Ruthenium-Catalyzed Nitro and Nitrile Compounds Coupling with Alcohols: Alternative Route for N-Substituted Amine Synthesis

NNO Pincer-Supported Pd(II)-Catalyzed Reductive N-Alkylation of Challenging Nitroarenes with Alcohols via Borrowing Hydrogen Strategy

A sustainable catalytic synthesis of selective monoalkylated amines from nitroarenes and alcohols by new palladium(II)-NNO pincer-type complexes has been described. Herein, a series of Pd(II) complexes [Pd(NNO)PPh3] (1-3) are synthesized and characterized by analytical and spectroscopic (IR, NMR, and HR-MS) methods. The solid-state molecular structures of two complexes are established by X-ray single-crystal diffraction. Furthermore, the catalytic N-alkylation of challenging nitroarenes with primary and secondary alcohols has been performed by the well-defined palladium(II) complexes via borrowing hydrogen strategy. The current protocol offers a wide range of monoalkylated amines (26 examples) with a maximum yield of 87% utilizing 1 mol % of catalyst loading. Gratifyingly, the catalytic system works well under mild reaction conditions and atom economy with water is the only byproduct. Furthermore, control experiments confirm the formation of probable intermediates (aniline, aldehyde, and imine), and deuterium labeling authenticates the borrowing hydrogen mechanism. A gram-scale synthesis of an alkylated product clearly demonstrates the synthetic efficacy of the present catalytic methodology.

Polyoxometalate-Driven Ease Conversion of Valuable Furfural to trans-N,N-4,5-Diaminocyclopenten-2-ones

We investigated the catalytic efficacy of silicotungstic acid (H₄SiW₁₂O₄₀) polyoxometalate (POM) toward the reaction between furfural and amines that selectively yields trans-N,N-4,5-substituted-diaminocyclopenten-2-ones (trans-DACPs). H₄SiW₁₂O₄₀ facilitates the synthesis of a library of trans-DACPs with loadings as low as 0.05 mol %, in open air, without additives, in short times and good to high isolated yields. The protocol was applied to secondary amines as well as to aromatic primary amines with pK_b higher than ca. 9. The present catalytic synthetic protocol has an extended substrate scope with high yields and represents, to the best of our knowledge, the first polyoxometalate-driven paradigm as an efficient method to produce cyclopentanone frameworks under mild reaction conditions.

Switching Selectivity in Copper-Catalyzed Transfer Hydrogenation of Nitriles to Primary Amine-Boranes and Secondary Amines under Mild Conditions

A simple and efficient copper-catalyzed selective transfer hydrogenation of nitriles to primary amine-boranes and secondary amines with an oxazaborolidine-BH₃ complex is reported. The selectivity control was achieved under mild conditions by switching the solvent and the copper catalysts. More than 30 primary amine-boranes and 40 secondary amines were synthesized via this strategy in high selectivity and yields of up to 95%. The strategy was applied to the synthesis of ¹⁵N labeled in 89% yield.

Tandem imine formation via auto-hydrogen transfer from alcohols to nitro compounds catalyzed by a nanomagnetically recyclable copper catalyst under solvent-free conditions

A direct imination reaction was developed by tandem reaction of alcohols and nitro compounds in the presence of Cu-isatin Schiff base-γ-Fe₂O₃ as a nanomagnetically recyclable catalyst under solvent-free conditions. By this method, various imines were prepared in good to high yields from one-pot reaction of various alcohols (primary aromatic and aliphatic) and nitro compounds (aromatic and aliphatic) via an auto-hydrogen transfer reaction. Use of an inexpensive and easily reusable catalyst, without requiring any additives or excess amounts of benzyl alcohol as the reaction solvent are the other advantages of this method. This catalytic system has the merits of cost effectiveness, environmental benignity, excellent recyclability and good reproducibility.

A direct imination reaction was developed by tandem reaction of alcohols and nitro compounds in the presence of Cu-isatin Schiff base-γ-Fe₂O₃ as a nanomagnetically recyclable catalyst.

