Aromatic-Amide-Derived Nonbiaryl Atropisomer as Highly Efficient Ligand for Asymmetric Silver-Catalyzed [3 + 2] Cycloaddition

Zn(II)-catalyzed asymmetric [3 + 2] cycloaddition of acyclic enones with azomethine ylides

The Zn(II)/UCD-Imphanol-catalyzed highly endo-selective [3 + 2] asymmetric cycloaddition of acyclic enones and azomethine ylides has been developed. Moderate to high yields (up to 94%) with excellent endo/exo selectivities (99 : 1) and enantioselectivities up to 96.5 : 3.5 er were obtained.

Transition Metal-Catalyzed Transformations of Chalcones

Chalcones are a class of naturally occurring flavonoid compounds associated to a variety of biological and pharmacological properties. Several reviews have been published describing the synthesis and biological properties of a vast array of analogues. However, overviews on the reactivity of chalcones has only been explored in a few accounts. To fill this gap, a systematic survey on the most recent developments in the transition metal-catalyzed transformation of chalcones was performed. The chemistry of copper, palladium, zinc, iron, manganese, nickel, ruthenium, cobalt, rhodium, iridium, silver, indium, gold, titanium, platinum, among others, as versatile catalysts will be highlighted, covering the literature from year 2000 to 2023, in more than 380 publications.

Regio- and Stereoselective Switchable Synthesis of (E)- and (Z)-N-Carbonylvinylated Pyrazoles

Regio- and stereoselective switchable synthesis of (E)- and (Z)-N-carbonylvinylated pyrazoles is first developed by using the Michael addition reaction of pyrazoles and conjugated carbonyl alkynes. Ag₂CO₃ plays a key role in the switchable synthesis of (E)- and (Z)-N-carbonylvinylated pyrazoles. Ag₂CO₃-free reactions lead to thermodynamically stable (E)-N-carbonylvinylated pyrazoles in excellent yields whereas reactions with Ag₂CO₃ give (Z)-N-carbonylvinylated pyrazoles in good yields. It is noteworthy that (E)- or (Z)-N¹-carbonylvinylated pyrazoles are obtained with high regioselectivity when asymmetrically substituted pyrazoles react with conjugated carbonyl alkynes. The method can also extend to the gram scale. A plausible mechanism is proposed on the basis of the detailed studies, wherein Ag⁺ acts as coordination guidance.

Asymmetric synthesis of aryl-substituted pyrrolidines by using CFAM ligand-AgOAc chiral system via 1,3-dipolar cycloaddition reaction

We have prepared a ligand library based on a ferrocenyl aziridinyl methanol core unit (simply called FAM) having a phenyl group, a cyclohexyl group, and a naphthyl group to be used in 1,3-dipolar cycloaddition (1,3-DC) reactions for the synthesis of chiral pyrrolidines. These chiral ligands were used with AgOAc in 1,3-DC reactions taking place between the aryl-substituted azomethine ylides and N-methylmaleimide as the dipolarophile. In each case, the expected aryl-substituted pyrrolidines were obtained in good to excellent yields with acceptable enantioselectivities favoring only the endo product. The chiral catalyst system CFAM4-AgOAc was also used in 1,3-DC reaction with different dipolarophiles such as dimethyl maleate, tert-butyl acrylate, methyl acrylate, trans-chalcone, and vinyl sulfone. In each case, the cycloadducts were obtained in acceptable yields albeit with low ee. Fortunately, it was possible to increase the ee up to >99% upon crystallization.

Atropisomers with Axial and Point Chirality: Synthesis and Applications

Enantiopure atropisomers have become increasingly important in asymmetric synthesis and catalysis, pharmaceutical science, and material science since the discovery of inherent features of axial chirality originating from rotational restriction. Despite the advances made in this field to date, it remains highly desirable to construct structurally diverse atropisomers with potentially useful functions. We propose superposition to match axial and point chirality as a potentially useful strategy to access structurally complex and diverse building blocks for organic synthesis and pharmaceutical science because merging atropisomeric backbones with one or more extra chiral elements can topologically broaden three-dimensional environments to create complex scaffolds with multiple tunable parameters. Over the past decade, we have successfully implemented a strategic design for the superposition of axial and point chirality to develop a series of enantiopure atropisomers and have utilized the synergistic functions of these molecules to enhance chirality transfer in various catalytic asymmetric transformations.In this Account, we present several novel atropisomers with superposed axial and point chirality developed in our laboratory. In our studies, this superposition strategy was used to design and synthesize both biaryl and non-biaryl atropisomers from commercially available chiral sources. Consequently, these atropisomers were used to demonstrate the importance of the synergetic functions of axial and point chirality in specific enantioselective reactions. For example, aromatic amide-derived atropisomers, simplified as Xing-Phos arrays, were broadly employed in Ag-catalyzed [3 + 2] cycloaddition by a series of reactions of aldiminoesters with activated alkenes and imines, as well as being used as chiral solvating agents for the discrimination of optically active mandelic acid derivatives. Considering the powerful potential of non-biaryl atropisomers for asymmetric catalysis, we also explored the transition-metal-catalyzed enantioselective construction of a novel backbone of non-biaryl atropisomers (Ar-alkene, Ar-N axis) bearing both axial and point chirality for the design and synthesis of chiral ligands and functional molecules.The studies presented herein are expected to stimulate further research efforts on the development of functional atropisomers by superposition of matching axial and point chirality. In addition to tunable electron and stereohindrance effects, the synergy between matching chiral elements of axial/point chirality and functional groups is proven to be a special function that cannot be ignored for promoting reactivity and chirality-transfer efficiency in enantioselective synthesis. Consequently, our novel types of scaffolds with superposed axial and point chirality that are capable of versatile coordination with various metal catalysts in asymmetric catalysis highlight the power of the superposition of matching axial and point chirality for the construction of synthetically useful atropisomers.

