A diol-functionalized ionic liquid: An efficient, simple, and recoverable "capture and release" reagent for aldehydes

Article abstract of DOI:10.1007/s00706-008-0005-6

A new diol-functionalized ionic liquid, 2,2-bis(1-(1-methylimidazolium) methylpropane-1,3-diol hexafluorophosphate, was synthesized and applied as a facile, efficient, and recoverable "capture and release" reagent for aldehydes. This method has the advant

Full text of DOI:10.1007/s00706-008-0005-6

Monatsh Chem (2009) 140:39–44
DOI 10.1007/s00706-008-0005-6
ORIGINAL PAPER
A diol-functionalized ionic liquid: an efficient, simple,
and recoverable ‘‘capture and release’’ reagent for aldehydes
Yueqin Cai Æ Ye Liu
Received: 7 May 2008 / Accepted: 4 June 2008 / Published online: 12 September 2008
Ó Springer-Verlag 2008
Abstract A new diol-functionalized ionic liquid, 2,2-
bis(1-(1-methylimidazolium)methylpropane-1,3-diol hexa-
fluorophosphate, was synthesized and applied as a facile,
efficient, and recoverable ‘‘capture and release’’ reagent for
aldehydes. This method has the advantages of homogeneous
reaction, heterogeneous separation, and recyclable uses.
active sites to organic substrates, solvent dependence, as
well as the difficulty in reaction monitoring. In recent
years, a variety of new techniques, such as fluorous-phase
[8–10], aqueous [11–13], as well as polyaromatic [14] and
PEG-supported reagents [15] have been developed. These
new reagents, however, have their own drawbacks, such as
high cost, relatively low loading, and the need for large
amounts of solvents.
Keywords Combinatorial chemistry Á
Functionalized ionic liquid Á Diol Á Heterocycles Á
Aldehydes
Recently, ionic liquids (ILs) became of intense interest
because of their unique chemical and physical characters,
such as lack of vapor pressure, ease of reuse, and facile
chemical modification. A wide variety of room temperature
ionic liquids, especially those derived from 1-n-alkyl-3-
methylimidazolium cations, has been demonstrated to have
versatile applications in organic synthesis [16–21]. In this
field, we have reported the use of amino- and carboxy-
functionalized ILs as scavengers for purification of
solution-phase parallel synthesis [22, 23]. It has been rec-
ognized that IL scavengers have the advantages of a
homogeneous reaction process along with the recoverable
and recyclable scavengers [22, 23]. Herein, as an extension
of this strategy, we describe a new method that utilizes a
diol-functionalized IL, 2,2-bis(1-(1-methylimidazolium)
methylpropane-1,3-diol hexafluorophosphate (1), as an
efficient and recyclable ‘‘capture-release’’ reagent for
aldehydes from a mixture.
Introduction
Over the past few years, the exploration and utilization
of combinatorial chemistry in conjunction with high
throughput biological screenings have rapidly evolved [1,
2
]. Polymer-supported scavengers are therefore becoming
widespread in chemical ensemble preparation for straight-
forward purification of reaction products [3–6]. One such
scavenger is of the ‘‘resin capture-release’’ reagent, which
uses the functionalized polymer scavengers to selectively
trap the desired products out of solution phase [7]. How-
ever, such scavengers suffer from limited mobility as a
result of restriction of the polymer matrix and the access of
Y. Cai (&)
School of Chemistry and Molecular Engineering,
East China University of Science and Technology,
Results and discussion
200237 Shanghai, China
e-mail: caiyueqin2006@126.com; caiyueqin@eyou.com
Investigation of capture and release of aldehydes via
diol-functionalized IL 1
Y. Liu
Shanghai Key Laboratory of Green Chemistry and Chemical
Processes, East China Normal University,
As shown in Scheme 1, the required diol-functionalized
2
00062 Shanghai, China
IL 1 was simply prepared from 1-methylimidazole and
123

4
0
Y. Cai, Y. Liu
Br
Br
+
N
N +
+ N
N +
N
_
N
_
Br
NH PF / H O
N
N
4
6
2
N
N
2
PF6
2
1
50 °C
HO
OH
HO
OH
HO
OH
1
Scheme 1
Scheme 2
+
N
N +
+ N
N +
_
_
CH CN
N
N
3
N
N
2
PF6
2 PF6
TiCl4
HO
OH
O
O
(Ar)RCHO
R(Ar)
+
N
N +
_
H O
2
N
N
2
PF6
+
(Ar)RCHO
p -TsOH
HO
OH
2
,2-bis(bromomethyl)-1,3-propanediol, followed by anion
Table 1 Capture of aldehydes or ketones via diol-functionalized IL 1
exchange with NH PF . To illustrate that 1 is an effective
4
b
Products Time/h Yield /%
6
Entry Substrate
‘
‘capture-release’’ reagent for selective and rapid isolation
1
Benzaldehyde
2
3
0.5
2
95
95
93
89
86
93
91
94
95
37
0
of aldehydes, the capture and release of different aldehydes
from 1 were examined (Scheme 2).
