Ligands For Asymmetric Synthesis Research Articles

Sparteine Thiourea: The Synthesis of an N Chiral Bispidine-Quinolizidine-Derived Organocatalyst and Applications in Asymmetric Synthesis of Dihydropyrano[c]chromenes.

Bispidine, a bridged bicyclic diamine, has been widely utilized as a rigid scaffold in chiral chelating ligands in asymmetric synthesis. In particular, a chiral bispidine-quinolizidine hybrid, such as sparteine, was utilized in asymmetric synthesis involving a metal, exhibiting superior catalytic activity. In this study, we report the design and synthesis of a series of sparteine-derived organocatalysts and the utilization of these catalysts in tandem Michael addition-cyclization reactions. These catalysts have shown excellent catalytic reactivity and enantioselectivity, and the corresponding dihydropyrano[c]chromenes have been prepared in ≤99% yield and ≤99% ee with a low catalyst loading. The recycled catalysts maintain a good catalytic performance even after four cycles, and a gram-scale reaction with a 1% catalyst loading is also performed, providing the product in 96% yield and 98% ee.

New Strategy for the Synthesis of Some Valuable Chiral 1,3-Diols with High Enantiomeric Purity: New Organocatalyst, Asymmetric Aldol Reaction, and Reduction.

Chiral 1,3-diols are highly valuable molecules used in industries such as pharmaceuticals, cosmetics, and agriculture. Therefore, in this study, a new strategy was developed to synthesize enantiomerically pure (>99% ee) 1,3-diols. New chiral 1,3-diols (5a-5q) with high enantiomeric purity were synthesized from aldol products chiral 1,3-keto alcohols (4a-4q), which are aldol products with different structures. Chiral 1,3-keto alcohols (4a-4q) were synthesized by a new asymmetric aldol method in the first step. This method was developed using a new proline-derived organocatalyst (3g) and Cu(OTf)2 as an additive in DMSO-H2O for the first time. Almost >99% ee was obtained using our developed aldol procedure. In the second step, original chiral diols (5a-5q) of high enantiomeric purity were obtained by asymmetric reduction of chiral keto alcohols with chiral oxazaborolidine reagents. In this way, a two-step asymmetric reaction was developed for chiral 1,3-diol enantiomers with high enantiomeric purity. The structures of all the original chiral compounds obtained were elucidated by infrared and nuclear magnetic resonance spectroscopy, mass spectrometry, and elemental analysis methods. Their enantiomeric excesses were determined by the chiral high-performance liquid chromatography method. Both keto alcohols and their corresponding chiral diols synthesized can be used as chiral starting materials and chiral source materials or intermediates in the synthesis of many biologically active molecules, or they can be used as chiral ligands in asymmetric synthesis, serving as organocatalysts.

A Review of the Synthesis of Oxazoline Derivatives.

Oxazolines are important heterocyclic systems due to their biological activities, such as antibacterial, antimalarial, anticancer, antiviral, anti-inflammatory, antifungal, antipyretic, and antileishmanial. They have been widely applied as chiral auxiliaries, polymers, catalysts, protecting groups, building blocks, and ligands in asymmetric synthesis. Due to their importance, many synthetic routes to prepare oxazoline moieties have been investigated and developed by researchers around the world. In this review, we summarized several synthetic methodologies published in the literature. The main substrates are nitriles, carboxylic acids, and acid derivatives, which react with a variety of reactants under conventional heating, microwave irradiation or ultrasound irradiation conditions. Syntheses via intramolecular cyclisation from amides have also been reported. Many publications have highlighted procedures based on solvent-free conditions using eco-friendly, reusable, and easy-availability catalysts.

Recent advances in the transformation reactions of the Betti base derivatives.

Betti bases are the products resulting from the one-pot multicomponent reaction involving 1-naphthol/2-naphthol, aliphatic/aromatic aldehydes, and secondary amines. This chemical process is commonly referred to as the Betti reaction. The significance of Betti bases in medicinal chemistry has grown substantially due to their diverse array of pharmacological applications. Furthermore, their synthetic utility is considerable, given their use as catalysts and ligands in asymmetric synthesis. Moreover, Mannich products, incorporating diverse functional groups such as -OH and -NH, find application in a range of organic reactions. This utilization enables the synthesis of novel C-C bond linkages and diverse heterocycles, including biologically active naphthoxazines, which hold biological applications such as antibacterial, antifungal and anticancer. The focus of this review article is on the application of aminonaphthol derivatives in transformation reactions and the synthesis of organic compounds, with particular emphasis on heterocycles.

Chiral Hydroxamic Acid Ligands in Asymmetric Synthesis: The Evolution of Metal‐Catalyzed Oxidation Reactions

AbstractAsymmetric oxidation reaction is one of the significant pathways in stereoselective reactions, which is a prominent performer in academic and industrial research. However, ligands are vital for planning an ideal metal‐catalyzed asymmetric oxidation reaction as they interact with the metal to construct catalytically active metal complexes, which can catalyze numerous asymmetric reactions. Designing and synthesizing novel chiral ligands is essential for researchers in modern asymmetric synthesis. In this course, exploring the applicability and the survey of hydroxamic acid as a vital ligand has been presented, which is essential for various metal‐catalyzed transformations.

