Dienyl copper derivatives

The aforementioned dienyl dicopper derivatives show the characteristic reactivity of orga-nocopper compounds. However, one limitation to the use of copper is that an electron-withdrawing group is usually required for reaction with alkynes. In order to develop an insertion protocol for alkynes bearing electron-donating groups, transmetalation of zirco-nacyclopentadienes to nickel was investigated. 

The presence of a discrete organometallic species as well as the stereochemistry of the metalated diene were first checked by iodinolysis and bromolysis,but the corresponding iodo- and bromodienes were found to be unstable and rapidly isomerized to a mixture of E and Z isomers. Thus, in order to have a better picture of the stereochemical outcome of the process, the crude reaction mixture was treated with AT-chlorosuccinimide (Scheme 37), and the corresponding chlorodiene 103 was isolated in 60% yield with an isomeric ratio >98 2. As alternative solution, the stereochemistry of the reaction was also determined by addition of allyl chloride, in the presence of a catalytic amount of copper salt, to the dienyl zirconocene derivative [74]. Skipped triene 104 was... 

As usual, to further increase the scope of the reaction, transmetalation of dienyl zirconium complexes, such as 124-127Zr, into the corresponding dienyl organocopper derivatives was performed. Surprisingly, when 126Zr was trans-metalated to copper derivatives by addition of a catalytic amount of CuCl/2LiCl in the presence of allyl chloride for 1 h at +50 °C, a partial isomerization of the dienyl system was found (Scheme 49). 

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... 

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