Synthesis of novel chiral ionic liquids and their phase behavior in mixtures with smectic and nematic liquid crystals

Article abstract of DOI:10.1002/hlca.200490247

Alkylation of 1-alkyl-1H-imidazoles 2a-f with citronellyl bromide 1b opens access to chiral 1H-imidazolium bromides 3a-f (Scheme 1). A similar strategy yielded the chiral pyridinium ionic liquid 6 (Scheme 2). Dialkylation of 1H-imidazole (7) gave the C₂-symmetric 1,3-dicitronellyl-1H- imidazolium bromide (8) (Scheme 3). Differential scanning calorimetry and optical polarizing microscopy revealed smectic mesophases for 1-citronellyl-3-tetradecy-1H-limidazolium bromide (3e) and 1- citronellylpyridinium bromide (6) (Table). In binary mixtures with smectic and nematic liquid crystals 9 and 10, 1-citronellyl-3-methyl-1H-imidazolium bromide (3a) behaved differently. Increasing quantities of 3a cause a decrease of the smectic-phase width for the mixture 3a/9 (Fig. 3), whereas the phase width of the nematic phase for 3a/10 remained nearly constant (Fig. 4).

Full text of DOI:10.1002/hlca.200490247

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Helvetica Chimica Acta Vol. 87(2004)
Synthesis of Novel Chiral Ionic Liquids and Their Phase Behavior in Mixtures
with Smectic and Nematic Liquid Crystals
by Martin Tosoni, Sabine Laschat*, and Angelika Baro
Institut f¸r Organische Chemie, Universit‰t Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart
(fax: ‡49-(0)711-685-4285; e-mail: sabine.laschat@oc.uni-stuttgart.de)
Alkylation of 1-alkyl-1H-imidazoles 2a f with citronellyl bromide 1b opens access to chiral 1H-
imidazolium bromides 3a f (Scheme 1). A similar strategy yielded the chiral pyridinium ionic liquid 6
(Scheme 2). Dialkylation of 1H-imidazole (7) gave the C2-symmetric 1,3-dicitronellyl-1H-imidazolium bromide
(8) (Scheme 3). Differential scanning calorimetry and optical polarizing microscopy revealed smectic
mesophases for 1-citronellyl-3-tetradecy-1H-limidazolium bromide (3e) and 1-citronellylpyridinium bromide
(6) (Table). In binary mixtures with smectic and nematic liquid crystals 9 and 10, 1-citronellyl-3-methyl-1H-
imidazolium bromide (3a) behaved differently. Increasing quantities of 3a cause a decrease of the smectic-
phase width for the mixture 3a/9 (Fig. 3), whereas the phase width of the nematic phase for 3a/10 remained
nearly constant (Fig.4).
Introduction. Since the seminal work by Seddon and co-workers [1], Levelut and
co-workers [2], Haramoto and co-workers [3], Kresse and co-workers [4], and others
[5], it has been recognized that room temperature ionic liquids are capable of forming
thermotropic mesophases. However, the issue of chiral mesogenic ionic liquids and
their miscibility with common liquid crystals has been only briefly explored [7][8]. This
might be due to the fact that the introduction of complex stereocenters often increases
the melting point [9]. The lack of suitable chiral ionic liquids with mesogenic properties
prompted us to investigate this subject in more detail. We anticipated that the
combination of alkyl-1H-imidazolium salts with chiral moieties derived from citronel-
lol (ˆ 3,7-dimethyloct-6-en-1-ol) should meet the requirements of chiral mesogenic
compounds and should generate suitable chiral dopants. The results towards this goal
are reported below.
Results and Discussion. The synthesis of chiral 1H-imidazolium salts 3 is outlined
in Scheme 1. Following a method by Sankaranarayanan and Chattopadhyay [10], (3R)-
citronellol (1a) was treated with PPh3 and Br2 in CH2Cl2 at room temperature to give
the corresponding bromide 1b in 68% yield, whereas the use of PBr3 and pyridine [11]
afforded only 25% of 1b. Bromide 1b was heated with 1-alkyl-1H-imidazoles 2a f for
several days, and, after evaporation of volatile starting materials, the 1H-imidazolium
salts 3a f were isolated as analytically pure compounds. Metathesis of 1H-imidazolium
bromides 3a and 3d with sodium tetrafluoroborate in acetone yielded the correspond-
ing salts 4a and 4d (Scheme 1).
