Journal of Chemical Research

A simple and practical protocol for the synthesis of symmetric thioureas and heterocyclic thiones has been developed. It involves the reaction of amines with phenyl chlorothionoformate in water to afford the symmetrical thioureas or heterocyclic thiones in good to excellent yields. Various amines including aromatic, aliphatic and chiral amines survived the reaction conditions. Mild conditions, simple work-up and high yields as well as using water as solvent are the major advantages of this protocol.

An efficient two-step route was developed for the synthesis of 1-aralkyl-4-benzylpiperazine derivatives by a Blanc reaction and alkylation. The key intermediate, N-benzylpiperazine, was prepared in an excellent yield by direct benzylation of commercially available piperazine under metal-free conditions.

A diastereo- and enantioselective base-catalysed aldol reaction of t-butyl isocyanoacetate with aldehydes under phase-transfer catalytic conditions yielded 19 4,5-disubstituted oxazolines, 16 of which are novel. Key to success was the use of a free 9-OH-containing cinchona alkaloid-based quaternary ammonium salt bearing bulky and electron-withdrawing aryl groups on the N-benzyl moiety. This process tolerates both aromatic and aliphatic aldehydes, affording the corresponding chiral oxazoline products in diastereoselectivities up to 20:1 and enantioselectivities up to 78% ee.

The preparation of seven β-acetamido esters, two of which are novel, has been achieved by a one-pot condensation reaction of an araldehyde, ethyl acetoacetate and acetyl chloride in the presence of CeO₂ nanoparticles under reflux conditions in acetonitrile. This method provides several advantages including easy workup, excellent yields, short reaction times, diastereoselective synthesis, reusability of the catalyst and low catalyst loading.

A facile solvent- and catalyst-free method for the synthesis of a series of imidazo[1,2-a]pyridines in good to excellent yields by the condensation of 2-aminopyridines with α-bromoketones under microwave irradiation has been developed. The important features of this method are that it is reasonably fast, very clean, high yielding, simple workup and environmentally benign.

Cyclocondensation of Schiff bases and substituted acetic acid with tosylimidazole afforded 2-azetidinones in good to excellent yields. This reaction works reliably well for monocyclic and spirocyclic 2-azetidinones. This reaction is green and efficient and the products can be purified by simple crystallisation.

The reaction of 2,6-bisbenzylidenecyclohexanones and phenylhydrazine in polyethylene glycol (PEG)-400 as a green and reusable solvent under catalyst-free conditions gave hexahydroindazoles as the major product and, in some cases, tetrahydroindazoles were also produced as a minor product. The products were easily separated by simple recrystallisation. The structures of the indazoles were confirmed using FTIR and NMR spectroscopy. Two X-ray structures are reported.

A convenient and facile four-component synthesis is described of 2-amino-3-cyanopyridine derivatives from readily available starting materials catalysed by doped nano-sized Cu₂O on melamine–formaldehyde resin (nano-Cu₂O–MFR). In this method, treatment of different aldehydes, ketones, malononitrile, and ammonium acetate in refluxing H₂O/EtOH (1:1) in the presence of doped nano-Cu₂O–MFR as a highly efficient heterogeneous catalyst affords the corresponding 2-amino-3-cyanopyridines in good to excellent yields. The nano-Cu₂O–MFR is a cheap and stable nano-catalyst that could be easily recovered and reused for many consecutive reaction runs without considerable decrease in its activity.

A new series of C1-glycosyl thiazole derivatives was synthesised by the reaction of 1-(1,3,4,6-tetra-O-acetyl-2-deoxy-β-D-glucopyranos-2-yl)thiourea with 2-bromoacetophenone derivatives. Subsequent removal of the acetyl groups were conducted using NaOMe–MeOH. The structures of all new products were confirmed by IR, ¹H NMR and HRMS (ESI). The acetylcholinesterase inhibitory activities of these new compounds were tested. Among them, N-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-β-D-glucopyranosyl)-4-(4-nitrophenyl)-1,3-thiazole-2-amine showed the best activity with an inhibition rate of 43.21%.

