The Theoretical Study on the Mechanism of [3+2] Cycloaddition Reactions between α,β-unsaturated Selenoaldehyde with Nitrone and with Nitrile Oxide

Abstract. The reaction mechanisms of [3+2] cycloaddition (32CA) between the α,β-unsaturated selenoaldehyde with nitrone and nitrile oxide were investigated theoretically using the molecular electron density theory (MEDT). Selenoaldehyde has two unsaturations which allow for the cycloaddition occurring. It was expected to undergo four regioisomeric reaction paths in two separate reactions with nitrone and nitrile oxide. The study was conducted using ab initio approach at MP2/6-31G(d) level of theory. Potential energy surfaces were generated from the energies of the stationary points involved in the mechanisms and the dominant reaction pathways were identified. It was found that Pathway 3 and 4 are the two competing reaction channels, where the cycloaddition reaction occurs at the selenium-analogue carbonyl group of selenoaldehyde. The reactivity indices were analysed at the ground state of the reactants to predict the reactivity of studied organic molecules in 32CA reactions. Analysis of the electronic structure of nitrone and nitrile oxide, the three-atom-components (TACs), and their participation in 32CA reactions towards selenoaldehyde allows establishing a useful classification of 32CA reactions into zwitterionin-type (zw-type) reactions involving TACs with a high zwitterionic character.                                           Resumen. Se estudia teoricamente, utilizando la teoria de la densidad electronica molecular (MEDT), el mecanismo de reaccion de la cicloadicion [3+2] (32CA) entre selenoaldehidos α, β insaturados con nitrona y oxido de nitrilo. El selenoaldehido tiene dos insaturaciones que permiten la cicloadicion. Se esperaba que la reaccion se llevara a cabo a lo largo de cuatro caminos regioisomericos en dos reacciones separadas con la nitrona y el oxido de nitrilo. Se realizo un estudio ab initio con el nivel de teoria MP2/6-31G(d). Se generaron superficies de energia potencial a partir de las energias de los puntos estacionarios involucrados en el mecanismo y se identificaron los caminos de reaccion dominantes. Se encontro que dos rutas, la 3 y la 4, son los canales de reaccion que compiten para que ocurra la cicloadicion en el grupo carbonilo analogo al selenio del selenoaldheido. Se analizaron los indices de reactividad de los estados basales de los reactivos para predecir la reactividad de las moleculas organicas estudiadas en las reacciones 32CA. El analisis de la estructura electronica de la nitrona y el oxido de nitrilo, de las componentes triatomicas (TACs) y de su participacion en las reacciones 32CA hacia el selenoaldheido permite clasificar a las reacciones 32CA en tipo zwitterionico (zw) que involucran a los TACs con un elevado caracter zwitterionico.