Hiyama coupling pyridines

As before, a silver ion and its counterion could act together in the transmetallation step, such as depicted in Scheme 10.44. Such a hypothesis seemed supported by the discovery in 2006 that 2-pyridinyl, but not 3-pyridinyl, allylsilanes reacted under similar conditions and transferred the pyridine moiety to various aryl iodides (Scheme 10.45).78 In this coupling, the nitrogen atom of the pyridinyl moiety probably played a role similar to that of the hydroxyl group in the silanol-based Hiyama couplings. 

Gros and co-workers have shown that the presence of electron-withdrawing substituents on the pyridine ring of 2-trimethylsilylpyridines provides sufficient activation to allow them to be useful partners in the Hiyama cross-coupling. 

Tricyclic fused 3-aminopyridines 93 could also be assembled via intramolecular CpCo(C2H4)2-catalyzed [2- -2-1-2] cycloaddition between ynamides, nitriles, and alkynes (Scheme 1.26) [47]. Of particular interest, one of the cycloadducts could be used in a rare type of silylated pyridine Hiyama cross-coupling to give 95 in 77 % yield. 

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