Palladium-Catalyzed C3-Carbaldehyde Directed Regioselective C2-Thioarylation of Indoles.

Palladium-catalyzed thioarylation of indoles by diaryl disulfides in the presence of phenyliododiacetate is reported. The directing potential of weakly coordinating aldehyde group present at 3-position of indole was exploited for regioselective C2-H thioarylation over the possible C4-H functionalization. Mechanistic studies reveal that the process involves initial generation of thioaryl radical followed by sequential C-H activation, thiolate transfer, and reductive elimination.

DMSO-DCE Triggered Chemodivergent C-Methylenation of Electron-Rich Arenes: An Easy Access to Diarylmethanes.

The chemodivergent property of dimethyl sulfoxide (DMSO) along with 1,2-dichloroethane (DCE) was exploited for the incorporation of a methylene group to form diarylmethanes through a dearomatization/rearomatization process. Methyl(methylene)sulfonium ions (CH2=S+-Me) were generated by simple heating of commonly used solvents such as DMSO and DCE. These ions were subsequently trapped by electron-rich arenes and heteroarenes, resulting in the synthesis of both symmetrical and unsymmetrical diarylmethanes. This protocol was further extended to access N-methylenamides by reacting 2-naphthol with amides or nitriles in the presence of DMSO and DCE.

Metal-Free C-H Sulfamidation of 1,4-Naphthoquinone in Water.

Direct sulfamidation of 1,4-naphthoquinones using N-methoxy sulfonamides under metal-free conditions in water was developed. Base-mediated nucleophilic addition of N-methoxy sulfonamides, followed by N-O bond cleavage allowed the formation of enesulfonamides. Further, the synthesis of pyrrolonaphthoquinones proved the practicability of the current approach.

Effects of microplastics, pesticides and nano-materials on fish health, oxidative stress and antioxidant defense mechanism.

Microplastics and pesticides are emerging contaminants in the marine biota, which cause many harmful effects on aquatic organisms, especially on fish. Fish is a staple and affordable food source, rich in animal protein, along with various vitamins, essential amino acids, and minerals. Exposure of fish to microplastics, pesticides, and various nanoparticles generates ROS and induces oxidative stress, inflammation, immunotoxicity, genotoxicity, and DNA damage and alters gut microbiota, thus reducing the growth and quality of fish. Changes in fish behavioral patterns, swimming, and feeding habits were also observed under exposures to the above contaminants. These contaminants also affect the Nrf-2, JNK, ERK, NF-κB, and MAPK signaling pathways. And Nrf2-KEAP1 signalling modulates redox status marinating enzymes in fish. Effects of pesticides, microplastics, and nanoparticles found to modulate many antioxidant enzymes, including superoxide dismutase, catalase, and glutathione system. So, to protect fish health from stress, the contribution of nano-technology or nano-formulations was researched. A decrease in fish nutritional quality and population significantly impacts on the human diet, influencing traditions and economics worldwide. On the other hand, traces of microplastics and pesticides in the habitat water can enter humans by consuming contaminated fish which may result in serious health hazards. This review summarizes the oxidative stress caused due to microplastics, pesticides and nano-particle contamination or exposure in fish habitat water and their impact on human health. As a rescue mechanism, the use of nano-technology in the management of fish health and disease was discussed.

Weak Chelating-Group-Directed Palladium-Catalyzed C-4 Arylation of Indoles.

A Pd(II)-catalyzed dehydrogenative remote C4-H coupling of indoles with unfunctionalized arenes at room temperature was reported. The weak chelating trifluoroacetyl group at the C3-position served as a directing group for the remote C4-H activation. Arenes with a wide range of substituents were employed as the coupling partner in the dehydrogenative cross-coupling reaction.

Arylative Methylation of 2,3-Dihydropyrazines and Pyrazinones Using Dimethyl Sulfoxide as a C1 Source.

