N,N'-dioxide-scandium(III)-catalyzed asymmetric Aza-Friedel-Crafts reaction of sesamol with aldimines

Visible-Light-Promoted Enantioselective Acylation and Alkylation of Aldimines Enabled by 9-Fluorenone Electron-Shuttle Catalysis

Chiral acyclic α-tertiary amino ketones are widely present in various natural products and pharmaceuticals; however, the direct synthesis of this pharmacophore through a robust strategy still presents significant challenges. The emerging photocatalysis provides a powerful approach to construct chemical bonds that are difficult to form via a traditional two-electron pathway. Herein, we developed visible-light-induced chiral Lewis acid-catalyzed highly enantioselective acylation/alkylation of aldimines enabled by cooperative FLN (9-fluorenone) electron-shuttle catalysis via radical addition. An array of α-tertiary amino ketones, β-amino alcohols, and chiral amines were achieved with high yields and good to excellent stereocontrol (87 examples, up to 84% yield, 96% ee). These products can be easily transformed into valuable and bioactive skeletons. Extensive control experiments, detailed mechanism studies, and density functional theory calculations elucidated the reaction process and highlighted the crucial role played by FLN.

Cu(II)-Catalyzed Enantioselective Aza-Friedel-Crafts Reaction of 1-Naphthols and Electron-Rich Phenols with Isatin-Derived Ketimines

New chiral ligands could be obtained by introducing proline moieties and imidazoline moieties to binaphthyl skeletons. The chiral ligands exhibited balanced rigidity and flexibility which could allow the change of the conformations during the reactions on one hand, and could provide sufficient asymmetric induction on the other. The proline moiety could act as a linker connecting the binaphthyl skeletons and the imidazoline moieties as well as a coordinating group for the central metal, and the electronic and steric properties of the imidazoline groups could be carefully fine-tuned by the use of different substituents. In the presence of Cu(II) catalyst bearing such chiral ligands, aza-Friedel-Crafts reaction of 1-naphthols and electron-rich phenols with isatin-derived ketimines provided the desired products with good to excellent yields and up to 99 % ee. The reactions showed good scalability, and excellent ee could still be obtained when the reaction was carried out in gram-scale.

Enantioselective Synthesis of Diarylmethylamines through the Aza-Friedel-Crafts Reaction of 1,3,5-Trialkoxy Benzenes and N-Sulfonyl Aldimines Catalyzed by BINOL-Derived Disulfonimides

A 1,1'-bi-2-naphthol (BINOL)-derived disulfonimide (DSI)-catalyzed enantioselective aza-Friedel-Crafts reaction between 1,3,5-trialkoxy benzenes and N-sulfonyl aldimines gives direct access to a series of chiral diarylmethylamines in good yields and good to excellent enantioselectivities (up to 97% ee). This reaction provides a useful protocol for the direct synthesis of diarylmethylamine derivatives.

Eco-friendly and efficient catalyst-free synthesis of N-sulfonylimines from sulfonamides and aldehydes: crucial role of Al2O3 as a reusable dehydrating agent

A green synthetic method for the synthesis of N-sulfonylimines was developed involving the straightforward condensation of sulfonamides with aldehydes under green and catalyst-free conditions, mediated by neutral Al₂O₃ as an efficient and reusable dehydrating agent. N-Sulfonylimines were produced in high yields and purity under simple experimental procedures.

Construction of chiral Betti base precursors containing a congested quaternary stereogenic center via chiral phosphoric acid-catalyzed arylation of isoindolinone-derived ketimines

Synthesis of enantioenriched Betti base precursors containing a congested quaternary stereocenter.

Highly Diastereoselective Chelation-Controlled 1,3-anti-Allylation of (S)-3-(Methoxymethyl)hexanal Enabled by Hydrate of Scandium Triflate

En route to the total synthesis of (+)-Neopeltolide, we explored Lewis acid-assisted diastereoselective allylation of MOM-protected 3-hydroxylhexanal with β-(2,2-diethoxyethyl)-substituted (allyl)tributylstannane. The hydrated form of scandium triflate was found to be essential for attaining high 1,3-anti-diastereoselectivity (d.r. 94:6), while the use of anhydrous catalyst resulted in a modest diastereocontrol (d.r. 76:24). The preferred 1,3-anti-selectivity in this transformation can be rationalized in the framework of the Reetz chelate model of asymmetric induction. The 1,3-anti-configuration of the product was confirmed by its conversion into the known C7-C16 building block of (+)-Neopeltolide. We also report an improved protocol for the synthesis of β-(2,2-diethoxyethyl)-substituted (allyl)tributylstannane, which can be utilized as a cost-efficient bipolar isoprenoid-type C5-building block in the synthesis of natural compounds.

Facile synthesis of chiral ε-sultams via an organocatalytic aza-Friedel-Crafts reaction

Chiral ε-sultams, with their unique strain cyclic structure, are a type of molecule with important biological activities. A facile enantioselective aza-Friedel-Crafts reaction of seven-membered cyclic N-sulfonylimines with naphthols was developed with a cinchona alkaloid-based bifunctional organocatalyst, giving chiral ε-sultams with an enantiomeric excess of up to 92%.

