Kharasch reaction: Cu-catalyzed and non-Kharasch metal-free peroxidation of barbituric acids

It was discovered that the Kharasch peroxidation of barbituric acids proceeds both with a Cu-catalyst and without a metal catalyst. Despite the presence of possible thermal-initiated side oxidation pathways, α-tert-butylperoxybarbiturates were selectively prepared from substituted barbituric acids and tert-butyl hydroperoxide.     

Oxidative sulfamidation of vinyl silanes: A route to diverse silylated N-Heterocycles

The reaction of trimethyl(vinyl)silane 1 and dimethyl(divinyl)silane 2 with various sulfonamides in the oxidative system (tert-BuOCl + NaI) has been studied and shown to be an efficient approach for the synthesis of silylated N-heterocycles. Triflamide demonstrated the reactivity principally different from that of arenesulfonamides. With silane 1, it afforded the products of iodochlorination and bis(triflamidation) (major), whereas arenesulfonamides gave N-arenesulfonylaziridines in up to 91% yield. Silane 2 with arenesulfonamides yielded the products of mono and bis(iodochlorination), mono and bis(aziridination), and 3,5-diiodo-4,4-dimethyl-1-(arylsulfonyl)-1,4-azasilinanes. By contrast, triflamide, apart from the products of halogenation and iodotriflamidation, unexpectedly gave 3-(trifluoromethylsulfonyl)-5-(triflamido)oxazolidine as the main product. The structure of most heterocyclic products is proved by X-ray analysis. The effect of the silyl group in the substrate and of the substituent in the reagent on the course of oxidative sulfamidation is discussed by comparing with all-carbon analogues.     

Green synthesis of gold nanoclusters using papaya juice for detection of l-lysine

P-AuNCs was rapidly synthesized, while papaya juice served as a capping and reducing agent. Due to the surface electron density increase-induced fluorescence enhancing principle, the prepared fluorescent probe provided high selectivity and sensitivity for monitoring L-lysine in human urines.     

Metal-free synthesis of novel indolizines from chromones and pyridinium salts via 1,3-dipolar cycloaddition,ring-opening and aromatization

A simple, efficient, and economical synthetic approach to construct a variety of stucturally novel indolizines bearing a phenolic hydroxy group has been developed through 1,3-dipolar cycloaddition of chromones and pyridinium salts. The methodology is tolerant of a wide range of functional groups and applicable to library synthesis.     

Polymerizable C70 derivatives with acrylate functionality for efficient and stable solar cells

Fullerene-based organic solar cells are generally suffering from severe microstructure evolution occurring in their bulk heterojunction active layers and thus are extremely stable. To address it, four polymerizable C₇₀ fullerene derivatives, [6,6]-phenyl-C₇₁-ethyl acrylate (PC₇₁EA), [6,6]-phenyl-C₇₁-propyl acrylate (PC₇₁PrA), [6,6]-phenyl-C₇₁-butyl acrylate (PC₇₁BA), and [6,6]-phenyl-C₇₁-pentyl acrylate (PC₇₁PeA), have been designed, synthesized, and investigated. These fullerene compounds have a molecular structure, shape and size very like the conventional C₇₀ fullerene acceptor, [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM), and have been found no different in their light absorption, redox potentials, and frontier orbital energy levels. Using these fullerene acrylates individually as acceptor and poly(3-hexylthiophene) as donor, organic solar cells have been fabricated and gave optimal efficiencies ranging from 3.32% to 4.16%, comparable to PC₇₁BM-based reference cells (4.06%). Owing to their acrylate functionality, these fullerene derivatives can turn into insoluble upon heating, and thus endow their solar cell devices much better thermostability than PC₇₁BM-based reference cells. The best one, coming from PC₇₁PeA devices, reported an optimal efficiency of 4.16%, and maintained 91.7% efficiency after heat treatment at 150 °C for 35 h. As a sharp contrast, the PC₇₁BM reference cell dropped its optimal efficiency from 4.06% to 0.48% only after 5 h heat treatment. X-ray diffraction, optical and atomic force microscopy, and space-charge-limited current method have been carried out to understand active layer structure, morphology, and charge mobility change during heat treatment.     

