Synthesis and properties of novel chiral-amine-functionalized ionic liquids

Article abstract of DOI:10.1016/j.tetasy.2006.07.018

A novel class of chiral-amine-functionalized ionic liquids (CAFILs) has been synthesized efficiently from natural amino acids, and their structures have been determined by spectroscopic analysis and low temperature X-ray diffraction analysis. The CAFILs have been characterized by physical properties such as melting point, glass transition temperature, thermal degradation and specific rotation. NMR measurements indicate that the CAFILs may be promising alternatives in the field of chiral discrimination.

Full text of DOI:10.1016/j.tetasy.2006.07.018

Tetrahedron: Asymmetry 17 (2006) 2028–2033
Synthesis and properties of novel chiral-amine-functionalized
ionic liquids
Shu-Ping Luo, Dan-Qian Xu, Hua-Dong Yue, Li-Ping Wang,
Wen-Long Yang and Zhen-Yuan Xu*
State Key Laboratory Breeding Base of Green Chemistry-Synthesis Technology, Zhejiang University of Technology,
Hangzhou 310014, China
Received 8 June 2006; accepted 18 July 2006
Abstract—A novel class of chiral-amine-functionalized ionic liquids (CAFILs) has been synthesized efficiently from natural amino acids,
and their structures have been determined by spectroscopic analysis and low temperature X-ray diffraction analysis. The CAFILs have
been characterized by physical properties such as melting point, glass transition temperature, thermal degradation and specific rotation.
NMR measurements indicate that the CAFILs may be promising alternatives in the field of chiral discrimination.
Ó 2006 Elsevier Ltd. All rights reserved.
1
. Introduction
hydroxyamination reactions of carbonyl compounds.7,8
Therefore, we designed a novel class of CILs with a chiral
amine base component being assembled to the imidazo-
lium-type ILs (Fig. 1). We envisioned that the incorpora-
tion of this chiral amine function should impart a
particularly effective asymmetric-induction pattern to the
ILs and, the resulting CILs could be more efficient than
conventional chiral solvents for the transfer of chirality in
asymmetric synthesis. On the other hand, these novel CILs
Ionic liquids (ILs) have attracted considerable attention as
environmentally friendly media for electrochemistry, chem-
ical engineering, materials science and especially for organ-
ic synthesis over the past decade. Recently, there have
been extensive studies of so-called task-specific ILs with
1
2
controllable physical and chemical properties. Among
these functionalized ILs, the chiral ionic liquids (CILs)
are of increasing importance due to their promising
applications for asymmetric synthesis, stereoselective poly-
merization, chiral chromatography, NMR chiral discrimi-
nation and liquid crystals. Seddon et al. reported the first
example of CILs with the chirality being brought by a lac-
9
can also be regarded as ionic-liquid-supported chiral
amines and, due to ILs’ peculiar properties, the resulting
chiral amines should hopefully play a significant role in
asymmetric organocatalysis in view of activity, enantio-
selectivity and stability of the catalysts. Herein, we report
3
tate anion in 1999. Ever since then, more novel CILs with
central, axial and planar chirality have been successively
4
,5
developed. However, CILs are still at a very much preli-
minary stage of development in view of their history and
applied scope.
NHR2
Y
6
N
N
R1
Since 2000, Chiral amines have been increasingly developed
as effective organocatalysts for direct asymmetric carbon–
carbon and carbon–heteroatom bond-forming reactions
involving enamine- and imine-catalysis, such as Aldol,
Mannich, Michael, a-amination, a-aminoxylation and a-
1
-3
1a-3a: R = Me, R = H, Y= Br, BF or PF
6
1
2
4
1
1
1
b-3b: R1= i-Pr, R2= H, Y= Br, BF4 or PF6
c-3c: R1= i-Bu, R2= H, Y=Br, BF4 or PF6
d-3d: R1= 2-Bu, R2= H, Y=Br, BF4 or PF6
1
e-3e: R1, R2= -(CH2)3-, Y=Br, BF4 or PF6
*
Corresponding author. Tel./fax: +86 571 88320066; e-mail: greenchem@
zjut.edu.cn
Figure 1. Chiral-amine-functionalized ionic liquids (CAFILs).
