During the last twenty years, our research group has been working with aromatic nitrosubstituted
compounds acting as electrophiles in Polar Diels-Alder (P-DA) reactions with different
dienes of diverse nucleophilicity. In this type of reaction, after the cycloaddition reaction, the nitrated
compounds obtained as the [4+2] cycloadducts suffer cis-extrusion with the loss of nitrous acid and a
subsequent aromatization. In this form, the reaction results are irreversible. On the other hand, the
microwave-assisted controlled heating become a powerful tool in organic synthesis as it makes the
reaction mixture undergo heating by a combination of thermal effects, dipolar polarization and ionic
conduction. As the Diels-Alder (D-A) reaction is one of the most important process in organic synthesis,
the microwave (MW) irradiation was applied instead of conventional heating, and this resulted in
better yields and shorter reaction times. Several substituted heterocyclic compounds were used as electrophiles
and different dienes as nucleophiles. Two experimental situations are involved: one in the
presence of Protic Ionic Liquids (PILs) as solvent and the other under solvent-free conditions. The analysis
is based on experimental data and theoretical calculations.
Keywords: Diels-Alder, microwave irradiation, nitro-heterocycles, ionic liquids, solvent-free conditions, DFT.
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