Direct Arylation of Substituted Pyridines with Arylboronic Acids Catalyzed by Iron(II) Oxalate

The direct arylation of substituted pyridines with several arylboronic acids has been developed. This transformation could proceed readily at ambient temperature using inexpensive reagents: iron(II) oxalate as a catalyst, potassium persulfate as a co‐oxidant, which can afford the arylated products in mild to good yields. The mechanism is presumed to proceed through a nucleophilic radical addition to the pyridines with in situ reoxidation.     

Cu-catalyzed direct ortho-chlorination/-oxygenation of aryls: Switching of oxidant,control the diversity of products

Highly regioselective copper catalyzed ortho-chlorination of aryl pyridines was achieved with TBHP as oxidant and 1,2-dichloroethane as chlorinating agent for the first time. Switching the oxidant from TBHP to benzoyl peroxide under identical reaction conditions effects ortho-oxygenation.     

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.     

Oxidative aromatization of Hantzsch 1,4-dihydropyridines by aqueous hydrogen peroxide-acetic acid

A simple method for the oxidative aromatization of Hantzsch 1,4-dihydropyridines to the corresponding pyridines is achieved by using hydrogen peroxide as green oxidant and acetic acid as catalyst in aqueous solution.     

Chloroacetate Promotes and Participates in the Oxidative Annulation of Pyridines/Isoquinoline by Using Oxygen as the Oxidant

The aerobic oxidative annulation of chalcones, pyridines/isoquinoline and ethyl chloroacetate to indolizines was achieved by cascade reaction. Various functional groups on chalcones were tolerated. And different pyridines derivatives could also be suitable substrates. Ethyl chloroacetate is an essential component in participating of the oxidative annulation process. Overall, this protocol is very practical and efficient by using molecular oxygen as oxidant with high selectivity for the annulation product.     

Metal-free,base catalyzed oxidative amination and denitration reaction: Regioselective synthesis of 3-arylimidazo[1,2-a]pyridines

A metal-free, regioselective strategy for the synthesis of 3-arylimidazo[1,2-a]pyridines from β-nitrostyrenes and 2-aminopyridines using triethylamine as the catalyst and H₂O₂ (30% aq.) as the oxidant is reported. The use of an inexpensive base and facile reaction conditions make this strategy a practical alternative for the synthesis of 3-arylimidazo[1,2-a]pyridines.     

Copper(II) mediated C–H methylthiolation of 2-phenyl pyridines with dimethyl sulfoxide using an amino acid ligand

A novel protocol for the C–H methylthiolation of 2-phenyl pyridines using DMSO as the methylthio source and an amino acid ligand is described. This simple procedure requires neither an oxidant nor additional solvent. The developed protocol tolerates a wide range of functional groups including methyl, methoxy, fluoro, chloro, and in particular the formyl group. This new strategy is highly regioselective and provides aryl methyl sulfides from 2-phenyl pyridines in moderate to good yields.     

Oxidation reactions using polymer-supported 2-benzenesulfonyl-3-(4-nitrophenyl)oxaziridine

A thermally stable polymer-supported oxidant has been developed. Polymer-supported 2-benzenesulfonyl-3-(4-nitrophenyl)oxaziridine was applied to microwave-assisted reactions that occurred at high temperatures and was shown to oxidize alkenes, silyl enol ethers, and pyridines to the corresponding epoxides and pyridine N-oxides in excellent to good yields and with much shorter reaction times. It also enabled tetrahydrobenzimidazoles to be oxidatively rearranged to spiro fused 5-imidazolones in a more efficient manner. Recycling of the polymer-supported oxidant is also possible with minimal loss of activity after several reoxidations.     

Regioselective,Solvent‐ and Metal‐Free Chalcogenation of Imidazo[1,2‐a]pyridines by Employing I2/DMSO as the Catalytic Oxidation System

Highly efficient molecular‐iodine‐catalyzed chalcogenations (S and Se) of imidazo[1,2‐a]pyridines were achieved by using diorganoyl dichalcogenides under solvent‐free conditions. This approach afforded the desired products that had been chalcogenated regioselectively at the C3 position in up to 96 % yield by using DMSO as an oxidant, in the absence of a metal catalyst, and under an inert atmosphere. This mild, green approach allowed the preparation of different types of chalcogenated imidazo[1,2‐a]pyridines with structural diversity. Furthermore, the current protocol was also extended to other N‐heterocyclic cores.     

Application of silica vanadic acid [SiO2-VO(OH)2] as a heterogeneous and recyclable catalyst for oxidative aromatization of Hantzsch 1,4-dihydropyridines at room temperature

A simple method for the oxidative aromatization of Hantzsch 1,4-dihydropyridines to the corresponding pyridines is described using hydrogen peroxide as green oxidant and silica vanadic acid as catalyst in acetonitrile at room temperature. The catalyst can be easily recovered and reused for 15 reaction cycles without considerable loss of activity.     

