Polyfunctional organozinc reagent preparation

P. Knochel, R. D. Singer, Preparation and Reactions of Polyfunctional Organozinc Reagents in Organic Synthesis, Chem. Rev. 1993, 93, 2117-2188. 

Methods of Preparation of Polyfunctional Organozinc Reagents 261 MnBr2 (5 mol%)... 

The reaction in the presence of a 1,2-diamine ligand requires a Lewis acid. Perhaps the most popular combination comprises franj-l,2-bistriflamidocyclohexane and (i-PrO)4Ti. Many polyfunctional compounds can be prepared in chiral form by this method. The organozinc reagents attack conjugated aldehydes in the 1,2-fashion. " However, the chemoselectivity can be changed by using NiCh instead of i-PrO)4Ti in the catalytic system. ... 

The oxidative addition of zinc dust to functionalized organic halides allows the preparation of a broad range of polyfunctional organozinc iodides such as 1-5 (10-14]. Several functional groups such as nitro or azide groups inhibit the radical-transfer reaction leading to the zinc reagent. On another hand, hydroxyl... 

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]. 

Addition to alkynes/ The polyfunctional zinc/coppcr reagents such as 1, prepared by reaction of organozinc halides with (CH1)2Cu(CN)Li2, reacts slowly with activated alkynes to provide. vyn-adducts, which can react with various electrophiles to provide alkenes (equation 1). An intramolecular version can result in alkylidcnccyclopcntanes (equation II). In contrast, attempts to use this intramolecular cyclization to obtain... 

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