Divergent synthesis of α-C-H methylated pyrazines and pyrazinones using dimethyl sulfoxide as a nonconventional methylating agent under metal-free conditions was reported. Dimethyl sulfoxide-coordinated bromine cation pools generated from the treatment of dimethyl sulfoxide and 1,2-dibromoethane undergo Pummerer-type fragmentation to afford an electrophilic methyl(methylene)sulfonium ion for reaction with a carbon nucleophile followed by aromatization to afford α-methylated pyrazines and pyrazinones.

Pd-Catalyzed desulfitative arylation of olefins by N-methoxysulfonamide.

A novel Pd-catalyzed protocol for the desulfitative Heck-type reaction of N-methoxy aryl sulfonamides with alkenes was reported. The cross-coupling reaction was performed successfully with a variety of olefins to obtain aryl alkenes. Different substituents on the aromatic ring of N-methoxysulfonamides were also found to be compatible with the reaction conditions. Expectedly, the reaction proceeds through CuCl2-promoted generation of the nitrogen radical and subsequent desulfonylation under thermal conditions to afford the aryl radical for the Pd-catalyzed coupling reaction. N-Methoxysulfonamide was further exploited for the synthesis of symmetrical biaryls in the presence of CuCl2.

Access to C4-arylated benzoxazoles from 2-amidophenol through C-H activation.

A Pd-catalyzed aerobic approach to access C4-aryl benzoxazoles by tandem C-H ortho-arylation and acid-mediated annulation of 2-amidophenol has been presented. The directing potential of the -NHCOR group over the -OH group was exploited for selective arylation adjacent to the amide group. Deuterium labeling experiments suggest that palladation predominantly occurs adjacent to the -NHCOR group and is the key step during benzoxazole formation. One-pot hydrolysis of the resulting C4-arylated benzoxazole was also accomplished to access structurally challenging 3-aryl aminophenols for further applications.

Correction: Synthesis of medium-sized (6-7-6) ring compounds by iron-catalyzed C-H activation/annulation.

Correction for 'Synthesis of medium-sized (6-7-6) ring compounds by iron-catalyzed dehydrogenative C-H activation/annulation' by Niranjan Panda et al., Org. Biomol. Chem., 2018, 16, 7861-7870.

Synthesis of medium-sized (6-7-6) ring compounds by iron-catalyzed C-H activation/annulation [corrected].

In this report, we have described a FeCl3-catalyzed process involving intramolecular annulation of o-phenoxy diarylacetylenes via hydroarylation to afford a series of biologically potent fused seven-membered (6-7-6) ring compounds under mild reaction conditions. This reaction was believed to proceed through Friedel-Crafts type sequential carbometallation followed by protonation to produce phenyldibenz[b,f]oxepines. This method was also extended to synthesize seven-membered rings that are fused with coumarins.

One-pot two-step synthesis of 3-iodo-4-aryloxy coumarins and their Pd/C-catalyzed annulation to coumestans.

An efficient protocol for the synthesis of various coumestans from the intramolecular annulation of 3-iodo-4-aryloxy coumarins through C-H activation has been developed. When 3-iodo-4-aryloxy coumarins were treated with 10% Pd/C (0.3 mol% Pd) in the presence of sodium acetate, the corresponding coumestans were produced in good to excellent yield. Reusability of the palladium catalyst was investigated in up to three consecutive cycles and it was found that the yield of the reaction was almost unaltered. Sequential iodination and O-arylation of 4-hydroxy coumarins leading to the 3-iodo-4-aryloxy coumarins were also achieved in a one-pot two-step process starting from aryl iodides in high yield. Pivalic acid was revealed to be the most effective additive for the later method to produce 3-iodo-4-phenoxy coumarins. Different functional groups bearing electron-donating as well as withdrawing groups are also tolerant to the reaction conditions.

Synthesis of Isocoumarins via Silver(I)-Mediated Annulation of Enol Esters.

Silver-mediated annulation of 2-iodo enol esters leading to 4- and 3,4-substituted isocoumarins was accomplished selectively at room temperature. Coupling of 2-iodo benzoic acids with enolates that were produced in situ from the simple esters was also performed to produce isocoumarins under analogous reaction conditions. Owing to the mildness of the current protocol, 4-acyl 3-substituted isocoumarins were efficiently produced without any deacylation.

