Organoselenium Catalysts Research Articles

Photo-induced organoselenium-catalyzed synthesis of 2-substituted quinazoline derivatives

Herein, a method for the synthesis of 2-substituted quinazoline derivatives from 2-aminobenzylamines and benzylamines using the synergistic action of visible light and organoselenium catalysts was established. Under visible light, the process employs diphenyl diselenide (PhSe)2 as a photocatalyst to achieve the best yield of 97 % in 3 h without the use of other powerful oxidants or selective fluorine excitation, and tolerated a variety of substrates with yields ranging from 60 % to 97 %. Moreover, substitution of benzylamine with benzaldehyde, benzoylformic acid or mandelic acid expanded the substrate scopes for synthesis of 2-substituted quinazolines and quinazolinones. This opens new avenues for further study of the catalytic reaction of organic selenium and promotes the development of green synthetic chemistry.

Recent Advances in the Use of Diorganyl Diselenides as Versatile Catalysts.

The importance of organoselenium compounds has been increasing in synthetic chemistry. These reagents are well-known as electrophiles and nucleophiles in many organic transformations, and in recent years, their functionality as catalysts has also been largely explored. The interest in organoselenium-based catalysts is due to their high efficacy, mild reaction conditions, strong functional compatibility, and great selectivity. Allied to organoselenium catalysts, the use of inorganic and organic oxidants that act by regenerating the catalytic species for the reaction pathway is common. Here, we provide a comprehensive review of the last five years of organic transformations promoted by diorganyl diselenide as a selenium-based catalyst. This report is divided into four sections: (1) cyclisation reactions, (2) addition reactions and oxidative functionalisation, (3) oxidation and reduction reactions, and (4) reactions involving phosphorus-containing starting materials.

Asymmetric Catalysis of Chiral Bifunctional Selenides and Selenonium Salts Bearing a Urea Group

AbstractCatalytic asymmetric reactions with chiral organoselenium catalysts have become one of the most important research topics in the field of organocatalysis. Despite the presence of several effective chiral selenium catalysts, further developments of new chiral organoseleniums are still desired due to their remarkable potential as asymmetric organocatalysts. Herein, we report the synthesis and asymmetric catalysis of chiral bifunctional selenides and selenonium salts bearing a urea group. The new chiral bifunctional selenide organocatalysts promote asymmetric halocyclizations with good to high levels of enantioselectivity. Furthermore, we report a reaction involving a precious example of a chiral tertiary selenonium salt‐catalyzed asymmetric phase‐transfer conjugate addition.

Catalytic, Enantioselective syn-Diamination of Alkenes.

The enantioselective, vicinal diamination of alkenes represents one of the stereocontrolled additions that remains an outstanding challenge in organic synthesis. A general solution to this problem would enable the efficient and selective preparation of widely useful, enantioenriched diamines for applications in medicinal chemistry and catalysis. In this article, we describe the first enantioselective, syn-diamination of simple alkenes mediated by a chiral, enantioenriched organoselenium catalyst together with a N,N'-bistosyl urea as the bifunctional nucleophile and N-fluorocollidinium tetrafluoroborate as the stoichiometric oxidant. Diaryl, aryl-alkyl, and alkyl-alkyl olefins bearing a variety of substituents are all diaminated in consistently high enantioselectivities but variable yields. The reaction likely proceeds through a Se(II)/Se(IV) redox catalytic cycle reminiscent of the syn-dichlorination reported previously. Furthermore, the syn-stereospecificity of the transformation shows promise for highly enantioselective diaminations of alkenes with no strong steric or electronic bias.

Organotellurium catalysis-enabled utilization of molecular oxygen as oxidant for oxidative deoximation reactions under solvent-free conditions

Catalyzed by commercially available (PhTe)2, molecular oxygen could be utilized as the mild, cheap and safe oxidant for oxidative deoximation reactions under solvent-free conditions. As the first report on organotellurium-catalyzed deoximation reaction, this work not only provides an efficient deoximation method, but also discloses new features of tellurium catalyst different from those of the organoselenium catalysts.

