Copper reagents, organo-, reactions with

But most of the time we are chiefly concerned with getting the carbon nucleophile to add 1,4. The synthesis of the unsaturated ketone 62 makes two more points. While we cannot do Sn2 reactions on vinyl halides, they make good organo-lithium and copper reagents and, in the... 

The choice of the organo-copper reagent is important. Thus reaction of (1) with dimethylcopperlithium yields only the linear product corresponding to (4),Bu = CH3. 

The organocopper is shown here as Me-Cu because its precise structure is not known. But there are other organocopper reagents that also undergo conjugate addition and are much better understood. The simplest result from the reaction of two equivalents of organo-lithium with one equivalent of a copper (1) salt such as CuBr in ether or THF solvent at low temperature. The lithium cuprates (R2CuLi) that are formed are not stable and must be used immediately. 

Allylic acetates or related compounds can also be displaced by organo-cuprates. A synthetic approach to prostaglandins (PC s) via cross-coupling of a vinylic copper reagent with an allylic electrophile has been elaborated (Corey and Mann, 1973). Notably the reaction of LXI and LXII proceeds exclusively by an Sn2 pathway. 

Transmetallation of 1,4-dilithio-l,3-butadienes with copper salt such as CuQ would lead to 1,4-dicopper-1,3-butadienes. Upon thermolysis or further treatment with other substrates, the organo-tf/-copper reagents could be transformed into a wide variety of compounds with interesting skeletons, which could be obtained by other methods or via the reactions of 1,4-dilithio-l,3-butadienes. 

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