Design, Synthesis, and Antibacterial Activities of Multi-functional C2-Functionalized 1,4-Naphthoquinonyl Organoseleniums.

A practical and efficient reaction for C2-selenylation of 1,4-naphthoquinones has been explored. This coupling reaction of two redox structural motifs, such as 2-bromo-1,4-naphthoquinone with diaryldiselenide / ebselen has been achieved by using sodium borohydride reducing agent at room temperature. Using this approach, several 2-selenylated-1,4-naphthoquinones were obtained in moderate to good yields and thoroughly characterized by multinuclear (1H, 13C, and 77Se) NMR, cyclic voltammetry, and mass spectrometry.

Substrate NOBINAc ligand affinity for Pd-catalyzed enantioselective C-H activation over reactive β-C-H bonds in ferrocenyl amines.

Ferrocenyl amines as directing groups for C-H activation have limitations as they are prone to undergo oxidation, allylic deamination, and β-hydride elimination. The fundamental challenge observed here is the competition between the desired C-H activation the vulnerable β-C-H bond activation of amines and fine-tuning of a suitable oxidant which avoids the oxidation of the β-C-H bond and ferrocene. Herein, the potential of an axially chiral NOBINAc ligand is revealed to implement the enantioselective Pd-catalyzed C-H activation process of ferrocenyl amines.

Regio- and diastereoselective synthesis of cyclobutylated phenothiazines [2 + 2] photocycloaddition: demonstrating wavelength-gated cycloreversion inside live cells.

Herein, we unveiled a regio- and diastereoselective synthesis of cyclobutylated phenothiazines, a unique class of structural congeners of phenothiazines visible-light-irradiated intermolecular [2 + 2]-cycloaddition reaction, from readily available naphthoquinones, 2-aminothiophenols, and styrenes, either in a two-step or three-component coupling process. By varying substitutions in all three coupling partners, a library of cyclobutylated phenothiazines, including late-stage derivatization with five commercial drugs, has been realized with up to 97% isolated yield. In contrast to the reported pathways, the developed [2 + 2]-photocycloaddition seems to proceed a 'photoinduced-electron-transfer' (PET) mechanism, which is well corroborated with the experimental observations, Rehm-Weller equation, and computation studies.

Temperature-Dependent Diastereodivergent [4 + 3] Annulation: Synthesis of Ferrocene-Fused Azepines via Rh(III) Catalysis.

Herein, we disclose the first temperature-dependent diastereodivergent [4 + 3] annulation of ferrocene--tosylamides C-H activation with allenes by a Rh catalyst. At room temperature, Rh-catalyzed [4 + 3] annulation selectively offered a kinetically controlled diastereomer [>20:1 diastereomeric ratio (dr)], whereas at 60 °C, a thermodynamically controlled diastereomer was obtained exclusively with >20:1 dr.

Benzoimidazolyl Organoseleniums: Antioxidant Activity and Catalysts for Selective Iodination of Arenes and Nitro-Michael Reaction.

Here, the synthesis and catalytic activities of benzoimidazole-derived organoselenium compounds have been explored. The synthesized bis(2-benzoimidazolyl) diselenide, having increased Lewis acidity on the selenium center, outperforms simple phenyl and -phenyl benzamide-based diselenides when compared for thiol peroxidase hydrogen peroxide decomposing antioxidant activity with a reduction rate of 18.6 ± 1.

Directing Group Strategy for the Isolation of Organoselenium(VI) Benzoselenonates: Metal-Free Catalysts for Hydrogen Evolution Reaction.

The exploration of fourth-period organoelements, particularly organoseleniums in their highest VI oxidation state, is limited owing to their stability and synthesis. Herein, the isolation of a new class of quinolinyl-embedded, hexavalent selenium(VI) benzoselenonates has been discussed and further evaluated for a metal-free electrocatalytic hydrogen evolution reaction (HER). The Se(VI) benzoselenonates exhibited high Faradaic efficiency (F.

Blue-Light Irradiated Mn(0)-Catalyzed Hydroxylation and C(sp )-H Functionalization of Unactivated Alkanes with C(sp )-H Bonds of Quinones for Alkylated Hydroxy Quinones and Parvaquone.

