Decadiene from Allenyllithium

If the solvent is removed too quickly, part of the relatively volatile silylation product may be swept off with the solvent. 

If an equivalent amount of the bromide is used, the product may be contaminated with bromoheptane, which has a comparable volatility. 

Whereas ethene and butyllithium do not react at all in THF in the temperature range of — 90 to +30 °C, allene is metallated quantitatively in a few minutes at temperatures around — 70 °C. If the reaction with butyllithium is carried out at considerably higher temperatures, isomerization into propynyllithium CH3C=C—Li may take place. pK values of allene and its derivatives have not been determined, but the resonance stabilization in the anions is expected to give rise to a pK value which is lower than that of ethene. Qualitative comparison of the rates of alkylation with alkyl bromides of metallated allenes and sp2-metallated alkenes gives the impression that the allenic intermediates react faster in spite of their (presumed) lower basicity. The yield-reducing dehydrohalogenation of the alkyl halides occurs to a lesser extent with metallated allenes [9]. 

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