Rhodium-Catalyzed Asymmetric Arylation of Cyclic N-Sulfonyl Aryl Alkyl Ketimines: Efficient Access to Highly Enantioenriched α-Tertiary Amines

Immobilization of Trifluoromethyl-Substituted Pyridine-Oxazoline Ligand and Its Application in Asymmetric Continuous Flow Synthesis of Benzosultams

This study presents an improved synthetic route to ligand (S)-4-(tert-butyl)-2-(5-(trifluoromethyl)pyridin-2-yl)-4,5-dihydrooxazole and its application as a highly active and enantioselective catalyst in the addition of arylboronic acids to cyclic N-sulfonylketimines. Immobilization of such a ligand was achieved using a commercially available starting material and a PS-PEG TentaGel S NH2 support, resulting in a stable heterogeneous catalyst. Although the anchored catalyst exhibited a slight reduction in enantioselectivity and a 4-fold decrease in reaction rate, it displayed remarkable stability, enabling 10 consecutive reaction cycles. Furthermore, the successful transition to a continuous flow system demonstrated even higher turnover numbers compared to batch arrangements. These findings provide valuable insights into the development of efficient flow reactors for continuous synthesis of benzosultams, further advancing the field of asymmetric catalysis.

δ-Acetoxy Allenoate as a 5C-Synthon in Domino-Annulation with Sulfamidate Imines: Ready Access to Coumarins

A DMAP-catalyzed sequential benzannulation and lactonization strategy in which δ-acetoxy allenoate functions as a 5C-synthon in its reaction with cyclic sulfamidate imines is reported. This platform delivers π-extended coumarin frameworks under metal-free conditions via allylic elimination followed by Mannich coupling, proton shifts, C-N bond cleavage, and lactonization as key steps. The driving force for this domino reaction is the formation of the diene-ammonium intermediate and O-S bond cleavage. ESI-HRMS has been useful in gaining insights into the reaction pathway.

Nickel-Catalyzed Enantioselective Reductive Arylation and Heteroarylation of Aldimines via an Elementary 1,4-Addition

Nickel catalysts of chiral pyrox ligands promoted enantioselective reductive arylation and heteroarylation of aldimines, using directly (hetero)aryl halides and sulfonates. The catalytic arylation can also be conducted with crude aldimines generated from condensation of aldehydes and azaaryl amines. Mechanistically, density functional theory (DFT) calculations and experiments pointed to an elementary step of 1,4-addition of aryl nickel(I) complexes to N-azaaryl aldimines.

Rh(I)-Catalyzed Enantioselective Arylation of Cyclic N-Sulfonyl Diketimines Using Planar-Chiral Phosphine-Olefin Ligands Based on a (Cyclopentadienyl)manganese(I) Scaffold with a Highly Fluorinated Aryl Phosphino Group

Catalytic enantioselective 1,2-addition reactions of arylboronic acids with 1,2,5-thiadiazoline 1,1-dioxide derivatives were achieved using planar-chiral phosphine-olefin ligand L5 with a bis[(2,3,4,5,6-pentafluoro)phenyl]phosphino group, showing ≤98% ee. The enantioselectivities of the addition products were improved by increasing the number of fluoro substituents on the aromatic ring of the ligand. X-ray crystallographic studies of 3aa and [RhCl/L5]₂ revealed the absolute configuration of the enantioenriched addition product 3 and the mode of phosphine-olefin bidentate coordination of L5 to a rhodium(I) cation.

Natural Product-Inspired Chiral Ligand Design: Aloperine and N-Substituted Aloperines-Induced Pd-Catalyzed Asymmetric Hydroarylation of Ketimines

A naturally occurring alkaloid aloperine was utilized as a chiral skeleton for the development of new ligands/catalysts in asymmetric synthesis. A number of N-substituted aloperines have been prepared, and a Pd-catalyzed asymmetric hydroarylation of ketimines using these chiral 1,3-diamine ligands was reported. A range of chiral sulfonyl amides were prepared in high yields and enantioselectivities. The stereoselectivity and structure relationships of aloperines have been studied. In addition, preliminary studies on the desymmetrization of meso-anhydride have also shown that these diamines have good potential in organocatalysis. These discoveries would provide a new future development for natural product-inspired chiral ligand design and developments.

Efficient synthesis of benzosultams containing continuous quaternary carbons via trapping active ylides with cyclic N-sulfonyl ketimines

A rapid and efficient method for the synthesis of benzosultams containing continuous quaternary carbons in a one pot fashion has been developed with moderate to excellent yields at room temperature under air. The resulting products exhibit good anticancer activity in osteosarcoma cells.