Application of aromatic amide-derived atropisomers as chiral solvating agents for discrimination of optically active mandelic acid derivatives in 1 H nuclear magnetic resonance spectroscopy

Non-biaryl atropisomers and their stereochemistry have attracted much attentions in the past years. However, application of the non-biaryl atropisomers as chiral solvating agents is yet to be explored. In this work, four aromatic amide-derived atropisomeric phosphine ligands (hosts) were used as chiral solvating agents to recognize various mandelic acid derivatives (guests) in ¹ H nuclear magnetic resonance (NMR) spectroscopy. It is found that chiral center configurations of the four hosts have different effects on the enantiorecognition to the used guests. In addition, the host and guest interaction was further investigated by determination of the host-guest complex stoichiometry using the Job's method and density functional theory calculation, respectively. Moreover, chiral analysis accuracy of these hosts was evaluated through relationship between enantiomeric excess values of 4-chloromandelic acid provided by NMR and gravimetry, respectively.

Diastereodivergent Synthesis of Chiral 4-Fluoropyrrolidines (exo and exo') Based on the Cu(II)-Catalyzed Asymmetric 1,3-Dipolar Cycloaddition

1,3-Dipolar cycloaddition of azomethine ylides and electron deficient alkenes is widely studied for rapid installation of pyrrolidine frameworks. Despite significant advances, the major limitations of this process are creating chiral pyrrolidines bearing a quaternary stereogenic center and controlling the diastereoselectivity. Herein, we present an exo-selective asymmetric 1,3-dipolar cycloaddition to access chiral pyrrolidines with four contiguous stereogenic centers, including a fluorinated quaternary stereogenic center at C4, wherein a Cu(OAc)₂/(S)-tol-BINAP catalyst and α-fluoro-α,β-unsaturated arylketone dipolarophiles are used. Epimerization promoted by 5.0 equiv of DBU at 90 °C results in the formation of chiral 4-fluoropyrrolidines (exo') while maintaining the optical purity.

Combined Dynamic Kinetic Resolution and C-H Functionalization for Facile Synthesis of Non-Biaryl-Atropisomer-Type Axially Chiral Organosilanes

Although asymmetric C-H functionalization has been available for the synthesis of structurally diverse molecules, catalytic dynamic kinetic resolution (DKR) approaches to change racemic stereogenic axes remain synthetic challenges in this field. Here, a concise palladium-catalyzed DKR was combined with C-H functionalization involving olefination and alkynylation for the highly efficient synthesis of non-biaryl-atropisomer-type (NBA) axially chiral oragnosilanes. The chemistry proceeded through two different and distinct DKR: first, an atroposelective C-H olefination or alkynylation produced axially chiral vinylsilanes or alkynylsilanes as a new family of non-biaryl atropisomers (NBA), and second, the extension of this DKR strategy to twofold o,o'-C-H functionalization led to the multifunctional axially chiral organosilicon compounds with up to >99 % ee.

The Discovery of Multifunctional Chiral P Ligands for the Catalytic Construction of Quaternary Carbon/Silicon and Multiple Stereogenic Centers

