Cycloaddition Reactions Of Nitrones Research Articles

Unveiling the mechanism and selectivity of the [3 + 2] cycloaddition reactions of nitrone with acetylene derivatives leading to anticancer 4-isoxazoline derivatives from the MEDT perspective

The [3 + 2] cycloaddition reactions of N-methyl-C-(2-furyl) nitrone (a) with a series of acetylene derivatives (4b), (5b), and (6b) have been studied at the B3LYP-D3/6-31G(d) computational level within the framework of Molecular Electron Density Theory. Topological analysis allows classifying the nitrone (a) as a zwitterionic (zw-) three-atom component (TAC) associated with high energy barrier. These 32CA reactions follow a one-step mechanism under kinetic control with highly asynchronous bond formation. Bonding Evolution Theory (BET) analysis indicates that no new covalent CO and CC bonds form at the transition states (TSs). Interestingly, the global electron density transfer (GEDT) between 0.08 and 0.18 e predicts low polar character of forward electron density transfer (FEDF) type with the electronic flux from the nitrone (a) to the acetylene derivatives. Electron localization function (ELF) and atom-in-molecules (AIM) topological analysis of the electron density at the TS structures characterize the non-concerted nature of these one-step zw-type 32CA reactions.

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.

Revealing the influence of tether length on the intramolecular [3 + 2] cycloaddition reactions of nitrones from the molecular electron density theory perspective

AbstractThe influence of ethylene substitution and the tether length between the two reacting counterparts on the selectivity and reactivity of the intramolecular [3 + 2] cycloaddition (IM32CA) reactions of cyclic nitrones leading to tricyclic isoxazolidines have been studied within the Molecular Electron Density theory at the MPWB1K/6‐311G(d,p) computational level. These zw‐type IM32CA reactions follow one‐step mechanism, and the activation barrier decreases with the introduction of electron withdrawing (EW) substituent at the alkene moiety in both the intramolecular and intermolecular versions. The IM32CA reactions involving unsubstituted alkene have non‐polar character with minimal electron density flux classified as null electron density flux type, while that involving the EW nitro substituted ethylene is more facile with a strong electron density flux from the nitrone to the ethylene moiety, classified as forward electron density flux type. The increase in the polar character of the IM32CA reaction decreases the activation Gibbs free energies associated with these intramolecular processes, while the highly polar IM32CA reactions are disfavored with respect to the intermolecular ones. Interestingly, the preferred regioselectivity observed in low polar IM32CA reactions having three methylene units between the nitrone and ethylene frameworks is reversed to that in nitrones separated with four methylene units, in conformity with the experimental outcome. Finally, electron localization function and quantum theory of atoms‐in‐molecules studies reveal that, in general, these IM32CA reactions involve early transition state structures in which the formation of new C‐C and C‐O single bonds have not yet started.

Revealing the cyclization selectivity in intramolecular [3 + 2] cycloaddition reactions of allenic nitrones from the molecular electron density theory perspective

Revealing the cyclization selectivity in intramolecular [3 + 2] cycloaddition reactions of allenic nitrones from the molecular electron density theory perspective

Heterocyclic Synthesis of Some New Isoxazolidine Derivatives via 1,3-Dipolar Cycloaddition of Nitrones to Styrene

A number of nitrones have been synthesized in three different procedures, starting with N-phenyl hydroxylamine, followed by the condensation reaction with some selected aldehydes. Furthermore, these nitrones were employed in the preparation of a number of new isoxazolidines. Cycloaddition reaction of nitrones to styrene produced the desired products.

Design and synthesis of novel enantiopure Bis(5-Isoxazolidine) derivatives: insights into their antioxidant and antimicrobial potential via in silico drug-likeness, pharmacokinetic, medicinal chemistry properties, and molecular docking studies

