Nickel-Catalyzed Highly Enantioselective Hydrogenation of β-Acetylamino Vinylsulfones: Access to Chiral β-Amido Sulfones

P-Stereogenic Phosphorus Ligands in Asymmetric Catalysis

Chiral phosphorus ligands play a crucial role in asymmetric catalysis for the efficient synthesis of useful optically active compounds. They are largely categorized into two classes: backbone chirality ligands and P-stereogenic phosphorus ligands. Most of the reported ligands belong to the former class. Privileged ones such as BINAP and DuPhos are frequently employed in a wide range of catalytic asymmetric transformations. In contrast, the latter class of P-stereogenic phosphorus ligands has remained a small family for many years mainly because of their synthetic difficulty. The late 1990s saw the emergence of novel P-stereogenic phosphorus ligands with their superior enantioinduction ability in Rh-catalyzed asymmetric hydrogenation reactions. Since then, numerous P-stereogenic phosphorus ligands have been synthesized and used in catalytic asymmetric reactions. This Review summarizes P-stereogenic phosphorus ligands reported thus far, including their stereochemical and electronic properties that afford high to excellent enantioselectivities. Examples of reactions that use this class of ligands are described together with their applications in the construction of key intermediates for the synthesis of optically active natural products and therapeutic agents. The literature covered dates back to 1968 up until December 2023, centering on studies published in the late 1990s and later years.

Arylthianthrenium Salts as the Aryl Sources: Visible Light/Copper Catalysis-Enabled Intermolecular Azidosulfonylation of Alkenes

The difunctionalization of alkenes using aryl thianthrenium salts as the aryl sources has been reported sporadically. However, the four-component difunctionalization of alkenes on the basis of aryl thianthrenium salts has not been reported thus far and still remains a challenge. Herein, a visible light/copper catalysis-enabled four-component reaction of aryl thianthrenium salts, DABCO·(SO2)2, alkenes, and TMSN3 is presented, which affords a facile approach to β-azidosulfones in good yields with broad substrate scope and excellent functional group tolerance. This strategy indirectly realizes the method for the synthesis of β-azidosulfones through site-selective aryl C-H bond functionalization and alkene difunctionalization. This developed method is an important complement to thianthrenium salts chemistry.

Regio- and Stereoselective Intermolecular 1,2-Difunctionalization of Terminal Alkynes: An Approach to Access (Z)-β-Amidovinylsulfones

We have developed the first I2/base-catalyzed regio- and stereoselective intermolecular β-amidosulfonylation of terminal alkynes using sodium sulfinates and quinoxalinone derivatives. The present methodology is compatible with a broad spectrum of various heterocyclic amides, terminal alkynes, and sodium sulfinates. It provides rapid access to valuable (Z)-β-amidovinyl sulfones at mild conditions. Moreover, the synthetic application of this methodology was demonstrated by the late-stage functionalization of numerous bioactive molecules.

Photocatalytic selective synthesis of (E)-β-aminovinyl sulfones and (E)-β-amidovinyl sulfones using Ru(bpy)3Cl2 as the catalyst

Selectively producing a variety of valuable compounds using controlled chemical reactions starting from a common material is an appealing yet complex concept. Herein, a photocatalytic approach for the selective synthesis of (E)-β-aminovinyl sulfones and (E)-β-amidovinyl sulfones from allenamides and sodium sulfinates was established. This reaction exhibits the traits of an eco-friendly solvent and adjustable amide cleavage, and can accommodate a diverse range of substrates with exceptional functional group tolerance. Based on control experiments and deuterium labeling experiments, a plausible radical reaction pathway is proposed.

Rh-Catalyzed Asymmetric Hydrogenation of α-Substituted Alkenyl Sulfones: Highly Chemo- and Enantioselective Access to Chiral Sulfones

Rh-(R,R)-f-spiroPhos complex-catalyzed asymmetric hydrogenation of α-substituted alkenyl sulfones has been achieved, affording the chiral γ-keto sulfones and simple α-alkyl-substituted sulfones in high yields (96-99%) with excellent chemo-/enantioselectivities (86-96% ee) and high turnover numbers (TONs) of up to 4000. The method provides an efficient and high-enantioselectivity strategy for chiral γ-keto sulfones and simple α-substituted sulfones under mild conditions. Moreover, the obtained hydrogenation product was transformed into other important chiral α-substituted sulfones.