In addition, pyridinium salt 6 was prepared in 98% yield by heating pyridine (5)
with bromide 1b at 458 for 4 d (Scheme 2).
¹ 2004 Verlag Helvetica Chimica Acta AG, Z¸rich

Helvetica Chimica Acta Vol. 87(2004)
2743
Scheme 1
Scheme 2
Dzyuba and Bartsch have reported surprising phase behavior of C2-symmetric 1H-
imidazolium salts with unbranched alkyl chains [12]. We assume that the phase
behavior of a C2-symmetric chiral 1H-imidazolium salt may differ from its C1-
symmetric counterparts, and thus, we prepared the 1,3-di-citronellyl-1H-imidazolium
bromide (8) from 1H-imidazole (7) by deprotonation with tetrabutylammonium
hydroxide and subsequent treatment with 2 equiv. of the chiral bromide 1b to give 8 in
58% yield (Scheme 3).
Scheme 3
The phase behavior of compounds 3a f, 4a,d, 6, and 8 was studied by both
differential scanning calorimetry (DSC) and optical polarizing microscopy. The results
from DSC measurements are summarized in the Table. The 1H-imidazolium bromides
3a c with a methyl, butyl, or hexyl side chain display only glass transitions during
repeated heating and cooling cycles. For the dodecyl-substituted compound 3d, a glass
transition as well as a crystalline-to-isotropic transition at 68 was observed. However, a
crystalline-to-mesogenic-phase transition at 98 and a mesogenic-phase-to-isotropic
transition at 458 were found for the tetradecyl-substituted salt 3e. In contrast to the
results of Seddon and co-workers [1], chiral 1H-imidazolium bromides with more than

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Helvetica Chimica Acta Vol. 87(2004)
Table. Phase-Transition Temperatures and Enthalpies of Chiral 1H-Imidazolium and Pyridinium Ionic Liquids
3, 4, 6, and 8
R
X
Tg
[8]
DCp
[kJ molÀ1
Tm
[8]
DH
[kJ molÀ1
Tc
[8]
DH
[kJ molÀ1
]
]
]
3a
3b
3c
3d
3e
3f
4a
4d
6
Me
Br
Br
Br
Br
Br
Br
BF4
BF4
Br
À 57101
À 52
C4H9
C6H13
C12H25
C14H29
C18H37
Me
159
539
À 57146
À 70
6a)
9b)
4.46
13.1
45c)
41a)
1.26
42.8
À 73
144
C12H25
728.1
À 47132
À 56
8
Br
200
a) Cr! I transition. b) Cr! mesogenic-phase transition. c) Mesogenic phase ! I transition.
14 C-atoms in the side chain, such as octadecyl derivative 3f, did not give a smectic A
phase but revealed only isotropic melting.
Replacing bromide by tetrafluoroborate as counterion resulted in minor changes of
the phase behavior in the case of 4a. Tetrafluoroborate 4d with the dodecyl side chain,
however, displayed isotropic melting instead of a glass transition as observed for the
corresponding bromide 3d. For both chiral pyridinium bromide 6 and the C2-
symmetrical 1H-imidazolium bromide 8, only a glass transition was detected. Under the
optical polarizing micro-scope, tetradecyl derivative 3e displayed textures of a
mesophase upon cooling from the isotropic liquid (Fig. 1).
Fig. 1. Texture of citronellyl-1H-imidazolium bromide 3e as seen between crossed polarizers at 248 upon cooling
from the isotropic liquid (magnification 100 Â )

Helvetica Chimica Acta Vol. 87(2004)
2745
In contrast to the DSC curves of 1-citronellylpyridinium bromide (6), showing only
a glass transition, a fan-shaped smectic texture was observed under the microscope
(Fig. 2). Unfortunately, we did not obtain suitable X-ray-diffraction results from the
smectic derivatives 3e and 6 due to their extremely high viscosity.
