Novel SO3H-functionalized ionic liquids catalyzed a simple, green and efficient procedure for Fischer indole synthesis in water under microwave irradiation

Novel SO3H-functionalized ionic liquids were successfully applied as catalysts for one-pot Fischer indole synthesis under microwave irradiation and in a water medium. Various types of indoles were prepared using single-carbonyl ketones/aldehydes or cyclohexandiones with aryhydrazine hydrochlorides in 86–96% yields in water under microwave irradiation. The indole products could be conveniently separated from the reaction mixture through filtration, and the catalytic system of [(HSO3-p)2im][CF3SO3]/H2O could be reused directly without any treatment. The entire process is simple, time saving, and environmentally friendly.

Graphical abstractNovel SO3H-functionalized ionic liquids were successfully applied as catalysts for one-pot Fischer indole synthesis under microwave irradiation and in a water medium. Various types of indoles were prepared using single-carbonyl ketones/aldehydes or cyclohexandiones with aryhydrazine hydrochlorides in 86–96% yields in water under microwave irradiation. The entire process is simple, time saving, and environmentally friendly.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The whole process was performed in water without using any organic solvents. ► The reaction–separation–recycle process was quite convenient. ► The catalytic system of [(HSO3-p)2im][CF3SO3]/H2O could be reused directly.