π‐Lewis‐Base‐Catalyzed Asymmetric Vinylogous Umpolung Reactions of Cyclopentadienones and Tropone

We disclose that the carbonates of 4‐hydroxy‐2‐cyclopentenones can form π‐allylpalladium‐based 1,2‐carbodipoles, which isomerize to interesting η 2 ‐Pd 0 ‐cyclopentadienone complexes. Compared with the labile parent cyclopentadienone, the HOMO energy of the related η 2 ‐complex was significantly raised via the back‐bonding of Pd 0 as a π‐Lewis base, rendering the uncoordinated C=C bond an electron‐richer dienophile in inverse‐electron‐demand aza‐Diels–Alder‐type reactions with diverse 1‐azadienes. The vinylogous (aza)Morita–Baylis–Hillman or cross Rauhut–Currier addition to (imine)carbonyls or activated alkenes, respectively, was also realized to afford chiral [4+2] or [2+2] cycloadducts, respectively, after trapping the re‐generated π‐allylpalladium species. New C 1 ‐symmetric ligands from simple chiral sources were developed, exhibiting high stereoselectivity even with racemic substrates via an unusual dynamic kinetic resolution process. Besides, tropone could be similarly activated by a Pd 0 complex.