2
2-Chlorobenzaldehyde
2,6-Dichlorobenzaldehyde
4-Dimethylaminobenzaldehyde
Cinnamaldehyde
3-Nitrobenzaldehyde
Phenyl acetaldehyde
Propionaldehyde
Valeraldehyde
3
4
2
Originally, the capture of benzaldehyde with 1 was cata-
lyzed by p-TsOH with toluene as the solvent [24, 25].
Unfortunately, the poor yield of the desired acetal resulted
probably from the restricted access of –OH in 1 to benzal-
dehyde (1 is insoluble in toluene). Surprisingly, by replacing
4
5
3
5
6
1
6
7
1
7
8
1
toluene with acetonitrile, and using TiCl as the catalyst, the
4
8
9
0.5
0.5
8
reaction of benzaldehyde with 1 occurred readily in homo-
geneous phase. After optimization of the reaction conditions,
it was found that the reaction could be accomplished within
9
10
11
12
13
14
15
16
17
10
11
12
13
14
15
16
Cyclohexanone
Benzophenone
8
0.5 h with 2.0 equiv. of 1. The resultant mixture was washed
with water and ethanol to remove an excess 1 and the side-
Acetophenone
8
0
Butan-2-one
8
0
product from TiCl hydrolysis, to yield the expected product
4
Heptan-3-one
8
0
a
a
in excellent yield (95%). The product was of high purity and
required no further purification.
Butan-2-one
8
0
Acetophenone
8
0
In order to determine the selective capture of the alde-
hyde group by 1, a range of aldehydes and ketones was
selected to react with 1 under the conditions established
above. As shown in Table 1, all aldehydes reacted with 1 to
give acetals in excellent yields (86–95%) within short time
Substrate (5 mmol), 1 (10 mmol), TiCl
(
4
(5 mmol), and CH
3
CN
CN
3
5 cm )
a
Substrate (5 mmol), 1 (20 mmol), TiCl
4
(5 mmol), and CH
3
3
(5 cm )
b
Isolated yield of acetals
(
0.5–3 h), regardless of aliphatic or aromatic aldehydes or
the electronic nature of the substituents (Table 1, entries
–9). All the products were well characterized by FT–IR
aromatic acetals was not observed under the same condi-
tions, even upon increasing loading of the diol-
functionalized IL (Table 1, entries 15–16).
1
1
and H NMR. However, in the cases of ketones, the reac-
tions were sluggish, and poor yields of the required
products were obtained (Table 1, entries 10–14). Cyclo-
hexanone with relatively low steric hindrance reacted with
The release of the aldehydes from 1-supported acetals of
Table 1 was investigated. (1) The acetals were hydrolyzed in
water in the presence of p-TsOH; (2) upon completion of
reaction (monitored by TLC), the mixture was extracted with
1
providing only 37%. The formation of other aliphatic or
1
23

A diol-functionalized ionic liquid for aldehydes
41
CH Cl ; (3) the combined organic phase was washed with
2
Table 2 Capture and release of of aldehydes via 1 from the mixture
2
aqueous NaHCO and brine, and then concentrated to give
3
Entry Compounds
in the mixture
Captured and released compound
via diol-functionalized IL 1
the aldehydes; (4) the aqueous phase was washed with
CH Cl and then concentrated in vacuo to afford the recov-
2
2
Percentage
of captured
Releasing yield
of the captured
ered 1. It was found that the aldehydes were successfully
detached from 1 without contamination of 1 (confirmed by
a
compounds /% compounds /%
b
1
1
H NMR analysis). The recovered 1 gave FT–IR and H
1
2
3
4
5
6
7
8
Benzaldehyde
Acetophenone
100
0
92
0
NMR spectrta similar to the freshly prepared compound.
