Here we report that palladium(0) complexes can coordinate in a η2 fashion to 1,3-dienes and significantly raise the energy of their highest occupied molecular orbital (HOMO) by donating the electrons from the d-orbitals to the empty antibonding molecular orbitals of double bonds (π*) via back-bonding. Thus, the uncoordinated double bond, as a more reactive partner on the basis of the principle of vinylogy, can directly attack imines, furnishing a formal hydrodienylation reaction enantioselectively. A chemoselective cascade vinylogous addition/allylic alkylation difunctionalization process between 1,3-dienes and imines with a nucleophilic group is also compatible, by trapping in situ formed π-allylpalladium species after initial ene addition. This π-Lewis base catalytic mode, featuring simple η2coordination, vinylogous activation, and compatibility with both conjugated neutral polyenes and electron-deficient polyenes, is elucidated by control experiments and density functional theory (DFT) calculations.

A chiral tertiary amine-catalyzed asymmetric γ-regioselective (4 + 3) annulation reaction of isatin-derived Morita− Baylis−Hillman carbonates and 1-azadienes was developed, delivering chiral azepane spirooxindoles with excellent stereoselectivity. In addition, by tuning the substituents of Morita−Baylis−Hillman carbonates, the switchable γ-(4 + 3) or α-(4 + 1) annulation reaction with o-quinone methides was observed to furnish benzo[b]oxepines or 2,3-dihydrobenzofurans, respectively, under similar catalytic conditions.

An enantioselective cascade reaction of N-alkylpyridinium and -quinolinium salts with o-hydroxybenzylideneacetones to access fused polyheterocycles through cross dienamine-mediated addition followed by trapping of the dearomatized enamine-type intermediates and aminal formation has been developed. A cascade assembly of N-benzyl-4-methylpyridinium salt and cyclic 2,4-dienones is further disclosed to give bridged frameworks via repetitive dearomatization and aromatization activation.

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.

The vinyl group tethered to furfurals could be LUMO-lowered by forming formal vinylogous iminium ion intermediates catalyzed by a chiral secondary amine and underwent asymmetric [3 + 2] cycloaddition reactions with N-trifluoroethylsubstituted isatin imines, furnishing a variety of spirooxindoles incorporating a 3,2′-pyrrolidine motif with excellent stereoselectivity. In addition, this strategy has been successfully expanded to a number of vinyl-substituted electron-rich heteroaryl aldehydes and even some specific aryl aldehydes.