N-Heterocyclic Carbene-Catalyzed Umpolung of Cyclopent-4-ene-1,3-diones for Activated Olefin-Isatin Cross-Coupling.

N-Heterocyclic carbene (NHC)-catalyzed umpolung of cyclopent-4-ene-1,3-diones that proceeds via the generation of nucleophilic deoxy-Breslow intermediates is presented. The carbene generated from a commercially available thiazolium salt catalyzed the cross-coupling between cyclopent-4-ene-1,3-diones and isatins to furnish the functionalized oxindoles in moderate to good yields with good functional group compatibility. The key deoxy-Breslow intermediates were isolated and characterized by X-ray analysis. Detailed mechanistic studies are also presented.