Microwave-assisted organic synthesis and transformations using benign reaction media

Aryl ketone synthesis via tandem orthoplatinated triarylphosphite-catalyzed addition reactions of arylboronic acids with aldehydes followed by oxidation

Tandem orthoplatinated triaryl phosphite-catalyzed addition reactions of arylboronic acids with aldehydes followed by oxidation to yield aryl ketones is described. 3-Pentanone was identified as a suitable oxidant for the tandem aryl ketone formation reaction. By using microwave energy, aryl ketones were obtained in high yields with the catalyst loading as low as 0.01%.

Chemistry by Nanocatalysis: First example of a solid-supported RAPTA complex for organic reactions in aqueous medium

A ruthenium-arene-PTA (RAPTA) complex has been supported for the first time on an inorganic solid, that is, silica-coated ferrite nanoparticles. The resulting magnetic material proved to be a general, very efficient and easily reusable catalyst for three synthetically useful organic transformations; selective nitrile hydration, redox isomerization of allylic alcohols, and heteroannulation of (Z)-enynols. The use of low metal concentration, environmentally friendly water as a reaction medium, with no use at all of organic solvent during or after the reactions, and microwaves as an alternative energy source renders the synthetic processes reported herein "truly" green and sustainable.

Heteropoly acid-catalyzed microwave-assisted three-component aza-Diels-Alder cyclizations: diastereoselective synthesis of potential drug candidates for Alzheimer's disease

A highly diastereoselective microwave-assisted three component synthesis of azabicyclo[2.2.2]octan-5-ones by a silicotungstic acid-catalyzed aza-Diels-Alder cyclization is described. The one-pot process involves the formation of the in situ generated Schiff base and its immediate cyclization with cyclohex-2-enone. The short reaction times, good yields and excellent diastereoselectivity make this annulation a practical and environmentally attractive method for the synthesis of the target compounds. Preliminary assays were carried out to determine the activity of the products in AChE as well as in amyloid β fibrillogenesis inhibition.

Solvent-free synthesis of novel chiral unsymmetrical urea molecular tweezers under microwave irradiation

Seven novel chiral unsymmetrical urea molecular tweezers based on 1, 3-phenoxyacetic acid have been designed and synthesised using solid K2CO3 as supporter in the solvent-free conditions under microwave irradiation. This method is simple, fast, efficient and eco-friendly. The structures of target compounds were characterised by IR, 1H NMR, MS spectra and elemental analyses and their molecular recognition properties were investigated by UV-Vis spectral titration. The preliminary results indicated that these molecular tweezers possess good selectivity for D/L amino acid methyl esters and some anions.

An efficient, microwave-assisted, one-pot synthesis of novel 5,6,7,8-tetrahydroquinoline-3-carbonitriles

An efficient, microwave-assisted synthesis of novel 2-alkoxy- 5,6,7,8-tetrahydroquinoline-3-carbonitriles, which have not hitherto been reported, via reactions of cyclohexanone and arylidene malononitriles in the corresponding alcohols in presence of sodium is described. All the newly synthesized compounds were characterized by the IR, 1H-NMR, 13C-NMR and mass spectroscopic techniques and by elemental analyses. The newly synthesized compounds were evaluated for their antibacterial and antifungal activities.

Synthesis of Novel Triazole Derivatives of Methyl 3-Oxocholanate Using Microwave Irradiation

An efficient rapid method for the synthesis of new triazole derivatives derived from methyl 3-oxocholanate under microwave irradiation has been developed. These new compounds were characterised by 1H NMR, IR, ESI-MS spectra and elemental analyses. Some of these triazoles were tested for antibacterial activity against Staphylococcus aureus, Candida albicans and Escherichia coli.

