Highly Enantioselective Organocatalytic Mannich Reaction of α-Benzylidene Succinimides with N-Boc Imines: Experimental and Theoretical Studies

The development of efficient and practical methods for the construction of chiral succinimide frameworks, which are the backbone of various natural products and widely studied in the field of pharmaceuticals, attracts considerable research attention. In this study, an asymmetric Mannich reaction of α-benzylidene succinimides with N-Boc imines was successfully performed using a bifunctional squaramide-type organocatalyst derived from quinine, affording the corresponding Mannich adduct with two contiguous stereocenters in high yields (up to 98%) with high diastereoselectivities (up to >20:1 dr) and excellent enantioselectivities (up to 99% ee). This protocol provides a direct approach to prepare chiral succinimide derivatives from simple starting material. Density Functional Theory (DFT) calculations with conformational search using an autosampling program revealed that the enantioselectivity profile was dominated by the deformation of the organocatalyst.

Asymmetric synthesis of β-amino cyanoesters with contiguous tetrasubstituted carbon centers by halogen-bonding catalysis with chiral halonium salt

β-Amino cyanoesters are important scaffolds because they can be transformed into useful chiral amines, amino acids, and amino alcohols. Halogen bonding, which can be formed between halogen atoms and electron-rich chemical species, is attractive because of its unique interaction in organic synthesis. Chiral halonium salts have been found to have strong halogen-bonding-donor abilities and work as powerful asymmetric catalysts. Recently, we have developed binaphthyl-based chiral halonium salts and applied them in several enantioselective reactions, which formed the corresponding products in high to excellent enantioselectivities. In this paper, the asymmetric synthesis of β-amino cyanoesters with contiguous tetrasubstituted carbon stereogenic centers by the Mannich reaction through chiral halonium salt catalysis is presented, which provided the corresponding products in excellent yields with up to 86% ee. To the best of our knowledge, the present paper is the first to report the asymmetric construction of β-amino cyanoesters with contiguous tetrasubstituted carbon stereogenic centers by the catalytic Mannich reaction.

Copper(ii)-catalyzed enantioselective decarboxylative Mannich reaction coordinated by supramolecular organic amine cages

Using supramolecular chiral cages to create a favorable chiral environment can effectively address the limitations of traditional metal asymmetric catalysis in controlling chiral catalytically active centers. However, achieving harmonious interactions among the molecular cage, the metal, and the substrate within the cavity remains a significant challenge. To overcome this, we have designed a pyridinium-modified, chiral-diamine-functionalized cage with a distinct bowl-shaped geometry. This structure features three quaternary ammonium linkers at the base and three chiral cyclohexanediamine units positioned at the rim. Acting as a supramolecular chiral ligand, the coordination of this cage with copper salts forms an optimal chiral environment that enables an efficient decarboxylative Mannich reaction between β-ketoacids and imines, yielding a broad range of chiral β-amino carbonyl compounds. Mechanistic studies and control experiments reveal that the coordinated Cu center is responsible for the substrate grabbing and preorganization within the cavity and the free NH group contributes to the enhanced enantioselectivity through hydrogen bonds, collaboratively enhancing the overall catalytic efficiency.

Modular Synthesis of α-Quaternary Chiral β-Lactams via Three-Component Asymmetric Kinugasa/Aldol or Kinugasa/Mannich Cascade Reactions

The β-lactam scaffolds are the prevalent structural units in antibiotics and natural products. Herein, three-component asymmetric Kinugasa/aldol and Kinugasa/Mannich cascade reactions have been developed for constructing α-quaternary chiral β-lactams. This method involved the tandem reaction of alkynes, nitrones and aldehydes (or imines), resulting in the formation of three sequential stereocenters controlled by copper(I) catalysts and chiral bis(oxazolidine) ligands. The developed protocol features high enantioselectivity, good reaction efficiency, and mild operational conditions, representing a practical and sustainable synthetic tool for the construction of functionalized chiral β-lactams.

