Polyfunctional lithium reagent

Similarly, the addition of triethylaluminum to the lithium reagent leads to a high a-regioselectivity (eq 4). A stereocontrolled s)ui-thesis of anh-homoallylic alcohols is possible by preparing the corresponding allylic boronic ester and subsequent reaction with an aldehyde. A stereoselective elimination allows the preparation of either ( )- or (Z)-dienes (eq 5). The isomeric reagent (1) is a useful reagent for the preparation of 2-substituted polyfunctional allylic silanes (eq 6). ... 

Rao and Knochel have reported the addition of copper reagents prepared by transmetallation from polyfunctional organozinc iodides to reactive alkynes in a stereochemically well-defined syn-addition. Intramolecular carbocupration of functionalized alkynyl-substituted alkylcopper species such as 74 obtained from the alkyl iodide 75 allows the preparation of highly substituted five-membered car-bocylcles giving stereochemically pure exo-alkylidenecyclopentane derivatives such as 76. The lower reactivity compared to the lithium- or magnesium-copper reagents does not allow the reaction with unactivated terminal alkynes but tolerates ester, nitrile or chloride functions (Scheme 9.23) [34]. 

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