Synthesis Of Nitrones Research Articles

Palladium-Catalyzed Synthesis of Nitrones Via Redox Cross-Coupling of Nitro Compounds and Alcohols.

A novel methodology for the synthesis of nitrones via palladium-catalyzed redox cross-coupling of nitro compounds and alcohols is established. The protocol is a mild, convenient, ligand-free, and scalable synthesis method that can be compatible with various nitro compounds and alcohols. Nitrone is a significant multifunctional platform synthon which can be synthesized directly and efficiently via this tactic from commercially available and cheap raw materials.

Synthesis of Nitrones and Nitroalkanes via Chiral Cyclic Imines.

A series of structurally chiral cyclic imines efficiently yields chiral nitrones and nitroalkanes. This is the first report of the synthesis of nitro groups by C═N bond cleavage of imines through a nitrone intermediate.

Recent Advances in the Direct N–C(sp2) Nitrone Synthesis from Oxime

Nitrones are pivotal in organic chemistry, especially for the synthesis of natural and biologically active compounds via 1,3‐dipolar cycloadditions and Kinugasa reactions. Although numerous methods have been reported for the synthesis of nitrones with an sp3 carbon connected to a nitrogen atom, the development of nitrones with an sp2 carbon linkage, including N‐vinyl, N‐aryl, and N‐alkoxycarbonyl nitrones, remains relatively underexplored. This review summarizes the current research trends and methodologies for the direct synthesis of nitrones, in which an sp2 carbon is directly bonded to a nitrogen atom, beginning with oximes.

Gold-catalyzed carbocyclization and imidization of alkyne-tethered diazo compounds with nitrosoarenes for the synthesis of nitrones and naphthalene derivatives.

A gold-catalyzed carbocyclization/imidization cascade reaction has been developed,leading a facile access to the synthesis of functionalized nitrones in moderate to good yields under mild conditions. The reaction initiated by a catalytic 6-endo-dig diazo-yne carbocyclization to form the key endocyclic vinyl carbene from alkyne-tethered diazo compounds, followed by addition with nitrosoarenes that features an imidization process. Notably, these resulting nitrone products could be smoothly converted into different substituted naphthalenol analogues, such as 4-aminonaphthalen-1-ol, naphthalene-1,4-dione, and naphthalene-1,4-diol derivatives, in high yields. Moreover, the generated products exhibited potential tumor suppression activity in tested cancer celllines; compound 3c (HCT116 cells, IC50 = 7.41μM; MCF-7 cells, IC50 = 14.28μM) exhibits higher anticancer potency than other tested compounds.

Access to Nitrones from Amines via Electrocatalysis at Room Temperature

AbstractA self‐enabled electrooxidative protocol for the synthesis of nitrones from bench stable amines has been developed under constant current electrolysis at room temperature, rendering metal and external oxidant‐free protocol in an alkaline medium. The electrocatalysis steps of reported strategy involve anodic oxidation of benzyl amines followed by cathodic reduction of nitro‐functional group in an undivided cell affording functional nitrones. The robustness of the electrocatalysis was reflected by tolerant substrate scope, oxidant‐free conditions, and an operationally friendly procedure. Moreover, the cyclic voltammetry and control experiment studies also support the electrochemical process in alkaline medium.magnified image

Visible-light-promoted nitrone synthesis from nitrosoarenes under catalyst- and additive-free conditions.

A green and sustainable nitrone formation reaction via visible-light-promoted reaction of aryl diazoacetates with nitrosoarenes is described. This protocol exhibits good functional group tolerance and broad substrate scope for both aryl diazoacetates with nitrosoarenes. Comparing the reported methods for the synthesis of nitrones from nitrosoarenes, the reaction described herein occurs under sole visible-light irradiation without the need of any catalysts and additives.

C−H Activation and Cross‐Coupling of Acyclic Aldonitrone

AbstractPalladium‐catalyzed activation of C(sp2)−H bond in a readily E,Z‐isomerizable aldonitrone, bearing an ester group at the C terminus, enabled its cross‐coupling with a variety of aryl and heteroaryl bromides to give ketonitrones, including products with functional groups not compatible with the classical nitrone synthesis via condensation with hydroxylamines. The reactions proceeded with very high (usually complete) E selectivity. The key to obtaining good yields of the cross‐coupling products was the use of sterically hindered carboxylic acid as additive and non‐polar solvent (toluene), in which the starting nitrone exists mainly as E isomer. Further use of the obtained ketonitrones in dipolar cycloaddition or nucleophilic addition has also been demonstrated.

