Reaction of Selenoamide Dianions with Thio- and Selenoformamides Leading to the Formation of 5-Aminoselenazoles: Photophysical and Electrochemical Properties

Nucleophilic Selenocyclization Reaction of Benzodiynes Promoted by Sodium Selenide: Synthesis of Isoselenochromenes

We describe here the synthesis of isoselenochromenes via a nucleophilic selenocyclization reaction of benzodiynes with sodium selenide. The central parameters that affect this cyclization reaction were studied, and the best reaction conditions were applied to different substrates to determine the scope of the method. The results indicated that isoselenochromenes were obtained in higher yields when the reactions were performed by the addition of NaBH4 (3 equiv), at room temperature, under nitrogen atmosphere, to a solution of elemental selenium (2 equiv) in dimethylformamide (2 mL). After 1 h, a benzodiynes (0.25 mmol) solution in EtOH (3 mL) was added at room temperature. The reaction was stirred at 75 °C until the starting material was consumed. The best conditions were applied to benzodiynes having electron-rich, electron poor aromatic rings, and alkyl groups directly bonded to the alkynes. The same reaction condition was extended to isothiochromene derivatives but failed to prepare isotelurochromenes. The isoselenochromenes were easily transformed into three new classes of organoselenium compounds using classical methods available in the literature. We also conducted several control experiments to propose a reaction mechanism.

Exo-trig selenocyclization of secondary allylic carboxamides using Woollins' reagent: en route to 2,5-disubstituted selenazolines

We report microwave-assisted selenation and exo-trig cyclization of secondary allylic carboxamides using Woollins' reagent, a serendipitous finding observed during an attempt to synthesize N-allylbenzoselenoamide compounds. This resulted in the first reported synthesis of 2-aryl-5-methyl selenazolines. Twenty-one diversified selenazolines and three late-stage-functionalized drug molecules were synthesized in 42-93% and 25-52% yield, respectively, and these were evaluated further for their anti-proliferative activity.

Construction of the 2-Amino-1,3-selenazole Skeleton via PhICl2/KSeCN-Mediated Selenocyanation/Cyclization

The construction of 2-amino-1,3-selenazole skeleton was realized via the PhICl₂/KSeCN-enabled electrophilic selenocyanation of β-enaminones and β-enamino esters followed by intramolecular cyclization under basic conditions. Compared to the classical Hantzsch strategy that utilizes selenourea or its analogues as starting materials or crucial intermediates, this method might represent an alternative approach for the assembly of 1,3-selenazole framework through a different pathway.

Indirect Electrosynthesis with Halogen Ions as Mediators

Organic electrosynthesis has gained increasing research interest as it harvests electric current as redox regents, thereby providing a sustainable alternative to conventional approaches. Compared with direct electrosynthesis, indirect electrosynthesis employs mediator(s) to lower the overpotentials for substrate activation, and enhance the reaction efficiency and functional group compatibility by shifting the heterogenous electron transfer process to be homogenous. As one of the most versatile and cost-efficient mediators, halogen mediators are always combined with an irreversible halogenation reaction. Thus, the electrochemical reaction between halogen mediators and substrates doesn't directly controlled by the two standard potentials difference. In this account, our recent developments in the area of halogen-mediated indirect electrosynthesis are summarized. The anodically generated halogen species from halogenide salts have the abilities to undergo electron-transfer (ET) or hydrogen-atom- transfer (HAT) processes. The reaction features, scopes, limitations, and mechanistic rationalisations are discussed in this account. We hope our studies will contribute to the future developments to broaden the scope of halogen-mediated electrosynthesis.

Base-Promoted Multicomponent Reactions: A Synthesis of 2-Amino-1,3-selenazole Derivatives

New practical synthesis of 2-amino-1,3-selenazole with transition metal-free multicomponent reaction is reported here. A series of 2-amino-1,3-selenazole derivatives were afforded by the nucleophilic addition of amines to isoselenocyanate formed in situ, followed by Michael addition reaction and aromatization. The products were isolated from moderate to excellent yields.

