Lithiation of 1,4-Dithiin and Subsequent Functionalization

A similar result can be obtained if the metallation is carried out with a 15% excess of BuLi /-BuOK in THF (60 ml), Et20 (30 ml) and hexane (42 ml), and methyl iodide is added after 15 min. 

Et20 renders the mixture less viscous at the low temperature. 

This temperature can be reached by occasionally dipping the flask in liquid nitrogen, and can be maintained by keeping the bottom of the flask just above the level of the nitrogen. Stirring is carried out at a low rate and the upper part of the flask is covered with cotton wool. 

Compared to l,2-bis(methylthio)ethene, the structural and electronic conditions for metallation of 1,4-dithiin are even more favourable. The additional double bond is likely to exert an electron-withdrawing influence, while the greater rigidity 

The 1-proton in 1,3-dienyl ethers and -thioethers is expected to be more acidic than that in vinyl ethers and vinyl sulfides, because the outer double bond is likely to exert some electron-withdrawing influence. However, addition of the base (in a conjugate fashion) will also be more facile than with the simple vinyl ethers and -thioethers. Reaction of 1-methylthio-l,3-butadiene with butyllithium or butyl-lithium. TMEDA in THF has been shown to result in conjugate addition [91]. The 

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