Metallation of 1.3-Dienyl Ethers and -Thioethers

Addition of BuLi to a mixture of a 1,3-dienyl ether or -thioether (E- or Z-) and t-BuOK in THF at 50 °C results in an instantaneous, and essentially quantitative Demetallation. In the absence of /-BuOK butyllithium adds to the sulfides in a conjugate fashion [91]. a-Metallation of the oxygen-e thers also has been carried out with /-BuLi in THF [81]  

The cyclic dienyl sulfide 2H-thiopyran is metallated in the 6-position by BuLi TMEDA in THF [93]  

Interaction between 2H-thiopyran and LDA in THF initially gives comparable amounts of the 6-lithio- and 2-lithio derivatives. After about 2 hour at — 60 °C only the 2-lithio intermediate is present in the solution. The same end result is obtained if diisopropylamine is added to a solution of the 6-lithio derivative. 

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