EnT-Mediated Amino-Sulfonylation of Alkenes with Bifunctional Sulfonamides: Access to β-Amino Sulfone Derivatives

β-Amino sulfones are commonly found structural motifs in biologically active compounds. Herein, we report a direct photocatalyzed amino-sulfonylation reaction of alkenes for the efficicient production of important compounds by simple hydrolysis without the need for additional oxidants and reductants. In this transformation, the sulfonamides worked as bifunctional reagents, simultaneously generating sulfonyl radicals and N-centered radicals which were added to alkene in a highly atom-economical fashion with high regioselectivity and diastereoselectivity. This approach showed high functional group tolerance and compatibility, facilitating the late-stage modification of some bioactive alkenes and sulfonamide molecules, thereby expanding the biologically relevant chemical space. Scaling up this reaction led to an efficient green synthesis of apremilast, one of the best-selling pharmceuticals, demonstrating the synthetic utility of the applied method. Moreover, mechanistic investigations suggest that an energy transfer (EnT) process was in operation.

Ni-Catalyzed Asymmetric Hydrogenation of α-Substituted α,β-Unsaturated Phosphine Oxides/Phosphonates/Phosphoric Acids

Efficient Ni/(S,S)-Ph-BPE-catalyzed asymmetric hydrogenation of α-substituted α,β-unsaturated phosphine oxides/phosphonates/phosphoric acids has been successfully developed, and a wide range of chiral α-substituted phosphines hydrogenation products were obtained in generally high yields with excellent enantioselective control (92%-99% yields, 84%->99% ee). This method features a cheap transition metal nickel catalytic system, high functional group tolerance, wide substrate scope generality, and excellent enantioselectivity. A plausible catalytic cycle was proposed for this asymmetric hydrogenation according to the results of deuterium-labeling experiments.

Construction of β-Amino Sulfones from Sodium Metabisulfite via a Radical 1,4-Amino Migration

A three-component reaction of alkenyl-tethered oxime ethers, sodium metabisulfite, and aryldiazonium tetrafluoroborates under mild conditions is developed. This reaction proceeds at room temperature without any oxidants or additives, affording β-amino sulfones with good functional group tolerance through aminosulfonylation of unactivated alkene. Mechanistic studies show that this transformation undergoes a radical process, including radical trapping with sulfur dioxide and radical 1,4-amino migration.

Usefulness of the Global E Factor as a Tool to Compare Different Catalytic Strategies: Four Case Studies

The global E factor (EG factor) has recently been introduced, in the context of asymmetric organocatalysis, as a new green chemistry metric to take into consideration the synthesis of the catalyst in the overall economy of the synthetic process of a given chiral molecule in optically pure form. Herein, its further usefulness in comparing diverse catalytic systems, even different from organocatalysts, is shown by the analysis of four case studies.

Accessing chiral sulfones bearing quaternary carbon stereocenters via photoinduced radical sulfur dioxide insertion and Truce-Smiles rearrangement

From the viewpoint of synthetic accessibility and functional group compatibility, photoredox-catalyzed sulfur dioxide insertion strategy enables in situ generation of functionalized sulfonyl radicals from easily accessible starting materials under mild conditions, thereby conferring broader application potential. Here we present two complementary photoinduced sulfur dioxide insertion systems to trigger radical asymmetric Truce-Smiles rearrangements for preparing a variety of chiral sulfones that bear a quaternary carbon stereocenter. This protocol features broad substrate scope and excellent stereospecificity. Aside from scalability, the introduction of a quaternary carbon stereocenter at position β to bioactive molecule-derived sulfones further demonstrates the practicality and potential of this methodology.

Recent Advances in the Enantioselective Synthesis of Chiral Amines via Transition Metal-Catalyzed Asymmetric Hydrogenation

Chiral amines are key structural motifs present in a wide variety of natural products, drugs, and other biologically active compounds. During the past decade, significant advances have been made with respect to the enantioselective synthesis of chiral amines, many of them based on catalytic asymmetric hydrogenation (AH). The present review covers the use of AH in the synthesis of chiral amines bearing a stereogenic center either in the α, β, or γ position with respect to the nitrogen atom, reported from 2010 to 2020. Therefore, we provide an overview of the recent advances in the AH of imines, enamides, enamines, allyl amines, and N-heteroaromatic compounds.

