Synthesis of 3-(2-thiopyridyl)indoles via the ruthenium catalyzed [2 + 2 + 2] cycloaddition of diynes and 3-thiocyanatoindoles

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.