Regioselective Syntheses of Substituted Pyridines and 2,2 '-Bipyridines by Cobalt-Catalyzed [2+2+2] Cycloaddition of alpha,omega-Diynes with Nitriles

[摘要]：In the presence of a 1,2-bis(diphenylphosphino) ethanecobalt(II) chloride-zinc catalyst in 1-methylpyrrolidin-2-one at room temperature to 50 degrees C, alpha,omega-diynes reacted with nitriles by a [2+2+2] cycloaddition pathway to give annulated pyridines or 2,2'-bipyridines. The regioselectivity of the reaction is controlled by a combination of steric and electronic effects. The reaction of diynes with a terminal trimethylsilyl group gave the corresponding 3-(trimethylsilyl) pyridines exclusively; these products could be proto-or halodesilylated to give the corresponding protonated or halogenated pyridines or 2,2'-bipyridines.

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