Nickel-Catalyzed Asymmetric Hydrogenation for the Synthesis of a Key Intermediate of Sitagliptin

Nickel-catalyzed enantioselective hydrogenation of enamines leading to the efficient synthesis of 3-R-Boc-amino-4-(2,4,5-trifluorophenyl)butyric esters, the key intermediate of the blockbuster antidiabetic drug (R)-SITAGLIPTIN, is described. The sitagliptin motifs were isolated in more than 99% yield and with 75-92% ee using the earth-abundant nickel catalyst. Upon chiral resolution with (R)- and (S)-1-phenylethylamines, the partially enantioenriched (R)- and (S)-Boc-3-amino-4-(2,4,5-trifluorophenyl)butanoic acids provided >99.5% ee of the crucial sitagliptin intermediate. The asymmetric hydrogenation protocol was scaled up to 10 g with consistency in yield and ee, and has been reproduced in multiple batches.

Combined Theoretical and Experimental Studies Unravel Multiple Pathways to Convergent Asymmetric Hydrogenation of Enamides

We present a highly efficient convergent asymmetric hydrogenation of E/Z mixtures of enamides catalyzed by N,P-iridium complexes supported by mechanistic studies. It was found that reduction of the olefinic isomers (E and Z geometries) produces chiral amides with the same absolute configuration (enantioconvergent hydrogenation). This allowed the hydrogenation of a wide range of E/Z mixtures of trisubstituted enamides with excellent enantioselectivity (up to 99% ee). A detailed mechanistic study using deuterium labeling and kinetic experiments revealed two different pathways for the observed enantioconvergence. For α-aryl enamides, fast isomerization of the double bond takes place, and the overall process results in kinetic resolution of the two isomers. For α-alkyl enamides, no double bond isomerization is detected, and competition experiments suggested that substrate chelation is responsible for the enantioconvergent stereochemical outcome. DFT calculations were performed to predict the correct absolute configuration of the products and strengthen the proposed mechanism of the iridium-catalyzed isomerization pathway.

C 1-Symmetric diphosphorus ligands in metal-catalyzed asymmetric hydrogenation to prepare chiral compounds

Asymmetric hydrogenation has remained an important and challenging research area in industry as well as academia due to its high atom economy and ability to induce chirality. Among several types of ligands, chiral bidentate phosphine ligands have played a pivotal role in developing asymmetric hydrogenation. Although C₂-symmetric chiral bidentate phosphine ligands have dominated the field, it has been found that several C₁-symmetric ligands are equally effective and, in many cases, have outperformed their C₂-symmetric counterparts. This review evaluates the possibility of the use of C₁-symmetric diphosphorus ligands in asymmetric hydrogenation to produce chiral compounds. The recent strategies and advances in the application of C₁-symmetric diphosphorus ligands in the metal-catalyzed asymmetric hydrogenation of a variety of CC bonds have been summarized. The potential of diphosphorus ligands in asymmetric hydrogenation to produce pharmaceutical intermediates, bioactive molecules, drug molecules, agrochemicals, and fragrances is discussed. Although asymmetric hydrogenation appears to be a problem that has been resolved, a deep dive into the recent literature reveals that there are several challenges that are yet to be addressed. The current asymmetric hydrogenation methods mostly employ precious metals, which are depleting at a fast pace. Therefore, scientific interventions to perform asymmetric hydrogenation using base metals or earth-abundant metals that can compete with established precious metals hold significant potential.

Nickel-catalyzed enantioselective umpolung hydrogenation for stereoselective synthesis of β-amido esters

Nickel complexes ligated by strongly donating diphosphines catalyze enantioselective hydrogenation for the preparation of acyclic and cyclic β-amido esters. A combination of acetic acid and indium powder provides protons and electrons to form nickel hydrido complexes under umpolung hydrogenation conditions.

