3,4-Difluoropyrrole-, 3,3,4,4-tetrafluoropyrrolidine- and pyrrolidine-based liquid crystals

Article abstract of DOI:10.1016/j.jfluchem.2013.07.022

A new class of liquid crystals was formed with N-heterocycles as the terminal group, such groups as a 3,4-difluoropyrrole, 3,3,4,4- tetrafluoropyrrolidine, or pyrrolidine. Their properties were modified by varying the terminal heterocycles and/or the leng

Full text of DOI:10.1016/j.jfluchem.2013.07.022

Journal of Fluorine Chemistry 156 (2013) 327–332
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
3,4-Difluoropyrrole-, 3,3,4,4-tetrafluoropyrrolidine- and
pyrrolidine-based liquid crystals
a
a
c
d
d
Peilian Liu , Hongren Chen , Stelck Daniel , Deyu Hang , Lei Zhao ,
a
a,b,
Hui Wang , Zhuo Zeng
*
a
College of Chemistry & Environment, South China Normal University, Guangzhou 510006, China
Key Laboratory of Organofluorine Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China
Department of Chemistry, University of Idaho, Moscow, ID 83844-2343, USA
b
c
d
Beijing Bayi Space LCD Materials Technology Co., Ltd., Beijing 102205, China
A R T I C L E I N F O
A B S T R A C T
Article history:
A new class of liquid crystals was formed with N-heterocycles as the terminal group, such groups as a
Received 3 May 2013
3
,4-difluoropyrrole, 3,3,4,4-tetrafluoropyrrolidine, or pyrrolidine. Their properties were modified by
Received in revised form 20 July 2013
Accepted 31 July 2013
varying the terminal heterocycles and/or the length of the alkyl chains on the cyclohexane liquid crystal
building block. A comparison of the non-fluorinated and fluorinated pyrrolidine and fluorinated pyrrole
as terminal group in the cyclohexane liquid crystals was studied. The mesophase behaviour was affected
by altering the polarity of the terminal N-heterocycle. Compounds n/m-4H having the terminal
pyrrolidine show a nematic phase. Comparatively, compounds 3/2-4F and 5/2-4F, having a fluorinated
pyrrolidine, exhibit SmG phase. With 3,4-difluoropyrrole as terminal group, n/m-2F exhibit the broadest
nematic phase range and good thermal stability, thus meeting the criterion for high performance liquid
crystals materials.
Available online 13 August 2013
Keywords:
Fluorine
Heterocycles
Liquid crystals
Mesophases
Phase transitions
ß 2013 Elsevier B.V. All rights reserved.
1
. Introduction
The development of stable mesophases with broad mesomor-
lead to the increasing of viscosity, which will delay the response
time [22]. Therefore, compounds that exhibit broad nematic phase
range, high dielectric anisotropy, moderate birefringence, and low
viscosity are promising for display applications.
phic ranges [1–3] and low viscosities [4–8] continues to be of great
interest. Liquid crystal compounds with fluorine and fluorinated
alkyl substituents with such physical properties offer significant
advantages over currently used liquid crystal materials [9–12]. The
location of fluoro substituents include terminal group [13], linking
arm [14], lateral and core position [15–17]. The introduction of a
fluorine atom or fluorinated group into liquid crystals systems will
change the properties of these materials, such as broadening the
nematic phase range, decreasing smectic phase range, lowering the
melting point and increasing the dielectric anisotropy [18,19].
For display applications, broad nematic phase range and good
chemical stability are essential factors, however complicated
interdependent relationship exists among dielectric anisotropy,
viscosity, birefringence, threshold voltage and response time [20].
Liquid crystals (LCs) with strongly positive dielectric anisotropy
help lower both the threshold voltage and power consumption
The substituents, 3,4-difluorobenzene and 3,4,5-trifluoroben-
zene, are chemically stable and are able to react with a variety of
liquid crystal building blocks. This makes them promising
candidates in the development of new liquid crystal materials.
There are reports of many 3,4-difluorophenol and 3,4,5-trifluor-
ophenol derivatives as TFT (thin film transistor) liquid crystal
materials. Some of these reported liquid crystal molecules
[18,23,24] are shown in Scheme 1. Using 3,4,5-trifluorophenol
as a building block one can achieve a high and stable dielectric
anisotropy yet maintain a low viscosity.