Facile Synthesis of Oxazolidinones as Potential Antibacterial Agents

An efficient microwave-assisted synthesis route for novel oxazolidinone analogues has been developed. The general synthesis of these compounds began with an L-proline-mediated three-component Mannich reaction between commercially available 3-fluoro-4-morpholinoaniline, aqueous formaldehyde and α-hydroxyacetone. This was followed by a one-step cyclisation to form the core structure of oxazolidinone antibiotics which was subsequently derivatized. The novel compounds were evaluated for their antibacterial activity against M. smegmatis. One of the novel oxazolidinone derivatives 18 a1 produced a MIC of 8 mg/L, comparable with the commercial Rifampicin. The methodology is a useful addition to the field since it can make highly sought-after oxazolidinone derivatives, using cheaper, less harsh commercially available reagents, in a short time and one pot.

Surface Decoration of Cellulose With Trifluoromethylphenyl Substituted Thiourea: A Robust Hydrogen-Bonding Catalyst in Conjunction With L-Proline for the Asymmetric Direct Mannich Reaction

Cellulose is one of the most abundant biopolymers in nature. Despite being the subject of research in various fields, it is not as famous as chitosan in catalyst design. Herein, a novel thiourea-functionalized cellulose (CTU-6) was synthesized as a robust hydrogen bonding catalyst with the degree of substitution (DS) of 0.84. CTU-6 was characterized using Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), x-ray powder diffraction (XRD), proton nuclear magnetic resonance spectroscopy (1HNMR), solid-state cross-polarization magic angle spinning carbon-13 nuclear magnetic resonance (CP/MAS 13C-NMR), thermal gravimetric analysis (TGA) and elementel analysis. CTU-6 catalyzed the direct asymmetric Mannich reaction between acetone, aniline, and various aromatic aldehydes in cooperation with L-proline. The reaction exhibited excellent enantioselectivity, achieving up to 98% enantiomeric excess (ee) at room temperature. Incorporating trifluoromethylphenyl-substituted thiourea into the cellulose framework leverages its ability to form hydrogen bonds, thereby enabling precise control over the asymmetric induction. This study highlights the potential of cellulose-based catalysts in advancing asymmetric synthesis and their versatility in various organic reactions in cooperation with small chiral ligands. This synergy not only facilitates the efficient catalytic process but also improves the stereochemical outcomes of the reactions. This method underscores the importance of utilizing renewable and versatile cellulose materials in combination with chiral auxiliaries to achieve high levels of enantioselectivity.

Unveiling the antibacterial efficacy of thiazolo [3,2-a] pyrimidine: Synthesis, molecular docking, and molecular dynamic simulation

Two series of C-Mannich base derivatives were synthesized and evaluated through the reaction of formaldehyde, two thiazolo-pyrimidine compounds, and various 2°-amines. The chemical structures and inherent properties of the synthesized compounds were authenticated using a variety of spectroscopic techniques. The aseptic bactericidal potential of the compounds was assessed alongside five common bacterial microbes, with Ampicillin employed as the reference drug. Compounds 9b and 9d demonstrated comparable antibacterial activity to ampicillin against Bacillus subtilis and Bacillus megaterium, respectively, at 100 μg/mL. Furthermore, compounds 9f and 10f exhibited noteworthy action against Staphylococcus aureus (MIC: 250 μg/mL). Compounds 10b and 10f displayed excellent efficacy versus Escherichia coli, boasting (MIC: 50 μg/mL). Molecular docking studies elucidated the necessary connections and energies of molecular entities with the E. coli DNA gyrase B enzyme, a pivotal target in bacterial DNA replication. Further thermodynamic stability of the ligand-receptor complex of 10b and 10f were further validated though 200 ns molecular dynamics simulation. The findings highlight the potential of these synthesized derivatives as effective antibacterial agents and provide valuable insights into their mechanism of action.

Asymmetric Synthesis of Functionalized α-Amino Acid Derivatives via the γ-Pyrone Carbaldimine-Based Organocatalytic Mannich Reaction

A powerful synthetic strategy for the asymmetric synthesis of enantiomerically enriched γ-functionalized α-amino acid derivatives based on the highly stereoselective proline-catalyzed Mannich-type reaction of pre-prepared or in situ-generated γ-pyrone-derived aldimines with carbonyl compounds and subsequent transformations of multifunctional reaction products has been developed. A significant positive nonlinear effect was detected for the key organocatalytic reaction. The developed strategy was applied for facile gram-scale preparation of (S)-γ-oxonorvaline, used for site-specific modification of proteins, and both enantiomers of amycolatolide A recently isolated from the lichen-derived actinomycete Amycolatopsis sp. YIM 130923.

