Kinetic Resolution of Axially Chiral 2-Amino-1,1′-Biaryls by Phase-Transfer-Catalyzed N-Allylation

NHC-Catalyzed Chemo- and Enantioselective Reaction between Aldehydes and Enals for Access to Axially Chiral Arylaldehydes

A chiral carbene-catalyzed chemo- and enantioselective reaction with racemic biaryl aldehydes and α-bromoenals is developed for access to axially chiral 2-arylbenzaldehydes through atroposelective dynamic kinetic resolution (DKR) processes. This atroposelective DKR strategy can tolerate a broad scope of substrates with diverse functionalities. The axially chiral 2-aryl benzaldehyde products generally afford moderate to good yields and enantioselectivities. The axially chiral molecules afforded from the current approach are variable through simple transformations to afford axially chiral functional molecules with excellent optical purities.

Palladium-Catalyzed Asymmetric Hydrogenolysis of Aryl Triflates for Construction of Axially Chiral Biaryls

Here we report the first palladium-catalyzed asymmetric hydrogenolysis of readily available aryl triflates via desymmetrization and kinetic resolution for facile construction of axially chiral biaryl scaffolds with excellent enantioselectivities and s selectivity factors. The axially chiral monophosphine ligands could be prepared from these chiral biaryl compounds and were further applied to palladium-catalyzed asymmetric allylic alkylation with excellent ee values and high branched and linear ratio, which demonstrated the potential utility of this methodology.

Enantioselective Synthesis of Axially Chiral Benzothiophene/Benzofuran-Fused Biaryls by N-Heterocyclic Carbene Catalyzed Arene Formation

Axially chiral biaryl scaffolds are prevalent in natural products, chiral ligands, and organocatalysts. However, N-heterocyclic carbene (NHC) catalyzed de novo construction of an aromatic ring with concomitant axial chirality induction for the synthesis of biaryl atropisomers is far less developed, and the efficient synthesis of axially chiral tetra-ortho-substituted biaryls remains an unsolved problem under NHC catalysis. Reported here is an NHC-catalyzed de novo synthesis of axially chiral benzothiophene/benzofuran-fused biaryls from enals and 2-benzyl-benzothiophene/benzofuran-3-carbaldehydes through a [2+4] annulation, decarboxylation, and oxidative aromatization cascade with central-to-axial chirality conversion. The developed method provides efficient and general access to novel axially chiral benzothiophene/benzofuran-fused biaryls in high enantioselectivities and works well for the synthesis of tetra-ortho-substituted biaryls.

Enantioselective Synthesis of 3,3'-Disubstituted 2-Amino-2'-hydroxy-1,1'-binaphthyls by Copper-Catalyzed Aerobic Oxidative Cross-Coupling

A challenging direct asymmetric catalytic aerobic oxidative cross-coupling of 2-naphthylamine and 2-naphthol, using a novel Cu^I /SPDO system, has been successfully developed for the first time. Enantioenriched 3,3'-disubstituted NOBINs were achieved and could be readily derived to divergent chiral ligands and catalysts. This reaction features high enantioselectivities (up to 96 % ee) and good yields (up to 80 %). The DFT calculations suggest that the F-H interactions between CF₃ of L17 and H-1,8 of 2-naphthol, and the π-π stacking between the two coupling partners could play vital roles in the enantiocontrol of this cross-coupling reaction.

Enantioselective Construction of Axially Chiral Amino Sulfide Vinyl Arenes by Chiral Sulfide-Catalyzed Electrophilic Carbothiolation of Alkynes

The enantioselective construction of axially chiral compounds by electrophilic carbothiolation of alkynes is disclosed for the first time. This enantioselective transformation is enabled by the use of a Ts-protected bifunctional sulfide catalyst and Ms-protected ortho-alkynylaryl amines (Ts=tosyl; Ms=mesyl). Both electrophilic arylthiolating and electrophilic trifluoromethylthiolating reagents are suitable for this reaction. The obtained products of axially chiral vinyl-aryl amino sulfides can be easily converted into biaryl amino sulfides, biaryl amino sulfoxides, biaryl amines, vinyl-aryl amines, and other valuable difunctionalized compounds.

Catalytic Kinetic Resolution by Enantioselective Aromatization: Conversion of Racemic Intermediates of the Barton-Zard Reaction into Enantioenriched 3-Arylpyrroles

Racemic 3,4-dihydro-2H-pyrroles, hypothetical intermediates of the Barton-Zard reaction, were synthesized in a highly diastereoselective manner and fully characterized for the first time. Kinetic resolution of the dihydropyrroles with a quinine-derived thiourea afforded the (+)-3-arylpyrrole products and recovered (+)-3,4-dihydro-2H-pyrroles with high efficiency (s-factor up to 153). The resolved (+)-3,4-dihydro-2H-pyrroles underwent subsequent aromatization with a quinidine-derived thiourea catalyst to afford (-)-3-arylpyrroles with excellent central-to-axial chirality transfer. In contrast to the well-accepted Barton-Zard mechanism, the aromatization of the 3,4-dihydro-2H-pyrroles in the presence of a bifunctional catalyst is believed to proceed by an unprecedented sequence involving syn elimination of HNO₂ and aromatization.

