Sodium Salts of Anionic Chiral Cobalt(III) Complexes as Catalysts of the Enantioselective Povarov Reaction

Visible Light-Mediated Cyclisation Reaction for the Synthesis of Highly-Substituted Tetrahydroquinolines and Quinolines

Condensation of 2-vinylanilines and conjugated aldehydes followed by an efficient light-mediated cyclisation selectively yields either substituted tetrahydroquinolines with typically high dr, or in the presence of an iridium photocatalyst the synthesis of quinoline derivatives is demonstrated. These atom economical processes require mild conditions, with the substrate scope demonstrating excellent site selectivity and functional group tolerance, including azaarene-bearing substrates. A thorough experimental mechanistic investigation explores multiple pathways and the key role that imine and iminium intermediates play in the absorption of visible light to generate reactive excited states. The synthetic utility of the reactions is demonstrated on gram scale quantities in both batch and flow, alongside further manipulation of the medicinally relevant products.

Asymmetric Synthesis of Hydroquinolines with α,α-Disubstitution through Organocatalyzed Kinetic Resolution

The first kinetic resolution of hydroquinoline derivatives with α,α-disubstitution has been achieved through asymmetric remote aminations with azodicarboxylates enabled by chiral phosphoric acid catalysis. Mechanistic studies suggest a monomeric catalyst pathway proceeding through rate- and enantio-determining electrophilic attack promoted by a network of attractive non-covalent interactions between the substrate and catalyst. Facile subsequent removal and transformations of the newly introduced hydrazine moiety enable these protocols to serve as powerful tools for asymmetric synthesis of N-heterocycles with α,α-disubstitution.

NHC-Catalyzed Chemoselective Reactions of Enals and Aminobenzaldehydes for Access to Chiral Dihydroquinolines

An N-heterocyclic carbene (NHC)-catalyzed reaction between α-bromoenals and 2-aminoaldehydes has been developed. Key steps include chemoselective reaction of the NHC catalyst with one of the aldehyde substrates (the bromoenal) to eventually generate an α,β-unsaturated acylazolium intermediate. Addition of the nitrogen atom of aminoaldehyde to the unsaturated azolium ester intermediate followed by intramolecular aldol reaction, β-lactone formation, and decarboxylation leads to chiral dihydroquinolines with high optical purity. The dihydroquinoline products, which are quickly prepared by using this method, can be readily transformed into a diverse set of functional molecules such as pyridines and chiral piperidines.

Assembling a Hybrid Pd Catalyst from a Chiral Anionic CoIII Complex and Ligand for Asymmetric C(sp3 )-H Functionalization

An unusual hybrid palladium catalyst containing an anionic chiral Co^III complex and a chiral phosphoramidite ligand shows a high capacity for catalyzing asymmetric thioamide-directed C(sp³ )-H arylation and delivers excellent yield and enantioselectivity (up to 99 % yield, 99 % ee). Significant synergy between the chiral ligand and the anion in terms of stereochemical control was observed. Mechanistic investigations have revealed both the nature of the C-H activation and the origin of the enantioselectivity.

Switchable Stereoselectivity in Bromoaminocyclization of Olefins: Using Brønsted Acids of Anionic Chiral Cobalt(III) Complexes

Brønsted acids of anionic chiral Co^III complexes act as bifunctional phase-transfer catalysts to shuttle the substrates across the solvent interface and control stereoselectivity. The diastereomeric chiral Co^III -templated Brønsted acids, with the same chiral ligands, enabled a switch in the enantioselective bromoaminocyclization of olefins to afford the two enantiomers of 2-substituted pyrrolidines with high enantioselectivities (up to 99:1 e.r.).

Catalytic Asymmetric Inverse-Electron-Demand Hetero-Diels-Alder Reactions

In this review, the recent developments in catalytic asymmetric inverse-electron-demand hetero-Diels-Alder reaction, which is recognized as one of the most powerful routes to construct highly functionalized and enantioenriched six-membered heterocycles, are described. The article is organized on the basis of different kinds of electron-deficient heterodienes, including α,β-unsaturated ketones/aldehydes, o-benzoquinones, α,β-unsaturated imines, N-aryl imines, o-benzoqinone imides, and other aza-olefins.