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Palladium-catalyzed annulation of 2-arylimidazo[1,2-a]pyridines for the synthesis of benzofuro[3,2-a]imidazo[5,1,2-cd]indolizines and 6-methyl-6H-imidazo[5′,1′,2′:3,4,5]indolizino[1,2-b]indoles with coumarins and N-methyl indoles has been described.

Ruthenium-catalyzed efficient and selective C–H alkenylation of pyridotriazoles with acrylates is described. The combination of metals (Ru and Fe) plays a crucial role in achieving quantitative yields of the desired products. The reaction is proposed to involve the formation of a ruthenium cyclometalated intermediate.

An expeditious approach for the synthesis of thiazolidin-2-imines and 1,3-thiazinan-2-imines through three-components coupling (TCC) of amines, isothiocynates and dihalides under metal-free conditi...

The synthesis of thiazolo[3,4-a]pyridin-3-imines through the denitrogenative transannulation of pyridotriazoles with isothiocyanates using BF3·Et2O as a catalyst is described. A combination of solvents (dichlorobenzene-dichloroethane) plays a crucial role in obtaining the desired products under transition metal-free conditions.

Hypervalent iodine mediated selective synthesis of imidazo[1,2-a]pyridine ethers using ethylene glycol as a methoxy ethanol source as well as solvent under metal-free conditions is described. The method is also applicable to other fused heterocycles such as benzo[d]imidazo[2,1-b]thiazoles, 2-(thiophen-2-yl)benzo[d]imidazo [2,1-b]thiazole and indazole. Control experiments suggest that, when the C-3 position of imidazo[1,2-a]pyridine is blocked, the reaction does not take place at any other position showing the regioselectivity of the present protocol.

A base promoted protocol for the synthesis of benzo[a]imidazo[5,1,2-cd]indolizines from 2-arylimidazo[1,2-a]pyridines and benzyne precursors under metal-free conditions has been developed. Without a transition metal, double C(sp2)–H activation of 2-phenylimidazo[1,2-a]pyridines under basic conditions was achieved. This method is also applicable for the annulation of imidazo[1,2-a]pyrimidine and naphthylamine under the same conditions. These annulated molecules showed fluorescence characteristics and hence their photo physical properties were evaluated.

Copper-catalyzed synthesis of disulfenylated imidazo[1,2-a]pyridines and indoles using elemental sulfur and haloarenes through one-pot, three component reaction by two C–S–C bond formations has bee...

Synthesis of 2,6-disubstituted pyridines from pyridotriazoles through palladium-catalyzed aerobic oxidative denitrogenative reactions has been described. Denitrogenation of arylated pyridotriazoles generates metal-carbene intermediates in situ and provides selectively 6-aryl-2-benzoylpyridines. The same conditions have been extended to regioselective C-3 and C-8 diarylation of several imidazo[1,2-a]pyridines.

Tetrabutylammonium hydroxide (TBAOH) was discovered as a highly efficient and green catalyst for aerobic oxidation of the α-methylene carbon of primary amines as well as benzylic groups into the corresponding amides and ketones under neat conditions. We described herein, ionic liquid TBAOH catalysed aerobic oxidation of benzyl amines to benzamides and with elemental sulfur; the corresponding benzylbenzothioamides were obtained under metal-free, oxidant-free and base-free conditions. Applicability at the gram scale for the synthesis of the desired amides/ketones is also demonstrated with the present protocol.

An expeditious approach for the synthesis of thiazolidin-2-imines and 1,3-thiazinan-2-imines through three-components coupling (TCC) of amines, isothiocynates and dihalides under metal-free conditions has been described. Dichloroethane (DCE) employed as two carbon (C2) source for the annulation and obtained saturated five membered heterocycles.With 1,3-dibromopropane, six membered heterocycles were obtained in good yields. The metal-free, broad substrate scope, functional group tolerance and applicability at gram scale synthesis are the advantages of the present protocol.

Correction for ‘Pd-catalyzed annulation of imidazo[1,2-a]pyridines with coumarins and indoles: synthesis of benzofuran and indole fused heterocycles’ by Rashmi Semwal et al., Chem. Commun., 2022, 58, 1585–1588, DOI: 10.1039/D1CC06803B.