In consideration of the fact that the ILs are highly pref-
erable in a green synthetic process due to its repeating usage,
we studied the recyclability of 1 for aldehyde capture and
release. As derived from Fig. 1, 1 could be recycled at least
four times without obvious decrease in reactivity. Thus,
benzaldehyde could be captured and then released from 1
with releasing yield of [92% per pass. These results pro-
vided strong evidence that 1 is a highly active and easily
manipulatory ‘‘capture and release’’ reagent for aldehydes.
2,6-Dichlorobenzaldehyde 100
Acetophenone
2,6-Dichlorobenzaldehyde 100
Cyclohexanone
2,6-Dichlorobenzaldehyde 100
91
0
0
91
0
0
90
0
Ethylbutylcetone
Benzaldehyde
0
100
0
93
0
p-Bromoanisole
2-Chlorobenzaldehyde
p-Bromoanisole
100
0
92
0
Capture and release of aldehydes via diol-
functionalized IL 1 from the complex mixture
2,6-Dichlorobenzaldehyde 100
p-Bromoanisole
2,6-Dichlorobenzaldehyde 63
2-Chlorobenzaldehyde 37
90
0
0
To explore the general practicability of our method, the
capture and the release of aldehydes mixed with other
compounds were examined (Table 2). Fortunately, it was
found that 2 equiv. of 1 could capture the target aldehyde
from the mixture with excellent yield (89–92%) in a short
time. Most significantly, due to the higher selectivity to
92
Compounds in the mixture (aldehyde 5 mmol and another compound
3
5 mmol), 1 (20 mmol), and TiCl (10 mmol) in CH CN (10 cm ) for
4
3
2 h
a
The amount of the released compounds after hydrolysis determined
by GC
–
CHO, 1 captured aldehydes more readily than ketones,
affording acetals as the only product with yields of [90%
after hydrolysis (entries 1–3). Without the competition to the
b
Isolate yield of aldehydes or ketones
which is usually used to capture aldehydes, cyclic ketones,
methyl ketones, and isocyanates [26–29], the diol-func-
tionalized IL 1 could selectively isolate aldehydes from the
mixture even in the presence of ketones.
–
CHO, the aldehydes were captured completely and then
could be released with high yields (entries 4–7). Reasonably,
for the mixtures composed of two types of active aldyhydes,
the specific selectivity to one individual could not be
observed (Entry 8). Most importantly, compared to NaHSO3,
In conclusion, we describe an efficient methodology in
which a diol-functionalized IL is applied to capture alde-
hydes from a mixture and then release pure aldehydes
without further purification. Compared to the reported
polymer-supported diol for aldehydes protection and iso-
lation, the developed 1, with the significant features of (1)
Conversion of benzalaldehyde via recovered 1
Releasing yield of benzalaldehyde from acetal
1
00
homogenous reaction (1 is soluble in CH CN) and heter-
3
8
6
4
2
0
0
0
0
0
ogeneous separation (acetals from 1 are insoluble in water),
(2) recoverable and recyclable nature of 1 derived from its
nature of an ionic liquid, and (3) efficient and selective
capture of aldehydes from a complex mixture and then
release of aldehydes with high purity, presents a significant
advancement over existing methodologies.
