Nickel-Catalyzed [2+2+2] Cycloaddition of Alkyne-Nitriles with Alkynes Assisted by Lewis Acids: Efficient Synthesis of Fused Pyridines.

A Ni/BPh catalyzed [2+2+2] cycloaddition of alkyne-nitriles with alkynes has been developed, which provides an efficient route to fused pyridines under mild reaction conditions. Mechanistic studies indicate that an azanickelacycle via heterocoupling of an alkyne with a nitrile moiety is possibly formed as a key reaction intermediate. The Lewis acid catalyst is crucial to the successful transformation, which is suggested to promote the oxidative cyclization process.