0957-4166/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2006.07.018

S.-P. Luo et al. / Tetrahedron: Asymmetry 17 (2006) 2028–2033
2029
the synthesis and properties of our novel chiral-amine-
functionalized ionic liquids (CAFILs).
As a preliminary study on the chiral discrimination ability
of the novel CAFILs, a mixture of 10 mg of racemic
Mosher’s acid with 40 mg of 2b in 0.5 mL water-saturated
1
9
CD Cl was probed by F NMR spectroscopy. The effect
2
2
2
. Results and discussion
of 2b caused a downfield shift (5.910 ppm) of the signal
corresponding to the CF group of the racemic acid, and
3
Synthesis of the novel CAFILs 1–3 commenced from
natural amino acids 4 [(S)-alanine, (S)-valine, (S)-leucine,
the split of the signal (J = 34.998 Hz) clearly illustrated
the existence of a strong diastereomeric interaction between
2b and Mosher’s acid (Fig. 3).
(
S)-isoleucine and (S)-proline] with fairly good overall
yields (66–71% yield). The key precursors 6 were synthe-
sized by reduction of the amino acid with NaBH /I
4
2
followed by a neutralization step and bromination with
3. Conclusions
PBr successively. CAFILs 1–3 were thus obtained after
3
N-alkylation of 6 to N-methylimidazole in refluxing MeCN
followed by neutralization with NaOH to give 1a–e, which
underwent anion metathesis using AgBF4 or KPF6 in
A novel class of chiral-amine-functionalized ionic liquids
have been designed and readily prepared in enantiopure
form from natural amino acids. Most of them show low
melting point or glass transition temperature, which makes
them potential alternatives for new chiral solvents. An
NMR chiral discrimination study indicates that these novel
CAFILs can provide a highly efficient chiral environment.
Their applications in enantioselective syntheses are under
investigation and will be reported in due course.
MeCN/H O at room temperature to afford 2a–e or 3a–e
2
(
Scheme 1). It is certain that the route is concise and
6
d
effective.
NHR2
COOH
NHR2
NaBH4/ I2
THF
1. HBr
OH
2. PBr3
R1
R1
_
>
>86%
_
88%
5
a-e
4. Experimental
4.1. General
4
a-e
NHR2
Br
N
N
N
NHR2
Br HBr
N
1
. CH3CN R1
. NaOH
>_ 92%
R1
All starting chemicals (include amino acids, NaBH , I ,
4
2
2
PBr3 and 1-methylimidazol) were commercial products
Aldrich or J&K chemical) of analytical grade. Organic
solvents were dried and purified before use by the usual
1a-e
6
a-e
(
AgBF4 or KPF6
CH3CN/H2O
NHR2
Y
N
1
13
19
N
methods. H NMR, C NMR and F NMR spectra were
1
R1
recorded on a Bruker ARX 400. Chemical shifts of H
and C were given in d relative to tetramethylsilane
TMS). Chemical shifts of F were given in d relative to
>
_95%
1
3
2
a-3e
19
(
4
a: R1= Me, R2= H; (S)-alanine
trifluoroacetic acid. The coupling constants J were given
in hertz. IR spectra were obtained on a Bruker EQUINOX
4
b: R1= i-Pr, R2= H; (S)-valine
4
c: R = i-Bu, R = H; (S)-leucine
1 2
55. Electrospray ionization (ESI) mass experiments were
4
4
d: R1= 2-Bu, R2= H; (S)-isoleucine
e: R1, R2= -(CH2)3-; (S)-proline
performed on a Finnigan LCQ Advantage. ESI-HRMS
spectra were obtained on a Bruker APEX III FTICR mass
spectrometer. Glass transition temperatures (T ) and melt-
Scheme 1. Synthesis of CAFILs 1–3.
g
ing points (T ) were recorded on a Thermal Analysis DSC
m
Q100 differential scanning calorimeter with heating rate at
All CAFILs were characterized by spectroscopic analysis
10 °C/min after initially cooling samples to ꢀ70 to ꢀ100 °C
1
13
of H NMR, C NMR, IR and MS. Furthermore, low
temperature X-ray diffraction analysis of a single crystal
under nitrogen. Decomposition temperatures (T ) were
dec
determined with a PerkinElmer Diamond thermogravimet-
ric/differential thermal analyzer module (TG/DTA) with
heating rate of 10 °C/min under nitrogen. Special rotation
values of the CAFILs in EtOH (c = 2) were obtained with
a Rudolph Autompol IV polarimeter.
