An Eco-Friendly Route to N-Arylindoles by Iron-Catalyzed [2+2+2] Cycloaddition of Diynes with (Indol-1-yl)alkynes

A new pathway to the synthesis of N-arylindoles has been developed that proceeds through an iron-catalyzed [2+2+2] cycloaddition reaction between diynes and indole-N-alkynes. The reaction is carried out in ethanol and employs a catalyst system that consists of iron(II) chloride tetrahydrate as the metal source, 2-[(2,6-diisopropylphenyl)iminomethyl]pyridine (dipimp) as the ligand, and zinc as the reducing agent. The method provides efficient access to 3-carbonyl/ester-substituted (indol-1-yl)arenes in good to excellent yields under green reaction conditions, and these products are structurally similar to other N-arylindole derivatives with potential medicinal value.