Cyclometalated Iridium Complex-Catalyzed N-Alkylation of Amines with Alcohols via Borrowing Hydrogen in Aqueous Media

This paper develops a methodology for cyclometalated iridium complex-catalyzed N-alkylation of amines with alcohols via borrowing hydrogen in the aqueous phase. The cyclometalated iridium catalyst-mediated N-alkylation of amines with alcohols displays high activity (S/C up to 10,000 and yield up to 96%) and ratio of amine/imine (up to >99:1) in a broad range of substrates (up to 46 examples) using water as the green and eco-friendly solvent. Most importantly, this transformation is simple, efficient, and can be performed at a gram scale, showcasing its potential for industrially synthesizing N-alkylamine compounds.

Tandem transformations and multicomponent reactions utilizing alcohols following dehydrogenation strategy

In this review, the progress of tandem transformation of nitro, nitrile and azide functionalities is summarised to develop new C–C and C–N bonds as well as multi-component reactions using alcohols.

Biomolecule-Mediated Generation of Ru Nanocatalyst for Sustainable Reduction of Nitrobenzene

A mild and sustainable synthetic route was followed for the generation of biomolecule-assisted Ru nanocatalyst under open as well as inert atmosphere using the polyphenol morin. The nanocatalyst was characterized thoroughly by powder X-ray diffraction, N₂ adsorption-desorption, high-resolution transmission electron microscopy, dynamic light scattering, X-ray photoelectron spectroscopy, absorption spectroscopy, Fourier transform infrared spectroscopy, fluorescence spectroscopy, thermogravimetric analysis, and inductively coupled plasma optical emission spectrometry. The nanocatalyst reveals excellent catalytic activity for the reduction of several substituted nitrobenzene to aniline derivatives under simple, mild, and environment-friendly conditions. The catalyst can be reused for four consecutive cycles without significant loss in its catalytic activity.

Copper-Catalyzed Redox Coupling of Nitroarenes with Sodium Sulfinates

A simple copper-catalyzed redox coupling of sodium sulfinates and nitroarenes is described. In this process, abundant and stable nitroarenes serve as both the nitrogen sources and oxidants, and sodium sulfinates act as both reactants and reductants. A variety of aromatic sulfonamides were obtained in moderate to good yields with broad substrate scope. No external additive is employed for this kind of transformation.

Tandem Transformation of Nitro Compounds into N-Methylated Amines: Greener Strategy for the Utilization of Methanol as a Methylating Agent

A simple air- and moisture-stable, highly efficient ruthenium NNN pincer complex is reported for the first time to catalyze the tandem transformation of various aromatic and aliphatic nitro compounds into the corresponding N-methylated amines in up to 98 % yield by using methanol as a green methylating agent. Gram-scale reactions of challenging nitro substrates demonstrated the practical application aspects of this catalytic system. Importantly, the N-methylamine moiety could be smoothly introduced to various complex molecular structures without using any expensive palladium/phosphine/amine-based cross-coupling reactions.

Supported bimetallic nano-alloys as highly active catalysts for the one-pot tandem synthesis of imines and secondary amines from nitrobenzene and alcohols

All-in-one: supported nanoalloys as efficient heterogeneous catalysts for the one-pot synthesis of imines and secondary amines directly from nitrobenzene and benzylic alcohols using a hydrogen auto transfer strategy.

Palladium-catalyzed N-arylsulfonamide formation from arylsulfonyl hydrazides and nitroarenes

Various N-arylsulfonamides were prepared from nitroarenes and arylsulfonyl hydrazides via hydrogen transfer methodology.

Catalyst-free reductive amination of aromatic aldehydes with ammonium formate and Hantzsch ester

The protocol of the reductive amination of aromatic aldehydes using ammonium formate and Hantzsch ester is described. It is a mild, convenient, acid- and catalyst-free system applied for the synthesis of both symmetric and asymmetric aromatic secondary amines.

