Additive-Controlled Switchable Selectivity from Cyanobenzenes to 2-Alkynylpyridines: Ruthenium(II)-Catalyzed [2+2+2] Cycloadditions of Diynes and Alkynylnitriles

摘要

A highly efficient additive-dependent chemoselective protocol for the synthesis of fused cyanoarenes and 2-alkynylpyridines has been developed by the reaction of 1,6-diynes with alkynylnitriles using chloro(pentamethylcyclopentadienyl) (cyclooctadiyne) ruthenium(II) as catalyst in dimethoxyethane (DME). The course of the reaction can be drastically altered simply by adding a catalytic amount of AgOTf as an additive resulting in a comprehensive shift in product formation from cyanoarenes to 2-alkynylpyridines. Theoretical studies clearly indicate that the neutral Ru-complex is responsible for the formation of cyanobenzenes, whereas the in situ generated cationic Ru-complex plays a crucial role in the 2-alkynylpyridines formation.