3+2] coupling of quinone monoacetals by combined acid-hydrogen bond donor

The expeditious and efficient [3+2] coupling approach of quinone monoacetals 1 with alkene nucleophiles 2 by the action of an activated Br?nsted acid in the presence of a hydrogen bond donor perfluorinated alcohol has been achieved. With the optimized combined acid, the reaction could proceed under mild conditions by only mixing the two reactants to afford the cycloadducts 3 in a short time (within 10 min) with good to quantitative yields.     

A convenient synthesis of coumarins using reusable ionic liquid as catalyst

Abstract

An efficient and convenient method has been developed for the synthesis of substituted coumarin derivatives using a Brønsted acidic ionic liquid as catalyst under solvent-free conditions. The catalyst can be reused for six consecutive runs without significant loss of activity.     

One-step, three-component synthesis of highly substituted pyridines using silica nanoparticle as reusable catalyst

One-step synthesis of ‘privileged medicinal scaffolds’, 2-amino-3,5-dicarbonitrile- 6-sulfanylpyridines, has been demonstrated via a multicomponent reaction of aldehydes, malononitrile, and thiols using silica nanoparticle (NP) as catalysts. The silica NP catalysts are very mild (nearly neutral in nature), effective, environmentally benign, and retain most of their activities after being reused for three times.     

Heterogeneous Baylis-Hillman using a polystyrene-bound 4-(N-benzyl-N-methylamino)pyridine as reusable catalyst

An insoluble Merrifield type resin having 4-aminopyridine units is a suitable and reusable heterogeneous catalyst for the Baylis-Hillman coupling of aromatic aldehydes and alpha,beta-unsaturated ketones.     

Selective esterification of glycerol with acetic acid to diacetin using antimony pentoxide as reusable catalyst

Glycerol can be obtained as a by-product during biodiesel manufacture. It is important to convert glycerol to value-added products. Glycerol esterification with acetic acid is one of the most promising approaches for glycerol utilization. It is usually difficult to obtain diacetin with good activity and selectivity. In this work, glycerol esterification with acetic acid over different metal oxides, such as Bi2O3, Sb2O3, Sn O2, Ti O2, Nb2O5 and Sb2O5, was investigated. It was found that in the six investigated metal oxides, only Sb2O5 resulted in good activity and selectivity to diacetin. Under the optimized conditions, the glycerol conversion reached 96.8%,and the selectivity to diacetin reached 54.2%, while the selectivity to monoacetin and triacetin was 33.2% and12.6%, respectively. The catalysts were characterized with FT-IR spectra of adsorbed pyridine, which indicated that in the six investigated metal oxides, only Sb2O5 possessed Br?nsted acid sites strong enough to protonate adsorbed pyridine. The good catalytic activity and selectivity to diacetin might be mainly attributable to the Br?nsted acid sites of Sb2O5. Reusability tests showed that with Sb2O5 as catalyst, after six reaction cycles, no significant change in the glycerol conversion and the selectivity to diacetin was observed.     

Efficient one-pot synthesis of 1-carbamatoalkyl-2-naphthols using aluminum methanesulfonate as a reusable catalyst

A wide range of 1-carbamatoalkyl-2-naphthols were synthesized via a one-pot three-component condensation of 2-naphthol, aldehydes, and carbamates in the presence of aluminum methanesulfonate at 70 °C under solvent-free conditions. The catalyst is reusable and could be recycled for several runs without any distinct decrease in its efficiency. A plausible mechanism for this three-component reaction was proposed.     

Ultrafast proton transfer of three novel quinone cyanine photoacids

Steady-state and time-resolved emission techniques were used to study the photoprotolytic properties of three recently synthesized strong quinone cyanine photoacids (QCy7 and its sulfonated derivatives). The rate coefficient of the excited-state proton transfer (ESPT), k(PT), of the three dyes is roughly 1.5 × 10(12) s(-1), a high value that is comparable to the solvation dynamics rate of large polar organic molecules in H(2)O and D(2)O. It is twice as fast as the proton transfer rate between two adjacent water molecules in liquid water. We found that, as expected, two of the sulfonated photoacids geminately recombines with the proton at an elevated rate. The accelerated geminate recombination process of the sulfonated derivatives is different from a simple diffusion process of protons. The ESPT rate coefficient of these molecules is the highest recorded thus far.     

Fluorine–proton correlation from isolated trifluoromethyl groups using unresolved J‐couplings

Fluorine‐containing compounds are rare in biological systems, so fluorine NMR spectroscopy can selectively detect and quantify fluorinated xenobiotics in crude biological extracts. The high sensitivity of fluorine NMR allows the detection of compounds containing isolated trifluoromethyl groups at nanogramme levels. However, it only provides limited structural information about trifluoromethyl‐containing compounds owing to the difficulty of interpreting fluorine chemical shifts and the low sensitivity of HOESY experiments used to correlate fluorine nuclei with protons in the same compound. This paper demonstrates that long‐range fluorine–proton J‐couplings can be used to correlate isolated trifluoromethyl groups with nearby protons with significantly higher sensitivity than HOESY. Fluorine‐observe fluorine–proton HMQC can even give correlations when the fluorine–proton J‐couplings are less than the observed fluorine resonance linewidth, so it provides a useful alternative source of structural information about fluorinated xenobiotics. Copyright © 2012 John Wiley & Sons, Ltd.     

