Vinyl halides metal-catalyzed cross-coupling, terminal

B. METAL-CATALYZED CROSS-COUPLING REACTIONS BETWEEN ARYL OR VINYL HALIDES WITH TERMINAL ACETYLENES... 

The stereospecific insertion of 2-monosubstituted alkenyl carbenoids was successfully employed in the preparation of 1-alkyl-1-zircono-dienes. The Z and E carbenoids of 1-chloro-l-lithio-l,3-butadiene (69 and 70, respectively) are generated in situ fromE- andZ-l,4-dichloro-2-butene [53] (Scheme 25). Inversion of configuration at the carbenoid carbon during the 1,2-metalate rearrangement stereospecifically yields terminal dienyl zirconocenes 71 and 72 [54] (Scheme 25). As the carbenoid-derived double bond is formed in 9 1=Z E for 69 and >20 1=E Z isomeric mixtures for 70, the metalated dienes 71 and 72 are expected to be formed with the same isomeric ratio. Carbon-carbon bond formation was achieved by palladium-catalyzed cross-coupling with allyl or vinyl halides to give the functionalized products with >95 5 stereopurity [55-57]. 

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