A series of novel compounds, mono-5-isoxazolidines, and bis (5-isoxazolidines) derivatives, were prepared as bicycloadducts. The new series of isoxazolidines were designed and synthesized via 1,3-dipolar cycloaddition reaction of nitrones with 3,9-Divinyl-2,4,8,10-tetra oxaspiro (5-5) undecane in the context of new antimicrobial and antioxidant drugs discovery and were fully characterized by FT-IR, 13C-NMR, and 1H-NMR spectroscopy. The physicochemical properties of all the novel cycloadducts, like bioactivity score and lipophilicity, were predicted using calculative methods. Similarly, the pharmacokinetic properties such as metabolism, absorption, distribution, and excretion (ADME) were also predicted. Most of the tested compounds exhibited antimicrobial properties to varying degrees against various bacterial species, including the Gram-negative bacteria Pseudomonas aeruginosa and Escherichia coli, and the Gram-positive bacteria Streptococcus pyogenus and Staphylococcus aureus, Antifungal properties were also observed against the tested fungi like Candida albicans, Aspergillus niger, and Aspergillus clavatus. The activity data exhibited that most compounds have high activity as compared to the standard drugs. In the range of graded doses, the results of some selected compounds revealed that some are high antioxidants while others are moderate or weak antioxidants. As evidenced by the molecular docking studies, the synthesized compounds showed good binding mode better than a standard drug, against the protein of a Pantothenate Synthetase enzyme (PDB-2X3F).

Stereoselective Synthesis of Novel Chiral Open-Chain D-Ribose and D-Glucose- Derived Nitrones through 1,3-Dipolar Cycloaddition of Maleimide and Maleic Acid and Investigation of Their Antimicrobial Activity Via Molecular Docking and ADMET Studies

Novel biologically active N-Sugar-derived isoxazolidines derivatives (2a, 2b, 3a, 3b) have been synthesized diastereospecifically by 1,3-dipolar cycloaddition reaction of nitrones (a, b) with maleimide and maleic acid. Nitrones were prepared in a pure form as chiral open-chain sugar-derived nitrones in an effort to explore a new type of antimicrobial agents. FTIR, 1H NMR, and 13C NMR spectrometric analysis characterized the structures of the compounds. The synthesized compounds were examined for their antimicrobial activity using the disk diffusion method against Gram-negative bacteria Escherichia coli; the Gram-positive bacteria staphylococcus aureus and against pathogenic fungi Candida albicans and Microsporum gypseum. Isoxazolidines (3a, 2a, 3b) proved to have strong antimicrobial activity compared to the standard drugs, as well as Drug-likeness and pharmacokinetic characteristics were predicted. Pharmacokinetic studies indicated that most derivatives exhibit acceptable predictive ADME properties and excellent fit with the Lipinski rules. Molecular docking was used to examine the binding interactions of the most active analogues with the active site of the DNA gyrase enzyme (PDB id 1KZN). Results showed that the enhanced activity of compounds (3a, 3b, 2a) exhibited stronger docking scores binding to the active site than the Nitrofurazone (standard drug). These findings suggest that analogues (3a, 3b) can be used as the best candidates for designing and discovering novel antimicrobial agents.

A Molecular Electron Density Theory Study of the Lewis Acid Catalyzed [3+2] Cycloaddition Reactions of Nitrones with Nucleophilic Ethylenes

AbstractThe BF3Lewis acid (LA) catalyzed [3+2] cycloaddition (32CA) reaction of 1‐pyrroline‐1‐oxide (PNO) with 2,3‐dihydrofuran (DHF) has been studied within the molecular electron density theory (MEDT) at theωB97X‐D/6‐311G(d,p) computational level. Electron localization function (ELF) characterizes PNO and the corresponding PNO : BF3complex as zwitterionic species. Conceptual DFT indices allow classifying PNO and DHF as marginal electrophiles and strong nucleophiles, while the PNO : BF3complex is a strong electrophile. Consequently, while the non‐catalyzed 32CA reaction is non‐polar, the BF3catalyzed one has a high polar character, revealed by the analysis of the global electron density transfer (GEDT) at the transition state structures. The BF3catalyzed 32CA reaction, which is classified as of reverse electron density flux (REDF), presents highexostereoselectivity, and totalorthoregioselectivity. The presence of the BF3catalyst decreases the activation enthalpy of the 32CA reaction in dichloromethane by 7.5 kcal mol−1, as a consequence of the increase of the polar character of the reaction, in complete agreement with the experimentally observed acceleration.

Unveiling the non-polar [3+2] cycloaddition reactions of cyclic nitrones with strained alkylidene cyclopropanes within a molecular electron density theory study.

