André Loupy

Microwave activation in phase transfer catalysis

Abstract 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.

Trois nouvelles voies de synthèse des dérivés 1,3-azoliques sous micro-ondes

Abstract Three new ways to synthesize 1,3 - azoles derivatives on mineral supports using Ca(OCl) 2 Al 2 O 3 or MnO 2 SiO 2 or by fusion “in dry media” are described. The reactions are activated under microwave irradiation in a monomode Synthewave 402 reactor. The reaction times are considerably shortened and the products are obtained in higher yields and better purity, than compared to conventional heating.

Solvent-free preparation of amides from acids and primary amines under microwave irradiation

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.

Reactivity and selectivity under microwaves in organic chemistry. Relation with medium effects and reaction mechanisms

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.

Alkylation of potassium acetate in “dry media” thermal activation in commercial microwave ovens

Abstract Microwave irradiation using commercial domestic ovens is very efficient to activate potassium acetate on alumina in the absence of solvent (“dry media”) giving rise to remarkable rate enhancements in alkylation reactions with long chain halides. These reactions can be performed quantitatively on appreciable amounts of materials in open standard pyrex vessels.

Inorganic solids in dry media an efficient way for developing microwave irradiation activated organic reactions

Abstract “Dry media” microwave irradiation accelerates pinacol rearrangement (on montmorillonite) or acetate alkylation (on alumina or silicagel) without the hazards due to high pressures in vessels when using solvents.

The effect of cations on nucleophilic additions to carbonyl compounds: carbonyl complexation control versus ionic association control. application to t

Abstract The fundamental influence of cations in nucleophilic additions to carbonyl compounds is discussed in terms of either carbonyl complexation or ionic association with the nucleophile. Since loose ion pairs react essentially under complexation control while tight ion pairs react under association control, an experimental criterion is proposed to determine which factor controls the reactivity (complexation or association) based on the kinetic effects of cryptand or crown-ether addition. An application of this duality is then examined for the regioselectivity of nucleophilic additions to α-enones and correlated with perturbational arguments based on ab initio calculations. Under complexation control, attack at carbon 2 is favoured, especially when a soft nucleophile is involved and the counter-ion is Li+ rather than Na+. Under association control two cases are considered according to whether the cation is directly bound or not to the nucleophilic center; in addition, the influence of hard or soft metals and the possibility of a cationic bridge in the transition state have been discussed. Several kinetic controlled reactions have been examined and interpreted in this way. An extension of this concept to other reactions will be considered.

Microwave assisted solvent-free synthesis of pyrazolo[3,4-b]quinolines and pyrazolo[3,4-c]pyrazoles using p-TsOH

Pyrazolo[3,4-b]quinolines and pyrazolo[3,4-c]pyrazoles have been synthesized from β-chlorovinylaldehydes and hydrazine hydrate/phenylhydrazine using p-TsOH under microwave irradiation.

Silica gel catalysed Knoevenagel condensation in dry media under microwave irradiation

Abstract Neutral silica gel catalysed efficiently the Knoevenagel condensation of carbonyl compounds on malononitrile in dry media under microwave irradiation. Synergy between dry media and microwaves is shown.

Microwave effects in solvent-free esters aminolysis

Solvent-free ester aminolysis was studied under microwave or conventional heating either in the absence of base or induced by KOtBu 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.