Pd(0)-Catalyzed Enantioselective and Regiodivergent Annulations of 1-Heterodienes and Racemic Allenes

Here, we demonstrate that Pd(0) can undergo direct oxidative addition to electron-deficient 1-azadienes without the additional assistance of Lewis or Bronsted acids, and the resultant azapalladacycle species can undertake migratory insertion into allenes with exclusive C2-regioselectivity. Fine dynamic kinetic transformation is achieved in the subsequent N-allylic alkylation of in situ formed pi-allylpalladium intermediates from racemic allenes, and high levels of enantioselectivity are generally obtained for the tetrahydropyridine products with an E-exo-double bond in a (4 + 2) annulation pattern. Moreover, switchable regiodivergent (4 + 1) or (4 + 2) annulations with different types of racemic allenes can be accomplished via ligand control. In addition, similar oxapalladacycles of Pd(0) and activated enones can be generated and assembled with racemic allenes to access dihydropyran derivatives enantioselectively, further enriching the diversity-oriented synthesis. An array of control experiments and spectroscopic analyses are conducted to confirm the formation of these unusual heteropalladacycle intermediates, and density functional theory (DFT) calculations are further carried out to illuminate the catalytic pathways.