A straightforward approach for the synthesis of novel fused thiopyrano [2, 3-b] indole derivatives from the Intramolecular Friedel-Crafts acylation

Abstract

In this research, a facile and efficient protocol for the regioselective synthesis of fused thiopyrano [2,3-b]indole-2-carboxylates using Eaton’s reagent (P2O5/MeSO3H) as an inexpensive, and easily available catalyst is developed under solvent-free condition at 80C. The reaction of various acetylenecarboxylates and indoline-2-(3H)-thiones using Eaton’s reagent affords fused indole heterocyclic compounds in good to excellent yields. This new method Compared to the Intramolecular Friedel-Crafts acylation has advantages of short reaction times, regioselectivity and ease of product isolation.