Metal Reagents Research Articles

Metal-Free Selective Air-Oxidation of Sulfides to Sulfoxides Using 2,2′-Azobis-(2,4-dimethyl-4-methoxyvaleronitrile) (V-70) and Isobutyraldehyde

AbstractSelective oxidation of sulfides to sulfoxides using ‘air’ was achieved using a combination of 2,2′-azobis-(2,4-dimethyl-4-methoxyvaleronitrile) (a radical initiator) and isobutyraldehyde (a co-oxidant). Various sulfides were successfully converted into their corresponding sulfoxides using this method. This approach promotes a sustainable oxidation process by excluding harmful oxidants, such as peroxides and metal reagents.

Improving efficiency and circularity of selective metals recovery from acid mine drainage

The mining sector in Europe is considered one of the main pillars of the economy. However, the mining activities generate a large volume of acid mine drainage containing dissolved metals, some of them with economic impact. In addition, the increasing global water scarcity makes it imperative to evaluate industrial wastewater as an alternative source for water reclamation. A treatment system based on reverse osmosis for metals concentration and water reclamation, followed by chemical precipitation for selective metals recovery, and electrodialysis with bipolar membranes for NaOH recovery and reuse is suggested in this work. The main objective is to improve the efficiency and circularity of precipitation processes by overcoming some of its main limitations, namely metal ions concentration and reagent consumption. The treatment system yielded promising results as 97 % of the water was recovered as reclaimed water, targeted metals (Al, Zn, Cu, Mn, Mg, and Ca) were selectively recovered at rates greater than 60 %, and up to 58 % of NaOH was recovered, potentially reusable in the precipitation process.

Acid-Promoted Self-Photocatalyzed Regioselective Oxidation: A Novel Strategy for Accessing Quinoxaline-2,3-diones.

Disclosed here is an efficient approach for the preparation of quinoxaline-2,3-diones using air (O2) as a green oxidant via acid-promoted self-photocatalyzed regioselective oxidation of quinoxalin-2(1H)-ones at C-3 position. This protocol presents a novel synthetic route for the preparation of quinoxaline-2,3-dione derivatives, featuring mild reaction conditions, simple operation, and a wide range of substrates, without the need for external photocatalysts, metal reagents, and strong oxidants.

Photogeneration of β-Borylsilyl Radical via Decarboxylation of N-Hydroxyphthalimide Esters.

Gem-borylsilylalkanes are versatile intermediates in organic synthesis, and the traditional synthesis methods have mainly focused on metal reagents, the insertion reactions of diazo compounds, and hydrosilylation/hydroborylation reactions of unsaturated bonds. Herein, a novel, efficient gem-borylsilylalkanes synthesis via a radical approach is reported. This method introduced a β-gem-borylsilyl NHPI ester as the precursor of the β-borylsilyl radical that, coupling with radical acceptors under photo conditions, and the corresponding gem-borylsilylalkanes bearing unsaturated bonds, facilitate subsequent transformations.

Transition metal-free thiophene construction in pure water by multiplied C-H functionalization with enaminones and elemental sulfur

A novel method for the synthesis of 2,4-disubstituted thiophenes via the reactions of N,N-disubstituted enaminones and elemental sulfur is developed. By simply heating the substrates in pure water in the presence of NaOH, the thiophene annulation practically takes place via the generation of one C-C and two C-S bonds via cascade dual C-H functionalization and C-N bond thiolation without using any transition metal reagent.

Copper(I) Iodide-Catalyzed Perfluoroalkoxylation Reaction of Alkyl Halides.

We report an efficient perfluoroalkoxylation reaction of alkyl halides catalyzed by copper(I) iodide (CuI), which facilitates the simultaneous activation of both perfluoroalkoxide and alkyl halides. This methodology is tolerant of a wide range of functional groups and eliminates the need for costly metal reagents. The reaction is conducted in a single step under mildly practical conditions.

Efficacy of radical reactions of isocyanides with heteroatom radicals in organic synthesis.