Experimental
Run 1
Run 2
Cyclings
Run 3
Run 4
All solvents and chemicals (aldehydes) were reagent grade
1
purchased commercially and used as received. H NMR
1
and C NMR spectra were recorded on a Bruker DRX-500
3
Fig. 1 Recyclability of 1 for capture and release of benzaldehyde
123

4
2
Y. Cai, Y. Liu
(
500 MHz) instrument with DMSO-d as solvent. ESI-MS
6
NCH), 7.80 (s, 2H, NCH), 9.15 (s, 1H, N (H) CN), 9.25
(s, 1H, N (H) CN) ppm.
was detected by Agilent 1100LC/MSDVL spectrometer.
FT–IR spectra were recorded on a Nicolet Nexus 670
FT–IR spectrometer (KBr pellet). Elemental analysis data
were recorded on a Vario EL III instrument. Their results
agreed favorably with the calculated values. GC–MS
analyses were recorded on an Agilent 6890 instrument
equipped with Agilent 5973 mass selective detector. GC
analyses were performed on SHIMADZU-14B equipped
with HP-1 capillary column (30 m 9 0.25 mm).
2
-(2-Chlorophenyl)-5,5-bis(1-(1-methylimidazolium)
methyl-1,3-dioxane hexafluorophosphate
3, C H N O ClP F )
(
2
0
25
4
2
2 12
White solid (3.23 g, 95%), mp 131 °C; FT–IR (KBr) ꢀm =
3
8
6
161, 3122, 2970, 1580, 1565, 1448, 1405, 1172, 1095,
-
1 1
42 cm ; H NMR (500 MHz, DMSO-d ,) d = 3.85 (s,
6
H, CH ), 4.01 (d, 2H, J = 12 Hz, O–CH ), 4.10 (d, 2H,
3
2
J = 14 Hz, O–CH ), 4.20 (s, 2H, N–CH ), 4.60 (s, 2H, N–
2
2
2,2-Bis(1-(1-methylimidazolium)methylpropane-1,3-diol
hexafluorophosphate (1, C H N O P F )
CH ), 5.75 (s, 1H, CH), 7.40–7.60 (m, 4H, Ph), 7.65 (s, 1H,
2
NCH), 7.75 (s, 1H, NCH), 7.80 (s, 1H, NCH), 7.85 (s, 1H,
NCH), 9.10 (s, 1H, N (H) CN), 9.20 (s, 1H, N (H) CN)
ppm.
1
3 22 4 2 2 12
A mixture of 2.05 g 1-methylimidazole (25 mmol) and
.60 g 2,2-bis (bromomethyl)-1, 3-propanediol (10 mmol)
2
was heated at 150 °C for 8 h under magnetic stirring.
After cooling to room temperature, the resultant solid
was washed with acetonitrile, and the solution of 3.26 g
2
-(2,6-Dichlorophenyl)-5,5-bis(1-(1-methylimidazolium)
methyl-1,3-dioxane hexafluorophosphate
4, C H N O Cl P F )
(
3
20 24
4
2
2 2 12
NH PF (20 mmol) in 20 cm of H O was then added.
4
6
2
White solid (3.31 g, 93%), mp 138 °C; FT–IR (KBr) ꢀm =
3
The obtained mixture was stirred at room temperature
for 1 h. After filtration, the white solid was washed with
ethanol and dried, giving 4.67 g (84%) of the desired
product. FT–IR (KBr) ꢀm = 3604, 3165, 3122, 2977, 2913,
165, 3122, 2967, 2935, 1584, 1561, 1436, 1401, 1173,
-
099, 1067, 834 cm ; H NMR (500 MHz, DMSO-d ,)
1 1
1
6
d = 3.80 (s, 6H, CH ), 3.90 (d, 2H, J = 11 Hz, O–CH ),
4
3
2
.01 (d, 2H, J = 12 Hz, O–CH ), 4.25 (s, 2H, N–CH ),
2 2
-
1
1
1
588, 1577, 1448, 1425, 1301, 1173, 1014, 846 cm ;
4
.75 (s, 2H, N–CH ), 6.15 (s, 1H, CH), 7.40–7.50 (m, 3H,
2
H NMR (500 MHz, DMSO-d ) d = 3.10 (d, 4H,
6
Ph), 7.55 (s, 1H, NCH), 7.65 (s, 1H, NCH), 7.75 (s, 1H,
NCH), 7.85 (s, 1H, NCH), 9.10 (s, 1H, N (H) CN), 9.15
J = 4 Hz, OH–CH ), 3.90 (s, 6H, CH ), 4.25 (s, 4H,
2
3
N–CH ), 5.25 (t, 2H, J = 5 Hz, OH), 7.70 (s, 2H, NCH),
2
(s, 1H, N (H) CN) ppm.
