γ‐Al2O3/triflic acid as cooperative catalysts for the tandem Michael addition/carbocyclization: An easy access to 2‐substituted pyrroloisoquinolines and 3‐substituted pyrrolidine‐2,5‐diones

A tandem Michael addition/carbocyclization of 3,4‐dimethoxyphenethyl maleimide with carbon and sulfur nucleophiles is accomplished via a relay catalysis using γ‐Al2O3/TfOH binary system. The X‐ray Photoelectron Spectroscopy (XPS) analysis of binary system indicates the presence of AlF3, AlO(OH) species. This approach provides an easy access to 2‐aryl or 2‐thio aryl pyrrolo[2,1‐a]isoquinolines in good yields in a tandem fashion. With suitable ratio of γ‐Al2O3/TfOH binary system, the Michael addition of N/C/S nucleophiles to N‐benzyl maleimide is also achieved. A key to the success of these reactions would be the generation of AlF3, AlO(OH) species from γ‐Al2O3 and TfOH, which might have delineated the disadvantageous background reactions usually displayed by a strong Brønsted acid such as TfOH.