This letter presents a non-conventional synthesis of meso-porphyrins in moderate yields, using catalytic quantities of hafnium (IV) bis(perfluorooctanesulfonyl)imide complex in a perfluorodecalin biphasic system. Various meso-tetraarylporphyrins were obtained in good yields. The catalyst is selectively dissolved in perfluorodecalin, and can be recovered simply by phase separation and reused several times without any obvious decrease of activity.

The present investigation reports the novel chemical reduction synthesis of air resistant copper nanostructures (particles or rods) at a high concentration (up to 0.3 M) with controlled size and shape in an aqueous media. These syntheses accomplished high yields using sodium borohydride as a reducing agent, L-(+)-tartaric acid as a new surfactant and antioxidant, and polyvinylpyrrolidone (PVP) as a capping agent. The input of extra inert gases was not necessary and this method is very simple and green. Some reaction parameters, such as amount of reactants or surfactant, pH, reaction time or rate and amount of reduction reagent, were effective for control in the size and shape of the nanoparticles. Furthermore, colloidal copper nanoparticles effectively catalytically degrade methyl orange. The synthesis method reported in this work might be useful for the large-scale production of Cu nanoparticles.

1,4-Bis[4-(4-benzoyl-5-phenylisoxazol-3-yl)-3-methyl-1-phenylpyrazol-5-yloxy]benzene and its derivatives were synthesised. The antioxidant activities of these compounds were investigated in vitro assay systems, such as lipid peroxidation, 1,1-diphenyl-2-picrylhydrazyl, 2,2′-azino-bis(3-ethyl-1,3-benzothiazoline-6-sulfonic acid), superoxide, hydroxyl radicals scavenging and reducing power assay. The results show that the target compounds with nitro- and chloro-substituents at the 4-position of the benzene ring had more effective antioxidant power and better radical scavenging activity (RSA) (%) values when compared to those of butylated hydroxytoluene, trolox, caffeic acid and ascorbic acid, respectively..

A facile strategy for enantioselective synthesis of (R)-salmeterol is described via a chiral auxiliary starting from 2-bromo-1-(2,2-dimethyl-4H-1,3-benzodioxin-6-yl)ethanone through four or five steps. The product was obtained in good purity, enantiomeric excess and yield.

3-Coumaranones were condensed with aldehydes on alumina or alumina–potassium fluoride without solvent under microwave irradiation or classical heating. Novel aurones and analogues bearing ferrocenyl, benzodioxole or benzodioxane groups were obtained in good yields without use of heavy metal reagents.

A direct synthetic protocol is developed for the synthesis of 1-substituted-1H-1,2,3,4-tetrazoles via a three-component condensation of primary amines, triethyl orthoformate and sodium azide in the presence of 5 mol% of trifluoromethanesulfonimide (HNTf₂) in glycerol at room temperature with good to excellent yields.

A series of novel quinazolin-4-amine derivatives containing p-toluenesulfonate moiety have been synthesised through the reaction of 4-chloro-7-methoxyquinazolin-6-yl acetate with substituted anilines in toluene solution at 90 °C. Further treatment of the synthesised compound with ammonium hydroxide gave the corresponding substituted quinazoline derivatives which were subsequently processed through the sulfonyl reaction into quinazolin-4-amines containing p-toluenesulfonate moiety in DMF. Their structures were established by elemental analysis, IR and ¹H NMR spectra.

An efficient synthesis of a series of 4-aryl-1-ethyl-7-methyl-1,9-dihydropyrano[4,3-b]pyrazolo[4,3-e]pyridin-5(4H)-one is reported by condensation of aryl aldehydes, 4-hydroxy-6-methyl-2H-pyran-2-one and 1-ethylpyrazol-5-amine in the presence of 10 mol% molecular I₂ in ethanol under reflux conditions through a one-pot reaction. The present method offers several advantages such as use of a metal-free catalyst, being inexpensive, high yielding and environmental acceptability.