1
0
of 1c’s hydrobromide salt unambiguously confirmed the
proposed chemical structure and (S)-configuration (Fig. 2).
Some representative properties of CAFILs are summarized
in Table 1. DSC measurements exhibited that these novel
CAFILs had a melting point (T ) or glass transition tem-
4.2. Experimental procedures
m
perature (T ) ranging from ꢀ49 to 145 °C. CAFILs bearing
g
ꢀ
BF anion had T /T values lower than those of other
4.2.1. General procedure for the synthesis of compounds
5. To a solution of NaBH (19.27 g, 0.5 mol) and (S)-
4
m
g
ꢀ
CAFILs, whereas CAFILs bearing Br anion had higher
values. TG determinations revealed that all CAFILs
had good thermal stabilities up to at least 210 °C. In addi-
tion, all CAFILs showed a trend of being more miscible in
polar solvents and much more immiscible in non-polar
solvents than the related non-functionalized imdazolium-
type ILs.
4
amino acids 4 (0.2 mol) in dry THF was dropped I2
(88.80 g, 0.35 mol)/THF solution at room temperature
for 5 h. The reaction mixture was stirred at reflux for an-
other 20 h and then cooled to room temperature. After
the mixture was treated with MeOH (40 mL), the solvents
were removed and, to the remaining residue was added

2030
S.-P. Luo et al. / Tetrahedron: Asymmetry 17 (2006) 2028–2033
Br11
C20
N13
C13
N12
N11
C14
C11
C12
C15
C17
C16
C18
C19
Br12
C78
Br71
C75
N71
C74
C71
C39
C37
N72
Br31
C77
C79
N31
C72
C76
C80
C34
N73
C35
N32
C31
C73
Br72
C38
C32
C36
N33
C33
C40
Br32
Br52
C60
C53 N53
C58
C52
C51
C54
C15
C56
N52
C14
C13
Br12
C57
N13
C55
C20
C12
C11
C19
N12
C59
N51
C17
Br51
C16
N11
C18
Br11
Figure 2. X-ray crystal structure of 1c’s hydrobromide salt.
2
0% NaOH aqueous solution (150 mL) and stirred under
several times and the residue was recrystallized from
reflux for 3 h. The resulting mixture was extracted three
times by ethyl acetate. The combined extracts were evapo-
rated, and the obtained crude product further purified by
distillation under high vacuum to give 5a–e as colourless
oils (over 88% yields).
i-PrOH to afford 6a–e (over 86% yields).
4.2.3. General procedure for the synthesis of CAFILs
1–3. A solution of N-methylimidazole (0.11 mol) and
compound 6 (0.1 mol) in CH CN was stirred at 80 °C for
3
8
h. After completion, the solvent was removed by distilla-
4
6
.2.2. General procedure for the synthesis of compounds
A mixture of (S)-amino alcohols 5 (0.15 mol) dissolved
tion, and the residue neutralized by NaOH and recrystal-
lized in EtOH to afford the CAFILs 1a–e (over 92%
yields). A mixture of 1 (0.09 mol), AgBF4 (or KPF6)
(0.09 mol) and 150 mL of CH CN/H O (1:1) was stirred
at room temperature for 2 h (or 20 h). Solvents of the mix-
ture were evaporated under vacuum. The residue was then
dissolved in EtOH to allow the inorganic salts to be precip-
itated and filtered off. After evaporating the solvent, the de-
sired CAFILs 2a–e (over 97% yields) and 3a–e (over 95%
yields) were obtained.