Generally, the synthesis of 3,4,5-trifluorophenol often uses the
grignard reagents as the starting material and the reaction should
be conducted under nitrogen or argon atmospheres, using air-free
techniques [25]. These stringent reaction conditions make the
preparation process difficult. It is possible that 3,4,5-trifluoro-
benzene in the LCs can be replaced by the fluorinated heterocycles,
inviting a study of structure and the change in properties of these
fluorinated liquid crystals (FLCs). Some of FLCs have been found to
display outstanding liquid crystal properties and open the way to
future perspective applications in optoelectronics [26,27]. A liquid
crystal display device using a liquid crystal composition containing
the 3,4-disubstituted pyrrole and drivable at low voltage was
[
21], but excessive strongly positive dielectric anisotropy often
*
Corresponding author at: College of Chemistry & Environment, South China
Normal University, Guangzhou 510006, China. Tel.: +86 20 39310258;
fax: +86 20 3931 0287.
E-mail addresses: zhuoz@scnu.edu.cn, zhuosioc@126.com (Z. Zeng).
0022-1139/$ – see front matter ß 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jfluchem.2013.07.022

3
28
P. Liu et al. / Journal of Fluorine Chemistry 156 (2013) 327–332
O
F
previous experiments, the aryl amines react with the trifluor-
omethanesulfonic acid polyfluoroalkyldiyl ester to give N-based
fluoro-heterocycles 4-(3,3,4,4-tetrafluoropyrrolidin-1-yl)-benze-
namine in high yield [29]. The trifluoromethanesulfonic acid
alkyldiyl and polyfluoroalkyldiyl esters 2a-b, were reacted with 4-
O
F
F
3 7
C H
O
F
3 7
C H
O
F
High dielectric anisotropy, low viscosity TFT Liquid Crystal
Scheme 1. 3,4-Difluorophenol, 3,4,5-trifluorophenol based liquid crystals.
3 3 2
aminophenol in the presence of Et N in CH CH OH to give 4-
pyrrolidin-1-yl-phenol, 3-4H, and 4-(3,3,4,4-tetrafluoropyrrolidin-
1-yl) phenol, 3-4F, respectively.
reported by Chisso Corporation [28]. Modification of the N-
heterocycles structure and/or the length of the alkyl chains on the
cyclohexane building block has shown marked influences in the
properties of these liquid crystals. In this work, we report a series of
cyclohexane-based liquid crystals with pyrrolidine, 3,3,4,4-tetra-
fluoropyrrolidine, and 3,4-difluoropyrrole as terminal group in an
effort to establish the impact of the fluorinated N-heterocycle on
the liquid crystal physical and chemical properties. Varying the
terminal N-heterocycles from pyrrolidine to 3,3,4,4-tetrafluoro-
pyrrolidine, further defluorination to the aromatic 3,4-difluor-
opyrrole, it is possible to increase or decrease the polarity and the
interlayer force which affects the mesophase behaviour and
physical properties.
The 3,4-difluoropyrrole was synthesized by the double
elimination H-F reaction of 3,3,4,4-tetrafluoropyrrolidine with
equimolar t-BuOK in DMSO as solvent at room temperature for
30 min as previously reported [30]. When 4-(3,3,4,4-tetrafluor-
opyrrolidin-1-yl) phenol, 3-4F was reacted with t-BuONa, a
higher concentration of the base (4 M), a higher reaction
temperature (100 8C) and a longer reaction time (12 h) were
required to drive the reaction to completion. The product 4-(1H-
3,4-difluoropyrrole-1-yl) phenol, 3-2F, was conveniently isolat-
ed by flash chromatography on silica gel with ethyl acetate-
petroleum ether (1:5) as an eluent to give a white solid in 80%
yield. Next, the cyclohexane-based liquid crystal building block
0
0
trans-4 -alkyl-(1,1 -mono or bicyclohexyl)-4-carboxylic acid
3CA, 5CA, 3CCA, and 5CCA) was esterified with the correspond-
ing phenol, 4-pyrrolidin-1-yl-phenol, 3-4H, 4-(3,3,4,4-tetra-
fluoropyrrolidin-1-yl) phenol, 3-4F, and 4-(1H-3,4-
(
2
. Results and discussion
2.1. Synthesis
difluoropyrrole-1-yl) phenol, 3-2F, using dicyclohexylcarbodii-
mide (DCC) and N,N-dimethylaminopyridine (DMAP) in dichlor-
omethane to give n/m-4H, n/m-4F, n/m-2F in high yield. This is
Novel liquid crystals n/m-4H and their fluorinated derivatives
n/m-4F, n/m-2F were synthesized as shown in Scheme 2. In the
R=C2F4 1a
R=C H 1b
HOCH RCH OH
2
2
2
4
i
R=C2F4 2a
R=C H 2b
TfOCH RCH OTf
2
2
2
4
NH
2
ii
OH
F
F
F
iii
HO
N
F
HO
N
HO
N
F
F
3
- 4H
iv
3- 4F
v
3
- 2F
O
F
F
vi
H2n+1Cn
F
F
O
N
m
n/m-4F
O
O
F
F
H2n+1Cn
H2n+1Cn
O
m
N
O
N
m
n/m-4H
n/m-2F
3 2 2 2 2 3
Reagents and conditions: i: (CF SO ) O, CH Cl , RT, 12h. ii: Et N, EtOH, 90 °C, 24h.
