Stereoselectivity ortholithiation

Sulphoxide removal using sulphoxide-lithium exchange is also effective. It was employed in tandem with a sulphoxide-directed stereoselective ortholithiation of the ferrocene 105 in the synthesis of the phosphine ligand 106 (Scheme 45). Ferrocene lithiation is discussed further in Section III. 

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. 

Usable vinyllithiums are obtained if (a) ortholithiation-resistant hydrazones derived from triisopropylphenylsulfonylhydrazine 15 are used,9 and (b) if the Shapiro reaction is carried out in a TMEDA-hexane mixture, which avoids protonation of the vinyllithium.10 For example, 16 forms stereoselectively from 15, with steric hindrance directing formation of the E hydrazone. The dianion of 16 decomposes at 0 °C to yield the vinyllithium 17 which reacts with electrophiles to yield products such as 18.11... 

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