An Improved Synthesis of Symmetrical Diselenides from Aromatic Aldehydes

An improved method for the synthesis of symmetrical diselenides is described. Reductive selenation of aromatic aldehydes with Se/CO/H₂O/Et₃N system in THF gave the corresponding aromatic diselenides in good yields.     

Simple and catalyst-free method for the synthesis of diaryl selenides by reactions of arylselenols and arenediazonium salts

We describe here a simple and catalyst-free method to synthesize diaryl selenides by reaction of arenediazonium tetrafluoroborate salts with arylselenols, generated in situ by using diaryl diselenides and hypophosphorous acid (H₃PO₂), using THF as solvent. This is a direct nucleophilic aromatic substitution (SNAr) reaction performed with diaryl diselenides and arenediazonium salts bearing electron-withdrawing and electron-donating groups affording the corresponding diaryl selenides in moderated to good yields.     

Biscarbamoyl diselenides as new carbamoylating reagents. Lewis acid promoted carbamoylation of aromatic compounds

The reaction of biscarbamoyl diselenides with aromatic compounds in the presence of Lewis acids resulted in Friedel-Crafts type carbamoylation (Gatterman amide synthesis) to give corresponding aromatic amides in good yields. This methodology was successfully applied to aroylation and benzylation by use of dibenzoyl diselenide and dibenzyl diselenide, respectively.     

Chiral Diselenides from Benzylamines: Catalysts in the Diethylzinc Addition to Aldehydes

A series of new chiral diselenides with a N-atom in the side chain was prepared by a short synthetic sequence (Scheme 1). Only 1 mol-% of these diselenides catalyzed very effectively the diethylzinc addition to various aromatic and α,β-unsaturated aldehydes yielding the secondary alcohols in up to 98% ee (Scheme 2 and Tables 1 and 2). An asymmetric amplification was observed with these catalysts. Detailed NMR studies were performed to characterize the catalytically active species.     

Synthesis of Selenol Esters from Acid Chlorides and Organic Diselenides in the Presence of the Zn/AlCl3 System

Summary.  Treatment of diphenyl and dibenzyl diselenides with aliphatic and aromatic acid chlorides in the presence of Zn/AlCl₃ affords selenol esters. Availability, low costs, and lack of toxicity of the catalysts, simple reaction work-up, and high yields under relatively mild condition are distinct advantages of this method. Corresponding author. E-mail: movassagh@hotmail.com Received August 26, 2002; accepted September 3, 2002 Published online April 3, 2003     

Synthesis of azido arylselenides and azido aryldiselenides: a new class of selenium-nitrogen compounds

We present here our results of the efficient synthesis of azido arylselenides and azido aryldiselenides under mild conditions. Starting from nitrogen-substituted benzenes, we incorporated selenium atom at aromatic ring and obtained amino arylselenides and diselenides in satisfactory yields. Treatment of these compounds with iso-pentyl nitrite (i-C₅H₁₁ONO) and azido trimethylsilane (Me₃SiN₃) in THF affords a variety of azido arylselenides and diselenides in good to excellent yields.     

Synthesis, structural, spectroscopic and electrochemical studies of carborane substituted naphthyl selenides

New unsymmetrical selenides bearing an o-carborane and a naphthalene ring as the substituents were prepared by the cleavage of the corresponding diselenides. The compounds were characterized by means of spectroscopic and analytical methods. (77)Se NMR signals of the selenium atoms attached to the carbon atoms of the carborane cages are shifted downfield in comparison to those bonded only to the aromatic rings, indicating an electron withdrawing effect of the o-carboranyl substituent. Compounds 1-(2-R-1,2-dicarba-closo-carboranyl)naphthyl selenides (R = Me, 1; Ph, 2) were characterized by means of single crystal X-ray diffraction. The influence of the electronic nature of the substituents attached to the selenium atoms on the structural parameters and packing properties of naphthyl selenides are discussed. Theoretical calculations and cyclic voltammetry (CV) studies were carried out to compare the bonding nature of carboranyl and analogous aryl selenium compounds. Cyclic voltammetry studies of naphthyl carboranyl mono and diselenides have shown that the carboranyl fragment polarizes the Se lone pair making it less prone to generate a Se-Se bond.     

Synthesis and Structure–Activity Correlation Studies of Secondary‐ and Tertiary‐Amine‐Based Glutathione Peroxidase Mimics