1
.80 (s, 2H, NCH), 9.15 (s, 2H, NHCN) ppm; C NMR
3
7
(
100 MHz, DMSO-d ) d = 137.8, 123.8, 123.4, 58.5,
2-(4-Dimethylamionphenyl)-5,5-bis
(1-(1-methylimidazolium)methyl-1,3-dioxane
6
-
8.7, 45.4, 35.9 ppm; ESI–MS m/z = 554.7 (M-H) ,
4
2
2
-
90.2 ([PF ] )
6
.
hexafluorophosphate (5, C22H N O P F )
32 5 2 2 12
2
White solid (3.05 g, 89%), mp 141 °C; FT–IR (KBr) ꢀm =
3168, 3126, 2967, 2908, 1580, 1561, 1448, 1367, 1173,
Typical procedure for the capture of aldehydes via
diol-functionalized IL 1
-
1091, 1029, 854 cm ; H NMR (500 MHz, DMSO-d
1 1
,)
6
d = 3.80 (s, 6H, N-CH ), 3.85 (s, 6H, CH ), 3.90 (d, 2H,
3
3
A mixture of 1 (10 mmol), aldehyde (5 mmol), and
0
J = 11 Hz, O–CH
4.10 (s, 2H, N–CH
2
), 4.01 (d, 2H, J = 12 Hz, O–CH
), 4.60 (s, 2H, N–CH ), 5.48 (s, 1H,
2
),
3
.949 g TiCl (5 mmol) in 5 cm acetonitrile was refluxed
4
2
2
under magnetic stirring (monitored by TLC). Upon com-
3
pletion, the obtained mixture was cooled and 10 cm H O
CH), 7.35 (m, 4H, Ph), 7.70 (s, 1H, NCH), 7.75 (s, 1H,
NCH), 7.80 (s, 1H, NCH), 7.85 (s, 1H, NCH), 9.10 (s, 1H,
N (H) CN), 9.15 (s, 1H, N (H) CN) ppm.
2
was added to precipitate the formed acetals. After filtration,
the solid was washed with H O and ethanol separately to
2
2-Styryl-5,5-bis(1-(1-methylimidazolium)methyl-1,3-diox-
ane hexafluorophosphate (6, C H N O P F )
remove excess 1 and the side-product from TiCl4
hydrolysis, and then dried under vacuum to give the cor-
responding acetal.
2
2 28 4 2 2 12
White solid (2.88 g, 86%), mp 121 °C; FT–IR (KBr) ꢀm =
169, 3118, 2967, 2924, 1577, 1553, 1460, 1172, 1142,
3
-
1 1
2-Phenyl-5,5-bis(1-(1-methylimidazolium)methyl-1,3-
dioxane hexafluorophosphate (2, C H N O P F )
835 cm ; H NMR (500 MHz, DMSO-d
2H, J = 8 Hz, O–CH ), 3.75 (t, 2H, J = 7 Hz, O–CH
3.80 (s, 3H, CH ), 3.83 (s, 3H, CH ), 4.20 (s, 2H,
N–CH ), 4.50 (s, 2H, N–CH ), 5.10 (s, 1H, CH), 7.25–
6
,) d = 3.63 (t,
),
2
0 26 4 2 2 12
2
2
White solid (3.06 g, 95%), mp 128 °C; FT–IR (KBr) ꢀm =
3
3
3
8
6
169, 3118, 2967, 2924, 1577, 1553, 1460, 1172, 1142,
1 1
2
2
-
35 cm ; H NMR (500 MHz, DMSO-d ,) d = 3.80 (s,
7.35 (m, 5H, Ph), 7.45 (s, 1H, =CH), 7.47 (s, 1H, =CH),
7.60 (s, 1H, NCH), 7.65 (s, 1H, NCH), 7.75 (s, 1H,
NCH), 7.80 (s, 1H, NCH), 9.01 (s, 1H, N (H) CN), 9.10
(s, 1H, N (H) CN) ppm.