iii : t-BuONa, DMSO, 100 °C, 12h. iv, v, vi : 3CA, or 3CCA, or 5CA, or 5CCA, DCC, DMAP, CHCl
5CA: n=5, m=1.
CCA: n=5, m=2
3
, 80 °C, 12h.
O
3
CA: n=3, m=1.
H2n+1Cn
3CCA: n=3, m=2.
5
OH
m
4
H, 4F, 2F represent pyrrolidine, 3,3,4,4-tetrafluoropyrrolidine, and 3,4- difluoropyrrole respectively
Scheme 2. Synthesis of N-heterocycles liquid crystals.

P. Liu et al. / Journal of Fluorine Chemistry 156 (2013) 327–332
329
Table 1
Compounds 3/2-4F, 5/1-2F, 5/2-2F, and 3/1-4H show three
endothermic peaks in the heating cycle, e.g., 3/2-4F (Cr 53.8 8C,
Thermal behaviour of the new compounds.
a
b
0 0
Cr 91.6 8C, SmG 208 8C), 5/1-2F (Cr 94 8C, Cr 110 8C, N 137 8C), 5/2-
Compounds Transition temperatures (8C)
T
d
(8C)
ꢀ
1
[
Enthalpies of transition] (J g
)
0
0
2
F (Cr 97 8C, Cr 131 8C, N 282 8C), 3/1-4H (Cr 73 8C, Cr 102 8C, N
0
3/2-2F
5/2-2F
3/1-2F
5/1-2F
3/2-4F
5/2-4F
3/1-4F
5/1-4F
3/2-4H
5/2-4H
3/1-4H
5/1-4H
Cr 157.5 [10.58], N 289.5 [1.89]
Iso 314
Iso 324
Iso 265
Iso 272
114 8C); a Cr–Cr transition was seen before the appearance of a
0
Cr 97.1 [4.00], Cr 131.0 [6.20], N 282.0 [1.00]
mesophase phase. The result was verified by POM as there was no
Cr 103.5 [10.98], N 133.6 [1.42]
0
mesophase between the Cr–Cr transition temperature ranges.
0
Cr 94.0 [10.58], Cr 110.0 [0.64], N 137.0 [0.68]
The nematic phase range of the liquid crystals with a 3,4-
difluoropyrrole as terminal group are broader than those with
pyrrolidine with the same cyclohexane building block, e.g., 3/2-2F
0
Cr 53.8 [3.49], Cr 91.60 [6.20], SmG 208.6 [6.08] Iso 313
Cr 113.0 [2.93], SmG 207.0 [6.95]
Cr 141.3[5.02]
Iso 328
Iso 293
Iso 309
Iso 349
Iso 340
Iso 298
Iso 306
Cr 136.2 [4.98]
(
Cr 157.5 8C, N 289.5 8C), which is broader than 3/2-4H (Cr 165.2 8C,
Cr 165.2 [6.30], N 276.2 [0.98]
Cr 159.3 [10.64], N 267.3 [1.86]
N 276.2 8C). Replacing the one-ring cyclohexane building block
(3CA, 5CA) with two-ring cyclohexane (3CCA, 5CCA) results in an
increase in the nematic phase range, e.g., 3/2-2F (Cr 157.5 8C, N
289.5 8C) and 3/1-2F (Cr 103.5 8C, N 133.6 8C). Two-ring cyclohex-
anes show a broad mesomorphism range from 100 8C to 151 8C. As
a result, the two-ring cyclohexane elongates the molecule to give
the appropriate length to width ratio, which is propitious to the
forming and stability of mesomorphism.
