An overview of nitrile imine based [3+2] cycloadditions over half a decade

Chromone-isoxazole hybrids molecules: synthesis, spectroscopic, MEDT, ELF, antibacterial, ADME-Tox, molecular docking and MD simulation investigations

A mechanistic study was performed within the molecular electron density theory at the B3LYP/6-311G (d,p) computational level to explain the regioselectivity observed. An electron localization function analysis was also performed, and the results confirm the zwitterionic-type (zw-type) mechanism of the cycloaddition reactions between nitrile oxide and alkylated 4H-chromene-2-carboxylate derivatives and shed more light on the obtained regioselectivity experimentally. In silico studies on the pharmacokinetics, ADME and toxicity tests of the compounds were also performed, and it was projected that compounds 5a, 5b, 5c and 5d are pharmacokinetic and have favorable ADME profiles. Moreover, docking and molecular dynamics investigations were conducted to evaluate the interactions, orientation and conformation of the target compounds on the active sites of four distinct enzymes. The results of this investigation showed that two compounds, 5a and 5c, interacted effectively with the S. aureus active site while maintaining acceptable binding energy.Communicated by Ramaswamy H. Sarma.

A quantum mechanistic investigation into the unusual reactions of nitrilimine and nitrile oxide with 2,3,4,5-tetraphenylcyclopentadienone

CONTEXT

The theoretical study investigates the [3 + 2] cycloaddition (32CA) reactions between C, N-diphenyl nitrilimine with 2,3,4,5-tetraphenylcyclopentadienone and benzonitrile oxide with 2,3,4,5-tetraphenylcyclopentadienone. Nitrilimines and nitrile oxides are dipoles used in the synthesis of several heterocyclic compounds, including spiropyrazoline oxindoles and isoxazolines. The derivatives of these compounds are found with different biological activities, such as ion channel blockers, anti-inflammatory and anticancer agents as well as antimalarial. Conceptual density functional theory (CDFT) analysis, along with the activation energies of the 32CA reaction between C, N-diphenyl nitrilimine with 2,3,4,5-tetraphenylcyclopentadienone, demonstrates concordance with the empirical findings. The 32CA reaction is found to proceed through a very polar single-step asynchronous mechanism. While deductions from the activation energies of the 32CA reaction between benzonitrile oxide and 2,3,4,5-tetraphenylcyclopentadienone are found to lead to the experimental product, the parr function analysis could not explain the observed chemo- and regioselectivity. This 32CA reaction is also found to proceed through a one-step asynchronous mechanism, though with a non-polar character. The modulation of substituents positioned at the reactive sites of the reactants is found to influence the kinetics, thermodynamics, and CDFT parameters of the two 32CA reactions, consequently impacting the observed selectivities.

METHODS

The 32CA reactions between C, N-diphenyl nitrilimine with 2,3,4,5-tetraphenylcyclopentadienone and benzonitrile oxide with 2,3,4,5-tetraphenylcyclopentadienone have been explored theoretically using the density functional theory method at the hybrid ωB97X-D coupled with the split valence triple-ξ (TZ) basis set as implemented in the Gaussian 09. Solvent effects were taken into account by full optimization of the gas phase geometries through the polarizable continuum model developed within the self-consistent reaction field.

[3 + 2] Cycloaddition Reaction of Vinylsulfonium Salts with Hydrazonoyl Halides: Synthesis of Pyrazoles

An efficient [3 + 2] cycloaddition reaction between in situ generated nitrile imines from hydrazonoyl halides and vinylsulfonium salts is developed. The nitrile imines are demonstrated to be a new class of reaction partner for vinylsulfonium salts to conduct the [3 + 2] cycloaddition reaction. The process provides a concise and efficient method for the construction of pyrazole derivatives under mild reaction conditions with broad substrate scope, good product yields, and high regioselectivity.

(3+2)-Cycloadditions of Levoglucosenone (LGO) with Fluorinated Nitrile Imines Derived from Trifluoroacetonitrile: An Experimental and Computational Study

The in situ-generated N-aryl nitrile imines derived from trifluoroacetonitrile smoothly undergo (3+2)-cycloadditions onto the enone fragment of the levoglucosenone molecule, yielding the corresponding, five-membered cycloadducts. In contrast to the 'classic' C(Ph),N(Ph) nitrile imine, reactions with fluorinated C(CF3),N(Ar) analogues lead to stable pyrazolines in a chemo- and stereoselective manner. Based on the result of X-ray single crystal diffraction analysis, their structures were established as exo-cycloadducts with the location of the N-Ar terminus of the 1,3-dipole at the α-position of the enone moiety. The DFT computation demonstrated that the observed reaction pathway results from the strong dominance of kinetic control over thermodynamic control.