Isocyanide is a promising synthetic reagent not only as a one-carbon homologation reagent but also as a nitrogen source for nitrogen-containing molecules. Because of their isoelectronic structure with carbon monoxide, isocyanides also react with nucleophiles, electrophiles, carbon radicals, and transition metal reagents, and are widely used in organic synthesis. On the other hand, the use of isocyanides in reactions with heteroatom radicals is limited. However, the reaction of isocyanides with heteroatom radicals is a promising synthetic tool for the construction of nitrogen-containing organic molecules modified with a variety of heteroatoms. In this Perspective, we review the addition and cyclization reactions of heteroatom radicals with isocyanides and discuss the synthetic prospects of the reaction of isocyanides with heteroatom radicals.

Photocatalytic Pyridine Synthesis with Enaminones and TMEDA under Metal-Free Conditions.

Reported herein is a new photocatalytic annulation for the synthesis of 2,3,4,6-tetrasubstituted pyridines with enaminones and N,N,N',N'-tetramethyl ethylenediamine (TMEDA). The photocatalytic reactions take place without requiring a transition metal reagent and provide products with broad scope. The methyl in TMEDA acts as the carbon source in pyridine ring construction, and BrCF2CO2Et plays the role of the terminal oxidant for free radical quenching.

Cobalt‐Catalyzed Enantioselective Alkenylation of Aldehydes

AbstractCatalytic enantioselective alkenylation of aldehydes with easily accessible alkenyl halides promoted by a chiral cobalt complex derived from a newly developed tridentate bisoxazolinephosphine is presented. Such processes represent an unprecedented reaction pathway for cobalt catalysis and a general approach that enable rapid construction of highly diversified enantioenriched allylic alcohols containing a 1,1‐, 1,2‐disubstituted and trisubstituted alkene as well as axial stereogenicity in up to 99 % yield and 99 : 1 er without the need of preformation of alkenyl–metal reagents. DFT calculations revealed the origin of enantioselectivity.

Development and validation of a dissolution test for andrographolide dispersible tablets using UV-Vis spectrophotometry

Background: Andrographolide, a terpenoid in an herbal plant, potentially has antidiabetic properties. Dispersible tablets are one of the pharmaceutical dosage forms used to improve acceptability. It is necessary to evaluate the dissolution profile to ensure the drug’s efficacy. Objective: This study aimed to determine the optimum condition of a dissolution test and its analysis for andrographolide dispersible tablets. Method: The optimisation process involves varying solvents, pH, and mole ratio of ARS-Cu(II)-andrographolide to determine the best conditions for the dissolution test of andrographolide dispersible tablets. Validation and analysis are conducted using spectrophotometry UV-Vis. Results: The optimal condition for the dissolution test was obtained with type II at 75 rpm, 900ml of citrate buffer medium with pH 3.1, and a temperature of 37±0.5ºC. The optimal analysis condition for the aliquot was obtained with Cu(II) metal and ARS reagents at pH 7, mole ratio 6:1:1.8, and a 15-minute optimum time. The maximum wavelength was 518nm using a UV-Vis spectrophotometer. The validation method has met the requirements. Conclusion: A dissolution test and its analytical method of andrographolide dispersible tablet have been validated.

Facile synthesis of homoallylamines via α-regioselectivity in ultrasonic mediation and γ-adduct syn-stereoselective allylation with AlCl3-catalysis

The allylation reaction of aldimines with allyl metal reagents is an important synthetic method for the preparation of homoallylamines. Therefore, we wish to report a highly regioselective and stereoselective allylation reaction under sonochemical Barbier-type reaction conditions. The high yields of regioselective α-adducts were achieved by reacting cinnamyl bromide, zinc, 1,2-dibromoethane, and aldimine in THF under sonochemical Barbier-type conditions. Highly regioselective and stereoselective allylation reactions were also achieved under Lewis acid-promoted Barbier-type reaction conditions.