.
in 20% HBr aqueous solution (130 mL) was concentrated
to dryness under reduced pressure. Owing to complete
removal of water, the residue was dissolved in hot EtOH
3
2
(
40 mL) and the solvent was evaporated in vacuum to give
amino alcohol hydrobromides. The obtained hydrobro-
mide salts were then mixed with PBr (25.44 g, 0.093 mol)
and refluxed for 10 min. After cooling, an excess of PBr3
was then removed by washing the mixture with Et O
3
2

S.-P. Luo et al. / Tetrahedron: Asymmetry 17 (2006) 2028–2033
2031
ꢀ
1
Table 1. Properties of CAFILs 1–3
122.937, 123.255, 136.928. IR (film, cm ): 3370 [c(N–
H)], 3121 [c(C–H) aromatic], 2971 and 2873 [c(C–H) ali-
phatic], 1575 and 1460 [c(C@C)], 1059 [c(BF)]. MS:
a
b
20
c
Entry
CAFILs
T
m
or T
g
(°C)
T
dec (°C)
½aꢁD
e
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
1a
2a
3a
1b
2b
3b
1c
2c
3c
1d
2d
3d
1e
2e
3e
131
ꢀ46
226
261
218
270
281
287
267
291
287
268
285
281
257
291
274
12.6
13.9
7.2
10.3
6.9
4.6
6.0
7.1
5.4
11.7
10.1
3.9
6.5
4.5
+
ꢀ
4
d
(ESI+) m/z 140 [MꢀBF ] , (ESIꢀ) m/z 87 [BF ] . HRMS:
4
+
e
(ESI+) m/z calcd for [C H N ] 140.1182, found
6
7 14 3
e
140.1173.
145
d
d
e
ꢀ49
38
4.3.3. 1-[(S)-(2-Amino)propyl]-3-methylimidazolium hexa-
fluorophosphate 3a. H NMR (DMSO-d ): d 0.98 (d,
J = 6 Hz, 3H), 3.11 (m, 1H), 3.80 (s, 3H), 3.85 (dd,
J = 5.2, 12.8 Hz, 1H), 4.02 (dd, J = 2.8, 12.8 1H), 7.44 (s,
H), 7.47 (s, 1H), 8.78 (s, 1H). C NMR (DMSO-d ): d
16.994, 35.845, 46.621, 52.133, 122.793, 123.695, 137.284.
IR (film, cm ): 3394 [c(N–H)], 3133 [c(C–H) aromatic],
2924 and 2873 [c(C–H) aliphatic], 1578 and 1421
1
134
6
d
ꢀ47
e
e
69
135
1
1
1
1
1
1
13
1
d
e
6
ꢀ35
73
141
ꢀ
1
e
d
d
ꢀ45
+
[
c(C@C)], 843 [c(PF)]. MS: (ESI+) m/z 140 [MꢀPF ] ,
67
2.7
6
ꢀ
a
b
c
(ESIꢀ) m/z 145 [PF ] . HRMS: (ESI+) m/z calcd for
6
The data were determined by DSC.
The data were determined by TG.
Solution in EtOH and c = 2.
+
[C H N ] 140.1182, found 140.1180.
7
14
3
d
e
4
.3.4. 1-[(S)-(2-Amino)isopentyl]-3-methylimidazolium bro-
mide 1b. H NMR (DMSO-d ): d 0.92 (dd, J = 6.4, 14.4
Glass transition temperature (T
g
).
1
Melting point (T ).
m
6
Hz, 6H), 1.62–1.65 (m, 1H), 2.81 (m, 1H), 3.89 (s, 3H),
4
1
.05 (dd, J = 10, 13.6 Hz, 1H), 4.28 (dd, J = 3.6, 13.6 Hz,
H), 7.78 (s, 1H), 7.87 (s, 1H), 9.31 (s, 1H). C NMR
1
3
(
DMSO-d ): d 17.319, 19.170, 31.121, 35.762, 52.710,
6
1
ꢀ
O
56.304, 122.884, 123.096, 136.951. IR (film, cm ): 3395
[c(N–H)], 3088 [c(C–H) aromatic], 2961 and 2876 [c(C–
H) aliphatic], 1563 and 1421 [c(C@C)]. MS: (ESI+) m/z
MeO
F C
H
O
3
+
ꢀ
in
168 [MꢀBr] , (ESIꢀ) m/z 80 [Br] . HRMS: (ESI+) m/z
+
calcd for [C H N ] 168.1495, found 168.1491.
