Preparation of Organocopper Reagents

Grignard and lithium reagents the copper intermediates do not react with Michler s ketone 40, 60, 69, 119) [Gilman Color Test I (123)]. 

The usual precautions taken when working with air- and water-sensitive reagents must be employed for working with organocopper compounds. 

Reactions of Organometallic Compounds with Copper Salts 

An attempt has been made to list in Table I all preparations of copper reagents of the type RCu from the reaction of a Grignard or lithium reagent with a copper salt, irrespective of whether or not a copper compound was actually isolated. 

In 1952 Gilman and co-workers reported that the yellow, ether-insoluble methylcopper dissolved to give a clear colorless solution on addition of a further equivalent of methyllithium 119). The new copper compound, of composition LiCu(CH3)2, is an ate complex now usually known as lithium dimethylcuprate. Mixed cuprates can be prepared from a preformed organocopper compound, RCu, and a lithium reagent 147, 259, 298, 301). 

Organo Cu reagents are commonly formed by reacting 2 equivalents of organo Li compound to a Cu(I) salt or complex  

The stereochemistry of the migrating group is retained. Moreover, vinyl cuprates are readily prepared from acetylenes [5m, 6,7]. 

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Scheme 2.17. Preparation of organocopper reagents from organoboranes.

If the reaction was carried out in THF with R2CuMgX or [RCuBr]MgX as the or-ganometallic reagent, a vinylic compound was prepared upon protonation. The E Z ratio of the product depends strongly on the type of organocopper reagent used. The reaction may proceed via the attack of Cu on the central carbon atom of the allene moiety, followed by transfer of the R group from Cu to the terminal carbon atom [54]. 

The conjugate addition of organocopper reagents to ot,(3-alkynic esters, ketones, aldehydes and acids is a useful method for the preparation of various tri- and tetra-substituted alkenes,87 although addition to aldehydes is less common.88 Use of a vinylcuprate results in the formation of a conjugated dienone, which further highlights the importance of this methodology (equation 43 ).87... 

Because of the toxicity of cadmium compounds two alternative methods for the preparation of ketones from carboxylic acid derivatives are worthy of attention. The first involves the reaction of organocopper reagents [formed from copper(i) iodide and an alkyllithium] with a carboxylic acid chloride.12 7a,b... 

R. J. K.Taylor, J. M. Herbert, Compilation of Organocopper Preparations, in Organocopper Reagents A Practical Approach (R. J. K. Taylor, Ed.), 307, Oxford University Press, Oxford, U.K., 1994. 

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