A Review on Development of Porous Aluminosilicate-Based Zeolite Adsorbent for Heavy Metal Pollution Treatment

Heavy metal contamination endangers human health and has been identified as a global issue. The rising concentration of heavy metals in industrial and domestic wastewater has prompted the quest for effective technologies and treatments to remove them. Zeolite is a promising material for eliminating heavy metals from diverse sources that pollute wastewater. Zeolite is a crystal comprised of hydrated aluminosilicates of alkali and alkaline earth metals in a threedimensional crystal network composed of easily controllable SiO4 4− and AlO4 5− . This review focuses on the critical analysis of the application of several zeolites for the adsorption of heavy metals from wastewater, namely Cd(II), As(III and V), Cr(III and VI), Cu(II), Pb(II), Ni(II), Mn(II), and Hg(II). The results of heavy metal removal reported by zeolites are summarized, and the chemical modification of zeolites with acid/base/salt reagents, surfactants, and metal reagents has been investigated, compared, and discussed. The adsorption/desorption capabilities, systems, operational parameters, isotherms, and kinetics of zeolites are then explained and compared.

Enzymatic one-step synthesis of natural 2-pyrones and new-to-nature derivatives from coenzyme A esters

The 2-pyrone moiety is present in a wide range of structurally diverse natural products with various biological activities. The plant biosynthetic routes towards these compounds mainly depend on the activity of either type III polyketide synthase-like 2-pyrone synthases or hydroxylating 2-oxoglutarate dependent dioxygenases. In the present study, the substrate specificity of these enzymes is investigated by a systematic screening using both natural and artificial substrates with the aims of efficiently forming (new) products and understanding the underlying catalytic mechanisms. In this framework, we focused on the in vitro functional characterization of a 2-pyrone synthase Gh2PS2 from Gerbera x hybrida and two dioxygenases AtF6’H1 and AtF6’H2 from Arabidopsis thaliana using a set of twenty aromatic and aliphatic CoA esters as substrates. UHPLC-ESI-HRMSn based analyses of reaction intermediates and products revealed a broad substrate specificity of the enzymes, enabling the facile "green" synthesis of this important class of natural products and derivatives in a one-step/one-pot reaction in aqueous environment without the need for halogenated or metal reagents and protective groups. Using protein modeling and substrate docking we identified amino acid residues that seem to be important for the observed product scope.

Bypassing Ammonia: From N2 to Nitrogen Heterocycles without N1 Intermediates or Transition Metals.

Diboradiazene compounds, derived in one step from the boron-mediated reduction of dinitrogen (N2), were treated separately with sulfur and acetic anhydride, providing heterocyclic compounds that are BN isosteres of thiophene and 1,3-oxazole, respectively. These simple reactions represent the final steps in two-step routes to complex heterocycles from N2 that both circumvent the need for transition metal reagents and completely bypass the traditional intermediate ammonia.

Umgehung von Ammoniak: Von N2 zu stickstoffhaltigen Heterocyclen ohne N1‐Zwischenprodukte oder Übergangsmetalle

AbstractDiboradiazenverbindungen, die in einem Schritt aus einer Bor‐vermittelten Aktivierung von Distickstoff (N2) stammen, wurden separat mit Schwefel und Essigsäureanhydrid umgesetzt. Hierbei entstanden neuartige heterocyclische Verbindungen, die BN‐Isostere von Thiophen bzw. 1,3‐Oxazol sind. Diese einfachen Reaktionen stellen die letzten Schritte einer zweistufigen Syntheseroute zu komplexen Heterocyclen aus N2 dar, die sowohl auf den Einsatz an Übergangsmetallreagenzien verzichten als auch das klassische Zwischenprodukt Ammoniak vollständig umgehen.

PIFA-mediated room temperature dehydrogenative annulation for the synthesis of 2-alkenyl oxazoles

The annulation reactions of N-substituted enamides via intramolecular dehydrogenative CC bond formation has been developed for the synthesis of 2-alkenyl oxazoles with phenyliodine(III) bis(trifluoroacetate) (PIFA) as the only oxidant. The method exhibits excellent synthetic scope at room temperature without using any metal reagent. In addition, the method has been proven to be applicable for the synthesis of 2-aryl oxazoles via the reactions of aroyl-based enamides. The reaction process initiated by the free radical resulting from the homo-cleavage of I-O bond in PIFA has been demonstrated by control experiments.

Nickel-catalyzed electrophiles-controlled enantioselective reductive arylative cyclization and enantiospecific reductive alkylative cyclization of 1,6-enynes.