Site-selective C(sp )-H functionalization of unreactive hydrocarbons is always challenging due to its inherited chemical inertness, slightly different reactivity of various C-H bonds, and intrinsically high bond dissociation energies. Here, a site-selective C-H alkylation of naphthoquinone with unactivated hydrocarbons using Mn (CO) as a catalyst under blue-light (457 nm) irradiation without any external acid or base and pre-functionalization is presented. The selective C-H functionalization of tertiary over secondary and secondary over primary C(sp )-H bonds in abundant chemical feedstocks was achieved, and hydroxylation of quinones was realized in situ by employing the developed methodology.

Bidentate Ligand Driven Intramolecularly Te…O Bonded Organotellurium Cations from Synthesis, Stability to Catalysis.

A new series of unsymmetrical phenyl tellurides derived from 2-N-(quinolin-8-yl) benzamide ligand has been synthesized in a practical manner by the copper-catalyzed method by using diaryl ditelluride and Mg as a reductant at room temperature. In order to augment the Lewis acidity of these newly formed unsymmetrical monotellurides, these have been transformed into corresponding unsymmetrical 2-N-(quinolin-8-yl)benzamide tellurium cations. Subsequently, these Lewis acidic tellurium cations were used as chalcogen bonding catalysts, enabling the synthesis of various substituted 1,2-dihydroquinolines by activating ketones with anilines under mild conditions.

2-Benzamide Tellurenyl Iodides: Synthesis and Their Catalytic Role in CO Mitigation.

Benzamide-derived organochalcogens (chalcogen=S, Se, and Te) have shown promising interest in biological and synthetic chemistry. Ebselen molecule derived from benzamide moiety is the most studied organoselenium. However, its heavier congener organotellurium is under-explored.

Coordination Behavior of the Tellurium Incorporated Mercuraazametallamacrocycle and Investigation of d ⋅⋅⋅d Interactions between Closed Shell (Ag Hg ) Metal Ions.

Herein, a new tellurium and mercury containing mercuraazametallamacrocycle has been prepared via (2+2) condensation of bis(o-aminophenyl)telluride and bis(o-formylphenyl)mercury(II). The isolated bright yellow solid of mercuraazametallamacrocycle has adopted unsymmetrical figure-of-eight conformation in the crystal structure. To study the metallophilic interactions between closed shell metal ions, the macrocyclic ligand has been treated with two equiv.

Blue Light Irradiated Metal-, Oxidant-, and Base-Free Cross-Dehydrogenative Coupling of C()-H and N-H Bonds: Amination of Naphthoquinones with Amines.

Herein, we report a blue-light-driven amination of C()-H bond of naphthoquinones and quinones with the N-H bond of primary and secondary amines for the synthesis of 2-amino-naphthoquinones and 2-amino-quinones. The coupling of naphthoquinones with a wide array of aliphatic, aromatic, chiral, primary, and secondary amines having electron donating (-CH, -OCH, -SCH), withdrawing (-F, -Cl, -Br, -I), and COH, -OH, -NH groups with acidic protons selectively occurred to afford C-N coupled 2-amino-naphthoquinones in 60-99% yields and hydrogen gas as a byproduct in methanol solvent without using any additional reagents, additives, and oxidant under the blue light irradiation. Mechanistic insight by DFT computation, controlled experiments, kinetic isotopic effect, and substitution effect of the substrates suggest that the reaction proceeds by radical pathway in which naphthoquinone forms a highly oxidizing naphthoquinonyl biradical upon irradiation of blue light (457 nm).

Detailed Insights into the Inhibitory Mechanism of New Ebselen Derivatives against Main Protease (M) of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2).

SARS-CoV-2 main protease (M/3CL) is a crucial target for therapeutics, which is responsible for viral polyprotein cleavage and plays a vital role in virus replication and survival. Recent studies suggest that 2-phenylbenzisoselenazol-3(2)-one (ebselen) is a potent covalent inhibitor of M, which affects its enzymatic activity and virus survival. Herein, we synthesized various ebselen derivatives to understand the mechanism of M inhibition by ebselen.

Synthesis of cobalt(II) phenolate selenoether complexes to mimic hydrogenase-like activity for hydrogen gas production.

Selenium-derived electrocatalysts have been well explored for electrocatalytic hydrogen evolution reactions to mimic hydrogenase-like activity; however, the stability of these synthetic mimics is yet to be enhanced. In this study, we report the synthesis and characterization of a series of 1,10-phenanthroline-cobalt(II) phenolate selenoether complexes using 1,10-phenanthroline and 6-nitro-1,10-phenanthroline-Co(II)-dichloride and substituted bis-selenophenolate ligands. The synthesized cobalt(II) phenolate selenoether complexes have been characterized by CHN analysis, mass spectrometry, single crystal XRD, and UV-visible absorption spectroscopy.