Practical and Scalable Kinetic Resolution of BINOLs Mediated by a Chiral Counterion

BINOLs are valuable and widely used building blocks, chiral ligands, and catalysts that are effective across a remarkable range of different chemical transformations. Here we demonstrate that an ammonium salt catalyzed kinetic resolution of racemic BINOLs with benzyl tosylate proceeds with s up to 46. This is a scalable and practical process that can be applied across >30 different C2 - and non-C2 -symmetric BINOLs. Implementation of this method enables the enantioselective synthesis of a wide range of BINOL derivatives with over 99:1 e.r.

Understanding the Reactivity and Selectivity of Fluxional Chiral DMAP-Catalyzed Kinetic Resolutions of Axially Chiral Biaryls

Fluxional chiral DMAP-catalyzed kinetic resolutions of axially chiral biaryls were examined using density functional theory. Computational analyses lead to a revised understanding of this reaction in which the interplay of numerous non-covalent interactions control the conformation and flexibility of the active catalyst, the preferred mechanism, and the stereoselectivity. Notably, while the DMAP catalyst itself is confirmed to be highly fluxional, electrostatically driven π⋅⋅⋅π⁺ interactions render the active, acylated form of the catalyst highly rigid, explaining its pronounced stereoselectivity.

Isothiourea-Catalysed Regioselective Acylative Kinetic Resolution of Axially Chiral Biaryl Diols

An operationally simple isothiourea-catalysed acylative kinetic resolution of unprotected 1,1'-biaryl-2,2'-diol derivatives has been developed to allow access to axially chiral compounds in highly enantioenriched form (s values up to 190). Investigation of the reaction scope and limitations provided three key observations: i) the diol motif of the substrate was essential for good conversion and high s values; ii) the use of an α,α-disubstituted mixed anhydride (2,2-diphenylacetic pivalic anhydride) was critical to minimize diacylation and give high selectivity; iii) the presence of substituents in the 3,3'-positions of the diol hindered effective acylation. This final observation was exploited for the highly regioselective acylative kinetic resolution of unsymmetrical biaryl diol substrates bearing a single 3-substituent. Based on the key observations identified, acylation transition state models have been proposed to explain the atropselectivity of this kinetic resolution.

Total Synthesis of Aurofusarin: Studies on the Atropisomeric Stability of Bis-Naphthoquinones

An efficient annulation involving pyrone addition to a quinone and Dieckmann condensation was developed for rapid assembly of a γ-naphthopyrone monomeric precursor to the bis-naphthoquinone natural product aurofusarin. Dimerization was achieved through PdII -catalyzed dehydrogenative coupling. Further studies employing asymmetric nucleophilic epoxidation indicate that the atropisomers of aurofusarin and derivatives are not configurationally stable at ambient temperature.

Organocatalytic Atroposelective Arylation of 2-Naphthylamines as a Practical Approach to Axially Chiral Biaryl Amino Alcohols

The first phosphoric acid catalyzed direct arylation of 2-naphthylamines with iminoquinones for the atroposelective synthesis of axially chiral biaryl amino alcohols has been developed. This reaction constitutes a highly functional-group-tolerant route for the rapid construction of enantioenriched axially chiral biaryl amino alcohols, and is a rare example of 2-naphthylamines acting as nucleophiles in an organocatalytic enantioselective transformation. Furthermore, the products, which feature various halogen atoms, provide access to structurally diverse axially chiral amino alcohols through further transformations.

Induction of Axial Chirality in 8-Arylquinolines through Halogenation Reactions Using Bifunctional Organocatalysts

The enantioselective syntheses of axially chiral heterobiaryls were accomplished through the aromatic electrophilic halogenation of 3-(quinolin-8-yl)phenols with bifunctional organocatalysts that control the molecular conformations during successive halogenations. Axially chiral quinoline derivatives, which have rarely been synthesized in an enantioselective catalytic manner, were afforded in moderate-to-good enantioselectivities through bromination, and an analogous protocol also enabled enantioselective iodination. In addition, this catalytic reaction, which allows enantioselective control through the use of mono-ortho-substituted substrates, allowed the asymmetric synthesis of 8-arylquinoline derivatives bearing two different halogen groups in high enantioselectivities.

Organocatalytic synthesis of axially chiral atropisomers

Axially chiral atropisomers are privileged frameworks present in ligands, catalysts and natural products. Organocatalytic mediated reactions offer an interesting and unique alternative for their synthesis.