Synthesis of Dibenzofurans via C-H Activation of o-Iodo Diaryl Ethers.

An efficient method for the synthesis of dibenzofuran from o-iododiaryl ether using reusable Pd/C under ligand-free conditions has been developed. Synthesis of o-iododiaryl ether was achieved in one pot through sequential iodination and O-arylation of phenol under mild reaction conditions.

Fe-catalyzed one-pot synthesis of 1,3-di- and 1,3,5-trisubstituted pyrazoles from hydrazones and vicinal diols.

An iron-catalyzed route for the regioselective synthesis of 1,3- and 1,3,5-substituted pyrazoles from the reaction of diarylhydrazones and vicinal diols has been developed. This method was found to be practical with wide substrate scope.

Stereoselective synthesis of enamides by Pd-catalyzed hydroamidation of electron deficient terminal alkynes.

Hydroamidation of electron-deficient terminal alkynes by amides in presence of Pd-catalyst has been exploited for the stereoselective synthesis of Z-enamides. The possible intramolecular hydrogen bonding between the amido proton and carbonyl oxygen of ester group provides the extra stability to the Z-isomer of vinyl-palladium complex, which subsequently undergoes protodepalladation and leads to the Z-enamide selectively. This process is found to be mild and operationally simple with broad substrate scope.

Decolourization of Methyl Orange using Fenton-like mesoporous Fe(2)O(3)-SiO(2) composite.

Rapid decolourization of Methyl Orange by Fenton-like mesoporous Fe(2)O(3)-SiO(2) catalyst has been reported. The effect of various parameters such as initial pH, initial H(2)O(2) concentration, Fe content in the catalyst and initial dye concentration on decolourization process were studied. The results show that 20mg of mesoporous Fe(2)O(3)/SiO(2) composite (with Si/Fe=10) was sufficient to decolourize 0.6 mg/ml of Methyl Orange in presence of 2 ml of H(2)O(2) at an initial pH of 2.93 within 20 min. The pH range for effective decolourization (≥90%) was found to be 1-3. Leaching tests indicated that the activity of the catalyst was almost unaffected up to three consecutive cycles although ≤0.2 ppm of Fe ion was leached into treated water in each run.

A sequential Pummerer-Diels-Alder route for the generation and trapping of furo[3,4-c]pyridines: synthesis of heterocyclic analogues of 1-arylnaphthalene lignans.

The Pummerer reaction of an o-benzoyl-substituted pyridylmethyl sulfoxide generates an alpha-thiocarbocation, the interception of which by a neighboring keto functionality produces an alpha-thio-substituted furo[3,4-c]pyridine as transient intermediate; the latter undergoes a Diels-Alder cycloaddition with an added dienophile. Base-induced ring opening of the cycloadduct followed by aromatization gives an isoquinoline derivative that may be looked upon as a heterocyclic analogue of 1-arylnaphthalene lignans. This procedure occurs readily with electron-poor dienophiles and the entire sequence can be run in one pot. The facility of the sequential Pummerer-Diels-Alder reaction hinges on the experimental conditions, the best results being obtained with heptafluorobutyric anhydride as the triggering agent in toluene containing a catalytic amount of p-toluenesulfonic acid. In the absence of a dienophile it is possible to isolate and characterize a rather unstable furo[3,4-c]pyridine derivative. An intramolecular variant of this protocol is also feasible with use of unactivated alkenyl tethers of variable length; however, the bridged cycloadducts are unisolable in these cases as they undergo spontaneous ring opening and aromatization to yield cycloalka[h]isoquinolines. The usefulness of the sequential Pummerer-Diels-Alder reaction is further demonstrated through the synthesis of a heterolignan with a built-in lactone ring via oxidation of the initial [4+2]-cycloadduct followed by extrusion of phenyl sulfinate and elaboration of the resulting hydoxylated isoquinoline derivative.