Isoxazolidine: A Privileged Scaffold for Organic and Medicinal Chemistry

Phosphine-catalyzed dearomative [3+2] cycloaddition of 4-nitroisoxazoles with allenoates or Morita-Baylis-Hillman carbonates

An efficient phosphine-catalyzed dearomative [3+2] annulation of 4-nitroisoxazoles with allenoates or Morita-Baylis-Hillman carbonates has been established for the convenient synthesis of bicyclic isoxazoline derivatives. This reaction approach showed a broad substrate scope, high functional group compatibility, and excellent regioselectivity and diastereoselectivity. Furthermore, the success at the gram-scale and synthetic applications of the obtained compound 3a demonstrate the great potential of this methodology for practical applications in organic synthesis.

Continuous Flow Electroselenocyclization of Allylamides and Unsaturated Oximes to Selenofunctionalized Oxazolines and Isoxazolines

The synthesis of selenofunctionalized oxazolines and isoxazolines from N-allyl benzamides and unsaturated oximes with diselenides was studied by utilizing a continuous flow electrochemical approach. At mild reaction conditions and short reaction times of 10 min product yields of up to 90% were achieved including a scale-up reaction. A broad substrate scope was studied and the reaction was shown to have a wide functional group tolerance.

Palladium-Catalyzed Ligand-Directed Divergent Decarboxylative Cycloadditions of Vinyloxazolidine-2,4-diones with 1,3,5-Triazinanes

This study demonstrates a highly efficient regiodivergent ligand-controlled palladium-catalyzed cycloaddition reaction of vinyloxazolidine-2,4-diones with 1,3,5-triazinanes. In the presence of a diphosphine ligand, the reaction proceeds via a (5+2) cycloaddition pathway to afford 1,3-diazepin-4-ones in excellent yields, while using a monophosphine ligand, the reaction proceeds smoothly via a (3+2) cycloaddition pathway to give imidazolidin-4-ones in good yields.

A. E. Albadri A, Patel H, Messaoudi S, Kadri A, M. Al-Hazmy S, Aouadi K. Synthesis, optical properties, DNA, β-cyclodextrin interaction, hydrogen isotope sensor and computational study of new enantiopure isoxazolidine derivative (ISoXD)

A novel isoxazolidine derivative (ISoXD) dye was successfully synthesized and comprehensively characterized. In this study, we conducted a thorough examination of its various properties, including optical characteristics, interactions with DNA and β-cyclodextrin (β-CD), molecular docking, molecular dynamic simulation, and density functional theory (DFT) calculations. Our investigation encompassed a systematic analysis of the absorption and emission spectra of ISoXD in diverse solvents. The observed variations in the spectroscopic data were attributed to the specific solvent's capacity to engage in hydrogen bonding interactions. Remarkably, the most pronounced intensities were observed in glycol, which can establish many hydrogen bonds with ISoXD. Furthermore, our study revealed a significant distinction in the fluorescence behavior of ISoXD when subjected to different solvents, particularly between CHCl3 and CDCl3. Moreover, we explored the fluorescence intensity of the ISoXD complex in the presence of various metals, both in ethanol and water. The ISoXD complex exhibited a substantial increase of fluorescence upon interaction with different metal ions. The utilization of DFT calculations allowed us to propose an intramolecular charge transfer (ICT) mechanism as a plausible explanation for this quenching phenomenon. The interaction of ISoXD with DNA and β-CD was studied using absorption spectra. The binding constant (K) and the standard Gibbs free energy change (ΔGo) for the interaction between DNA and β-CD with ISoXD were determined. In docking study, ISoXD exhibited significant docking scores (-6.511) and MM-GBSA binding free energies (-66.27 kcal/mol) within the PARP-1 binding cavity. Its binding pattern closely resembles to the co-crystal ligand veliparib, and during a 100ns MD simulation, ISoXD displayed strong stability and formed robust hydrogen bonds with key amino acids. These findings suggest ISoXD's potential as a PARP-1 inhibitor for further investigation in therapeutic development.

