Synthesis of fused-tricyclic indole derivatives through an acid-promoted skeletal rearrangement

We developed a novel method for synthesizing fused-tricyclic indole derivatives with a 3-aminomethyl indole motif through a reaction cascade involving ipso-Friedel-Crafts alkylation of phenols, rearomatization of the spirocyclohexadienone unit, and iso-Pictet-Spengler reaction. Using TFA as an acid promoter, six-, seven-, and eight-membered ring-fused indoles were obtained in 31-99% yield.