Palladium/N,N'-Disulfonyl Bisimidazoline-Catalyzed Enantioselective Addition of Arylboronic Acids to Cyclic N-Sulfonyl Ketimines

The combination of Pd(TFA)₂ and an N,N'-disulfonyl bisimidazoline ligand shows high catalytic activity and excellent asymmetric induction in the addition of arylboronic acids to cyclic N-sulfonyl ketimines including benzo[d]isothiazole-1,1-dioxides, benzo[e][1,2,3]oxathiazine-2,2-dioxides, and 1,2,5-thiadiazole-1,1-dioxides, by which three types of chiral quaternary carbon-containing sultams with substantial substitution diversity were synthesized with high yields and excellent enantioselectivities (up to >99% ee). The current catalysis demonstrated a remarkable tolerance to oxygen and thus provided an operationally simple approach for constructing enantioenriched cyclic quaternary stereocenters.

Recent Advances in Catalytic Synthesis of Benzosultams

Benzosultams represent one category of multi-heteroatom heterocyclic scaffolds, which have been frequently found in pharmaceuticals, agricultural agents, and chiral catalysts. Given the diversely significant functions of these compounds in organic and medicinal chemistry, great efforts have been made to develop novel catalytic systems for the efficient construction of benzosultam motifs over the past decades. Herein, in this review, we mainly summarize the recent advances in the field of catalytic synthesis of benzosultams from 2017 to August of 2020, with an emphasis on the scopes and mechanisms of representative reactions.

The enantioselective construction of trifluoromethylated quaternary stereocenters via the Rh-catalyzed asymmetric dehydrated arylation of unprotected hemiaminals

An effective Rh/chiral diene catalyst system for the highly enantioselective synthesis of chiral benzosultams bearing trifluoromethylated quaternary carbon stereocenters has been developed.

Synthesis of Sultams and Cyclic N-Sulfonyl Ketimines via Iron-Catalyzed Intramolecular Aliphatic C-H Amidation

Cyclic sulfonamides (sultams) play a unique role in drug discovery and synthetic chemistry. A direct synthesis of sultams by an intramolecular C(sp³)-H amidation reaction using an iron complex in situ derived from Fe(ClO₄)₂ and aminopyridine ligand is reported. This strategy features a readily available catalyst and tolerates a broad variety of substrates as demonstrated by 22 examples (up to 89% yield). A one-pot iron-catalyzed amidation/oxidation procedure for the synthesis of cyclic N-sulfonyl ketimines is also realized with up to 92% yield (eight examples). The synthetic utility of the method is validated by a gram-scale reaction and derivatization of the products to ring-fused sultams.

Copper-Catalyzed Asymmetric Arylation of N-Heteroaryl Aldimines: Elementary Step of a 1,4-Insertion

Copper complexes of monodentate phosphoramidites efficiently promote asymmetric arylation of N-azaaryl aldimines with arylboroxines. DFT calculations and experiments support an elementary step of 1,4-insertion in the reaction pathway, a step in which an aryl-copper species adds directly across four atoms of C=N-C=N in the N-azaaryl aldimines.

Ru(ii)-Catalyzed spirocyclization of aryl N-sulfonyl ketimines with aryl isocyanates through an aromatic C-H bond activation

A novel one-pot strategy has been developed for the construction of spiro-isoindolinone-benzosultams through a Ru(ii)-catalyzed sequential C-C and C-N bond formation. This method is highly atom-economical and compatible with a wide range of substituents. This is the first report on the spirocyclization of 3-aryl N-sulfonyl ketimines with aryl isocyanates to produce highly rigid and pharmaceutically relevant spirocycles through a C-H bond activation.

Palladium-Catalyzed Enantioselective Synthesis of Cyclic Sulfamidates and Application to a Synthesis of Verubecestat

An enantioselective arylation reaction catalyzed by palladium complexed with substituted phosphinooxazoline (PHOX) ligands is described. Aza-quaternary stereocenters are readily accessible through the arylation reaction between cyclic iminosulfates and a wide variety of arylboronic acids, including electron-poor and ortho-substituted arylboronic acids. This reaction was applied to the preparation of verubecestat, which is currently undergoing clinical evaluation for the treatment of Alzheimer's disease.