Light-Driven Carbon-Carbon Coupling of α-sp-CH of Aliphatic Alcohols with sp-CH Bond of 1,4-Naphthoquinones.

Here, an α-selective C-H bond functionalization of primary aliphatic alcohols with 1,4-naphthoquinones yielded C-C coupled products driven by blue-LED light under catalyst, metal, base, and reagent-free conditions. In this transformation, cleavage of three C-H bonds (two sp-C-H, one sp-C-H, and one O-H) and four new bonds formed, leading to fluorescent 2-acylated-1,4-naphthohydroquinones.

A base-free copper-assisted synthesis of -symmetric spirotelluranes and biaryls based on divergent stoichiometry of NaTe.

A one pot Cu(I)-assisted synthetic methodology has been developed for the preparation of biologically important -symmetric spirodiaza, benzyloxy and benzoxytelluranes from 2-bromo--aryl benzamides, benzyl alcohols, and benzoic acids by using the tellurium dianion (Te) under base-free conditions. Furthermore, C-C coupled biaryl 1,1'-diamides have been prepared by using an excess of NaTe under the same reaction conditions. The synthesized spirodiazatelluranes served as a potent catalyst for the reduction of HO and nitro-Michael reactions.

Tetravalent Spiroselenurane Catalysts: Intramolecular Se···N Chalcogen Bond-Driven Catalytic Disproportionation of HO to HO and O and Activation of I and NBS.

Chalcogen-bonding interactions have recently gained considerable attention in the field of synthetic chemistry, structure, and bonding. Here, three organo-spiroselenuranes, having a Se(IV) center with a strong intramolecular Se···N chalcogen-bonded interaction, have been isolated by the oxidation of the respective (2-benzamide) selenides derived from an 8-aminoquinoline ligand. Further, the synthesized spiroselenuranes, when assayed for their antioxidant activity, show disproportionation of hydrogen peroxide into HO and O with first-order kinetics with respect to HO for the first time by any organoselenium molecules as monitored by H NMR spectroscopy.

Isolation of monomeric copper(II) phenolate selenoether complexes using chelating -bisphenylselenide-phenolate ligands and their electrocatalytic hydrogen gas evolution activity.

A series of novel copper(II) phenolate selenoether complexes have been synthesized and structurally characterized for the first time from copper(I) phenanthroline and various substituted -bisphenylselenide-phenol chelating ligands. The synthesized complexes exhibit Jahn-Teller distortion in their geometry and varied from distorted square planar to distorted octahedral by varying the substituent in the bis-selenophenolate ligand. The synthesized complexes electrocatalyze the hydrogen evolution reaction (HER) with a faradaic efficiency of up to 89%, and it was observed that the distorted square pyramidal geometry is the optimum geometry for the maximum efficiency of these copper complexes.

Proton reduction by a bimetallic zinc selenolate electrocatalyst.

The development of alternative energy sources is the utmost priority of developing society. Unlike many prior homogeneous electrocatalysts that rely on a change in the oxidation state of the metal center and/or electrochemically active ligand, here we report the synthesis and structural characterization of a bimetallic zinc selenolate complex consisting of a redox silent zinc metal ion and a tridentate ligand that catalyzes the reduction of protons into hydrogen gas electrochemically and displays one of the highest reported TOF for a homogeneous TM-metal free ligand centered HER catalyst, 509 s. The current-voltage analysis confirms the onset overpotential of 0.

Janus -faced oxidant and antioxidant profiles of organo diselenides.

To date, organoseleniums are pre-eminent for peroxide decomposition and radical quenching antioxidant activities. On the contrary, here, a series of Janus-faced aminophenolic diselenides have been prepared from substituted 2-iodoaniline and selenium powder using copper-catalyzed methodology. Subsequently, condensation with substituted salicylaldehyde afforded the Schiff base, which on reduction, yielded the desired substituted aminophenolic diselenides in 72%-88% yields.

Radical Chain Breaking Bis(ortho-organoselenium) Substituted Phenolic Antioxidants.

