Synthesis of Chromen[4,3-b]pyrrolidines by Intramolecular 1,3-Dipolar Cycloadditions of Azomethine Ylides: An Experimental and Computational Assessment of the Origin of Stereocontrol

Azomethine ylides, generated from imine-derived O-cinnamyl or O-crotonyl salicylaldeyde and α-amino acids, undergo intramolecular 1,3-dipolar cycloaddition, leading to chromene[4,3-b]pyrrolidines. Two reaction conditions are used: (a) microwave-assisted heating (200 W, 185 °C) of a neat mixture of reagents, and (b) conventional heating (170 °C) in PEG-400 as solvent. In both cases, a mixture of two epimers at the α-position of the nitrogen atom in the pyrrolidine nucleus was formed through the less energetic endo-approach (B/C ring fusion). In many cases, the formation of the stereoisomer bearing a trans-arrangement into the B/C ring fusion was observed in high proportions. Comprehensive computational and kinetic simulation studies are detailed. An analysis of the stability of transient 1,3-dipoles, followed by an assessment of the intramolecular pathways and kinetics are also reported.

Tema 3, parte 4: El API DOM

En esta presentación se describe el API DOM1 para JavaScript, que permite manipular dinámicamente documentos HTML y XML.

Cas pràctic 4. Psicologia Evolutiva de 3 a 6 anys

a) Detectar aspectes o variables personals i contextuals que afecten el desenvolupament integral del xiquet/a. b) Conèixer l’impacte que determinades situacions personals o ambientals produeixen en els diferents àmbits del desenvolupament. c) Analitzar les relacions que hi ha entre els diferents agents i com afecten el desenvolupament del xiquet/a. d) Debatre propostes i actuacions per a minimitzar o potenciar l’impacte de determinats agents en el desenvolupament del xiquet/a.