Aldehydes, conjugate addition organocuprates

C-Trapping. Alkylation or hydroxy alkylation (i.e., reaction with RCHO) of enolates derived from conjugate addition of organocuprates affords vicinal dialkylated products. However, the reaction is confined to highly reactive alkylating agents such as methyl, allyl, propargyl, benzyl, and a-halocarbonyl compounds or aldehydes. 

An interesting observation from organocuprate chemistry is that the initial step in 1,4-addition to enones may be electron transfer. Thus the relative reactivity of enones toward conjugate addition parallels their ease of reduction. One problem with any reaction between a ketone or aldehyde and a metal alkyl is deprotonation, when a hydrogens are present, to yield an enolate. Given the considerable basicity of metal alkyls, this side reaction should be anticipated. 

The effect of trimethylchlorosilane on the conjugate addition of organocuprates has been investigated with a,/ -unsaturated esters and amides7 in addition to the already discussed a,/ -unsaturated aldehydes and enones. 

A species of intermediate stoichiometry between organocop-per(I) and organocuprate(I) (RCu and R2CuLi, respectively) has been described as MesCu3Li2 =MeCu +(Me2CuLi)2. While the structure of the reagent has yet to be determined, it has proved to be useful for the conjugate addition of Me to a,/3-unsaturated aldehydes. ... 

The Cu-catalyzed conjugate addition of organomanganese reagents to a,/3-ethyle-nic aldehydes gives similar results than those obtained via lithium organocuprates in the presence of trimethylchlorosilane (Scheme 13.41) [36]. However, the reaction is easier to carry out since the aldehyde is obtained in one step instead of the two steps required with an organocuprate. It is important since the partial aldoli-... 

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