Search Results (411)

Asymmetric synthesis of chiral hydroxysulfones, key pharmaceutical intermediates, is challenging. We report an efficient synthesis from readily available materials via a one-pot photo-biocatalytic cascade reaction in aqueous conditions, utilizing visible light as an energy source. This sustainable process achieves up to 84% yields and 99% ee. Engineered ketoreductase produces R-configured products with high conversion and enantioselectivity across diverse substrates. Molecular dynamics (MD) simulations explored enzyme–substrate interactions and their influence on reaction activity and stereoselectivity. Full article

The regio- and stereoselective adjacent bifunctionalization of olefins with amine and halogen groups can be effectively accomplished through catalytic haloamination methods. Stereoselective haloamination has emerged as a pivotal methodology for the introduction of halogen functional groups into chiral amines, demonstrating substantial applications in medicinal chemistry and organic synthesis. Since 1999, significant advancements have been achieved in this field, driven by innovations in catalytic systems and methodologies. The stereoselective haloamination of both functionalized and nonfunctionalized alkenes employing chiral catalysts has emerged as a prominent area of research. This review provides a comprehensive overview of the research progress in stereoselective haloamination reactions from 1999 to 2023. It examines the innovations in catalyst design that have facilitated more efficient and selective transformations. The review also analyzes the optimization of reaction conditions, which has been crucial in improving the overall performance and applicability of these reactions. Furthermore, it explores the diverse range of haloamination reactions that have been developed, emphasizing their potential for the synthesis of complex and valuable chemical structures. Additionally, this review offers insightful perspectives on future research directions in stereoselective haloamination reactions. Full article

Spirocyclic architectures, which feature two rings sharing a single atom, are common in natural products and exhibit beneficial biological and material properties. Due to the significance of these architectures, biocatalytic dearomative spirocyclization has recently emerged as a powerful approach for constructing three-dimensional spirocyclic frameworks under mild, sustainable conditions and with exquisite stereocontrol. This review surveys the latest advances in biocatalyzed spirocyclization of all-carbon arenes (phenols and benzenes), aza-aromatics (indoles and pyrroles), and oxa-aromatics (furans). We highlight cytochrome P450s, flavin-dependent monooxygenases, multicopper oxidases, and novel metalloenzyme platforms that effect regio- and stereoselective oxidative coupling, epoxidation/semi-pinacol rearrangement, and radical-mediated cyclization to produce diverse spirocycles. Mechanistic insights gleaned from structural, computational, and isotope-labeling studies are discussed where necessary to help the readers further understand the reported reactions. Collectively, these examples demonstrate the transformative potential of biocatalysis to streamline access to spirocyclic scaffolds that are challenging to prepare through traditional methods, underscoring biocatalysis as a transformative tool for synthesizing pharmaceutically relevant spiroscaffolds while adhering to green chemistry paradigms to ultimately contribute to a cleaner and more sustainable future. Full article

Fluorinated organic molecules have become indispensable in modern chemistry, owing to the unique properties imparted by fluorine to other compounds, including enhanced metabolic stability, controlled lipophilicity, and improved bioavailability. The site-selective incorporation of fluorine atoms into organic frameworks is essential in pharmaceutical, agrochemical, and material science research. In recent years, catalytic fluorination has become an important methodology for the efficient and selective incorporation of fluorine atoms into complex molecular architectures. This review highlights advances in catalytic fluorination reactions over the past six years and describes the contributions of transition metal catalysts, photocatalysts, organocatalysts, and electrochemical systems that have enabled site-selective fluorination under a variety of conditions. Particular attention is given to the use of well-defined fluorinating agents, including Selectfluor, N-fluorobenzenesulfonimide (NFSI), AlkylFluor, Synfluor, and hypervalent iodine reagents. These reagents have been combined with diverse catalytic systems, such as AgNO₃, Rh(II), Mo-based complexes, Co(II)-salen, and various organocatalysts, including β,β-diaryl serine catalysts, isothiourea catalysts, and chiral phase-transfer catalysts. This review summarizes proposed mechanisms reported in the original studies and discusses examples of electrophilic, nucleophilic, radical, photoredox, and electrochemical fluorination pathways. Recent developments in stereoselective and more sustainable protocols are also examined. By consolidating these strategies, this article provides an up-to-date perspective on catalytic fluorination and its impact on synthetic organic chemistry. Full article

Chiral ansa-η⁵-complexes of transition metals have shown remarkable efficacy in organometallic synthesis and catalysis. Additionally, enantiomerically pure ansa-complexes hold promise for the development of novel chiral materials and pharmaceuticals. The discovery and synthesis of a diverse range of group IVB and IIIB metal complexes represents a significant milestone in the advancement of stereoselective catalytic methods for constructing metal-C, C-C, C-H, and C-heteroatom bonds. The synthesis of enantiomerically pure metallocenes can be accomplished through several strategies: utilizing optically active precursors of η⁵-ligands, separation of diastereomers of complexes with enantiomerically pure agents, and synthesis via the stereocontrolled reactions of enantiomerically pure σ-complexes with prochiral anions of η⁵-ligands. This review focuses on the analysis of various nuances of the synthesis of enantiomerically pure ansa-η⁵-complexes of titanium and lanthanum families. Their applicability as effective catalysts in asymmetric carbomagnesiation, carbo- and cycloalumination, oligo- and polymerization, Diels–Alder cycloaddition, reactions of zirconaaziridines, cyclization, hydrosilylation, hydrogenation, hydroamination, and other processes are highlighted as well. Full article

