Oxone®-mediated direct arylselenylation of imidazo[2,1-b]thiazoles,imidazo[1,2-a]pyridines and 1H-pyrazoles

Oxone mediated reaction of imidazo[2,1-b]thiazole, imidazo[1,2-a]pyridine and 1H-pyrazole derivatives with diaryl diselenides is presented here. The methodology represents an efficient and simple protocol for carrying out the selective synthesis of 5-arylselanyl-imidazo[2,1-b]thiazoles, 3-arylselanyl-imidazo[1,2-a]pyridines and 4-arylselanyl-1H-pyrazoles in high yields using a stable, nontoxic and cheap oxidant. The reactions were conducted at 60?°C in air using acetonitrile as solvent. Alternatively, the use of ultrasound irradiation is presented as a tool for fast and efficient energy transfer that significantly reduced the reaction time.     

Electrochemical oxidative selenylation of imidazo[1,2–a]pyridines with diselenides

Electrochemical oxidative selenylation of imidazo[1,2–a]pyridines has been developed. The reaction proceeds in an undivided electrochemical cell equipped with glassy carbon electrodes employing LiClO₄ as a supporting electrolyte. This approach is environmentally benign by using shelf-stable diselenides as selenium source and electrons as oxidizing reagents. The present protocol offers a facile way to prepare 3-selenylated imidazopyridine derivatives.     

Synthesis of imidazo[1,2-a]pyridine in the presence of iodine–water catalytic system

We have devised an expedient, cleaner, and environmentally friendly approach for ‘on water’ mediated synthesis of imidazo[1,2-a]pyridine derivatives. The synthesis involves in situ formation of imines followed by addition of alkyne to give the desired products in excellent yield.     

DMSO–POCl3: a reagent for methylthiolation of imidazo[1,2-a]pyridines and other imidazo-fused heterocycles

A practical and metal free method for methylthiolation of imidazo[1,2-a]pyridines and other imidazo-fused heterocycles using DMSO–POCl₃ complex is reported. The reactions are carried out at room temperature that give the corresponding methylthiolated products in good to excellent yield. Further, its application to indole has been demonstrated.     

A recyclable Cu-catalyzed C–N coupling reaction in water and its application to synthesis of imidazo[1,2-a]quinoxaline

Polystyrene-supported pyrrole-2-carbohydrazide (PSP) was synthesized and combined with CuI to make up a recyclable heterogeneous catalytic system for Ullmann-type C–N coupling reaction in water. In which, a variety of functionalized aryl halides animated efficiently with anilines, benzylamine, aliphatic amines, and imidazole. its preliminary application resulted in a more practical synthesis of imidazo[1,2-a]quinoxaline.     

One-pot synthesis of imidazo[1,2-α]pyridine thioethers using imidazo[1,2-α]pyridines,arylsulfonyl chlorides and hydrazine

Abstract

A one-pot reaction of making RS-substituted imidazo[1,2-α]pyridine derivatives by directly using aryl or alkylsulfonyl chloride and hydrazine was developed, selectively giving good yields of the expected products. Compared with previously reported methods of using ArSO₂NHNH₂ as a sulfur source, this method is much cheaper, more practical and convenient and enriches current methods to make thioether-containing compounds, providing a good example of green chemistry.     

Synthesis of 3-aroylimidazo[1,2-a]pyridines via CuCl2 catalyzed tandem dual carbon–nitrogen bonding

A novel tandem approach has been demonstrated for the direct synthesis of bioactive 3-aroylimidazo[1,2-a]pyridines from chalcones and 2-aminopyridines. The reported tandem reaction is atom-economical and expected to proceed via 1,4-Michael addition followed by copper catalyzed oxidative C–N bonding. Catalytic amount of copper was found to be crucial for the success of tandem reaction and it altered the reaction pathway to furnish entirely new products. This protocol proved to be convenient as reaction proceeds smoothly without the necessity of any ligand in the presence of air as oxidant.     

Intramolecular Ullmann-type C−N coupling for the synthesis of substituted benzo[4,5]imidazo[1,2-a]pyrrolo[3,4-c]pyridines

An efficient CuI catalyzed intramolecular Ullmann-type C−N coupling reaction is described here. Newly substituted 1H-benzo[4,5]imidazo[1,2-a]pyrrolo[3,4-c]pyridine-1,3,5(2H, 11H)-trione has been easily synthesized from ortho halogenated N-substituted pyrrolo[3,4-c]pyridine-1,3,6(5H)-triones in presence of CuI catalyst and K₂CO₃ base without any ligand. This procedure is based on intramolecular Ullmann-type reaction and provides a proficient method of making fused tetracyclic heterocycles.     

Regioselective synthesis of C-2 substituted imidazo[4,5-b]pyridines utilizing palladium catalysed C–N bond forming reactions with enolizable heterocycles

In this Letter we report a rapid and facile access to C2-substituted imidazo[4,5-b]pyridine analogues utilizing palladium mediated Buchwald–Hartwig cross-coupling reactions. The use of enolizable heterocycles as cross-coupling partners resulted in a wide range of imidazo[4,5-b]pyridine analogues which are prone to have medicinal relevance. Xantphos and Pd(OAc)₂ were found to be more effective for the coupling of 2-halo imidazo[4,5-b]pyridines with pyridone nucleophiles. A regioselective approach for the synthesis of 2-substituted 3H-imidazo[4,5-b]pyridine and 1H-imidazo[4,5-b]pyridine is also reported.     