The role of cyclopropane substitution on the ethylene in zw-type [3+2] cycloaddition (32CA) reactions of cyclic nitrones has been studied within Molecular Electron Density Theory (MEDT) at the ωB97X-D/6-311G(d,p) computational level. Electron Localization Function (ELF) analysis of the ethylenes shows that the presence the cyclopropane only slightly increases the electron density in the C–C bonding region. Analysis of the Conceptual DFT reactivity indices indicates that the presence of the cyclopropane does not produce any remarkable change in the reactivity of these strained ethylenes. The marginal electrophilic character of ethylene makes the zw-type 32CA reactions of non-polar character. The presence of the cyclopropane in the ethylene decreases the activation enthalpy of the 32CA reactions by only 1.7 and 2.6 kcal mol−1, and also decreases the ortho regioselectivity. The loss of the strain present in the cyclopropane is responsible for the reduction of the activation enthalpy and the increase of the reaction enthalpy in these non-polar 32CA reactions. The presence of the cyclopropane does not cause any change, neither in the transition state structure (TS) geometries nor in their electronic structure. The very low global electron density transfer (GEDT) computed at the TSs confirms the non-polar character of these 32CA reactions. The ortho regioselectivity experimentally observed in these non-polar 32CA reactions is determined by the most favorable two-center interaction between the less electronegative C1 carbon of nitrone and the non-substituted methylene C5 carbon of the ethylenes.

Unveiling the intramolecular [3 + 2] cycloaddition reactions ofC,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.

Contrasting Diastereoselectivity between Cyclic Nitrones and Azomethine Ylides. Stereocontrolled Pathways to cis-anti-anti-cis-Oxazatetraquinanes from a Bicyclic Nitrone.

A study of [3 + 2] cycloaddition reactions of a bicyclic nitrone with various cyclopentenes has clarified the diastereomeric preferences as a function of the olefinic structure. It has also identified an important stereochemical difference between nitrones and the analogous azomethine ylides in [3 + 2] cycloaddition reactions.

Regio- and stereoselectivity of the [3+2] cycloaddition of nitrones with methyl-acetophenone: A DFT investigation

A theoretical study of the regio- and stereoselectivities of the [3 + 2] cycloaddition reactions of nitrones with substituted alkene (methyl acetophenone) is investigated using density functional theory (DFT) and carried out at B3LYP/6-311+G(d,p) level. The reactivity of these cycloadditions is rationalized by FMO model, activation energy calculations, and philicity indexes. The electronic populations have been calculated from natural orbital, which based on charges by using NBO analysis, MK and CHelpG electrostatic population. The four possible pathways, fused and bridged regioisomeric modes, and the two stereoisomeric approaches endo and exo for the cycloaddition reactions are analyzed and discussed. Analysis of TS geometries and bond lengths demonstrate that these reactions follow a one-step mechanism with asynchronous transition states. The activation energy indicated a favored endo approach along the four reaction pathways.

1,3-Dipolar cycloaddition of nitrones: synthesis of multisubstituted, diverse range of heterocyclic compounds

The 1,3-dipolar cycloaddition reaction of nitrone is one of the most important methods for the synthesis of different sizes of heterocycles which have enormous applications in natural products, biologically active molecules and pharmaceuticals.

Regio- and stereoselective (3 + 2)-cycloaddition reactions of nitrones with cyclic allenes.

An effective approach to access functionalized 2H-cyclonona(deca)[d]isoxazoles and 15-oxo-3,10-methanobenzo[b][1]azacyclododecines has been developed by the reaction of N-aryl-C,C-bis(methoxycarbonyl)nitrones with cyclonona(deca)-1,2-dienes in a one-pot fashion. The reaction of N-aryl-C-(phenylcarbamoyl)nitrones with these allenes proceeds strictly regioselectively giving the mixtures of diastereomeric isoxazolidines containing a double bond at the C4-position of the isoxazolidine ring. The quantum chemical calculations show that the regioselectivity of these reactions is in good agreement with the reactivity indices of the considered compounds.

Insights into the mechanism and regioselectivity of the [3 + 2] cycloaddition reactions of cyclic nitrone to nitrile functions with a molecular electron density theory perspective

