Dialkynyl selenides: Synthesis, 13C NMR spectra,and molecular orbital calculations

Reactions of SeCl₄ with lithium bis(trimethylsilyl)amide and terminal acetylenes in the presence of BuLi or AIBN afforded the corresponding dialkynyl selenides in moderate to high yields. The reaction may proceed via a selenium amide 7 and an alkynyl selenium amide 8 . The comparison of ¹³C NMR spectra of dialkynyl selenides and tellurides has disclosed that the differences of the chemical shift of acetylenic carbons between Se and Te derivatives are consistent regardless of their substitution patterns. Ab initio molecular orbital calculations are reported for dialkynyl ether and chalcogenides. The calculated structures, charge distributions, and orbital energies are discussed.     

The reaction of selenophosphonates with carbonyl compounds. Vinylic selenides

Selenophosphonates of the general formula (EtO)₂P(O)CHRSePh were prepared and their reactions with aldehydes and ketones investigated. The products formed are vinylic selenides having predominantly the E configuration. Hydrolytic cleavage of these products gives the corresponding ketones.     

Stereoselective Z-iodoalkoxylation of 1,2-allenyl sulfides or selenides

Iodoalkylation of 1,2-allenyl sulfides or selenides with I₂ in MeCN/ROH (20:1) afforded Z-3-alkoxy-2-iodopropenyl sulfides or selenides in high stereoselectivity and moderate to good yields. The carbon-iodine bonds in these compounds may undergo Suzuki, Negishi, and Sonogashira coupling reaction smoothly.     

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.     

Hydroselenation of alkynes using NaBH4/BMIMBF4: easy access to vinyl selenides

A general and easy method for the synthesis of several vinyl selenides using NaBH₄ and BMIMBF₄ as a recyclable solvent is described. This efficient and improved method furnishes the corresponding vinyl chalcogenides preferentially with Z configuration. We also observed that when the same protocol was applied to phenyl acetylene, (E)-bis-phenylseleno styrene was obtained in good yield and with high selectivity.     

Hydrothiolation of terminal alkynes with diaryl disulfides and diphenyl diselenide: selective synthesis of (Z)-1-alkenyl sulfides and selenides

A simple, stereoselective and efficient method for the hydrothiolation of terminal alkynes with diaryl disulfides and diphenyl diselenide has been developed. In the presence of CuI, rongalite, and Cs₂CO₃, a variety of disulfides underwent the reaction of terminal alkynes stereoselectively to afford the corresponding (Z)-1-alkenyl sulfides in moderate to excellent yields. It is noteworthy that hydroselenations of 1,2-diphenyldiselane with alkynes are also conducted smoothly to afford (Z)-1-alkenyl selenides in good yields under the standard conditions.     

Vibrational spectra and molecular conformations of unbranched dialkyl selenides

The IR and Raman spectra of six unbranched dialkyl selenides, namely ethylmethyl selenide, methylpropyl selenide, butylmethyl selenide, diethyl selenide, ethylpropyl selenide and dipropyl selenide, have been systematically investigated. The spectra are analysed on the basis of the spectral examination and the normal coordinate treatment. The CH₂-Se stretching wavenumbers of the dialkyl selenides correlate well with the conformation about the CSe-C-C bond axes. The molecular conformation in the solid and liquid states is studied by utilizing this correlation in conjunction with the wave-numbers of the CH₂ rocking and skeletal deformation vibrations. The conformational stability in the liquid state is also examined and the enthalpy difference between the trans and gauche forms of ethylmethyl selenide is obtained as 0.22 ± 0.05 kcal mol^?1, the gauche form being more stable. The conformational stability of dialkyl ethers, sulphides and selenides are comparatively discussed.     

Selenium-77 chemical shifts of cyclodiphosphazane selenides

Isomeric cyclodiphosphazane selenides, R(X)P(NBu¹)₂P(Y)R (R=OMe or NMe₂, X=Se, Y=lone pair; R=OMe or NMe₂, X=Y=Se) display large differences (34–122 ppm) in ⁷⁷Se chemical shift. The ⁷⁷Se shifts of these and related amino derivatives are well to low field of the ⁷⁷Se shifts of analogous acyclic phosphorus selenides.     