Tetrabutylammonium bromide media aza-Michael addition of 1,2,3,6-tetrahydrophthalimide to symmetrical fumaric esters and acrylic esters under solvent-free conditions

The aza-Michael addition of 1,2,3,6-tetrahydrophthalimide with symmetrical fumaric esters has been performed efficiently in a solvent-free system at 100 °C and using 1,4-diazabicyclo[2.2.2]octane (DABCO) as a base in the presence of tetrabutylammonium bromide (TBAB). The products were obtained in good to high yields within 2.5-7.0 h. This reaction worked well on linear alkyl fumarates and was not effective with nonlinear alkyl fumarates. Although the reaction was also applicable to acrylates such as n-butyl acrylate, methacrylates and crotonates were not suitable Michael acceptors for this reaction.

Reproducible microwave-assisted acid hydrolysis of proteins using a household microwave oven and its combination with LC-ESI MS/MS for mapping protein sequences and modifications

A new set-up for microwave-assisted acid hydrolysis (MAAH) with high efficiency and reproducibility to degrade proteins into peptides for mass spectrometry analysis is described. It is based on the use of an inexpensive domestic microwave oven and can be used for low volume protein solution digestion. This set-up has been combined with liquid chromatography electrospray ionization quadrupole time-of-flight mass spectrometry (LC-ESI QTOF MS) for mapping protein sequences and characterizing phosphoproteins. It is demonstrated that for bovine serum albumin (BSA), with a molecular mass of about 67,000 Da, 1292 peptides (669 unique sequences) can be detected from a 2 microg hydrolysate generated by trifluoroacetic acid (TFA) MAAH. These peptides cover the entire protein sequence, allowing the identification of an amino acid substitution in a natural variant of BSA. It is shown that for a simple phosphoprotein containing one phosphoform, beta-casein, direct analysis of the hydrolysate generates a comprehensive peptide map that can be used to identify all five known phosphorylation sites. For characterizing a complex phosphoprotein consisting of different phosphoforms with varying numbers of phosphate groups and/or phosphorylation sites, such as bovine alpha(S1)-casein, immobilized metal-ion affinity chromatography (IMAC) is used to enrich the phosphopeptides from the hydrolysate, followed by LC-ESI MS analysis. The MS/MS data generated from the initial hydrolysate and the phosphopeptide-enriched fraction, in combination with MS analysis of the intact protein sample, allow us to reveal the presence of three different phosphoforms of bovine alpha(S1)-casein and assign the phosphorylation sites to each phosphoform with high confidence.

One-pot Synthesis of New Carbamate-Type Molecular Tweezers Derived from Deoxycholic Acid under Microwave Irradiation

A rapid, safe, and efficient method for the preparation of new carbamate type molecular tweezers based on deoxycholic acid was reported. Eleven new molecular tweezers have been synthesised in good yield(91–96%). The structures of these receptors were confirmed by 1H NMR, IR, MS spectra and elemental analysis. These molecular tweezers not only recognised neutral molecules, but also showed good enantioselectivity for D-amino acid methyl esters.

Access to small size distributions of nanoparticles by microwave-assisted synthesis. Formation of Ag nanoparticles in aqueous carboxymethylcellulose solutions in batch and continuous-flow reactors

This article examines the effect(s) of the 2.45-GHz microwave (MW) radiation in the synthesis of silver nanoparticles in aqueous media by reduction of the diaminesilver(i) complex, [Ag(NH(3))(2)](+), with carboxymethylcellulose (CMC) in both batch-type and continuous-flow reactor systems with a particular emphasis on the characteristics of the microwaves in this process and the size distributions. This microwave thermally-assisted synthesis is compared to a conventional heating (CH) method, both requiring a reaction temperature of 100 degrees C to produce the nanoparticles, in both cases leading to the formation of silver colloids with different size distributions. Reduction of the diaminesilver(i) precursor complex, [Ag(NH(3))(2)](+), by CMC depended on the solution temperature. Cooling the reactor during the heating process driven with 390-Watt microwaves (MW-390W/Cool protocol) yielded silver nanoparticles with sizes spanning the range 1-2 nm. By contrast, the size distribution of Ag nanoparticles with 170-Watt microwaves (no cooling; MW-170W protocol) was in the range 1.4-3.6 nm (average size approximately 3 nm). The overall results suggest the potential for a scale-up process in the microwave-assisted synthesis of nanoparticles. Based on the present data, a flow-through microwave reactor system is herein proposed for the continuous production of silver nanoparticles. The novel flow reactor system (flow rate, 600 mL min(-1)) coupled to 1200-Watt microwave radiation generated silver nanoparticles with a size distribution 0.7-2.8 nm (average size ca. 1.5 nm).