Enantioselective organocatalytic strategies to access noncanonical α-amino acids

Organocatalytic asymmetric synthesis has evolved over the years and continues to attract the interest of many researchers worldwide. Enantiopure noncanonical amino acids (ncAAs) are valuable building blocks in organic synthesis, medicinal chemistry, and chemical biology. They are employed in the elaboration of peptides and proteins with enhanced activities and/or improved properties compared to their natural counterparts, as chiral catalysts, in chiral ligand design, and as chiral building blocks for asymmetric syntheses of complex molecules, including natural products. The linkage of ncAA synthesis and enantioselective organocatalysis, the subject of this perspective, tries to imitate the natural biosynthetic process. Herein, we present contemporary and earlier developments in the field of organocatalytic activation of simple feedstock materials, providing potential ncAAs with diverse side chains, unique three-dimensional structures, and a high degree of functionality. These asymmetric organocatalytic strategies, useful for forging a wide range of C-C, C-H, and C-N bonds and/or combinations thereof, vary from classical name reactions, such as Ugi, Strecker, and Mannich reactions, to the most advanced concepts such as deracemisation, transamination, and carbene N-H insertion. Concurrently, we present some interesting mechanistic studies/models, providing information on the chirality transfer process. Finally, this perspective highlights, through the diversity of the amino acids (AAs) not selected by nature for protein incorporation, the most generic modes of activation, induction, and reactivity commonly used, such as chiral enamine, hydrogen bonding, Brønsted acids/bases, and phase-transfer organocatalysis, reflecting their increasingly important role in organic and applied chemistry.

Enantioselective Synthesis of Biphenyl-Bridged ϵ-Sultams by Organocatalytic Mannich Reactions of Cyclic N-Sulfonylimines with Unactivated Ketones

A highly enantioselective Mannich reaction of biphenyl-bridged seven-membered cyclic N-sulfonylimines with methyl alkyl ketones is disclosed in this study. The reaction was performed under organocatalysis by using a quinine-derived primary amine as the catalyst in combination with a Brønsted acid as the co-catalyst. High yields (up to 89 %) and excellent enantioselectivities (up to 97 % ee) were observed. For methyl alkyl ketones containing a larger alkyl substituent, specific regioselective addition to the C=N bond is favored at the methyl group. On the contrary, ketones containing a smaller alkyl substituent or hydroxyacetone substrates gave major syn selective Mannich products at the methylene group.

A novel recyclable organocatalyst for the gram-scale enantioselective synthesis of (S)-baclofen

Synthesizing organocatalysts is often a long and cost-intensive process, therefore, the recovery and reuse of the catalysts are particularly important to establish sustainable organocatalytic transformations. In this work, we demonstrate the synthesis, application, and recycling of a new lipophilic cinchona squaramide organocatalyst. The synthesized lipophilic organocatalyst was applied in Michael additions. The catalyst was utilized to promote the Michael addition of cyclohexyl Meldrum's acid to 4-chloro-trans-β-nitrostyrene (quantitative yield, up to 96% ee). Moreover, 1 mol % of the catalyst was feasible to conduct the gram-scale preparation of baclofen precursor (89% yield, 96% ee). Finally, thanks to the lipophilic character of the catalyst, it was easily recycled after the reaction by replacing the non-polar reaction solvent with a polar solvent, acetonitrile, with 91-100% efficiency, and the catalyst was reused in five reaction cycles without the loss of activity and selectivity.

Mechanochemical asymmetric three-component Mannich reaction involving unreactive arylamines

We report here a mechanochemical protocol for an asymmetric three-component Mannich reaction involving unreactive arylamines with simple cyclic ketones and arylaldehydes catalyzed by (S)-proline with a chiral diol. In this mechanochemical protocol, ball milling enables reaction acceleration and enantioselectivity control. The reported asymmetric three-component Mannich reactions usually involve reactive arylamines such as p-anisidine and phenylamine, while the catalytic asymmetric Mannich reactions involving unreactive arylamines in solution did not proceed smoothly or gave low yields and enantioselectivities. However, the use of ball-milling techniques overcomes the deficiency of the batch systems in solution and avoids the use of toxic organic solvents. The desired products were obtained in moderate-to-good yields (49%-80%) with good-to-high enantioselectivities (up to 99% ee). This is the first example of a mechanochemically activated catalytic asymmetric three-component Mannich reaction involving unreactive arylamines.

