Visible light induced halogen bond assisted Friedel‐Crafts reaction of indole and chalcones

Abstract

Abstract. The use of halogen bonding interactions as an alternative to acid and metal catalysts for substrate activation has gained popularity in recent years. In this work we demonstrate a halogen bond assisted activation of chalcones under visible light irradiation for the Friedel‐Crafts reaction with indole to yield β‐indolylketones. The simple and scalable protocol uses the readily available CBr4 as halogen bond catalyst. The targets are produced in 31‐94% of yield with excellent functional group tolerance. The proposed mechanism of the reaction is supported by UV‐vis, fluorescence, and NMR spectroscopic studies. Further it is demonstrated that the β‐indolylketones can be oxidised to indole substituted α,β‐unsaturated ketones by DDQ or cyclized to thieno[2,3‐b]indoles in the presence of elemental sulfur and base.