0
Cr 73.2 [1.12], Cr 102.2 [5.25], N 114.2 [1.68]
Cr 101.8 [6.0], N 116.8 [0.88]
a
Cr, SmG, N, Iso indicate crystal, smectic phase G, nematic phase and isotropic
phase, respectively.
b
Decomposition temperature.
the first example of the cyclohexane-based liquid crystals with
N-heterocycles, pyrrolidine, 3,3,4,4-tetrafluoropyrrolidine, and
The introduction of fluorine atoms into liquid crystal molecular
causes the change in physical properties. In general, the new
compounds with 3,4-difluoropyrrole as terminal group exhibit the
highest clearing point, e.g., comparing with the analogous 3,3,4,4-
tetrafluoropyrrolidine, and pyrrolidine terminal compounds, e.g.,
3
,4-difluoropyrrole, as terminal group, most of which display
broad mesomorphic range and high thermal stability.
2.2. Liquid crystalline properties
5/2-2F and 5/2-4F, at Cp. 282.5 8C and 207 8C respectively while 5/
As shown in Table 1, the new compounds containing N-
2-4H has Cp. 267.3 8C. The lower melting temperature and higher
clearing point is advantageous for potential application.
heterocycles as the end group display good liquid crystal
properties. The three factors which affect the mesomorphic
behaviour include: (1) the structure of the N-heterocycles; (2)
the polyfluoroalkyl or fluorine substituent group on the N-
heterocycles; and (3) the nature of the cyclohexane liquid crystal
building block.
Transition temperatures and enthalpies of transition for
compounds n/m-4F, n/m-2F and n/m-4H are given in Table 1.
All the synthesized compounds show thermotropic liquid crystal-
line phases except compounds 3/1-4F and 5/1-4F, whereby the
mesomorphism type is dramatically dependent on the type of N-
heterocycles. Investigations by DSC and POM show compounds 3/
Thermal stabilities, which range from 270 8C to 350 8C and
depend on the heterocycle and the cyclohexane building block,
were determined by thermal gravimetric analysis (TGA). Data
show that the decomposition temperatures were higher than the
clearing point for these compounds. The decomposition tempera-
tures of the new compounds are shown in Table 1. In general, the
new compounds with one-ring cyclohexane are thermally less
stable than their two-ring cyclohexane analogue. The new
compounds with 3,3,4,4-tetrafluoropyrrolidine, and 3,4-difluor-
opyrrole as terminal group show similar thermal stability and are
mesophase stable to high temperature.
1
-4F and 5/1-4F melt into isotropic liquids at 141.3 8C and 136.2 8C
The typical structures of the liquid crystals 3/2-4H, 3/2-4F, and
3/2-2F, with the same cyclohexane building block and different N-
heterocycles as terminal group, were investigated by X-Ray
diffraction. The diffraction patterns obtained for 3/2-2F and 3/2-
4H are given in the supporting information. The 3/2-2F and 3/2-4H,
with 3,4-difluoropyrrole and pyrrolidine terminal group, only a
wide diffraction peak was observed in the wide angle region and no
diffraction peak was found in the small angle region. This indicates
that no lamellar ordering exists in the mesophase. The diffraction
directly and no texture of liquid crystal being observed. The series
of n/m-4H and n/m-2F with terminal pyrrolidine and 3,4-
difluoropyrrole showed a typical nematic phase. Their nematic
phase was evidenced based on its schlieren texture as shown in
Fig. 1. The mosaic texture of SmG can be seen in n/m-4F which is
the n/m-4H fluoroalkyl derivatives, e.g., 5/2-4F (Cr 113 8C, SmG
0
2
07 8C) and 3/2-4F (Cr 53.8 8C, Cr 91.6 8C, SmG 208 8C). An
example of such a texture is given in the supporting information.
Figure 1. POM texture for 3/2-2F at 240 8C.
Figure 2. XRD diffraction pattern for 3/2-4F recorded at 150 8C.

3
30
P. Liu et al. / Journal of Fluorine Chemistry 156 (2013) 327–332
pattern of 3/2-4F is given in the Fig. 2. In the case of 3/2-4F with
slowly added over 1 h. The mixture was stirred for 12 h, then
washed with water (3 ꢁ 30 mL), and dried over anhydrous sodium
sulfate. The solvent was removed under vacuum to give
trifluoromethanesulfonic acid 2,2,3,3-tretrafluoro-1,4-butanedily
ester.
