A rationalization of microwave effects in organic synthesis based on the nature of the reaction medium and mechanistic considerations is proposed. With accurate and strict control of experiments, it ...may be possible to distinguish thermal and specific (non-purely thermal) effects. Specific microwave effects may be understood by considering evolution of the polarity of systems during the course of the reaction and the position of the transition state along the reaction coordinates. The most favourable encountered cases concern unimolecular or bimolecular reactions between neutral molecules (as dipoles are developed in the TS) and anionic reactions of tight ion pairs, i.e. involving charge localized anions (leading to ionic dissociation in TS). Specific effects are most likely to be observed under solvent-free conditions (green chemistry procedures) or in non-polar solvent and when the reaction mechanisms involve the formation of polar and late transition states (difficult reactions).
A microwave-assisted three-component, regioselective one-pot synthesis of spiroindole-thiazolidinones (
6a–
l) is carried out using montmorillonite KSF as solid support.
A microwave-assisted ...three-component, regioselective one-pot cyclocondensation method has been developed for the synthesis of a series of novel spiroindole-thiazolidinones (
6a–
l) using an environmentally benign procedure at atmospheric pressure in open vessel. This rapid method produces pure products in high yields within few minutes in comparison to a conventional two-step procedure. The crystal structure of one representative compound has been determined by X-ray diffraction. The synthesized compounds have been screened ‘in vitro’ for antifungal activity against
Rhizoctonia solani,
Fusarium oxysporum and
Collectotrichum capsici. All compounds have shown good activity against these pathogens.
The first example of the use of chiral ionic liquids as reaction media in the asymmetric Baylis–Hillman reaction was described using
N-alkyl-
N-methylephedrinium salts. Good yields and significant ...enantiomeric excesses were obtained.
The first example of the use of chiral ionic liquids as reaction media in the asymmetric Baylis–Hillman reaction was described using
N-alkyl-
N-methylephedrinium salts. Good yields and significant enantiomeric excesses were obtained.
Synthesis of amides via pyrolysis of the salts obtained by mixing neat primary amines and carboxylic acids were realized under solvent-free conditions within short times and appreciable yields under ...microwave activation. The evident specific non-thermal microwave effects are attributed to polarity increase during the course of the reaction, due to development of a dipole in the transition state.
Synthesis of amides via pyrolysis of corresponding salts obtained by mixing neat primary amines and carboxylic acids were realized under solvent-free conditions within short times and appreciable yields under microwave activation. Specific non-thermal microwave effects are evidenced and attributed to enhancements in microwave–materials interaction due to polarity increase (formation of a polar transition state) during the course of the reaction.
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.
Phase transfer catalysis can be efficiently coupled to microwave activation essentially in solvent-free conditions. Reactions are generally more rapid and products often purer than under conventional ...heating. This method constitutes a clean, economical, efficient and safe technology in organic synthesis. A review of the up-to-date experiments in this field is reported here.
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.
Solvent-free ester aminolysis was studied under microwave or conventional heating either in the absence of base or induced by KO
tBu with or without a phase transfer agent. The specific microwave ...effects were shown to be dependent on the conditions and discussed in terms of relative polarities of ground and transition states.
Solvent-free aminolysis was studied under microwave or conventional heating either in the absence of base or induced by KO
tBu with or without phase transfer agent. The specific microwave effects were shown to be dependent on the conditions and discussed in terms of relative polarities of ground and transition states.
Solvent-free methods are especially adapted to organic synthesis under Green Chemistry conditions. When coupled to microwave (MW) irradiation, it results in very efficient and clean procedures with ...noticeable improvements over classical methods. To take advantage of MW specific effects, the most suitable cases involve reactions with polar mechanisms with increase of the polarity during the progress of the reaction and late transition states along the reaction coordinates. Striking examples are described therein.