Fig. 2. Texture of pyridinium bromide 6 as seen between crossed polarizers at À568 upon cooling from the
isotropic liquid (magnification 200 Â )
Although the citronellyl moiety did not lead to the formation of chiral mesophases,
we investigated the possibility of using short-chain derivative 3a (R ˆ Me) as a chiral
dopant. Contact preparation with the known smectic mesogen 9 [1] and the nematic
mesogen 10 revealed complete miscibility. Thus, binary mixtures of 3a and 9 were
studied by DSC. The resulting phase diagram is depicted in Fig. 3. With increasing
amounts of chiral dopant 3a, the width of the smectic A phase steadily decreased. In the
case of almost equimolar quantities of 3a and 9, only melting was found. No additional
smectic C* phase could be detected.
Finally, binary mixtures of 1H-imidazolium bromide 3a and the nematic benzyli-
deneaniline 10 were investigated. As can be seen from Fig. 4, the phase width of the
nematic phase remained almost constant over an extended range (x(3a) ˆ 0 0.7), and
again no chiral mesophase was observed.

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Helvetica Chimica Acta Vol. 87(2004)
Fig. 3. Phase diagram of a binary mixture of (R)-1-citronellyl-3-methyl-1H-imidazolium bromide (3a) and the
known smectic mesogen 1-dodecyl-3-methyl-1H-imidazolium bromide 9
Fig. 4. Phase diagram of a binary mixture of (R)-1-citronellyl-3-methyl-1H-imidazolium bromide (3a) and the
nematic mesogen 4-butyl-N-[(1E)-(4-methoxyphenyl)methylene]benzenamine (10)
Conclusions. Chiral citronellyl-derived ionic liquids 3 with potential mesomorphic
properties are conveniently available. However, the relationship between molecular
structure (chain length, counterion, symmetry) and mesomorphic properties is not
easily deduced as compared to the unbranched analogues. Thus, further investigations

Helvetica Chimica Acta Vol. 87(2004)
2747
are necessary to design chiral mesomorphic ionic liquids suitable for applications in
liquid-crystal chemistry.
Generous financial support by the Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Industrie,
and the Ministerium f¸r Wissenschaft, Forschung und Kunst des Landes Baden-W¸rttemberg is gratefully
acknowledged.
Experimental Part
General. FT-IR Spectra: vƒ in cmÀ1. NMR Spectra: Bruker AC-250 Fand Bruker ARX-500; d in ppm and J in
Hz. FAB-MS: m/z (rel. %).
1-Butyl-1H-imidazole (2b). To a soln. of 7 (27.2 g, 0.39 mol) in MeOH (56 ml), aq. 10n NaOH (52 ml) was
added. The stirred mixture was heated to 708, and 1-bromobutane (54.8 ml, 0.52 mol) was added dropwise over
3 h. After 2 h at r.t., the mixture was evaporated, the residue taken up in CHCl3 (60 ml) and separated from
precipitated NaBr, the org. soln. dried (Na2SO4) and evaporated, and the residue distilled under vacuum
through a Vigreux column (20 cm): 2b (29.0 g, 60%). B.p. 948/8 Torr. 1H-NMR (250 MHz, CDCl3): 0.94 (t, J ˆ
7.3, Me(4')); 1.31(m, CH2(3')); 1.76 (m, CH2(2')); 3.93 (t, J ˆ 7.1, CH (1')); 6.90 (s, HÀC(5)), 7.05 (s, HÀC(4)),
2
7.46 (s, HÀC(2)). 13C-NMR (63 MHz, CDCl3): 13.5 (Me(4')); 19.7(C(3 ')); 33.1 (C(2')); 46.7(C(1 ')); 118.8
(C(4)); 129.3 (C(5)); 137.1 (C(2)).
Preparation of 2c f: General Procedure. A soln. of 7 (10 mmol) in abs. THF (8 ml) was added to a stirred
soln. of NaH (1.5 equiv. of a 55% suspension in oil) and abs. THF (4 ml). After stirring at r.t. for 1 h, a soln. of
the 1-bromoalkane (1.0 equiv.) in abs. THF (6 ml) was added followed by Bu4NI (ca. 0.03 equiv.). The mixture
was stirred under N2 at r.t. for the given times, and filtered. The filtrate was evaporated and the residue
fractionally distilled under vacuum through a Vigreux column (20 cm).