9
18
3
4
.3.5. 1-[(S)-(2-Amino)isopentyl]-3-methylimidazolium tetra-
1
fluoroborate 2b. H NMR (DMSO-d ): d 0.89 (d,
6
NH2
BF4
J = 6.8 Hz, 3H), 0.93 (d, J = 6.8 Hz, 3H), 1.60 (m, 1H),
N
N
2
4
7
.74 (m, 1H), 3.85 (s, 3H), 3.90 (dd, J = 4.0, 9.6 Hz, 1H),
.20 (dd, J = 4.0, 9.6 Hz, 1H), 7.66 (t, J = 1.6 Hz, 1H),
.71 (t, J = 1.6 Hz, 1H), 9.03 (s, 1H). C NMR (DMSO-
1
3
d ): d 17.145, 19.147, 31.318, 35.663, 53.180, 56.297,
6
ꢀ
1
1
22.876, 123.127, 136.890. IR (film, cm ): 3390 [c(N–
H)], 3162 [c(C–H) aromatic], 2966 and 2879 [c(C–H) ali-
phatic], 1574 and 1433 [c(C@C)], 1060 [c(BF)]. MS:
7
.70
7.60
7.50
7.40
7.30
7.20
7.10
7.00
6.90
19
+
ꢀ
4
Figure 3. F NMR of rac-Mosher’s acid in 2b.
(ESI+) m/z 168 [MꢀBF ] , (ESIꢀ) m/z 87 [BF ] . HRMS:
4
+
(
ESI+) m/z calcd for [C H N ] 168.1495, found
9 18 3
4
.3. Spectroscopic data
168.1501.
4
1
3
4
.3.1. 1-[(S)-(2-Amino)propyl]-3-methylimidazolium bromide
4.3.6. 1-[(S)-(2-Amino)isopentyl]-3-methylimidazolium hexa-
1
1
a. H NMR (DMSO-d ): d 1.14 (3H), 3.36 (s, dr, NH ),
fluorophosphate 3b. H NMR (DMSO-d ): d 0.94 (dd,
6
2
6
.45–3.52 (m, 1H), 3.87 (s, 3H), 4.14–4.21 (m, 1H), 4.15–
J = 5.6, 12 Hz, 6H), 1.68–1.72 (m, 1H), 2.91–294 (m,
1
3
.31 (m, 1H), 7.75 (s, 1H), 7.77 (s, 1H), 9.18 (s, 1H).
C
1H), 3.89 (s, 3H), 4.06–4.12 (m, 1H), 4.29–4.32 (m, 1H),
1
3
NMR (DMSO-d ): d 18.480, 20.535, 35.708, 46.514,
7.76 (s, 1H), 7.86 (s, 1H), 9.28 (s, 1H). C NMR
6
ꢀ
1
5
[
5.766, 122.876, 123.058, 136.814. IR (film, cm ): 3428
c(N–H)], 3143 [c(C–H) aromatic], 2925 and 2835 [c(C–
H) aliphatic], 1555 and 1412 [c(C@C)]. MS: (ESI+) m/z
(DMSO-d ): d 17.418, 19.041, 30.916, 35.875, 52.262,
6
ꢀ1
56.297, 122.907, 123.202, 137.042. IR (film, cm ): 3457
[c(N–H)], 3169 [c(C–H) aromatic], 2921 and 2886 [c(C–
H) aliphatic], 1576 and 1437 [c(C@C)], 838 [c(PF)]. MS:
+
ꢀ
1
40 [MꢀBr] , (ESIꢀ) m/z 80 [Br] . HRMS: (ESI+) m/z
+
+
ꢀ
6
calcd for [C H N ] 140.1182, found 140.1178.
7 14 3
(ESI+) m/z 168 [MꢀPF ] , (ESIꢀ) m/z 145 [PF ] .
6
+
HRMS: (ESI+) m/z calcd for [C H N ] 168.1495, found
9 18 3
4
.3.2. 1-[(S)-(2-Amino)propyl]-3-methylimidazolium tetra-
168.1492.
