Bro̷nsted Acid-Catalyzed [5+1] and [4+1] Annulation of Cyclic Anhydrides with o -Alkynylanilines to Construct Fused-N-Heterocycles.

An unprecedented p -TsOH and MsOH-catalyzed construction of valuable isoindolo/pyrido/pyrrolo-quinolinediones and isoindolo-indolones is demonstrated through annulation reactions of cyclic anhydrides or o -formylbenzoates with o -alkynylanilines. The metal-free Bro̷nsted acid-mediated new [5+1] and [4+1] fused-cyclization is an operationally simple, highly regioselective, atom economical, high yielding, sustainable, and catalytically efficient approach.