1-Hexyl-1H-imidazole (2c): Reaction time 16 h, yield 2.60 g (10%). Colorless liquid. B.p. 948/4 Torr.
1H-NMR (250 MHz, CDCl3): 0.87( t, J ˆ 6.1, Me(6')); 1.24 1.32 (m, CH2(3'), CH2(4'), CH2(5')); 1.70 1.80 (m,
CH2(2')); 3.91 (t, J ˆ 7.2, CH (1')); 6.89 (s, HÀC(5)); 7.04 (s, HÀC(4)); 7.44 (s, HÀC(2)).
2
1-Dodecyl-1H-imidazole (2d): Reaction time 22 h, yield 6.0 g (62%). Colorless liquid. B.p. 1258/0.08 Torr.
1H-NMR (250 MHz, CDCl3): 0.87( t, J ˆ 6.1, Me(12')), 1.25 (m, CH2(3') to CH2(11')); 1.77 (m, CH2(2')); 3.92 (t,
J ˆ 7.1, CH (1')); 6.90 (s, HÀC(5)); 7.04 (s, HÀC(4)); 7.44 (s, HÀC(2)). 13C-NMR (63 MHz, CDCl3): 14.1
2
(Me(12')); 20.8 (C(11')); 22.7 31.9 (C(2 ') to C(10')); 47.1 (C(1')); 118.8 (C(4)); 129.4 (C(5)); 137.1 (C(2)).
1-Tetradecyl-1H-imidazole (2e): Reaction time 23 h, yield 6.47g (66%). Colorless liquid. B.p. 142 8/0.001
Torr. 1H-NMR (250 MHz, CDCl3): 0.96 (t, J ˆ 7.2, Me(14')); 1.31 (m, CH2(3') to CH2(13')); 1.77 (m, CH2(2'));
3.91 (t, J ˆ 7.0, CH (1')); 6.90 (s, HÀC(5)); 7.05 (s, HÀC(4)); 7.46 (s, HÀC(2)).
2
1-Octadecyl-1H-imidazole (2f): Reaction time 24 h, yield 3.28 g (55%). Pale yellow solid, 1108/0.01 Torr.
1H-NMR (250, CDCl3): 0.88 (t, J ˆ 6.6, Me(18')), 1.25(m, CH2(3') to CH2(17')); 1.77 (m, CH2(2')); 3.92 (t, J ˆ 7.1,
CH2(1')); 6.90 (s, HÀC(5)); 7.05 (s, HÀC(4)); 7.47 (s, HÀC(2)). 13C-NMR (63 MHz, CDCl3): 14.1 (Me(18'));
22.7(C(17 ')); 26.6 31.9 (C(2') to C(16')); 47.1 (C(1')); 118.8 (C(4)); 129.3 (C(5)); 137.1 (C(2)).
Preparation of 3a f: General Procedure. A soln. of 1b (0.22 g, 1.0 mmol) and the respective 1-alkyl-1H-
imidazole 2 (1.0 mmol) was heated at 408 for 5 d. Removal of volatile unreacted starting materials at 408/0.1
0.001 Torr for 2 d gave products 3.
1-[(3R)-3,7-Dimethyloct-6-enyl]-3-methyl-1H-imidazolium Bromide (3a): Yield 1.31 g (78%). Pale yellow
viscous oil. [a]2D2 ˆ À1.4 (c ˆ 1.00, CHCl3). FT-IR: 3129m and 3052m (CÀH, arom.), 2960s, 2916s and 2853s
(CÀH, aliph.), 1568m, 1452m, 1378m, 1168vs, 1117w, 1019w, 985w, 828m, 7 52m, 654m. 1H-NMR (500 MHz,
CDCl3): 0.90 (d, J ˆ 6.7, Me(3')); 1.19 1.79 (m, CH2(2'), CH2(4')); 1.59 (s, Me(8')); 1.67( s, Me(7')); 1.91 2.03
(m, HÀC(3'); CH2(5')); 4.15 (s, NMe); 4.29 4.39 (m, CH2(1')); 5.05 (t, J ˆ 6.9, HÀC(6')); 7.46 (s, HÀC(5)); 7.70
(s, HÀC(4)); 10.40 (s, HÀC(2)). 13C-NMR (125 MHz, CDCl3): 17.8 (MeÀC(7')); 19.1 (MeÀC(3')); 25.2 (C(5'));
25.7(C(8 ')); 29.9 (C(3')); 36.7(C(2 ')); 36.8 (MeN); 37.4 (C(4')); 48.4 (C(1')); 121.9 (C(5)); 123.9 (C(4));124.0
‡
‡
‡
(C(6')); 131.8, (C(7')); 137.0 (C(2)). FAB-MS: 521 (5, C H50BrN4 ), 221 (100, M ), 83 (7, CH7N2 ), 69 (2,
28
4
‡
‡
C3H5N2 ), 41 (2, C2H3N ). Anal. calc. for C14H25BrN2 (301.27): C 55.81, H 8.36, Br 26.52, N 9.30; found: C 55.68,
H 8.31, Br 26.52, N 9.18.
