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.

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-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.

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.

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.

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.

Copper-catalyzed aerobic oxidative amination of C(sp(3))-H bonds: synthesis of imidazo[1,5-a]pyridines.

Copper-catalyzed synthesis of imidazo[1,5-a]pyridine-1-carboxylates through oxidative amination of C(sp(3))-H bonds under mild aerobic conditions with broad substrate scope is described. Use of naturally abundant air as the sole oxidant was found to be efficient and selective. The present protocol is also applicable for direct synthesis of functionalized imidazo[1,5-a]pyridines from amino acid derivatives.

Copper-mediated synthesis of pyrazolo[1,5-a]pyridines through oxidative linkage of C-C/N-N bonds.

Copper-mediated synthesis of pyrazolo[1,5-a]pyridine-3-carboxylates through oxidative linkage of C-C and N-N bonds under mild reaction conditions is described. This protocol is applicable to a variety of pyridyl esters as well as various benzonitriles including nicotinonitrile, isonicotinonitrile and thiophene-2-carbonitrile. Better yields were observed with electron withdrawing substituted benzonitriles.

N-chlorosuccinimide-promoted regioselective sulfenylation of imidazoheterocycles at room temperature.

Regioselective sulfenylation of imidazoheterocycles with thiophenols at room temperature is reported. Sulfenylation is promoted by N-chlorosuccinimide under metal-free conditions with a broad range of substrate scopes.