Enantio- and Diastereoselective Mannich Reactions of ß-Dicarbonyls by Second Stage Diastereoconvergent Crystallization

The synthesis of chiral α-monosubstituted-ß-dicarbonyls is a challenging task in asymmetric catalysis due to the rapid, typically uncontrolled, product racemization or epimerization under most reaction conditions. For this reason, diastereoselective additions of unsubstituted ß-dicarbonyls to π-electrophiles are unusual. Herein, we disclose a simple catalytic crystallization-driven enantio- and diastereoselective Mannich reaction for the synthesis of stereodefined α-monosubstituted-ß-keto esters, dissymmetric ß-diesters, dissymmetric ß-diketones, and ß-keto amides that productively leverages product epimerization in solution. Mechanistic studies suggest a scenario where the initial enantioselective, diastereodivergent skeletal assembly is catalyzed by a chiral tertiary amine organocatalyst, which then facilitates second stage crystallization-induced diastereoconvergence to provide the challenging α-stereocenter in excellent stereoselectivity.

Sterically Hindered and Deconjugative α-Regioselective Asymmetric Mannich Reaction of Meinwald Rearrangement-Intermediate

Compared to γ-addition, the α-addition of α-branched β,γ-unsaturated aldehydes faces larger steric hindrance and disrupts the π-π conjugation, which might be why very few examples are reported. In this article, a highly diastereo- and enantioselective α-regioselective Mannich reaction of isatin-derived ketimines with α-, β- or γ-branched β,γ-unsaturated aldehydes, generated in situ from Meinwald rearrangement of vinyl epoxides, is realized by using chiral N,N'-dioxide/Sc^III catalysts. A series of chiral α-quaternary allyl aldehydes and homoallylic alcohols with vicinal multisubstituted stereocenters are constructed in excellent yields, good d.r. and excellent ee values. Experimental studies and DFT (density functional theory) calculations reveal that the large steric hindrance of the ligand and the Boc (tButyloxy carbonyl) protecting group of imines are critical factors for the α-regioselectivity.

Сatalytic Asymmetric Synthesis of C-Chiral Phosphonates

The current review is devoted to the achievements in the development of methods for the catalytic asymmetric synthesis of phosphonates containing a chiral center in the side chain. C-chiral phosphonates are widely represented among natural compounds with various biological activities as insecticides, herbicides, antibiotics, and bioregulators. Synthetic representatives of this class have found practical application as biologically active compounds. The review summarizes methods of asymmetric metal complex catalysis and organocatalysis as applied to such reactions as phospha-aldol reaction, two-component and three-component phospha-Mannich reaction, phospha-Michael reaction, as well as hydrogenation of unsaturated phosphonates and phosphine oxides, ketophosphonates, and iminophosphonates. Methods for the asymmetric hydride reduction of C=X phosphonates (X=O, S, NR) are also discussed in detail. The review presents updated literature reports, as well as original research by the author.

Asymmetric oxidative Mannich reactions promoted by photocatalysis and electrochemistry

The asymmetric Mannich reaction is an essential method in contemporary organic chemistry. As a representative of clean and green synthesis methods, photochemical and electrochemical oxidation strategies have re-emerged in recent years, providing new ideas for asymmetric Mannich reactions. Numerous chiral β-amino carbonyl compounds have been accessed in satisfactory yields with excellent enantioselectivity via such novel asymmetric oxidative Mannich reactions. This minireview highlights plentiful advances in asymmetric oxidative Mannich reactions that rely on photoredox or anodic-oxidation and covers the literature from 2014 to date. Furthermore, the future development of this field is envisaged.

Organocatalytic enantioselective Mannich reaction of isoxazol-5(4H)-ones to isatin-derived ketimines

An efficient organocatalytic asymmetric Mannich reaction between isoxazol-5(4H)-ones and isatin-derived ketimines has been developed.

Concise enantioselective synthesis of non-proteinogenic α-aminoacids via an organocatalytic Mannich-type reaction

Scalable asymmetric synthesis of non-proteinogenic (S)-aminoacids and their derivatives based on an organocatalyzed Mannich-type reaction involving allomaltol applicable to subsequent RuIII-catalyzed oxidative cleavage has been developed.