Alkenylzirconium derivatives

Scheme 1.23. Pd- or Ni-catalyzed cross-coupling reactions of alkenylzirconium derivatives by Zr-to-Pd (or Ni) transmetallation.

SCHEME 25. Alkenylzinc species obtained from alkenylzirconium derivatives... 

The Ni-catalyzed reaction of ( )-l-aIkenylalanes and ( )-l-alkenylzirconium derivatives with aryl halides (ArX) gave the corresponding cross-coupled products in good yields, as shown in Table 5.1. 

Subsequent studies have shown that alkenylzirconium derivatives generated in situ by hydrozirconation [46] of alkynes also undergo Pd- or Ni-catalyzed cross-coupling. As observed with alkenylalanes, Ni catalysts are generally satisfactory in the cases of alkenyl-aryl coupling [47] (Scheme 1-12), whereas Pd catalysts are more selective and distinctly superior to Ni catalysts in alkenyl-alkenyl and alkenyl-alkynyl coupling [48] (Scheme 1-13). 

Negishi, E., Van Horn, D. E. Selective carbon-carbon bond formation via transition metal catalysis. 4. A novel approach to cross-coupling exemplified by the nickel-catalyzed reaction of alkenylzirconium derivatives with aryl halides. J. Am. Chem. Soc. 1977, 99, 3168-3170. 

In cases where the Pd- or Ni-catalyzed cross-coupling reactions of alkenylalu-minum and alkenylzirconium derivatives are sluggish, addition of Zn salts (e.g., ZnCl2 and ZnBr2) has significantly accelerated these reactions in many cases (double metal... 

The reaction of alkenyManes and alkenylzirconium derivatives with 1-iodoalkynes doubly catalyzed with a Pd-phosphine complex and ZnCl2 appears to be the first example of this protocol. A related alkenylboron reaction was published shortly thereafter. Some additional examples involving Cu, Zn, and Sn are also known. These results are shown in Scheme 11. 

B.iv.b. Regioselective Synthesis of Benzene Derivatives via Pd-Catalyzed Cross-Coupling of 4-Halo-2-cyclobuten-l-ones. The Pd-catalyzed reaction of 4-chloro-2-cyclobuten-l-ones with alkenylzirconium derivatives or alkenyltins and heteroaryltins followed by thermolysis at 100 °C has regioselectively (—95%) produced multiply substituted benzenet" (Scheme 17) and heteroarene-fused benzene derivatives (Scheme 18), respectively. 

Aside from the stoichiometric construction of steroidal side chains by the reaction of alkenylzirconium derivatives with steroidal 7r-allylpalladiums, a one-pot synthesis of a-famesene and its 6Z-isomer from generanyl and neryl chlorides, respectively, reported in 1981 appears to be the first example of natural product syntheses via Pd-catalyzed allylation (Scheme 21). 

Negishi finds that the palladium-catalysed coupling reaction of -1-alkenylzirconium derivatives (71) with alkenyl halides gives 1,3-dienes with high regio- and stereo-selectivity. Furthermore, the conditions will tolerate functionality in the molecule, such as THP ethers. In this respect, the procedure may offer a wider scope of application than the corresponding organoalanes derived from acetylenes. 

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