Electrochemical sulfonylation of enamides with sodium sulfinates to access β-amidovinyl sulfones

The electrochemical sulfonylation of enamides with sodium sulfinates was developed in an undivided cell in constant current mode, leading to the formation of β-amidovinyl sulfones in moderate to good yields. The catalyst-, electrolyte- and oxidant-free protocol features good functional group tolerance and employs electric current as a green oxidant. Mechanistic insights into the reaction indicate that the reaction may proceed via a radical mechanism.

Nickel-Catalyzed Asymmetric Hydrogenation for Kinetic Resolution of [2.2]Paracyclophane-Derived Cyclic N-Sulfonylimines

Nickel-catalyzed asymmetric hydrogenation for kinetic resolution of [2.2]paracyclophane-derived cyclic N-sulfonylimines was successfully developed. High selectivity factors were observed in most cases (s up to 89), providing the recovered materials and hydrogenation products in good yields with high levels of enantiopurity. The recovered materials and hydrogenation products are useful synthetic intermediates for the synthesis of planar chiral [2.2]paracyclophane-based compounds.

Metal- and Base-Free C(sp2)-H Arylsulfonylation of Enamides for Synthesis of (E)-β-Amidovinyl Sulfones via the Insertion of Sulfur Dioxide

A metal- and base-free C(sp²)-H direct arylsulfonylation of secondary and tertiary enamides with aryldiazonium salts and ex situ generated SO₂ (from SOgen) is presented. This method runs smoothly to produce β-amidovinyl sulfones with excellent stereoselectivities in moderate to excellent yields. Moreover, this strategy features good functional group tolerance and environmentally benign reaction conditions. Mechanistic experiments indicate that this sulfonylation may proceed in a radical pathway.

Recent Progress on the Synthesis of Chiral Sulfones

Chiral sulfones extensively exist in drugs, agricultural chemicals, chiral organic intermediates, and functional materials. Their importance causes the rapid development of their synthetic methods in recent years. Many transition metal complex catalysts with chiral ligands and chiral organocatalysts are adopted in synthesis of chiral sulfones. Most of the methods to construct chiral sulfones are based on the reduction of unsaturated sulfones and the introduction of sulfone groups into unsaturated hydrocarbons. This review describes all classes of asymmetric reactions for synthesis of chiral sulfones.

Pd-Catalyzed Regio-, Diastereo-, and Enantioselective [3 + 2] Cycloaddition Reactions: Access to Chiral Cyclopentyl Sulfones

The palladium-catalyzed [3 + 2] cycloaddition using in situ generated sulfone-TMM species to construct various chiral cyclopentyl sulfones in a highly regio-, diastereo- (dr >15:1), and enantioselective (up to 99% ee) manner is reported. The present strategy can tolerate different types of sulfone-TMM donors and acceptors, and enables the construction of three chiral centers in a single step, specifically with a chiral center bearing the sulfone moiety. The robust chiral diamidophosphite ligand is the key to the reactivity and selectivities of this transformation.

Nickel-Catalyzed Asymmetric Hydrogenation of Cyclic Alkenyl Sulfones, Benzo[b]thiophene 1,1-Dioxides, with Mechanistic Studies

A highly efficient catalytic system based on the cheap transition metal nickel for the asymmetric hydrogenation of challenging cyclic alkenyl sulfones, 3-substituted benzo[b]thiophene 1,1-dioxides, was first successfully developed. A series of hydrogenation products, chiral 2,3-dihydrobenzo[b]thiophene 1,1-dioxides, were obtained in high yields (95-99%) with excellent enantioselectivities (90-99% ee). According to the results of nonlinear effect studies, deuterium-labeling experiments, and DFT calculation investigations, a reasonable catalytic mechanism for this nickel-catalyzed asymmetric hydrogenation was provided, which displayed that the two added hydrogen atoms of the hydrogenation products could be from H₂ through the insertion of Ni-H and subsequent hydrogenolysis.

