In this study we analyzed the behavior of N-mesylnitroindoles acting as electrophilic dienophiles in polar Diels-Alder reactions joint to isoprene as nucleophilic diene. The analysis was developed considering the experimental results when microwave irradiation with toluene or protic ionic liquids as solvents were used. In a similar way, the free solvent conditions were analyzed. These results were compared with the ones of conventional heating and it was found that the reactions under microwave irradiation are better than those developed in thermal conditions.

Considering the mechanism study, a unique and notably asynchronous transition state was found. We can note that, in the presence of an ionic liquid, the charge transfer is higher in relation with free solvent conditions. Based on the vibration frequencies, the microwave effect looks to be independent of the solvent used.

As a consequence of the theoretical study we can conclude that for these reactions the free solvent condition and protic ionic liquids as solvent offer similar results under microwave irradiation. However the solvent-free condition is far more favorable to environmental sustainability.