A Quick Access to 1-(2-Pyridyl)indoles via Solvent-Free Ruthenium(II)-Catalyzed Chemo- and Regioselective [2+2+2] Cycloaddition of α,ω-Diynes and N-Cyanoindoles

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(pentamethylcyclopentadi-enyl)(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.