In this study, a series of secondary‐ and tertiary‐amino‐substituted diaryl diselenides were synthesized and studied for their glutathione peroxidase (GPx) like antioxidant activities with H₂O₂, cumene hydroperoxide, or tBuOOH as substrates and with PhSH or glutathione (GSH) as thiol cosubstrates. This study reveals that replacement of the tert‐amino groups in benzylamine‐based diselenides by sec‐amino moieties drastically enhances the catalytic activities in both the aromatic thiol (PhSH) and GSH assay systems. Particularly, the N‐propyl‐ and N‐isopropylamino‐substituted diselenides are 8–18 times more active than the corresponding N,N‐dipropyl‐ and N,N‐diisopropylamine‐based compounds in all three peroxide systems when GSH is used as the thiol cosubstrate. Although the catalytic mechanism of sec‐amino‐substituted diselenides is similar to that of the tert‐amine‐based compounds, differences in the stability and reactivity of some of the key intermediates account for the differences in the GPx‐like activities. It is observed that the sec‐amino groups are better than the tert‐amino moieties for generating the catalytically active selenols. This is due to the absence of any significant thiol‐exchange reactions in the selenenyl sulfides derived from sec‐amine‐based diselenides. Furthermore, the seleninic acids (RSeO₂H) derived from the sec‐amine‐based compounds are more stable toward further reactions with peroxides than their tert‐amine‐based analogues.     

Copper‐Catalyzed CH Bond Direct Chalcogenation of Aromatic Compounds Leading to Diaryl Sulfides,Selenides, and Diselenides by Using Elemental Sulfur and Selenium as Chalcogen Sources Under Oxidative Conditions

The reactions of aromatic compounds and elemental chalcogens catalyzed by a copper salt with molecular oxygen as an oxidant were carried out. The reaction of 3‐substituted imidazo[1,5‐a]pyridines and elemental sulfur in the presence of CuTC (copper(I) thiophenecarboxylate) gave the corresponding bisimidazopyridyl sulfides in good to quantitative yields. The reaction proceeded even under aerobic oxidation conditions. The use of a polar solvent was crucial for the reaction, and DMSO (dimethyl sulfoxide) in particular stimulated the reaction. The reaction could be applied to common aromatic compounds, such as N‐methyl indole and dialkyl anilines. The reaction of indole proceeded at the nucleophilic C3 position rather than at the acidic C2 position. In addition, the reaction of dialkyl anilines proceeded with an ortho, para orientation. The reactions of imidazopyridines and elemental selenium under similar conditions gave the corresponding bisimidazopyridyl diselenides along with bisimidazopyridyl monoselenides. The resulting diselenides were readily converted to the corresponding monoselenides with unreacted imidazopyridines under the same conditions. The reaction could be applied to the copolymerization of bifunctional bisimidazopyridines and elemental sulfur to give oligomeric copolymers in quantitative yield.     

First detection of a selenenyl fluoride ArSe-F by NMR spectroscopy: the nature of Ar2Se2/XeF2 and ArSe-SiMe3/XeF2 reagents

Arylselenenyl fluorides ArSeF are obtained from diselenides Ar2Se2 or arylselenotrimethylsilanes ArSe-SiMe3, and XeF2. They are detected by low-temperature 19F and 77Se NMR spectroscopy. Substitution in the ortho position of the aromatic ring to provide electronic or steric protection is a requirement for their formation. ArSe--F compounds decompose according to 3 ArSe-F-->[ArSe-SeF2Ar]+ArSe-F-->ArSeF3+Ar2Se2. Reaction energies for this disproportionation as well as that of the sulfur and tellurium homologues have been calculated with MP2, CCSD(T,) and B3 LYP methods. They were found to be increasingly exothermic in the sequence S相似文献   

Glutathione peroxidase-like antioxidant activity of diaryl diselenides: a mechanistic study.

The synthesis, structure, and thiol peroxidase-like antioxidant activities of several diaryl diselenides having intramolecularly coordinating amino groups are described. The diselenides derived from enantiomerically pure R-(+)- and S-(-)-N,N-dimethyl(1-ferrocenylethyl)amine show excellent peroxidase activity. To investigate the mechanistic role of various organoselenium intermediates, a detailed in situ characterization of the intermediates has been carried out by (77)Se NMR spectroscopy. While most of the diselenides exert their peroxidase activity via selenol, selenenic acid, and selenenyl sulfide intermediates, the differences in the relative activities of the diselenides are due to the varying degree of intramolecular Se.N interaction. The diselenides having strong Se.N interactions are found to be inactive due to the ability of their selenenyl sulfide derivatives to enhance the reverse GPx cycle (RSeSR + H(2)O(2) = RSeOH). In these cases, the nucleophilic attack of thiol takes place preferentially at selenium rather than sulfur and this reduces the formation of selenol by terminating the forward reaction. On the other hand, the diselenides having weak Se.N interactions are found to be more active due to the fast reaction of the selenenyl sulfide derivatives with thiol to produce diphenyl disulfide and the expected selenol (RSeSR + PhSH = PhSSPh + RSeH). The unsubstituted diaryl diselenides are found to be less active due to the slow reactions of these diselenides with thiol and hydrogen peroxide and also due to the instability of the intermediates. The catalytic cycles of 18 and 19 strongly resemble the mechanism by which the natural enzyme, glutathione peroxidase, catalyzes the reduction of hydroperoxides.     