We report herein an effective method for the halogenation of imidazo-fused heterocycles using readily available sodium salts (NaCl/NaBr/NaI) as halogen source and K2S2O8 (or) oxone as promoter. A variety of C-3 halogenated imidazo[1,2- a]pyridines and benzo[d]imidazo[2,1- b]thiazoles were obtained in good to excellent yields. The present method of halogenation has been also extended to 2-aminopyridines, 2-aminopyrimidine, indole, and isoquinoline with moderate to excellent yields.

Iodine catalyzed C (sp3)–H functionalization of tosylhydrazones with β-enamino esters under visible light irradiation for the synthesis of trisubstituted pyrroles has been described. The present method is also applicable to α- substituted tosylhydrazones to yield the tetra-substituted pyrroles.

We report a novel and efficient method for the oxidation of benzylic carbons (amines and cyanides) into corresponding benzamides using a catalytic amount of I2 and TBHP as the green oxidant via the C–H bond cleavage of the benzylic carbon under mild reaction conditions. According to the literature survey, this is the first report for the oxidative amidation of benzylamines and decyanation of benzyl cyanides in one pot under metal-free conditions.

A facile and efficient route for the synthesis of 2,4-disubstituted imidazoles from benzimidamides and vinyl azides through [3 + 2] cyclization under catalyst-free conditions has been described. The method is compatible for a broad range of functional groups with good to excellent yields.

Synthesis of heteroamides through oxidative amidation of methylarenes with hetero aromatic amines using tert-Butyl hydroperoxide (TBHP) as oxidant has been described. The present method represents a significant development for the oxidative amidation of methylarenes to obtain heteroamides which does not require metal catalyst and TBHP act as only oxidant. Methylarenes are easy to handle, stable, commercially available (by-products in gasoline industry) and used as carbonyl source for amide synthesis. The reaction proceeds through the imine intermediate formation and its subsequent oxidation by TBHP provides the desired amides.

We describe herein a catalyst-free selective C−H sulfenylation of imidazo[1,2-a]pyridines using sulfonothioates as odorless source of thioarylated reagent in an aqueous medium. The method works for a variety of substituted imidazo[1,2-a]pyridines with broad functional group tolerance. The methodology has been extends to selective sulfernylation of indoles and imidazothiazoles. The sulfonothioates are activated exclusively in aqueous medium rather than organic solvent media and the feasibility of the process for scale-up studies have been demonstrated.

The synthesis of functionalized pyrazolo[1,5-a]pyridines through oxidative [3+2] cycloaddition of N-aminopyridines with α,β-unsaturated carbonyl compounds or electron-withdrawing olefins is described. The reactions proceed in N-methylpyrrolidone as the solvent under metal-free conditions at room temperature.

Visible light promoted hydroperoxidation of styrenes using hydroxylamine and molecular oxygen from air under metal-free and additive-free conditions at room temperature is described. Hydroperoxides were further converted into corresponding hydroxy compounds and α-oxygenated ketones in high yields under ambient conditions.

Copper–mediated synthesis of various pyrazolo[1, 5–a]pyridine-3-carboxylates has been described. The biological activities of these molecules have been evaluated against various human cancer cell lines A549 (Lung adenocarcinoma cell line), MCF-7 (Breast carcinoma cell line), HCT-116 (Colon cancer cell line), and PC-3 (Prostate cancer cell line) through SRB assay. Compound 247 led to accumulation MCF-7 cells in G1-phase and revealed its important role in mitotic cell cycle progression.

This paper demonstrates an integrated zero liquid discharge (ZLD) process for time-dependent recovery of 5-hydroxymethyl furfural (HMF), levulinic acid (LA) and potassium, nitrogen and sulphur rich mother liquor (KNS-ML) - manure from agar/agarose containing seaweed aqueous solution using transition metal-free KHSO4 as an eco-friendly and reusable catalyst. The selectivity of HMF is higher at 115 °C in 3 h and favorable to LA in 6 h in autoclave conditions. The proposed concept could be fine-tuned for the selective production of 5-HMF (up to 91% yield) or levulinic acid (56% yield) in the presence of the KHSO4 catalyst. We have also achieved recyclability of KHSO4 up to nine (09) cycles and the gram-scale reaction has been demonstrated. The (KNS-ML) obtained after nine cycles followed by neutralization with ammonia solution utilized for manure makes the process zero-liquid discharge and more cost-effective. The efficacy of the KNS-ML after nine cycles has been tested on groundnut plants.

The synthesis of imidazo[1,5-a]pyridines through denitrogenative transannulation of pyridotriazoles with nitriles using BF3·Et2O as catalyst has been described. The combination of solvents (dichlorobenzene-dichloroethane) plays a crucial role in achieving quantitative yields of desired products under metal-free conditions.

