Selenium Dioxide As an Alternative Reagent for the Direct α-Selenoamidation of Aryl Methyl Ketones

Herbal Polyphenols as Selenium Reducers in the Green Synthesis of Selenium Nanoparticles: Antibacterial and Antioxidant Capabilities of the Obtained SeNPs

Selenium is an essential trace element for the proper functioning of the human body. In recent years, great attention has been paid to selenium nanoparticles (SeNPs) due to their potential for medicinal applications. In this study, herbal extracts were used in the green synthesis of SeNPs. The influence of herbal species, the ratio of the reagents, and post-reaction heating on the antibacterial and antioxidant properties of obtained SeNPs were investigated. The relationship between these properties and the physical parameters of obtained nanoparticles (e.g., size, shape) was also studied. It has been proven that SeNPs showed higher antioxidant and antibacterial properties in comparison to herbal extracts taken for their synthesis. Heating of the post-reaction mixture did not affect the SeNP size, shape, or other studied properties.

Organoselenium Compounds: Chemistry and Applications in Organic Synthesis

Selenium, originally described as a toxin, turns out to be a crucial trace element for life that appears as selenocysteine and its dimer, selenocystine. From the point of view of drug developments, selenium-containing drugs are isosteres of sulfur and oxygen with the advantage that the presence of the selenium atom confers antioxidant properties and high lipophilicity, which would increase cell membrane permeation leading to better oral bioavailability. In this article, we have focused on the relevant features of the selenium atom, above all, the corresponding synthetic approaches to access a variety of organoselenium molecules along with the proposed reaction mechanisms. The preparation and biological properties of selenosugars, including selenoglycosides, selenonucleosides, selenopeptides, and other selenium-containing compounds will be treated. We have attempted to condense the most important aspects and interesting examples of the chemistry of selenium into a single article.

Selective Synthesis of Bis-Heterocycles via Mono- and Di-Selenylation of Pyrazoles and Other Heteroarenes

The insertion of selenium was achieved in the form of mono-selenides and di-selenides for the preparation of novel bis-heterocyclic compounds. This method is more general and provides scaffold diversity with high yields of products. The concentration-dependent mono- and di-selenylation reaction selectivity was achieved using SeO₂ as an efficient selenylating reagent.

Selenium Dioxide-Mediated Bromination of α,β-Unsaturated Ketones Using N-Bromosuccinimide in the Presence of p-Toluenesulfonic Acid: A Versatile Route for the Synthesis of α'-Bromo-4-arylbut-3-en-2-one and α',α'-Dibromo-4-arylbut-3-en-2-one

An efficient method for the synthesis of α,β-unsaturated α'-bromoketones and α,β-unsaturated α',α'-dibromoketones is described using N-bromosuccinimide (NBS) as the brominating agent mediated by selenium dioxide (SeO₂) in the presence of p-toluenesulfonic acid (PTSA) monohydrate in toluene. The method is simple, employing easily available shelf reagents to afford a wide range of products in good yields. The method highlighted that simple fine-tuning of the reaction conditions and molar equivalents of the reactants easily affords either mono- or dibrominated products in excellent yields. A number of these products have not been reported in the literature. All of the reactions were carried out in gram-scale quantities.

Amidation-Ketonization-Selenation of Terminal Alkynes Using TEMPO and Elemental Selenium

Herein, we present a novel silver- or copper-mediated direct amidation-ketonization-selenation of terminal alkynes for the synthesis of α-oxo-selenoamides. The reaction utilized easily accessible elemental selenium as the source of selenium. In addition, the ¹⁸O labeling experiment revealed that TEMPO is the oxygen source of the carbonyl group. The reaction takes advantage of an unsaturated C≡C bond to construct new C═O, C═Se, and C-N bonds in one step.

Trifluoroacetic Acid-Mediated Oxidative Self-Condensation of Acetophenones in the Presence of SeO2: A Serendipitous Approach for the Synthesis of Fused [1,3]Dioxolo[4,5-d][1,3]dioxoles

A method for the synthesis of fused 1,3-dioxolanes was developed by self-condensation of glyoxal generated in situ by oxidation of acetophenones with SeO2 in the presence of trifluoroacetic acid. Three molecules of the glyoxal generated by oxidation of ketone with SeO2 condensed to form architecturally novel oxygen-containing heterocycles (3a-aryldihydro-[1,3]dioxolo[4,5-d][1,3] dioxole-2,5-diyl)bis(phenylmethanones). This reaction provides a unique methodology for the construction of four C-O bonds in a concerted fashion, generating highly embedded oxygen heterocycles from readily available ketones using affordable shelf reagents and simple reaction conditions.

