Abstract
Chiral imidazolium salts that can be classified as ionic liquids (ILs) were derived
from the ‘chiral pool’ precursors camphor, β-pinene, and tartaric acid. ILs containing
chiral imidazolium cations as well as chiral anions were synthesized. Furthermore,
the anion of the IL 1-methyl-3-[(S)-2′-methylbutyl]imidazolium tosylate was substituted on an ion-exchange resin for
the chiral (S)-camphorsulfonate anion thus forming the first well-characterized ‘doubly chiral’
IL.
Keywords
imidazolium salts - ionic liquids - chiral anions, chiral cations
References
For reviews on ionic liquids, see:
<A NAME="RM00705SS-1A">1a</A>
Song CE.
Chem. Commun.
2004,
1033
<A NAME="RM00705SS-1B">1b</A>
Dupont J.
de Souza RF.
Suarez PAZ.
Chem. Rev.
2002,
102:
3667
<A NAME="RM00705SS-1C">1c</A>
Sheldon R.
Chem. Commun.
2001,
2399
<A NAME="RM00705SS-1D">1d</A>
Wasserscheid P.
Keim W.
Angew. Chem. Int. Ed.
2000,
39:
3772
<A NAME="RM00705SS-1E">1e</A>
Welton T.
Chem. Rev.
1999,
99:
2071
<A NAME="RM00705SS-2A">2a</A>
Arduengo AJ.
Harlow RL.
Kline M.
J. Am. Chem. Soc.
1991,
113:
361
<A NAME="RM00705SS-2B">2b</A>
Herrmann WA.
Köcher C.
Angew. Chem., Int. Ed. Engl.
1997,
36:
2162
<A NAME="RM00705SS-3A">3a</A>
Baudequin C.
Baudoux J.
Levillain J.
Cahard D.
Gaumont A.-C.
Plaquevent J.-C.
Tetrahedron: Asymmetry
2003,
14:
3081 ; and references therein
<A NAME="RM00705SS-3B">3b</A>
Levillain J.
Dubant G.
Abrunhosa I.
Gulea M.
Gaumont A.-C.
Chem. Commun.
2003,
2914
<A NAME="RM00705SS-4A">4a</A>
Perry MC.
Cui X.
Powell MT.
Hou D.-R.
Reibenspies JH.
Burgess K.
J. Am. Chem. Soc.
2003,
125:
113
<A NAME="RM00705SS-4B">4b</A>
Seo H.
Park H.-J.
Kim BY.
Lee JH.
Son SU.
Chung YK.
Organometallics
2003,
22:
618
<A NAME="RM00705SS-4C">4c</A>
Seiders TJ.
Ward DW.
Grubbs RH.
Org. Lett.
2001,
3:
3325
<A NAME="RM00705SS-4D">4d</A>
Herrmann WA.
Goossen LJ.
Köcher C.
Artus GRJ.
Angew. Chem., Int. Ed. Engl.
1996,
35:
2805
For non-racemic chiral imidazolium salts, see:
<A NAME="RM00705SS-5A">5a</A>
Tosoni M.
Laschat S.
Baro A.
Helv. Chim. Acta
2004,
87:
2742
<A NAME="RM00705SS-5B">5b</A>
Jodry JJ.
Mikami K.
Tetrahedron Lett.
2004,
45:
4429
<A NAME="RM00705SS-5C">5c</A>
Bao W.
Wang Z.
Li Y.
J. Org. Chem.
2003,
68:
591
<A NAME="RM00705SS-5D">5d</A>
Ishida Y.
Miyauchi H.
Saigo K.
Chem. Commun.
2002,
2240
<A NAME="RM00705SS-5E">5e</A>
Earle MJ.
McCormac PB.
Seddon KR.
Green Chem.
1999,
1:
23
To the best of our knowledge only two examples thereof exist:
<A NAME="RM00705SS-6A">6a</A>
Ref. 5e.
<A NAME="RM00705SS-6B">6b</A>
Fukumoto K.
Yoshizawa M.
Ohno H.
J. Am. Chem. Soc.
2005,
127:
2398
<A NAME="RM00705SS-7">7</A>
Horwath J.
Al-Hashimy NA.
Tetrahedron Lett.
2001,
42:
5777
<A NAME="RM00705SS-8">8</A>
Presumably, methylimidazolium formation is due to Hoffmann type elimination. NMR spectroscopy
of crude reaction mixtures indicated concomitant alkene formation.
<A NAME="RM00705SS-9">9</A> For di- and polycationic ILs, see:
Lall SI.
Mancheno D.
Castro S.
Behaj V.
Cohen JI.
Engel R.
Chem. Commun.
2000,
2413
For chiral dicationic imidazolium salts, see:
<A NAME="RM00705SS-10A">10a</A>
Clyne DS.
Jin J.
Genest E.
Gallucci JC.
Rajan Babu TV.
Org. Lett.
2000,
2:
1125
<A NAME="RM00705SS-10B">10b</A>
Marshall C.
Ward MF.
Harrison WTA.
Tetrahedron Lett.
2004,
45:
5703
<A NAME="RM00705SS-11">11</A>
Howarth J.
Hanlon K.
Fayne D.
McCormac P.
Tetrahedron Lett.
1997,
38:
3097
<A NAME="RM00705SS-12">12</A>
The interchange of anions of similar size, such as OTf-, sulfonates, or BF4
- in the usual CH2Cl2-H2O system is not possible.
<A NAME="RM00705SS-13">13</A>
We found that the classical ILs BMI·BF4 or BMI·PF6 are obtained in a purer form by the ion-exchange method than by the standard CH2Cl2-H2O extraction method.
<A NAME="RM00705SS-14">14</A>
Kagan HB.
Dang T.-P.
J. Am. Chem. Soc.
1972,
94:
6429
<A NAME="RM00705SS-15">15</A>
Fieser L. F.
Fieser M. A.
Reagents for Organic Synthesis, Vol. 1
Wiley;
New York:
1967.
p.1179