Oxidation of Organic Compounds by Sulfonated Porous Carbon and Hydrogen Peroxide

 The oxidation of organic compounds by sulfonated porous carbon and H2O2 was studied at room temperature. Alkyl and aryl sulfides were oxidized to the corresponding sulfoxides or sulfones in excellent yields. Secondary alcohols were also converted to the corresponding esters/lactones and aldehydes to methyl esters in good yields. Moreover, aliphatic tertiary amines and substituted pyridines were oxidized to N-oxides.     

Synthesis of 1,3-diarylated imidazo[1,5-a]pyridines with a combinatorial approach: metal-catalyzed cross-coupling reactions of 1-halo-3-arylimidazo[1,5-a]pyridines with arylmetal reagents

The halogenation of 3-arylimidazo[1,5-a]pyridines was carried out with iodine, bromine, N-chlorosuccinimide, and 1-fluoro-2,4,6-trimethylpyridinium tetrafluoroborate as halogenating agents to give selectively halogenated products 1-halo-3-arylimidazo[1,5-a]pyridines in good to excellent yields. Kumada-Tamao-Corriu cross-coupling of the obtained 1-iodo-3-arylimidazo[1,5-a]pyridines and aryl Grignard reagents led to 1,3-diarylated imidazo[1,5-a]pyridines in good to excellent yields. Suzuki-Miyaura cross-coupling of the 1-bromo-3-phenylimidazo[1,5-a]pyridine and p- or m-methoxycarbonylphenylboronic acids furnished the coupling product in respective yields of 91% and 61%. The obtained 1,3-diarylated imidazo[1,5-a]pyridines showed a wide variety of fluorescent emissions in a wavelength range of 449-533 nm with improved quantum yields compared to monoarylated ones.     

Coupling-isomerization-N,S-ketene acetal-addition sequences--a three-component approach to highly fluorescent pyrrolo[2,3-b]pyridines, [1,8]naphthyridines, and pyrido[2,3-b]azepines

Annelated 2-amino pyridines such as pyrrolo[2,3-b]pyridines, [1,8]naphthyridines, and pyrido[2,3-b]azepines can be synthesized in moderate to good yields in a consecutive one-pot three-component process by a coupling-isomerization-enamine-addition-cyclocondensation sequence of an electron-poor (hetero)aryl halide, a terminal propargyl N-tosylamine, and an N,S-ketene acetal. After the coupling-isomerization sequence, a Diels-Alder reaction with inverse electron demand of the intermediate enimine and the N,S-ketene acetal and subsequent aromatization furnish annelated 2-amino pyridines 4 that were unambiguously characterized by numerous X-ray structure analyses. These heterocycles are highly fluorescent and partially pH sensitive, and their electronic structure was studied with spectroscopic and computational methods.     

Synthèse de benzopyrannopyridines et de dihydrobenzoquinoléines

Cycloaddition between α,β-unsaturated ketones and vinyl ethers gave 2-alkoxydihydropyrans. On treatment with hydroxylamine hydrochloride, these adducts afforded the corresponding substituted pyridines in good to moderate yields. By applying this scheme we could obtain benzopyrannopyridines and dihydrobenzoquinolines. Structures have been studied by spectroscopic methods.     

Reaction of 4-iminothiazolidin-2-one with acetylacetone

By the reaction of acetylacetone and arylazoacetylacetones with 4-iminothiazolidin-2-one thiazolo[4,5-b]pyridines were obtained in good yields. Optimum reaction conditions were chosen and some properties of compounds obtained were studied.     

Nickel-Catalyzed Reductive Alkylation of Halogenated Pyridines with Secondary Alkyl Bromides

This article highlights Ni-catalyzed cross-electrophile coupling of halogenated pyridines with secondary alkyl bromides using zinc as the terminal reductant. With this protocol, we have successfully achieved different alkyl-substituted pyridines in moderate to excellent yields.     

Synthesis and solid state study of pyridine- and pyrimidine-based fragment libraries

A library of pyridines and pyrimidines has been synthesised in excellent yields employing microwave and flow chemistry methodologies. Work-up bottlenecks have been facilitated substantially by the use of supported reagents and many of the final compounds have been studied in the solid state by single crystal X-ray diffraction.     

1-Alkynyl- and 1-alkenyl-3-arylimidazo[1,5-a]pyridines: synthesis, photophysical properties, and observation of a linear correlation between the fluorescent wavelength and Hammett substituent constants

1-Alkynyl- and 1-alkenyl-3-arylimidazo[1,5-a]pyridines were synthesized. The Sonogashira coupling of 3-aryl-1-iodoimidazo[1,5-a]pyridines and various terminal alkynes with Pd(PPh(3))(2)Cl(2) (10 mol %) and CuI (10 mol %) in triethylamine at 80 °C for 12 h afforded the corresponding 1-alkenyl-3-arylimidazo[1,5-a]pyridines in good to excellent yields. The Mizoroki-Heck reaction of 3-aryl-1-iodoimidazo[1,5-a]pyridines and various styrene derivatives proceeded smoothly with Pd(OAc)(2) (5 mol %), IMes·HCl (10 mol %), and Cs(2)CO(3) (2 equiv) in DMA at 130 °C for 20 h to give the alkenylated imidazo[1,5-a]pyridines in moderate to high yields. The fluorescence maxima and fluorescence quantum yields of the alkynylated products were 458-560 nm and Φ(F) = 0.08-0.26 in chloroform solution, and those of the alkenylated imidazopyridines were 479-537 nm and Φ(F) = 0.03-0.13. The absorption behaviors of the obtained alkynylated and alkenylated imidazo[1,5-a]pyridines showed a good fit to the values predicted by TDDFT calculations at the B3LYP/6-311++G(d,p) level. In addition, the alkynylated imidazo[1,5-a]pyridines obtained showed linear correlations between the Hammett substituent constants of the substituents on the arylalkynyl group and their fluorescence wavelengths.     