Insights into the mechanism of [3+2] cycloaddition reactions between N-benzyl fluoro nitrone and maleimides, its selectivity and solvent effects

We present a theoretical study of the [3+2] cycloaddition (32CA) reactions of N-benzyl fluoro nitrone with a series of maleimides producing isoxazolidines. We use the Molecular Electron Density Theory at the MPWB1K/6-311G(d) level. We focus on the reaction mechanism, selectivity, solvent, and temperature effects. In addition, we perform topological analyses at the minimal and transition states to identify the intermolecular interactions. Electron Localization Function approach classifies the N-benzyl fluoro nitrone as zwitterionic (zw-) three-atom components (TACs), associated with a high energy barrier. The low polar character of the reaction is evaluated using the Conceptual Density Functional Theory analysis of the reactants, confirmed by the low global electron density transfer computed at the transition states. Computations show that these 32CA reactions follow a one-step mechanism under kinetic control, with highly asynchronous bond formation and no new covalent bond is formed at the TS. Besides, the potential energy surfaces along the reaction pathways in gas phase and in solvent are mapped. The corresponding Gibbs free energy profiles reveal that the exo-cycloadducts are kinetically and thermodynamically more favored than endo-cycloadducts, in agreement with the exo-selectivity observed experimentally. In particular, we found that solvent and temperature did not affect this selectivity and mainly influence the activation energies and the exothermic character of these 32CA reactions.

Facile Synthesis of Some New Peptidomimetic β3 -and β2,3 -Amino Alcohols Possessing Pyridyl Moiety via Reductive Ring Opening of Pyridyl-isoxazolidines

Regio- and stereoselective 1,3-dipolar cycloadditions of C-(3-pyridyl)-N-phenylnitrone (2) with variedly substituted dipolarophiles (3, 4) were carried out to obtain substituted pyridyl-isoxazolidines (5-8). Reductive cleavage of pyridyl-isoxazolidines (5-8) with ammonium formate, methanol-THF solvents, at ambient temperature, in the presence of Pd/C provided a facile route for the synthesis of β3 -and β2,3 -amino alcohols (9-12), with a substitution pattern having pronounced influence on torsional angles. The obtained compounds (9-12) are valuable scaffolds which can be utilized for peptidomimetics. Thus, the present methodology for reductive opening of isoxazolidine ring avoids the disadvantages of using expensive apparatus and hazards involved in the use of hydrogen gas. The preferential formation of amino-alcohols in case of bicyclic isoxazolidines (8a-c), which precludes any recyclization is rationalized by DFT calculations.

A Convenient Synthesis of Novel Isoxazolidine and Isoxazole Isoquinolinones Fused Hybrids

Isoxazolidine, isoxazole, and isoquinolinone rings are present in the structure of several natural products and/or pharmaceutically interesting compounds. In this work, facile and efficient pathways have been developed for the preparation of fused frameworks bearing those heterocycles. The successful approaches for both isoxazolidine/isoquinolinone and isoxazole/isoquinolinone hybrid syntheses relied initially on 1,3-dipolar cycloadditions of nitrones and nitrile oxides to indenone and 2-propargylbenzamide, respectively. The construction of the isoquinolinone lactam system followed by performing a selective Schmidt reaction for isoxazolidine derivatives (two steps overall), whereas the isoxazole lactams were reached via an Ullmann-type cyclisation (three steps overall). Key observations were made regarding the stereo- and regioselectivities of the reactions employed, and small libraries of the targeted hybrids were prepared, demonstrating the general applicability of these strategies.

Natural products with 1,2-oxazine scaffold: occurrence, chemical diversity, bioactivity, synthesis, and biosynthesis

Covering: up to the end of July, 20231,2-Oxazine is a heterocyclic scaffold rarely found in natural products and is characterized by a directly connected N-O bond in a six-membered ring. Since the discovery of geneserine, the first 1,2-oxazine-containing natural product (1,2-oxazine NP) being isolated from Calabar bean (Physostigma venenosum) in 1925, a total of 76 naturally occurring 1,2-oxazine NPs have been isolated and identified from various sources, which have attracted the attention of researchers in the field of natural product chemistry, organic synthesis, biosynthesis, and pharmacology. This review summarizes the chemical family of 1,2-oxazine NPs, focusing on their source organisms, structural diversities, chemical synthesis, and biosynthesis.

