Steric-Hindrance-Induced Regio- and Chemoselective Oxidation of Aromatic Amines

Controllable Selective Oxidation of Anilines to Azoxybenzenes and Nitrobenzenes by Regulating the Base

The importance of selectively oxidizing aniline into value-added chemicals azoxybenzene and nitrobenzene is well-recognized in organic synthesis. However, the lack of control over selectivity and the complex synthesis of costly catalysts significantly hinder these reactions' industrial applications. In this work, an environmentally friendly approach was developed for the selective oxidization of substituted anilines. This method involves adjusting the strength of alkalinity with peroxide as the oxidant, without the addition of any metals or additives. A mild base (NaF) facilitated azoxybenzene formation, while a stronger base (NaOMe) enabled the synthesis of nitroaromatics. These protocols are user-friendly and scalable, accommodating various substitution patterns and functional groups, yielding products with high to excellent yields. The findings of this work present a framework for investigating base catalysis in organic synthesis and provide a viable and effective approach for selectively oxidizing aniline.

Site-Selective Nitration of Aryl Germanes at Room Temperature

We report a site-selective ipso-nitration of aryl germanes in the presence of boronic esters, silanes, halogens, and additional functionalities. The protocol is characterized by operational simplicity, proceeds at room temperature, and is enabled by [Ru(bpy)3](PF6)2/blue light photocatalysis. Owing to the exquisite robustness of the [Ge] functionality, nitrations of alternative functional handles in the presence of the germane are also feasible, as showcased herein.

Reusable Cobalt-Catalyzed Selective Transfer Hydrogenation of Azoarenes and Nitroarenes

Herein, control transfer hydrogenation (TH) of azoarenes to hydrazo compounds is established employing easy-to-synthesize reusable cobalt catalyst using lower amounts of N₂H₄·H₂O under mild conditions. With this effective methodology, a library of symmetrical and unsymmetrical azoarene derivatives was successfully converted to their corresponding hydrazo derivatives. Further, this protocol was extended to the TH of nitroarenes to amines with good-to-excellent yields. Several kinetic studies along with Hammett studies were carried out to understand the plausible mechanism and the electronic effects in this transformation. This inexpensive catalyst can be recycled up to five times without considerable loss of catalytic activity.

3-Substituted Blatter Radicals: Cyclization of N-Arylguanidines and N-Arylamidines to Benzo[e][1,2,4]triazines and PhLi Addition

A series of 3-amino- and 3-alkyl-substituted 1-phenyl-1,4-dihydrobenzo[e][1,2,4]triazin-4-yls was prepared in four steps involving N-arylation, cyclization of N-arylguanidines and N-arylamidines, reduction of the resulting N-oxides to benzo[e][1,2,4]triazines, and subsequent addition of PhLi followed by aerial oxidation. The resulting seven C(3)-substituted benzo[e][1,2,4]triazin-4-yls were analyzed by spectroscopic and electrochemical methods augmented with density functional theory (DFT) methods. Electrochemical data were compared to DFT results and correlated with substituent parameters.

Synthesis of Nitroarenes by Oxidation of Aryl Amines

Nitro compounds are an important class of organic molecules with broad application in organic synthesis, medicinal chemistry, and materials science. Among the variety of methodologies available for their synthesis, the direct oxidation of primary amines represents an attractive alternative route. Efforts towards the development of oxidative procedures for the synthesis of nitro derivatives have spanned over the past decades, leading to a wide variety of protocols for the selective oxidative conversion of amines to nitro derivatives. Methods for the synthesis of nitroarenes via oxidation of aryl amines, with particular emphasis on recent advances in the field, are summarised in this review.

Selective Mild Oxidation of Anilines into Nitroarenes by Catalytic Activation of Mesoporous Frameworks Linked with Gold-Loaded Mn3 O4 Nanoparticles

This work reports the synthesis and catalytic application of mesoporous Au-loaded Mn3 O4 nanoparticle assemblies (MNAs) with different Au contents, i. e., 0.2, 0.5 and 1 wt %, towards the selective oxidation of anilines into the corresponding nitroarenes. Among common oxidants, as well as several supported gold nanoparticle platforms, Au/Mn3 O4 MNAs containing 0.5 wt % Au with an average particle size of 3-4 nm show the best catalytic performance in the presence of tert-butyl hydroperoxide (TBHP) as a mild oxidant. In all cases, the corresponding nitroarenes were isolated in high to excellent yields (85-97 %) and selectivity (>98 %) from acetonitrile or greener solvents, such as ethyl acetate, after simple flash chromatography purification. The 0.5 % Au/Mn3 O4 catalyst can be isolated and reused four times without a significant loss of its activity and can be applied successfully to a lab-scale reaction of p-toluidine (1 mmol) leading to the p-nitrotulene in 83 % yield. The presence of AuNPs on the Mn3 O4 surface enhances the catalytic activity for the formation of the desired nitroarene. A reasonable mechanism was proposed including the plausible formation of two intermediates, the corresponding N-aryl hydroxylamine and the nitrosoarene.

Hypervalent iodine(iii) induced oxidative olefination of benzylamines using Wittig reagents

We have developed hypervalent iodine mediated oxidative olefination of 1° and 2° amines using 2C-Wittig reagents for the synthesis of α,β-unsaturated esters.