Sodium Selenosulfate from Sodium Sulfite and Selenium Powder: An Odorless Selenylating Reagent for Alkyl Halides to Produce Dialkyl Diselenide Catalysts

Na2SeSO3, which can be generated in situ by the reaction of Na2SO3 with Se power, was found to be an odorless reagent for the selenenylation of alkyl halides to produce dialkyl diselenides. These products have been recently shown to be good catalysts for the Baeyer–Villiger oxidation of carbonyl compounds, for the selective oxidation of alkenes, or for the oxidative deoximation of oximes. By using aqueous EtOH as the solvent and avoiding the generation of a malodourous selenol intermediate, the selenylation reaction with Na2SeSO3 is much more environmentally friendly than conventional methods. Owing to the cheap and abundant starting materials and selenium reagents, our novel synthetic method reduces the production costs of dialkyl diselenides as organoselenium catalysts, thereby advancing practical applications of organoselenium-catalysis technologies.

A cost‐effective shortcut to prepare organoselenium catalysts via decarboxylative coupling of phenylacetic acid with elemental selenium

An interesting decarboxylative coupling reaction of phenylacetic acid with elemental selenium was discovered and employed for the preparation efficient organoselenium catalysts for Baeyer–Villiger reaction and oxidative deoximation reaction. Compared with the traditionally used Grignard reagent method, the decarboxylative coupling reaction with selenium powders provides a shortcut for the preparation of organoselenium catalysts free of carcinogenic organohalide starting materials, toxic and odorous selenol intermediates and magnesium salt solid wastes. This may be helpful for reducing the cost of selenium catalysts to facilitate the application of organoselenium‐catalyzed green reactions in large‐scale production.

Solid-State 77Se NMR of Organoselenium Compounds through Cross Polarization Magic Angle Spinning (CPMAS) Method

Characterization of selenium states by 77Se NMR is quite important to provide vital information for mechanism studies in organoselenium-catalyzed reactions. With the development of heterogeneous polymer-supported organoselenium catalysts, the solid state 77Se NMR comes to the spotlight. It is necessary to figure out an advanced protocol that provides good quality spectra within limited time because solid state 77Se NMR measurements are always time consuming due to the long relaxation time and the relatively low sensitivity. Studies on small molecules and several novel polymer-supported organoselenium materials in this article showed that cross polarization (CP) method with the assistance of magic angle spinning (MAS) was more efficient to get high quality spectra than the methods by using single pulse (SP) or high power 1H decoupling (HPHD) combined with MAS. These results lead to a good understanding of the effect of the molecular structure, the heteronuclear coupling, the long-range ordering of the solid (crystal or amorphous), and the symmetry of 77Se on quality of their spectra.

C–H Pyridination with Organoselenium Catalysts

C–H Pyridination with Organoselenium Catalysts

Cinchona-Alkaloids Based Isoselenazolones: Synthesis and Their Catalytic Reactivity in Asymmetric Bromolactonization of Alkenoic Acid

A series of chiral isoselenazolones have been synthesized and characterized by multinuclear (1H, 13C, and 77Se) NMR, mass spectrometry, and single crystal X-ray crystallography. Catalytic reactivity of synthesized chiral isoselenazolones was studied in the enantioselective bromolactonization of alkenoic acids using N-bromosuccinimide as a source of bromine. A series of alkenoic acid underwent bromolactonization successfully in the presence of 10 mol% of chiral isoselenazolone catalyst and excellent yields of bromolactones were obtained with high diastereoselectivity and moderate enantioselectivity. Isoselenazolone catalyst derived from quininamine afforded bromolactones in 82–94 % yield with 1−47 % enantioselectivity while rest of the isoselenazolones derived from simple chiral (S)-phenylethyl, and (S)-naphthylethyl, quinidin, and cinchonidin-amine afforded poor enantioselectivity in the bromolactonization reaction. Furthermore, isoselenazolone having Se–N bond gave best enantioselectivity in the bromolactonization of 5-phenyl-4-pentenoic acid as compared to the isothiazolone having S–N bond. Also isoselenazolone gave best enantioselectivity than the corresponding methyl selenide and diselenide bearing the same quininamine auxiliary in the organoselenium catalyst. Crystal structure and enantioselectivity outcome in bromolactonization on similar isoselenazolone catalysts; quininamine based (intramolecular Se…N distance 3.56 A, ee 47 %); cinchonidinamine based (Se…N distances 3.80 A, ee 17 %), and 7-methyl-amide and quininamine based (Se…N distances 3.72 A, ee 28 %) suggests that intramolecular Se…N interaction could be the crucial parameter for the enantioselectivity outcome of the reaction.

