One-pot synthesis of 2-substituted quinoxalines using K10-montmorillonite as heterogeneous catalyst

An efficient one-pot synthesis of 2-substituted quinoxalines from 1,2-diamines and phenacyl bromides is developed using K10-montmorillonite (K10 clay) as a catalyst at 50 °C in acetonitrile medium. This method offers an easy route for the synthesis of substituted quinoxalines in high yields. A plausible mechanism is proposed in which quinoxalines are formed via dehydration–dehydrohalogenation–cyclization sequence. Further, the K10 clay catalyst is recovered by simple filtration and reused six times without any loss in its catalytic activity.     

Expeditious reaction of ninhydrin with active methylene compounds on montmorillonite K10 clay

Abstract  Ninhydrin reacted expeditiously with thirteen active methylene compounds on montmorillonite K10 clay at room temperature to furnish, in 5 min, a Knoevenagel condensate in one case, aldols in six cases, aldol-derived cyclic hemiketals in three cases, and interesting products in the remaining three cases. Almost identical results were obtained, but faster, when the reactions were carried out in water on steam-bath. The structures of two novel products were also confirmed by single-crystal X-ray diffraction analysis. Graphical abstract        

Improved methodologies for synthesis of prenylated xanthones by microwave irradiation and combination of heterogeneous catalysis (K10 clay) with microwave irradiation

Eleven prenylated xanthone derivatives (4-9, 11-15) have been synthesized for the first time by the microwave irradiation method. Prenylation of the xanthone building blocks 1 and 2 with prenyl bromide in alkaline medium, using microwave irradiation, gave the oxyprenylated xanthones 4 and 6, as major products in high yields, as well as diprenylated by-products (5, 7, 8, and 9) in very low yields. Microwave irradiation of oxyprenylated xanthones 4 and 6 furnished three new Claisen rearranged products (11, 14, and 15), as well as the previously described dihydrofuranoxanthones (12, 13). Furthermore, three new (19, 20, 21) and three previously described (16, 17, 18) dihydropyranoxanthones have also been prepared by a one-pot synthesis from xanthones 1, 2, and 3, using Montmorillonite K10 clay as a heterogeneous catalyst and a combination of Montmorillonite K10 clay with microwave irradiation in various conditions. The presence of solvent and the type of the clay (commercial or dry) were found to have a strong influence on the product yields. This is the first report of using these methodologies for the synthesis of dihydropyranoxanthone derivatives. The structures of the prenylated xanthones obtained were established by IR, UV, HRMS, and NMR (¹H, ¹³C, HSQC, and HMBC) techniques.     

Chemoselective fluorination of 2-hydroxy-3,4,7,8-tetrahydro-2H-chromen-5(6H)-ones using DAST

In this study, diethylaminosulfur trifluoride (DAST) was successfully applied in monofluorination reactions of some trifluoromethyl substituted 2-hydroxy-2H-chromenones, employing a general, mild, and efficient methodology. The fluorinated compounds (2-fluoro-2H-chromenones) were synthesized as unique products by a chemoselective reaction in 63-81% yield despite the presence of different reactive sites subjected to reactions with DAST.     

One-pot synthesis of 3,4-dihydropyrimidin-2(1H)-ones using boric acid as catalyst

A simple effective synthesis of 3,4-dihydropyrimidin-2(1H)-one derivatives, using boric acid as catalyst, from aromatic aldehydes, 1,3-dicarbonyl compounds and urea in glacial acetic acid is described. Compared with the classical Biginelli reaction conditions, this new method has the advantage of excellent yields (86-97%) and short reaction time (0.5-2 h).     

(E)-3-Halo-2-styryl-4H-chromen-4-ones: synthesis and transformation to novel pyrazoles

New methods for the synthesis of (E)-3-halo-2-styryl-4H-chromen-4-ones were established. The reaction of these compounds with hydrazine hydrate afforded new and unexpected 3(5)-aryl-5(3)-[2-(2-hydroxyphenyl)-2-hydrazonoethyl]-1H-pyrazoles, which upon acid hydrolysis gave 3(5)-aryl-5(3)-[2-(2-hydroxyphenyl)-2-oxoethyl]-1H-pyrazoles. The reaction mechanisms for these transformations, involving 1,6- followed by 1,4-conjugate additions, are discussed and the structures of all new compounds were established by NMR studies.     