Pseudo five-component process for the synthesis of functionalized tricarboxamides using CuI nanoparticles as reusable catalyst

An efficient and multicomponent method has been developed for the synthesis of functionalized tricarboxamides at room temperature using CuI nanoparticles as catalyst. This method involved fivecomponent coupling reactions of Meldrum's acid, isocyanides with aromatic aldehydes and amines at room temperature. Atom economy, wide range of products, excellent yields in short time and mild reaction conditions are some of the important features of this protocol. Notably, this catalyst could be recycled and reused for several times without significantly decreasing the catalytic activity.     

Facile one-pot synthesis of polysubstituted quinolines under solvent-free conditions using sulfamic acid as a reusable catalyst

Abstract  

A facile one-pot synthesis of polysubstituted quinoline derivatives has been demonstrated by using sulfamic acid as a reusable catalyst under solvent-free conditions. The synthetic method provides the basis and advantages of a simple experimental procedure and easy recovery and reuse of catalyst, which makes it a highly practical and environmentally benign pathway for the synthesis of polysubstituted quinolines. Interestingly, this one-pot synthesis could produce the products regioselectively in the presence of dis-symmetrical arylamines.     

Efficient and solvent-free synthesis of bis-indolylmethanes using silica gel supported aluminium chloride as a reusable catalyst

Stable and non-hygroscopic silica gel supported aluminium chloride（SiO₂-AlCl₃）,which is prepared easily from cheap and commercially available compounds was found to be an environmentally friendly heterogeneous catalyst for the condensation of indole with aldehydes and ketones to afford bis-indolylmethanes at room temperature under solvent-free conditions.The catalyst can be reused up to five times after simple washing with ether.     

Very efficient, reusable copper catalyst for carbene transfer reactions under biphasic conditions using ionic liquids

[reaction: see text] The complex {[HC(3,5-Me(2)pz)(3)]Cu(NCMe)}BF(4) catalyzes the transfer of the :CHCO(2)Et unit from ethyl diazoacetate to several saturated and unsaturated substrates with very high yields and under biphasic conditions using the ionic liquid [bmim][PF(6)] and hexane as the reaction medium. The catalyst has been tested for several cycles of recovery and reuse without any loss of activity.     

Facile and green synthesis of triarylmethanes using silica sulfuric acid as a reusable catalyst under solvent-free conditions

A facile and environmentally-benign protocol has been developed for the synthesis of triarylmethanes (TAMs) from the reaction of different arenes and aldehydes in the presence of silica sulfuric acid (SSA) as a heterogeneous and reusable catalyst under solvent-free conditions. Easy work-up, short reaction times, high yields, high selectivity, mild and green conditions are other salient features of this method.     

Efficient hydroxycarbonylation of aryl iodides using recoverable and reusable carbon aerogels doped with palladium nanoparticles as catalyst

Electron-rich and electron-poor aryl iodides are converted, in high to excellent yields, into the corresponding carboxylic acids through a hydroxycarboxylation reaction catalyzed by a recoverable and reusable phosphine free palladium-carbon aerogel catalyst using lithium formate and acetic anhydride as an internal condensed source of carbon monoxide. The catalyst system can be reused several times without any appreciable loss of activity.     

Solvent-Free one pot synthesis of benzo-[b]-1,4-diazepines using reusable sulfamic acid catalyst

α-β-Unsaturated carbonyl compounds on condensation with o-phenylenediamine in the presence of catalyst sulfamic acid under solvent free conditions, resulted in the formation of corresponding benzo-[b]-1,4-diazepines in excellent yields.     

A green protocol for the N-formylation of amines using molybdate sulfuric acid as a reusable solid catalyst

A novel and efficient method for the N-formylation of amines via the reaction of orthoformates and amines is developed. The reactions are mediated by a catalytic amount of molybdate sulfuric acid as a heterogeneous solid acid.     

Highly active and reusable catalyst for fries rearrangement of phenyl acetate

Silica-12-tungstophosphoric acid core-shell nanoparticles were prepared by sol-gel method followed by steaming. The catalytic activity of fresh and steamed catalysts was studied in Fries rearrangement of phenyl acetate. The reaction parameters, such as catalyst loading and reaction temperature, were optimized. The structural properties of the prepared catalysts were analyzed by X-ray diffraction and transmission electron microscopy techniques. The nature and strength of acid sites in the catalysts were analyzed by pyridine adsorption followed by infrared spectroscopy and differential scanning calorimetry measurements. The XRD and TEM analyses confirm the formation of silica-12-tungstophosphoric acid core-shell nanoparticles during steaming process. Acidity measurement indicates that both fresh and steamed catalyst samples carry weak acid sites and Brøsted acid sites. In addition, the steaming of heteropoly acid contained silica enhances the strength of Brøsted acid sites. The catalytic activity of fresh as well as steamed catalysts in liquid-phase Fries rearrangement showed that the steam treated sample exhibits higher conversion and selectivity to the desired product compared to the fresh catalyst sample. The higher activity of steam treated catalysts has been explained in terms of surface acidity of the catalysts. Reusability of the steamed catalyst shows that there is no appreciable change either in the conversion rate or product selectivity.