The development of highly effective chiral ligands is a key topic in enhancing the catalytic activity and selectivity in metal-catalyzed asymmetric synthesis. Traditionally, the difficulty of ligand synthesis, insufficient accuracy in controlling the stereoselectivity, and poor universality of the systems often become obstacles in this field. Using the concept of nonequivalent coordination to the metal, our group has designed and synthesized a series of new chiral catalysts to access various carbon/silicon and/or multiple stereogenic centers containing products with excellent chemo-, diastereo-, and enantioselectivity.In this Account, we summarize a series of new phosphine ligands with multiple stereogenic centers that have been developed in our laboratory. These ligands exhibited good to excellent performance in the transition-metal-catalyzed enantioselective construction of quaternary carbon/silicon and multiple stereogenic centers. In the first section, notable examples of the design and synthesis of new chiral ligands by non-covalent interaction-based multisite activation are described. The integrations of axial chirality, atom-centered chirality, and chiral anions and multifunctional groups into a single scaffold are individually highlighted, as represented by Ar-BINMOLs and their derivative ligands, HZNU-Phos, Fei-Phos, and Xing-Phos. In the second, third, and fourth sections, the enantioselective construction of quaternary carbon stereocenters, multiple stereogenic centers, and silicon stereogenic centers using our newly developed chiral ligands is summarized. These sections refer to detailed reaction information in the chiral-ligand-controlled asymmetric catalysis based on the concept of nonequivalent coordination with multisite activation. Accordingly, a wide array of transition metal and main-group metal catalysts has been applied to the enantioselective synthesis of chiral heterocycles, amino acid derivatives, cyclic ketones, alkenes, and organosilicon compounds bearing one to five stereocenters.This Account shows that this new model of multifunctional ligand-controlled catalysts exhibits excellent stereocontrol and catalytic efficiency, especially in a stereodivergent and atom-economical fashion. Furthermore, a brief mechanistic understanding of the origin of enantioselectivity from our newly developed chiral catalyst systems could inspire further development of new ligands and enhancement of enantioselective synthesis by asymmetric metal catalysis.

Divergent synthesis of pyrrolidine and glutamic acid derivatives using a macrocyclic phase-transfer catalyst under high-pressure conditions

The reactivity of the glycine ketimine ester with α,β-unsaturated ketones in the presence of macrocyclic hybrid phase-transfer catalysts under high pressure conditions has been investigated.

Recent advances in organocatalytic asymmetric multicomponent cascade reactions for enantioselective synthesis of spirooxindoles

Catalytic asymmetric MCCRs for enantioselective synthesis of spirooxindoles by using chiral phosphoric acids, amines, bifunctional thiourea/squaramides and metal-based reagents as catalysts.

Design and Synthesis of TY-Phos and Application in Palladium-Catalyzed Enantioselective Fluoroarylation of gem-Difluoroalkenes

The first example of highly enantioselective fluoroarylation of gem-difluoroalkenes with aryl halides is presented by using a new chiral sulfinamide phosphine (Sadphos) type ligand TY-Phos. N-Me-TY-Phos can be easily synthesized on a gram scale from readily available starting materials in three steps. Salient features of this work including readily available starting materials, good yields, high enantioselectivities as well as broad substrate scope make this approach very practical and attractive. Notably, the asymmetric synthesis of an analogue of a biologically active molecule is also reported.

Organocatalytic synthesis of chiral CF3-containing oxazolidines and 1,2-amino alcohols: asymmetric oxa-1,3-dipolar cycloaddition of trifluoroethylamine-derived azomethine ylides

A series of CF₃-containing oxazolidines were constructed via organocatalytic asymmetric oxa-1,3-dipolar cycloaddition. These oxazolidines could undergo facile conversion to CF₃-containing 1,2-amino alcohols with vicinal stereogenic centers.

Catalytic asymmetric cycloaddition of unsymmetrical EWG-activated alkenes to fully substituted pyrrolidines bearing three different carbonyl groups

A unique 1,3-dipolar [3+2] cycloaddition of alkyl 4-oxo-4-arylbut-2-enoates bearing two different electron-withdrawing groups was completed by using the silver/(R)-DTBM-Segphos catalyst system, which gives the corresponding fully substituted pyrrolidines with four stereogenic centers in good yields and with excellent enantioselectivities (up to 98% ee).

Stereochemical diversity in pyrrolidine synthesis by catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides

The pyrrolidine ring is a privileged structural motif in synthetic and medicinal chemisty. This review aims to highlight the high versatility of the catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides for access to different types of stereochemical patterns in enantioselective pyrrolidine synthesis. Special attention will be paid to stereodivergent procedures giving rise to different stereoisomers from the same starting materials.

A AgOAc/quinine-derived aminophosphine complex as an efficient catalyst for diastereo- and enantioselective 1,3-dipolar cycloaddition of α,β-unsaturated 7-azaindoline amides and azomethine ylides

The Dixon’s catalyst system is effective for the asymmetric 1,3-dipolar cycloaddition.

Synthesis of 1,2,4-Trisubstituted-(1H)-imidazoles through Cu(OTf)2-/I2-Catalyzed C-C Bond Cleavage of Chalcones and Benzylamines

1,2,4-Trisubstituted-(1H)-imidazoles have been synthesized by the Cu(OTf)₂- and I₂-catalyzed unusual C-C bond cleavage of chalcones and benzylamines. After the α,β-unsaturated C-C bond cleavage, the β-portion is eliminated from the reaction. Various aryl- and heteroaryl-substituted chalcones and benzylamines were well tolerated in this unusual transformation to yield the trisubstituted-(1H)-imidazoles.