3
,3,4,4-tetrafluoropyrrolidine as terminal group, a strong sharp
˚
scattering at 3.778 corresponding to the d spacing of 23.4 A was
given in the small angle region. In the wide angle region, four
scattering at 11.278, 12.008, 18.508, and 18.708 corresponding to
˚
˚
˚
˚
the d spacing of 7.85 A, 7.34 A, 4.80 A, and 4.70 A respectively were
obtained. The SmG showed several sharp diffraction peaks in the
wide angle region in previous reports [31–33]. The SmG Phase was
assigned for 3/2-4F by the photomicrographs optical texture as
well as X-ray diffraction (XRD) spectrum characterization.
4.3. General procedure for the preparation of 4-(3,3,4,4-
tetrafluoropyrrolidin-1-yl) phenol (3-4F)
Trifluoromethanesulfonic acid 2,2,3,3,-tretrafluoro-1,4-butane-
3
diyl ester 2a (5 mmol), 4-aminophenol (5 mmol), and Et N
3
. Conclusion
(12.5 mmol) in 15 mL ethanol were placed in a Pyrex glass tube,
sealed, heated at 90 8C for 24 h. After cooling, the organic solvent
was removed under reduced pressure. 30 mL of dichloromethane
was added to the residue and was then washed with water
A new class of N-heterocycles based liquid crystals were
synthesized that employed 3,4-difluoropyrrole, 3,3,4,4-tetrafluor-
opyrrolidine, and pyrrolidine as terminal group. Their melting
points, decomposition temperatures, clearing points, mesomorph-
ism type were determined. The properties of these liquid crystals
can be adjusted by using different N-heterocycles, cyclohexane
building blocks, fluoroalkyl and fluorine substituents on the N-
heterocycles. They show a wide mesophase range and are
mesophase stable to high temperatures. The mesophase behaviour
was affected by altering the terminal N-heterocycle. Compounds n/
m-4H having the terminal pyrrolidine show a broad nematic range.
With 3,4-difluoropyrrole as terminal group, n/m-2F exhibit the
broadest nematic range and good thermal stability. Compounds 3/
(3 ꢁ 30 mL), dried over anhydrous Na
2 4
SO . After the solvent was
removed, the crude product was chromatographed on silica gel
with ethyl acetate-petroleum ether (1:5) as an eluent to give white
1
solid. 75% yield. H NMR (CDCl
3
)
d
(ppm): 6.81 (d, J = 8.6 Hz, 2H),
1
9
3
6.44 (d, J = 8.8 Hz, 2H), 3.74 (t, J = 10.4 Hz, 4H). F NMR (CDCl ) d
(ppm): ꢀ121.95 (m, 4F). MS (ESI) m/z: 234.91(M ). Anal. Calcd (%)
for C10 NO (235.18): C, 51.07; H, 3.86; N, 5.96. Found: C, 51.06;
+
9 4
H F
H, 3.83; N, 5.97.
4.4. General procedure for the preparation of 4-(1H-3,4-
difluoropyrrole-1-yl) phenol (3-2F)
2
-4F and 5/2-4F, bearing fluorinated pyrrolidine, exhibit SmG
Phase. The two CF groups increase the molecular polarity. It would
2
4-(3,3,4,4-Tetrafluoropyrrolidin-1-yl) phenol 3-4F (2 mmol),
sodium tert-butoxide (16 mmol) in 10 mL dimethyl sulfoxide were
placed in a Pyrex glass tube, sealed, heated at 100 8C for 12 h. After
cooling, 30 mL dichloromethane was added to the reaction mixture
and then washed with water (3 ꢁ 30 mL) and dried over anhydrous
favour the enhancement of interlayer interactions which contrib-
ute to the formation of layer arrangement smectic phase. New
compounds with one-ring cyclohexane building block are ther-
mally less stable than their two-ring cyclohexane analogue. The
fluorinated heterocycles can replace the expensive 3,4-difluor-
obenzene and 3,4,5-trifluorobenzene in LCs to form promising
liquid crystal materials.
2 4
Na SO . After the solvent was removed, the crude product was
chromatographed on silica gel with ethyl acetate–petroleum ether
1
(1:5) as an eluent to give white solid. 80% yield. H NMR (CDCl
3
) d
(
ppm): 7.14 (d, J = 8.7 Hz, 2H), 6.87 (d, J = 8.7 Hz, 2H), 6.61 (s, 2H),
1
9
4
. Experimental
4.89 (s, 1H). F NMR (CDCl
z: 196.27(M +H ). Anal. Calcd (%) for: C10 NO (195.17): C,
3
)
d
(ppm): ꢀ178.29 (s, 2F). MS (ESI) m/
+
+
7 2
H F
4.1. General considerations
61.54; H, 3.62; N, 7.18. Found: C, 61.55; H, 3.64; N, 7.16.