Intermolecular 1,3-Dipolar Cycloaddition Reaction of N-Carbamoyl Nitrones Generated by N-Selective Carbamoylation of Oximes with Isocyanates

N-Selective carbamoylation reaction of oximes with isocyanates generates nitrones, which undergo 1,3-dipolar cycloaddition with various dipolarophiles to afford diverse isoxazolidines. Notably, combinations of highly electron-rich oxime and highly electron-deficient dipolarophile exhibited high reactivity, with product yields of up to 94 %. The substituent on the isoxazolidine-nitrogen atom could be successfully removed without loss of the cyclic structure. Computational studies have also elucidated the mechanism of the reaction and origin of stereoselectivity.

Synthesis of Bridged Cycloisoxazoline Scaffolds via Rhodium-Catalyzed Coupling of Nitrones with Cyclic Carbonate

Bridged isoxazolidines were synthesized via Rh(III)-catalyzed C-H allylation of α-aryl nitrones with 5-methylene-1,3-dioxan-2-one. The nitrone group serves as a directing group and 1,3-dipole in the C-H activation/[3 + 2] cycloaddition cascade, exhibiting excellent chemo- and stereoselectivity along with good functional group compatibility. The resulting skeletal structure was conveniently modified to produce a range of important chemical frameworks, and the protocol was applied to biologically active molecules.

Stable peri-Naphthoisatogens without C2 Protection: Synthesis via Aldrone Condensation, Optical Properties and 1,3-Dipolar Cycloaddition Reaction

peri-Annulation of naphthalane, an important tool for realization of wide range of functional materials, is presently accomplished with limited few functional groups like imide, amide and diamine-derivative (perimidine). To increase the diversity, we have incorporated α-keto aldonitrone as a new functional group, and herein report about five peri-naphthoisatogens (PNTIs) dyes. The synthesis were accomplished using an unusual reaction of aromatic nitro group, which is nucleophilic attack of a C-nucleophile (enol) to the N-atom of nitro group. In five different 5-alkylamino-8-nitro-1-acetylnaphthalenes, intramolecular acid-catalyzed nucleophilic attack of enol moiety to the N-atom of nitro group produced α-keto aldonitrone via addition-elimination mechanism. The PNTIs showed characteristics of 1,3-dipole and reacted with ethyl acrylate to produce isoxazolidine ring, which subsequently converted into aza phenalenone derivative via ring cleavage. Both the PNTI and the corresponding derivative strongly absorb in the visible region, displaying absorption maximum at 551 and 561 nm (in CHCl3 ) respectively. Compared to the popular analogous dye naphthalene monoimides, PNTIs showed bathochromic shift of absorption maximum by more than 100 nm. The emission maximum for the PNTI and its derivative in chloroform were observed at 594 and 635 nm respectively.

Brønsted acid-catalyzed annulation reaction of hydroxamic acids: synthesis of cyclopentane-fused isoxazolidines and their benzilic amide rearrangement

Readily available hydroxamic acids were leveraged to access challenging nitrones in the presence of H3PO4 as a Brønsted acid catalyst and engaged in an intramolecular (3+2) annulation reaction to make valuable cyclopentane-fused isoxazolidines with high yields and excellent diastereoselectivity. The products were further utilized in a unique base-promoted benzilic amide rearrangement to provide cyclopentane-fused γ-lactams bearing three contiguous stereocenters as a single diastereomer.