1
fluoroborate 2a. H NMR (DMSO-d ): d 1.03 (d,
6
J = 6 Hz, 3H), 3.22 (dd, J = 6, 11.6 Hz, 1H), 3.86 (s,
4.3.7. 1-[(S)-(2-Amino)isohexyl]-3-methylimidazolium bro-
1
3
H), 3.96 (dd, J = 7.6, 13.6 Hz, 1H), 4.15 (dd, J = 4,
mide 1c. H NMR (CDCl ): d 1.00 (dd, J = 6.4,
3
1
3
1
3.6 Hz, 1H), 7.67 (s, 1H), 7.68 (s, 1H), 9.00 (s, 1H).
C
12.8 Hz, 6H), 1.75–1.79 (m, 1H), 2.92–2.94 (m, 1H), 4.08
NMR (DMSO-d ): d 20.042, 35.701, 46.575, 55.409,
(s, 3H), 4.26 (dd, J = 10, 12.8 Hz, 1H), 4.39 (d,
6

2032
S.-P. Luo et al. / Tetrahedron: Asymmetry 17 (2006) 2028–2033
J = 12.8 Hz, 1H), 7.45 (s, 1H), 7.59 (s, 1H), 10.07 (s, 1H).
4.3.12. 1-[(S)-(2-Amino)-3-methylpentyl]-3-methylimidazo-
1
3
1
C NMR (DMSO-d ): d 17.517, 18.495, 29.976, 35.853,
lium hexafluorophosphate 3d. H NMR (DMSO-d ): d
6
6
5
0.624, 55.902, 122.876, 123.483, 137.193. IR (film,
0.89 (d, J = 7.2, 6H), 1.09–1.25 (m, 1H), 1.34–1.46 (m,
1H), 1.46–1.59 (m, 1H), 2.83 (m, 1H), 3.90 (s, 3H), 4.03
(dd, J = 10, 13.2 Hz, 1H), 4.27 (d, J = 13.2 Hz, 1H), 7.78
ꢀ
1
cm ): 3434 [c(N–H)], 3133 [c(C–H) aromatic], 2944 and
2
873 [c(C–H) aliphatic], 1581 and 1459 [c(C@C)]. MS:
+
ꢀ
13
(
ESI+) m/z 182 [MꢀBr] , (ESIꢀ) m/z 80 [Br] . HRMS:
(s, 1H), 7.86 (s, 1H), 9.33 (s, 1H). C NMR (DMSO-d6):
+
(
ESI+) m/z calcd for [C H N ] 182.1652, found
d 11.594, 15.060, 24.288, 35.792, 38.582, 52.566, 55.485,
1
0
20
3
ꢀ
1
1
82.1649.
122.937, 123.043, 136.973. IR (film, cm ): 3392 [c(N–
H)], 3166 [c(C–H) aromatic], 2966 and 2879 [c(C–H) ali-
phatic], 1572 and 1431 [c(C@C)], 843 [c(PF)]. MS:
4
.3.8. 1-[(S)-(2-Amino)isohexyl]-3-methylimidazolium tetra-
1
+
ꢀ
6
fluoroborate 2c. H NMR (DMSO-d ): d 0.98 (dd,
J = 7.2, 8.8 Hz, 6H), 1.06 (m, 2H), 1.85 (m, 1H), 3.25 (m,
(ESI+) m/z 182 [MꢀPF ] , (ESIꢀ) m/z 145 [PF ] .
6
6
+
HRMS: (ESI+) m/z calcd for [C H N ] 182.1645, found
10 20 3
1
H), 3.87 (s, 3H), 4.20 (dd, J = 10, 14 Hz, 1H), 4.37 (dd,
182.1653.
