From a humorous post to a detailed quantum-chemical study: isocyanate synthesis revisited

Isocyanates play an essential role in modern manufacturing processes, especially in polyurethane production. There are numerous synthesis strategies for isocyanates both under industrial and laboratory conditions, which do not prevent searching for alternative highly efficient synthetic protocols. Here, we report a detailed theoretical investigation of the mechanism of sulfur dioxide-catalyzed rearrangement of phenylnitrile oxide into phenyl isocyanate, which was first reported in 1977. The DLPNO-CCSD(T) method and up-to-date DFT protocols were used to perform a highly accurate quantum-chemical study of the rearrangement mechanism. An overview of various organic and inorganic catalysts has revealed other potential catalysts, such as sulfur trioxide and selenium dioxide. Furthermore, the present study elucidated how substituents in phenylnitrile oxide influence reaction kinetics. This study was performed by a self-organized collaboration of scientists initiated by a humorous post on the VK social network.

Electrochemical selenocyclization of 2-ethynylanilines with diselenides: facile and efficient access to 3-selenylindoles

An efficient electrochemical selenocyclization strategy for the synthesis of 3-selenylindoles from 2-ethynylanilines and diselenides has been developed in simple tube- or beaker-type undivided cells under ambient conditions. Notably, these sustainable transformations are completed within a short time with low equivalents of charges, diselenides and electrolytes, exhibiting a broad substrate scope with excellent functional group compatibility. Moreover, a gram-scale electrosynthesis and late-stage functionalization of complex molecules further demonstrate the practical synthetic potential of this facile electrochemical system.

Mono and Dinuclear Palladium Pincer Complexes of NNSe Ligand as a Catalyst for Decarboxylative Direct C-H Heteroarylation of (Hetero)arenes

This report describes the synthesis of a new NNSe pincer ligand and its mono- and dinuclear palladium(II) pincer complexes. In the absence of a base, a dinuclear palladium pincer complex (C1) was isolated, while in the presence of Et3 N base a mononuclear palladium pincer complex (C2) was obtained. The new ligand and complexes were characterized using techniques like 1 H, 13 C{1 H} nuclear magnetic resonance (NMR), fourier transform infrared (FTIR), high-resolution mass spectrometry (HRMS), ultraviolet-visible (UV-Visible), and cyclic voltammetry. Both the complexes showed pincer coordination mode with a distorted square planar geometry. The complex C1 has two pincer ligands attached through a Pd-Pd bond in a dinuclear pincer fashion. The air and moisture-insensitive, thermally robust palladium pincer complexes were used as the catalyst for decarboxylative direct C-H heteroarylation of (hetero)arenes. Among the complexes, dinuclear pincer complex C1 showed better catalytic activity. A variety of (hetero)arenes were successfully activated (43-87 % yield) using only 2.5 mol % of catalyst loading under mild reaction conditions. The PPh3 and Hg poisoning experiments suggested a homogeneous nature of catalysis. A plausible reaction pathway was proposed for the dinuclear palladium pincer complex catalyzed decarboxylative C-H bond activation reaction of (hetero)arenes.

Silver-catalyzed direct selanylation of indoles: synthesis and mechanistic insights

Herein we describe the Ag(i)-catalyzed direct selanylation of indoles with diorganoyl diselenides. The reaction gave 3-selanylindoles with high regioselectivity and also allowed direct access to 2-selanylindoles when the C3 position of the indole ring was blocked via a process similar to Plancher rearrangement. Experimental analyses and density functional theory calculations were carried out in order to picture the reaction mechanism. Among the pathways considered (via concerted metalation-deprotonation, Ag(iii), radical, and electrophilic aromatic substitution), our findings support a classic electrophilic aromatic substitution via Lewis adducts between Ag(i) and diorganoyl diselenides. The results also afforded new insights into the interactions between Ag(i) and diorganoyl diselenides.

In the Chalcogenoxide Elimination Panorama: Systematic Insight into a Key Reaction

The selenoxide elimination is a well-known reaction in organochalcogen chemistry, with wide synthetic, biological, and toxicological implications. In this work, we apply benchmarked density functional theory (DFT) calculations to investigate different aspects of the title reaction in three (bio)chemically relevant models, spanning minimal systems of theoretical interests as well as biological or synthetic organochalcogenides. The activation strain analysis (ASA) methodology is employed along a suitable reaction coordinate to obtain insight into the role of the chalcogen and of the oxidation state, to pinpoint the factors that tune the elimination reactivity of the investigated systems. Lastly, we computationally validate the hypothesis that telluroxides eliminate more slowly than selenoxides because of a detrimental hydration process that leads to unreactive hydrates.

