Trans lithiobetaine

Lithium salts effect, that the intermediate betaines do not react further. These lithiobetaines which are quite stable may be deprotonated. Deprotonation is equal to the lost of one stereogenic centre. Use of a steric hindered proton donator then leads to the trans lithiobetaine. The reaction takes normal course, if lithium is exchanged by potassium. 

A different reaction mode of lithiobetaines is used in the Schlosser variant of the Wittig reaction. Here, too, one starts from a nonstabilized ylide and works under non-salt-free conditions. However, the Schlosser variant is an olefination which gives a pure frans-alkene rather than a trans.cis mixture. The experimental procedure looks like magic at first ... 

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