Construction of Divergent Fused Heterocycles via an Acid-Promoted Intramolecular ipso-Friedel–Crafts Alkylation of Phenol Derivatives

Two different cascade cyclization processes were developed using aryl group-substituted propargyl alcohol derivatives with a p-hydroxybenzylamine unit as common substrates. Using TFA as an acid promoter, an intramolecular ipso-Friedel–Crafts alkylation of phenol derivatives, formation of an iminium cation via a rearomatization-promoted C–C bond cleavage, an aza-Prins reaction, and a 6-membered ring formation proceeded sequentially, producing a variety of fused-tricyclic dihydroquinoline derivatives in 45–99% yield. In addition, a one-pot sequential silver acetate-catalyzed hydroamination/etherification–acid-promoted skeletal rearrangement was examined using the same series of substrates, affording fused-tricyclic indole/benzofuran derivatives in 66–89% yield.