An atom‐economic and highly efficient vinylogous umpolung strategy is developed for deconjugated carbonyl compounds, which generate electron‐deficient π‐allylpalladium complexes with Pd(OAc)2 under ligand‐free conditions. In cooperation with a chiral‐phosphonium‐based phase‐transfer catalyst, the asymmetric direct oxidative allylic alkylations of 3‐substituted oxindoles are furnished under O2 atmosphere. The γ‐ or even remote ϵ‐regioselective alkylation products, with substantial substituents, are delivered with excellent enantioselectivity, and can be further used to access diverse chiral spirocyclic architectures effectively. The Mukaiyama dienol silyl ether can be utilized similarly, indicating that the current active π‐allylpalladium species results from tautomerization of the PdII‐dienolate intermediate.
An asymmetric α-regioselective
allenylation reaction of activated ketimines with 3-butynoates is
disclosed under Cu(I) catalysis, probably via the generation of nucleophilic
γ-allenylcopper species in the presence of diisopropylethylamine.
A broad range of imines, derived from diverse ketones such as isatins,
pyrazolediones, isoquinoline-1,3,4-triones, and even trifluoromethyl
alkynyl ketones, can be utilized, generally affording the corresponding
α-allenyl amine derivatives in high yields (≤97%) with
excellent enantioselectivities (≤99% ee).
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.
A cascade vinylogous 1,6-Michael addition/1,4-proton shift/aza-Michael addition/hemiaminal formation sequence of 1,2-diaza-1,3-dienes and β-substituted 2-butenals has been developed under the influence of dienamine activation of a chiral secondary amine. This method exhibits high regio- and chemoselectivity and provides an efficient and straightforward approach to bicyclic l,8-diazabicyclo[3.3.0]octane skeletons with a tetrasubstituted stereogenic center with fair to excellent enantioselectivity.
Here we report Pd(0)-catalysed asymmetric inverse-electron-demand oxa-Diels-Alder reactions between the carbonates of 4-hydroxy-2-cyclopentenones and α-cyano chalcones, by in situ generating η2-Pd(0)-cyclopentadienone complexes as HOMO-raised dienophiles, and diastereodivergent synthesis could be...
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