Trapping of Arynes with In Situ Generated Aryltrifluoromethylnitrones Enables Access to Trifluoromethylated Benzoxazolines

Herein, we report a rare example of trapping arynes using in situ generated aryltrifluoromethylnitrone to access an important class of trifluoromethylated benzoxazolines. This three-component strategy involves a nitrone formation/[3 + 2] cycloaddition/thermal rearrangement cascade and furnishes trifluoromethylated benzoxazolines in high yields. The scope of the reaction is quite broad with respect to aryltrifluorodiazoethanes, nitrosoarenes, and arynes. The proposed reaction pathway is supported through the isolation and characterization of the key reaction intermediates phenyltrifluoromethylnitrone and benzisoxazoline.

Chirality Sensing of N-Heterocycles via 19F NMR

Methods to rapidly detect and differentiate chiral N-heterocyclic compounds become increasingly important owing to the widespread application of N-heterocycles in drug discovery and materials science. We herein report a ¹⁹F NMR-based chemosensing approach for the prompt enantioanalysis of various N-heterocycles, where the dynamic binding between the analytes and a chiral ¹⁹F-labeled palladium probe create characteristic ¹⁹F NMR signals assignable to each enantiomer. The open binding site of the probe allows the effective recognition of bulky analytes that are otherwise difficult to detect. The chirality center distal to the binding site is found sufficient for the probe to discriminate the stereoconfiguration of the analyte. The utility of the method in the screening of reaction conditions for the asymmetric synthesis of lansoprazole is demonstrated.

Cu(OAc)2-catalyzed three-component cycloaddition of malonates, nitrosoarenes and alkenes: access to isoxazolidines

The Cu(OAc)₂-catalyzed one-pot three-component cycloaddition of malonates, nitrosoarenes and alkenes is described. A wide range of isoxazolidines could be obtained in moderate to excellent yields via this method. Mechanistic investigations indicated that the key step in this catalytic system is the straightforward formation of nitrone intermediates through the Cu(OAc)₂-catalyzed reaction of malonates with nitrosoarenes.

Lewis-Acid-Catalyzed Reductive Hydroalkoxylation of Propargylic N-Hydroxylamines Gives Stereoselective Access to Isoxazolidines

Lewis-acid-catalyzed 5-endo-dig reductive hydroalkoxylation cascade on propargylic N-hydroxylamine gave expedient, stereoselective access to isoxazolidine derivatives. The developed method provides a new approach toward the synthesis of isoxazolidine, a biologically privileged scaffold. The synthetic potential of the developed methodology was demonstrated by synthesizing 1,3-aminoalcohol, 4-aminotetrahydropyran, and sedamine natural products.

Asymmetric reactions involving aryne intermediates

Although arynes are usually considered fleeting intermediates, they are highly valuable synthons because they enable the introduction of aromatic rings and the simultaneous formation of new bonds at two sites. Although catalytic reactions using transition metals are excellent method for constructing complex polycyclic aromatic molecules in a single step, the use of asymmetric catalysis for the capture of arynes remains a crucial goal for the progress of aryne chemistry. Catalytic asymmetric reactions of arenes are challenging, requiring sufficient interactions between the neutral and highly reactive short-lived aryne intermediates in a stereo-controlled fashion. In addition, spontaneous decomposition, as well as side reactions, has hindered their development and, until recently, highly enantioselective reactions using arynes had remained elusive. This Review highlights asymmetric reactions using arynes, featuring diastereoselective, enantioselective and catalytic enantioselective reactions.

Recent Advances in the Synthesis of Di- and Trisubstituted Hydroxylamines

As an underrepresented functional group in bioorganic and medicinal chemistry, the hydroxylamine unit has historically received little attention from the synthetic community. Recent developments, however, suggest that hydroxylamines may have broader applications such that a review covering recent developments in the synthesis of this functional group is timely. With this in mind, this review primarily covers developments in the past 15 years in the preparation of di- and trisubstituted hydroxylamines. The mechanism of the reactions and key features and shortcomings are discussed throughout the review.

