acidic catalyst for the synthesis of isoindolo[2,1-a]quinazoline-5,11-dione derivatives under green conditions. Thus the Wang-OSO3H catalyzed MCR of isatoic anhydride, 2-formylbenzoic acid and various amines in pure water afforded a range of desired product in good to excellent (86-94%) yield. The methodology can be performed under open air and is amenable for scale-up synthesis. The catalyst can be recovered