Alkynes Gilman cuprate reactions

The basicity of Gilman cuprates is so low that they do not undergo acid/base reactions with acetylene or higher terminal alkynes. Instead, they can add to their C=C triple bond (Fig-... 

Fig. 16.17. Mechanism of the carbocupration of acetylene (R = H) or terminal alkynes (R H) with a saturated Gilman cuprate. The unsaturated Gilman cuprate I is obtained via the cuprolithiation product E and the resulting carbolithiation product F in several steps—and stereoselectively. Iodolysis of I leads to the formation of the iodoalkenes J with complete retention of configuration. Note The last step but one in this figure does not only afford I, but again the initial Gilman cuprate A B, too. The latter reenters the reaction chain "at the top" so that in the end the entire saturated (and more reactive) initial cuprate is incorporated into the unsaturated (and less reactive) cuprate (I). - Caution The organometallic compounds depicted here contain two-electron, multi-center bonds. Other than in "normal" cases, i.e., those with two-electron, two-center bonds, the lines cannot be automatically equated with the number of electron pairs. This is why only three electron shift arrows can be used to illustrate the reaction process. The fourth red arrow—in boldface— is not an electron shift arrow, but only indicates the site where the lithium atom binds next.

Work in the reactions of alkyl halides with the more conventional Gilman cuprates has slackened considerably. Synthetically, alkylations have been performed employing alkynes as the second, disposable ligand in cuprates. In the transfer of vinyl groups, this allows aminomethylation or thiomethylation without the addition of HMPA or triethyl phosphite and without loss of alkene geometric integrity (equation 10)14. The addition of pentynylcopper to a-lithiated formamidines allows alkylation with primary alkyl iodides (equation ll)15. 

The basicity of Gilman cuprates is so low that they do not undergo acid/base reactions with acetylene or higher terminal alkynes. Instead, Gilman cuprates effect the car-bocupration of the C=C triple bond (Figures 13.12 and 13.13). This reaction formally resembles the hydroboration of a C=C triple bond ( see example in Figure 13.10). The regioselectivity also is the same hence, the metal is connected to the Cl center of a terminal alkyne. Finally, the reaction shows the same stereoselectivity as in the case of the hydroboration of a C=C triple bond carbocupration occurs as a cis addition. 

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