Per-O-acetylation of sugars catalysed by montmorillonite K-10

The inexpensive solid acid, montmorillonite K-10, is shown to be an efficient catalyst for the per-O-acetylation of several mono -, di - and trisaccharides. The pyranose forms accounted for 75–100% of the acetylated products.     

Montmorillonite K-10 clay catalyzed solvent-free synthesis of bis-indolylindane-1,3-dione, 2-(1′,3′-dihydro-1H-[2,3′]biindolyl-2′-ylidene)-indan-1,3-dione and bisindolylindeno[1,2-b]quinoxaline under microwave irradiation

An environmentally benign protocol has been described for the synthesis of novel 2-(1′,3′-dihydro-1H-[2,3′]biindolyl-2′-ylidene)-indan-1,3-diones/bis-indolylindane-1,3-diones from ninhydrin and 3-substituted/unsubstituted indoles. It uses montmorillonite K-10 as catalyst in a solvent-free condition under microwave irradiation. The method was also used for the synthesis of novel bisindolylindeno[1,2-b]quinoxaline derivatives.     

Bismuth-catalyzed allylic oxidation using t-butyl hydroperoxide

Bismuth(III) salts are efficient catalysts for the selective allylic oxidation using tert-butyl hydroperoxide. BiCl₃ is especially effective and can be easily recovered and reused as BiOCl. Using BiCl₃/K-10 as catalyst, an increase in the reaction rate was observed.     

Synthesis of quinolines by a solid acid-catalyzed microwave-assisted domino cyclization-aromatization approach

A microwave-assisted solid acid-catalyzed synthesis of quinolines from anilines and cinnamaldehydes is described. Use of montmorillonite K-10 results in a one-pot process; the cyclization and oxidation steps readily take place in a domino approach. Reactions were completed in a matter of minutes and provided excellent yields. The efficient and ecofriendly catalyst and the convenience of the product isolation make this process an attractive alternative for the synthesis of these important heterocycles.     

An efficient Friedel-Crafts alkylation of nitrogen heterocycles catalyzed by antimony trichloride/montmorillonite K-10

It has been found that SbCl₃ supported on montmorillonite K-10 is an efficient and reusable catalyst for Friedel-Crafts alkylation of nitrogen heterocycles such as indoles and pyrroles with epoxides. The reaction gives the corresponding C-alkylated derivatives in good to excellent yields with a high regioselectivity.     

An efficient synthesis of dihydrofuranyl spirooxindoles from isatin-derived propargylic alcohols and 1,3-dicarbonyls

Various dihydrofuranyl spirooxindoles have been synthesized via montmorillonite K-10-catalyzed propargylation of 1,3-dicarbonyl compounds with isatin-derived propargylic alcohols and subsequent base-mediated 5-exo-dig cyclization.     

Chemoselective anti-Markovnikov hydroamination of α,β-ethylenic compounds with amines using montmorillonite clay

The catalytic activity of montmorillonite clays as a catalyst for the hydroamination of α,β-ethylenic compounds with amines was tested. Aniline and substituted anilines reacted with α,β-ethylenic compounds in the presence of catalytic amount of commercially available clay to afford exclusively anti-Markovnikov adduct in excellent yields. Aniline reacted with ethyl acrylate to yield only anti-Markovnikov adduct N-[2-(ethoxycarbonyl)ethyl]aniline (mono-addition product). No Markovnikov adduct (N-[1-(ethoxycarbonyl)ethyl]aniline and double addition product N,N-bis[2-(ethoxycarbonyl)ethyl]aniline were formed under selected reaction conditions. For a better exploitation of the catalytic activity in terms of increased activity and improved selectivity for the mono-addition product, the reaction parameters were optimized in terms of temperature, solvent, reactant mole ratio. Under optimized reaction conditions, montmorillonite clay K-10 showed a superior catalytic performance in the hydroamination of ethyl acrylate with aniline with a conversion of aniline to mono-addition product (almost 100% chemoselectivity) with a high rate constant 0.3414 min⁻¹ compared to the reported protocols. The dependence of conversion of aniline over different types of montmorillonite clays (K-10, K-20, K-30, Al-Pillared clay and untreated clay) has also been discussed. The activities of clay for the hydroamination of different aromatic and aliphatic amines have also been investigated. Under harsh reaction conditions (increased temperature and long reaction time) small amounts of di-addition products were observed. The kinetics data has been interpreted using the initial rate approach model.     

