Reactions with allylic sulfinyl carbanions

Sulfoxides (R1—SO—R2), which are tricoordinate sulfur compounds, are chiral when R1 and R2 are different, and a-sulfmyl carbanions derived from optically active sulfoxides are known to retain the chirality. Therefore, these chiral carbanions usually give products which are rich in one diastereomer upon treatment with some prochiral reagents. Thus, optically active sulfoxides have been used as versatile reagents for asymmetric syntheses of many naturally occurring products116, since optically active a-sulfinyl carbanions can cause asymmetric induction in the C—C bond formation due to their close vicinity. In the following four subsections various reactions of a-sulfinyl carbanions are described (A) alkylation and acylation, (B) addition to unsaturated bonds such as C=0, C=N or C= N, (C) nucleophilic addition to a, /5-unsaturated sulfoxides, and (D) reactions of allylic sulfoxides. 

A novel synthesis of allyl sulfoxides has been developed by the reaction of primary o -lithiosulfinyl carbanions with group 6 Fischer carbene complexes (Scheme 9).49 The Fischer carbene complex experiments involve a 1,2-addition of two molecules of sulfinyl carbanion to give an intermediate that, after a -elimination, furnishes the mentioned product. 

The reactions between a-metalloalkyl sulfoxides and electrophiles have been extensively studied. Although alkylations of the sodium or potassium salts of dialkyl sulfoxides are not always very efficient since a,a -dialkylated sulfoxides are often produced (or stilbene in the case of methyl-sulfinyl carbanion and benzyl bromide ), those employing the lithioalkyl aryl sulfoxides work more efficiently with alkyl or allyl halides " and with epoxides. " " Typical examples of these alkylations, allylations and hydroxyalkylations (from epoxides) are illustrated in Scheme 86. 

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