Allenylmetal compounds

Scheme 9.4 Configuration assignments for allenylmetal compounds (M = metal).

Scheme 9.5 Possible racemization pathways for chiral allenylmetal compounds.

Allenyllithium reagents are commonly prepared through lithiation of propargylic halides or by deprotonation of alkynes or certain allenes (Eq. 9.1). Lithiated allenes often serve as precursors to stable allenylmetal compounds such as stannanes or silanes. They can also be employed for the in situ synthesis of allenylzinc, -titanium and -boronate compounds, which can be further transformed to substitution products not accessible from their allenyllithio precursors. 

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