Titanocene(III)-Mediated 5‑exo-trig Radical Cyclization: En Route to Spirooxindole-Based Tetrahydrofuran and Bicyclic Lactone

The isatin core system is of immense importance due to
the highly reactive prochiral C-3 position, which paves an easy way
to construct large arrays of spirooxindole heterocyclic motifs. Herein,
we depict an isatin-derived and 3,3′-disubstituted oxindole-appended
epoxy-acrylate undergoing Cp2Ti­(III)­Cl-mediated reductive
oxirane-ring opening with concomitant intramolecular 5-exo-trig radical
cyclization leading to tetrahydrofuran-based oxa-spirooxindole systems.
The fused spirooxindole structural feature is embedded in many natural
products and tends to exhibit a wide spectrum of biological activities.
The presence of more than one quaternary center and the availability
of multiple functional groups like hydroxyl, ester, or lactone in
the resultant products expand the scope of synthetic applications
of the newly acquired oxa-spirooxindole molecules.