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 η2‐Pd0‐cyclopentadienone complexes. Compared with the labile parent cyclopentadienone, the HOMO energy of the related η2‐complex was significantly raised via the back‐bonding of Pd0 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 C1‐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 Pd0 complex. π‐Allylpalladium‐based 1,2‐carbodipoles were generated from the carbonate derivatives of 4‐hydroxy‐2‐cyclopentenones and isomerized in situ to electronically neutral η2‐Pd0‐cyclopentadienone complexes. These HOMO‐raised cyclopentadienones participate, via π‐Lewis base activation, in inverse‐electron‐demand Diels–Alder‐type cycloadditions and cascade Morita–Baylis–Hillman‐ or Rauhut–Currier‐type addition/allylic substitution reactions with diverse electrophiles.