Design, Synthesis, and Applications of ortho -Sulfur Substituted Arylphosphanes

Design, Synthesis, and Applications of <i>ortho</i> -Sulfur Substituted Arylphosphanes

Enantioselective Reductive Homocoupling of Allylic Acetates Enabled by Dual Photoredox/Palladium Catalysis: Access to C2-Symmetrical 1,5-Dienes

Transition-metal-catalyzed reductive coupling reactions have emerged as powerful protocols to construct C-C bonds. However, the development of enantioselective C(sp3)-C(sp3) reductive coupling remains challenging. Herein, we report a highly regio-, diastereo-, and enantioselective reductive homocoupling of allylic acetates through cooperative palladium and photoredox catalysis using diisopropylethylamine or Hantzsch ester as a homogeneous organic reductant. This straightforward protocol enables the stereoselective construction of C(sp3)-C(sp3) bonds under mild reaction conditions. A series of C2-symmetrical chiral 1,5-dienes were easily prepared with excellent enantioselectivities (up to >99% ee), diastereoselectivities (up to >95:5 dr), and regioselectivities (up to >95:5 rr). The resultant chiral 1,5-dienes can be directly used as chiral ligands in asymmetric synthesis, and they can be also transformed into other valuable chiral ligands.

Tandem Iridium Catalysis as a General Strategy for Atroposelective Construction of Axially Chiral Styrenes.

Axially chiral styrenes are of great interest since they may serve as a class of novel chiral ligands in asymmetric synthesis. However, only recently have strategies been developed for their enantioselective preparation. Thus, the development of novel and efficient methodologies is highly desirable. Herein, we reported the first tandem iridium catalysis as a general strategy for the synthesis of axially chiral styrenes enabled by Asymmetric Allylic Substitution-Isomerization (AASI) using cinnamyl carbonate analogues as electrophiles and naphthols as nucleophiles. In this approach, axially chiral styrenes were generated through two independent iridium-catalytic cycles: iridium-catalyzed asymmetric allylic substitution and in situ isomerization via stereospecific 1,3-hydride transfer catalyzed by the same iridium catalyst. Both experimental and computational studies demonstrated that the isomerization proceeded by iridium-catalyzed benzylic C-H bond oxidative addition, followed by terminal C-H reductive elimination. Amid the central-to-axial chirality transfer, the hydroxyl of naphthol plays a crucial role in ensuring the stereospecificity by coordinating with the Ir(I) center. The process accommodated broad functional group compatibility. The products were generated in excellent yields with excellent to high enantioselectivities, which could be transformed to various axially chiral molecules.

Syntheses and Transformations of Sulfoximines

Sulfoximines are widely used as medicines, agricultural chemicals, chiral precursors, and chiral ligands in asymmetric synthesis, as well as pivotal intermediates for the construction of heterocyclic compounds. NH-sulfoximines may be synthesized from thioethers, sulfoxides, sulfilimines, and sulfinamides. NH-sulfoximines can undergo various transformations, such as arylations, alkylations, vinylations, and alkynylations. Here, we review the methods that have been applied to the syntheses and transformations of NH-sulfoximines.

Challenging Atroposelective C–H Arylation

AbstractAtropisomeric molecules are privileged scaffolds, not only as ligands for asymmetric synthesis, but also as biologically active products and advanced materials. Although very attractive from a sustainability viewpoint, the direct construction of the stereogenic axis through asymmetric C–H arylation is very challenging and consequently only a few examples have been reported. This short review summarizes these very recent results on the atropo-enantio or diastereo­selective synthesis of atropisomeric (hetero)biaryl molecules; transformations during which the Ar–Ar atropisomeric axis is formed during the C–H activation process.1 Introduction2 Atropo-enantioselective Intermolecular Pd-Catalyzed C–H Arylation of Thiophene Derivatives3 Atropodiastereoselective Intermolecular Pd-Catalyzed C–H Arylation towards Terphenyl Scaffolds Bearing Two Atropisomeric Axes4 Atropo-enantioselective Intramolecular Pd-Catalyzed C–H Arylation towards Atropisomeric Benzodiazepinones5 Atropo-enantioselective Intermolecular Pd-Catalyzed C–H Arylation of Heteroarenes6 Rh-Catalyzed Atropo-enantioselective C–H Arylation of Diazonaphthoquinones7 Conclusion

Organocatalytic Asymmetric Atroposelective Construction of Axially Chiral 1,4-Distyrene 2,3-Naphthalene Diols.

An efficient organocatalytic construction of enantioenriched axially chiral 1,4-distyrene 2,3-naphthalene diols through the nucleophilic addition of α-amido sulfone to in situ generated vinylidene o-quinone methide is described. The reaction pathway was investigated by isolating reaction intermediates and performing a kinetic resolution process. Axially chiral 1,4-distyrene 2,3-naphthalene diol was used as the chiral ligand for the enantioselective addition of diethylzinc to naphthalene formaldehyde. The preliminary results revealed that these adducts could be potentially used as ligands in asymmetric synthesis.

