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-atomcomponents (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.