EDTA-catalyzed synthesis of 3,4-dihydroquinoxalin-2-amine derivatives by a three-component coupling of one-pot condensation reactions in an aqueous medium

This paper describes a simple and efficient one-pot synthetic approach for the preparation of biologically interesting 3,4-dihydroquinoxalin-2-amine derivatives using EDTA-catalyzed three-component reactions of o-phenylenediamines, carbonyl compounds, and isocyanides in an aqueous medium. This method is of great value because of its environmentally benign character, high yields, and ease of handling.     

Bifunctional solid catalysts for chemoselective hydrogenation-cyclisation-amination cascade reactions of relevance for the synthesis of pharmaceuticals

The benzodiazepines olanzapine and clozapine are nowadays manufactured by a three-step process with a final yield below 50%. An approach to environmentally-friendly intensive processes consists in the development of multifunctional solid catalyst able to catalyze multistep reactions. Here, a bifunctional metal-acid solid catalyst has been prepared and is able to carry out hydrogenation-cyclisation-amination reactions in a cascade process. The catalytic system is illustrated for the synthesis of these important antipsychotics, being an alternative for the current industrial process that requires three steps batch reactions, using mineral acids and bases, and stoichiometric amounts of SnCl₂.     

Acyl pyruvates as synthons in the Biginelli reaction

Chlorotrimethylsilane-promoted Biginelli-type reaction of ethyl 2,4-dioxo-4-phenylbutanoate, benzaldehyde, and various (thio)ureas is explored. The outcome of the reaction depends on the structure of the (thio)urea used and is strongly affected by the acceptor electronic properties of the COOEt substituent in the molecule of the starting β-dicarbonyl compound. The di- and tetrahydropyrimidine derivatives obtained possess two functional groups with orthogonal reactivity, and thus represent promising building blocks for drug discovery.     

An efficient one-pot multicomponent approach to 5-amino-7-aryl-8-nitrothiazolo[3,2-a]pyridines

A series of thiazolo[3,2-a]pyridines have been prepared using a multicomponent reaction between aromatic aldehydes, 2-nitromethylenethiazolidine and nitriles containing an active methylene group (malononitrile, ethyl 2-cyanoacetate and 2-phenylsulfonylacetonitrile) in the presence of Et₃N under mild conditions with high yields. One of the compounds shows promising anticancer activity across a range of cancer cell lines.     

Comparison of theoretical methods for assessing the heat of formation of C1 and C2 chlorofluorocarbons and hydrochlorofluorocarbons

The heat of formation of a number of key C₁ and C₂ chlorofluorocarbons and hydrochlorofluorocarbons have been calculated by G3, G3MP2, G3MP2B3 and G3B3 methods. Based on the results of the atomization approach, it was found that the errors are approximately dependent upon the number of C-F or C-Cl bonds. Moreover, the bond additive correction (BAC) procedure and isodesmic reactions approach improved the accuracy and decreased these system errors significantly. The extended comparison between the BAC procedure and isodesmic reaction approaches had been made; the latter yielded the best results and showed broader applicability.     

One-pot synthesis of stilbenes by dehydrohalogenation-Heck olefination and multicomponent Wittig-Heck reaction

A variant of olefination reaction involving in situ generation of styrene by either one-pot dehydrohalogenation-Heck or one-pot multicomponent Wittig-Heck reaction is developed.     

Recurring angular distribution patterns in resonant heavy-ion reactions

It has been noticed that a distinct resemblance exists at large angles among angular distributions measured for reaction channels at the energies of some resonance-like structures in the ¹²C+¹²C and ¹⁴C+¹⁶O systems. It is pointed out that such forms are typical of a diffraction pattern of a broad band of coherent partial waves. Received: 5 October 1998 / Revised version: 8 December 1998