Enantioselective amine α-functionalization via palladium-catalysed C-H arylation of thioamides.

Saturated aza-heterocycles are highly privileged building blocks that are commonly encountered in bioactive compounds and approved therapeutic agents. These N-heterocycles are also incorporated as chiral auxiliaries and ligands in asymmetric synthesis. As such, development of methods to functionalize the α-methylene C–H bonds of these systems enantioselectively is of great importance, especially in drug discovery. Currently, enantioselective lithiation with (–)-sparteine followed by Pd(0) catalyzed cross coupling to prepare α-arylated amines is largely limited to pyrrolidines. Here we report a Pd(II)-catalyzed enantioselective α-C–H coupling of a wide range of amines, including ethyl amines, azetidines, pyrrolidines, piperidines, azepanes, indolines, and tetrahydroisoquinolines. Chiral phosphoric acids are demonstrated as effective anionic ligands for the enantioselective coupling of methylene C–H bonds with aryl boronic acids. This catalytic reaction not only affords high enantioselectivities, but also provides exclusive regioselectivity in the presence of two methylene groups in different steric environments.

Hydroxytetraphenylenes as Chiral Ligands: Application to Asymmetric Darzens Reaction of Diazoacetamide with Aldehydes

Hydroxytetraphenylenes with rigid conformations are potential candidates for employment as chiral ligands in asymmetric synthesis. Highly diastereo- and enantioselective Darzens reactions between aldehydes and diazo-<i>N</i>,<i>N</i>-dimethylacetamide were found to be catalyzed by a chiral titanium complex formed in situ from Ti(O<i> ⁱ </i>Pr)₄ and chiral 1,16-dihydroxytetraphenylene, leading to the formation of <i>cis</i>-glycidic amides in moderate to high yields with excellent enantiomeric purities (40–99% yield, up to 99% ee).

The stereochemistry of baishouwubenzophenone, a unique atropisomer from C. wilfordii

Baishouwubenzophenone (1), possessing a unique atropisomeric feature, has been isolated from the roots of Cynanchum wilfordii. The congested structure makes it showing optical activity and consequently the absolute configuration was identified by experimental CD and computational approaches. Configurational assignment was further confirmed by exciton chirality method. The structural features in baishouwubenzophenone molecule allow it to be a potential atropisomeric ligand in asymmetric synthesis.

Substituent effects on axial chirality in 1-aryl-3,4-dihydroisoquinolines: controlling the rate of bond rotation

A series of 1-aryl-3,4-dihydroisoquinolines (DHIQs) were synthesized and their barriers to bond rotation were determined by means of VT-NMR, dynamic HPLC or racemization studies. Although they all presented lower rotational stability than the related 1-arylisoquinolines (such as QUINAP), certain 1-aryl-DHIQ structures had a sufficiently high barrier to bond rotation to show axial chirality. These compounds included 1-(2-triflyl-1-naphthyl)-4,5-dihydroisoquinoline 4h and 1-(2-diphenylphosphanyl-1-naphthyl)-4,5-dihydroisoquinoline 4i. This discovery opens the door to the development of a new group of axially chiral N,P ligands for asymmetric synthesis and also potentially to new strategies for the synthesis of axially chiral 1-arylisoquinolines.

Progress in Efficient Chiral Phosphine Ligand

Synthesis and application of chiral phosphine ligand is an important research area in the field of asymmetric syn- thesis. According to the chiral center and the structural characteristics, the recent development of efficient chiral phosphine ligand in asymmetric synthesis is reviewed, and the prospects of chiral phosphine ligand are also discussed. Keywords chiral; phosphine ligand; asymmetric synthesis

Fine tuning of molecular and supramolecular properties of simple trianglimines – the role of the functional group

Readily available chiral, triangular poly-azamacrocycles can act as receptors, low molecular weight supergelators and ligands in asymmetric synthesis.

Ferrocene

Ferrocene (1) is an organometallic compound composed of two cyclopentadienyl anions located on both sides of the iron(II) cation. The first report on its synthesis was published in 1951.[1] It was obtained accidentally by Kealy and Pauson, who actually tried to synthetize fulvene by the reaction of (cyclopentadienyl)magnesium bromide with FeCl2 (Scheme [1]). Instead, they isolated an orange coloured solid, which displayed high resistance towards bases and acids. Based on the observed (physico)chemical properties, its structure was determined as a new type of ‘sandwich compounds’.[2] In general, 1 is considered a prototype of metallocenes represented by organometallics, including nickelocene, titanocene, and cobaltocene.[3] In recent years, 1 and its derivatives have attracted great attention as materials with special properties, ligands for asymmetric synthesis, and as important pharmacophores.[4]

Recent applications of chiral N-tert-butanesulfinyl imines, chiral diene ligands and chiral sulfur–olefin ligands in asymmetric synthesis

The highly efficient asymmetric reactions of chiral sulfinyl auxiliary, diene ligands and sulfur–olefin ligands are presented.

Aziridine-Ring Ligands in Asymmetric Synthesis

Aziridine-Ring Ligands in Asymmetric Synthesis