1-Butyl-3-[(3R)-3,7-dimethyloct-6-enyl]-1H-imidazolium Bromide (3b): Yield 1.20 g (46%). Pale yellow
viscous oil. [a]2D2 ˆ À2.2 (c ˆ 1.00, CHCl3). FT-IR: 3129m and 3050m (CÀH, arom.), 2956s, 2924s and 2856s
(CÀH, aliph.), 1562s, 1455s, 1378s, 1163vs, 1118w, 1023w, 985w, 829m, 7 7m5, 645m. 1H-NMR (500 MHz,
CDCl3): 0.97( t, J ˆ 7.4, Me(4'')); 0.99 (d, J ˆ 6.6, MeÀC(3')); 1.19 1.80 (m, CH2(2'), CH2(4'), CH2(3'')); 1.59 (s,
Me(8')); 1.67( s, MeÀC(7')); 1.90 2.05 (m, HÀC(3'), CH2(5'), CH2(2'')); 4.32 4.43 (m, CH2(1'), CH2(1''));
5.05 (dt, J ˆ 1.1, 6.4, HÀC(6')); 7.52 (t, J ˆ 1.7, HÀC(5)); 7.64 (t, J ˆ 1.5, HÀC(4)); 10.54 (s, HÀC(2)). 13C-NMR

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Helvetica Chimica Acta Vol. 87(2004)
(125 MHz, CDCl3): 13.5 (Me(4'')); 17.7 (MeÀC(7')); 19.1 (MeÀC(3')); 19.5 (C(3'')); 25.3 (C(5')); 25.7(C(8 '));
30.0 (C(3')); 32.2 (C(2'')); 36.7(C(2 ')); 37.4 (C(4')); 48.4 (C(1')); 49.8 (C(1'')); 122.0 (C(5)); 122.4 (C(4)); 124.1
‡
‡
‡
(C(6')); 131.7(C(7 ')); 137.0 (C(2)). FAB-MS: 605 (2, C H62BrN4 ), 263 (100, M ), 69 (5, C3H5N2 ), 41 (2,
34
‡
C2H3N ). Anal. calc. for C17H31BrN2 (343.27): C 59.47, H 9.10, Br 23.27, N 8.16; found: C 58.99, H 9.08, Br 23.26,
N 8.12.