Recent advances in zinc complexes for stereoselective ring-opening polymerization (ROP) and copolymerization (ROCOP) highlight their pivotal role in synthesizing biodegradable aliphatic polyesters and polycarbonates. These materials address the urgent demand for sustainable alternatives to petroleum-based plastics, with stereochemical control directly impacting polymer crystallinity, thermal stability, and degradability. Zinc catalysts, leveraging low toxicity and versatile coordination chemistry, enable precise stereoregulation, whose performance is modulated by ligand steric/electronic effects, coordination geometry, and reaction conditions. This review summarizes the recent developments in zinc complexes for stereoselective ROP and ROCOP, focusing on ligand design strategies to enhance catalytic performance. Full article

1,3-Dipolar cycloadditions on nitrone dipoles are key reactions to access five-membered heterocycles, which are useful intermediates in the synthesis of biologically relevant glycomimetics. The good atomic balance and high stereoselectivity characteristic of such reactions make them good candidates for the development of green protocols. In the present work, these features were maximized by avoiding the use of organic solvents and considering starting materials derived from biomass. Reactions involving (acyclic and cyclic) carbohydrate-derived nitrones as dipoles and levoglucosenone as dipolarophile were considered. Performing selected 1,3-dipolar cycloadditions in neat conditions showed reduced reaction times, maintaining similar selectivity and yields with respect to the classical protocols. The use of microwave irradiation and orbital shaking were also exploited to increase the sustainability of the synthetic protocols. The collected results highlight the potential of solvent-free 1,3-dipolar cycloadditions in the design of efficient synthetic routes according to green chemistry principles, such as prevention, atom economy, safer solvents and auxiliaries, and use of renewable feedstocks. Full article

The phenomena of regio- and stereoselectivity and the molecular mechanism of the [2 + 2] cycloaddition reaction between (E)-2-arylnitroethenes and the ynamine molecular system were analyzed using wb97xd/6-311 + G(d) (PCM) quantumchemical calculations. It was found that, independently of the stepwise nature of the cycloaddition, the full retention of the stereoconfiguration of the nitroalkene can be interpreted and explained. Next, the analysis of the electronic properties of the localized reaction intermediate suggests its possible zwitterionic nature. Additionally, the solvent and the substituent effect on the reaction course were also evaluated. In consequence, the proposed mechanism can be treated as general for some groups of [2 + 2] cycloaddition processes. Lastly, for the model process, the full Bonding Evolution Theory (BET) analysis along the reaction coordinate was performed. It was found that the [2 + 2] cycloaddition reaction between (E)-2-phenylonitroethene and ynamine begins with the formation of two pseudoradical centers at the C2 and C3 atoms. First, a C2-C3 single bond is formed in phase V by combining two pseudoradical centers, while the formation of a second C4-C1 single bond begins at the last, eleventh phase of the reaction path. A BET analysis of intermediate (I) allows it to be classified as a compound with a pseudoradical structure. Next to zwitterions and biradicals, it is evidently new type of intermediate on the path of the [2 + 2] cycloaddition reaction. Full article

We synthesized 16 representatives of a new class of tetraene macrodiolides with two pharmacophore cis,cis-1,5-diene fragments of the molecule in their structure in rather high yields (from 67 to 84%), which, in turn, were synthesized by a catalytic intermolecular cyclocondensation reaction of α,ω-alka-nZ,(n+4)Z-diendiols with α,ω-alka-nZ,(n+4)Z-diendioic acids using Hf(OTf)₄. The synthesis of starting substrates with 1Z,5Z-diene moieties with a high degree of stereoselectivity was carried out using the authors’ original reaction of catalytic homo-cyclomagnesiation of O-containing allenes. The cytotoxic potential of the examined compounds was assessed using the following cell lines: Jurkat, K562, U937, HL60, HEK293, and Wi-38 (fibroblasts). Biological tests of the synthesized compounds showed a direct effect on mitochondrial biogenesis by the dissociation of oxidation and phosphorylation and the release of cytochrome P450 into the cell cytosol, as well as the induction of mitochondrial apoptosis. The selectivity index demonstrates significant variability, ranging from approximately 2.5 to 5.3 for Jurkat cells and from 3.0 to 5.8 for the other cell lines. Full article