All the reagents used were analytical reagents purchased from
4.5. General procedure for the preparation of 4-pyrrolidin-1-yl-
phenol (3-4H)
1
19
commercial sources and used as received. H and
F were
recorded on a 400 MHz nuclear magnetic resonance spectrometer
operating at 400 and 376 MHz respectively. Chemical shifts were
Trifluoromethanesulfonic acid 1,4-butanediyl ester 2b
(5 mmol), 4-aminophenol (5 mmol), and Et N (12.5 mmol) in
3
1
19
reported relative to Me
either CDCl unless otherwise specified. Thermogravimetric
analysis (TGA) measurements were performed at a heating rate
4
Si for H and CCl
3
F for F. The solvent was
3
15 mL ethanol were placed in a Pyrex glass tube, sealed, heated at
90 8C for 24 h. After cooling, the organic solvent was removed
under reduced pressure to the residue was added 30 mL
dichloromethane then washed with water (3 ꢁ 30 mL), dried over
ꢀ1
of 10 8C min with a Netzsch STA409PC (Germany) instrument.
ꢀ
1
The DSC was recorded at a scan rate of 2 8C min on a Netzsch
DSC200PC apparatus. Optical micrographs were observed with a
polarizing optical microscope (POM) (Nikon LINKAM-THMSE600)
equipped with a heating plate (HCS601). Variable-temperature X-
ray diffraction (XRD) experiments were performed on a Bruker D8
2 4
anhydrous Na SO . After the solvent was removed, the crude
product was chromatographed on silica gel with ethyl acetate–
1
petroleum ether (1:5) as an eluent to give white solid, 78% yield. H
NMR (DMSO)
d (ppm): 8.48(s, 1H), 6.62 (d, J = 8.8, 2H), 6.39 (d,
Advance X-ray diffractometer (using Cu Ka1 radiation of a
J = 8.8, 2H), 3.10 (t, J = 7.2, 4H), 1.90 (m, 4H). MS (ESI) m/z: 164.20
(M +H ).
+
+
˚
wavelength of 1.54 A) with temperature controller. Elemental
analyses were performed on an EXETER CE-440 Elemental
Analyzer.
4.6. General procedure for the preparation of n/m-4F, n/m-2F and n/
m-4H
4.2. General procedure for the preparation of
trifluoromethanesulfonic acid 2,2,3,3-tretrafluoro-1,4-butanediyl
4-(3,3,4,4-Tetrafluoropyrrolidin-1-yl) phenol 3-4F, 4-(1H-3,4-
difluoropyrrole-1-yl) phenol 3-2F or 4-pyrrolidin-1-yl-phenol 3-
ester 2a and trifluoromethanesulfonic acid 1,4-butanedily ester 2b
4H (1 mmol), trans-4-(trans-4-n-alkylcyclohexyl)cyclohexanecar-
2
,2,3,3-Tetrafluoro-1,4-butanediol 1a, or 1,4-butanediol 1b
boxylic acid or trans-4-n-alkylcyclohexanecarboxylic acid
(1 mmol), N,N -dicyclohexyl carbodiimide (DCC) (1 mmol), 4-
0
(
1 mmol), pyridine (3 mmol) and dichloromethylene (20 mL) were
stirred at room temperature. After 30 min, trifluoromethanesul-
fonic anhydride (2.5 mmol) in 10 mL dichloromethylene was
dimethylaminopyridine (DMAP) (0.05 mmol) in 10 mL chloroform
were placed in a Pyrex glass tube, sealed, heated at 80 8C for 12 h.

P. Liu et al. / Journal of Fluorine Chemistry 156 (2013) 327–332
331
After cooling, the white solid was filtrated off, the solvent was
Anal. Calcd (%) for: C22
H
29
F
4
NO
2
(415.46): C, 63.60; H, 7.04; N, 3.37.
removed under vacuum, and then the crude product was
chromatographed on silica gel with dichloromethylene–petroleum
ether (2:1) as an eluent to give n/m-4F, n/m-2F and n/m-4H.
Trans-4-(trans-4-n-propylcyclohexyl)cyclohexanecarboxylic
Found: C, 63.62; H, 7.05; N, 3.40.
