Kaoru Nobuoka

Solute–solvent interactions in imidazolium camphorsulfonate ionic liquids

We directly observe the interaction between 1-butyl-3-methylimidazolium (bmim) or 1-butyl-2,3-dimethylimidazolium (bm(2)im) and the solute, ethyl acrylate (EA), which is the popular dienophile in the Diels-Alder reaction and an H-bonding acceptor, by using specially designed electrospray mass spectrometry. In imidazolium ionic liquids, cation-anion interactions are controlled by selecting the appropriate anion, and the naked C(2)-H of imidazolium, which loosely interacts with its counterion, can readily interact with an H-bonding acceptable solute. The ion-counterion (solvent-solvent) interaction affects the ion-solute (solvent-solute) interaction. This relation is one of the key criteria for selecting the cation-anion combination in tailoring ILs.

Stereoselectivity of the Diels–Alder reaction in ionic liquids with cyano moieties: effect of the charge delocalization of anions on the relation of solvent–solvent and solute–solvent interactions

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.

Proline Based Chiral Ionic Liquids for Enantioselective Michael Reaction

Chiral ionic liquids, starting from (S)-proline, have been prepared and evaluated the ability of a chiral catalyst. In Michael reaction of trans-β-nitrostyrene and cyclohexanone, all the reactions were carried out under homogeneous conditions without any solvent except for excess cyclohexanone. The chiral ionic liquid catalyst with the positive charge delocalized bulky pyrrolidinium cation shows excellent yields (up to 92%), diastereoselectivities (syn/anti = 96/4), and enantioselectivities (up to 95% ee) and could be reused at least three times without any loss of its catalytic activity. Such results demonstrated a promising new approach for green and economic chiral synthesis by using the chiral ionic liquids as a chiral catalyst and a chiral medium.

A simple method for efficient synthesis of tetrapyridyl-porphyrin using Adler method in acidic ionic liquids

We investigated the preparation of tetraphenylporphyrin (TPP) using the several acidic ionic liquids, [HC4im][X] (X− = CF3SO3−, ClO4−, Cl−, CF3CO2−, and BF4−), as acid catalytic media. For such ionic liquids, the anion (X−) of [HC4im][X] is related to the acidity of the ionic liquid, and affects porphyrin formation. This synthetic method using acidic ionic liquids can also be applied to other meso-substituted phenyl porphyrins and 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (TPyP), which has 4-pyridyl moieties at four meso positions. In [HC4im][CF3CO2], TPyP could be obtained in 11% yield, and the [HC4im][CF3CO2] could be reused at least 3 times without any loss of its catalytic activity. The TPyP synthesis methodology using acidic ionic liquids can remove the ionic liquids from TPyP by easy filtration in contrast to the traditional Alder method, which needs vacuum distillation or liquid–liquid extraction for removing propionic acid. Our proposed porphyrin preparation method using the acidic ionic liquids potentially have wide applications to various useful porphyrin analogues.