J = 2.8, 14 Hz, 1H), 7.73 (s, 1H), 7.77 (s, 1H), 9.10 (s,
1
3
1
3
H). C NMR (DMSO-d ): d 17.441, 18.229, 29.642,
6
4
.3.13. 1-[(S)-(2-Pyrrolidinyl)methyl]-3-methylimidazolium
): d 1.69–1.74 (m, 1H),
6
5.822, 50.139, 55.667, 122.846, 123.627, 137.231. IR (film,
cm ): 3409 [c(N–H)], 3089 [c(C–H) aromatic], 2963 and
1
ꢀ
1
bromide 1e. H NMR (DMSO-d
1
.90–1.94 (m, 1H), 2.00–2.01 (m, 1H), 2.10–2.14 (m, 1H),
2
876 [c(C–H) aliphatic], 1565 and 1463 [c(C@C)], 1057
+
3.16–3.21 (m, 1H), 3.26–3.31 (m, 1H), 3.90 (s, 3H), 3.99–
4.03 (m, 1H), 4.62–4.67 (m, 2H), 7.80 (s, 1H), 7.91 (s,
[
[
c(BF)]. MS: (ESI+) m/z 182 [MꢀBF ] , (ESIꢀ) m/z 87
4
ꢀ
+
BF ] . HRMS: (ESI+) m/z calcd for [C H N ]
13
4
10 20
3
1
2
1
H), 9.29 (s, 1H). C NMR (DMSO-d ): d 23.133,
7.779, 36.390, 45.139, 49.012, 59.257, 122.854, 124.197,
37.572. IR (film, cm ): 3403 [c(N–H)], 3133 [c(C–H) aro-
6
1
82.1652, found 182.1663.
ꢀ1
4
.3.9. 1-[(S)-(2-Amino)isohexyl]-3-methylimidazolium hexa-
1
matic], 2944 and 2873 [c(C–H) aliphatic], 1566 and 1412
fluorophosphate 3c. H NMR (DMSO-d ): d 0.87 (dd,
J = 4, 6.8 Hz, 6H), 1.00 (m, 2H), 1.56–1.61 (m, 1H),
+
6
[
c(C@C)]. MS: (ESI+) m/z 166 [MꢀBr] , (ESIꢀ) m/z 80
ꢀ
9 16 3
+
[
Br] . HRMS: (ESI+) m/z calcd for [C H N ]
2
4
.70–2.75 (m, 1H), 3.82 (s, 3H), 3.86–3.93 (m, 1H), 4.16–
.20 (m, 1H), 7.58 (s, 1H), 7.65 (s, 1H), 9.02 (s, 1H).
1
3
166.1339, found 166.1338.
C
NMR (DMSO-d ): d 17.441, 19.359, 31.598, 35.981,
6
5
3.461, 56.600, 123.104, 123.392, 137.133. IR (film,
4.3.14. 1-[(S)-(2-Pyrrolidinyl)methyl]-3-methylimidazolium
ꢀ
1
1
cm ): 3422 [c(N–H)], 3170 [c(C–H) aromatic], 2968 and
tetrafluoroborate 2e. H NMR (DMSO-d ): d 1.70–1.77
6
2
880 [c(C–H) aliphatic], 1574 and 1431 [c(C@C)], 837
(m, 1H), 1.88–1.95 (m, 1H), 1.97–2.05 (m, 1H), 2.08–2.15
(m, 1H), 3.17–3.23 (m, 1H), 3.29–3.30 (m, 1H), 3.90 (s,
3H), 4.00–4.04 (m, 1H), 4.56–4.67 (m, 2H), 7.79 (s, 1H),
+
[
[
c(PF)]. MS: (ESI+) m/z 182 [MꢀPF ] , (ESIꢀ) m/z 145
6
ꢀ
+
PF ] . HRMS: (ESI+) m/z calcd for [C H N ]
6
10 20
3
1
3
1
82.1652, found 182.1656.
7.87 (s, 1H), 9.23 (s, 1H), 9.25 (s, dr, NH). C NMR
DMSO-d ): d 23.222, 27.885, 36.477, 45.850, 49.452,
(
6
ꢀ
1
4
.3.10. 1-[(S)-(2-Amino)-3-methylpentyl]-3-methylimidazo-
59.340, 123.091, 124.578, 137.787. IR (film, cm ): 3406
[c(N–H)], 3062 [c(C–H) aromatic], 2955 and 2868 [c(C–
H) aliphatic], 1570 and 1459 [c(C@C)], 1071 [c(BF)]. MS:
1
lium bromide 1d. H NMR (DMSO-d ): d 0.90 (t,
J = 7 Hz, 3H), 0.95 (d, J = 6.8 Hz, 3H), 1.15–1.22 (m,
1
3
6
+
ꢀ
] . HRMS:
4
H), 1.48–1.62 (m, 2H), 3.18 (m, 1H), 3.37 (s, dr, NH2),
.87 (s, 3H), 4.16 (dd, J = 10.4, 13.2 Hz, 1H), 4.33 (d,
(ESI+) m/z 166 [MꢀBF
4
] , (ESIꢀ) m/z 87 [BF
+
(ESI+) m/z calcd for [C
H
9
N
]
166.1339, found
16
3
J = 13.2 Hz, 1H), 7.74 (s, 1H), 7.81 (s, 1H), 9.19 (s, 1H).
