Utilizing Graphene Oxide (GO) Catalysed Cascade in the Synthesis of Tetracyclic Pyrano[3,4‐b]indole Derivatives

Abstract

AbstractA simple, highly effective synthesis of tetracyclic pyrano[3,4‐b]indoles derivatives from simple 2‐indolylmethanols and trione alkenes has been accomplished through oxa‐Michael addition‐Friedel–Crafts reaction‐cyclization cascade promoted by a cheap and green graphene oxide catalyst. Under mild conditions, the reaction afforded a range of pyrano[3,4‐b]indole scaffolds, which are an important structural unit of different bioactive molecules, in excellent yields. Most importantly, in the cascade reaction of 2‐indolylmethanols with trione alkenes, the nanocatalyst not only activates trione alkene substrates by forming hydrogen‐bonding, but also promotes the following intramolecular ring formation and dehydration. Moreover, graphene oxide showed high recyclability in this reaction and could be used in gram scale synthesis. To the best of our knowledge, graphene oxide is used for the first time in the synthesis of functionalized tetracyclic dihydropyranoindole derivatives.