Metal-free direct regioselective thiolation of imidazoheterocycles in water at room temperature

A metal-free direct thiolation of imidazoheterocycles with various thiophenol in water at room temperature has been developed. In addition, the chemistry provides several advantages including mild condition, high yields, good functional group tolerance, green solvents and suitable for large-scale operations.     

Metal-free synthesis of 3,3-disubstituted oxindoles via 1,2-alkylarylation of activated alkenes with alcohols

Metal-free synthesis of 3,3-disubstituted oxindoles utilizing N-arylacrylamides and simple alcohols is developed. It provides an efficient method for preparing a series of hydroxyl-containing oxindole derivatives. This reaction is proposed to proceed through oxidative radical cyclization mechanism. The remarkable features of the reaction are metal-free condition and excellent functional group tolerance.     

Fast oxidation of secondary alcohols by the bromate-bromide system using cyclic microwave heating in acidic water

We report an improved, gentle, cyclic microwave activation technique for the oxidation of secondary alcohols using nonhazardous hypobromous acid (BrOH) as the reagent in acidic water. Several aliphatic and aromatic secondary alcohols were successfully oxidized to the corresponding ketones using this technique in high yields and with only minor amounts of side products.     

Zinc triflate catalyzed acylation of alcohols,phenols, and thiophenols

An expedient procedure for the acylation of alcohols, phenols, and thiophenols using catalytic amount of Zn(OTf)₂ is described. This procedure is highly suitable for industrial application due to use of less toxic metal as a part of catalyst, short reaction time at ambient temperature, without any racemization of chiral alcohols.     

On the role of triflic acid in the metal triflate-catalysed acylation of alcohols

The acylation of alcohols by anhydrides, catalysed by a wide range of metal triflates, is a powerful and mild method for the preparation of a variety of esters. Mechanistic insights demonstrate that triflic acid is generated under these reaction conditions and that, at least, two competing catalytic cycles are operating at the same time: a rapid one involving triflic acid and a slower one involving the metal triflate.     

Metal-free sulfonylation of quinones with sulfonyl hydrazides in water: Facile access to mono-sulfonylated hydroquinones

This paper describes a simple and practical protocol for the direct synthesis of monosulfonylated hydroquinones through a transition-metal-free cross-coupling between quinones and sulfonyl hydrazides in water. The procedure tolerates a variety of quinones and widely available sulfonyl hydrazides.     

纳米尺度氧化石墨烯层作为高效碳催化剂用于苄醇与芳香醛的绿色氧化

合成了纳米尺度氧化石墨烯(NGO)层,用作碳催化剂高效催化苄醇与芳香醛的氧化反应.对于醇氧化反应,当80℃时H2O2存在下,NGOs(20 wt％)可高效催化醇选择性生成醛,其反应速率和产率取决于醇上取代基的性质.对于4-硝基苄醇,反应24 h后,只有10％可转换为相应羧酸.相反,4-甲氧基苄醇和二苯基甲醇分别反应仅9和3h则可完全转化为对应的羧酸和酮.NGO碳催化剂上芳香醛氧化速率高于醇氧化速率.对于所有的醛,采用7 wt％ NGO作催化剂,在70℃反应2-3 h后,就可完全转化为相应羧酸.我们讨论了NGO催化剂结构对苄醇和芳香醛氧化反应影响的可能机理.     

Hafnium inspired activation of highly hindered anhydrides in the acylation of alcohols and polyols

A novel and highly efficient method for activating highly hindered acid anhydrides towards the acylation of alcohols and carbohydrate-derived polyols has been developed. This new method relies on the capacity of the hafnium triflate catalyst Hf(OTf)₂ to activate highly hindered acid anhydrides, and to direct the acylation reaction. This new acylation protocol is mild and proceed at room temperature with low catalyst loading. The method is versatile and has been extended to different alcohol substrates with different steric encumbrance as well as carbohydrate-derived polyols to afford the corresponding ester products in good to excellent yields.     

The green and effective oxidation of alcohols to carboxylic acids with molecular oxygen via biocatalytic reaction

A clean and effective alcohol oxidizing system using three enzymes has been developed. Regeneration of NAD⁺ by NADH oxidase with molecular oxygen enabled to oxidize alcohols to carboxylic acids in good yield under mild conditions (25 °C, 1 atm).     

Metal-free oxidative cyclization of 2-amino-benzamides, 2-aminobenzenesulfonamide or 2-(aminomethyl)anilines with primary alcohols for the synthesis of quinazolinones and their analogues

A general metal-free oxidative cyclization process has been developed for the synthesis of quinazolinones, benzothiadiazines and quinazolines. By this protocol, a range of substituted 2-aminobenzamides, 2-aminobenzenesulfonamide and 2-(aminomethyl)anilines react with various alcohols, leading to the desired annulated products smoothly. This protocol features many advantages as broad substrate scope, mild reaction conditions, low environmental pollution, high atom-economy and good to excellent yields.     

Cyclization/acylation reactions by nickel-catalyzed reactions of 1,6-ynal and 1,6-enyne derivatives with acylzirconocene chloride

NiCl₂(PPh₃)₂-catalyzed reactions of 1,6-ynal or 1,6-enyne compounds with n-nonanoylzirconocene chloride afforded stereoselectively cyclopentane derivatives or bicyclo[3.1.0] compounds by catalytic cyclization/acylation reactions, which would involve (i) the primary formation of a metallacycle followed by (ii) the transfer of an acyl group from the acylzirconocene complex (transmetalation).     

