Rogério A. Gariani

Synthesis of bis(indolyl)methanes using ammonium niobium oxalate (ANO) as an efficient and recyclable catalyst

A green and efficient procedure was developed for the synthesis of bis(indolyl)methanes using ammonium niobium oxalate (ANO) NH4[NbO(C2O4)2(H2O)x]·nH2O as the catalyst and water or glycerol as the solvent. Products were obtained in good to excellent yields under conventional heating (water, 50 °C) or under sonication (glycerol, 110 °C). In the reaction in water, the catalyst was easily reused for further reactions without loss of activity.

In Situ Generation of n‐Butanethiol and Its Reaction with Electron‐Deficient Olefines

Abstract n‐Butanethiol is generated in situ by sequential addition of n‐butyllithium and water to elemental sulfur. The n‐butanethiol formed was reacted with electron‐deficient olefines to give Michael‐type addition products in good yields. The method avoids the manipulation of the bad‐smelling n‐butanethiol.

Proline derivatives as organocatalysts for the aldol reaction in conventional and non-conventional reaction media

Abstract Different l-proline derivatives were investigated as organocatalysts for the aldol condensation reaction between acetone and 4-nitrobenzaldehyde, in a conventional organic solvent (DMSO), in supercritical carbon dioxide, and in mixtures of this solvent and 1-allyl-3-alkyllimidazolium chlorides ionic liquids. The catalysts evaluated were: (S)-pyrrolidine-2-carboxylic acid (l-proline), (R)-thiazolidine-4-carboxylic acid (l-thioproline), (2S,4R)-4-[dimethyl(phenyl)silyl]oxy-pyrrolidine-2-carboxylic acid (dimethylphenylsilyloxy-l-proline), (2S,4R)-4-(tert-butyldimethylsilyl)oxy-pyrrolidine-2-carboxylic acid (butyldimethylsilyloxy-l-proline), and (2S,3R,4R,5S,6R)-6-(acetoxymethyl)-3-[(S)-pyrrolidine-2-carboxamido]-tetrahydro-2H-pyran-2,4,5-triyl triacetate (peracetylated glucosamine-l-proline). One of the catalysts tested, the tert-butyldimethylsilyloxy-l-proline, was very effective, allowing lower reaction times, resulting in better yields and enantiomeric excesses than l-proline itself, both in organic solvent (DMSO) and in sc-CO2 or a mixture of sc-CO2 and ionic liquids. The use of the ionic liquid resulted in better yields and enantiomeric excesses in sc-CO2. The other catalysts tested were not as effective, resulting in yields and enantiomeric excesses similar or inferior to the ones obtained with l-proline.