Application of Photochemical Synthesis of Nitrone under Continuous Flow in Undergraduate Laboratory Teaching

Application of Photochemical Synthesis of Nitrone under Continuous Flow in Undergraduate Laboratory Teaching

Synthesis of Novel Cyclic Nitrones with gem‐Difluoroalkyl Side Chains Through Cascade Reactions

New five‐membered cyclic nitrones with gem‐difluoroalkyl groups in γ‐position have been prepared by a 3‐step sequence starting from propargylic alcohols. This domino process involves a base‐mediated isomerization reaction to enones, which are trapped in situ by nitroalkane anions. In a final step, starting from these key precursors, a reduction‐cyclization process affords the target molecules. Mono‐ and bicyclic nitrones have been prepared by this route which allows, as well, the synthesis of nitrones with functional groups in terminal position of the side chain.

Rhodium(III)‐Catalyzed Asymmetric Access to Spirocycles through C−H Activation and Axial‐to‐Central Chirality Transfer

AbstractAxial‐to‐central chirality transfer is an important strategy to construct chiral centers, where the axially chiral reagents are mostly limited to atropomerically stable ones. Reported herein is a RhIII‐catalyzed enantioselective spiroannulative synthesis of nitrones. The coupling proceeds via C−H arylation to give an atropomerically metastable biaryl, followed by intramolecular dearomative trapping under oxidative conditions with high degree of chirality transfer.

Rhodium(III)-Catalyzed Asymmetric Access to Spirocycles through C-H Activation and Axial-to-Central Chirality Transfer.

Axial-to-central chirality transfer is an important strategy to construct chiral centers, where the axially chiral reagents are mostly limited to atropomerically stable ones. Reported herein is a RhIII -catalyzed enantioselective spiroannulative synthesis of nitrones. The coupling proceeds via C-H arylation to give an atropomerically metastable biaryl, followed by intramolecular dearomative trapping under oxidative conditions with high degree of chirality transfer.

Preparation and Characterization of Acetic Acid-Functionalized Fe3O4@SiO2 Nanoparticles as an Efficient Nanocatalyst for the Synthesis of Nitrones in Water

Magnetic materials grafted with acetic acid (Fe3O4@SiO2COOH MNPs) were successfully prepared from the incorporation of bromoacetic acid as a functional group on the surface of magnetite silica nanoparticles. The catalyst has been characterized by Fourier transform infrared spectroscopy, X-ray diffraction, elemental analysis, energy-dispersive X-ray spectroscopy, thermogravimetric analysis, scanning electron microscopy and transition electron microscopy. Next, the efficiency of this acid catalyst was examined for the synthesis of the nitrones from diaminoglyoxime in the water at room temperature. The present approach provides several advantages such as environmentally benign, excellent yields, straightforward, short reaction times, good recyclability of catalyst, cost-effective and facile catalyst separation for the preparation of nitrones compounds as an important privileged medicinal scaffold.

A green synthesis of nitrones in glycerol

An eco-friendly and efficient synthesis of nitrones is presented by condensation of an equimolar amount of aldehydes and N-substituted hydroxylamine hydrochlorides in glycerol as a recyclable solvent-catalyst. This novel protocol provides rapid and mild access to a series of nitrone derivatives in good to excellent yields in the absence of catalyst and base. SYNOPSIS In this study, a base-free protocol by using glycerol as the solvent-catalyst was applied for an eco-friendly synthesis of nitrones from the condensation of aldehydes and N-substituted hydroxylamine hydrochlorides.

Direct Synthesis of Nitrones via Transition-Metal-Free Ring-Opening of N-Tosylaziridines with the Nitrogen Atom of Various (E)-Aldoximes and (E)-Ketoximes

The KOH-, K2CO3-, or Et3N-catalyzed ring-opening reaction of N-tosylaziridines using the nitrogen atom of a series of (E)-aldoximes and (E)-ketoximes as a nucleophilic atom instead of an oxygen atom was developed to construct various nitrones under mild reaction conditions. Diverse (E)-aldoximes and (E)-ketoximes were demonstrated to be compatible with this reaction and the products of O-ring-opening reactions were not detected for most examples.

Nitrone Synthesis via Pair Electrochemical Coupling of Nitro-Compounds with Benzyl Alcohol Derivatives.

