Sulfoxides, Sulfonium Salts and Selenoxides

Sulfoxides have a tetrahedral structure about the sulfur atom in which there are two alkyl and/or aryl substituents, an oxygen and a lone pair. The lone pair in sulfoxides does not undergo inversion, unlike its counterpart in amines, and so sulfoxides are configurationally stable several examples of enantiomerically pure sulfoxides, e.g. 46, have been obtained. 

One example of a naturally occurring sulfoxide, available from turnips, is S-methylcysteine S-oxide (47) the CIP configuration at sulfur is (S), Draw a perspective diagram of this molecule. 

In sulfinic acids, RS(0)0H, sulfur is in the same oxidation state as in sulfoxides, and many esters of sulfinic acid (sulfinates) are known in which separate enantiomers have been isolated. If the ester is composed of a chiral alcohol, e.g. menthol, the resultant sulfinate is diastereomeric. Menthyl / -toluenesulfinate (48) has been used in synthesis. 

Sulfonium salts are of general form R1R2R3S+X. In these salts, positively charged sulfur has a lone pair of electrons, in addition to the substituent groups indicated. Sulfur is tetrahedral in sulfonium salts and salts of the above general type are accordingly chiral. Sulfonium sulfur does not undergo rapid inversion, and sulfonium salts have been 

Appropriately substituted sulfoxides, sulfinate esters and sulfonium salts exist as stable enantiomers. Some important examples exist in nature. 

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