Visible-light-induced cascade reaction: a sustainable approach towards molecular complexity

Photoredox catalysis has demonstrated rapid evolution in the field of synthetic organic chemistry. On the other hand, the splendour of cascade reactions in providing complex molecular architectures renders them a cutting-edge research area. Therefore, the merging of photocatalysis with cascade synthesis brings out a synthetic paradigm with immense potential. The development of photocascade catalysis for a target molecule with a particular molecular skeleton and stereochemical framework presents certain challenges but provides a robust and environmentally benign synthetic alternative. This comprehensive review assembles all the accomplishments and highlights of visible-light-induced cascade reactions with literature coverage up to October 2022.

Catalytic Asymmetric Hydroalkoxylation and Formal Hydration and Hydroaminoxylation of Conjugated Dienes

The straightforward construction of stereogenic centers bearing unprotected functional groups, as in nature, has been a persistent pursuit in synthetic chemistry. Abundant applications of free enantioenriched allyl alcohol and allyl hydroxylamine motifs have made the asymmetric hydration and hydroaminoxylation of conjugated dienes from water and hydroxylamine, respectively, intriguing and efficient routes that have, however, been unachievable thus far. A fundamental challenge is the failure to realize transition-metal-catalyzed enantioselective C-O bond constructions via hydrofunctionalization of conjugated dienes. Here, we perform a comprehensive study toward the stereoselective formal hydration and hydroaminoxylation of conjugated dienes by synthesizing a set of new P,N-ligands and identifying an aryl-derived oxime as a surrogate for both water and hydroxylamine. Asymmetric hydroalkoxylation with new P,N-ligands is also elucidated. Furthermore, versatile derivatizations following hydration provide indirect but concise routes to formal hydrophenoxylation, hydrofluoroalkoxylation, and hydrocarboxylation of conjugated dienes that have been unreported thus far. Finally, a ligand-to-ligand hydrogen transfer process is proposed based on the results of preliminary mechanistic experiments.

B(C6F5)3-Catalyzed Diastereoselective and Divergent Reactions of Vinyldiazo Esters with Nitrones: Synthesis of Highly Functionalized Diazo Compounds

Herein we report a mild, transition-metal-free, highly diastereoselective Lewis acid catalyzed methodology toward the synthesis of isoxazolidine-based diazo compounds from the reaction between vinyldiazo esters and nitrones. Interestingly, the isoxazolidine products were identified to have contrasting diastereoselectivity to previously reported metal-catalyzed reactions. Furthermore, the same catalyst can be used with enol diazo esters, prompting the formation of Mukaiyama-Mannich products. These diazo products can then be further functionalized to afford benzo[b]azepine and pyrrolidinone derivatives.

Additive-free synthesis of fused tricyclic cyanoisoxazolidines using in situ formed cyanonitrones

Herein, we disclose the first report on the generation of cyanonitrone in situ from diazoacetonitrile and nitrosoarene, and its subsequent [3+2] cycloaddition with oxabicyclic alkenes to access fused tricyclic cyanoisoxazolidines. Further, this methodology could be extended to access fused tricyclic trifluoromethylated and phosphonylated isoxazolidines. Surprisingly, the reductive ring-opening of cyanoisoxazolidines was followed by a spontaneous lactonization to produce fused tricyclic amino lactones. Moreover, the N-O bond of the obtained tricyclic trifluoromethylated isoxazolidines could be cleaved to obtain 1,3-amino alcohols.

Photo-induced redox cascade reaction of nitroarenes and amines

A photo-induced redox cascade reaction has been developed for the chemoselective construction of isoxazolidine derivatives from stable and easily available nitroarenes and amines.

Leveraging Alkyne-Oximium Cyclization for the Stereoselective Synthesis of Isoxazolidine

A TMSOTf-mediated highly diastereoselective synthesis of isoxazolidine bearing three contiguous stereocenters is described. This method utilizes O-propargyl hydroxylamines as a novel building block for the rapid assembly of the isoxazolidines via alkyne-oximium cyclization. The strategy could be used in the synthesis of enantiomerically enriched isoxazolidines. Reductive cleavage of the N-O bond efficiently gives the corresponding 1,3-aminodiols with precise control over all stereocenters formed.

