Zirconium-catalyzed carboalumination of alkynes

The stereospecific construction of the trisubstituted double bond of the side chain at C-1 of carbazomadurins A (253) and B (254) was achieved using Negishi s zirconium-catalyzed carboalumination of alkynes 758 and 763, respectively. Reaction of 5-methyl-l-hexyne (758) with trimethylalane in the presence of zirconocene dichloride, followed by the addition of iodine, afforded the vinyl iodide 759 with the desired E-configuration of the double bond. Halogen-metal exchange with ferf-butyllithium, and reaction of the intermediate vinyllithium compound with tributyltin chloride, provided the vinylstannane 751a (603) (Scheme 5.79). 

Negishi, E.-i., Kondakov, D. Y., Choueiry, D., Kasai, K., Takahashi, T. Multiple Mechanistic Pathways for Zirconium-Catalyzed Carboalumination of Alkynes. Requirements for Cyclic Carbometalation Processes Involving C-H Activation. J. Am. Chem. Soc. 1996,118, 9577-9588. 

Among the most prominent examples of this reaction are the carbocupra-tion [5], the zirconium-catalyzed carboalumination [9-12], the nickel-catalyzed carbozincation [13-14], the allylmetalation of metalated alkynes [15], the allyl-zirconation [16], the allylgallation [17], the allylmanganation [18-19], and the alkyllithiation [20] reactions. 

The carbometalation reaction has been reviewed recently [28-30]. Negishi has demonstrated that zirconium(TV) complexes catalyze the carboalumination of MesAl to various alkynes and enynes [31]. Also the Zr-catalyzed asymmetric carboalumination of aUcenes (ZACA reaction) [32-34] has found important applications in the synthesis of natural products [35-37]. Especially efficient was the asymmetric synthesis of insect pheromones such as (S. / ./ ,S. / ,S)-4,6,8,10,16,18-hexamethyl-docosane (88) (Scheme 8) [38]. 

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