically pure form by resolution. 

If the lone pair in (38) or (39) is replaced by a double bond to oxygen the resulting sulphone is obviously achiral but if it is instead replaced by a double bond to nitrogen, we get another type of chiral sulphur compound, the sulphoximines (40) which have also been used for asymmetric synthesis (see section 5.1.3). The sulphonium salts (41) are also potentially chiral. A review of the chiral compounds of sulphur is available,... 

Chiral sulphoxides are the most important group of compounds among a vast number of various types of chiral organosulphur compounds. In the first period of the development of sulphur stereochemistry, optically active sulphoxides were mainly used as model compounds in stereochemical studies2 5 6. At present, chiral sulphoxides play an important role in asymmetric synthesis, especially in an asymmetric C—C bond formation257. Therefore, much effort has been devoted to elaboration of convenient methods for their synthesis. Until now, optically active sulphoxides have been obtained in the following ways optical resolution, asymmetric synthesis, kinetic resolution and stereospecific synthesis. These methods are briefly discussed below. 

Kobayashi obtained enantiopure phthalocyanines by introducing a helical type chiral element, or a chain containing an asymmetric carbon. The use of two or four chiral binaphthyl substituents [(P) or (5)] or [(M) or (/ )], attached to the phthalocyanine via oxo or sulphur bridges, leads to compounds of the type BNpPcM and TNpPcM with M = H2, Zn and Co (Figure 6.32). 

Reactions of Sulphoxides.—The general features of the reactions of sulphoxides can be illustrated by reference to the simplest structural types, without regard for stereochemical details. A minority of the new work published within the period under review falls within this category when the well-defined uses of dimethyl sulphoxide as a reagent are considered separately (p. 50), but interpretation of the reactions of sulphinyl compounds with chirality at sulphur fully in view is the outstanding feature of recent work. 

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