6
H, CH ), 3.90 (d, 2H, J = 10 Hz, O–CH ), 4.10 (d, 2H,
3
2
J = 12 Hz, O–CH ), 4.25 (s, 2H, N–CH ), 4.60 (s, 2H, N–
2
2
CH ), 5.50 (s, 1H, CH), 7.40 (m, 5H, Ph), 7.60 (s, 2H,
2
1
23

A diol-functionalized ionic liquid for aldehydes
43
2
1
-(3-Nitrophenyl)-5,5-bis(1-(1-methylimidazolium)methyl-
,3-dioxane hexafluorophosphate (7, C H N O P F )
d = 1.45 (m, 4H, CH ), 1.60 (m, 2H, CH ), 3.10 (m, 4H,
CH ), 3.65 (s, 2H, O–CH ), 3.80 (s, 6H, N–CH ), 4.20 (s,
2 2 3
2
2
2
0
25
5
4
2
12
White solid (3.20 g, 93%), mp 143 °C; FT–IR (KBr) ꢀm =
4H, N–CH ), 4.30 (s, 2H, O–CH ), 7.55 (s, 2H, NCH), 7.75
2 2
3
8
6
2
173, 3118, 2982, 2916, 1565, 1452, 1176, 1009,
1 1
(s, 2H, NCH), 8.90 (s, 2H, N (H) CN) ppm.
-
62 cm ; H NMR (500 MHz, DMSO-d ,) d = 3.75 (s,
6
H, N–CH ), 4.05 (d, 2H, J = 11 Hz, O–CH ), 4.20 (d,
3
Typical procedure for release of aldehydes
from diol-functionalized IL 1
2
H, J = 12 Hz, O–CH ), 4.45 (s, 2H, N–CH ), 4.55 (s, 2H,
2
2
N–CH ), 5.80 (s, 1H, CH), 7.60–7.85 (m, 4H, Ph), 8.15 (s,
2
1
H, NCH), 8.11 (s, 1H, NCH), 8.25 (s, 1H, NCH), 8.30 (s,
H, NCH), 9.10 (s, 2H, N (H) CN) ppm.
Acetal 2 (3.06 g, 0.48 mmol) and 2 mg p-TsOH
3
(0.01 mmol) were mixed with 10 cm H O and refluxed
1
2
under magnetic stirring for 2 h. After cooling to room
temperature, the reaction mixture was extracted with
2-Benzyl-5,5-bis(1-(1-methylimidazolium)methyl-1,3-
dioxane hexafluorophosphate (8, C H N O P F )
White solid (2.99 g, 91%), mp 123 °C; FT–IR (KBr) ꢀm =
2
1
28
4
2
2
12
3
CH Cl (10 cm 9 3). The combined organic layers were
2
2
3
washed with 10 cm saturated aqu. NaHCO and 10 cm
3
3
3
169, 3126, 2980, 2898, 1580, 1565, 1389, 1173, 1126,
brine. After drying (Na SO ) and filtration, the organic
2
-
079, 1017, 850 cm ; H NMR (500 MHz, DMSO-d ,)
1
1
4
1
6
phase was concentrated in vacuo. Due to the fact that the
aldehydes are commercial products, it is only necessary to
state that 0.49 g (98%) benzaldehyde identical with the
educt was obtained.
d = 2.65 (d, J = 6 Hz, 2H, Ph–CH ), 3.75 (s, 6H, N–
2
CH ), 3.90 (d, 2H, J = 11 Hz, O–CH ), 4.05 (d, 2H,
3
2
J = 10 Hz, O–CH ), 4.15 (s, 2H, N–CH ), 4.65 (s, 2H, N–
2
2
CH ), 5.35 (s, 1H, CH), 7.35–7.45 (m, 5H, Ph), 7.65 (s, 1H,
2
NCH), 7.70 (s, 1H, NCH), 7.85 (s, 1H, NCH), 7.90 (s, 1H,
NCH), 9.05 (s, 1H, N (H) CN), 9.10 (s, 1H, N (H) CN)
ppm.