A stereoselective and scalable strategy for the synthesis of phosphorus-containing bicyclic and tricyclic compounds from 1-phenylphosphin-2-en-4-one 1-oxide is presented. This activated dienophile, available in both racemic and enantiopure forms, undergoes smooth [4+2] cycloadditions with acyclic and cyclic dienes, affording products with excellent yields and controlled stereochemistry. Notably, the cis/trans-fusion of the cycloadducts (phosphadecalones and phosphahexahydrochrysene) can be selectively controlled by fine-tuning the conditions of microwave-assisted cycloaddition reaction. The influence of temperature, time, and steric effects on cis/trans and endo/exo selectivity was examined in detail. The molecular structure, including the absolute configuration, of eight products has been determined by X-ray crystallography. These analyses further established the endo-selective nature of the cycloaddition, favoring the P=O face of the dienophile. Post-cycloaddition transformations of selected P-stereogenic phosphadecalone, such as isomerization, reduction and deoxygenation, demonstrate the synthetic versatility of the resulting products. Full article

A library of neoisopulegol-based amino and thiol adducts was developed from (+)-neoisopulegol, derived from commercially available (−)-isopulegol. Michael addition of different nucleophiles towards its highly active α,β-unsaturated γ-lactone motif was accomplished, resulting in diverse amino and thiol analogs in stereoselective reactions. Then, the lactone ring was opened, with NH₃ and benzylamine furnishing primary amide and N-benzyl-substituted amide derivatives, respectively. The in vitro antimicrobial effect of prepared compounds was also explored. The results revealed that naphthylmethyl-substituted β-aminolactone, the most promising compound, displayed selective inhibition for the Gram-positive bacteria S. aureus with an MIC (minimum inhibitory concentration) value of 12.5 μM. A docking study was performed to interpret the obtained results. Full article

Domino reactions are powerful tools for the straightforward synthesis of complex molecules with a particular emphasis on functionalized azacycles. We report a contribution in this field, implemented via a new thia–Michael/aldol sequence between readily accessible N-alkoxyacrylamides and α,β-unsaturated carbonyls, for access to polysubstituted δ-lactams with acceptable-to-good yields and good selectivity. This method, initially developed in a two-component approach and characterized by the mildness of its reaction conditions, was shown to be compatible with various thiophenol derivatives and to employ a simple pre-thiasilylation step in a one-pot process. This further extension to the monotype aza–Michael/thia–Michael/aldol sequence establishes a proof-of-concept that acrylamides can react as both 1,3-bis-nucleophiles and 1,4-electrophiles in a single flask operation. Full article

The stereoselective synthesis of bicyclo[3.2.0]heptanes via an anion radical [2+2] photocycloaddition of aryl bis-enone derivatives was investigated. By employing chiral oxazolidinone auxiliaries bound to aryl bis-enone substrates, enantioenriched, highly substituted bicyclo[3.2.0]heptanes have been synthesized. The reaction, mediated by Eosin Y and promoted by LiBr under visible light irradiation, has been studied both experimentally and computationally to elucidate the mechanism and stereoselective outcomes. The process proceeds via a syn-closure pathway, leading to the formation of the corresponding cis-anti diastereoisomers as major products isolated and characterized by X-ray analysis; DFT calculations provided useful insights and computational support which allow a plausible reaction mechanism to be proposed that agrees with the collected experimental data. Full article

Given the crucial roles of carbohydrates in energy supply, biochemical processes, signaling events and the pathogenesis of several diseases, the development of carbohydrate analogues, called glycomimetics, is a key research area in Glycobiology, Pharmacology, and Medicinal Chemistry. Among the many structural transformations explored, the replacement of endo- and exocyclic oxygen atoms by carbon (carbasugars) or heteroatoms, such as nitrogen (aza- and iminosugars), phosphorous (phosphasugars), sulfur (thiosugars), selenium (selenosugars) or tellurium (tellurosugars) have garnered significant attention. These isosteric substitutions can modulate the carbohydrate bioavailability, stability, and bioactivity, while introducing new properties, such as redox activity, interactions with pathological lectins and enzymes, or cytotoxic effects. In this manuscript we have focused on three major families of glycomimetics: thio-, seleno-, and tellurosugars. We provide a comprehensive review of the most relevant synthetic pathways leading to substitutions primarily at the endocyclic and glycosidic positions. The scope includes metal-catalyzed reactions, organocatalysis, electro- and photochemical transformations, free-radical processes, and automated syntheses. Additionally, mechanistic insights, stereoselectivity, and biological properties are also discussed. The structural diversity and promising bioactivities of these glycomimetics underscore their significance in this research area. Full article

An efficient stereoselective strategy for the synthesis of chiral bisspiro barbituric acid–oxindole derivatives was developed. The asymmetric Michael addition/cyclization tandem reaction between benzylidene barbituric acids and oxindolylmalonitriles was catalyzed by squaramide catalyst, and the corresponding spirocyclic products were obtained in good-to-high yields (up to 97%) with excellent stereoselectivities (up to >99% ee, >20:1 dr). At the same time, the practicality of the reaction was verified by the gram-scale preparation reaction. Full article