Lewis Acid-Mediated Isothiocyanation and Chlorination of Quinoxalin-2(1H)-ones under Visible Light Conditions.

Lewis acid-mediated selective C3-isothiocyanation of quinoxalin-2(1H)-ones using N-thiocyanatosaccharin as an isothiocyanate source under visible light conditions at room temperature is described. Under similar conditions with N-chlorosaccharin, the C3-chlorination of quinoxalin-2(1H)-ones achieved a 2 h time frame. Good to an excellent yield of products was obtained in both cases with broad functional group tolerance. Control experiments suggest that the reaction proceeds through a radical mechanism. The present procedure demonstrates the applicability at gram-scale reactions and highlights the subsequent conversion of isothiocyanates into representative thiourea derivatives, and one of the chloro derivatives transformed to glycogen phosphorylase inhibitors.

Correction: Pd-catalyzed annulation of imidazo[1,2-a]pyridines with coumarins and indoles: synthesis of benzofuran and indole fused heterocycles.

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.

Pd-catalyzed annulation of imidazo[1,2-a]pyridines with coumarins and indoles: synthesis of benzofuran and indole fused heterocycles.

Palladium-catalyzed annulation of imidazo[1,2-a]pyridines with coumarins provided benzofuran fused transannulated products in good to excellent yields via a decarbonylative approach, while imidazo[1,2-a]pyridines with N-methyl indoles in the presence of palladium and base yielded conjugated imidazopyridine fused indole derivatives. Additional experiments revealed that the presence of the phenyl ring at the C-2 position of imidazo[1,2-a]pyridines is essential for the annulation than the alkyl groups. Both transformations follow the ionic mechanism by Pd-catalyzed double C-H bond activation. All the annulated products were shown to exhibit high fluorescence characteristics and their photophysical properties were evaluated.

Copper-Catalyzed Multicomponent Reactions (MCRs) for Disulfenylation of Imidazo[1,2-a]pyridines Using Elemental Sulfur and Arylhalides and Intramolecular Cyclization of Haloimidazo[1,2-a]pyridines.

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 been developed. The method has a broad substrate scope with a variety of substituted haloarenes. The conditions were also applied for the synthesis of benzothieno-imidazo[1,2-a]pyridines in excellent yields (99%) through intramolecular sulfenocyclization of 2-(2-halophenyl)imidazo[1,2-a]pyridines using sulfur powder.

Pd-Catalyzed regioselective synthesis of 2,6-disubstituted pyridines through denitrogenation of pyridotriazoles and 3,8-diarylation of imidazo[1,2-a]pyridines.

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.

Indium-Catalyzed Denitrogenative Transannulation of Pyridotriazoles: Synthesis of Pyrido[1,2- a]indoles.

Pyrido[1,2- a]indoles are known for medicinally and pharmaceutically important compounds; however, the efficient synthetic routes are scarce in the literature. We report herein a convenient and efficient route to synthesize these molecules through indium-catalyzed transannulation of pyridotriazoles with arenes. A library of compounds have been synthesized employing the method developed with various substituted pyrido[1,2- a]indole derivatives in moderate to good yields. The density functional theory study using SMDDCB-M06/6-31++G(d,p)/LANL2DZ//B3LYP/6-31G(d)/LANL2DZ method suggests that the reactions proceed via indium-carbenoid complex.

Sodium Salts (NaI/NaBr/NaCl) for the Halogenation of Imidazo-Fused Heterocycles.

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.

Visible-Light-Induced C (sp3)-H Functionalization of Tosylhydrazones: Synthesis of Polysubstituted Pyrroles under Metal-Free Conditions.

Iodine catalyzed C (sp3)-H functionalization of tosylhydrazones with ß-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.

I2-Catalyzed Oxidative Amidation of Benzylamines and Benzyl Cyanides under Mild Conditions.

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.

Visible-light-promoted selective C-H amination of heteroarenes with heteroaromatic amines under metal-free conditions.

The regioselective C-H amination of quinoline amides (C5) and imidazopyridines (C3) under transition-metal-free conditions at room temperature with a high degree of functional group tolerance is reported. The C-H amination promoted by visible light in the presence of a photocatalyst with a wide range of heteroamines makes the present protocol more sustainable.

Synthesis of Imidazo[1,2-a]pyridines: C-H Functionalization in the Direction of C-S Bond Formation.

Imidazo[1,2-a]pyridines play an important role in medicinal chemistry. In spite of very drastic developments on syntheses and functionalization in this area, the use of inexpensive catalysts and mild reaction conditions constitutes an important role in pharmaceutical applications. This account describes our recent efforts on the development of new methods for the synthesis of imidazo[1,2-a]pyridines using readily available starting substrates and catalysts under very mild reaction conditions. In the direction of enhancement of biological activity, we also described the synthesis of functionalized imidazo [1,2-a]pyridine derivatives.

Catalyst-Free Synthesis of 2,4-Disubstituted-1H-imidazoles through [3 + 2] Cyclization of Vinyl Azides with Amidines.

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.

Design, synthesis and cytotoxicity studies of novel pyrazolo[1, 5-a]pyridine derivatives.

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.

Copper-Catalyzed Three-Component System for Arylsulfenylation of Imidazopyridines with Elemental Sulfur.

A one-pot three-component reaction for the regioselective synthesis of thioarylated imidazoheterocycles from aryl halides and elemental sulfur using copper(I) iodide as a catalyst has been developed. Reactions proceed with high efficiency and afford thioarylated imidazoheterocycles in good yields with broad functional group tolerance.

Lewis Acid-Catalyzed Denitrogenative Transannulation of Pyridotriazoles with Nitriles: Synthesis of Imidazopyridines.

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.

Phenyliodonium Diacetate Mediated Oxidative Functionalization of Styrenes with Molecular Oxygen: Synthesis of α-Oxygenated Ketones.

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 ß-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.

Copper-Catalyzed Denitrogenative Transannulation Reaction of Pyridotriazoles: Synthesis of Imidazo[1,5-a]pyridines with Amines and Amino Acids.

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.

Dual role of p-tosylchloride: copper-catalyzed sulfenylation and metal free methylthiolation of imidazo[1,2-a]pyridines.

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.

Copper-catalyzed C(sp(3))-H functionalization of ketones with vinyl azides: synthesis of substituted-1H-pyrroles.

Copper-catalyzed C(sp(3))-H functionalization of ketones with vinyl azides for the synthesis of substituted pyrroles has been developed. The method is a straightforward and efficient way to access a series of 2,3,5-trisubstituted-1H-pyrroles in modest to excellent yields with broad functional group tolerance under mild conditions.

Synthesis of Indolizines through Oxidative Linkage of C-C and C-N Bonds from 2-Pyridylacetates.

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.