A Physical Organic Approach towards Statistical Modeling of Tetrazole and Azide Decomposition

Nitrogen atom-rich heterocycles and organic azides have found extensive use in many sectors of modern chemistry from drug discovery to energetic materials. The prediction and understanding of their energetic properties are thus key to the safe and effective application of these compounds. In this work, we disclose the use of multivariate linear regression modeling for the prediction of the decomposition temperature and impact sensitivity of structurally diverse tetrazoles and organic azides. We report a data-driven approach for property prediction featuring a collection of quantum mechanical parameters and computational workflows. The statistical models reported herein carry predictive accuracy as well as chemical interpretability. Model validation was successfully accomplished via tetrazole test sets with parameters generated exclusively in silico. Mechanistic analysis of the statistical models indicated distinct divergent pathways of thermal and impact-initiated decomposition.

Trifluoromethylated 4,5-Dihydro-1,2,4-triazin-6(1H)-ones via (3+3)-Annulation of Nitrile Imines with α-Amino Esters

The synthesis of two series of monocyclic and bicyclic trifluoromethylated 4,5-dihydro-1,2,4-triazin-6(1H)-one derivatives based on (3+3)-annulation of methyl esters derived from natural α-amino acids with in situ generated trifluoroacetonitrile imines has been described. The devised protocol is characterized by a wide scope, easily accessible substrates, remarkable functional group tolerance, and high chemical yield. In reactions with chiral starting materials, no racemization at the stereogenic centers was observed and the respective enantiomerically pure products were obtained. Selected functional group interconversions carried out under catalytic hydrogenation and mild PTC oxidation conditions were also demonstrated.

Synthesis, Characterization, DFT Mechanistic Study, Antimicrobial Activity, Molecular Modeling, and ADMET Properties of Novel Pyrazole-isoxazoline Hybrids

A series of new heterocycle hybrids incorporating pyrazole and isoxazoline rings was successfully synthesized, characterized, and evaluated for their antimicrobial responses. The synthesized compounds were obtained utilizing N-alkylation and 1,3-dipolar cycloaddition reactions, as well as their structures were established through spectroscopic methods and confirmed by mass spectrometry. To get more light on the regioselective synthesis of new hybrid compounds, mechanistic studies were performed using DFT calculations with B3LYP/6-31G(d,p) basis set. Additionally, the results of the preliminary screening indicate that some of the examined hybrids showed potent antimicrobial activity, compared to standard drugs. The results confirm that the antimicrobial activity is strongly dependent on the nature of the substituents linked pyrazole and isoxazoline rings. Furthermore, molecular docking studies were conducted to highlight the interaction modes between the investigated hybrid compounds and the Escherichia coli and Candida albicans receptors. Notably, the results demonstrate that the investigated compounds have strong protein binding affinities. The stability of the formed complexes by the binding between the hybrid compound 6c, and the target proteins was also confirmed using a 100 ns molecular dynamics simulation. Finally, the prediction of ADMET properties suggests that almost all hybrid compounds possess good pharmacokinetic profiles and no signs of observed toxicity, except for compounds 6e, 6f, and 6g.

Fluorinated and Non-Fluorinated 1,4-Diarylpyrazoles via MnO2-Mediated Mechanochemical Deacylative Oxidation of 5-Acylpyrazolines

A solvent-free two-step synthesis of polyfunctionalized pyrazoles under ball-milling mechanochemical conditions was developed. The protocol comprises (3 + 2)-cycloaddition of in situ generated nitrile imines and chalcones, followed by oxidation of the initially formed 5-acylpyrazolines with activated MnO₂. The second step proceeds via an exclusive deacylative pathway, to give a series of 1,4-diarylpyrazoles functionalized with a fluorinated (CF₃) or non-fluorinated (Ph, COOEt, Ac) substituent at C(3) of the heterocyclic ring. In contrast, MnO₂-mediated oxidation of a model isomeric 4-acylpyrazoline proceeded with low chemoselectivity, leading to fully substituted pyrazole as a major product formed via dehydrogenative aromatization. The presented approach extends the scope of the known methods carried out in organic solvents and enables the preparation of polyfunctionalized pyrazoles, which are of general interest in medicine and material sciences.

Regioselective Synthesis of 5-Trifluoromethyl 1,2,4-Triazoles via [3 + 2]-Cycloaddition of Nitrile Imines with CF3CN

We herein describe a general approach to 5-trifluoromethyl 1,2,4-triazoles via the [3 + 2]-cycloaddition of nitrile imines generated in situ from hydrazonyl chloride with CF₃CN, utilizing 2,2,2-trifluoroacetaldehyde O-(aryl)oxime as the precursor of trifluoroacetonitrile. Various functional groups, including alkyl-substituted hydrazonyl chloride, were tolerated during cycloaddition. Furthermore, the gram-scale synthesis and common downstream transformations proved the potential synthetic relevance of this developed methodology.