The first application of 4-alkoxy-1,1,1-trifluoroalk-3-en-2-ones in a three-component condensation protocol for the synthesis of 3-acyl-4-aryl-2-(trifluoromethyl)-2-hydroxy-3,4,7,8-tetrahydro-2H-chromen-5(6H)-ones

The one-pot, simple and efficient three-component condensation protocol for the preparation of a series of twenty-five new 3-acyl-4-aryl-2-(trifluoromethyl)-2-hydroxy-3,4,7,8-tetrahydro-2H-chromen-5(6H)-ones, where aryl = Ph, 4-tolyl, 4-ClPh, 4-NO₂Ph and 4-CHOPh, and acyl = Ac, Bz, 4-FBz, furan-2-oyl, thien-2-oyl and naphth-1-oyl, employing 1,3-cyclohexanedione, five aryl aldehydes and for the first time, six 4-alkyl(aryl/heteroaryl)-4-methoxy-1,1,1-trifluoroalk-3-en-2-ones, is described. Yields in 15-75% were obtained when the MCRs were performed in the presence of a catalytic amount of triethylamine (25 mol%) and in ethanol as solvent under reflux for 16 h. A representative X-ray diffraction data for 3-acetyl-4-phenyl-2-(trifluoromethyl)-2-hydroxy-3,4,7,8-tetrahydro-2H-chromen-5(6H)-one is also showed.     

Synthesis of 2-amino-3-cyano-4H-chromen-4-ylphosphonates and 2-amino-4H-chromenes catalyzed by tetramethylguanidine

Synthesis of 2-amino-4H-chromen-4-ylphosphonates and 2-amino-4H-chromenes has been accomplished by the reaction of salicylaldehyde, malononitrile, dialkyl/diphenylphosphites catalyzed by 1,1,3,3-tetramethylguanidine (TMG) under neat conditions at room temperature. The applicability of catalytic TMG for the synthesis of 2-amino-4H-chromenes also has been described. The mild reaction conditions, simple work-up procedure, and use of TMG as an inexpensive catalyst provides an economical protocol for the preparation of important phosphorus-containing compounds.     

Efficient stepwise and one pot three-component synthesis of 2-amino-4-(2-oxo-2H-chromen-3-yl)thiophene-3-carbonitriles

Environmentally benign conditions have been developed for the synthesis of 2-amino-4-(2-oxo-2H-chromen-3-yl)thiophene-3-carbonitriles (3) starting from 3-acetyl-2H-chromen-2-one (1) through the intermediacy of 2-(1-(2-oxo-2H-chromen-3-yl)ethylidene)malononitrile (2) using the Knoevenagel condensation followed by the Gewald reaction. Alternatively, 3 could also be prepared in a one pot method by treating equimolar amounts of 1, malononitrile, and elemental sulfur. The merits of this preparation are mild reaction conditions, easy work-up procedure, and good yields.     

Synthesis of 2-substituted 3-ethyl-3H-imidazo[4,5-b]pyridines catalyzed by Al-exchanged K10 clay as solid acids

A series of imidazopyridine derivatives have been synthesized efficiently via intramolecular cyclization in excellent yields using Al³⁺-exchanged on K10 montmorillonite clay (Al³⁺-K10 clay) as a reusable heterogeneous catalyst. To the best of our knowledge, this is the first report to utilize Al³⁺-K10 as a catalyst for imidazopyridine synthesis. Many functional groups are tolerated during the synthesis of targeted compounds. The catalyst is reused at least five times with a slight decrease in the yield. This catalyst is environmentally benign, cost-effective, and also provides other advantages such as nontoxicity, operational/experimental simplicity, and mild reaction conditions.     

