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

We disclosed the carbonates of 4-hydroxy-2-cyclopentenones could form π-allylpalladium-based 1,2-carbodipoles, which would 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 as an electron-richer dienophile in inverse-electron-demand aza-Diels-Alder-type reaction with diverse 1-azadienes. The vinylogous (aza)Morita-Baylis-Hillman or cross Rauhut-Currier addition to (imines)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.