Synthesis of 3,3-Spiroindolines via FeCl₃‑Mediated Cyclization of Aryl- or Alkene-Containing 3‑Substituted N–Ac Indoles

We report the cyclization of 3-substituted <i>N</i>-acetylindoles for the straightforward synthesis of 3,3-spiroindolines via the Friedel–Crafts reaction of an appended aryl group or the formal [2 + 2] cycloaddition of an appended alkene. Our strategy involves an Umpolung of the C2C3 bond of the indole nucleus during FeCl₃-mediated hydroarylation or annulation reactions