Cu-Catalyzed 1,2-Dihydroisoquinolines Synthesis from o‑Ethynyl Benzacetals and Sulfonyl Azides

An efficient synthesis of 1,3-/1,1-dialkoxy 1,2-dihydroisoquinolines from o-ethynylbenzacetals and sulfonyl azides via a cascade process combining copper-catalyzed alkyne–azide cycloaddition (CuAAC), Dimroth rearrangement, 1,5-OR shift/1,5-H shift, and 6π-electrocyclic ring closure (6π-ERC) is described. Extension of the produced 1,3-dialkoxy-1,2-dihydroisoquinolines to isoquinolium salts is also disclosed.