Selective Synthesis of 3‑(9H‑Carbazol-2-yl)indolin-2-ones and Spiro[tetrahydrocarbazole-3,3′-oxindoles] via a HOTf Catalyzed Three-Component Reaction

A HOTf catalyzed three-component reaction of indoles, acetophenones, and (E)-3-phenacylideneoxindolinones resulted in the unexpected polysubstituted 3-(9H-carbazol-2-yl)­indolin-2-ones in good yields. A similar reaction with various cyclic ketones afforded the corresponding carbocyclic fused 3-(9H-carbazol-2-yl)­indolin-2-ones. On the other hand, (E)-3-arylideneoxindolinones in the three-component reaction gave the expected spiro­[tetrahydrocarbazole-3,3′-oxindoles] through a domino alkenylation/Diels–Alder reaction. The unusual different reactivity of (E)-3-phenacylideneoxindolinones and (E)-3-arylideneoxindolinones in the three-component reactions was believed to involve the different reaction paths caused by the existence of the carbonyl group.