Recyclable Sulfonated Amorphous Carbon Catalyzed Friedel–Crafts Alkylation of Indoles with α,β‐Unsaturated Carbonyl Compounds in Water

Green practice: A sulfonated amorphous carbon-based solid acid derived from D-glucose was synthesized. It was explored for its catalytic efficiency in Friedel–Crafts reactions of indoles with various α,β-unsaturated carbonyl compounds in H2O or H2O/THF at room temperature. Moderate to excellent yields (67–96 %) were afforded. The catalyst could be recycled up to five times without any significant loss of catalytic activity.