A comprehensive study of the CuAAC in PEG2000 as the solvent showed that Cu(i) is stabilised regardless of the source of the catalyst.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A rapid and efficient procedure for the synthesis of N-arylamines by aromatic nucleophilic substitution of activated as well as unactivated aryl halides with various amines using solvent-free microwaves activation under green chemistry conditions was described. Good to excellent yields were obtained in very short reaction time.

This article reports on the chemical functionalization of hydrogen-terminated porous silicon (PSi−H) nanostructures with alkenes, aldehydes, and alkyl halides under microwave irradiation. The technique allows for the introduction of different functional groups on the surface. The use of microwave irradiation has a net effect on the hydrosilylation reaction rate. However, no specific microwave effect was observed when the freshly prepared PSi−H surface was modified with an alkene bearing an aldehyde function. The reaction takes place at both the carbon−carbon and the carbon−oxygen double bonds. The polar aldehyde functional group did not show a dominant effect in directing the reaction selectively at the carbonyl group.

Ferrocenyl imines 3a-f were synthesized using solvent-free methods by mixing ferrocene carbaldehyde 1 with amines 2a-f under microwave irradiation. The imines were obtained in good yield in short reaction times.

Camphor-derived sulfonylhydrazines proved to be very active for organocatalyzed Diels–Alder cycloadditions with cyclopentadiene. Good chemical yields and enantiomeric excesses up to 89% and 88% are obtained for endo/exo adducts.

A new air- and moisture-stable palladium complex with salicylaldehyde N(4)-hexamethyleneiminylthiosemicarbazone has been synthesized. According to its crystal structure, the metal is bonded to 2equiv monoanionic thiosemicarbazone moieties in a N,S-bidentate fashion, forming two five-membered chelate rings, while additional intramolecular bonds stabilize the structure. In contrast to other palladium complexes with thiosemicarbazones, this complex was inactive towards the Suzuki–Miyaura coupling under aerobic conditions, by conventional heating. On the other hand, microwave irradiation promoted the effective catalytic activity of the complex for the coupling of aryl bromides and chlorides with phenylboronic acid in DMF/H2O, under aerobic conditions, with turnover numbers of up to 37,000.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Some 3-aryloxy-1,2-epoxypropanes, interesting as potential synthons in β-adrenergic receptor antagonists preparation, were obtained in excellent yields (65–96% within 2–17min) by microwave activation (monomode system) using solid–liquid solvent-free phase transfer catalysis (PTC). The best results for the O-alkylation of some phenols with epichlorohydrin were obtained using TBAB and NaOH/K2CO3 (1:4mol/mol) as phase transfer catalyst and more acceptable basic system, respectively. These new procedure is compared with classical methods. Significant specific microwave effect (non-purely thermal) was evidenced in all cases. They were discussed in terms of reaction medium and mechanism, taking into account the variations in polarity of the systems.

(S)-(−)-(Benzotriazol-1-yl)- and (S)-(−)-(benzotriazol-2-yl)-alkan-2-ols 7a–9a, 7b–9b and their (R)-(+)-acetates 10a–12a and 10b–12b were prepared in high enantiomeric excess via lipase from Pseudomonas fluorescens (Amano AK) catalyzed enantioselective acetylation of racemic alcohols 4a–6a and 4b–6b with vinyl acetate in tert-butyl methyl ether or toluene at 23°C. The enantioselectivity of this transformation was dependent on the length of the alkyl chain with E-values ranging from 30 to 57. Several benzotriazole substituted ketones 1a–3a and 1b–3b were synthesized from 1H-benzotriazole and corresponding haloketones. These compounds were stereoselectively reduced with Baker’s yeast in water or in organic solvent containing 5% v/v of water at 30°C to give the (S)-(−)-alcohol. Better stereoselectivity was observed in the kinetic resolution of racemic alcohols 4a–6a and 4b–6b (ee=69–92% at 44–52% conversion) compared to reduction of corresponding prochiral ketones 1a–3a and 1b–3b with Baker’s yeast (ee=40–67% at 39–89% conversion). Enhanced enantioselectivities were observed at lower temperatures.

The condensation of a series of arylacetonitriles with aldehydes can be carried out by mixing equivalent amounts of reagents with neat powdered KOH at room temperature for 3-60 min depending on the aldehyde steric hindrance. At higher temperature (110 degrees C), yields were generally higher and purity increased within very short reaction times (1-5 min). With pentamethylphenylacetonitrile, a phase transfer agent was necessary to give a satisfactory yield. (c) 2005 Elsevier Ltd. All rights reserved.

The condensation of phenylacetonitrile with 4-methoxybenzaldehyde can be carried out by two solvent-free methods: i) using neat powdered KOH at room temperature with equivalent amounts of aldehyde, nitrile and base for 3 min, and ii) using K2CO3 in the presence of a phase transfer agent for 3 min under microwave activation or conventional heating. By extending the reaction time up to 10 min, four different products were obtained from phenyl or nitrile group migration. With nonanenitrile, only the second method could be applied to give two kinds of condensed compounds with or without phenyl (or nitrile) group migration. The intervention of non-thermal MW-specific effects was proved in some cases and interpreted.

A successful application of microwave irradiation, in which phthalocyanines were synthesized under solventless conditions from 1,2-phthalonitrile or phthalic anhydride and urea in the presence of metal templates is described. It was found that in comparison with conventional heating, the microwave process is a very useful alternative for cyclotetramerization processes because of reduction of the reaction time, better yield, and easy-to-perform procedure.