Cobalt(II)-catalyzed direct acetylation of alcohols with acetic acid

Cobalt(II) chloride hexahydrate (CoCl₂·6H₂O) efficiently catalyzes the acetylation of alcohols with AcOH in high yields. This protocol is also effective with other carboxylic acids, trifluoroacetic acid, propanoic acid, phenylacetic acid and benzoic acid, affording the corresponding acylated products in moderate to good yields. Removal of water is not necessary in these reactions. The catalyst can be filtered and recycled without loss of activity.     

Intermolecular palladium-catalyzed coupling of 2-halopyridines and alcohols for the preparation of pyridine ether PPAR agonists

A series of pyridine ether PPAR agonists were synthesized through intermolecular palladium-catalyzed coupling of 2-halopyridines and alcohols. This method proved to be versatile, efficient, and amenable to parallel synthesis.     

Chemometrics assisted spectrophotometric determination of pyridine in water and wastewater

The paper reports a direct method for the determination of pyridine in water and wastewater samples based on ultraviolet spectrophotometric measurements using multi-way modeling techniques. Parallel factor analysis (PARAFAC) and multi-way partial least squares (N-PLS) regression methods were employed for the decomposition of spectra and quantification of pyridine. The study was carried out in the pH range of 1.0-12.0 and concentration range of 0.67-51.7 μg mL⁻¹ of pyridine. Both the three-way PARAFAC and tri-PLS1 models successfully predicted the concentration of pyridine in synthetic (spiked) river water and field wastewater samples. The mean recovery obtained from PARAFAC regression model were 97.39% for the spiked and 99.84% for the field wastewater samples, respectively. The sensitivity and precision of the method for pyridine determination were 0.58% and 5.95%, respectively. The N-PLS regression model yielded mean recoveries of 99.29% and 100.18% for the spiked and field wastewater samples, respectively. The prediction accuracy of the methods was evaluated through the root mean square error of prediction (RMSEP). For PARAFAC, it was 0.65 and 0.82 μg mL⁻¹ for spiked river water and field wastewater samples, respectively, while for N-PLS, it was 0.25 and 0.37 μg mL⁻¹, respectively. Both the PARAFAC and N-PLS methods, thus, yielded satisfactory results for the prediction of pyridine concentration in water and wastewater samples.     

Tris(pentafluorophenyl)borane catalyzed acylation of alcohols,phenols, amines,and thiophenols under solvent-free condition

The acylation of alcohols, phenols, amines, and thiophenols was accomplished with 0.5 mol % of tris(pentafluorophenyl)borane [B(C₆F₅)₃] at ambient temperature under solvent-free condition. Major advantages of this method include high yield, short reaction time, simple procedure, compatibility with sensitive protecting groups as well as other functional groups, absence of racemization of optical active compounds, and epimerization of sugars.     

Borylation of aryldiazonium salts at room temperature in an aqueous solution under catalyst-free conditions

A general and convenient borylation reaction of aryldiazonium tetrafluoroborate salts with B₂pin₂ has been developed. In this catalytic system, no catalyst, additional ligands or additives were required. The reaction proceeded smoothly in an aqueous solution, and a variety of arylboronates were isolated in moderate to excellent yields under mild reaction conditions.     

DIPEA catalyzed step-by-step synthesis and photophysical properties of thieno[2,3-b]pyridine derivatives

A series of novel 5,6-disubstituted ethyl 3-amino-4-cyanothieno[2,3-b]pyridine-2-carboxylates was synthesized. The reaction conditions were thoroughly studied and intermediate ethyl 2-((3,4-dicyanopyridin-2-yl)thio)acetates were successfully isolated in good yields. For all synthesized compounds, spectral-fluorescent properties were carefully investigated and correlation thereof with chemical structure was found.     

A TEMPO-like nitroxide combined with an alkyl-substituted pyridine: An efficient catalytic system for the selective oxidation of alcohols with iodine

An efficient method for the oxidation of alcohols to aldehydes or ketones in a two-phase CH₂Cl₂/NaHCO₃ (aq.) system, using iodine and catalytic amounts of 4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxyl and 2,4,6-trimethylpyridine, was developed. The performance of the method was demonstrated by the selective oxidation of 37 variously substituted alcohols in ≥90% yield, including the gram-scale synthesis of the important chemical 2,5-diformylfuran from biomass-derived 5-hydroxylmethylfurfural.     

Arylation of pyridine N-oxides via a ligand-free Suzuki reaction in water

We report a practical and highly efficient protocol for the arylation of pyridine N-oxides with arylboronic acid through palladium-catalyzed Suzuki reaction in water.This ligand-free Suzuki reaction is performed in the presence of diisopropylamine and gives 2-or 3-arylated pyridyl N-oxide derivatives in good to excellent yields within 1 h.     

Ionic liquid-supported TEMPO as catalyst in the oxidation of alcohols to aldehydes and ketones

We describe an efficient synthesis of an ionic liquid-supported TEMPO which was used for the oxidation of alcohols to aldehydes and ketones. The predictable solubility of ionic liquids allows an easy separation of the oxidation products from reagents. Furthermore, the oxidation can be carried out using an ionic liquid as the solvent instead of dichloromethane; and the IL-supported TEMPO can be recycled and used several times without the loss of efficiency.