166.1335.
1
3
C NMR (DMSO-d ): d 11.549, 14.423, 24.387, 35.807,
6
3
7.240, 50.526, 54.985, 122.914, 123.415, 137.155. IR (film,
4
.3.15. 1-[(S)-(2-Pyrrolidinyl)methyl]-3-methylimidazolium
ꢀ
1
cm ): 3421 [c(N–H)], 3075 [c(C–H) aromatic], 2963 and
2
1
hexafluorophosphate 3e. H NMR (DMSO-d ): d 1.67–
6
873 [c(C–H) aliphatic], 1564 and 1389 [c(C@C)]. MS:
1
3
4
.77 (m, 1H), 1.86–2.08 (m, 2H), 2.10–2.16 (m, 1H),
+
ꢀ
(
ESI+) m/z 182 [MꢀBr] , (ESIꢀ) m/z 80 [Br] . HRMS:
.12–3.36 (m, 2H), 3.87 (s, 3H), 4.00–4.03 (m, 1H), 4.56–
+
(
ESI+) m/z calcd for [C H N ] 182.1645, found
13
1
0
20
3
.66 (m, 2H), 7.79 (s, 1H), 7.86 (s, 1H), 9.23 (s, 1H).
C
1
82.1679.
NMR (DMSO-d ): d 22.620, 27.306, 35.928, 44.793,
6
4
8.524, 58.776, 122.482, 123.847, 137.231. IR (film,
4
.3.11. 1-[(S)-(2-Amino)-3-methylpentyl]-3-methylimidazo-
ꢀ1
cm ): 3406 [c(N–H)], 3070 [c(C–H) aromatic], 2949 and
1
lium tetrafluoroborate 2d. H NMR (DMSO-d ): d 0.90
6
2
870 [c(C–H) aliphatic], 1560 and 1420 [c(C@C)], 839
(
dd, J = 6.4, 13.2 Hz, 6H), 1.14–1.18 (m, 1H), 1.29–1.38
+
[c(PF)]. MS: (ESI+) m/z 166 [MꢀPF ] , (ESIꢀ) m/z 145
6
(
m, 1H), 1.47–1.51 (m, 1H), 2.74–2.76 (m, 1H), 3.85 (s,
ꢀ
+
[
PF ] . HRMS: (ESI+) m/z calcd for [C H N ]
6
9
16
3
3
1
H), 3.88 (dd, J = 3.2, 12.8 Hz, 1H), 4.19 (dd, J = 2.4,
166.1339, found 166.1342.
1
3
2.8 Hz, 1H), 7.66 (s, 1H), 7.72 (s, 1H), 9.06 (s, 1H).
C
NMR (DMSO-d ): d 11.480, 14.991, 24.205, 35.648,
6
5
3.028, 55.432, 122.922, 123.043, 136.890. IR (film,
ꢀ
1
cm ): 3401 [c(N–H)], 3163 [c(C–H) aromatic], 2967 and
Acknowledgements
2
879 [c(C–H) aliphatic], 1574 and 1429 [c(C@C)], 1061
+
[
[
c(BF)]. MS: (ESI+) m/z 182 [MꢀBF ] , (ESIꢀ) m/z 87
The authors acknowledge the Ministry of Science and
Technology of China for the financial support of National
Basic Research Program of China (2003CB114400).
4
ꢀ
+
BF ] . HRMS: (ESI+) m/z calcd for [C H N ]
4
10 20
3
1
82.1645, found 182.1665.

S.-P. Luo et al. / Tetrahedron: Asymmetry 17 (2006) 2028–2033
2033
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0. Crystal structure of 1c’s hydrobromide salt: CCDC 608255.