Trans-4-n-pentylcyclohexanecarboxylic acid 4 -(3,4-difluoro-
pyrrole-1-yl) phenyl ester (5/1-2F). 80% yield; white solid; H NMR
(CDCl ) d (ppm): 7.24 (d, J = 8.7 Hz, 2H), 7.10 (d, J = 8.8 Hz, 2H), 6.68
3
(s, 2H), 2.45 (t, J = 12.2 Hz, 1H), 2.12 (d, J = 12.2 Hz, 2H), 1.87 (d,
J = 12.4 Hz, 2H), 1.56 (t, J = 11.6 Hz, 2H), 1.37–1.16 (m, 9H), 1.04–
0
1
0
acid 4 -(3,3,4,4-tetrafluoropyrrolidin-1-yl) phenyl ester (3/2-4F).
1
8
2
2
4
1
7% yield; white solid; H NMR (CDCl
3
)
d
(ppm): 6.99 (d, J = 8.7 Hz,
1
9
H), 6.51 (d, J = 8.8 Hz, 2H), 3.86–3.75 (m, 4H), 2.4–2.38 (m, 1H),
.14 (d, J = 12.4 Hz, 2H), 1.85 (d, J = 10.4 Hz, 2H), 1.74 (t, J = 14.7 Hz,
H), 1.51 (t, J = 12.3 Hz, 2H), 1.30 (m, J = 13.7, 6.9 Hz, 2H), 1.18–
0.94 (m, 2H), 0.89 (t, J = 6.7 Hz, 3H). F NMR (CDCl
3
)
d
(ppm):
ꢀ122.69 (m, 4F). MS (ESI) m/z: 375.3 (M ). Anal. Calcd (%) for:
NO (375.2): C, 70.38; H, 7.25; N, 3.73. Found: C, 70.31; H,
7.21; N, 3.72.
+
C
22
H
27
F
2
2
1
9
.07 (m, 6H), 1.04–0.95 (m, 3H), 0.87 (t, J = 7.2 Hz, 5H). F NMR
+
(CDCl
3
)
d
(ppm): ꢀ122.69 (m, 4F). MS (ESI) m/z: 469.50 (M ). Anal.
NO (469.56): C, 66.51; H, 7.51; N, 2.98.
Trans-4-(trans-4-n-propylcyclohexyl)cyclohexanecarboxylic
0
Calcd (%) for: C26
H
35
F
4
2
acid 4 -(pyrrolidin-1-yl) phenyl ester (3/2-4H). 78% yield; white
1
Found: C, 66.47; H, 7.46; N, 3.00.
solid; H NMR (CDCl
3
)
d
(ppm): 6.90 (d, J = 8.5 Hz, 2H), 6.51 (d,
Trans-4-(trans-4-n-propylcyclohexyl)cyclohexanecarboxylic
J = 7.5 Hz, 2H), 3.26 (t, J = 12.3 Hz, 4H), 2.41 (t, J = 12.1 Hz, 1H), 2.13
(d, J = 12.3 Hz, 2H), 1.99 (m, 4H), 1.84 (d, J = 10.5 Hz, 2H), 1.73 (t,
J = 14.2 Hz, 4H), 1.52 (m, 3H), 1.34–1.26 (m, 2H), 1.7–0.96 (m, 9H),
0
acid 4 -(1H-3,4-difluoropyrrole-1-yl) phenyl ester (3/2-2F). 85%
1
yield; white solid; H NMR (CDCl
3
)
d
(ppm): 7.24 (d, J = 8.7 Hz,
+
+
2
2
H), 7.10 (d, J = 8.7 Hz, 2H), 6.68 (s, 2H), 2.46 (t, J = 12.2 Hz, 1H),
.15 (d, J = 12.3 Hz, 2H), 1.86 (d, J = 10.3 Hz, 2H), 1.74 (t,
0.89–0.85 (m, 4H). MS (ESI) m/z: 398.56 (M +H ). Anal. Calcd (%)
for: C26 (397.59): C, 78.54; H, 9.89; N, 3.52. Found: C, 78.59;
H
39NO
2
J = 14.6 Hz, 4H), 1.53 (q, J = 12.0 Hz, 2H), 1.31 (m, 2H), 1.19–
H, 9.90; N, 3.55.
1
9
0
.96 (m, 9H), 0.87 (t, J = 7.1 Hz, 5H). F NMR (CDCl
3
)
d
(ppm):
177.34 (s, 2F). MS (ESI) m/z: 452.10 (M +Na ). Anal. Calcd (%)
NO (429.54): C, 72.70; H, 7.74; N, 3.26. Found: C,
Trans-4-(trans-4-n-pentylcyclohexyl)cyclohexanecarboxylic
+
+
0
1
ꢀ
acid 4 -(pyrrolidin-1-yl) phenyl ester (5/2-4H). 76% yield; white
for: C26
H
33
F
2
2
solid; H NMR (CDCl
3
)
d
(ppm): 6.90 (d, J = 8.2 Hz, 2H), 6.51 (d,
7
2.34; H, 7.73; N, 3.29.