2-((3-(4-Methoxyphenyl)-4,5-dihydroisoxazol-5-yl)methyl)benzo[d]isothiazol-3(2H)-one1,1-dioxide

In this work, a novel compound N-(3-(4-methoxyphenyl)isoxazolin-5-yl)methylsaccharin has been synthesized. The molecular structure of the compound was determined using various spectroscopic techniques and confirmed by a single-crystal X-ray diffraction analysis. In the single crystal, C–H…O hydrogen bonds between neighboring molecules form chains along the a-axis direction. Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from H…H (35.7%), H…O/O…H (33.7%), and H…C/C…H (13%) interactions. The optimized structure calculated using density functional theory at the B3LYP/6–311 G(d,p) level is compared with the experimentally determined structure in the solid state. The calculated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy gap is 4.9266 eV.

Highly diastereoselective synthesis of benzothiazolo[3,2-a]pyridines via [4 + 2] annulation reaction of 2-vinylbenzothiazoles and azlactones

An efficient AgOTf-catalyzed [4 + 2] annulation reaction of 2-vinylbenzothiazoles and azlactones was successfully performed under mild reaction conditions. With this approach, a series of novel benzothiazolo[3,2-a]pyridine derivatives was readily obtained in good to excellent yields (68-96%), with high diastereoselectivities and tolerating quite a broad scope of substituents. By using chiral phosphoric acid catalyst, the desired products were obtained in high enantioselectivities, up to -94%. This methodology provides a rapid and useful method for constructing fused benzothiazole derivatives.

Free energy perturbation (FEP)-guided scaffold hopping

Scaffold hopping refers to computer-aided screening for active compounds with different structures against the same receptor to enrich privileged scaffolds, which is a topic of high interest in organic and medicinal chemistry. However, most approaches cannot efficiently predict the potency level of candidates after scaffold hopping. Herein, we identified potent PDE5 inhibitors with a novel scaffold via a free energy perturbation (FEP)-guided scaffold-hopping strategy, and FEP shows great advantages to precisely predict the theoretical binding potencies ΔG FEP between ligands and their target, which were more consistent with the experimental binding potencies ΔG EXP (the mean absolute deviations| Δ G FEP - Δ G EXP |  < 2 kcal/mol) than those ΔG MM-PBSA or ΔG MM-GBSA predicted by the MM-PBSA or MM-GBSA method. Lead L12 had an IC50 of 8.7 nmol/L and exhibited a different binding pattern in its crystal structure with PDE5 from the famous starting drug tadalafil. Our work provides the first report via the FEP-guided scaffold hopping strategy for potent inhibitor discovery with a novel scaffold, implying that it will have a variety of future applications in rational molecular design and drug discovery.

Solvent-free synthesis of nitrone-containing template as a chemosensor for selective detection of Cu(II) in water

A state-of-the-art method was developed for repurposing nitrone-containing compounds in the chemosensory field, the ability of the designed molecules to chelate metal cations was evaluated, and their unprecedented solubility in water was confirmed. A facile, rapid, and solvent-free method of synthesizing small molecular mass chemosensors was developed by using a modulative α-aryl-N-aryl nitrone template. α-(Z)-Imidazol-4-ylmethylen-N-phenyl nitrone (Nit1) and α-(Z)-2-pyridyl-N-phenyl nitrone (Nit2) were prepared in 15 min, isolated in less than 60 min with ca. 90% yield, and screened against nine metal cations. Nit1 is a small-molecular-mass compound (188 g mol^-1) that is water-soluble and has specificity for sensing Cu²⁺ with an association constant of K = 1.53 × 10¹⁰ and a limit of detection (LOD) of 0.06 ppm. These properties make Nit1 a competitive chemosensor for the detection of Cu²⁺ in aqueous solution. The nitrone-containing template used in this study is a step forward for new and small chemosensory entities.

