Developing a p ‐Toluenesulfonic Acid/Benzenesulfonic Acid/Water Mixture as Sustainable Medium for Aqueous Diels–Alder Reactions of Hydrophobic Anthracenes and Various Dienophiles

Aqueous Diels–Alder reactions are highly attractive for green chemistry because of their 100% atom economy and solvent waste mitigation. Despite significant effort, reactions involving hydrophobic dienes and water‐sensitive dienophiles, or vice versa, remain challenging. Herein, we implemented an efficient Diels–Alder reaction in a mixture of aqueous p ‐toluenesulfonic acid and benzenesulfonic acid as a recyclable medium. The methodology features good compatibility with hydrophobic anthracenes and water‐sensitive dienophiles, excellent yields, and chromatography‐free product isolation. The aqueous medium could easily be recovered and reused multiple times without additional processing.