(R)-DM-SEGPHOS-Ag(I)-Catalyzed Enantioselective Synthesis of Pyrrolidines and Pyrrolizidines via (1,3)- and Double (1,3)-Dipolar Cycloaddition Reactions

An efficient diastereo- and enantioselective route to access a wide range of highly substituted pyrrolidine and pyrrolizidine derivatives has been described via (1,3)- and double (1,3)-dipolar cycloaddition reactions catalyzed by the (R)-DM-SEGPHOS-Ag(I) complex. The reactions proceed smoothly at ambient temperature, affording a variety of pyrrolidines and pyrrolizidines in high yields (up to 93%) with up to 99:1 dr and excellent enantioselectivities (up to 98% ee) without any additives. The newly synthesized pyrrolidine and pyrrolizidine derivatives contain four and seven contiguous stereogenic centers, respectively. Moreover, the synthetic utility of enantioenriched products has been demonstrated by transforming them into various synthetically useful advanced intermediates.

Highly efficient desymmetrization of cyclopropenes to azabicyclo[3.1.0]hexanes with five continuous stereogenic centers by copper-catalyzed [3 + 2] cycloadditions

An unprecedented copper-catalyzed desymmetrization/cycloaddition reaction of 1,1-disubstituted cyclopropenes provides an efficient access to azabicyclo[3.1.0]hexanes bearing five continuous carbon-stereogenic centers.

Synthesis of spiropyrrolidine oxindolesviaAg-catalyzed stereo- and regioselective 1,3-dipolar cycloaddition of indole-based azomethine ylides with chalcones

In excess of 100 new compounds were prepared in moderate to high yields (50–95%) with good to excellent diastereoselectivity (11 : 1 → 20 : 1 dr) by Ag-catalyzed 1,3-dipolar cycloaddition.

Chiral Organosulfur Ligands/Catalysts with a Stereogenic Sulfur Atom: Applications in Asymmetric Synthesis

Asymmetric synthesis, in which chiral organocatalysts or metal complexes with chiral ligands are used, has become the most valuable methodology for the preparation of enantiomerically pure organic compounds. Among such catalysts/ligands, a growing number constitute various organosulfur compounds. This Review provides comprehensive and critical information on the plethora of sulfur-based chiral ligands and organocatalysts used in asymmetric synthesis, which have been published within the last 15 years. However, it is confined to the presentation of only those chiral catalysts/ligands that possess a stereogenic sulfur atom and includes sulfoxides, sulfinamides, N-sulfinyl ureas, sulfoximines, and some related S-chiral derivatives.

Cu(i)-catalyzed Michael addition of ketiminoesters to β-trifluoromethyl β,β-disubstituted enones: rapid access to 1-pyrrolines bearing a quaternary all-carbon stereocenter

Chiral pyrrolines with two contiguous stereocenters, including a trifluoromethylated quaternary all-carbon stereocenter, were provided from β-trifluoromethyl β,β-disubstituted enones and glycine ketoimino ester.

Synthesis of pyrrolidine-3-carboxylic acid derivatives via asymmetric Michael addition reactions of carboxylate-substituted enones

An enantioselective Michael addition reaction system was developed. Using the reaction system, 5-methylpyrrolidine-3-carboxylic acid was synthesized in two steps.

Enantioselective Silver-Catalyzed Transformations

This review collects the major progress in the field of enantioselective transformations promoted by chiral silver catalysts, covering the literature since 2008, well illustrating the power of these especially mild Lewis acid catalysts to provide novel asymmetric reactions.

Stereoselective Ag-Catalyzed 1,3-Dipolar Cycloaddition of Activated Trifluoromethyl-Substituted Azomethine Ylides

A silver-catalyzed 1,3-dipolar cycloaddition of fluorinated azomethine ylides and activated olefins is reported. The reaction offers a straightforward and atom-economical procedure for the preparation of fluorinated pyrrolidines. Broad scope and high levels of diastereoselectivity have been achieved simply by using AgOAc/PPh3 as the catalyst system. The high efficiency of the cycloaddition relies on the presence of a metal-coordinating group on the imine moiety, such as an ester or heteroaryl group. The asymmetric version of the cycloaddition has been developed by using Taniaphos as a chiral ligand.

Palladium-catalyzed Si–C bond-forming silylation of aryl iodides with hydrosilanes: an enhanced enantioselective synthesis of silicon-stereogenic silanes by desymmetrization

An enantioselective Pd-catalyzed silicon–carbon bond-forming silylation reaction of aryl iodides with hydrosilanes for the synthesis of silicon-stereogenic silanes has been developed with good enantioselectivity under mild conditions.