N-Acylation of anilines with 1, 3-diketones promoted by AIBN (2-2′-azoisobutyronitrile) under metal-free and peroxide-free conditions in the presence of molecular oxygen as oxidant has been described. This protocol proceeds by the oxidative cleavage of C–C bond with simultaneous intermolecular C–N bond formation under mild conditions.

Synthesis of α-oxygenated ketones from styrenes mediated by phenyliodonium diacetate in the presence of molecular oxygen and N-hydroxyphthalimide or N-hydroxybenzotriazole has been described. Addition of carbonyl oxygen at the α-position and formation of C-O bond at the β-position of styrenes was achieved under metal-free conditions. The present method is applicable for wide range of styrenes with a variety of functional groups.

Iodine catalyzed synthesis of indolizine-1-carboxylates through oxidative C C and C N bond formations by the reaction of 2-pyridyl acetates with alkynes and alkenes without metal, oxidant, and base. This procedure is compatible with a broad range of functional groups in both alkynes and alkenes with good yields. The reaction proceeds through a tandem C C bond formation followed by an intramolecular cyclization.

The copper-catalyzed aerobic oxidative synthesis of imidazo[1,5-a]pyridines via cascade denitrogenative transannulation reaction of pyridotriazoles with benzylamines with good functional group tolerance is developed. The present methodology is also applicable to amino acids to obtain imidazo[1,5-a]pyridines via decarboxylative oxidative cyclization.

An organic solvent-free process for the preparation of 2,6-dibromo-4-nitroaniline, (an important intermediate in the synthesis of azo disperse dyes) from 4-nitroaniline using 2 : 1 bromide–bromate salts under an aqueous acidic medium at ambient conditions has been developed. The 2 : 1 bromide–bromate couple could be obtained by mixing pure NaBr/NaBrO3 salts or by adjusting the 5 : 1 mole ratio of NaBr/NaBrO3 (obtained in an aqueous solution as an intermediate from the bromine manufacture industry by a cold process) to 2 : 1 by the addition of a suitable oxidant. After completion of the reaction the product was purified by simple filtration and washing with water. The aqueous acidic filtrate was recycled up to five times without loss of purity and yield of the product. The method was extended to other aromatic substrates.

Copper-catalyzed regioselective C-3 sulfenylation of imidazo[1,2-a]pyridines using p-tosylchloride as a benign source of sulfenylating agents has been developed. On the other hand, p-tosylchloride mediated thiomethylation of imidazo[1,2-a]pyridines with dimethylsulfoxide as a source of thiomethylation under metal-free conditions was also described.

Herein we have discussed the robust design and synthetic methodology of polyaniline based exceptional chemical and mechanical stable composite membrane for acid recovery by diffusion dialysis. Physicochemical characterization of the membrane was carried out to find its hydrophilic/hydrophobic characteristic and its effect on separation of HCl and H2SO4 from the simulated solution. The high retention of sulfuric acid or high permeation of HCl was explained on the basis of Gibbs free energy of hydration of Cl− and SO42− ions. The obtained diffusion coefficient (UH+) for PANI and A-PANI membrane was in the range of 0.013–0.042 m h−1 for HCl, H2SO4 and effluent solution. The maximum acid recovery was 43% for A-PANI and 32% for PANI. The acid recovery for locally available effluent solution was ∼34% indicating potential use of synthesized membranes in acid recovery by diffusion dialysis.

Iodine catalyzed C (sp

Oxidative esterification of aliphatic primary alcohols with bromide and bromate couple in aqueous acidic medium at room temperature is reported with a wide range of substrate scope for both aliphatic and cyclic alcohols and obtained excellent yields of products.

Synthesis of indolizine-1-carboxylates through the Ortoleva-King reaction of 2-pyridylacetate followed by the Aldol condensation under mild reaction conditions has been described. This protocol is compatible with a broad range of functional groups, and it has been also successfully extended to unsaturated ketones, bringing about the regioselective formation of benzoyl-substituted indolizines through Michael addition followed by C-N bond formation, which are difficult to prepare by previous methods in a single step.

Iodine catalyzed synthesis of 2,5-disubstituted oxazoles from N-arylethylamides through intramolecular C(sp3)–H functionalization under metal-free conditions is described. The method is tolerable to a wide range of substrates having a variety of functional groups with moderate to good yields of the products.