3-[(3R)-3,7-Dimethyloct-6-enyl]-3-hexyl-1H-imidazolium Bromide (3c): Yield 1.58 g (84%). Pale yellow
viscous oil. [a]2D2 ˆ À1.1 (c ˆ 1.00, CHCl3). FT-IR: 3128m and 3050m (CÀH, arom.), 2958s, 2926s and 2871s
(CÀH, aliph.), 1562s, 1456s, 1377s, 1164vs, 1116w, 1022w, 985w, 948w, 827m, 7 52m, 633m. 1H-NMR (500 MHz,
CDCl3): 0.87( t, J ˆ 7.0, Me(6'')); 0.99 (d, J ˆ 6.7, MeÀ(3')); 1.19 1.80 (m, CH2(2'), CH2(4'), CH2(3''), CH2(4''),
CH2(5'')); 1.59 (s, Me(8')); 1.67( s, MeÀ(7')); 1.91 2.03 (m, HÀC(3'), CH2(5'), CH2(2'')); 4.32 4.43 (m,
CH2(1'), CH2(1'')); 5.05 (dt, J ˆ 1.1, 6.4, HÀC(6')); 7.53 (t, J ˆ 1.7, HÀC(5)); 7.61 (t, J ˆ 1.7Hz, H ÀC(4)); 10.56
(s, HÀC(2)). 13C-NMR (125 MHz, CDCl3): 14.3 (Me(6'')); 18.1 (MeÀC(7')); 19.4 (MeÀC(3')); 22.7(C(5 ''));
25.6 (C(5')); 26.0 (C(8')); 26.2 (C(3'')); 30.3 (C(3')); 30.6 (C(4'')); 31.4 (C(2'')); 37.0 (C(2')); 37.7 (C(4')); 48.5
(C(1')); 50.4 (C(1'')); 122.4 (C(5)); 122.7(C(4)); 124.4 (C(6 ')); 132.0 (C(7')); 137.4 (C(2)). FAB-MS: 661 (4,
‡
‡
‡
‡
‡
C38H70BrN4 ), 291 (100, M ), 221 (2, C14H25N2 ), 69 (4, C3H5N2 ), 41 (2, C2H3N ). Anal. calcd. for C19H35BrN2
(371.40): C 61.44, H 9.50, Br 21.51, N 7.54; found: C 61.21, H 9.69, Br 21.41, N 7.32.
1-[(3R)-3,7-Dimethyloct-6-enyl]-3-dodecyl-1H-imidazolium Bromide (3d): Yield 1.94 g (85%). Pale
yellow viscous oil. [a]2D2 ˆ À1.0 (c ˆ 1.00, CHCl3). 1H-NMR (250 MHz, CDCl3): 0.88 (t, J ˆ 6.6, Me(12''));
0.99 (d, J ˆ 6.5, MeÀC(3')); 1.18 1.40 (m, CH2(2'), CH2(4'), CH2(3'') to CH2(11'')); 1.59 (s, Me(8')); 1.67( s,
MeÀC(7')); 1.92 2.00 (m, HÀC(3'), CH2(5'), CH2(2'')); 4.34 4.41 (m, CH2(1'), CH2(1'')); 5.05 (t, J ˆ 1.3,
HÀC(6')); 7.44 (t, J ˆ 1.8, HÀC(5)); 7.48 (t, J ˆ 1.8, HÀC(4)); 10.55 (s, HÀC(2)). 13C-NMR (63 MHz, CDCl3):
14.1 (Me(12'')); 17.7 (MeÀC(7')); 19.1 (MeÀC(3')); 22.7(C(11 '')); 25.3 (C(5')); 25.7(C(8 ')); 26.3 (C(3''));
29.0 30.4 (C(4'') to C(10'')); 31.9 (C(2'')); 36.7(C(2 ')); 37.4 (C(4')); 48.4 (C(1')); 50.2 (C(1'')); 121.6 (C(5));
‡
‡
122.1 (C(4)); 124.1 (C(6')); 131.8 (C(7')); 137.3 (C(2)). FAB-MS: 375 (100, M ), 69 (7, CH5N2 ), 41 (3,
3
‡
C2H3N ). Anal. calc. for C25H37BrN2 (455.56): C 65.91, H 10.40, Br 17.54, N 6.15; found: C 66.49, H 10.60,
Br 15.48, N 5.98.