Facile Synthesis of 2H-1,4-Benzothiazin-3(4H)-ketoximes and 2H-1,4-Benzoselenazin-3(4H)-ketoximes Promoted by SmI2

Abstract

2H-1,4-Benzothiazin-3(4H)-ketoximes and 2H-1,4-benzoselenazin-3(4H)-ketoximes were synthesized by the reductive cyclization of bis(o-nitrophenyl) disulfides or diselenides with aromatic or aliphatic β-nitroethylenes using SmI₂ in moderate to good yields under mild conditions.     

Catalytic Antioxidant Activity of Bis-Aniline-Derived Diselenides as GPx Mimics

Herein, we describe a simple and efficient route to access aniline-derived diselenides and evaluate their antioxidant/GPx-mimetic properties. The diselenides were obtained in good yields via ipso-substitution/reduction from the readily available 2-nitroaromatic halides (Cl, Br, I). These diselenides present GPx-mimetic properties, showing better antioxidant activity than the standard GPx-mimetic compounds, ebselen and diphenyl diselenide. DFT analysis demonstrated that the electronic properties of the substituents determine the charge delocalization and the partial charge on selenium, which correlate with the catalytic performances. The amino group concurs in the stabilization of the selenolate intermediate through a hydrogen bond with the selenium.     

An indium-TMSCl promoted reaction of diphenyl diselenides and aldehydes: novel routes to selenoacetals and alkyl phenyl selenides

The reaction of diphenyl diselenides with aldehydes in the presence of In-TMSCl has been investigated. Aliphatic aldehydes provide the corresponding selenoacetals, whereas aromatic aldehydes lead predominantly to alkyl phenyl selenides under the same reaction conditions. This constitutes a new approach for the synthesis of selenoacetals and selenides from aldehydes.     

Diselenide-assisted sulfuration of dienes

Various diselenides assist in the sulfuration of dienes giving cyclic di- and tetrasulfides as main products. The reaction requires a 2-fold excess of diselenides to be efficient. Catalytic amounts of diselenides result in lower yields. This is likely due to secondary reactions (polymerization, aromatization) occurring during extended reaction times under catalytic conditions. It was verified that the sulfur-transferring properties of diselenatetrasulfides are virtually identical to those of diselenides combined with sulfur. Contrary to previous claims, not only the cyclic diselenatetrasulfide but also linear diselenatetrasulfides (RSeS_nSeR) transfer sulfur to dienes. A mechanism is proposed and its implications to the nature of diatomic sulfur are discussed.     

Diorganyl dichalcogenides with intramolecular coordination interactions: the synthesis and structure of bis(4,6-dimethylpyrimidin-2-yl) diselenide

Bis(4,6-dimethylpyrimidin-2-yl) diselenide, a new representative of dihetaryl diselenides, was obtained by successively treating selenourea with hydrochloric acid, acetylacetone, potassium hydroxide, and the system iodine—potassium iodide. The unusual planar trans-conformation of this compound (X-ray diffraction data) is stabilized by intramolecular attractive nonvalent Se…N interactions (Se…N, 2.926(1) Å) and stacking of the π-systems of the aromatic heterocycles (the centers of the pyrimidine rings are spaced apart at 3.365(2) Å). The energy parameters of the factors that make the molecular structure flattened were estimated by quantum chemical DFT calculations.     

The reaction of o-nitro- and p-nitro-phenyl selenocyanates with arylthiols

The interaction of o-nitro- and p-nitro-phenyl selenocyanate with aromatic thiols p-thiocresol, p-chlorothiophenol, 4-bromothiophenol, o-mercaptobenzoic acid and pentafluorothiophenol in non-aqueous media and under an atmosphere of dry nitrogen has been investigated. The main products are the diselenide or the selenenyl sulphide depending on the reactants. Hydrogen cyanide is given in all cases. The IR and Raman spectra of the diselenides and selenenyl sulphides are considered.     

Cleavage of Se-Se Bond by Sm/cat. CoCl2 System: A Novel Method for the Synthesis of Selenoesters

The Sm/cat. CoCl₂ system promoted diselenides to react with anhydrides or acyl chlorides to afford selenoesters in good yield under mild and neutral conditions.     

One-pot synthesis of selenocarbamates from isocyanates and diselenides using the Zn/AlCl3 system

Several N-alkyl/aryl-Se-alkyl/(aryl)selenocarbamates were prepared from various isocyanates and diselenides by reductive cleavage of Se-Se bond with the Zn/AlCl3 system in dry acetonitrile at 80℃.     

一种合成二硒化钠和有机二硒化物的新方法

二硒化物是有机合成中重要的原料及中间体,有些二硒化物还具有生物活性或催化活性。现已有多种方法合成二硒化物,其中用碱金属二硒化物与卤代烷发生取代反应制备二硒化物是较为直接的方法。二硒化钠（Na2Se2)是一种常用的二硒阴离子试剂,它可通过多种方法制得,由Klayman报道的在质子性溶剂、中性条件下用硼氢化钠（NaBH4)还原硒粉（Se)的方法,由于其简便易行常被采用。我们在用此法制备二硒化物时,发现在碱性条件下,反应以一种新的方式进行,相对于Klayman方法具有很多优点,现报道如下。