Phosphine-Catalyzed [3+2] Annulation of N-2,2,2-Trifluoroethylisatin Ketimines with γ-Substituted Allenoates: Synthesis of Spiro[indoline-3,2′-pyrrole]

Synthesis of spiro[indoline-3,2 '-pyrrole] scaffold compounds from N-2,2,2-trifluoroethylisatin ketimines and gamma-substituted allenoates through a phosphine-catalyzed [3+2] annulation process has been developed, which could afford an unprecedented access to spirocyclic oxindoles with functionalized CF3 moiety containing five-membered rings. The new synthetic protocol used readily available N-2,2,2-trifluoroethylisatin ketimines as the starting materials, inexpensive PPh3 as the catalyst, and the corresponding products were obtained with yields up to 85 % under mild conditions.