Copper salts transmetalation

The copper salt is believed to function by promoting the transmetallation stage. 

Alternatively, copper salts can themselves be engaged in transmetalation with a nucleophilic coupling partner to give organocopper intermediates, which then either enter the Pd-catalyzed... 

It is believed that the copper salts facilitate transmetalation by generating a highly reactive organocuprate intermediate. 

Generally, organocopper compounds can be prepared by transmetallation between copper salts and organometallic reagents such as RLi, RMgX, and RZnX.53,53a,53b Copper alkynides can be obtained by reaction of terminal alkynes... 

Transmetalations of alkenylstannanes with copper salts are reversible if they are performed with CuCl in polar solvents [101]. This has found application in cyclization reactions (Scheme 2.49) [102]. 

The ortholithiated products 19 and 22 will then react with a wide range of electrophiles the only reported important exceptions are enolisable aldehydes and allylic halides. Products requiring these electrophiles are best made by first transmetallating the organolithium to a Grignard reagent with MgCl2 or copper salts . 

As indicated in Section ni.B, deprotonation of a carbamate affords a dipole-stabilized a-amino-organolithium that can be transmetalated with copper salts to form cuprates, thereby expanding the versatility of the organolithium. Suitable electrophiles include enones, alkenyl, alkynyl, allenyl and dienyl carboxylic acid derivatives, nitriles and sulfoxides. Dieter and coworkers have shown that the same process can be accomplished via transmetalation of a stannane (Scheme 36). The procedure is particularly... 

Transmetallation of the dimetallic species 186a or 186b with CuCN led to a new organometallic species formulated as 191 which displayed remarkable thermal stability. Addition of reactive alkylating agents such as allyl bromide to 191 directly produced compound 192. Indeed, once the first alkylation occurred, the copper salts present in... 

Subsequent developments indicated that transmetallation to copper was also possible in both catalytic and stoichiometric senses, with the use of the THF soluble copper salt CuCN.2LiCl being especially convenient.7 The formation of these functionalized copper reagents has allowed a substantial increase in the range of products which may be prepared from organozinc halides.8... 

In the presence of a copper salt, aromatic aldehydes, a,/3-unsaturated aldehydes, formates, and formamides react with 38 at or below room temperature to give the corresponding insertion products in good yield.289 This catalytic reaction shows similar stereo- and regiochemistry as does the thermal reaction of formamides. A transmetallation mechanism via an organocopper intermediate has been proposed for the Cu-catalyzed insertion. 

As mentioned in Section 9.12.2.1.1, the boron-zinc exchange can be performed stereoselectively if diisopropyl-zinc instead of diethylzinc is used. For example, hydroboration of the chiral, racemic endocyclic olefin 134 with diethylzinc, followed by twofold transmetallation and electrophilic capture of the resulting copper intermediate with allyl bromide was used for the highly diastereoselective formation of the stereotriad in product 136 (Scheme 35).35,35a 103 QorreSp0nding enantioselective transformations were carried out with chiral boranes and catalytic amounts of copper salts (see Section 9.12.2.2.2).36... 

Copper salts have become crucial additives for bond forming reactions between carbon and heteroatoms such as N, O, S, or P. While many involve a transmetalation see Transmetalation) step from Pd, Ni, Sn, B, Te, Se, Mg, and so on, several of these cross-coupling see Coupling) reactions occur with copper as the only metal present. Typically, a (bidentate) ligand is used for stabilization of a copper-containing intermediate, while enhancing reactivity of the copper catalyst. 

You will see several examples of transmetallation with copper salts in the next chapter. 

---