Multicomponent reaction of conjugated enynones with malononitrile and sodium alkoxides: Complex reaction mechanism of the formation of pyridine derivatives

Reaction of conjugated enynones,1,5-diarylpent-2-en-4-yn-1-ones, with malononitrile and sodium alkoxides in the corresponding alcohols at room temperature for 3–23 h results in the formation of two types of compounds (E)-/(Z)-6-aryl-4-(2-arylethenyl)-2-alkoxypyridine-3-carbonitriles (substituted nicotinonitriles), as the major reaction products in yields up to ca. 40–80%, and 6-aryl-4-arylethynyl-2-alkoxypyridines, as the minor reaction products in yields of 5–17%. Plausible mechanism of this complex and multistep reaction is discussed. The obtained pyridines possess fluorescent properties.     

Prototropic behavior of cyclohexane substituted urethane and urea compounds. Observation of H-bond mediated 4HJH1H3 coupling constants across urea fragments

Two 1-aryl-3-cyclohexylurea and two 1-aryl-3-cyclohexylurethane with and without alkyl tail in aryl fragments were synthesized and their variable-temperature ¹H NMR spectra in chloroform, DMSO and DMF were recorded. The temperature dependences of chemical shift of NH protons for all compounds have been observed. The type of dependence has been explained by the aggregation of molecules and formation of ionic structures. The formation of intermolecular complexes leads to possible formation of symmetrical N1 ^{… …} H ^……N3 intramolecular hydrogen bond in urea fragment. As a result,^4hJ_H1H3 trans-hydrogen bond scalar coupling constants have been observed for the first time in low molecular weight compounds using a simple one-dimensional ¹H NMR experiment. The formation of strong intramolecular H-bond leads to π-conjugation not only with spacer but with phenyl ring too. It support the Gilli conception that RAHB formation is a result of π-electron delocalization. The presence in urea fragment of such kind interaction leads to formation of ionic structure, which has been detected by NMR and UV spectroscopies. The formation of ionic structure can explain the catalytic activity of such compounds and the mechanism of transformation in organic and bioorganic reactions in which involved the urea compounds.     

Modifications of 5,12-dihydroindolo[3,2-a]carbazole scaffold via its regioselective C2,9-formylation and C2,9-acetylation

The effective approaches for regioselective double formylation and acetylation of 5,12-dialkyl-6,7-diaryl-substituted 5,12-dihydroindolo[3,2-a]carbazoles by their treatment with dichloromethyl methyl ether in the presence of SnCl₄ or with acetyl chloride in the presence of AlCl₃ to afford the 2,9-diformyl or 2,9-diacetyl derivatives, respectively, were developed. Furthermore, new 2,9-bis(2,2-dicyanovinyl) derivatives were synthesized by the Knoevenagel condensation of diformyl-containing substrates with malononitrile, when new 2,9-bis(quinoxaline-2-yl)- and 2,9-bis(benzo[g]quinoxaline-2-yl) derivatives were formed via microwave-promoted oxidation of diacetyl-containing substrates with SeO₂ to the corresponding diglyoxals, followed by the reaction of these intermediates with o-phenylendiamine or 2,3-diaminonaphthalene, respectively. The basic optical and electrochemical properties of some 5,12-dihydroindolo[3,2-a]carbazoles were investigated.     

A novel approach to biologically relevant oxazolo[5,4-d]pyrimidine-5,7-diones via readily available diazobarbituric acid derivatives

An alternative route from 1,3-disubstituted barbituric acids to biologically relevant oxazolo[5,4-d]pyrimidine-5,7-diones was developed that features sulfonyl-azide-free (SAFE) diazo transfer and Rh₂(esp)₂-catalyzed cycloaddition of the resulting 5-diazobarbituric acids with aliphatic and aromatic nitriles. Besides being shorter compared to the previously described approaches, the method allows introduction of alkyl substituents at the 1,3-oxazole ring of the fused heterocyclic system.     

Transition metal-mediated or catalyzed hydrocarboxylation of olefins with CO2

The development of new methods to incorporate carbon dioxide into organic molecules is of special significance and interest as it is an abundantly available and recyclable C1 source. Catalytic hydrocarboxylation of readily available olefins with CO₂ represents a highly atom- and step-economic approach toward transformations of CO₂ into widely-used aliphatic acids. However, due to relatively lower reactivity of them, this goal has been always a formidable challenge. Herein we review relevant progress on transition metal-mediated or catalyzed methodologies toward the desired hydrocarboxylation, with an emphasis on the development of two main pathways, including transition-metal-catalyzed cyclometallation of olefin and CO₂ and direct addition of alkylmetal to CO₂.     