ROS-Scavenging Selenofluoxetine Derivatives Inhibit In Vivo Serotonin Reuptake

While the neurochemistry that underpins the behavioral phenotypes of depression is the subject of many studies, oxidative stress caused by the inflammation comorbid with depression has not adequately been addressed. In this study, we described novel antidepressant-antioxidant agents consisting of selenium-modified fluoxetine derivatives to simultaneously target serotonin reuptake (antidepressant action) and oxidative stress. Excitingly, we show that one of these agents (1-F) carries the ability to inhibit serotonin reuptake in vivo in mice. We therefore present a frontier dual strategy that paves the way for the future of antidepressant therapies.

"Green Is the Color": An Update on Ecofriendly Aspects of Organoselenium Chemistry

Organoselenium compounds have been successfully applied in biological, medicinal and material sciences, as well as a powerful tool for modern organic synthesis, attracting the attention of the scientific community. This great success is mainly due to the breaking of paradigm demonstrated by innumerous works, that the selenium compounds were toxic and would have a potential impact on the environment. In this update review, we highlight the relevance of these compounds in several fields of research as well as the possibility to synthesize them through more environmentally sustainable methodologies, involving catalytic processes, flow chemistry, electrosynthesis, as well as by the use of alternative energy sources, including mechanochemical, photochemistry, sonochemical and microwave irradiation.

Synthesis and Evaluation of Antioxidant, Anti-Edematogenic and Antinociceptive Properties of Selenium-Sulfa Compounds

Herein we describe results for the synthesis and synthetic application of 4-amino-3-(arylselenyl)benzenesulfonamides, and preliminary evaluation of antioxidant, anti-edematogenic and antinociceptive properties. This class of compounds was synthesized in good yields by a reaction of commercially available sulfanilamide and diorganyl diselenides in the presence of 10 mol% of I2 . Furthermore, the synthesized compound 4-amino-3-(phenylselenyl)benzenesulfonamide (3 a) was evaluated on complete Freund's adjuvant (CFA)-induced acute inflammatory pain. Dose- and time-response curves of antinociceptive effect of compound 3 a were performed using this experimental model. Also, the effect of compound 3 a was monitored in a hot-plate test to evaluate the acute non-inflammatory antinociception. The open-field test was performed to evaluate the locomotor and exploratory behaviors of mice. Oxidative stress markers, such as glutathione peroxidase activity; reactive species, non-protein thiols, and lipid peroxidation levels were performed to investigate the antioxidant action of compound 3 a. Our findings suggest that the antioxidant effect of compound 3 a may contribute to reducing the nociception and suppress the signaling pathways of inflammation on the local injury induced by CFA. Thus, compound 3 a reduced the paw edema as well as the hyperalgesic behavior in mice, being a promising therapeutic agent for the treatment of painful conditions.

PhSe(O)OH/Al(NO3)3-Catalyzed selectivity controllable oxidation of sulphide owing to the synergistic effect of Se, Al3+ and nitrate

Catalyzed by PhSe(O)OH/Al(NO3)3, selective oxidation of sulphides to produce sulfoxides or sulphones could be achieved under mild conditions. The synergistic effect of Se, Al3+ and nitrate is the key factor for the reaction.

Bis-triazolylchalcogenium-Functionalized Benzothiadiazole Derivatives as Light-up Sensors for DNA and BSA

A range of bis-triazolylchalcogenium-BTD 3 was synthesized by a copper-catalyzed azide-alkyne cycloaddition of azido arylchalcogenides 1 and 4,7-diethynylbenzo[c][1,2,5]thiadiazole 2. Eight new compounds were obtained in moderate to good yields using 1 mol % of copper(II) acetate monohydrate under mild reaction conditions. In addition, the synthesized bis-triazolylchalcogenium-BTD 3a-3h were investigated regarding their photophysical, electrochemical, and biomolecule binding properties in solution. In general, compounds presented strong absorption bands at the 250-450 nm region and cyan to green emission properties. The redox process attributed to the chalcogen atom was observed by electrochemical analysis (CV techniques). In addition, spectroscopic studies by UV-vis, steady-state emission fluorescence, and molecular docking calculations evidenced the ability of each derivative to establish interactions with calf-thymus DNA (CT-DNA) and bovine serum albumin (BSA). The behavior presented for this new class of compounds makes them a promising tool as optical sensors for biomolecules.

