Palladium-Catalyzed Asymmetric (4 + 2) Annulation of γ-Methylidene-δ-valerolactones with Alkenes: Enantioselective Synthesis of Functionalized Chiral Cyclohexyl Spirooxindoles.

An unprecedented asymmetric catalytic (4 + 2) annulation reaction of aryl-substituted γ-methylidene-δ-valerolactones (GMDVs) with isatin-derived para-quinone methides (p-QMs) has been developed under the catalysis of palladium(0) and (S,S,S)-(-)-Xyl-SKP, offering a new approach for the diastereo- and enantioselective synthesis of chiral cyclohexadienone-fused cyclohexyl spirooxindoles. Significantly, three highly congested contiguous tetrasubstituted carbon atoms embedded in bispirocyclic skeleton, of which two are vicinal quaternary stereogenic centers, are forged in an effective and selective manner (up to 99% yield, up to 95% ee, >20/1 dr). The current reaction represents the first exploration of enantioselective catalytic (4 + 2) annulation forming the six-membered carbocycles in the chemistry of both GMDVs and p-QMs.

P(NMe2)3-Mediated Umpolung Spirocyclopropanation Reaction of p-Quinone Methides: Diastereoselective Synthesis of Spirocyclopropane-Cyclohexadienones.

An unprecedented umpolung spirocyclopropanation reaction of p-quinone methides and α-keto carbonyls is described. Our umpolung strategy based on 1,6-conjugate addition and intramolecular nucleophilic substitution offers a new method for effective access to a series of highly functionalized spirocyclohexadienonyl cyclopropanes having two vicinal quaternary carbons in ≤98% yield and >20:1 dr. Significantly, cyclic and acyclic topological structures of α-keto carbonyls as 1,1-dipole one-carbon synthons have a distinct influence on the stereochemistry of products, showing a reversal of diastereoselectivity in this P(NMe2)3-mediated umpolung spirocyclopropanation.

Palladium-Catalyzed Asymmetric (2+3) Annulation of p-Quinone Methides with Trimethylenemethanes: Enantioselective Synthesis of Functionalized Chiral Spirocyclopentyl p-Dienones.

A novel asymmetric catalytic (2+3) annulation of p-quinone methides with CN-substituted trimethylenemethane is described under palladium catalysis, providing an alternative approach for the enantioselective construction of highly functionalized chiral spirocyclopentyl p-dienones. Driven by the significant improvement in the reactivity and enantioselectivity, a novel type of non-C2-symmetric phosphoramidite ligand from the chirality-matched combination of (S)-BINOL and sterically demanding amine derived from l-hydroxyproline is evolved and explored for the protocol presented here.

Asymmetric Catalytic [4+5] Annulation of ortho-Quinone Methides with Vinylethylene Carbonates and its Extension to Stereoselective Tandem Rearrangement.

Palladium-catalyzed asymmetric [4+5] annulation of ortho-quinone methides (o-QMs) with substituted vinylethylene carbonates (VECs) is described for the first time, giving a novel enantioselective approach to chiral nine-membered benzoheterocycles. Based on this designed [4+5] annulation, an unprecedented silica gel-promoted tandem rearrangement reaction featuring a unique asymmetric aromatic Claisen rearrangement is explored at room temperature, offering a new method for asymmetric construction of all-carbon quaternary stereocenters embedded in chiral functionalized homoallylic alcohols.

Highly Enantioselective Construction of Hajos-Wiechert Ketone Skeletons via an Organocatalytic Vinylogous Michael/Stetter Relay Sequence.

A highly enantioselective supramolecular iminium-catalyzed vinylogous Michael addition/Stetter relay sequence has been developed. This transformation provided a series of Hajos-Wiechert-type fused bicyclic diones with three continuous stereogenic centers in good yields with excellent enantioselectivities. The obtained products can be easily transformed into other structures with potential synthetic value.

Kinetic resolution via supramolecular iminium catalysis: multiactivation enables the asymmetric synthesis of ß-aryl substituted aldehydes and densely functionalized cyclohexanes.

The kinetic resolution of ß-aryl substituted 1,7-dioxo compounds with α,ß-unsaturated aldehydes affording enantioenriched ß-aryl substituted aldehydes as well as densely functionalized cyclohexanes is presented. The two enantioenriched products were obtained in reasonable yields with high diastereo- and enantioselectivities under supramolecular iminium catalysis which activates both the substrates and the reactive intermediates.

Catalytic Enantioselective α-Fluorination of 2-Acyl Imidazoles via Iridium Complexes.

The first highly enantioselective α-fluorination of 2-acyl imidazoles utilizing iridium catalysis has been accomplished. This transformation features mild conditions and a remarkably broad substrate scope, providing an efficient and highly enantioselective approach to obtain a wide range of fluorine-containing 2-acyl imidazoles which are found in a variety of bioactive compounds and prodrugs. A large scale synthesis has also been tested to demonstrate the potential utility of this fluorination method.