Typical applications of solvent-free conditions and microwave activation are described. Non-purely thermal specific effects are evidenced and discussed in terms of reaction medium and mechanisms, ...taking into account the variations in polarity of the systems.
A recyclable heterogeneous hydroxyapatite-supported palladium(0) catalyst was prepared by a simple procedure and successfully applied for the selective reduction of carbon-carbon double bond in ...α,beta-unsaturated ketones using HCOONH4 as hydrogen transfer agent. The workup procedure is simple, and the catalyst could be recovered by simple filtration and recycled for five consecutive runs without significant loss of activity. PUBLICATION ABSTRACT
Functional groups were selectively introduced at the C-2 position of isophorone via the epoxide ring-opening with several nucleophiles. Various behaviours were observed depending on the reaction ...conditions and the nature of nucleophilic reagents. Electronic and steric effects of the reactants were discussed. The best experimental systems involved LiClO
4 salt effect in acetonitrile, phase transfer catalysis or KF–alumina under solvent-free conditions under microwaves.
Subsequent evolution of 2-substitued isophorones is connected to X and Y (CO
2Et, CN, COMe, CONH
2).
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.
Graphical Abstract
Selective synthesis of α-bromo and α,α-dibromoalkanones using dioxane–dibromide and silica gel in solvent-free conditions under microwave irradiation has been reported. The amount of ...dioxane–dibromide, silica gel and time of irradiation are keys for the selective synthesis of α-bromo and α,α-dibromoalkanones.
Graphic
Practical and simple techniques are described for using nonmodified domestic microwave ovens as safe and convenient laboratory devices to obtain numerous esters. High pressures are avoided by ...conducting reactions with reactants impregnated on solid mineral supports in "dry media" or by phase transfer catalysis (PTC) in the absence of organic solvents. Two kinds of microwave effects are involved: (1) displacement of the equilibrium by evaporation of volatile polar molecules (water or alcohols) in esterifications and transesterifications; (2) acceleration of ionic reactions in carboxylate alkylations. As solvents are avoided, there is no need for sealed vessels and water separators.
Fischer condensation was performed in 50-60% yield in lower temperatures and shorter times if conducted in solvent-free acid medium under microwave irradiation.
2-Ethoxymethylene-3-oxobutanenitrile is a versatile trifunctional reagent that allows the introduction of a three-carbon moiety to amine-substrates. The reaction of the title compound with hydrazines ...has been studied leading to appropriate substituted pyrazoles
4–
11
. Reactions with other dinitrogen nucleophiles were studied giving access to a set of fused pyrimidines
13
. All types of compounds displayed biological activity against bacteria, filamentous fungi and tumour HeLa cells, but not for yeasts. Pyrazole
10
and pyrimidine
13d
have been found to possess the broadest activity.
Graphical Abstract
The presence of a salt in a reaction involving an ion pair brings about a second ion pair that dramatically changes the course of the reaction. This "special salt effect" is examined in two broad ...classes of reactions: between nucleophiles and electrophiles and electron transfer.