TBAI-catalyzed oxidative coupling of aminopyridines with β-keto esters and 1,3-diones-synthesis of imidazo[1,2-a]pyridines

TBAI could catalyze the direct oxidative C-N coupling of 2-aminopyridines with β-keto esters and 1,3-diones, which affords imidazo[1,2-a]pyridines as the products. The reaction was realized under metal-free conditions by using tert-butyl hydroperoxide (TBHP) as the oxidant.     

Synthesis of novel spiro[benzo[4,5]thiazolo[3,2-a]chromeno[2,3-d]pyrimidine-14,3′-indoline]-1,2′,13(2H)-triones via three component reaction

A new and efficient method for the synthesis of hitherto unreported spiro[benzo[4,5]thiazolo[3,2-a]chromeno[2,3-d]pyrimidine-14,3′-indoline]-1,2′,13(2H)-triones was developed via the Domino Knoevenagel condensation–Michael addition–intermolecular cyclization sequences of isatin derivatives, cyclohexane-1,3-diones, and 2-hydroxy-4H-benzo[4,5]thiazolo[3,2-a]pyrimidin-4-ones, employing 12-tungstophosphoric acid (H₃PW₁₂O₄₀) as an effective and inexpensive catalyst.     

A convenient synthesis of tetrazolo[1,5-a]-α-cycloalkanones

A convenient synthesis of a series of tetrazolo[1,5-a]-α-cycloalkanones 4a-d with the carbonyl group attached at the tetrazole carbon is described. The sequence entails the formation of an exocyclic olefin at the α-methylene position and subsequent ozonolysis. The reactions proceed under mild conditions, and the tetrazole moiety is well tolerated.     

DBU as a scaffold for the synthesis of [1,3]oxazolo[2’,3’ : 2,3]pyrimido-[1,2-a]azepines: annulation with aromatic cyanopropargylic alcohols

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One-step synthesis of thiazolo[3,2-a]pyridines by a multicomponent reaction of β-enaminonitriles, α,β-unsaturated aldehydes, and 2-aminothiol hydrochlorides

A wide library of 3,7,8,8a-tetrahydro-2H-thiazolo[3,2-a]pyridines has been prepared by simple heating in acetonitrile of β-enaminonitriles, α,β-unsaturated aldehydes and 2-aminothiol hydrochlorides. Chemical yields depend on the nature, hindrance, and position of the substituents. The scope, limitations, and stereocontrol associated to this three-component reaction have been studied in detail. In general, the diastereoinduction observed in the three new stereogenic centers generated in the pro-chiral α,β-unsaturated aldehyde is low.     

Palladium-catalyzed oxidative C–H/C–H cross-couplings of thiazolo[5,4-d]pyrimidine with aromatic (hetero)cycles

A novel Pd(II)-catalyzed dehydrogenative cross-coupling reaction of thiazolo[5,4-d]pyrimidine with unactivated (hetero)arenes via C–H bond activation was achieved. This protocol provides a straightforward and operationally simple method for the synthesis of 2-arylsubstituted thiazolo[5,4-d]pyrimidines of interest in pharmaceutical sciences.     

Synthesis of Substituted Pyrido[1,2-a]benzimidazoles by Ruthenium-Catalyzed C−H Bond Activation and Tandem Cyclization of 2-Arylimidazo[1,2-a]pyridines with Iodonium Ylides

Ruthenium-catalyzed C−H bond activation and tandem cyclization of 2-arylimidazo[1,2-a]pyridines with iodonium ylides proceed efficiently. For the first time, the easily available iodonium ylides and inexpensive ruthenium complex were employed to synthesize pyrido[1,2-a]benzimidazole derivatives in good yields under simple and easy-to-operate conditions. Several primary mechanism investigations and synthetic applications involving gram-scale preparation, derivatization reactions and the transformation of iodonium ylide generated in situ have also been conducted.     

Tandem Parham cyclisation--α-amidoalkylation reaction in the synthesis of the isoindolo[1,2-a]isoquinoline skeleton of nuevamine-type alkaloids

C-12b substituted isoindolo[1,2-a]isoquinolones 4 are prepared efficiently via a tandem Parham cyclisation--α-amidoalkylation reaction. Thus, Parham cyclisation on imide 1 generates a 12b-hydroxy isoindolo[1,2-a]isoquinolone, which is an immediate precursor of an N-acyliminium ion. Intermolecular alkylation with different π-nucleophiles (allyl silanes or enol ethers) is accomplished upon treatment with Lewis acids (BF₃·OEt₂, TiCl₄) to obtain nuevamine-type derivatives in high yields (69-95%) under mild conditions.     

Piperidine–iodine a dual system catalyst for synthesis of coumarin bearing pyrrolo[1,2-a]quinoxaline derivatives via a one-pot three-component reaction

The synthesis of 3-(4-alkyl-4,5-dihydropyrrolo[1,2-a]quinoxalin-4-yl)-2H-chromen-2-one derivatives by a three-component reaction of salicylaldehyde, β-keto esters, and 1-(2-aminophenyl)pyrrole using piperidine–iodine as a dual system catalyst is reported. Good yields, mild reaction conditions, and ease of handling are the main aspects of the method. The structural assignments are supported by ¹H NMR, ¹³C NMR, and X-ray crystallography data.