Franca Bigi

A revision of the Biginelli reaction under solid acid catalysis. Solvent-free synthesis of dihydropyrimidines over montmorillonite KSF

Abstract The reaction of aldehydes, β-dicarbonyl compounds and urea (Biginelli reaction) has been performed over solid acid catalysis, under solventless conditions or in water affording dihydropyrimidines in good yield and selectivity. Dihydropyrimidines4 were obtained in good yield and selectivity by reacting aldehydes, β-dicarbonyl compounds and ureas in the presence of montmorillonite KSF under solventless conditions. Download : Download full-size image

Selected syntheses of ureas through phosgenesubstitutes

Ureas have been traditionally synthesised by methodologies mainly based on the use of dangerous reagents such as phosgene and isocyanates. In the last few years, however, these reagents have been increasingly substituted by cleaner alternative and inherently safer compounds since the goal of the modern environmentally friendly synthetic chemistry is the development and optimisation of reaction conditions to reduce or eliminate the use and production of hazardous materials while maximising energy usage. Thus different and sometimes sophisticated phosgene substitutes such as bis(4-nitrophenyl)carbonate, triphosgene, di-tert-butyl dicarbonate, 1,1-carbonylbisimidazole, 1,1-carbonylbisbenzotriazole, S,S-dimethyldithiocarbonate and trihaloacetylchlorides have been utilised as safer reagents which can be stored and handled without special precautions. Moreover, the large scale production of urea derivatives has been more conveniently performed by using simpler and cheaper raw materials such as CO and CO2 in catalytic processes, avoiding production of large amounts of saline by-products which represent the main constituent of chemical waste.

Clean synthesis in water. Part 2: Uncatalysed condensation reaction of Meldrum's acid and aldehydes

Abstract The environment-friendly condensation of Meldrums acid and aromatic, heteroaromatic and hindered aliphatic aldehydes is performed carrying out the reaction in water at 75°C for 2 h, avoiding the addition of any catalyst.

Clean synthesis in water: uncatalysed preparation of ylidenemalononitriles

A simple, efficient and environment-friendly procedure is developed for the condensation of malononitrile with aromatic, heteroaromatic and aliphatic aldehydes in water. The ylidenemalononitriles 3 are synthesised in high yields (84–98%) and selectivities (87–98%) in distilled water at 65 °C for 1 h, avoiding the addition of any catalyst.

Supported organic catalysts: synthesis of (E)-nitrostyrenes from nitroalkanes and aromatic aldehydes over propylamine supported on MCM-41 silica as a reusable catalyst

Abstract MCM-41-supported propylamine showed high catalytic efficiency in the nitroaldol condensation between nitroalkanes and aromatic aldehydes.

Solvent free tetrahydropyranylation of phenols and alcohols over zeolites HSZ as reusable catalysts

Abstract Phenols and alcohols are tetrahydropyranylated in the presence of zeolites HSZ in good to excellent yields and selectivities. Addition of methanol performs the complete deprotection.

Multicomponent reactions under clay catalysis

Three-component reactions for the synthesis of substituted dihydropyrimidines (4), chromenes (8) and tetrahydroquinolines (11) have been performed in water and in the presence of a montmorillonite KSF clay. The products, easily isolated from the reaction mixture by crystallisation, are obtained in high yield and selectivity and the catalyst can be recycled for many runs without losing its activity.

Uncatalysed reactions in water: Part 2. Preparation of 3-carboxycoumarins

A simple, efficient and environmentally friendly procedure has been developed for the reaction of Meldrum’s acid with salicylaldehydes. 3-Carboxycoumarins 5 were synthesised in high yields (78–96%) and excellent selectivities (95–98%) by carrying out the reaction in water at reflux for 10 h, avoiding the addition of any catalyst.

Oxidative coupling of dichloroaluminium phenolates: Highly selective synthesis of hydroxylated Bi- and tetraaryls

Abstract Dichloroaluminium phenolates 4 undergo highly selective FeCl3-promoted oxidative coupling. Variously substituted symmetric 2,2′-dihydroxy biaryls 2 are obtained in good yields and excellent selectivities. The chelation control in the final reaction products 7 promotes the chemoselectivity of the process.

REGIOSELECTIVE ELECTROPHILIC ALKYLATION OF ANILINES WITH PHENYLACETYLENE IN THE PRESENCE OF MONTMORILLONITE KSF

Abstract Substituted anilines react with phenylacetylene in the presence of montmorillonite KSF affording 1,1-diarylethylenes 3 in good yields and excellent selectivities. In the presence of an excess of phenylacetylene, para-toluidine and para-anisidine give the corresponding 2,6-bis(1-phenylvinyl)anilines.