The Three-Component Synthesis of 4-Sulfonyl-1,2,3-triazoles via a Sequential Aerobic Copper-Catalyzed Sulfonylation and Dimroth Cyclization

4-Sulfonyl-1,2,3-triazole scaffolds possess promising bioactivities and applications as anion binders. However, these structures remain relatively unexplored and efficient synthetic procedures for their synthesis remain desirable. A practical room-temperature, aerobic copper-catalyzed three-component reaction of aromatic ketones, sodium sulfinates, and azides is reported. This procedure allows for facile access to 4-sulfonyl-1,5-disubstituted-1,2,3-triazoles in yields ranging from 34 to 89%. The reaction proceeds via a sequential aerobic copper(II)chloride-catalyzed oxidative sulfonylation and the Dimroth azide–enolate cycloaddition.

Recent advances for the synthesis of chiral sulfones with the sulfone moiety directly connected to the chiral center

The recent development of strategies for the asymmetric synthesis of chiral sulfones with sulfone moieties directly connected to the stereocenters.

Asymmetric hydrogenation catalyzed by first-row transition metal complexes

This review focuses on asymmetric direct and transfer hydrogenation with first-row transition metal complexes. The reaction mechanisms and the models of enantiomeric induction were summarized and emphasized.

Achiral and chiral NNN-pincer nickel complexes with oxazolinyl backbones: application in transfer hydrogenation of ketones

NNN-based achiral and chiral (oxazolinyl)amido-pincer nickel complexes are developed and employed for the catalytic transfer hydrogenation of ketones.

Recent Developments in Transition-Metal-Catalyzed Asymmetric Hydrogenation of Enamides

The catalytic asymmetric hydrogenation of prochiral olefins is one of the most widely studied and utilized transformations in asymmetric synthesis. This straightforward, atom economical, inherently direct and sustainable strategy induces chirality in a broad range of substrates and is widely relevant for both industrial applications and academic research. In addition, the asymmetric hydrogenation of enamides has been widely used for the synthesis of chiral amines and their derivatives. In this review, we summarize the recent work in this field, focusing on the development of new catalytic systems and on the extension of these asymmetric reductions to new classes of enamides.

1 Introduction

2 Asymmetric Hydrogenation of Trisubstituted Enamides

2.1 Ruthenium Catalysts

2.2 Rhodium Catalysts

2.3 Iridium Catalysts

2.4 Nickel Catalysts

2.5 Cobalt Catalysts

3 Asymmetric Hydrogenation of Tetrasubstituted Enamides

3.1 Ruthenium Catalysts

3.2 Rhodium Catalysts

3.3 Nickel Catalysts

4 Asymmetric Hydrogenation of Terminal Enamides

4.1 Rhodium Catalysts

4.2 Cobalt Catalysts

5 Rhodium-Catalyzed Asymmetric Hydrogenation of Miscellaneous Enamides

6 Conclusions

Noncovalent Interaction-Assisted Ferrocenyl Phosphine Ligands in Asymmetric Catalysis

Noncovalent interactions are ubiquitous in nature and are responsible for the precision control in enzyme catalysis via the cooperation of multiple active sites. Inspired by this principle, noncovalent interaction-assisted transition metal catalysis has emerged recently as a powerful tool and has attracted intense interest. However, it is still highly desirable to develop efficient and operationally convenient ligands along this line with new structural motifs. Based on the specific nature of hydrogen bonding and ion pairing interactions, we developed a series of noncovalent interaction-assisted chiral ferrocenyl phosphine ligands, including Zhaophos, Wudaphos, and miscellaneous SPO-Wudaphos. Due to the assistance of noncovalent interactions, this catalytic mode is capable of achieving transition metal catalyzed asymmetric hydrogenation and other transformations with remarkable improvement of reactivity and selectivity. In some specific challenging cases, this probably represents one of the most productive methods. Moreover, these ligands are easily prepared, air stable, and highly tunable, meeting the requirements of industrial application.In this Account, we give a concise review of recent advances in asymmetric catalysis. By means of hydrogen bonding interactions, Rh- and Ir-Zhaophos complexes exhibited excellent activities and enantioselectivities in asymmetric hydrogenation of a wide range of substrates: C═C bonds of substituted conjugate alkenes with neutral hydrogen bond acceptors, including nitro groups, carbonyl groups (ketones, esters, amides, maleinimides, and anhydrides), ethers, and sulfones; C═N bonds of substituted iminium salts with chloride as an anionic hydrogen bond acceptor, including N-H imines and cyclic imines; N-heteroaromatic compounds with HCl as an additive, including unprotected quinolines, isoquinolines, and indoles; carbocation of substituted oxocarbenium ions. By means of ion pairing interactions, Rh-Wudaphos complexes enabled the catalytic asymmetric hydrogenation of α-substituted unsaturated carboxylic acids, carboxy-directed α,α-disubstituted terminal olefins, and sodium α-arylethenylsulfonates. Rh-SPO-Wudaphos utilized both hydrogen bonding and ion pairing interactions in asymmetric hydrogenation of α-substituted unsaturated carboxylic acids and phosphonic acids. In addition, Zhaophos has achieved highly selective intramolecular reductive amination and inter- and intramolecular asymmetric decarboxylative allylation. Investigations into mechanism implied that noncovalent interactions were involved in the catalytic cycle and played a critical role for both high reactivity and selectivity. Notably, a rare ionic hydrogenation pathway has been proposed in some cases. Furthermore, these catalytic systems have been used in the gram-scale synthesis of natural products and pharmaceuticals.