Selenium-Catalyzed Reduction of Hydroperoxides in Chemistry and Biology

Among the chalcogens, selenium is the key element for catalyzed H2O2 reduction. In organic synthesis, catalytic amounts of organo mono- and di-selenides are largely used in different classes of oxidations, in which H2O2 alone is poorly efficient. Biological hydroperoxide metabolism is dominated by peroxidases and thioredoxin reductases, which balance hydroperoxide challenge and contribute to redox regulation. When their selenocysteine is replaced by cysteine, the cellular antioxidant defense system is impaired. Finally, classes of organoselenides have been synthesized with the aim of mimicking the biological strategy of glutathione peroxidases, but their therapeutic application has so far been limited. Moreover, their therapeutic use may be doubted, because H2O2 is not only toxic but also serves as an important messenger. Therefore, over-optimization of H2O2 reduction may lead to unexpected disturbances of metabolic regulation. Common to all these systems is the nucleophilic attack of selenium to one oxygen of the peroxide bond promoting its disruption. In this contribution, we revisit selected examples from chemistry and biology, and, by using results from accurate quantum mechanical modelling, we provide an accurate unified picture of selenium's capacity of reducing hydroperoxides. There is clear evidence that the selenoenzymes remain superior in terms of catalytic efficiency.

Cobaltoceniumselenolate Gold(I) Complexes: Synthesis, Spectroscopic, Structural and Anticancer Properties

Cobaltoceniumselenolate is an unusual, highly air-sensitive, mesoionic compound containing a very soft anionic selenium donor atom. Here we explore its coordination chemistry with Au(I) metal centers and show that its hetero- and homoleptic gold complexes are highly colored, air-stable compounds, which were characterized by 1H/13C/31P/77Se NMR, IR, UV-Vis, HR-MS and single crystal XRD. Cytotoxicity of these polar, water-soluble complexes was studied against various standard cancer cell lines (A549MDA-MB-231, HT-29) revealing good anticancer activity of all three complexes.

SELENIUM AS A VERSATILE REAGENT IN ORGANIC SYNTHESIS: MORE THAN ALLYLIC OXIDATION

For many years since its discovery, Selenium has played the role of a bad boy who became a hero in organic transformations. Selenium dioxide, for instance, is one of the most remembered reagents in allylic oxidations, having been applied in the synthesis of several naturally occurring products. The main goal of this review is to show the recent advances in the use of classical and new selenium reagents in organic synthesis. As demonstrated through around 60 references discussed in this study, selenium can go even forward as a versatile reagent. We bring a collection of selenium reagents and their transformations that are still hidden from most synthetic organic chemists.

Synthesis of benzo[b]chalcogenophenes fused to selenophenes via intramolecular electrophilic cyclization of 1,3-diynes

We describe herein an alternative and transition-metal-free procedure for the access of benzo[b]chalcogenophenes fused to selenophenes via intramolecular cyclization of 1,3-diynes. This efficient protocol involves a double cyclization of 1,3-diynyl chalcogen derivatives promoted by the electrophilic species of organoselenium generated in situ by the oxidative cleavage of the Se-Se bond of dibutyl diselenide using Oxone® in acetonitrile as solvent in an open-flask at 80 °C. In this study, 15 selenophenes with broad substrate scope were prepared in moderate to excellent yields (55-98%) with short reaction times (0.5-3.0 h).

Transition-metal-free C-S, C-Se, and C-Te Bond Formation from Organoboron Compounds

The present review describes the successful application of organoboron compounds in transition-metal-free C-S, C-Se, and C-Te bond formations. We presented studies regarding these C-Chalcogen bond formations using organoboron reagents, such as boronic acids, boronic esters, borate anions, and several sources of chalcogen atoms/moieties. Moreover, a broad range of transition-metal-free approaches to synthesize sulfides, selenides, and tellurides were described using conventional heating methods, which are sometimes green since they use green solvents, safe reagents, among others. Furthermore, protocols using alternative energy sources, including ultrasound, microwave irradiation, photocatalysis, and electrolytic processes, were also shown to be suitable. These protocols were applied to prepare a broad scope of functionalized chalcogenides with high molecular diversity. These studies and their proposed mechanisms were also reported herein in addition to the reuse of reaction promoters.

Ebselen-Agents for Sensing, Imaging and Labeling: Facile and Full-Featured Application in Biochemical Analysis

Phenyl-1,2-benzoselenazol-3(2H)-one (ebselen) is a classical mimic of glutathione peroxidase (GPx). Thioredoxin interaction endows ebselen attractive biological functions, such as antioxidation and anti-infection, as well as versatile therapeutic usage. Accordingly, application of ebselen analogues in biosensing, chemical labeling, imaging analysis, disease pathology, drug development, clinical treatment, etc. have been widely developed, in which mercaptans, reactive oxygen species, reactive sulfur species, peptides, and proteins were involved. Herein, focusing on the application of ebselen-agents in biochemistry, we have made a systematic summary and comprehensive review. First, we summarized both the classical and the innovative methods for preparing ebselen-agents to present the synthetic strategies. Then we discussed the full functional applicability of ebselen analogues in three fields of biochemical analysis including the fluorescence sensing and bioimaging, derivatization for high throughput fluorescence analysis, and the labeling gents for proteomics. Finally, we discussed the current challenges and perspectives for ebselen-agents as analytical tools in biological research. By presenting the multifunctional applicability of ebselen, we hope this review could appeal researchers to design the ebselen-related biomaterials for biochemical analysis.

