Efficient synthesis of pyrano[4,3-b]indol-1(5H)-ones from CO2 and alkynyl indoles promoted by a protic ionic liquid

An efficient method was developed for the synthesis of pyrano[4,3-b]indol-1(5H)-ones, which uses a protic ionic liquid [HTBD+][TFE-] as both the solvent and reaction promoter. The reactions could be efficiently carried out at atmospheric pressures of CO2, and various pyrano[4,3-b]indol-1(5H)-ones bearing versatile functionalities were obtained in moderate to high yields (71-99%). (C) 2020 Elsevier Ltd. All rights reserved.