Iridium-catalyzed [2+2+2] cycloaddition of α,ω-diynes with alkynyl ketones and alkynyl esters

We found that the combination of [Ir(cod)Cl]₂ and rac-BINAP served as an efficient catalyst for the [2+2+2] cycloaddition of 2,7-nonadiyne derivatives and related compounds with alkynyl ketones and alkynyl esters. The corresponding products were obtained in high yields under mild reaction conditions.     

[2+2] Cycloaddition of electron-poor acetylenes to (E)-3-dimethylamino-1-heteroaryl-prop-2-en-1-ones: synthesis of highly functionalized 1-heteroaroyl-1,3-butadienes

Microwave-assisted [2+2] cycloaddition of (E)-3-dimethylamino-1-heteroaryl-prop-2-en-1-ones to dimethyl acetylenedicarboxylates gives (2E,3E)-dimethyl-2-[(dimethylamino)methylene]-3-(substituted)succinates in 8-91% yield. In the case of a 4,5-dihydrothiazoline derivative, cycloaddition also took place at the endocyclic CN double bond.     

Lipase-catalyzed resolution of β-hydroxy selenides

Eleven β-hydroxy selenides were kinetically resolved using an immobilized lipase (Amano PS-C II) in toluene in the presence of vinyl acetate at 30 °C. This approach provided, in several cases, both enantiomers in high enantiomeric excess. The role of the size of substituents and the behaviour of cyclic β-hydroxy selenides is also discussed. Enantiopure β-hydroxy selenides are useful building blocks. As an application of this chemistry, enantiopure (1S,2R)-indene oxide was obtained in one step from the proper enantiopure β-hydroxy selenide.     

Conformational analysis of secondary arylalkylphosphine selenides

Conformational analysis of bis(2-phenylalkyl)phosphine selenides was performed by the dipole moment method and quantum-chemical calculations. Bis(2-phenylpropyl)phosphine selenide was found to exist as a mixture of several conformers, the most energetically favorable of which being characterized by gauche (non-eclipsed) orientation of the P=Se and $C_{sp^3 } - C_{sp^3 } $ bonds.     

Cesium hydroxide-catalyzed hydrothiolation of alkynyl selenides to highly stereo- and regioselectively synthesize(Z)- -organoseleno-2-arylthio-1-alkenes

In the presence of catalytic amount of cesium hydroxide the hydrothiolation of alkynyl selenides occurred at room temperature in DMF under nitrogen atmosphere to give exclusive(Z)-1-organoseleno-2-arylthio-1-alkene in excellent yields.It could provide a new and expedient way for the preparation of(Z)-1-arylseleno-2-arylthio-1-alkene.     

Triorganotin aryl selenides

The SnSe bond in trimethyltin aryl selenides is cleaved on reaction with selenenyl halides, sulphenyl halides, alkyl halides and allyl halides. Thus Me₃SnSePh reacts with PhSeCl, 4-Me-2-NO₂C₆H₃SCl, RI (R = CH₃ or Ph₃SnCH₂) and CH₂CHCH₂Br to give PhSeSePh, 4-Me-2-NO₂C₆H₃SSePh, RSePh and CH₂CHCH₂SePh, respectively. The diselenide, PhSeSePh, is also obtained from Me₃SnSePh on reaction with either 4-MeC₆H₄SO₂Cl or NaIO₄. Exchange reactions also occur between Me₃SnSePh and Ph₃SnCl or PhHgCl.     

Cross-coupling of alkenyl,aryl or allylic selenides and grignard reagents catalyzed by nickel-phosphine complexes

Alkenyl, aryl or allylic selenides smoothly couple with Grignard reagents in the presence of Ni(II)-phosphine complexes as catalysts to afford the corresponding unsaturated compounds in good yields. The reactivity order of coupling reaction with BuMgBr catalyzed by NiCl₂ [Ph₂PCH₂CH₂CH₂PPh₂] was found to be PhSeMe « PhCl > PhSMe by the competitive reactions.     

A general method for the formation of diaryl selenides using copper(I) catalysts

We report a mild, palladium-free synthetic protocol for the cross coupling reaction of aryl iodides and phenyl selenol using 10 mol% CuI/neocuproine, NaOt-Bu or K₂CO₃ as base, in toluene, at 110°C. Using this protocol, we show that a variety of diaryl selenides can be synthesized in good yields from commercially available aryl iodides.     