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.

Selenocyanation of Aryl and Styryl Methyl Ketones in the Presence of Selenium Dioxide and Malononitrile: An Approach for the Synthesis of α-Carbonyl Selenocyanates

A convenient method has been developed for the synthesis of α-carbonyl selenocyanates from aryl methyl ketones/styryl methyl ketones using selenium dioxide as the selenating agent under simple reaction conditions. This reaction has notable advantages over the traditional methods in terms of accessibility and affordability of the starting materials. The method features the interaction of aryl methyl ketones/styryl methyl ketones with selenium dioxide and malononitrile to afford a series of α-carbonyl selenocyanates in moderate to good yields.

Zero-, one-, two- and three-dimensional supramolecular architectures sustained by Se…O chalcogen bonding: A crystallographic survey

The Cambridge Structural Database was evaluated for crystals containing Se…O chalcogen bonding interactions. These secondary bonding interactions are found to operate independently of complementary intermolecular interactions in about 13% of the structures they can potentially form. This number rises significantly when more specific interactions are considered, e.g. Se…O(carbonyl) interactions occur in 50% of cases where they can potentially form. In about 55% of cases, the supramolecular assemblies sustained by Se…O(oxygen) interactions are one-dimensional architectures, with the next most prominent being zero-dimensional assemblies, at 30%.

Copper-catalyzed domino synthesis of benzo[d]imidazo[5,1-b][1,3]selenazoles involving sequential intermolecular cycloaddition and intramolecular Ullmann-type C–Se bond formation

A copper-catalyzed domino synthesis of benzo[d]imidazo[5,1-b][1,3]selenazoles involving sequential intermolecular cycloaddition and intramolecular Ullmann-type C–Se bond formation has been developed.

Lewis acid-promoted formation of benzoselenazole derivatives using SeO2 as a selenium source

A new one-pot method of using both ortho-inactivated anilines and acetophenones (or methylquinolines) which possess an active H in the α-position of ketones (or benzyl positions) as starting materials to make benzoselenazole derivatives has been developed, which uses SeO2 as a selenium agent. This method first establishes SeO2 as a source of selenium to form benzoselenazole derivatives, which enriches the synthesis method of benzoselenazole. This method has several advantages, including good yields, simple operation, and availability of raw materials. Furthermore, the reaction could be easily scaled and its practical value in organic synthesis is displayed.

Metal-Free Three-Component Coupling Reaction of Ketones with Electron-rich Arenes and Selenium Dioxide for the Synthesis of α-Arylselanyl Ketones

A metal-free three-component coupling reaction of aryl alkyl/alkyl ketones, SeO₂, and phenols/anisoles is described. This multicomponent reaction provides a straightforward and facile pathway for the synthesis of α-((4-hydroxy/methoxyphenyl)selanyl)-aryl alkyl/alkyl ketones in the presence of p-toluenesulfonic acid for the C-Se bond formation process. The method offers an attractive and simple procedure using commonly available shelf reagents to deliver organoselenides that, to our knowledge, are being reported here for the first time.

PTSA-Catalyzed Reaction of Alkyl/Aryl Methyl Ketones with Aliphatic Alcohols in the Presence of Selenium Dioxide: A Protocol for the Generation of an α-Ketoacetals Library

A novel approach has been developed for the synthesis of a wide range of α-ketoacetals by the reaction of alkyl/aryl methyl ketones and aliphatic alcohols in the presence of selenium dioxide catalyzed by p-toluenesufonic acid. This method represents a general route to obtain a wide variety of α-ketoacetals in a simple, rapid, and practical manner. This approach is particularly attractive because of the easy availability of the starting materials, mild reaction temperature, and good yields of the products. The resulting α-ketoacetals are of much synthetic value as organic intermediates.

Using SeO2 as a selenium source to make RSe-substituted aniline and imidazo[1,2-a]pyridine derivatives

A mild and practical method is developed for the synthesis of ArSe-substituted aniline and imidazo[1,2-a]pyridine derivatives using SeO₂ as a selenium agent.