Lewis acid-catalyzed domino ring-opening and annulation reaction of spiro-oxindole aziridines with indoles^a.

^aReactions were performed with 1.0 mmol of 1a and 1.0 mmol of 2a in CH₂Cl₂ (5 mL) in the presence of BF₃·OEt₂ (10 mol%) at 0 °C for 5–10 min.