Synthesis of Oxygen‐Based Isoquinolinium 1,4‐Zwitterions and Their Application in the Synthesis of Pyrrolo[2,1‐ a ]isoquinolines

A 1,3‐dipolar [3 + 2] cycloaddition/rearrangement cascade process of α ‐alkynyl trifluoromethyl sulfoxides with isoquinoline N ‐oxides toward oxygen‐based isoquinolinium 1,4‐zwitterions bearing a trifluoromethylsulfinyl group is presented. The reaction is readily scalable, and the resulting 1,4‐zwitterions exhibit good bench stability. Furthermore, these zwitterions serve as versatile intermediates in catalyst‐free [3 + 2] cycloaddition/elimination cascades with conjugated ynones, enabling efficient synthesis of biologically relevant pyrrolo[2,1‐ a ]isoquinolines.