Gold-catalyzed direct cycloketalization of acetonide-tethered alkynes in the presence of water

A methodology for the direct preparation of bridged acetals from acetonide-tethered alkynes under gold catalysis in the presence of water has been developed. The bicyclic ring structures bearing a bridged five-membered ring arise from the regioselective bis-oxycyclization by initial attack of the oxygen atom to the internal alkyne carbon. © 2012 Elsevier Ltd. All rights reserved.Peer Reviewe

Novel Aspects on the Preparation of Spirocyclic and Fused Unusual β-Lactams

Capítulo 1, pp 1-48β-Lactam antibiotics have occupied a central role in the fight against pathogenic bacteria and the subsequent rise in quality of life for the world population as a whole. However, the extensive use of common β-lactam antibiotics such as penicillins and cephalosporins in medicine has resulted in an increasing number of resistant strains of bacteria through mutation and β-lactamase gene transfer. The resistance of bacteria to the classical β-lactam antibiotics can be overcome, e.g., by using novel β-lactam moieties in drugs which show much higher stability towards these resistance bacteria. In addition, there are many important nonantibiotic uses of 2-azetidinones in fields ranging from enzyme inhibition to gene activation. These biological activities, combined with the use of these products as starting materials to prepare α- and β-amino acids, alkaloids, heterocycles, taxoids, and other types of compounds of biological and medicinal interest, provide the motivation to explore new methodologies for the synthesis of substances based on the β-lactam core. The aim of this chapter is to provide a survey of the types of reactions used to prepare non-conventional spirocyclic and fused β-lactams, concentrating on the advances that have been made in the last decade, and in particular in the last five years. We will draw special attention to radical cyclizations, cycloaddition reactions, and transition metal-catalyzed reactions.Peer reviewe

Novel achievements with an old metal: Copper-promoted synthesis of four-membered azacycles

The synthesis of four-membered azacycles is of importance because of the chemical and biological relevance of these compounds. Recent progress in copper-catalyzed reactions has been applicable to a variety of research fields, such as heterocyclic synthesis. The aim of the current review is to summarize the synthesis of strained four-membered ring taking advantage of copper catalyzed and mediated processes. © 2014 The Royal Society of Chemistry.Peer Reviewe

Síntesis, resolución y estudio de propiedades quirópticas de cetonas policíclicas

El presente trabajo forma parte de un plan de investigación programado en colaboración con los profesores W. Klyne y D. N. Kirk, del Departament of Chemistry del Westfield College de Londres, los cuales vienen realizando desde hace algunos años un amplio estudio sobre el dicroismo circular de cetonas policíclicas quirales, de estructura relacionada con la de oxo-compuestos esteroídicos, en la región espectral correspondiente a longitudes de onda de 350-185 nm, que permita el establecimiento de correlaciones estructurales entre el signo y magnitud de los efectos Cotton debidos a las transiciones n© p* y n© s* que presentan estos compuestos y su estereoquímica. En este tipo de investigación es necesario el estudio de moléculas modelo de estructura simplificada que permitan con mayor facilidad de inducción de reglas empíricas. Con este propósito hemos llevado a cabo la obtención de algunas cetonas policíclicas recémicas, dentro de la serie de decalona extendida todo-trans, que posteriormente fueron objeto de resolución óptica y finalmente estudiadas por dicroismo circular. Se han sintetizado por primera vez las siguientes cetonas racémicas:1. (±)-trans-sin-trans-sin-trans-2-perhidronaftacenona. 2. (±)-trans-sin-trans-1-perhidroantracenona.3.(±)-trans-anti-trans-2-perhidrofenantrenona. Su obtención ha sido fruto de un planteamiento sintético general al cual se llega mediante la consideración cuidadosa de sus estructuras y de un examen crítico de las distintas alternativas de síntesis de las mismas, y que se basa en el empleo sistemático, aunque no exclusivo, de dos tipos básicos de reacciones: la secuencia de anelación de Robinson y la reducción de agrupamientos enónicos con Liu/NH3. Se describen y se discuten igualmente una larga lista de productos intermedios y subproductos de síntesis involucrados en la preparación de tales sustratos cetónicos. La resolución óptica de las cetonas perhidronadtacénica y perhidroantracénica, efectuada por vía indirecta a través de sus OH-eq alcoholes, por recristalización fraccionada de la mezcla de ésteres diastereómeros obtenidos con el ácido 3ß-acetoxi-?5-etiénico nos ha permitido preparar muestras ópticamente puras de tales cetonas policíclicas y de algunos de sus derivados (alcoholes y acetatos). Se analizan los espectros de dicroismo circular obtenidos para las diferentes formas enantiómeras puras en disolventes de distinta polaridad, y se comparan con los de sustancias naturales de estructuras referibles (en especial de tipo esteroídico). A partir de estos datos se deduce la contribución al valor de ?e de los nuevos elementos estructurales introducidos en los esqueletos base. Las principales conclusiones que se deducen de nuestro estudio pueden resumirse en los siguientes puntos: 1. Comparando los valores de ?e observados para la cetona tetracíclica con los de su ciclohomóloga tricíclica referible se observa un incremento en el valor absoluto de ?e de 0. 2 unidades, debido a que el zig-zag primario se incrementa en dos nuevos enlaces C-C con la introducción de un anillo extra. 2. Los valores de ?e observados para la cetona tricíclica no difieren significativamente de los de la trans-1-decalona, debido a que el nuevo anillo no altera el sistema de enlace en zig-zag primario