A novel variant of the medicinally relevant 1,2,5-benzothiadiazepin-4-one-1,1-dioxide scaffold accessed via the downstream modification of Castagnoli-Cushman lactams

Downstream modification of piperazin-2-ones obtained by the Castagnoli-Cushman reaction leads to a novel version of the medicinally relevant 1,2,5-benzothiadiazepin-4-one-1,1-dioxide scaffold. The relative stereochemistry remained trans as evidenced by the spectroscopic data and the single-crystal X-ray analysis.     

Synthesis of novel rhodanine based functionalized furans from the reaction of tert-butyl isocyanide with acetylenic esters in the presence of rhodanine acetic acid derivatives

The reactive 1:1 intermediate produced from the reaction of tert-butyl isocyanide and dialkyl acetylenedicarboxylates was trapped by rhodanine-N-acetic acid derivatives to generate polyfunctionalized furan rings in fairly good yields.     

Halogenation of 1,1-diarylethylenes by N-halosuccinimides

An efficient method for the preparation of 2,2-diarylvinyl halides from the corresponding 1,1-diarylethylenes has been developed. N-Halosuccinimides (N-bromosuccinimide or N-chlorosuccinimide) were used as the halogenation reagents. The practicability of this method is highlighted by its simple operation, broad substrate scope and capability for large-scale reaction.     

The use of ∝-diazo-γ-butyrolactone in the Büchner-Curtius-Schlotterbeck reaction of cyclic ketones: A facile entry into spirocyclic scaffolds

The first example of the Büchner-Curtius-Schlotterbeck reaction of cyclic ketones with a stabilized cyclic diazo compound partner is described. The approach towards spirocyclic scaffolds has been exemplified with readily available ∝-diazo-γ-butyrolactone. The reaction proved to be viable with BF₃?OEt₂ as the preferred catalyst and displayed substantial sensitivity to the size of the cyclic ketone.     

First Cp*Co(III)-catalyzed Mizoroki-Heck coupling reactions of alkenes and aryl bromide/iodide

A Cp*Co(CO)I₂ catalyzed Mizoroki-Heck coupling of alkenes and aryl halide is established at feasible reaction conditions. The Cp*Co(III) catalyst excellently work to couple the aryl iodide and alkene, and produce up to 94% yield of the coupling product. In case of the coupling of aryl bromide and alkene, slightly reduced activity of the catalyst was observed, and moderate to good yield of the product was obtained. Apart from functionally different styrene, the catalyst was also able to activate the acrylates, which seems difficult to be activated by other reported metal complexes. The coupling proposed herein is tolerant a wide variety of aryl halides, stryenes, and acrylates enable to form CC bond using inexpensive metal in catalysis. Hence, the present catalyst is highly economical, consists a non-endangered metal and is highly efficient for Heck coupling reaction. Moreover, the cobalt metal in high oxidation state (+3) is not much explored for the CC cross-coupling reactions.     

On water direct arylation of imidazo[1,2-a]pyridines with aryl halides

A simple, mild, and ecofriendly protocol for a palladium-catalysed direct arylation of imidazo[1,2-a]pyridines with aryl halides on water is reported. This protocol does not require any ligand and tolerate variety of functional groups on both the coupling partners. The simple base KOH is highly efficient in this transformation.

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Reactions of alkyl 4-hydroxybut-2-ynoates with arenes under superelectrophilic activation with triflic acid or HUSY zeolite: Alternative propargylation or allenylation of arenes,and synthesis of furan-2-ones

Reactions of alkyl 4-aryl(or 4,4-diaryl)-4-hydroxybut-2-ynoates [Ar(H or Ar')(OH)C⁴–C³≡C²–CO₂Alk] with arenes under the action of triflic acid TfOH or HUSY zeolite result in the formation of two main compounds, aryl substituted furan-2-ones or products of propargylation of electron rich arenes. Key reactive intermediates in these transformations are the corresponding O,O-diprotonated forms of starting butynoates, Ar(H or Ar')(⁺OH₂)C⁴–C³≡C²– C(=O⁺H)(OAlk), dehydration of which gives rise to mesomeric propargyl-allenyl cations Ar(H or Ar')(OH)⁴C⁺–C³≡C²–C(=O⁺H)(OAlk) ? Ar(H or Ar')(OH)⁴C = C³ = ²C⁺–C(=O⁺H)(OAlk), having two electrophilic centers on the carbons C4 and C2 respectively. Reactions of these species with arenes at C4 lead to products of arene propargylation, alternatively, reactions at C2 result in allenylation of arenes, followed by further transformation into furan-2-ones. Using quantum chemical calculations by the DFT method, it has been shown that the reactivity of such propargyl-allenyl cations is mainly explained by orbital factors. Plausible reaction mechanism is discussed.     