Microwave-Assisted Synthesis of New Steroidal Thiosemicarbazones Derived from methyl 3-Oxocholanate under Solvent-Free Conditions

A series of novel steroidal thiosemicarbazones derived from methyl 3-oxocholanate were synthesised in good yields via microwave irradiation under solvent-free conditions. The structures of the compounds were confirmed by spectroscopic data. Compared to the conventional method, microwave irradiation was a fast and simple method. These compounds were tested for antibacterial activity against S. aureus, S. pyogenes, and E. coli bacteria.

Synthesis of Novel Alkoxycarbonyl Thiosemicarbazide Molecular Tweezers derived from Deoxycholic Acid under Microwave Irradiation

A series of novel 12α-alkoxycarbonyl thiosemicarbazide molecular tweezers based on 3α-(1-naphthoyl) deoxycholic acid methyl ester were synthesised under microwave irradiation. Their structures were characterised by 1H NMR, IR, MS spectra and elemental analysis. Their chiral recognition properties for the methyl esters of amino acids were investigated. The preliminary results showed that these molecular tweezers have good enantioselective recognition for D/L-amino acid methyl esters.

An Efficient and Reusable PdCl2/TBAF System for the Heck Reaction Under Ligand- and Solvent-Free Conditions

PdCl2 combined with TBAF (n-Bu4NF) were found to be efficient conditions for the Heck reactions. In the presence of PdCl2 and TBAF, a variety of aryl halides were coupled with alkenes smoothly in moderate to good yields. Moreover, the PdCl2/TBAF system could be recovered and reused several times in the reaction. Note that these reactions are conducted under solvent-free, ligand-free and reusable conditions.

Microwave-Assisted Synthesis of Novel Aryloxyacetyl Hydrazones Molecular Tweezers under Solvent-Free Conditions

A rapid, efficient and eco-friendly method for the preparation of new aryl-1,4-bisoxyacetylhydrazone molecular tweezers was reported. The reaction is accelerated by microwave irradiation under solvent-free conditions in the presence of solid Al2O3. The structures of these new molecular tweezers were characterised by 1H NMR, IR, MS spectra and elemental analysis.

New frontiers in materials science opened by ionic liquids

Ionic liquids (ILs) including ambient-temperature molten salts, which exist in the liquid state even at room temperature, have a long research history. However, their applications were once limited because ILs were considered as highly moisture-sensitive solvents that should be handled in a glove box. After the first synthesis of moisture-stable ILs in 1992, their unique physicochemical properties became known in all scientific fields. ILs are composed solely of ions and exhibit several specific liquid-like properties, e.g., some ILs enable dissolution of insoluble bio-related materials and the use as tailor-made lubricants in industrial applications under extreme physicochemical conditions. Hybridization of ILs and other materials provides quasi-solid materials, which can be used to fabricate highly functional devices. ILs are also used as reaction media for electrochemical and chemical synthesis of nanomaterials. In addition, the negligible vapor pressure of ILs allows the fabrication of electrochemical devices that are operated under ambient conditions, and many liquid-vacuum technologies, such as X-ray photoelectron spectroscopy (XPS) analysis of liquids, electron microscopy of liquids, and sputtering and physical vapor deposition onto liquids. In this article, we review recent studies on ILs that are employed as functional advanced materials, advanced mediums for materials production, and components for preparing highly functional materials.