1-[(3R)-3,7-Dimethyloct-6-enyl]-3-tetradecyl-1H-imidazolium Bromide (3e): Yield 2.28 g (94%). Pale
yellow viscous oil. [a]2D2 ˆ À0.9 (c ˆ 1.00, CHCl3). 1H-NMR (500 MHz, CDCl3): 0.88 (t, J ˆ 6.9, Me(14'')); 0.99
(d, J ˆ 6.7, MeÀC(3')); 1.20 1.42 (m, CH2(2'), CH2(4'), CH2(3'') to CH2(13'')); 1.59 (s, Me(8')); 1.67( s,
MeÀC(7')); 1.91 2.02 (m, HÀC(3'), CH2(5'), CH2(2'')); 4.32 4.42 (m, CH2(1'), CH2(1'')); 5.05 (t, J ˆ 7.0,
HÀC(6')); 7.48 (s, HÀC(5)); 7.52 (s, HÀC(4)); 10.53 (s, HÀC(2)). 13C-NMR (125 MHz, CDCl3): 14.4
(Me(14'')); 18.0 (MeÀC(7')); 19.5 (MeÀC(3')); 23.0 (C(13'')); 25.6 (C(5')); 26.0 (C(8')); 26.6 (C(3'')); 29.3
30.7(C(4 '') to C(12'')); 32.2 (C(2'')); 37.0 (C(2')); 37.7 (C(4')); 48.7(C(1 ')); 50.5 (C(1'')); 122.3 (C(5)); 122.5
‡
‡
‡
(C(4)); 124.4 (C(6')); 132.0 (C(7')); 137.6 (C(2)). FAB-MS: 403 (100, M ), 69 (8, C3H5N2 ), 41 (3, C2H3N ).
Anal. calc. for C27H51BrN2 (483.61): C 67.06, H 10.63, Br 16.52, N 5.79; found: C 66.30, H 10.81, Br 15.41, N 5.40.
1-[(3R)-3,7-Dimethyloct-6-enyl]-3-octadecyl-1H-imidazolium Bromide (3f): Yield 1.94 g (72%). Pale
yellow viscous oil. [a]2D2 ˆ À0.4 (c ˆ 1.00, CHCl3). 1H-NMR (250 MHz, CDCl3): 0.88 (t, J ˆ 6.5, Me(18'')); 0.99
(d, J ˆ 6.5, MeÀ(3')); 1.25 1.48 (m, CH2(2'), CH2(4'), CH2(3'') to CH2(17'')); 1.59 (s, Me(8')); 1.67( s,
MeÀC(7')); 1.90 2.03 (m, HÀC(3'), CH2(5'), CH2(2'')); 4.34 4.40 (m, CH2(1'), CH2(1'')); 5.05 (t, J ˆ 7.1,
HÀC(6')); 7.39 (t, J ˆ 1.7, HÀC(5)); 7.42 (t, J ˆ 1.7, HÀC(4)); 10.64 (s, HÀC(2)). 13C-NMR (63 MHz, CDCl3):
14.1 (Me(18'')); 17.8 (MeÀC(7')); 19.1 (MeÀC(3')); 22.7(C(17 '')); 25.3 (C(5')); 25.7(C(8 ')); 26.3 (C(3''));
29.0 31.9 (C(4'') to C(16'')); 32.1 (C(2'')); 36.7(C(2 ')); 37.4 (C(4')); 48.5 (C(1')); 50.2 (C(1'')); 121.7(C(5));
121.9 (C(4)); 124.0 (C(6')); 131.8 (C(7')); 137.5 (C(2)). Anal. calc. for C H59BrN2 (539.72): C 68.99, H 11.02,
31
Br 14.80, N 5.19; found: C 67.18, H 11.11, Br 14.43, N 4.94.
Preparation of 4a,d: General Procedure. NaBF4 (0.19 g, 1.73 mmol) was added to a soln. of 3a or 3d
(1.73 mmol) in acetone (25 50 ml), and the mixture was stirred at r.t. for 2 h. Precipitated NaBr was filtered off,
and the filtrate was evaporated. The residue was taken up in CH2Cl2 and the soln. washed with H2O (2 Â 25 ml)
and evaporated. The residue was dried at r.t. 0.1 0.001 Torr for 4a. For 4d Et2O was added to the residue and the
mixture stored at À188 for 16 h. Et2O was decanted and the precipitated waxy solid was dried at r.t./0.1 0.001
Torr.
1-[(3R)-3,7-Dimethyloct-6-enyl]-3-methyl-1H-imidazolium Tetrafluoroborate (4a): Yield 0.51 g (98%).
[a]2D2 ˆ À1.2 (c ˆ 1.00, CHCl3). Anal. calc. for C14H25BF4N2 (308.17): C 54.56, H 8.18, N 9.09; found: C 54.57,
H 8.12, N 8.96.
1-[(3R)-3,7-Dimethyloct-6-enyl]-3-dodecyl-1H-imidazolium Tetrafluoroborate (4d). Yield 0.54 g (99%).
