Propargyl, lithio, with alkyl

In a method for propargylating an alkyl halide without allylic rearrangement, the halide is treated with lithio-l-trimethylsilylpropyne (122) which is a lithium compound protected by an SiMca group.Attack by the ambident nucleophile... 

These reactions are thought to proceed by initial formation of the lithio propargylic alcohol adduct, which undergoes a reversible Brook rearrangement (Eq. 9.14). The resulting propargyllithium species can equilibrate with the allenyl isomer and subsequent reaction with the alkyl iodide electrophile takes place at the allenic site. An intramolecular version of this alkylation reaction leads to cyclic allenylidene products (Eq. 9.15). 

In an attempt to alleviate the problems associated with the instability of diethyl 1-lithio-l, 1-difluoromethylphosphonate, a study of the reactivity of the corresponding organocadmium compound was performed in 1981. It reacts with a variety of allyl, propargyl, and benzyl bromides or iodides in THF at room temperature to afford the alkylated products in 7-64% yields (Scheme 3.71, M = CdBr, X = Br, I), but these compounds are contaminated with variable quantities of protonated carbanion. ... 

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