Synthesis of l-Selenocysteine and α-Methyl-l-Selenocysteine Derivatives Using Woollins’ Reagent and Their Application as Chiral Selenium Catalysts

The reaction of oxazolines, which were synthesized from l-serine methyl ester, with Woollins’ reagent in refluxing acetonitrile for 2 h and subsequent treatment of the crude products with sodium borohydride gave l-selenocysteine derivatives in up to 82 % yield without occurring racemization. Similar reaction protocols were applied for α-methyl-l-serine derivatives to afford various optically pure α-methyl-l-selenocysteine derivatives in moderate yields (~43 %). The obtained α-methylselenocysteine derivatives were applied as a catalyst for asymmetric cyclization of β,γ-unsaturated acids to α,β-unsaturated lactones in the presence of ammonium persulfate. The highest optical yield (27 % e.e.) was achieved when N,N′-diacetyl-α,α′-dimethyl-l-selenocystine diethyl ester was employed as a catalyst. Thus, potential usability of selenoamino acid derivatives as chiral organoselenium catalysts was demonstrated.

Organoselenium-catalyzed selectivity-switchable oxidation of β-ionone

The selectivities of the oxidations of β-ionone 1 were switched by the organoselenium catalyst used. [3,5-(CF3)2C6H3Se]2 led to (E)-5,6-epoxy-β-ionone (2, 72% yield), while (PhCH2Se)2 gave the major Baeyer–Villiger oxidation product 3 in excellent yield (91%).

Design and preparation of a polymer resin-supported organoselenium catalyst with industrial potential

Hexavalent Se? Yes! Selenium on polymers exhibits quite different properties compared to that in small molecules. Hexavalent Se, rare in organoselenium chemistry, is found to be the major species on polymers. The high-valent Se species on recyclable polymer resins could quickly catalyze the oxidation reaction of cyclohexene in water to producetrans-1,2-cyclohexanediol in almost quantitative yield with no excess H2O2.

Construction and evaluation of nitric oxide generating vascular graft material loaded with organoselenium catalyst via layer-by-layer self-assembly.

A new biomimetic material for artificial blood vessel with in situ catalytic generation of nitric oxide (NO) was prepared in this study. Organoselenium immobilized polyethyleneimine as NO donor catalyst and sodium alginate were alternately loaded onto the surface of electrospun polycaprolactone matrix via electrostatic layer-by-layer self-assembly. This material revealed significant NO generation when contacting NO donor S-nitrosoglutathione (GSNO). Adhesion and spreading of smooth muscle cells were inhibited on this material in the presence of GSNO, while proliferation of endothelial cells was promoted. In vitro platelet adhesion and arteriovenous shunt experiments demonstrated good antithrombotic properties of this material, with inhibited platelet activation and aggregation, and prevention of acute thrombosis. This study may provide a new method of improving cellular function and antithrombotic property of vascular grafts.

Organoselenium‐Catalyzed Baeyer–Villiger Oxidation of α,β‐Unsaturated Ketones by Hydrogen Peroxide to Access Vinyl Esters

AbstractBy carefully screening the organoselenium pre‐catalysts and optimizing the reaction conditions, simple dibenzyl diselenide was found to be the best pre‐catalyst for Baeyer–Villiger oxidation of (E)‐α,β‐unsaturated ketones with the green oxidant hydrogen peroxide at room temperature. The organoselenium catalyst used in this reaction could be recycled and reused several times. This new method was suitable not only for methyl unsaturated ketones, but also for alkyl and aryl unsaturated ketones. Therefore, it provided a direct, mild, practical, highly functional group‐tolerant process for the chemoselective preparation of the versatile (E)‐vinyl esters from the readily available (E)‐α,β‐unsaturated ketones. A possible mechanism was also proposed to rationalize the activity of the organoselenium catalyst in the presence of hydrogen peroxide in this Baeyer–Villiger oxidation reaction.magnified image

Recyclable (PhSe)2-catalyzed selective oxidation of isatin by H2O2: a practical and waste-free access to isatoic anhydride under mild and neutral conditions

A practical and waste-free synthesis of isatoic anhydride was reported. The feature of this methodology is the simple isolation procedure by filtration, which facilitates the direct recovery and reuse of both organoselenium catalysts and solvents.