Sonochemical synthesis of methyl-4-(hetero)arylmethylene isoxazole-5(4H)-ones using SnII-montmorillonite

Tin exchanged montmorillonite K10 (Sn^II-Mont K10) was prepared by ion exchange between SnCl₂ and montmorillonite K10. The Sn^II-Mont K10 was characterized by X-ray diffraction, scanning electron microscope and energy-dispersive X-ray spectroscopy. The synthesized Sn^II-Mont K10 was used as a recoverable solid catalyst for synthesis of 3-methyl-4-arylmethylene isoxazole-5(4H)-ones via one-pot multicomponent cyclocondensation of hydroxylamine hydrochloride, ethyl acetoacetate and benzaldehyde derivatives in water under ultrasound irradiations. The yields of products were obtained 87–96%. The remarkable advantages of this method are a low-cost and eco-friendliness catalyst, rapid completion of the reactions, and avoidance of using organic solvents, excellent yield and mild conditions.     

Microwave-assisted solid acid-catalyzed one-pot synthesis of isobenzofuran-1(3H)-ones

A new, solid acid-catalyzed microwave-assisted environmentally benign synthesis of isobenzofuran-1(3H)-ones is described. Montmorillonite K-10 appeared to be an excellent catalyst for the condensation and successive lactonization reactions. Reaction of phthalaldehydic acid (2-carboxybenzaldehyde) with methylaryl and cyclic ketones was initiated by microwave irradiation and occurred in one step. The reactions were complete in 10–30 minutes providing excellent yields (90–98%).     

Diversity oriented synthesis of fused-ring 1,3-oxazines from carbohydrates as biorenewable feedstocks

Microwave enhanced diversity oriented synthesis (MEDOS) of various N- and O-heterocyclic systems fused with 1,3-oxazine ring is reported. The synthesis represents a new montmorillonite K-10 clay-catalyzed green protocol, which utilizes d-glucose/d-xylose as biorenewable feedstocks. d-Glucose/d-xylose-derived 1,3-oxazin-2-ones(thiones) either directly undergo K-10 clay-catalyzed cyclization to yield pyrano-/furo-1,3-oxazine systems under solvent-free microwave irradiation conditions or afford azolo-/azino-1,3-oxazines when subjected to Malaprade reaction followed by cyclization with appropriate reagents, viz. phenylhydrazine, hydroxylamine, acetamidine, phenylurea and semi(thiosemi)carbazide.     

Proton-exchanged montmorillonite-mediated reactions of methoxybenzyl esters and ethers

Proton-exchanged montmorillonite (H-mont) was found to be an eco-friendly and cost-effective catalyst for the generation of O-methylated quinone methides (QM) from the corresponding p or o-methoxybenzyl esters and ethers. Nucleophilic trapping of the O-methylated QM with arenes, alcohols, 1,3-dicarbonyl compounds, silyl enol ethers, and allylsilanes has been carried out, respectively, leading to eco-friendly benzylation reactions. Using this protocol, H-mont-mediated deprotection of PMB-protected esters and ethers have been realized for the first time. This work would pave the way for further exploration in O-alkylated QM that are of chemical and biological significance.     

Three-component coupling strategy for the expeditious synthesis of novel 4-aminobenzoxazinone N-nucleosides

One-pot montmorillonite K-10 clay-supported three-component reactions of substituted salicylaldehydes, ribosyl/deoxyribosylureas and ammonium acetate expeditiously yield the novel N-nucleosides, 4-amino-3,4-dihydro-3-(β-d-ribo- or β-d-2′-deoxyribofuranosyl)-2H-benz[e]-1,3-oxazin-2-ones, via cycloisomerisation of an aldimine intermediate under solvent-free microwave irradiation conditions.     

An efficient synthesis of 1,5-benzodiazepine derivatives catalyzed by a solid superacid sulfated zirconia

2,3-Dihydro-1H-1,5-benzodiazepines are synthesized by the condensation of o-phenylendiamine and various ketones in the presence of a versatile solid superacid catalyst ‘sulfated zirconia’ under solvent free conditions.     

