“[Hmim]HSO4 Catalyzed An Eco-friendly Synthesis of 3-Substituted Indole Derivatives

Abstract

Multicomponent reactions (MCRs) represent nowadays challenging frontier in synthetic organic chemistry. MCRs proved to be a very useful tool for the synthesis of structurally complex molecules, in particular natural products and in the field of drug discovery. Several examples of ‘classic’ organic processes were recently described in terms of a MCR version.^1,2 The indole moiety is a prominent structural motif which is embodied in a myriad of natural products and molecules of pharmaceutical interest in a variety of therapeutic areas.³ They possess a wide spectrum of biological activities such as antibacterial, anticonvulsant, and antihypertensive activity.⁴ Bis-Indole-based compounds have been reported to have broad-spectrum antibacterial activities against antibiotic-resistant strains and are currently being pursued as topical agents.⁵ Hapalindole A isolated from the blue green algae Hapalosiphon fontinalis is a 3-substituted indole derivatives. It exhibits potent antibacterial and antimycotic activities.⁶ There are various report on synthesis of 3-substituted indole derivatives synthesized by Lewis acid catalysis such as Ytterbium triflate,⁷ PMA–SiO₂,⁸ Yb(OTf)₃-SiO₂,⁹ Bromodimethylsulfonium bromide,¹⁰ FeCl₃,¹¹ InCl₃¹²and AgOTf¹³ much attention has been paid to the synthesis of them for a long while.