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

We disclose that the carbonates of 4-hydroxy-2-cyclopentenones can form pi-allylpalladium-based 1,2-carbodipoles, which isomerize to interesting eta(2)-Pd-0-cyclopentadienone complexes. Compared with the labile parent cyclopentadienone, the HOMO energy of the related eta(2)-complex was significantly raised via the back-bonding of Pd-0 as a pi-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 pi-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.

Automated summary

The study reveals that carbonates of 4-hydroxy-2-cyclopentenones can form unique palladium complexes for inverse-electron-demand aza-Diels-Alder reactions, along with the synthesis of chiral cycloadducts through cross Rauhut-Currier addition. Additionally, new chiral ligands have been developed for high stereoselectivity even with racemic substrates.