Synthesis of bis(2-haloalkyl) selanes and selenides based on selenium dioxide and terminal alkenes

Selenium tetrahalides generated from selenium dioxide and hydrogen halides (HCl, HBr) reacted with hex-1-ene, hept-1-ene, and oct-1-ene at a SeO₂?alkene molar ratio of 1: 2 to give mixtures of dihalobis-(2-haloalkyl)-λ⁴-selanes (yield 80?90%) and bis(2-haloalkyl) selenides (yield 5?12%). Halogenation of the resulting mixtures afforded 85?93% (calculated on the initial SeO₂) of the corresponding dihalobis(2-haloalkyl)-λ⁴-selanes, and the reduction of the same mixtures with Na₂S₂O₅ gave bis(2-haloalkyl) selenides in 80?86% yield. In the reaction with a SeO₂?alkene ratio of 5: 8, pure dihalobis(2-haloalkyl)-λ⁴-selanes were formed in 84?93% yield. Dichlorobis(2-chloro-2-phenylethyl)-λ⁴-selane was obtained in 72% yield in the reaction of SeO₂?HCl with styrene.     

Preparation of bis(2-pyridyl) diselenide derivatives: Synthesis of selenazolo[5,4-b]pyridines and unsymmetrical diorganyl selenides,and evaluation of antioxidant and anticholinesterasic activities

We describe here an alternative method to prepare bis(2-pyridyl) diselenide derivatives using reduced selenium species, generated in situ, and different 2-chloropyridines promoted by p-TSOH in PEG-400 as solvent. This is a straightforward protocol to prepare bis(3-amino-2-pyridyl) diselenides unprecedented to date. Still, this article describe the employment of synthesized bis(3-amino-2-pyridyl) diselenide and a diverse array of aryl aldehydes to afford the corresponding 2-aryl-selenazolo[5,4-b]pyridines in satisfactory yields and, in a short reaction time under basic condition. Furthermore, when the bis(3-amino-2-pyridyl) diselenide reacted with aliphatic halides, in the presence of NaBH₄, a wide range of unsymmetrical diorganyl selenides was obtained. To complete this investigation the bis(3-amino-2-pyridyl) diselenide was evaluated for its inhibitory effect on the acetylcholinesterase (AChE) activity and free radical-scavenging capacity. Results demonstrated that this compound was antioxidant and inhibitor of the AChE activity, being a promising therapeutic agent for the treatment of Alzheimer’s disease and other neurodegenerative disorders.     

Enol-mediated delivery of H2Se from γ-keto selenides: mechanistic insight and evaluation

Like hydrogen sulfide (H₂S), its chalcogen congener, hydrogen selenide (H₂Se), is an emerging molecule of interest given its endogenous expression and purported biological activity. However, unlike H₂S, detailed investigations into the chemical biology of H₂Se are limited and little is known about its innate physiological functions, cellular targets, and therapeutic potential. The obscurity surrounding these fundamental questions is largely due to a lack of small molecule donors that can effectively increase the bioavailability of H₂Se through their continuous liberation of the transient biomolecule under physiologically relevant conditions. Driven by this unmet demand for H₂Se-releasing moieties, we report that γ-keto selenides provide a useful platform for H₂Se donation via an α-deprotonation/β-elimination pathway that is highly dependent on both pH and alpha proton acidity. These attributes afforded a small library of donors with highly variable rates of release (higher alpha proton acidity = faster selenide liberation), which is accelerated under neutral to slightly basic conditions—a feature that is unique and complimentary to previously reported H₂Se donors. We also demonstrate the impressive anticancer activity of γ-keto selenides in both HeLa and HCT116 cells in culture, which is likely to stimulate additional interest and research into the biological activity and anticancer effects of H₂Se. Collectively, these results indicate that γ-keto selenides provide a highly versatile and effective framework for H₂Se donation.

Like hydrogen sulfide (H₂S), its chalcogen congener, hydrogen selenide (H₂Se), is an emerging biomolecule of interest. Therefore, small molecule donors that effectively increase its bioavailability are desired to further probe H₂Se chemical biology.     

Synthesis and characterisation of trisarylphosphine selenides: Further insight into the effect of fluoroalkylation on the electronic properties of trisarylphosphines

Variations in the magnitude of the ¹J_SeP coupling constants for a range of phosphorus(V) selenides allow the efficiency of different spacer groups at insulating the phosphorus centre in triarylphosphines from highly electron-withdrawing perfluoroalkyl groups to be established.