Highly ordered combined structure of anodic TiO2 nanotubes and TiO2 nanoparticles prepared by a novel route for dye-sensitized solar cells

Combined structure of anodic TiO₂ nanotubes and TiO₂ nanoparticles (TiNTs-TiNPs) has been synthesized by a facile combination of hydrothermal and chemical vapor deposition methods. Ordered TiO₂ nanotubes with smooth walls were fabricated by two step anodization method in ethylene glycol containing NH₄F at 50 V. This nanotubular array after annealing at 450 °C was subjected to the hydrothermally produced gaseous environment in an autoclave with diluted TiCl₄ solution at its bottom. Vapors of TiCl₄ were allowed to react chemically with water vapors for predefined time durations at 180 °C that resulted in the deposition of TiO₂ nanoparticles on tubes’ surface and side walls. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed that for one hour reaction duration, nanoparticles were evenly coated on the walls of nanotubes, whereas, longer durations tend to deteriorate the tubular structure. Consequently, the ordered TiNTs-TiNPs array produced after one hour coating has shown better performance for dye-sensitized solar cell DSSC) in back illumination mode with 130% increase in efficiency as compared to the device based on bare TiO₂ nanotubes. The same photoanode has higher reflective properties with higher scattering ability. The solar cell based on this photoanode exhibits higher external quantum efficiency and effective charge transport properties. This study shows that porous ordered 1D structures based on TiO₂ are of crucial importance for the high performance of DSSCs.     

Enhanced photocatalytic activity and stability of AgBr/BiOBr/graphene heterojunction for phenol degradation under visible light

In this work, we have reported synthesis of AgBr/BiOBr photocatalyst supported on graphene (Gr) using facile precipitation method. AgBr/BiOBr/Gr was characterized using various spectral techniques like FESEM, TEM, XRD, FTIR, XPS, Raman and PL analyses. AgBr/BiOBr/Gr had improved visible light absorption. PL studies indicated the reduction in recombination of photogenerated electron hole pair of AGBr/BiOBr/Gr. AFM analysis confirmed the thickness of AGBr/BiOBr/Gr was less than 8.0 nm. The higher dispersibility of photocatalyst was ascertained by Tyndall effect. AgBr/BiOBr/Gr photocatalyst was effectively used for the photodegradation of phenol from simulated water. The phenol degradation process was remarkably influenced by adsorption process. The concurrent adsorption and photocatalytic was effective for degradation of phenol. The phenol was completely mineralized into CO₂ and H₂O in 6 h. The degradation process followed pseudo first order kinetics. The results confirmed that integration of AgBr/BiOBr with graphene caused an increase in photocatalytic activity due to reduced recombination of photogenerated electron hole pair and electron sink behavior of graphene for photogenerated electrons of BiOBr. AgBr/BiOBr/Gr photocatalyst displayed significant stability and recyclability for ten catalytic cycles.     

Novel quinazolin-4(3H)-one derivatives containing a 1,3,4-oxadiazole thioether moiety as potential bactericides and fungicides: Design,synthesis, characterization and 3D-QSAR analysis

A series of quinazolin-4(3H)-one derivatives containing a 1,3,4-oxadiazole thioether moiety were designed, synthesized and evaluated for their biological activities against phytopathogenic microorganisms. Antimicrobial bioassays in vitro indicated that most of the target compounds exhibited more significant antibacterial activities against Xanthomonas oryzae pv. oryzae (Xoo) than the agricultural bactericide thiadiazole-copper. A comparative molecular similarity index analysis (CoMSIA) model with cross-validated q² and non-cross-validated r² values of 0.561 and 0.882 was generated to investigate the structure-activity relationships of title compounds against Xoo. Title compound 6w, which was rationally designed under the guidance of obtained CoMSIA model, exhibited the excellent anti-Xoo effect in vitro with an EC₅₀ value of 29.10 μg/mL, which is approximately 3-folds more effective than thiadiazole-copper (113.93 μg/mL). In addition, compound 6i demonstrated the impressive antifungal effects against Rhizoctonia solani (Rs) and Fusarium graminearum (Fg) in vitro, with the corresponding EC₅₀ values of 11.01 μg/mL and 36.00 μg/mL, which is obviously better than the agricultural fungicide hymexazol (76.74 μg/mL and 56.19 μg/mL, respectively). The above researches indicate that quinazolin-4(3H)-one derivatives containing a 1,3,4-oxadiazole thioether moiety could be further studied as template molecules of novel agricultural microbicides.