Environmentally benign one-pot synthesis and antimicrobial activity of 1-methyl-2,6-diarylpiperidin-4-ones

An efficient and environmentally benign one-pot method for the synthesis of 1-methyl-2,6-diarylpiperidin-4-ones using montmorillonite K-10 as a catalyst has been developed. Antimicrobial activity of the compounds has been tested against selected representatives of Gram-positive and Gram-negative bacteria and fungi.     

The reaction of N-tosyl imines with heteroaromatic compounds: a new access to triheteroarylmethanes

Useful triheteroarylmethanes were prepared by the double Friedel-Crafts reaction of a wide variety of aromatic N-tosyl imines with furan, thiophene, and pyrrole in the presence of Cu(OTf)₂ and Montmorillonite K-10 clay catalysts.     

Chemoselective annulation of 1,3-dithiin, -thiazine and -oxathiin rings on thiazoles using a green protocol

Tandem Knoevenagel and Michael reactions of 3-arylrhodanines, aromatic aldehydes and ammonium N-aryldithiocarbamates diastereoselectively yield dithioesters, thiazol-5-ylmethyl N-aryldithiocarbamates, under solvent-free microwave irradiation conditions in a one-pot procedure. Under the same conditions, the dithioesters are chemoselectively and expeditiously annulated with montmorillonite K-10 clay, Li⁺-montmorillonite clay and I₂ to give thiazolo-1,3-dithiins, -thiazines and -oxathiins, respectively.     

Electrochemical attachment of motile bacterial cells to gold

Selective attachment of Escherichia coli K-12 bacterial cells to charged gold surfaces was demonstrated. Electrostatic binding of E. coli K-12 bacterial cells to positively charged surfaces was observed starting at +750 mV. The binding of E. coli K-12 cells to positively charged gold surfaces is proposed to occur due to long-range electrostatic interactions between the negatively charged O-chain of lipopolysaccharide (LPS) molecules protruding the bacterial cell body and the electrode surface. Removing LPS alters the cellular surface charge and results in cellular attachment to negatively charged surfaces. Thus, applying an electrical potential allows for the direct, real time detection of live, dead or damaged bacterial cells. The attachment of E. coli K-12 bacterial cells to surfaces with an applied potential substantiates the hypothesis that an electrostatic interaction is responsible for the binding of bacterial cells to positively charged molecular assemblies on surfaces used for building bacterial microarrays.     

An Efficient Method for the Synthesis of 3-Cyano-6-hydroxy-2(1H)-pyridinones under Microwave Irradiation and Solvent-free Conditions

Summary. Three component condensation of alkylacetoacetates, primary amines, and alkyl cyanoacetates catalyzed by solid supports under microwave irradiation gave N-alkyl 3-cyano-6-hydroxy-2(1H)-pyridinones with high yields. Upon carrying out the reaction under the same condition on acidic alumina, zeolite HY, silica gel, and montmorillonite K-10, the best yields were achieved by silica gel. Corresponding author. E-mail: balalaie@yahoo.com Received August 28, 2002; accepted September 3, 2002     

Montmorillonite K-10 as a Reusable Catalyst for Fischer Type of Glycosylation under Microwave Irradiation

Montmorillonite K10 catalyzed Fischer type glycosylation was studied for various monosacharides with different alcohols under microwave irradiation. The method was found to be efficient, economic, simple and time saving and the catalyst montmorillonite K-10 was reused three times without loss of catalytic activity and anomeric selectivity. With glycerol, the method gave products glycosylated at primary alcohols only.     

A clay-mediated, regioselective synthesis of 2-(aryl/alkyl)amino-thiazolo[4,5-c]carbazoles

The 3-aminocarbazoles 1a-e were condensed with phenyl and benzyl isothiocyanates on montmorillonite K10 clay or TLC-grade silica gel at room temperature to furnish efficiently the N-phenyl and N-benzylthioureidocarbazoles, 2a-e and 2f, respectively, within minutes. When adsorbed on montmorillonite K10 clay impregnated with para-toluene sulfonic acid (1:1, w/w) and heated at 60-70 °C, 2a-e and 2f furnished the 2-anilino and 2-benzylaminothiazolo[4,5-c]carbazoles, 3a-e and 3f, respectively, regioselectively in high yields. The cyclisation was also effective for the N-methylthioureidocarbazoles 2g-i.