Angel Gabriel Sathicq

Solvent‐Free Approach to 3,4‐Dihydropyrimidin‐2(1H)‐(thio)ones: Biginelli Reaction Catalyzed by a Wells–Dawson Reusable Heteropolyacid

Abstract The Biginelli reaction is performed in an efficient, simple, solvent‐free procedure, using a small amount of H6P2W18O62 · 24H2O, a reusable heteropolyacid catalyst with Wells–Dawson structure. Both aromatic and aliphatic aldehydes, and different β‐dicarbonyl compounds and urea or thiourea, were used as starting materials. Seventeen examples of dihydropyrimidinones and dihydropyrimidinethiones were prepared by heating the reactants either in refluxing acetonitrile or in the absence of solvent. Operational simplicity, the use of a noncorrosive, reusable catalyst in solventless conditions, short reaction times, and very good to excellent yields in most of the selected examples are the main advantages of the method.

Selective Oxidation of Sulfides to Sulfoxides Using Modified Keggin Heteropolyacids as Catalyst

GRAPHICAL ABSTRACT Abstract The use of modified Keggin phosphomolybdic heteropolyacids (HPA) (V and Al) as catalysts in the selective oxidation of sulfides to the corresponding sulfoxides is reported. Excellent yields were obtained (13 examples: 79%–95%), using 35% (w/v) aqueous hydrogen peroxide as oxidant, and acetonitrile as solvent at 25°C. The relationship between the electron densities of the sulfur atoms, which was estimated by molecular theoretical calculations, and the oxidative relativities of the sulfur-containing compounds was also investigated. The results indicate that the time for 100% conversion decreases with an increase in electron density.

p-Sulfonic acid calix[4]arene-functionalized alkyl-bridged organosilica in esterification reactions

Two new p-sulfonic acid calix[4]arene- and p-sulfonic acid calix[6]arene-functionalized organosilica have been synthesized using a sol–gel method and applied as heterogeneous catalysts in esterification reactions. The catalytic performance was evaluated using the esterification of carboxylic acids with ethanol, and good catalytic activity (i.e., 55–88%) was observed under the optimum reaction conditions. This study reports the first promising example of the successful employment of calix[n]arenes as a heterogeneous catalyst for catalytic esterification. The catalyst was easily separated by filtration and reused five times without any significant loss of activity.

Valorization of Oleuropein via Tunable Acid-Promoted Methanolysis

The acid-promoted methanolysis of oleuropein was studied using a variety of homogeneous and heterogeneous acid catalysts. Exclusive cleavage of the acetal bond between the glucoside and the monoterpene subunits or further hydrolysis of the hydroxytyrosol ester and subsequent intramolecular rearrangement were observed upon identification of the most efficient catalyst and experimental conditions. Furthermore, selected conditions were tested using oleuropein under continuous flow and using a crude mixture extracted from olive leaves under batch. Formation of (-)-methyl elenolate was also observed in this study, which is a reported precursor for the synthesis of the antihypertensive drug (-)-ajmalicine.