Sulphinyl group nucleophilicity

Ferrocene is best deprotonated by f-BuLi/f-BuOK in THF at 0 since BuLi alone will not lithiate ferrocene in the absence of TMEDA and leads to multiple lithiation in the presence of TMEDA. In the example in Scheme 134, a sulphur electrophile and a Kagan-Sharpless epoxidation lead to the enantiomerically pure sulphinyl ferrocene 278. The sulphinyl group directs stereoselective ortholithiation (see Section I.B.2), allowing the formation of products such as 279. Nucleophilic attack at sulphur is avoided by using triisopropylphenyllithium for this lithiation. 

Reactions.—Thietan 1-oxide is reduced more readily than thiolan 1-oxide by aqueous sodium hydrogen sulphite or iodide ion. This observation was rationalized in terms of mechanisms involving nucleophilic displacement of a hydroxy-group (formed by protonation at sulphinyl oxygen) at sulphur by bisulphite or iodide ion. ... 

Reactions of Saturated Sulphoxides and Selenoxides.—The main reactions of saturated sulphoxides and selenoxides are associated with the nucleophilic properties of the sulphinyl and seleninyl groups, and their activating effect on the adjacent saturated carbon atoms. The Pummerer rearrangement (as well as rearrangements of unsaturated sulphoxides discussed in a later section) and alkene-forming eliminations are instances of the former property the main consequence of the latter property, the formation of sulphinyl-stabilized carbanions, is covered in Chapter 2. 

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