2 resultados para Stochastic Context-Free L-Grammar
em Universidad de Alicante
Resumo:
Tenint com a rerefons la cultura del culte al cos i el context del problema epidemiològic que amaga la pandèmia de l’obesitat, s’analitzarà la doble càrrega sanitària que per a molts sectors de la població, particularment el més endarrerits social i econòmicament, representa patir els efectes del sobrepès i les complicacions que solen comportar moltes de les anomenades dietes miracle.
Resumo:
Recoverable (Sa)-binam-l-prolinamide in combination with benzoic acid is used as catalysts in the direct aldol reaction between cycloalkyl, alkyl, and α-functionalized ketones and aldehydes under solvent-free reaction conditions. Three different methods are assayed: simple conventional magnetic stirring, magnetic stirring after previous dissolution in THF and evaporation, and ball mill technique. These procedures allow one to reduce not only the amount of required ketone to 2 equiv but also the reaction time to give the aldol products with regio-, diastereo-, and enantioselectivities comparable to those in organic or aqueous solvents. Generally anti-isomers are mainly obtained with enantioselectivities up to 97%. The reaction can be carried out under these conditions also using aldehydes as nucleophiles, yielding after in situ reduction of the aldol products the corresponding chiral 1,3-diols with moderate to high enantioselectivities mainly as anti-isomers. The aldol reaction has been studied by the use of positive ESI-MS technique, providing the evidence of the formation of the corresponding enamine−iminium intermediates.