Facile synthesis of 3,4-fused tricyclic indoles with a seven-membered ring through a three-component reaction of 4-hydroxyindole, aldehyde, and malonodinitrile or ethyl cyanoacetate

Abstract

Three-component reactions of 4-hydroxyindole, aldehydes, and malonodinitrile or ethyl cyanoacetate were developed for the first time by using either potassium fluoride or diethylamine as a catalyst, which provided an easy access to 3,4-fused tricyclic indoles in good to excellent yield. The merits of this synthesis route are attributed to its simplicity, practicality, efficiency, and eco-friendliness, as well as the easy availability of the catalyst.