[a]2D2 ˆ À1.0 (c ˆ 1.00, CHCl3). Anal. calc. for C25H47BF4N2 (462.46): C 64.93, H 10.24, N 6.06; found: C 64.81,
H 10.27, N 6.05.

Helvetica Chimica Acta Vol. 87(2004)
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1-[(3R)-3,7-Dimethyloct-6-enyl]pyridinium Bromide (6). A soln. of 1b (1.10 g, 5.02 mmol) and pyridine (5,
0.40 g, 5.02 mmol) was heated at 458 for 4 d. Removal of volatile unreacted starting materials at 408/0.1 0.001
Torr for 2 d gave 6 (1.47g, 98%). Yellow viscous oil. [ a]2D2 ˆ À4.7( c ˆ 1.00, CHCl3). 1H-NMR (500 MHz,
CDCl3): 0.91 (d, J ˆ 6.7, MeÀ(3')); 1.20 1.48 (m, CH2(2'), CH2(4')); 1.59 (s, Me(8')); 1.67( s, MeÀC(7')); 1.89
2.11 (m, HÀC(3'), CH2(5')); 4.95 (m, HÀC(6')); 5.05 (m, CH2(1')); 8.24 (m, HÀC(3), HÀC(5)); 8.61 (m,
HÀC(4)); 9.55 (m, HÀC(2), HÀC(6)). 13C-NMR (125 MHz, CDCl3): 17.8 (MeÀC(7')); 19.3 (MeÀC(3')); 25.2
(C(5')); 25.7(C(8 ')); 30.0 (C(3')); 36.7(C(2 ')); 39.2 (C(4')); 60.6 (C(1')); 124.0 (C(6'));128.7(C(3), C(5)), 131.8
‡
‡
(C(4)); 145.2, 145.3 (C(2), C(6)). FAB-MS: 218 (100, M ), 80 (3, C5H6N ).
1,3-Bis[(3R)-3,7-dimethyloct-6-enyl]-1H-imidazolium Bromide (8). A soln. of 1b (2.20 g, 10.04 mmol), 7
(0.34 g, 5.02 mmol), and 40% Bu4NOH soln. (0.20 g) was stirred at r.t. for 3 d. The mixture was then evaporated
and washed with Et2O (3 Â 15 ml; removal of all starting materials). The viscous light yellow liquid was dried at
1
408/0.1 0.001 Torr for 2 d: 8 (1.25 g, 58%). Pale yellow oil. H-NMR (250 MHz, CDCl3): 0.98 (d, J ˆ 6.6, 6 H,
Me(3')); 1.15 1.56 (m, 8 H, CH2(2'), CH2(4')); 1.59 (s, 6 H, Me(8')); 1.67( s, 6 H, MeÀC(7')); 1.75 2.04 (m,
6 H, HÀC(3'), CH2(5')); 4.32 4.42 (m, 4 H, CH2(1')); 5.05 (t, J ˆ 7.1, 2 H, HÀC(6')); 7.51 (2s, HÀC(5),
HÀC(4)); 10.50 (s, HÀC(2)). 13C-NMR (63 MHz, CDCl3): 17.7 (MeÀC(7')); 19.1 (MeÀC(3')); 25.2 (C(5'));
25.7(C(8 ')); 29.7, 29.9 (C(3')); 36.7(C(2 ')); 37.4 (C(4')); 48.4 (C(1')); 122.0 (C(5)); 124.0 (C(6')); 124.1 (C(4));
‡
‡
‡
‡
131.7(C(7 ')); 137.0 (C(2)). FAB-MS: 345 (100,M ), 207(4, C 13H23N2 ), 69 (12, C3H5N2 ), 41 (4, C2H3N ). Anal.
calcd. for C23H41BrN2 (325.49): C 64.92, H 9.71, Br 18.78, N 6.58; found: C 61.50, H 9.30, Br 16.56, N 7.411).
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Received July 19, 2004
1
)
Due to the high viscosity of 8, trace amounts of solvent could not be completely removed, resulting in poor
elemental analysis. However, the H-NMR revealed a purity of ꢀ 98%.
1