Facile and efficient synthesis of 3,4,5-substituted furan-2(5H)-ones by using β-cyclodextrin as reusable catalyst

3,4,5-Substituted furan-2(5H)-one derivatives were synthesized by using β-cyclodextrin as a catalyst in water via biomimetic approach. β-Cyclodextrin can be recovered and reused.     

Efficient synthesis of chiral non-racemic 6-(furan-3-yl)-5,6-dihydro-pyran-2-ones

The title compounds are accessible in high yields and enantioselectivities by a five-step sequence involving in the key-step asymmetric aldol condensations of masked acetoacetic esters to 3-formyl furan.     

Solvent-free microwave synthesis of 4-hydroxy-3-phenylquinolin-2(1H)-ones and variants using activated arylmalonates

The disclosure herein describes the rapid synthesis of 4-hydroxy-3-phenylquinolin-2(1H)-ones and variants via a solvent-free microwave cyclocondensation reaction using di-(2,4,6-trichlorophenyl)-2-phenylmalonate, which improves the general scope of this reaction.     

One-pot synthesis of quinolin-2-(1H)-ones via tandem Ugi-Knoevenagel condensations

A new application of the Ugi reaction in the synthesis of heterocyclic compounds is described. Substituted quinolin-2-(1H)-ones are formed in one-pot sequential Ugi four-component condensation and intramolecular Knoevenagel cyclization between o-acylanilines, aldehydes, malonic or tosylacetic acids and cyclohexyl isocyanide.     

A new approach to the synthesis of 4-(N-aryl)carbamoylmethyl-4,5-dihydropyridazin-3(2H)-ones

Reaction of N-aryl substituted maleimides with aliphatic ketazines leads to the formation of 4,5-dihydropyridazin-3(2H)-ones in moderate yields. The reaction proceeds through 1,4-addition of an azine to the maleimide double bond, as confirmed by separation of the corresponding adducts in some cases, which are then converted into 4,5-dihydropyridazin-3(2H)-ones. In addition, the solid-state synthesis of 4,5-dihydropyridazin-3(2H)-ones is demonstrated for the first time.     

Absorption spectroscopic investigations on M[Al (OC3H7i)4]3 (M = Pr, Nd) - catalysed reduction of ketones

Transition metal (Mo, V and Cr) incorporated montmorillonite KSF and K10, catalyzed the liquid phase benzylation of o-xylene by benzyl chloride efficiently with high selectivity towards monoalkylated product. Mo catalysts showed the highest catalytic activities. The catalysts were characterized by XRD, surface area, pore volume and acidity measurements and by temperature programmed desorption of ammonia.This revised version was published online in December 2005 with corrections to the Cover Date.     

Re-cyclization of 3-(E)-methyl 3-(4-oxo-4H-chromen-3-yl)acrylate with amines and their potential mechanism

The synthesis of 2-pyridone derivatives from different substituted amines and various 3-(E)-methyl 3-(4-oxo-4H-chromen-3-yl)acrylate derivatives was proposed and described. The optimized reaction conditions and the generality of the reaction were investigated, respectively. Moreover, less side products could be formed than the traditional method. Finally, based on the fact that (E)-methyl 2-(7-methoxy-4-oxo-3-((phenylamino)methylene)chroman-2-yl)acetate was separated and determined via X-ray single crystal diffraction, we could propose an interesting and reasonable reaction mechanism for the first time. The reaction could render this method particularly attractive for the efficient preparation of biologically and medicinally interesting molecules.     

A one-pot synthesis of 3,3′-methylenebis(2-arylamino-4H-chromen-4-one) from C-(4-oxo-4H-1-benzopyran-3-yl)-N-arylnitrone

2-(Arylamino)-4-oxo-4H-chromene-3-carbaldehyde 3 (R² = aryl) produces 12H-chromeno[2,3-b]quinolin-12-one 4 when treated with sarcosine, piperidine or diethylamine, but produces 3,3′-methylenebis(2-arylamino-4H-chromen-4-one) 8 when treated with the same amine in the presence of an excess of formaldehyde. Compound 3 (R² = alkyl) was found to be less reactive than the N-aryl analogues towards the deformylative Mannich-type reaction.