Transition metal-catalyzed asymmetric cyclization of 1,6-enynes is a powerful tool for the construction of chiral nitrogen-containing heterocycles. Despite notable achievements, these transformations have been largely limited to the use of aryl or alkenyl metal reagents, and stereoselective or stereospecific alkylative cyclization of 1,6-enynes remains unexploited. Herein, we report Ni-catalyzed enantioselective reductive anti-arylative cyclization of 1,6-enynes with aryl iodides, providing enantioenriched six-membered carbo- and heterocycles in good yields with excellent enantioselectivities. Additionally, we have realized Ni-catalyzed enantiospecific reductive cis-alkylative cyclization of 1,6-enynes with alkyl bromides, furnishing chiral five-membered heterocycles with high regioselectivity and stereochemical fidelity. Mechanistic studies reveal that the arylative cyclization of 1,6-enynes is initiated by the oxidative addition of Ni(0) to aryl halides and the alkylative cyclization is triggered by the oxidative addition of Ni(0) to allylic acetates. The utility of this strategy is further demonstrated in the enantioselective synthesis of the antiepileptic drug Brivaracetam.

Autonomous execution of highly reactive chemical transformations in the Schlenkputer

We design a modular programmable inert-atmosphere Schlenkputer (Schlenk-line computer) for the synthesis and manipulation of highly reactive compounds, including those that are air and moisture sensitive or pyrophoric. Here, to do this, we constructed a programmable Schlenk line using the Chemputer architecture for the inertization of glassware that can achieve a vacuum line pressure of 1.5 × 10−3 mbar, and integrated a range of automated Schlenk glassware for the handling, storage and isolation of reactive compounds at sub-ppm levels of O2 and H2O. This has enabled automation of a range of common organometallic reaction types for the synthesis of four highly reactive compounds: [Cp2TiIII(MeCN)2]+, CeIII{N(SiMe3)2}3, B(C6F5)3 and {DippNacNacMgI}2, which are variously sensitive to temperature, pressure, water and oxygen. Automated crystallization, filtration and sublimation are demonstrated, along with analysis using inline nuclear magnetic resonance or reaction sampling for ultraviolet–visible spectroscopy. Finally, we demonstrate low-temperature reactivity down to −90 °C as well as safe handling and quenching of alkali metal reagents using dynamic feedback from an in situ temperature probe.

Alloying effect of rare-earth tritellurides on the charge density wave and magnetic properties

Among many van der Waals materials rare-earth tritellurides (RTe3) allow studying several phenomena like magnetic, superconducting, and charge density wave (CDW). These studies show the effect of cationic alloying of antiferromagnetic RTe3 for fully tunable near room-temperature CDW properties. DyxGd1−xTe3 and DyxTb1−xTe3 alloys were synthesized through a chemical vapor transport technique, and the rare-earth element composition was controlled by changing the ratio of rare-earth metal reagents. The results show that the lattice parameters can be continuously tuned with the composition of the rare-earth cations leading to the variation of the internal chemical pressure. Temperature-dependent Raman spectroscopy and electric transport measurement show that the CDW transition temperature (TCDW) of RTe3 alloys varies with lattice parameters/chemical pressure spanning across 300–380 K. Additional magnetism studies offer the first insights into the magnetic ordering in RTe3 alloys. The emergence of multiple magnetic transitions implies complex magnetic interactions that arise from interactions between different rare-earth elements. Overall findings introduce ways to control the CDW behavior and provide valuable insights into the magnetic ordering in RTe3 alloys, contributing to further investigation and a better understanding of their properties.

Additive-free synthesis of β-keto phosphorodithioates via geminal hydro-phosphorodithiolation of sulfoxonium ylides with P4S10 and alcohols

A simple and additive-free protocol has been developed for the preparation of β-keto phosphorodithioates through the three-component reaction of easily available sulfoxonium ylides, P4S10, and alcohols. The present geminal hydro-phosphorodithiolation reaction was performed at room temperature to construct a series of β-keto phosphorodithioates in the absence of any metal reagents, bases, or additives.