Regio- and Enantioselective (Het)arylation of β-Alkenyl Pyrroline to α-Aryl-β-alkenyl Pyrrolidines

Regio- and enantioselective direct arylation of β-alkenyl pyrroline is reported. A wide range of electron-rich arenes and heteroarenes reacted under mild conditions with different β-alkenyl pyrrolines to provide structurally diverse α-aryl-β-alkenyl pyrrolidines with very good yields and excellent regioselectivity. Enantioselective reaction in the presence of Lewis acids and chiral phosphoric acids provided the desired arylated product with 73% enantiomeric excess.

A Novel Sc(OTf)3 -Catalyzed (2+2+1)-Cycloannulation/Aza-Friedel-Crafts Alkylation Sequence toward Multicyclic 2-Pyrrolines

The rapid assembly of molecular complexity continues to be at the forefront of novel reaction development. In the pursuit of that goal, we herein report a novel Sc(OTf)₃ -catalyzed, one-pot multicomponent reaction that furnishes complex multicyclic 2-pyrrolines with excellent overall yields and perfect diastereocontrol. This process is based on our previously established (2+2+1)-cycloannulation of in situ generated 1-azaallyl cations, 1,3-dicarbonyls and primary amines. The newly formed and highly reactive aminal moiety is readily substituted with indoles and pyrroles both as external and internal π-nucleophiles to provide densely functionalized N-heterocycles with four new σ-bonds and two vicinal quaternary stereogenic centers. In addition, DFT calculations have been conducted to further characterize the intermediate 1-azaallyl cations.

Visible-Light, Iodine-Promoted Formation of N-Sulfonyl Imines and N-Alkylsulfonamides from Aldehydes and Hypervalent Iodine Reagents

Alternative synthetic methodology for the direct installation of sulfonamide functionality is a highly desirable goal within the domain of drug discovery and development. The formation of synthetically valuable N-sulfonyl imines from a range of aldehydes, sulfonamides, and PhI(OAc)₂ under practical and mild reaction conditions has been developed. According to mechanistic studies described within, the reaction proceeds through an initial step involving a radical initiator (generated either by visible-light or heat) to activate the reacting substrates. The reaction provides a synthetically useful and operationally simple, relatively mild alternative to the traditional formation of N-sulfonyl imines that utilizes stable, widely available reagents.

Synthesis of Benzyl Amines via Copper-Catalyzed Enantioselective Aza-Friedel-Crafts Addition of Phenols to N-Sulfonyl Aldimines

A new copper-catalyzed enantioselective aza-Freidel-Crafts reaction between phenols and N-sulfonyl aldimines that provides chiral secondary benzylamines in good to excellent yields and excellent enantioselectivities (up to 99% ee) is disclosed. In particular, excellent scope with alkylimines was observed for the first time. The synthetic utility of the products was demonstrated in the first enantioselective synthesis of a dual orexin receptor antagonist, a compound that contains an amine-bearing stereocenter adjacent to a bis- ortho-functionalized arene.

Lewis acid-catalyzed Friedel–Crafts reactions toward highly versatile, α-quaternary oxime ethers

Tertiary 2-hydroxy oxime ethers are converted into α-functionalized, all-carbon-substituted products under Lewis acid catalysis in a S_N1-reaction.

Total Synthesis of (+)-Gracilamine Based on an Oxidative Phenolic Coupling Reaction and Determination of Its Absolute Configuration

The enantioselective total synthesis of (+)-gracilamine (1) is described. The strategy features a diastereoselective phenolic coupling reaction followed by a regioselective intramolecular aza-Michael reaction to construct the ABCE ring system. The configuration at C3a in 1 was controlled by the stereocenter at C9a, which was selectively generated (91 % ee) by an organocatalytic enantioselective aza-Friedel-Crafts reaction developed by our research group. This synthesis revealed that the absolute configuration of (+)-gracilamine is 3aR, 4S, 5S, 6R, 7aS, 8R, 9aS.

Chiral cobalt(ii) complex catalyzed Friedel–Crafts aromatization for the synthesis of axially chiral biaryldiols

An efficient Lewis-acid-catalyzed asymmetric Friedel–Crafts aromatization between p-benzoquinone derivatives and 2-naphthols has been developed by using a chiral cobalt(ii) complex of N,N′-dioxide.

Asymmetric synthesis of chromans via the Friedel–Crafts alkylation–hemiketalization catalysed by an N,N′-dioxide scandium(iii) complex

The direct and sequential Friedel–Crafts alkylation/hemiketalization procedures for the synthesis of chiral chromans resulted in excellent yields, high enantioselectivities and high diastereoselectivities for a broad range of substrates.

Formation of N-sulfonyl imines from iminoiodinanes by iodine-promoted, N-centered radical sulfonamidation of aldehydes

A light-promoted, non-traditional carbonyl activation via a N-centered radical (NCR) species to produce activated imines using iminoiodinanes is reported.

Construction of highly enantioselective spiro-oxindole derivatives with fused chromene via organocascade catalysis

A first highly enantioselective addition of naphthols and sesamol to indolylidene cyanoacetate derived from isatins was carried out in the presence of bi-functional quinine thiourea as organocatalyst.

Organocatalytic enantioselective aza-Friedel–Crafts reaction of 2-naphthols with benzoxathiazine 2,2-dioxides

An organocatalytic enantioselective aza-Friedel–Crafts addition of 2-naphthols to benzoxathiazine 2,2-dioxides is described using a quinine-derived bifunctional catalyst.