Construction of Axially Chiral Styrenes Linking an Indole Moiety by Chiral Phosphoric Acid

Catalytic Asymmetric Dearomatization of 2,3-Disubstituted Indoles by a [4 + 2] Cycloaddition Reaction with In Situ Generated Vinylidene ortho-Quinone Methides: Access to Polycyclic Fused Indolines

A protocol of enantioselective dearomatization of 2,3-disubstituted indoles by an organocatalytic intermolecular (4 + 2) cycloaddition reaction with in situ generated vinylidene ortho-quinone methide has been documented. A wide range of polycyclic 2,3-fused indolines containing vicinal quaternary carbon stereocenters was readily prepared in high yields and with excellent diastereo- and enantioselectivities.

Stable Axially Chiral Cyclohexylidenes from Catalytic Asymmetric Knoevenagel Condensation

Axially chiral cycloalkylidenes are interesting but less developed axially chiral molecules. Here, a bispidine-based chiral amine catalytic system was developed to promote efficiently the asymmetric Knoevenagel condensation of N-protected oxindoles and benzofuranones with 4-substituted cyclohexanones. A variety of alkylidenecycloalkanes with stable axial chirality were obtained in good yields and fairly good er (enantiomeric ratio). Based on the absolute configuration determination of product and DFT calculations, a possible mechanism of stereoselective induction was proposed.

Organocatalytic Asymmetric Dearomative Spirocyclization/Oxa-Michael Addition Sequence: Synthesis of Polycyclic Tetralones

Herein, an organocatalytic asymmetric dearomative spirocyclization/oxa-Michael addition sequence with a newly designed substrate having two naphthol motifs has been developed. The reaction proceeds through in situ chiral vinylidene ortho-quinone methide (VQM) intermediate formation, dearomative spirocyclization of naphthol, and an oxa-Michael addition reaction. The densely functionalized tetralone products were formed in high yields with high diastereo- and enantioselectivities.

Organocatalytic Synthesis of Furan-Embedded Styrene Atropisomers

Herein, we report the first synthesis of furan-embedded styrene atropisomers via the reaction between 1-(aryl-ethynyl)-naphthalen-2-ol and γ-hydroxyenone. The reaction proceeds through in situ furan formation from γ-hydroxyenone. The styrene derivatives were obtained in moderate to good yields with high diastereoselectivities with a catalytic amount of PTSA. Few applications such as triazole formation and cross-coupling reactions have been demonstrated. A preliminary catalytic asymmetric version was also reported.

Atroposelective Synthesis of Axially Chiral Styrenes Connecting an Axially Chiral Naphthyl-indole Moiety Using Chiral Phosphoric Acid Catalysis

The organocatalytic asymmetric reactions of C2-unsubstituted racemic naphthyl-indoles with orthoalkynylnaphthols were employed to synthesize axially chiral styrenes connected to an axially chiral naphthyl-indole unit. Utilizing chiral phosphoric acid as the catalyst, these axially chiral styrenes were prepared in good yields (up to 96%) and excellent stereoselectivity (up to >99.9% ee, >20:1 dr, and >99:1 E/Z) in mild conditions. Moreover, further synthetic transformations were achieved with high yields and excellent stereocontrol.

Asymmetric Hydrophosphinylation of Alkynes: Facile Access to Axially Chiral Styrene-Phosphines

A Cu/CPA co-catalytic system has been developed for achieving the direct hydrophosphinylation of alkynes with phosphine oxides in delivering novel axially chiral phosphorus-containing alkenes in high yields and excellent enantioselectivities (up to 99 % yield and 99 % ee). DFT calculations were performed to elucidate the reaction pathway and the origin of enantiocontrol. This streamlined and modular methodology establishes a new platform for the design and application of new axially chiral styrene-phosphine ligands.

Divergent Coupling of ortho-Alkynylnaphthols and Benzofurans: [4 + 2] Cycloaddition and Friedel-Crafts Reaction

Catalytic direct [4 + 2] cycloaddition reactions and Friedel-Crafts reactions of ortho-alkynylnaphthols with benzofurans have been developed, affording functionalized hydrobenzofuro[3,2-b]chromans and hydroarylation products, respectively, in high yields with high chemoselectivity.

Recent Advances in the Catalytic Asymmetric Friedel-Crafts Reactions of Indoles

Functionalized chiral indole derivatives are privileged and versatile organic frameworks encountered in numerous pharmaceutically active agents and biologically active natural products. The catalytic asymmetric Friedel-Crafts reaction of indoles, catalyzed by chiral metal complexes or chiral organocatalysts, is one of the most powerful and atom-economical approaches to access optically active indole derivatives. Consequently, a wide range of electrophilic partners including α,β-unsaturated ketones, esters, amides, imines, β,γ-unsaturated α-keto- and α-ketiminoesters, ketimines, nitroalkenes, and many others have been successfully employed to achieve a plethora of functionalized chiral indole moieties. In particular, strategies for C-H functionalization in the phenyl of indoles require incorporation of a directing or blocking group in the phenyl or azole ring of indole. The discovery of chiral catalysts which can control enantiodiscrimination has gained a great deal of attention in recent years. This review will provide an updated account on the application of the asymmetric Friedel-Crafts reaction of indoles in the synthesis of diverse chiral indole derivatives, covering the timeframe from 2011 to today.

Enantioselective Friedel-Crafts Reaction of 2-Alkynyphenols with Aromatic Ethers by Chiral Brønsted Acid Catalysis

Herein, we report chiral strong Brønsted acid-catalyzed enantioselective Friedel-Crafts reaction of 2-alkynyphenols with aromatic ethers. The reaction affords the corresponding axially chiral styrenes in up to 91% yield and 97% ee.

Synthesis of aryl-fused 1,4-oxathiepines from pyridinium 1,4-zwitterionic thiolates and vinylidene ortho-quinone methides

Synthesis of aryl-fused 1,4-oxathiepines from pyridinium 1,4-zwitterionic thiolates with vinylidene ortho-quinone methides generated in situ via a formal (3 + 4) pathway.