Dehydrogenative Synthesis of 2,2′‐Bipyridyls through Regioselective Pyridine Dimerization

2,2′‐Bipyridyls have been utilized as indispensable ligands in metal‐catalyzed reactions. The most streamlined approach for the synthesis of 2,2′‐bipyridyls is the dehydrogenative dimerization of unfunctionalized pyridine. Herein, we report on the palladium‐catalyzed dehydrogenative synthesis of 2,2′‐bipyridyl derivatives. The Pd catalysis effectively works with an Ag^I salt as the oxidant in the presence of pivalic acid. A variety of pyridines regioselectively react at the C2‐positions. This dimerization method is applicable for challenging substrates such as sterically hindered 3‐substituted pyridines, where the pyridines regioselectively react at the C2‐position. This reaction enables the concise synthesis of twisted 3,3′‐disubstituted‐2,2′‐bipyridyls as an underdeveloped class of ligands.     

Coupling Reactions of Heteroarenes with Phosphites under Silver Catalysis

A silver-catalyzed dehydrogenative cross-coupling reaction of substituted furans, thiophene, thioazole, and pyrrole 1a-e with dialkyl phosphites 2 was first developed to afford corresponding phosphonated products 3a-h with up to 89% yield and good regioselectivities. Moreover, an unprecedented coupling of various substituted pyridines 1f-k with dialkyl phosphites 2 using AgNO(3) as a catalyst and K(2)S(2)O(8) as an oxidant, followed by reduction with Na(2)S(2)O(3), was also realized to furnish desired pyridine phosphonates 3i-q in satisfactory yields with good regioselectivities.     

Facile One‐Pot Synthesis of [1, 2, 3]Triazolo[1, 5‐a]Pyridines from 2‐Acylpyridines by Copper(II)‐Catalyzed Oxidative NN Bond Formation

An efficient and simple method for the synthesis of various [1, 2, 3]triazolo[1, 5‐a]pyridines has been established. The method involves a copper(II)‐catalyzed oxidative N?N bond formation that uses atmospheric oxygen as the terminal oxidant following hydrazonation in one pot. The use of ethyl acetate as the solvent dramatically promotes the oxidative N?N bond‐formation reaction and enables the application of oxidative cyclization in the efficient one‐pot reaction. A mechanism for the reaction was proposed on the basis of the results of a spectroscopic study.     

FERRIC CHLORIDE HEXAHYDRATE: A CONVENIENT REAGENT FOR THE OXIDATION OF HANTZSCH 1,4-DIHYDROPYRIDINES

A general and practical route for the moderate yield oxidative conversion of readily accessible 1,4-dihydropyridines (1,4-DHPs) to the corresponding pyridines was described using a relatively benign oxidant, i.e. ferric chloride hexahydrate (FeCl₃·6H₂O). The reaction was carried out under mild and convenient condition. However, oxidation of 4-isopropyl-1,4-DHP 1b with FeCl₃·6H₂O afforded the dealkylated pyridine 2a.     

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.     

1,1,2,2-Tetrahydroperoxy-1,2-Diphenylethane: An efficient and high oxygen content oxidant in various oxidative reactions

Several oxidative approaches namely thiocyanation of aromatic compounds, epoxidation of alkenes, amidation of aromatic aldehydes, epoxidation of α, β-unsaturated ketones, oxidation of sulfides to sulfoxides and sulfones, bayer-villeger reaction, bromination and iodation of aniline and phenol derivatives oxidative esterification, oxidation of pyridines and oxidation of secondary, allylic and benzyllic alcohols were carried out using 1,1,2,2-Tetrahydroperoxy-1,2-Diphenylethane as the potential solid oxidant which can be stored for several months without any loss in its activity. All of the procedures were accomplished via mild reaction conditions and the products were afforded in high yields and short reaction times.     

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.     

Alkylation of Pyridines at Their 4‐Positions with Styrenes plus Yttrium Reagent or Benzyl Grignard Reagents

A new regioselective alkylation of pyridines at their 4‐position was achieved with styrenes in the presence of yttrium trichloride, BuLi, and diisobutylaluminium hydride (DIBAL‐H) in THF. Alternatively, similar products were more simply prepared from pyridines and benzyl Grignard reagents. These reactions are not only a useful preparation of 4‐substituted pyridines but are also complementary to other relevant reactions usually giving 2‐substituted pyridines.     

Functionalized sulfur-containing compounds. 13. Synthesis of substituted 3-amino-2-(organylsulfinyl)-and-(organylsulfonyl)thieno[2,3-b]pyridines

A method for the synthesis of substituted 3-amino-2-(organylsulfinyl)thieno[2,3-b]pyridines by the Thorpe—Ziegler intramolecular cyclization of substituted 3-cyano-2-[(organyl-sulfinyl)methylthio]pyridines was proposed. 3-Amino-2-(organylsulfonyl)thieno[2,3-b]pyridines were obtained by reactions of substituted 3-cyanopyridine-2-thiones with chloromethyl organyl sulfones. The reaction intermediates 3-cyano-2-[(organylsulfonyl)methylthio]pyridines were transformed into 3-amino-2-(organylsulfonyl)thieno[2,3-b]pyridines. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 510–515, March, 2006.     

2-,3-和4-溴甲基吡啶的水解反应的动力学研究

用HPLC测定了2-、3-和4-溴甲基吡啶在60℃、离子强度μ为0.15、pH 0.9～9.9的缓冲溶液中水解成相应的羟甲基吡啶的反应速度.通过数学处理,求得溴甲基吡啶的一级和二级反应速度常数以及溴甲基吡啶共轭酸的一级反应速度常数.水解反应的可能机理是S_N1和S_N2.