In the last years, ionic liquids have been used as substitutes to common solvents since they combine good solubility properties with small vapor pressures. Herein, the Diels-Alder reactions of cyclopentadiene (CP) with acrolein, methyl acrylate and acrylonitrile in ionic liquids ([Emim][N(Tf)]), ([Hbim][N(Tf)]) and ([Bmim][OTf]) have been modeled with density functional theory to explore the effect of ionic liquids on the endo selectivity in the adducts. Besides the hydogen bonding interactions between the cation and the diene in all the structures, endo transition structures are slightly better stabilized than exo transition structures because of the favorable interactions between the H's of the CP ring and the O's of the [N(Tf)] and [OTf] anions of the IL's. In this study, B3LYP/6-31 + G* and M06-2X/6-31 + G* calculations have demonstrated that endo selectivity in the Diels-Alder reactions can be achieved in the presence of ionic liquids in agreement with experiments.
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