Pd(0)-Catalyzed\nEnantioselective and Regiodivergent\nAnnulations of 1‑Heterodienes and Racemic Allenes

Here,\nwe demonstrate that Pd(0) can undergo direct oxidative addition\nto electron-deficient 1-azadienes without the additional assistance\nof Lewis or Bro̷nsted acids, and the resultant azapalladacycle\nspecies can undertake migratory insertion into allenes with exclusive\nC2-regioselectivity. Fine dynamic kinetic transformation is achieved\nin the subsequent <i>N</i>-allylic alkylation of in situ\nformed π-allylpalladium intermediates from racemic allenes,\nand high levels of enantioselectivity are generally obtained for the\ntetrahydropyridine products with an <i>E</i>-<i>exo</i>-double bond in a (4 + 2) annulation pattern. Moreover, switchable\nregiodivergent (4 + 1) or (4 + 2) annulations with different types\nof racemic allenes can be accomplished via ligand control. In addition,\nsimilar oxapalladacycles of Pd(0) and activated enones can be generated\nand assembled with racemic allenes to access dihydropyran derivatives\nenantioselectively, further enriching the diversity-oriented synthesis.\nAn array of control experiments and spectroscopic analyses are conducted\nto confirm the formation of these unusual heteropalladacycle intermediates,\nand density functional theory (DFT) calculations are further carried\nout to illuminate the catalytic pathways.