CeCl3 catalyzed imino Diels-Alder reactions: hydrated vs anhydrous

Aza-Diels-Alder reaction is a straightforward way to synthesize useful nitrogen containing heterocyclic structures.1 In particular, the known reaction between imines and Danishefsky’s diene has proved to be an excellent way to obtain the 1,2-substituted-2,3-dihydropyridinone scaffold, widely present in bioactive small molecules and versatile building block for the synthesis of more complex structures.2 The reaction of Danishefsky’s diene with aromatic imines has been widely studied in last years, anyway less examples of the same reaction involving imines derived from aliphatic amines or aldehydes are present. For this reason the possibility to extend the potentiality of this reaction performing it on a large variety of imines was studied, under the Lewis acid promoting system CeCl3.7H2O/CuI, previously applied with success3 in many other synthetic methodologies. Imines 3 were prepared by direct condensation of aliphatic or aromatic amines and aldehydes and then the diene was added together with the catalyst, obtaining dihydropyridinones 4 with good to excellent yields in short reaction times. To extend the scope of this work, also imines derived from aminoacids were tested as dienophiles. The only moderate diastereoselectivity and the long time needed with some homochiral dienophiles prompted us to have a deeper insight into the mechanism, with the conclusion that the reaction proceed also through a slower competitive Mannich-Michael pathway, favoured by the presence of water in the catalyst. 1) Buonora, P.; Olsen, J.-C.; Oh, T. Tetrahedron 2001, 57, 6099-6138. 2) Cant, A. A.; Sutherland, A. Synthesis 2012, 44, 1935-1950. 3) Bartoli, G.; Marcantoni, E.; Marcolini, M.; Sambri, L. Chem. Rev. 2010, 110, 6104-6143

A formação da mão-de-obra para a indústria química: uma retrospectiva histórica

This paper presents a brief review of the socio-historical evolution of the chemical technician and his/her productive praxis, as well as his/her High-School level technical education as situated in the social and political environment in the realm of science and technology. Such an individual is seen as the subject of transforming action, so the approach taken here is not restricted to an immediatic ideology of professional training, but rather attempts to eliminate that reproductive perspective which considers social relations as gears in the capitalist system.Este artigo apresenta uma breve retrospectiva da evolução sociohistórica do técnico em Química e da sua praxis produtiva, voltando-se para uma educação técnica de nível médio, no âmbito social, político e científico-tecnológico. Visa um sujeito de ação transformadora, não se restringindo a uma ideologia imediatista de formação profissional; busca eliminar a perspectiva reprodutivista das relações sociais como engrenagem do sistema capitalista.15116

An Efficient Lewis Acid Catalyzed Povarov Reaction for the One-Pot Stereocontrolled Synthesis of Polyfunctionalized Tetrahydroquinolines

An easy and efficient synthetic methodology for the one-pot stereocontrolled synthesis of tetrahydroquinolines through Lewis acid activated Povarov reaction is described. The protocol takes advantage of the very cheap, easy to handle, and environmentally friendly cerium trichloride as catalyst and allows to obtain either the anti- or the syn-isomer of the final tetrahydroquinoline with good selectivity, by performing the reaction in solvent or solventless conditions. The scope of the reaction is expanded to the one-pot synthesis of N-alkyltetrahydroquinolines through a very efficient iminium-Povarov approach. A deeper insight on the reaction system was provided by the study on the side reactions occurring in the reaction conditions and on the nature of the stereoselectivity

Synthesis of Enantiopure 2-(Aminoalkyl)phenol Derivatives and Their Application as Catalysts in Stereoselective Reactions

Enantiopure 2-(aminoalkyl)phenol derivatives are an interesting class of compounds widely used in homogeneous ligand accelerated catalysis. A series of practical and convenient methods available for their preparation are revised, together with the methodologies for the determination of their configuration. The uses of these compounds in metal catalysed asymmetric reactions in the addition of dialkyl zinc reagents to aldehydes and in the reduction of ketones with borane are described. Moreover 2-(aminoalkyl)phenol derivatives have found use also as chiral shift reagents for carboxylic acids

Chemo- and stereoselective reduction of enaminones for the preparation of biologically active compounds

The chemistry of the preparation of β-enamino ketones and β-enamino esters and their use as useful starting materials in reductive procedures for the preparation of biologically active natural products is described. Enaminones are very stable compounds and can be easily prepared, starting from cheap and easily available starting materials. Therefore they constitute also excellent starting materials in organic synthesis. Several chemo- and regioselective methodologies for their preparation have been developed also recently. The possibility to use enantiopure chiral amines for the preparation of enamino ketones and enamino esters makes available useful starting materials for the preparation of enantiopure biologically active compounds. Moreover, it is possible to obtain more complex enaminones by regio-and stereoselective functionalization of the more accessible ones. Recently numerous methodologies for the chemo- and stereoselective reduction of enaminones have been developed, that constitute useful alternative pathways to the numerous literature procedures for the preparation of γ-amino alcohols, β-amino acids, aminoalkyl phenols and their derivatives. γ-Aminoalcohols and aminoalkylphenols are a class of very stable compounds that find useful applications in asymmetric catalysis as chelant for the preparation of chiral enantiopure metallic catalysts