Recent advances in rhodium-catalyzed asymmetric synthesis of heterocycles

Heterocycles are crucial structural motifs that are ubiquitously present in biologically active natural products and pharmaceutically important compounds. Over the past few decades, great attention has been paid to develop efficient methodologies for the construction of diverse enantioenriched heterocyclic frameworks. This review focuses on the recent impressive progress and advances in the asymmetric synthesis of heterocycles under rhodium catalysis.

Enantioselective synthesis of gem-diarylalkanes by transition metal-catalyzed asymmetric arylations (TMCAAr)

To date, enantiomerically enriched molecules containing gem(1,1)-diaryl containing tertiary or quaternary stereogenic centers have been readily accessed by transition metal-catalyzed enantioselective or stereoconvergent aryl transfer reactions.

Chiral gem(1,1)-diaryl containing tertiary or quaternary stereogenic centers are present in many natural products and important pharmacophores. While numerous catalytic asymmetric methods enable access to 1,1-diaryl motifs, transition metal-catalyzed asymmetric arylations (TMCAAr) are one of the most powerful methods to prepare enantiopure gem-diarylalkane compounds. The main methodology includes enantioselective 1,2- or 1,4-additions across C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O, C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> N and C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C bonds by arylmetallic reagents; aryl cross-couplings of olefins, benzylic (pseudo)halides and aziridines; asymmetric aryl substitution reactions of allylic substrates; and isotopic benzylic C–H arylation.

Pd(ii), Ni(ii) and Co(ii)-catalyzed enantioselective additions of organoboron reagents to ketimines

This feature article highlights the development of Pd(ii), Ni(ii), and Co(ii)-catalyzed asymmetric additions of organoboron reagents to ketimines.

Highly enantioselective synthesis of α-tertiary chiral amino acid derivatives through rhodium-catalyzed asymmetric arylation of cyclic N-sulfonyl α-ketimino esters

A simple sulfur-olefin ligand promoted Rh-catalyzed highly enantioselective arylation of cyclic α-ketimino esters with arylboronic acids is described.

Enantioselective Rhodium-Catalyzed Coupling of Arylboronic Acids, 1,3-Enynes, and Imines by Alkenyl-to-Allyl 1,4-Rhodium(I) Migration

A chiral rhodium complex catalyzes the highly enantioselective coupling of arylboronic acids, 1,3-enynes, and imines to give homoallylic sulfamates. The key step is the generation of allylrhodium(I) species by alkenyl-to-allyl 1,4-rhodium(I) migration.

An asymmetric Brønsted acid-catalyzed Friedel–Crafts reaction of indoles with cyclic N-sulfimines

A highly enantioselective organocatalytic Friedel–Crafts reaction of indoles with cyclic N-sulfimines using a chiral phosphoric acid as an organocatalyst has been developed.

Highly enantioselective Rh/chiral sulfur-olefin-catalyzed arylation of alkyl-substituted non-benzofused cyclic N-sulfonyl ketimines

An effective catalyst system for the highly enantioselective synthesis of α-arylalkyl-substituted sulfamidates with a quaternary stereogenic center has been developed.

Ni(ii)-catalyzed asymmetric addition of arylboronic acids to cyclic imines

A Ni(ii)-catalyzed asymmetric addition of arylboronic acids to cyclic imines has been realized using a tropos biphenyl phosphine-oxazoline ligand.

Umpolung Addition of Aldehydes to Aryl Imines

One of the classical ways to synthesize amines involves the coupling of carbonyl compounds and imines, either through enolate chemistry or acyl-based carbanion equivalents. We herein report an alternative strategy that is based on the use of aldehydes as alkyl carbanion equivalents in a reductive coupling with aryl imines. A wide array of secondary amines can be synthesized in moderate to high yields. This reaction is mediated by hydrazine and catalyzed by ruthenium(II) complexes, and it tolerates various functional groups, such as esters, amides, and nitriles.

Rh-Catalyzed arylation of fluorinated ketones with arylboronic acids

The Rh-catalyzed arylation of fluorinated ketones with boronic acids is reported. This efficient process allows access to fluorinated alcohols in high yields under mild conditions. Competition experiments suggest that difluoromethyl ketones are more reactive than trifluoromethyl ketones in this process, despite their decreased electronic activation, an effect we postulate to be steric in origin.

Enantioselective synthesis of quaternary α-aminophosphonates by Pd-catalyzed arylation of cyclic α-ketiminophosphonates with arylboronic acids

A highly enantioselective addition of arylboronic acids to cyclic α-ketiminophosphonates is reported using a chiral palladium phosphinooxazoline catalyst, providing an efficient and facile route to quaternary α-aminophosphonates in high yields and up to 99.9% enantioselectivity.