Magnesium Methoxide-Assisted Synthesis of 2,4,6-Triaryl Pyridines

A new three-component reaction of chalcones, ketones, and ammonia assisted by magnesium methoxide is described. The corresponding 2,4,6-triaryl pyridines (Kröhnke pyridines) are formed in fair to good yields (34–76%) within 3 h. The method also provides a facile way to synthesize 2(6)-difluoromethyl pyridines via an interesting mechanism.     

Reactions of 2-Pyridyl Substituted Phosphine Oxides and Phosphonium Salts with Organometallic Reagents and in Aqueous Media

Phosphine oxides bearing two or three 2-pyridyl groups react with organometallic reagents affording 2,2′-bipyridyl, 2-substituted pyridines and pyridine in good yields. Phosphonium salts and phosphine oxides, bearing at least two 2-pyridyl or substituted 2-pyridyl groups also give the corresponding 2,2′-bipyridyls and pyridines upon treatment with acid or neutral solvents such as water and alcohols in substantial yields. The 2,2′-bipyridyls are considered to be formed by ligand coupling within the pentacoordinated phosphorus intermediate formed incipiently during the reaction.     

Cobalt-Catalyzed Pyridine Syntheses from Alkynes and Nitriles

Soluble organocobalt catalysts permit selective formation of substituted pyridines under mild conditions in a single step: mono-, di-, and trisubstituted pyridines can be obtained at will in high conversions and high yields from nitriles and alkynes. Polynuclear derivatives such as bipyridines can also be prepared by this method.     

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％）.     

N-propargylic beta-enaminones: common intermediates for the synthesis of polysubstituted pyrroles and pyridines.

N-Propargylic beta-enaminones have been used as common intermediates for the synthesis of polysubstituted pyrroles and pyridines. Best results have been obtained using DMSO as solvent. In the presence of Cs(2)CO(3) N-propargylic beta-enaminones are cyclized to pyrroles in good to high yields, whereas omitting bases and using CuBr leads to the selective formation of pyridines.     

Regioselective synthesis of 1,2,4,5-tetrasubstituted pyridines from Baylis-Hillman adducts via consecutive [3+2+1] annulation protocol

An efficient synthetic method of poly-substituted pyridines was developed. Various poly-substituted pyridines were prepared from the combination of Baylis-Hillman adducts (3 carbons), activated methylene compounds (2 carbons) and ammonium acetate (1 nitrogen) via [3+2+1] annulation protocol in good yields, regioselectively.     

Synthesis of imidazo[1,2a]pyridines via three-component reaction of 2-aminopyridines, aldehydes and alkynes

A novel three-component reaction towards the synthesis of imidazo[1,2a]pyridines was independently developed based on 2-aminopyridines, aldehydes and alkynes, and thereby imidazo[1,2a]pyridines were obtained in acceptable yields by the CuSO4/TsOH catalyzed three-component reaction.     

A new synthesis of 2-substituted pyridines via aluminum chloride induced heteroarylation of arenes and heteroarenes

[reaction: see text] We herein report a new synthesis of 2-(hetero)aryl-substituted pyridines via heteroarylation of arenes/heteroarenes through AlCl(3)-induced C-C bond-forming reactions. 2-Halopyridines bearing an electron-withdrawing group were reacted with a number of (hetero)arenes to give 2-aryl/heteroaryl-substituted pyridines in good yields.     

One-pot synthesis of imidazo[1,2-a]pyridines from benzyl halides or benzyl tosylates, 2-aminopyridines and isocyanides

A one-pot synthesis of imidazo[1,2-a]pyridines is described. Benzyl halides or benzyl tosylates are oxidized to aldehydes under mild Kornblum conditions which then undergo a three-component reaction with various 2-aminopyridines and isocyanides to afford the imidazo[1,2-a]pyridines in excellent yields.     

The reactions of some halogenated pyridines with methoxide and methanethiolate ions in dimethylformamide

The reactions of 2,6- and 2,5-dibromopyridines and of 2,3- and 3,5-dichloropyridines with sodium isopropanethiolate and methanethiolate afforded the products of mono- or of bis-substitution depending on the experimental conditions. The same pyridines reacted with sodium methoxide to give good yields of the mono-substituted products; bis-substitution occurred easily only in the case of the 2,6-dibromo- and of the 3,5-dichloropyridine. The syntheses of some methoxy thiomethoxypyridine, starting from the halogeno methoxypyridines or from the halogeno thiomethoxypyhdines are also described. The bis-(alkylthio)pyridines can be fragmented by sodium in HMPA to give the bis(mercapto)pyridines.     

Iodobenzene‐Catalyzed Synthesis of Imidazo[1,2‐a]pyridines from Aryl Ketones with mCPBA in Ionic Liquid

Iodobenzene‐catalyzed synthesis of imidazo[1,2‐a]pyridines from aryl ketones with mCPBA as a cooxidant in ionic liquid is described. The method is simple, rapid and practical, generating Imidazo[1,2‐a]pyridines from the aryl ketone without isolation of α‐tosyloxyketones in good to excellent yields.     

Direct Asymmetric Dearomatization of Pyridines and Pyrazines by Iridium‐Catalyzed Allylic Amination Reactions

The first iridium‐catalyzed intramolecular asymmetric allylic dearomatization reaction of pyridines and pyrazines has been realized. 2,3‐Dihydroindolizine and 6,7‐dihydropyrrolo[1,2‐a]pyrazine derivatives were obtained with excellent yields and enantioselectivity. This methodology features dearomatization by direct N‐allylic alkylation of pyridines or pyrazines under mild reaction conditions.