Here we report a paired electrochemical coupling of readily accessible nitro-compounds with benzyl alcohols to yield nitrone derivatives. In this work, electrochemical behavior of nitrobenzene and benzyl alcohol derivatives was studied by cyclic voltammetry and controlled potential coulommetry. Electrochemical reactions have been performed in aqueous/ethanol (or acetonitrile)solutions by employing common graphite electrodes and a simple controlled current protocol which can make this strategy more appealing than other conventional pathways.

Semi-synthesis of a novel hybrid isoxazolidino withaferin via chemoselective and diastereoselective 1,3-dipolar nitrone cycloaddition reaction

A facile, atom-economic synthesis of isoxazilidino withaferin, a novel hybrid of withaferin A, has been accomplished via two-step reaction of nitrone synthesis followed by nitrone 1,3-dipolar cycloaddition. The reaction is highly chemoselective (preferential reaction only on one of the two double bonds present on withaferin A) and diastereoselective affording exclusively the cis-fused products. The structure was determined by detailed analysis of 1D, 2D NMR and mass spectral data.

Synthesis and Transformations of Nitrones for Organic Synthesis.

Nitrones are important compounds and are highly useful in many aspects. The first part describes the methods for synthesis of nitrones, which are useful and environmentally friendly. Catalytic oxidations, condensations, and other useful reactions are described. The nitrones thus obtained are key intermediates for the synthesis of biologically important nitrogen compounds. The second part describes the fundamental transformations of nitrones, which will provide the strategies and means for the construction of nitrogen compounds. The reactions with nucleophiles or radicals, C-H functionalization, and various addition reactions are described. The last reactions are particularly important for highly selective carbon-carbon bond formations. 1,3-Dipolar cycloaddition reactions are excluded because the size of the review is limited and excellent reviews have been published in Chemical Reviews.

Visible-light-initiated one-pot clean synthesis of nitrone from nitrobenzene and benzyl alcohol over CdS photocatalyst

The controlled visible-light mediated conversion of nitroaromatics to versatile nitrogen-containing intermediates is of great significance but still remains a challenge. Herein, we report for the first time a facile visible-light-initiated one-pot strategy for clean and efficient synthesis of nitrone from nitrobenzene and benzyl alcohol. It integrates the controlled photocatalytic reduction of nitrobenzene to phenylhydroxylamine by photogenerated electrons with the selective photocatalytic oxidation of benzyl alcohol to benzaldehyde by photoinduced holes over a low-cost CdS photocatalyst with a suitable reduction capability, followed by spontaneous condensation of the as-formed hydroxylamine and aldehyde at ambient pressure and room temperature. Furthermore, by modulating cocatalyst and illumination time, for the conversion of the same reactants, the other two useful nitrogen-containing compounds, imine and secondary amine, were also successfully synthesized. The reaction mechanisms for flexible synthesis of the three target products are proposed.

Metal-free approach for the ʟ-proline mediated synthesis of nitrones from nitrosobenzene

An efficient, and metal-free approach for the ʟ-proline mediated synthesis of nitrones from nitrosobenzene and benzaldehydes has been established. The reaction undergoes very efficiently at room temperature in methanol as a solvent. The reaction is assumed to involve that the initial formation of azomethine ylide and [2 + 3] cycloaddition of nitrosobenzene, followed by the subsequent retro [2 + 3] cycloaddition could offer the desired nitrone.

Cooperative Multifunctional Catalysts for Nitrone Synthesis: Platinum Nanoclusters in Amine‐Functionalized Metal–Organic Frameworks

AbstractNitrones are key intermediates in organic synthesis and the pharmaceutical industry. The heterogeneous synthesis of nitrones with multifunctional catalysts is extremely attractive but rarely explored. Herein, we report ultrasmall platinum nanoclusters (PtNCs) encapsulated in amine‐functionalized Zr metal–organic framework (MOF), UiO‐66‐NH2 (Pt@UiO‐66‐NH2) as a multifunctional catalyst in the one‐pot tandem synthesis of nitrones. By virtue of the cooperative interplay among the selective hydrogenation activity provided by the ultrasmall PtNCs and Lewis acidity/basicity/nanoconfinement endowed by UiO‐66‐NH2, Pt@UiO‐66‐NH2 exhibits remarkable activity and selectivity, in comparison to Pt/carbon, Pt@UiO‐66, and Pd@UiO‐66‐NH2. Pt@UiO‐66‐NH2 also outperforms Pt nanoparticles supported on the external surface of the same MOF (Pt/UiO‐66‐NH2). To our knowledge, this work demonstrates the first examples of one‐pot synthesis of nitrones using recyclable multifunctional heterogeneous catalysts.