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

Herein, we report a divergent construction of spirooxindoles and furan-containing 3,3-disubstituted oxindoles from acrylamides and (E)-beta-chloroenones through (Cs2CO3 or K2CO3)-assisted palladium catalysis, respectively. The sigma-alkylpalladium(ii) species generated from acrylamide and (E)-beta-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 sigma-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 sigma-alkylpalladium(ii)-catalyzed allenyl ketone activation-cyclization, palladium carbene migratory insertion, and beta-hydride elimination. Computational studies provide valuable insights into the modes of carbopalladation cyclization, sigma-alkylpalladium(ii) species, spirocyclic palladacycle, regioselectivity of allene insertion, key step of Pd-carbene migratory insertion, and importance of chloride anions in catalyst regeneration. Divergent synthesis of spirooxindoles and furan-containing oxindoles via base-controlled palladium catalysis was achieved. The key intermediates, allene insertion, and Pd-carbene migratory insertion are supported by DFT calculations.