Mechanistic Understanding of the Pd(0)-Catalyzed Coupling Cyclization of 1,2-Allenyl Ketones with Aryl Halides: A Computational Study

Abstract

The Pd(0)-catalyzed coupling cyclization of 1,2-allenyl ketones with aryl halides to construct multisubstituted furan derivatives has been developed. Nevertheless, the detailed mechanism of this reaction, proceeding via either the Pd(II)-carbenoid or the π-allyl-Pd(II) intermediate, still remains debatable. Herein, computational studies were performed to provide mechanistic insights into the reactions, and substituent-dependent mechanistic pathways were revealed. Computational results suggest that the substituents, R1–R3 attached to 1,2-allenyl ketones and R4 attached to the aryl moiety of aryl halides, could play significant roles in the variation of the mechanistic pathway. It would be favorable to form the Pd(II)-carbenoid intermediate when R1 is an aryl/alkyl group or steric hindrance is present between R2 and R3. For the substrate of aryl halide, the aryl moiety bearing electron-donating group (R4) at the para position is more ready to undergo migratory insertion to form the π-allyl-Pd(II) intermediate than that with electron-withdrawing group. The factors responsible for the formation of both Pd(II)-carbenoid and π-allyl-Pd(II) intermediates are discussed.