On the solvent‐ and temperature‐driven stereoselectivity of the Diels–Alder cycloaddition reactions of furan with maleic anhydride and maleimide

Abstract

AbstractIn quantum chemical calculations, the Diels–Alder (DA) cycloaddition reaction of furan with maleic anhydride favors the endo‐isomer kinetically in the gas phase. This preference, however, changes in favor of the exo‐isomer on inclusion of solvent effects. For example, in acetonitrile, the exo‐isomer was calculated to form twice as fast as the endo‐isomer at room temperature, an observation that corroborates well with the experiments. The free energy change of the reaction is such that it allows faster reversal of the endo‐isomer to the reactants in an equilibrium process and, thus, the predominance of the more stable exo‐isomer eventually. The reaction of furan with maleimide is similar to that with maleic anhydride. However, it predominantly favors endo‐selectivity at temperatures below 320 K, which is also in excellent agreement with the experimental studies of temperature dependence of this DA reaction. Further, a gedanken calculation of the DA reaction of furan with cyclopropene has been investigated to delineate the effect of the retro‐pathway on stereoselectivity.