The presence of a chalcogen atom at the ortho-position of phenols enhances their radical chain-breaking activity. Here, a copper(I)-catalyzed reaction of 2,6-dibromo- and 2,6-diiodophenols with diorganodiselenides has been studied for the introduction of two organoselenium substituents at both ortho-positions of the phenolic radical chain-breaking antioxidants, which afforded 2,6-diorganoseleno-substituted phenols in 80-92% yields having electron-donating CH , and electron-withdrawing CN and CHO functionalities. Additionally, 2,6-diiodophenols with electron-withdrawing CHO and CN groups also afforded novel 5,5'-selenobis(4-hydroxy-3-(phenylselanyl)benzaldehyde) and 5,5'-selenobis(4-hydroxy-3-(phenylselanyl)benzonitrile) consisting of three selenium and two phenolic moieties along with 2,6-diorganoseleno-substituted phenols has been synthesized.

Synthesis of Chiral-Substituted 2-Aryl-ferrocenes by the Catellani Reaction.

A palladium-catalyzed and norbornene-mediated methodology has been developed for the synthesis of chiral 2-aryl-ferroceneamides from chiral 2-iodo-,-diisopropylferrocencarboxamide, iodoarenes, and alkenes using a JohnPhos ligand and potassium carbonate as a base in dimethylformamide at 105 °C. The developed three-component coupling protocol allows the compatibility of electron-withdrawing fluoro, chloro, ester, and nitro and electron-donating methyl, methoxy, dimethoxy, benzyl ether-substituted iodo-benzenes, other iodoarenes, such as iodo-naphthalene, heteroarenes, such as iodothiophene, and terminating substrates, such as methyl, ethyl, -butyl acrylates, and substituted styrenes with 2-iodo-,-diisopropylferrocencarboxamide. Furthermore, the developed three-component Catellani method proceeded with the retention of the configuration of the planar chiral ferrocene, which depends on the role of the participating carbon-iodine bond in ferrocene.

8-Aminoquinoline-Assisted Synthesis and Crystal Structure Studies of Ferrocenyl Aryl Sulfones.

A copper-catalyzed 8-aminoquinoline-directed oxidative cross-coupling of the C-H bond of ferrocene with sodium arylsulfinates has been achieved. The robust copper catalyst tolerates a range of methyl, tert-butyl, bromo, chloro, iodo and nitro functional groups in the phenyl ring, and set the stage for the synthesis of substituted ferrocene sulfones. Furthermore, X-ray crystal structure study on several ferrocenyl sulfones reveals the tetrahedral geometry around sulfur; interestingly, the O-S-O angle is larger than the electropositive substituent C-S-C angle which could be explained by Bent's rule.

Copper-Mediated Selective Mono- and Sequential Organochalcogenation of C-H Bonds: Synthesis of Hybrid Unsymmetrical Aryl Ferrocene Chalcogenides.

An 8-aminoquinoline-directed, copper/1,10-phenanthroline-mediated selective mono-organothiolation of the C-H bond in ferroceneamide has been developed using aryl/alkyl disulfide substrates. The sequential ferrocene C-H organochalcogenation (chalcogen = S, Se, and Te) has also been established for the synthesis of novel hybrid unsymmetrical aryl chalcogenides with the aid of a catalytic amount of Cu(OAc) under ambient reaction conditions. The developed protocol results in a broad functional group tolerance to allow alkyl-, aryl-, heteroaryl-, bromo-, chloro-, and nitro-containing diorgano dichalcogenides as coupling partners.

An efficient copper-catalyzed synthesis of symmetrical bis(N-arylbenzamide) selenides and their conversion to hypervalent spirodiazaselenuranes and hydroxy congeners.

A copper catalyzed efficient synthetic method has been developed to access bis(N-arylbenzamide) selenides from 2-halo-N-arylbenzamide substrates and disodium selenide in HMPA at 110 °C. The developed protocol tolerates substituents in both N-aryl and benzamide rings of the 2-halobenzamide substrates and provides an array of bis(N-arylbenzamide) selenides in practical yields. The resulting selenides were transformed into hypervalent spirodiazaselenuranes by oxidation using aqueous hydrogen peroxide.

An Organodiselenide with Dual Mimic Function of Sulfhydryl Oxidases and Glutathione Peroxidases: Aerial Oxidation of Organothiols to Organodisulfides.

A novel organodiselenide, which mimics sulfhydryl oxidases and glutathione peroxidase (GPx) enzymes for oxidation of thiols by oxygen and hydrogen peroxide, respectively, into disulfides has been presented. The developed catalyst oxidizes an array of organothiols into respective disulfides in practical yields by using aerial O to avoid any reagents/additives, base, and light source. The synthesized diselenide also catalyzes the reduction of hydrogen peroxide into water by following the GPx enzymatic catalytic cycle with a reduction rate of 49.