Synthesis and triplet sensitization of bis(arylselanyl)BOPHYs; potential application in triplet–triplet annihilation upconversion

Bis(arylselanyl)BOPHYs 1 and 2 were prepared as novel triplet photosensitizers, TTA-UC behavior of 1 with 9,10-diphenylanthracene being investigated.

Synergetic catalysis of Se and Cu allowing diethoxylation of halomethylene ketones using O2 as the mild oxidant

Catalyzed by PhSe(O)OH/Cu(OAc)₂, sp³-C–H alkylation of bromomethylene ketones produced useful α-carbonyl acetals under mild conditions. Bromo-containing substrates could release HBr during the reaction, avoiding the use of acidic additives.

Catalytic epoxidation of β-ionone with molecular oxygen using selenium-doped silica materials

Se-doped silica could catalyze the β-ionone epoxidation reaction. Interestingly, by doping with fluorine in the catalyst, the reaction selectivity was significantly enhanced. The metal-free process is suitable for pharmaceutical synthesis.

Recent Advances in the Synthesis of Selenophenes and Their Derivatives

The selenophene derivatives are an important class of selenium-based heterocyclics. These compounds play an important role in prospecting new drugs, as well as in the development of new light-emitting materials. During the last years, several methods have been emerging to access the selenophene scaffold, employing a diversity of cyclization-based synthetic strategies, involving specific reaction partners and particularities. This review presents a comprehensive discussion on the recent advances in the synthesis of selenophene-based compounds, starting from different precursors, highlighting the main differences, the advantages, and limitations among them.

Fluorescent Benzoselenadiazoles: Synthesis, Characterization, and Quantification of Intracellular Lipid Droplets and Multicellular Model Staining

In this work, we described the synthesis of 10 new fluorescent 2,1,3-benzoselenadiazole small-molecule derivatives and their chemical- and photocharacterizations. The new derivatives could, for the first time, be successfully applied as selective live cell imaging probes (at nanomolar concentrations) and stained lipid-based structures preferentially. Density functional theory (DFT) calculations were used to help in understanding the photophysical data and the intramolecular charge-transfer (ICT) processes of the synthesized dyes. Some derivatives showed impressive cellular responses, allowing them to be tested as probes in a complex multicellular model (i.e., Caenorhabditis elegans). When compared with the commercially available dye, the new fluorescent compounds showed far better results both at the cellular level and inside the live worm. Inside the multicellular complex model, the tested probes also showed selectivity, a feature not observed when the commercial dye was used to carry out the bioimaging experiments.

Continuous Bioinspired Oxidation of Sulfides

A simple, efficient, and selective oxidation under flow conditions of sulfides into their corresponding sulfoxides and sulfones is reported herein, using as a catalyst perselenic acid generated in situ by the oxidation of selenium (IV) oxide in a diluted aqueous solution of hydrogen peroxide as the final oxidant. The scope of the proposed methodology was investigated using aryl alkyl sulfides, aryl vinyl sulfides, and dialkyl sulfides as substrates, evidencing, in general, a good applicability. The scaled-up synthesis of (methylsulfonyl)benzene was also demonstrated, leading to its gram-scale preparation.

Synthesis and anticancer activity of bis(2-arylimidazo[1,2-a]pyridin-3-yl) selenides and diselenides: the copper-catalyzed tandem C-H selenation of 2-arylimidazo[1,2-a]pyridine with selenium

Most heteroaryl selenides and diselenides are biologically active, with some reported to act as antioxidants and show activities that are medicinally relevant; hence, the development of efficient methods for their synthesis is an important objective. Herein, a simple method for the synthesis of selenides and diselenides bearing imidazo[1,2-a]pyridine rings and their anticancer activity are described. The double C-H selenation of imidazo[1,2-a]pyridine with Se powder was catalyzed by CuI (10 mol %) ligated with 1,10-phenanthroline (10 mol %) at 130 °C under aerobic conditions. The selenides or diselenides were prepared almost selectively using selenium powder in an appropriate quantity under otherwise identical reaction conditions. The prepared selenides and diselenides bearing two imidazo[1,2-a]pyridine rings were all novel compounds. Among the prepared diselenides and selenides that exhibited cytotoxicity against cancer cells, bis[2-(4-methoxyphenyl)imidazo[1,2-a]pyridin-3-yl] diselenide showed an excellent anticancer activity and low cytotoxicity toward noncancer cells, suggesting that this diselenide is a potential lead compound for anticancer therapy.