Metallation of Ethyl Vinyl Ether

Successful (sp2)metallation of A N-disubstituted formamides and -thioamides with LDA was reported some ten years ago [108-111]  

The deprotonations proceed with extreme ease, even at temperatures in the region of — 100°C.Most of the reactions reported are couplings with carbonyl compounds. The species have a low thermostability, and one may wonder whether their basicity (and polarizability) is sufficiently high to warrant good yields with electrophiles that are considerably less reactive than carbonyl compounds, e.g. alkyl halides. 

Although /-butyllithium has been successfully applied to metallate methyl vinyl ether, one might prefer to use the cheaper and less dangerous combination of ra-BuLi and r-BuOK for the metallation of simple vinyl ethers. If an excess of ethyl vinyl ether is used, quantitative metallation can be obtained. Some derivatization reactions give much better results with the lithium compounds. The requisite transformation into the lithiovinyl ethers can be carried out by addition of a solution of anhydrous lithium bromide in THF. 

An excess of 0.01 mol is used to compensate for losses caused by small amounts of oxygen and moisture present in the solvents and the apparatus and by f-BuOH in the t-BuOK. 

An alternative, efficient way to prepare potassiated ethyl vinyl ether consists in treating the vinyl ether with BuLi f-BuOK TMEDA in hexane at —20 °C. 

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