One-pot synthesis of secondary amines from alcohols and nitroarenes on TiO2 loaded with Pd nanoparticles under UV irradiation

TiO₂ loaded with Pd nanoparticles, when irradiated by UV light in alcohols with nitroarenes, successfully produces the corresponding secondary amines with almost quantitative yield, via tandem photocatalytic and catalytic reactions.

Substitution of alcohols by N-nucleophiles via transition metal-catalyzed dehydrogenation

This review summarizes the recent advances in transition metal-catalyzed dehydrogenative substitution of alcohols by N-nucleophiles since 2009.

Supported gold-catalyzed and ammonia-promoted selective synthesis of quinazolines in aqueous media

A highly efficient and selective synthesis of 2,4-disubstituted quinazolines via a hydrogen-transfer strategy was developed under the catalysis of nano-Au/TiO₂ and the assistance of nitrogen source-promotion.

Palladium-catalyzed one pot 2-arylquinazoline formation via hydrogen-transfer strategy

The palladium catalytic system was first applied to 2-arylquinazoline synthesis via hydrogen transfer methodology. Various (E)-2-nitrobenzaldehyde O-methyl oximes reacted easily with alcohols or benzyl amines to provide N-heterocyclic compounds in good to high yields. Similarly, the heterocyclic products could be prepared by the reaction of 1-(2-nitrophenyl)ethanone, urea and benzyl alcohols. In these reactions, the nitro group was reduced in situ by hydrogen generated from the alcohol dehydrogenation step.

Chlorine as an indicator in the controllable preparation of active nano-gold catalyst

The controllable preparation of nano-gold catalyst maintains a challenge. Except the parameters have been revealed before, here we'd like to show that controllable preparation of active nano-gold catalyst can be achieved using chlorine as an indicator. By tracing the chlorine concentration in the washing step, a series of Au/Fe₂O₃ catalysts were prepared with co-precipitation method. The applying of these catalysts in CO oxidation and reductive nitrobenzene N-alkylation suggested the active catalysts were prepared from solutions containing ~2 ppm chlorine. The catalytic activity dropped dramatically if the chlorine concentration is >4–6 or ≪1 ppm. Extensive characterizations revealed that the active catalyst was composed by nano-gold on the edge of Fe₂O₃ particle with 8.92 Au-Au coordination numbers. Although the real role of chlorine in the variation of catalyst structure and activity was still ambiguous, the current results should promote the controllable preparation of active nano-Au catalyst.

Ultrasounds in melted poly(ethylene glycol) promote copper-catalyzed cyanation of aryl halides with K(4)[Fe(CN)(6)]

Melted poly(ethylene glycols) (PEGs) were used for the first time as solvent for the sonochemically promoted cyanation of aryl halides employing inexpensive and safe K4[Fe(CN)6] and a relatively low amount of Cu-based catalyst. The Mw (weight-average polymer molecular weight) of PEG proved to notably influence the substrate conversion, which is indicative of a strong dependence of the sonication efficacy on solvent properties. Gel permeation chromatography (GPC), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) contributed to the characterization of the polymer and the elucidation of the catalytic system.

Ultrasound-assisted solventless synthesis of amines by in situ oxidation/reductive amination of benzyl halides

Ultrasound-assisted solventless oxidation/reductive amination of benzyl halides was developed as a facile, efficient, and environmentally friendly method toward N-alkylated amines.

Rapid and efficient access to secondary arylmethylamines

Ammoniomethyl trifluoroborates are very powerful reagents that can be used to access biologically relevant aryl- and heteroaryl-methylamine motifs via Suzuki-Miyaura cross-couplings. Until now, this method was limited to the production of tertiary and primary amines. The synthesis of a large array of secondary ammoniomethyltrifluoroborates has been achieved through a one step nucleophilic substitution reaction on the potassium bromomethyltrifluoroborate. Smooth cross-coupling conditions have been designed, based on the use of an aminobiphenyl palladium precatalyst, to couple these trifluoroborates efficiently with aryl bromides. This strategy offers a new way to access biologically relevant motifs and allows, with the previously developed methods, access to all three classes of aminomethylarenes.