Solid-liquid phase transfer catalysis coupled with microwave irradiation was shown to be an efficient method for SNAr reaction of halogenated quinoline and pyridine with alkoxides and phenoxides. Whereas for phenoxylation there is no need for any solvent, the addition of small amount of non-polar solvent is necessary during methoxylation for accurate monitoring of temperatures. Yields and conditions involved here constitute a noticeable improvement over classical methods within the frame of Green Chemistry. Specific MW effects were evidenced for phenoxylation and interpreted in terms of late position of the transition state along the reaction coordinates.

The half-life of N-hexanoyl-l-homoserine lactone (C6-HSL) was determined under various pH and temperature conditions, and in several plant environments. C6-HSL was sensitive to alkaline pH, a process that was also temperature-dependent. In addition, C6-HSL disappeared from plant environments, i.e. axenic monocot and dicot plants cultivated under gnotobiotic, hydroponic conditions, albeit with variable kinetics. The disappearance was rapid at the root system of legume plants such as clover or Lotus, and slow or non-existent at the root system of monocots such as wheat or corn. These variable kinetics were not dependent upon pH changes that may have affected the growth media of the plants. Furthermore, C6-HSL did not accumulate in the plant, and the plant did not produce inhibitors of the C6-HSL signal. HPLC analyses revealed that C6-HSL disappeared from the media, and hence, Lotus exhibited a natural C6-HSL inactivating ability. This ability was not specific for C6-HSL and allowed the degradation of other N-acyl-homoserine lactones such as 3-oxo-C6-HSL, 3-oxo-octanoyl-HSL and 3-oxo-decanoyl-HSL. Preliminary investigation revealed that the inactivating ability is temperature-dependant and possibly of enzymatic origin.

Bacteria degrading the quorum-sensing (QS) signal molecule N-hexanoylhomoserine lactone were isolated from a tobacco rhizosphere. Twenty-five isolates degrading this homoserine lactone fell into six groups according to their genomic REP-PCR and rrs PCR-RFLP profiles. Representative strains from each group were identified as members of the genera Pseudomonas, Comamonas, Variovorax and Rhodococcus: all these isolates degraded N-acylhomoserine lactones other than the hexanoic acid derivative, albeit with different specificity and kinetics. One of these isolates, Rhodococcus erythropolis strain W2, was used to quench QS-regulated functions of other microbes. In vitro, W2 strongly interfered with violacein production by Chromobacterium violaceum, and transfer of pathogenicity in Agrobacterium tumefaciens. In planta, R. erythropolis W2 markedly reduced the pathogenicity of Pectobacterium carotovorum subsp. carotovorum in potato tubers. These series of results reveal the diversity of the QS-interfering bacteria in the rhizosphere and demonstrate the validity of targeting QS signal molecules to control pathogens with natural bacterial isolates.

This paper describes the chemical functionalization of hydrogen-terminated porous silicon surfaces with simple and functional 1-alkenes under microwave irradiation to give organic monolayers covalently attached to the surface through Si−C bonds. Using microwaves as a source of energy led to a remarkable increase in the rate of the hydrosilylation reaction and a higher surface coverage. This technique yields highly stable organic monolayers and allows the introduction of different functional groups on the surface (acid and ester) required for immobilization of more complex structures on the surface.

To synthesize manganese hexathiohypodiphosphate, stoichiometric mixtures of manganese, red phosphorus, and α-sulfur, together with potassium chloride, underwent low-energy ball milling under ambient conditions followed by exposure to the electromagnetic beam of a monomode microwave. X-ray diffraction patterns show that Mn2P2S6 (structure MI, or H) has formed, as well as small amounts of intercalated KCl [these findings are supported by infrared (IR) observation]. Also some α-MnS have been formed. Electron diffraction patterns show the existence of structure H. They also reveal the emergence of the (up to now hypothetical) orthohexagonal structure and of some «turbostratic» layered material whose nature is not yet understood. Superconducting quantum interference device (SQUID) measurements show a ferromagnetic behavior, which can be assigned to the formation of some manganese monophosphide. Tetraethyl chloride ammonium is then easily intercalated as revealed by X-ray patterns and IR measurements. Finally, it has been shown that all three parameters (ball milling, microwave exposure, and presence of KCl as a catalyst) are necessary to form manganese hexathiophosphate. Filtrations and decantations lead to a pure hexathiophosphate compound.

High- or low-energy mechanochemistry is frequently used to synthesize chemical compounds. The present work is devoted to the possible synthesis of ditin hexathiodiphosphate Sn2P2S6 by low-energy ball-milling: first, directly from its atomic components, second, by ball-milling followed by a microwave treatment. Stoichiometric ratio powders were milled by means of 10 steel balls (2.0 g each) under ambient atmosphere for 80 h or so. Afterwards, the samples were studied by X-ray spectroscopy, energy dispersive X-ray spectroscopy, IR and DSC. The resulting diffraction patterns showed the formation of the desired compound. The ball-milled powder was also studied by transmission electron microscopy which revealed its ferroelectric character. Some previous confusing conclusions about the various crystalline forms of Sn2P2S6 are re-examined. With Mn, Fe, Ni or In instead of Sn, no hexathiodiphosphates were formed through direct ball-milling. (C) 2003 Elsevier Ltd. All rights reserved.

A rapid and easy to accomplish solvent-free labelling procedure with diethyl-[2-14C]-malonate in the presence of Phase Transfer Catalyst is reported. Radiochemical preparation by this method shows important advantages over routine methods.