Amperometric S-nitrosothiol sensor with enhanced sensitivity based on organoselenium catalysts

A new S-nitrosothiol (RSNO) detection strategy based on an electrochemical sensor is described for rapidly estimating levels of total RSNOs in blood and other biological samples. The sensor employs a cellulose dialysis membrane covalently modified with an organoselenium catalyst that converts RSNOs to NO at the distal tip of an amperometric NO sensor. The sensor is characterized by very low detection limits (<20nM), good long-term stability, and can be employed for the rapid detection of total low-molecular-weight (LMW) RSNO levels in whole blood samples using a simple standard addition method. A strategy for detecting macromolecular RSNOs is also demonstrated via use of a transnitrosation reaction with added LMW thiols allowing the estimation of total RSNO levels in blood. The sensor is shown to exhibit high selectivity over nitrosamines and nitrite. Such RSNO detection is potentially useful to reveal correlation between blood RSNO levels and endothelial cell dysfunction, which often is associated with cardiovascular diseases.

New Recoverable Organoselenium Catalyst for Hydroperoxide Oxidation of Organic Substrates

New benzisoselenazol-3(2H)-one covalently bounded to a silica support was synthesized and characterized. It was used as an effective, selective, and easy-to-regenerate catalyst for t-BuOOH and H2O2 oxidation of alkyl arenes to alkyl aryl ketones, aromatic aldehydes to arene carboxylic acids, and sulfoxides and/or sulfones.

Photoinstability of S-Nitrosothiols during Sampling of Whole Blood: A Likely Source of Error and Variability in S-Nitrosothiol Measurements

The determination of reference intervals for the concentration of total S-nitrosothiols (RSNOs) in blood is a highly controversial topic, likely because of the inherent instability of these species. Most currently available techniques to quantify RSNOs in blood require considerable sample handling and multiple pretreatment steps during which light exposure is difficult to completely eliminate. We investigated the effect of brief light exposure on the stability of RSNO species in blood during the initial sampling process. A novel amperometric RSNO sensor, based on an immobilized organoselenium catalyst at the distal tip of an electrochemical nitric oxide detector, was used to determine RSNO species in diluted whole blood without centrifugation or pretreatment. Porcine blood was collected into aluminum foil-wrapped syringes via a 12-inch butterfly needle tube assembly. Two blood samples were collected from the same animal -- one with the butterfly needle tubing wrapped in aluminum foil and one with the tubing exposed to ambient room light. The RSNO concentrations in these sequential blood samples were determined by a standard addition procedure. Eight sets of measurements were made in 6 animals. Samples exposed to light yielded RSNO concentrations only 23.6% (7.2%) [mean (SD)] of the RSNO concentrations determined in samples that were shielded from light and obtained from the same animals. These results suggest significant photoinstablity of RSNOs in whole blood and indicate the critical importance of proper light protection during sampling and processing of blood samples for the accurate determinations of endogenous RSNO concentrations.

S-Nitrosothiol Detection via Amperometric Nitric Oxide Sensor with Surface Modified Hydrogel Layer Containing Immobilized Organoselenium Catalyst

A novel electrochemical device for the direct detection of S-nitrosothiol species (RSNO) is proposed by modifying an amperometric nitric oxide (NO) gas sensor with thin hydrogel layer containing an immobilized organoselenium catalyst. The diselenide, 3,3'-dipropionicdiselenide, is covalently coupled to primary amine groups in polyethylenimine (PEI), which is further cross-linked to form a hydrogel layer on a dialysis membrane support. Such a polymer film containing the organoselenium moiety is capable of decomposing S-nitrosothiols to generate NO(g) at the distal tip of the NO sensor. Under optimized conditions, various RSNOs (e.g., nitrosocysteine (CysNO), nitrosoglutathione (GSNO), etc.) are reversibly detected at </=0.1 microM levels, with sensor lifetimes of at least 10 days. The presence of reducing agents (e.g., glutathione) added to the test solution enhances the amperometric dynamic range output to approximately 25 microM levels of RSNO species. Sensitivities observed for different small molecule RSNO species are nearly equivalent, in sharp contrast to the behavior observed previously for a similar RSNO sensing configuration based on an immobilized Cu(I/II) catalytic layer. It is further shown that the new RSNO sensors can be used to assess the "NO-generating" ability of fresh blood samples by effectively detecting the total level of reactive low molecular-weight RSNO species present in such samples.