In imidazolium ILs, the negative charge delocalization induced by multiple electron-withdrawing cyano groups can be useful in regulating the microscopic environment in imidazolium ILs. For this anion design, the ion–counterion (solvent–solvent) interaction is weakened, the ion–solute (solvent–solute) interaction is facilitated, and the bulkiness of the anion is increased. The electrostatic interaction with the cation has a strong effect on the ion states of the ILs and the stereoselectivity in the Diels–Alder reaction. These regulation methods potentially have wide applications to various useful reactions using ILs.