Divergent reactivity of acrylamides and β-chloroenones under base-controlled palladium catalysis: construction of spirooxindoles and furan-containing 3,3-disubstituted oxindoles

Abstract

Herein, we report a divergent construction of spirooxindoles and furan-containing 3,3-disubstituted oxindoles from acrylamides and (E)-β-chloroenones through (Cs₂CO₃ or K₂CO₃)-assisted palladium catalysis, respectively. The σ-alkylpalladium(II) species generated from acrylamide and (E)-β-chloroenone as a 1,2-allenyl ketone surrogate can be involved in two typically catalytic cascades. The formation of spirooxindoles is thought to proceed via σ-alkylpalladium(II) species followed by a sequence of C–H activation, highly regioselective allene insertion, and reduction elimination. The synthesis of furan-containing oxindoles proceeds through σ-alkylpalladium(II)-catalyzed allenyl ketone activation–cyclization, palladium carbene migratory insertion, and β-hydride elimination. Computational studies provide valuable insights into the modes of carbopalladation cyclization, σ-alkylpalladium(II) species, spirocyclic palladacycle, regioselectivity of allene insertion, key step of Pd–carbene migratory insertion, and importance of chloride anions in catalyst regeneration.