A molecular electron density theory study is presented for [3 + 2] cycloaddition (32CA) reactions of 2,2-dimethyl-1-pyrroline-1-oxide with the nitrile functions to analyse the mechanism and experimentally observed regioselectivity. Electron localisation function (ELF) study predicts zwitter-ionic character of the cyclic nitrone, allowing its participation in zw-type 32CA reactions associated with high energy barrier demanding overcome through appropriate electrophilic–nucleophilic interactions. Analysis of the CDFT indices predict the global electronic flux from the strong nucleophilic nitrone to the electrophilic nitrile functions. These 32CA reactions are endergonic with reactions Gibbs free energies between 5.5 and 39.2 $$\text{kcal}{\cdot}\text{mol}^{-1}$$ in toluene. The ortho regiochemical pathway is preferred owing to the higher thermodynamic stability of the 2,3-dihydro-1,2,4-oxadiazole derivatives. The 32CA reaction of the nitrile function with carbomethoxy substituent is more facile relative to that with the phenyl substituent. Bonding evolution theory study predicts one-step mechanism with early TSs for the ortho pathway, while a one-step-two-stage mechanism is predicted for the meta reaction path, in conformity with the ELF and AIM topological studies at the TSs.

Diastereoselective thermal [3+2] cycloaddition reactions of nitrone possessing an amide functional group as hydrogen bond donor/acceptor

High diastereoselectivity in the [3+2] cycloaddition reactions of a series of maleimides with a nitrone capable of hydrogen bonding have been carried out. The cycloaddition reaction proceeded in highly diastereoselective manner leading to novel pyrrolo[3,4- d ]isoxazolidines with good yields. NMR studies revealed that in the performed cycloaddition reactions, a pair of diastereomers are formed in all cases and the cis -diastereomeric product is the favorite cycloadduct with de values up to 90%. It would appear that the presence of amide functionality at the phenyl moiety of nitrone can influence the diastereomeric ratio in the cycloaddition reactions and cis stereoselectivity is most likely dependent on the presence of this group. The nature of the cycloadddition process was interpreted in the framework of theMolecular Electron Density Theory.

Synthesis of 1,2,5‐Oxadiazinane Derivatives by Photochemical Cycloaddition of Nitrones with Diaminomethanes

Abstract1,2,5‐Oxadiazinanes have a unique heterocyclic skeleton and are expected to be applicable to the synthesis of drugs. However, there have been few reported methodologies to synthesize these structures. We report a facile synthesis of 1,2,5‐oxadiazinanes that is accomplished by the unprecedented photochemical cycloaddition reaction of nitrones with diaminomethanes. The photoreaction is a formal [3+3] cycloaddition, where a nitrone and a diaminomethane act as the 1,3‐dipole and the 1,3‐synthon, respectively. The reaction is significantly accelerated with benzophenone as a photosensitizer. A high degree of diastereoselective addition (d.r. >99 : 1) is observed in the reaction of (Z)‐N‐benzyl‐1‐phenylmethanimine oxide with di(pyrrolidin‐1‐yl)methane.

Intramolecular [3 + 2] nitrone cycloaddition reaction: highly regio and diastereoselective synthesis of bicyclo[3.2.1]octane scaffolds.

A regio and diastereoselective strategy has been developed for the synthesis of complex bicyclo[3.2.1]octane scaffolds from the reaction of readily accessible vinylogous carbonates with N-substituted hydroxylamine hydrochlorides via intramolecular 1,3-dipolar nitrone cycloaddition reaction. Wide varieties of bicyclic isoxazolidines were synthesized in high yields under catalyst free conditions through a highly efficient and operationally simple protocol.

Asymmetric [3+2] cycloaddition reaction of a chiral cyclic nitrone for the synthesis of new tropane alkaloids

The 1,3-dipolar cycloaddition of a chiral nitrone with α,β-unsaturated lactones was carried out to give the corresponding isoxazolidines. Tetrahydro-1,3-oxazines with an oxa-tropane skeleton were obtained in one step by alkylation. The structures of several of these compounds were corroborated by X-ray diffraction and molecular modelling studies confirmed the results and proposed a mechanism for their formation.

Nitrone-Modified Gold Nanoparticles: Synthesis, Characterization, and Their Potential as 18F-Labeled Positron Emission Tomography Probes via I-SPANC.

A novel bioorthogonal gold nanoparticle (AuNP) template displaying interfacial nitrone functional groups for bioorthogonal interfacial strain-promoted alkyne–nitrone cycloaddition reactions has been synthesized. These nitrone–AuNPs were characterized in detail using 1H nuclear magnetic resonance spectroscopy, transmission electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy, and a nanoparticle raw formula was calculated. The ability to control the conjugation of molecules of interest at the molecular level onto the nitrone–AuNP template allowed us to create a novel methodology for the synthesis of AuNP-based radiolabeled probes.