The recovery of diol-functionalized IL 1
Only the recipe to obtain 1 from the de-acetalization has to
be given here. After hydrolysis of the formed acetal,
benzaldehyde and p-TsOH were extracted out with
CH Cl . The left aqueous layer was concentrated to afford
2-Ethyl-5,5-bis(1-(1-methylimidazolium)methyl-1,3-
dioxane hexafluorophosphate (9, C H N O P F )
1
6 26 4 2 2 12
White solid (2.80 g, 94%), mp 94 °C; FT–IR (KBr) ꢀm =
2
2
3
161, 3122, 2935, 2897, 1569, 1445, 1417, 1304, 1176,
-
the white solid as the released diol-functionalized IL 1 with
high purity after washing ethanol and dryness in vacuo.
1
1
1
017, 846 cm
;
H
NMR (500 MHz, DMSO-d6,)
d = 0.95 (t, 3H, J = 8 Hz, CH ), 1.30 (m, 2H, CH –
3
2
Acknowledgments We acknowledge the National Natural Science
Foundation of China (no. 20673039, 20533010, 20590366), China
Postdoctoral Science Po-undation (no. 44021220), and the Science
and Technology Commission of Shanghai Municipality (no.
06JC14023) for financial support.
CH ), 3.85 (s, 6H, N–CH ), 3.95 (d, 2H, J = 12 Hz, O–
3
3
CH ), 4.03 (d, 2H, J = 12 Hz, O–CH ), 4.15 (s, 2H,
2
2
N–CH ), 4.55 (s, 2H, N–CH ), 5.50 (s, 1H, CH), 7.65 (s,
2
2
1
H, NCH), 7.70 (s, 1H, NCH), 7.75 (s, 1H, NCH), 7.80
s, 1H, NCH), 9.01 (s, 1H, N (H) CN), 9.06 (s, 1H, N (H)
CN) ppm.
(
References
2-Butyl-5,5-bis(1-(1-methylimidazolium)methyl-1,3-
dioxane hexafluorophosphate (10, C H N O P F )
White solid (2.96 g, 95%), mp 99 °C; FT–IR (KBr); ꢀm =
1
8 30 4 2 2 12
1
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3
8
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168, 3134, 2924, 2897, 1565, 1448, 1429, 1180, 1021,
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1 1
54 cm ; H NMR (500 MHz, DMSO-d ,) d = 1.05 (t,
6
3
4
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3
2
3
CH –CH ), 1.95 (m, 2H, CH –CH), 3.90 (s, 6H, N–CH ),
2
2
2
3
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2
O–CH ), 4.20 (s, 2H, N–CH ), 4.55 (s, 2H, N–CH ), 5.55
2
2
2
6
7
. Warmus JS, Silva MI (2000) Org Lett 13:1807
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(
s, 1H, CH), 7.65 (s, 1H, NCH), 7.70 (s, 1H, NCH), 7.75 (s,
H, NCH), 7.80 (s, 1H, NCH), 9.10 (s, 1H, N (H) CN), 9.15
s, 1H, N (H) CN) ppm.
1
(
8. Linclau B, Singh AK, Curran DP (1999) J Org Chem 64:2835
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9
2-Cyclohexyl-5,5-bis(1-(1-methylimidazolium)methyl-1,3-
dioxane hexafluorophosphate (11, C H N O P F )
1
0. Zhang W, Chen CHT, Nagashima T (2003) Tetrahedron Lett
4:2065
1
9 30 4 2 2 12
4
White solid (1.17 g, 37%), mp 117 °C; FT–IR (KBr); ꢀm =
1
1
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-
1
1
1
029, 854 cm
;
H NMR (500 MHz, DMSO-d6,)
123

4
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1
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1
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1
2
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1
23