Heterogeneous Olefin Hydrogenation Enabled by a Highly-Reduced Nickel(-II) Catalyst Precursor

The hydrogenation of olefins, styrenes, enoates, imines, and sterically hindered tri-substituted olefins was accomplished using the pre-catalyst dilithiumbis(cycloocta-1,5-diene)nickelate(-II) (1). The mild conditions tolerate hydroxyl, halide, ester, and lactone functionalities. Mechanistic studies, including reaction progress analyses, poisoning experiments, and multinuclear NMR monitoring, indicate that a heterotopic (nickel nanoparticle) catalyst is in operation.

Synthesis of chiral α-substituted α-amino acid and amine derivatives through Ni-catalyzed asymmetric hydrogenation

Highly efficient Ni-catalyzed asymmetric hydrogenation of cyclic N-sulfonyl ketimino esters was, for the first time, successfully developed, providing various chiral α-monosubstituted α-amino acid derivatives with excellent results (97-99% yields, 90 to >99% ee). Cyclic N-sulfonyl ketimines were also hydrogenated well to afford chiral amine derivatives with 98-99% yields and 97 to >99% ee. The gram-scale asymmetric hydrogenation was performed well with 85% yield and 99% ee using only 0.2 mol% catalyst.

Enantioconvergent and enantiodivergent catalytic hydrogenation of isomeric olefins

The asymmetric catalytic hydrogenation of olefins is one of the most widely studied and utilised transformations in asymmetric synthesis. This straightforward and atom-economical strategy can provide excellent enantioselectivity for a broad variety of substrates and is widely relevant for both industrial applications and academic research. In many instances the hydrogenation is stereospecific in the regard that the E-Z-geometry of the olefin governs the stereochemistry of the hydrogenation, producing an enantiodivergent outcome. Interestingly, the possibility to hydrogenate E- and Z-isomer mixtures to a single stereoisomer in an enantioconvergent manner has been reported. This avoids the need for synthesis of geometrically pure alkene starting materials and therefore constitutes a significant practical advantage. This review article aims to provide an overview of the different stereochemical outcomes in the hydrogenation of olefins. Although the field is well developed and selectivity models have been proposed for a number of catalytic systems, an organized collection of enantioconvergent results, as opposed to the more common enantiodivergent case, might promote new investigation into these phenomena.

Recent advances in the direct β-C(sp2)–H functionalization of enamides

Recent advances in the direct β-C(sp²)–H functionalization of enamides, mainly including arylation, alkenylation, alkynylation, alkylation, acylation, sulfonylation, phosphorylation, and others, are reported.

Nickel-Catalyzed Chemoselective Asymmetric Hydrogenation of α,β-Unsaturated Ketoimines: An Efficient Approach to Chiral Allylic Amines

An efficient synthetic route to chiral allylic amines has been developed by nickel/(S,S)-Ph-BPE complex catalyzed chemoselective asymmetric hydrogenation of α,β-unsaturated ketoimines. Varieties of α,β-unsaturated ketoimines have been well tolerated in this transformation to give chiral allylic amines with high yields and excellent ee values (up to 99% yield, up to 99% ee). A gram-scale reaction with 0.2 mol % catalyst loading has also been achieved.