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.magnified image
A highly efficient protocol for the synthesis of 3-(2-thiopyridyl)indoles via the ruthenium(ii) catalyzed [2 + 2 + 2] cycloaddition reaction of α,ω-diynes with 3-thiocyanatoindoles under mild reaction conditions has been developed. A variety of 3-(2-thiopyridyl)indole derivatives were prepared by the reaction of the aforesaid substrates in the presence of a readily available chloro(pentamethylcyclopentadienyl)(cyclooctadiyne)ruthenium(ii) catalyst in ethanol with good to excellent yields. This atom economical methodology provides us efficient access to 3-(2-thiopyridyl)indole skeletons with close structural similarity to other pyridyl indole thioethers that have potential medicinal value.
An efficient protocol for the synthesis of cyanoarenes has been developed via an iron-catalyzed chemoselective [2 + 2 + 2] cycloaddition reaction of diynes with alkynylnitriles under mild reaction conditions with good to excellent yields. The reaction is catalyzed by the combination of FeCl·4HO as a metal source, 2-(2,6-diisopropylphenyl)iminomethylpyridine (dipimp) as a ligand, and Zn as a reducing agent in DME solvent. The protocol was further extended to the synthesis of 2,2'-dicyanobiarene skeletons from the reaction of tetraynes with alkynylnitriles.
A new route to synthesize 1‐(2‐pyridyl)indole scaffolds via the solvent‐free, ruthenium(II)‐catalyzed, chemo‐ and regioselective [2+2+2] cycloaddition reaction of diynes with N‐cyanoindoles has been developed with good to excellent yields. Among the various transition metal‐based catalysts known for cycloaddition reaction to synthesize pyridine derivatives, chloro(pentamethylcyclopentadienyl)(cyclooctadiene)ruthenium(II) was established to be the best catalyst for this system. This efficient methodology provides 3‐substituted 1‐(2‐pyridyl)indole scaffolds having very close structural similarity with biological drug molecules.magnified image
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