Sc(OTf)3-Catalyzed [3+2]-Cycloaddition of Diazoacetoacetate Enones and N-Aryl Nitrones: Diastereoselective Synthesis of Functionalized Isoxazolidines with Three Contiguous Stereogenic Centers

A catalytic [3+2]-cycloaddition using Sc(OTf)3 as a Lewis acid catalyst is developed. This catalytic 1,3-dipolar cycloaddition dia­stereoselectively transforms diazoacetoacetate enones and N-aryl nitrones into highly functionalized isoxazolidines bearing three contiguous chiral centers. The feasibility of the uncatalyzed 1,3-dipolar cycloaddition is postulated by DFT calculations and substantiated experimentally.

Time-economical synthesis of selenofunctionalized heterocycles via I2O5-mediated selenylative heterocyclization

A time-economical and robust synthesis of various selenofunctionalized heterocycles was accomplished via I₂O₅-mediated selenocyclizations of olefins with diselenides. Using this method, 116 selenomethyl-substituted heterocycles were synthesized with up to 97% isolated yield in minutes. Additional features of this new protocol include the use of an inorganic oxidant, mild conditions, and easy operation. Preliminary investigations suggest that the transformation operates through selenenyl iodide-induced electrophilic cyclization.

Recent advances in transition-metal catalyzed directed C–H functionalization with fluorinated building blocks

This review focuses on the advances in transition-metal catalyzed reactions with fluorinated building blocks via directed C–H bond activation for the construction of diverse organic molecules with an insight into the probable mechanistic pathway.

Unveiling the intramolecular [3 + 2] cycloaddition reactions of C,N-disubstituted nitrones from the molecular electron density theory perspective

The zwitterionic type intramolecular [3 + 2] cycloaddition reactions of nitrones show remarkable substituent effects and varying reactivities in the cases of cyclic and acyclic alkenes.

Regio- and stereo-selective construction of cis-indeno[1,2-c]isoxazoles via a C–H allylation/1,3-dipolar cycloaddition cascade

Synthesis of fused cis-indole[1,2-c]isoxazoles with excellent regio- and stereo-selectivity via a rhodium-catalyzed C–H allylation/intramolecular 1,3-dipolar cycloaddition cascade has been realized.

Annulation of phosphole sulfides via [3 + 2] cycloaddition with nitrones

We developed a facile pathway for the construction of the phospholene fused isoxazolidine skeleton through the [3 + 2] cycloaddition reaction of phosphole sulfides.

Hydrazones as Substrates in the Synthesis of Isoxazolidines via a KOH-Promoted One-Pot Three-Component Cycloaddition with Nitroso Compounds and Olefins

Hydrazones have been employed as the starting materials in a KOH-mediated one-pot three-component cycloaddition with readily accessible nitroso compounds and olefins to construct various isoxazolidines. Compared with diazo compounds as starting materials, this methodology could afford a wider range of products in good to excellent yields and diastereoselectivities for most substrates, and hydrazones are cheaper, more accessible, and safer substrates. The experimental study shows that the choice of suitable hydrazones is crucial.

Imbuing an Old Heterocycle with the Power of Modern Catalysis: An Isoxazolidin-5-one Story

Isoxazolidin-5-ones have been regarded as β-amino acid surrogates owing to their labile N-O bond. While many efforts have been devoted to the catalytic enantioselective synthesis of the core of this heterocycle, its further transformation has been less explored, especially in the context of catalysis. This review summarizes the author's research on the development of catalytic reactions using isoxazolidin-5-ones as substrates. Asymmetric catalysis has proven effective for C-C bond formation at the carbonyl α-carbon. Catalytic asymmetric allylation and direct Mannich-type reactions have been developed. Further, the resulting products have been readily converted into the corresponding quaternary β^2,2-amino acids. Moreover, isoxazolidin-5-ones have been identified as alkyl nitrene precursors in the presence of a suitable metal catalyst. The generated metallonitrene undergoes either the electrophilic amination of the aromatic ring or aliphatic C-H insertion, affording a series of cyclic β-amino acids. A remarkable difference in chemoselectivity between rhodium and copper alkyl nitrenes has also been demonstrated, highlighting the unique nature of the underexplored reactive intermediates. The various linear and cyclic β-amino acids obtained through the study are likely to find great utility in a broad range of chemical sciences.