Total Syntheses of (-)-Minovincine and (-)-Aspidofractinine through a Sequence of Cascade Reactions

We report 8‐step syntheses of (−)‐minovincine and (−)‐aspidofractinine using easily available and inexpensive reagents and catalyst. A key element of the strategy was the utilization of a sequence of cascade reactions to rapidly construct the penta‐ and hexacyclic frameworks. These cascade transformations included organocatalytic Michael‐aldol condensation, a multistep anionic Michael‐S_N2 cascade reaction, and Mannich reaction interrupted Fischer indolization. To streamline the synthetic routes, we also investigated the deliberate use of steric effect to secure various chemo‐ and regioselective transformations.

Mechanism-based structure-activity relationship (SAR) analysis of aromatic amines and nitroaromatics carcinogenicity via statistical analyses based on CPDB

Cancer is a leading cause of human mortality around the globe. In this study, mechanism-based SAR (Structure-Activity Relationship) was employed to investigate the carcinogenicity of aromatic amines and nitroaromatics based on CPDB. Principal component analysis and cluster analysis were used to construct the SAR model. Principle component analysis generated three principal components from 12 mechanism-based descriptors. The extracted principal components were later used for cluster analysis, which divided the selected 55 chemicals into six clusters. The three principal components were proposed to describe the "transport", "reactivity" and "electrophilicity" properties of the chemicals. Cluster analysis indicated that the relevant "transport" properties positively correlated with the carcinogenic potential and were contributing factors in determining the carcinogenicity of the studied chemicals. The mechanism-based SAR analysis suggested the electron donating groups, electron withdrawing groups and planarity are significant factors in determining the carcinogenic potency for studied aromatic compounds. The present study may provide insights into the relationship between the three proposed properties and the carcinogenesis of aromatic amines and nitroaromatics.

Novel 8-nitroquinolin-2(1H)-ones as NTR-bioactivated antikinetoplastid molecules: Synthesis, electrochemical and SAR study

To study the antiparasitic 8-nitroquinolin-2(1H)-one pharmacophore, a series of 31 derivatives was synthesized in 1-5 steps and evaluated in vitro against both Leishmania infantum and Trypanosoma brucei brucei. In parallel, the reduction potential of all molecules was measured by cyclic voltammetry. Structure-activity relationships first indicated that antileishmanial activity depends on an intramolecular hydrogen bond (described by X-ray diffraction) between the lactam function and the nitro group, which is responsible for an important shift of the redox potential (+0.3 V in comparison with 8-nitroquinoline). With the assistance of computational chemistry, a set of derivatives presenting a large range of redox potentials (from -1.1 to -0.45 V) was designed and provided a list of suitable molecules to be synthesized and tested. This approach highlighted that, in this series, only substrates with a redox potential above -0.6 V display activity toward L. infantum. Nevertheless, such relation between redox potentials and in vitro antiparasitic activities was not observed in T. b. brucei. Compound 22 is a new hit compound in the series, displaying both antileishmanial and antitrypanosomal activity along with a low cytotoxicity on the human HepG2 cell line. Compound 22 is selectively bioactivated by the type 1 nitroreductases (NTR1) of L. donovani and T. brucei brucei. Moreover, despite being mutagenic in the Ames test, as most of nitroaromatic derivatives, compound 22 was not genotoxic in the comet assay. Preliminary in vitro pharmacokinetic parameters were finally determined and pointed out a good in vitro microsomal stability (half-life > 40 min) and a 92% binding to human albumin.

Metal-free hypervalent iodine/TEMPO mediated oxidation of amines and mechanistic insight into the reaction pathways

A highly efficient metal free approach for the oxidation of primary and secondary amines to their corresponding aldehydes and ketones using PhI(OAc)₂ in combination with a catalytic amount of TEMPO as an oxidizing agent is described. This protocol is rapid and provides diverse products under milder reaction conditions in excellent yields. In addition, the mechanistic study is well demonstrated by spectroscopic methods.

A highly efficient, metal free rapid protocol studied mechanistically the oxidation of primary and secondary amines to their corresponding carbonyl compounds using PhI(OAc)₂ and catalytic TEMPO to provide diverse products in excellent yields.

NH4I/tert-Butyl Hydroperoxide-Promoted Oxidative C–N Cleavage of Tertiary Amines Leading to Nitroaromatic Compounds

A NH4I/ tert-butyl hydroperoxide-promoted oxidation of tertiary N-aryl- N,N-dialkylamines in DMSO has been developed to access nitroaromatic compounds. This methodology involves sequential N-dealkylation reactions in one-pot and a radical pathway is proposed.

Amberlyst-15 catalysed oxidative esterification of aldehydes using a H2O2 trapped oxidant as a terminal oxidant

A simple and efficient method has been developed for the selective oxidative esterification of aldehydes using commercially available Amberlyst-15 as a catalyst.

Nonanebis(peroxoic acid) mediated efficient and selective oxidation of sulfide

Metal free, chemoselective oxidation of sulfide using aliphatic diperoxyacid.

Copper-catalyzed rapid C–H nitration of 8-aminoquinolines by using sodium nitrite as the nitro source under mild conditions

We report the first example of copper(ii) catalyzed remote C–H nitration of 8-aminoquinoline amides by using sodium nitrite as nitration reagent under mild conditions in 1 minute which undergoes single electron process.