Recent Advances on C-Se Bond-forming Reactions at Low and Room Temperature

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Over the last decades, many methods have been reported for the synthesis of selenium- heterocyclic scaffolds because of their interesting reactivities and applications in the medicinal as well as in the material chemistry. This review describes the recent numerous useful methodologies on C-Se bond formation reactions which were basically carried out at low and room temperature.

Co(iii) complexes of (1,3-selenazol-2-yl)hydrazones and their sulphur analogues

The first Co(iii) complexes with (1,3-selenazol-2-yl)hydrazones as an unexplored class of ligands were prepared and characterized by NMR spectroscopy and X-ray diffraction analysis. The novel ligands act as NNN tridentate chelators forming octahedral Co(iii) complexes. The impact of structural changes on ligands' periphery as well as that of isosteric replacement of sulphur with selenium on the electrochemical and electronic absorption features of complexes are explored. To support the experimental data, density functional theory (DFT) calculations were also conducted. Theoretical NMR chemical shifts, the relative energies and natural bond orbital (NBO) analysis are calculated within the DFT approach, while the singlet excited state energies and HOMO-LUMO energy gap were calculated with time-dependent density functional theory (TD-DFT). The electrophilic f^- and nucleophilic f⁺ Fukui functions are well adapted to find the electrophile and nucleophile centres in the molecules. Both (1,3-selenazol-2-yl)- and (1,3-thiazol-2-yl)hydrazone Co(iii) complexes showed potent antimicrobial and antioxidant activity. A significant difference among them was a smaller cytotoxicity of selenium compounds.

Synthesis and Single Crystal Structures of Substituted-1,3-Selenazol-2-amines

The synthesis and X-ray single crystal structures of a series of new 4-substituted-1,3-selenazol-2-amines is reported. The efficient preparation of these compounds was carried out by two-component cyclization of the selenoureas with equimolar amounts of α-haloketones. The selenoureas were obtained from the reaction of Woollins’ reagent with cyanamides, followed by hydrolysis with water. All new compounds have been characterized by IR spectroscopy, multi-NMR (¹H, ¹³C, ⁷⁷Se) spectroscopy, accurate mass measurement and single crystal X-ray structure analysis.

Acid-Responsive Absorption and Emission of 5-N-Arylaminothiazoles: Emission of White Light from a Single Fluorescent Dye and a Lewis Acid

Solutions of 5-N-arylaminothiazoles containing pyridyl groups exhibited clear halochromism and halofluorism upon addition of Brønsted and Lewis acids. The addition of triflic acid to solutions of 5-N-arylaminothiazoles in Et2O induced bathochromic shifts of the absorption and emission bands. DFT calculations suggested that the spectral changes arise from the protonation of the pyridyl group of the thiazoles in Et2O. Single-crystal X-ray diffraction analysis of a thiazole and its protonated form revealed the change of the conformation around the thiazole ring. The emission of white light was accomplished from a single fluorescent dye by adjusting the ratio of dye and B(C6F5)3, whereby the International Commission on Illumination coordinates showed a linear change from blue to orange.

Dipolar Dyes with a Pyrrolo[2,3-b]quinoxaline Skeleton Containing a Cyano Group and a Bridged Tertiary Amino Group: Synthesis, Solvatofluorochromism, and Bioimaging

Two strongly polarized dipolar chromophores possessing a cyclic tertiary amino group at one terminus of the molecule and a CN group at the opposite terminus were designed and synthesized. Their rigid skeleton contains the rarely studied pyrrolo[2,3-b]quinoxaline ring system. The photophysical properties of these regioisomeric dyes were different owing to differing π conjugation between the CN group and the electron-donor moiety. These dipolar molecules showed very intense emission, strong solvatofluorochromism, and sufficient two-photon brightness for bioimaging. One of these regioisomeric dyes, namely, 11-carbonitrile-2,3,4,5,6,7-hexahydro-1H-3a,8,13,13b-tetraazabenzo[b]cyclohepta[1,2,3-jk]fluorene, was successfully utilized in two-photon imaging of mouse organ tissues and showed distinct tissue morphology with high resolution.