Stereoselective cyanation of 4-formyl and 4-imino-β-lactams: Application to the synthesis of polyfunctionalized γ-lactams

The stereoselective reaction of 4-oxoazetidine-2-carbaldehydes and their corresponding imines with cyanide-based reagents give β-lactam α-aminonitriles, which are chameleonic building blocks for the controlled synthesis of a variety of new compounds including functionalized γ-lactams, succinimide derivatives, and diamino-lactams derivatives in optically pure form. © 2012 Elsevier Ltd. All rights reserved.Peer Reviewe

Iodine recycling via 1,3-migration in iodoindoles under metal catalysis

3-Substituted (indol-2-yl)-α-allenols show divergent patterns of reactivity under metal catalysis. An unprecedented intramolecular 1,3-iodine migration is described. © 2013 The Royal Society of Chemistry.Peer Reviewe

Вопросы воспитания в советской школе

Gold-catalyzed hydroarylation reaction of β-lactam-tethered allenyl indoles gives azeto-oxepino­[4,5-<i>b</i>]­indol-2-ones, tetrahydroazeto-azocino­[3,4-<i>b</i>]­indol-2-ones, and hexahydroazeto-azepino­[3,4-<i>b</i>]­indol-2-ones with very high levels of stereo- and regioselectivity, the 7-<i>exo</i> and 8-<i>endo</i> carbocyclization modes by attack of the indole group toward either the internal or the terminal allene carbon, respectively, being favored. Hydroarylation across the central carbon of the allene moiety has not been detected. The controlled gold-catalyzed annulations allowed the formation of fused β-lactams without harming the sensitive four-membered heterocycle. Besides, a novel gold-catalyzed domino process, namely, the allenic hydroarylation/N1–C4 β-lactam bond breakage to afford dihydro-oxepino­[4,5-<i>b</i>]­indole-4-carboxamides, has been discovered

Use of Schizosaccharomyces strains for wine fermentation? Effect on the wine composition and food safety

Schizosaccharomyceswas initially considered as a spoilage yeast because of the production of undesirable metabolites such as acetic acid, hydrogen sulfide, or acetaldehyde, but it currently seems to be of great value in enology.o ced Nevertheless, Schizosaccharomyces can reduce all of the malic acid in must, leading to malolactic fermentation. Malolactic fermentation is a highly complicated process in enology and leads to a higher concentration of biogenic amines, so the use of Schizosaccharomyces pombe can be an excellent tool for assuring wine safety. Schizosaccharomyces also has much more potential than only reducing the malic acid content, such as increasing the level of pyruvic acid and thus the vinylphenolic pyranoanthocyanin content. Until now, few commercial strains have been available and little research on the selection of appropriate yeast strains with such potential has been conducted. In this study, selected and wild Sc. pombe strains were used along with a Saccharomyces cerevisiae strain to ferment red grape must. The results showed significant differences in several parameters including non-volatile and volatile compounds, anthocyanins, biogenic amines and sensory parameters

High Power RF Discharge Detection Technique Based on the In-Phase and Quadrature Signals

[EN] High power radio frequency (RF) breakdown testing is a subject of great relevance in the space industry, due to the increasing need of higher transmission power and smaller devices. This work presents a novel RF breakdown detection system, which monitors the same parameters as the microwave nulling system but with several advantages. Where microwave nulling-a de facto standard in RF breakdown testing-is narrowband and requires continuous tuning to keep its sensitivity, the proposed technique is broadband and maintains its performance for any RF signal. On top of that, defining the detection threshold is cumbersome due to the lack of an international standardized criterion. Small responses may appear in the detection system during the test and, sometimes, it is not possible to determine if these are an actual RF breakdown or random noise. This new detection system uses a larger analysis bandwidth, thus reducing the cases in which a small response is difficult to be classified. The proposed detection method represents a major step forward in high power testing as it runs without human intervention, warning the operator or decreasing the RF power automatically much faster than any human operator.This work was supported in part by the "Ministerio de Ciencia e Innovacion," Spanish Government, under Project PID2019-103982RB-C41, and in part by the European High RF Power Space Laboratory of the European Space Agency and Val Space Consortium for contributing with its installations, Laboratory co-funded by the European Regional Development Fund-A way of making Europe.Monerris-Belda, O.; Cervera Marín, R.; Rodríguez Jodar, M.; Diaz-Caballero, E.; Alcaide Guillén, C.; Petit, J.; Boria Esbert, VE.... (2021). High Power RF Discharge Detection Technique Based on the In-Phase and Quadrature Signals. IEEE Transactions on Microwave Theory and Techniques. 69(12):5429-5438. https://doi.org/10.1109/TMTT.2021.312065754295438691