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.     

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.     

Transition-metal-free,visible-light-mediated regioselective C–H trifluoromethylation of imidazo[1,2-a]pyridines

A transition-metal-free, visible-light-induced trifluoromethylation of imidazo[1,2-a]pyridines has been developed at mild conditions by employing cheap and commercially available anthraquinone-2-carboxylic acid (AQN-2-CO₂H) as the photo-organocatalyst, and Langlois reagent as the trifluoromethylating reagent. A series of 3-(trifluoromethyl)imidazo[1,2-a]pyridine derivatives with broad functionalities could be conveniently and efficiently obtained by direct regioselective functionalization.     

Copper-catalyzed direct oxidative C(sp2)-H α-sulfenylation of enaminones with disulfides or thiophenols: Synthesis of polyfunctionalized aminothioalkenes

A copper(II)-catalyzed protocol for the construction of aminothioalkenes has been achieved that is based on the reaction of enaminones with disulfides/thiophenols in the presence of tert-butyl hydroperoxide (TBHP) to give good to excellent yields. This study provides a new strategy for the formation of C(sp²)?S bonds via direct α-sulfenylation of C(sp²)?H bonds.     

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.     

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.     

Pd-Cu–Mediated Synthesis of 2-Substituted Imidazo[1,2-α]pyridines in Water

The reaction of 2-amino-1-(2-propynyl)pyridinium bromide with various iodobenzenes, catalyzed by Pd-Cu, in the presence of sodium lauryl sulfate as the surfactant and cesium carbonate as the base, in water, leads to the formation of 2-substituted imidazo[1,2-α]pyridines.     

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.     

Synthesis of imidazol[1,2-α]pyridine thioethers via using sulfur powder and halides as reactants

Structure containing the CS bond exist widely in nature, drugs and chemical materials. Here, a novel sulfenylation protocol employing an aryl or alkyl halide and odorless and cheap S as reagents was developed, generating regioselective alkyl-S- and Ar-S-substituted imidazol[1,2-α]pyridine derivatives in good yields under relatively environmentally friendly and mild conditions. This protocol enriches current thioether-producing methods, making up for the shortcomings of previous sulfenylation methods which can only make MeS- and ArS-substituted imidazol[1,2-α]pyridine derivatives.     

One-pot Copper Nanoparticle-catalyzed Synthesis of Imidazo[1,2-α]pyridines Under Solvent-free Conditions

A direct and efficient approach to synthesize imidazo[1,2-α]pyridines through three-component one-pot reaction of 2-aminopyridine,aldehyde and terminal alkyne catalyzed by Cu-nanoparticles under solvent-free conditions has been developed.This method provides a rapid access to substituted imidazo[1,2-α]pyridines with good yields（up to 85％）.     

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.     

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.     

Transition metal-free dearomatization of halonaphthols with C（sp3）-electrophiles

The first intermolecular electrophilic dearomatization of halonaphthols with benzyl/allyl bromides is described. Halonaphthols are used as carbon-nucleophiles in dearomatization to form three-dimensional cyclic enones with excellent chemoselectivity, in which etherification of phenolic hydroxyl group could be restrained well by using cesium carbonate as the base. A wide range of cyclic enones is directly prepared from various substituted benzyl/allyl bromides and halonaphthols. Mechanistic inves...     

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.     

Synthesis of imidazo[5,1-b]thiazoles or spiro-β-lactams by reaction of imines with mesoionic compounds or ketenes generated from N-acyl-thiazolidine-2-carboxylic acids

New mesoionic compounds (2H, 3H-thiazolo[3,2-c]oxazol-7-ones) (β) or ketenes ((3-acyl-1,3-thiazolidin-2-ylidene)methanone) (β′) were generated from N-acetyl and N-benzoyl-thiazolidine-2-carboxylic acids (7a,b) using different methods, and their reactivity towards N-(phenylmethylene)benzenesulfonamide (2) and N-(phenylmethylene)aniline (3) was tested. When (7a,b) were treated with (2) and acetic anhydride in refluxing toluene solution, only imidazo[5,1-b]thiazoles (8a,b) were obtained from the mesoionic compound intermediates (β). When the ketene intermediates (β′) were generated from (7a,b) by means of Mukaiyama's reagent, only spiro-β-lactams (9a,b) were isolated.     

Synthesis of 2,2-diaryl-1,1-difluoroethenes via Pd-catalyzed dehydrosulfonylative cross-coupling of α-[difluoro(phenylsulfonyl)methyl]benzyl tosylates with arylboronic acids

By using PhSO₂CF₂H as the difluoromethylidene equivalent, a novel method for connecting aromatic aldehydes and arylboronic acids via consecutive reactions was developed to obtain structurally diverse 2,2-diaryl-1,1-difluoroethenes. The key step is the palladium-catalyzed dehydrosulfonylative cross-coupling of tosylates that are prepared from PhSO₂CF₂H, aromatic aldehydes and tosyl chloride. Mechanistic investigations showed that the reaction proceeds mainly through base-mediated dehydrosulfonylation followed by palladium-catalyzed C(sp²)-C(sp²) cross-coupling reaction.     

Reaction of Imidazo[1,2‐a]pyridines with Aliphatic Aldehydes: A Simple and Efficient Method for the Preparation of Novel C‐3 Vinylic Derivativesof Imidazo[1,2‐a]pyridines

A simple and efficient method for the preparation of novel C‐3 vinylic derivatives of imidazo[1,2‐a]pyridines has been developed by the reaction of imidazo [1,2‐a]pyridines with appropriate aliphatic aldehydes in acetic acid in a sealed tube.     

Cyclization of alk-4-ynals with o-diaminoarenes as a selective one-pot synthesis of arylmethylidene-substituted 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazoles and 7,8-dihydro-6H-pyrrolo[1’,2’:1,2]imidazo[4,5-b]pyridines

Russian Chemical Bulletin - A one-pot synthesis of arylmethylidene-substituted 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazoles based on the reaction of alk-4-ynals with 1,2-diaminobenzenes in DMSO at...     

N-[1-(Benzotriazol-1-yl)alkyl]amides from N-acyl-α-amino acids or N-alkylamides

A variety of N-(1-methoxyalkyl)amides react with benzotriazole in the presence of PPh₃·HBF₄ and organic bases (Hünig's base, DBU or DABCO) or solid-state-supported bases (SiO₂-Pip or IRA-67) in CHCl₃ to give N-[1-(benzotriazol-1-yl)alkyl]amides in good yields. The most convenient and efficient procedure for obtaining N-[1-(benzotriazol-1-yl)alkyl]amides consists, however, of the addition of benzotriazole sodium salt to a solution of crude 1-(N-acylamino)alkyltriphenylphosphonium salt, obtained in situ from N-(1-methoxyalkyl)amides and PPh₃·HBF₄. A combination of these reactions with the recently described electrochemical decarboxylative α-methoxylation of N-acyl-α-amino acids in the presence of SiO₂-Pip enables an effective two-pot transformation of N-acyl-α-amino acids to N-[1-(benzotriazol-1-yl)alkyl]amides.