Alain Petit

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.

Solvent-Free Synthesis of Decyl D-Glycopyranosides Under Focused Microwave Irradiation

Abstract A three step microwave assisted solvent-free synthesis of decyl D-glucopyranoside with 1-decanol was established for D-glucose and extended to D-galactose, D-mannose and N-troc-D-glucosamine with 70% average overall yield for the three steps (peracetylation, glycosylation and saponification). Rate enhancements and reduction of the reaction time were observed for the two last steps carried out under microwave irradiation when compared to conventional heating in the same conditions.

Microwave Irradiation in Dry Media: A New and Easy Method for Synthesis of Tetrapyrrolic Compounds

Abstract We report a simple and quick synthesis of tetrapyrrolic macrocycle in dry media conditions, under microwave irradiation. Heating in microwave oven pyrrole and benzaldehyde adsorbed on a solid acidic support affords tetraphenylporphyrin within ten minutes with very simplified treatment and purification.

Coupling focused microwaves and solvent-free phase transfer catalysis: Application to the synthesis of new furanic diethers

Abstract A new family of furanic ethers was obtained by alkylation of 2,5-furandimethanol or furfuryl alcohol under microwave in phase transfer catalysis (PTC) conditions in the absence of solvent. Products were synthesized in good yields (> 80 %) within 10 min or less. Compounds were analysed by NMR, mass spectrometry and their thermal behaviours were studied by DSC. When compared to conventional heating, everything equal elsewhere, reaction times were improved under microwave conditions at a restitute power of 30 Watts when performed under stirring in a monomode reactor (Synthewave 402 Prolabo).

Solvent-free synthesis of 4-aryl substituted 5-alkoxycarbonyl-6-methyl-3,4-dihydropyridones under microwave irradiation

Abstract 4-Aryl substituted 5-alkoxycarbonyl-6-methyl-3,4-dihydropyridones have been prepared in one-pot condensation from Meldrums acid, methyl acetoacetate and the appropriate benzaldehyde in the presence of ammonium acetate using microwave irradiation without solvent. This rapid method produced pure products in high yields (81–91%) due essentially to a specific non-thermal microwave effect (17–28%) by conventional heating under the same conditions.

Studies on chemical oxidative copolymerization of aniline and o-alkoxysulfonated anilines:: I. Synthesis and characterization of novel self-doped polyanilines

Abstract The chemical oxidative copolymerization of aniline (An) with o -alkoxysulfonated anilines, i.e., 1-( o -amino)-propane-3-sulfonic acid (APPrS) and 1-( o -amino)-butane-3-sulfonic acid (APBuS), was a new way to produce water-soluble and self-doped polyaniline derivatives. Poly(An- co -APPrS) and poly(An- co -APBuS) were obtained in H 2 SO 4 acidic medium by chemical oxidation, using ammonium persulfate, of a comonomer mixture containing An and APPrS, or APBuS, in various initial ratios. The copolymers thus obtained with high or low yields, were characterized by elemental microanalysis, FTIR spectroscopy, size exclusion chromatography and conductivity measurements. Due to the electron-donating effects of the alkoxysulfonated groups, the two aniline-derivatives were easily incorporated in the macromolecular chains and strongly enhanced water-solubility of the products. The electrical conductivities of these copolymers, which depend on both self- and external-dopings, were reduced by the incorporation of alkoxysulfonated substituents compared with the one of parent polyaniline.

Towards the rehabilitation of the Leuckart reductive amination reaction using microwave technology

Abstract Leuckart reductive amination of carbonyl compounds was dramatically enhanced with respect to conventional heating by a specific microwave effect when the reaction was performed, under solvent-free conditions, in a monomode microwave reactor. Excellent isolated yields (up to 97%) were attained within short reaction times (typically, 30 minutes)

Solvent-Free Microwave-Assisted Aromatic Nucleophilic Substitution − Synthesis of Aromatic Ethers

Specific (not purely thermal) microwave effects are shown to be highly dependent on the nature of the nucleophilic ion pairs and on the substituents and leaving groups on the aromatic substrates. This can be interpreted in terms of a polarity enhancement during the progress of the reaction and a shift of the position of the transition state along the reaction coordinates. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Protein encapsulation in biodegradable amphiphilic microspheres. I. Polymer synthesis and characterization and microsphere elaboration

Polymerization of lactide on monomethoxypolyoxyethylene (MPOE), using stannous octoate as a catalyst, was carried out in bulk and in solvent. Polymerization in a solvent permits one to work at a lower temperature and thus to prevent transesterification reactions. The copolymers synthesized in solvent exhibited a lower polydispersity and a polylactic acid (PLA) block longer and closer to the expected one. Therefore, this procedure was used to synthesize a series of diblock copolymers MPOE-D,L-PLA, keeping the PLA chain constant (45,000 g/mol), the MPOE block increasing from 2000 to 5000, 10,000, 15,000, and 20,000 g/mol. The longer the MPOE chain, the higher the water uptake in the MPOE-PLA films and the lower the glass transition temperature of the copolymers. The synthesized copolymers were used to prepare microspheres by the double-emulsion method. The PLA microspheres possess a smooth surface, whereas those made from copolymers have a rough surface with irregularity increasing with the molecular weight of MPOE. The size of these microspheres depends on the amphiphilic nature of the copolymers, their hydrophilicity, and their intrinsic viscosity in the organic solvent.

Improvements in 1,3-dipolar cycloaddition of nitrones to fluorinated dipolarophiles under solvent-free microwave activation

Abstract 1,3-Dipolar cycloadditions between ethyl trifluoracetoacetate or α-trifluoromethylstyrene and N -(benzylidene)methylamine N -oxide were performed in the absence of solvent. Under microwave irradiation in a monomode Maxidigest Prolabo reactor, quantitative yields were obtained within 3 min. Compared to conventional heating under the same conditions, the yields are significantly increased (from 55%–64% to 88.98%). Classical conditions using boiling toluene (65% within 24–48 h) are now considerably improved.