Trans-4-n-propylcyclohexanecarboxylic acid 4 -(3,3,4,4-tetra-
fluoropyrrolidin-1-yl) phenyl ester (3/1-4F). 85% yield; white
J = 8.1 Hz, 2H), 3.26 (t, J = 12.3 Hz, 4H), 2.42 (t, J = 12.1 Hz, 1H), 2.14
(d, J = 12.5 Hz, 2H), 1.99 (m, 4H), 1.88–1.65 (m, 7H), 1.52 (m, 2H),
1.36–1.19 (m, 15H), 1.17–0.84 (m, 4H). MS (ESI) m/z: 426.57 (M ).
0
+
1
solid; H NMR (CDCl
J = 8.9 Hz, 2H), 3.80 (m, 4H), 2.45 (m, 1H), 2.12 (d, J = 11.6 Hz, 2H),
.86 (d, J = 13.6 Hz, 2H), 1.54 (m, 2H), 1.41–1.14 (m, 6H), 1.08–0.85
3
)
d
(ppm): 6.99 (d, J = 8.9 Hz, 2H), 6.51 (d,
Anal. Calcd (%) for: C28
Found: C, 78.90; H, 10.01; N, 3.05.
Trans-4-n-propylcyclohexanecarboxylic acid 4 -(pyrrolidin-1-
2
H43NO (426.65): C, 79.01; H, 10.18; N, 3.29.
0
1
1
9
1
(m, 4H). F NMR (CDCl
3
)
d
(ppm): ꢀ122.69 (m, 4F). MS (ESI) m/z:
3
yl) phenyl ester (3/1-4H). 79% yield; white solid; H NMR (CDCl ) d
+
+
3
88.2 (M +H ). Anal. Calcd (%) for: C20 NO (387.41): C, 62.00;
H
25
F
4
2
(ppm): 6.91 (d, J = 8.4 Hz, 2H), 6.52 (d, J =7.3 Hz, 2H), 3.26 (t,
J = 12.1 Hz, 4H), 2.44 (t, J = 12.1 Hz, 1H), 2.12 (d, J = 12.5 Hz, 2H),
2.00 (m, 4H), 1.86 (d, J = 12.1 Hz, 2H), 1.55 (m, 2H), 1.31 (m, 4H),
H, 6.50; N, 3.62. Found: C, 62.02; H, 6.54; N, 3.63.
0
Trans-4-n-propylcyclohexanecarboxylic acid 4 -(3,4-difluoro-
1
+
pyrrole-1-yl) phenyl ester (3/1-2F). 86% yield; white solid; H NMR
1.23–1.14 (m, 2H), 0.94 (m, 4H). MS (ESI) m/z: 315.55 (M ). Anal.
(
(
CDCl
3
)
d
(ppm): 7.24 (d, J = 8.7 Hz, 2H), 7.11 (d, J = 8.8 Hz, 2H), 6.68
Calcd (%) for: C20
C, 76.40; H, 10.30; N, 4.61.
Trans-4-n-pentylcyclohexanecarboxylic acid 4 -(pyrrolidin-1-
2
H29NO (315.45): C, 76.15; H, 9.27; N, 4.44. Found:
s, 2H), 2.48 (t, J = 12.1 Hz, 1H), 2.13 (d, J = 12.4 Hz, 2H), 1.88 (d,
0
J = 12.5 Hz, 2H), 1.63–1.48 (m, 2H), 1.40–1.26 (m, 3H), 1.25–1.15
1
9
1
(
(
m, 2H), 0.98 (d, J = 12.7 Hz, 2H), 0.90 (t, J = 7.1 Hz, 3H). F NMR
3
yl) phenyl ester (5/1-4H). 75% yield; white solid; H NMR (CDCl ) d
+
CDCl
3
)
d
(ppm): ꢀ177.34 (s, 2F). MS (ESI) m/z: 347.85 (M ). Anal.
NO (347.80): C, 69.15; H, 6.67; N, 4.03.
(ppm): 6.90 (d, J = 8.4 Hz, 2H), 6.51 (d, J = 7.8 Hz, 2H), 3.26 (t,
J = 12.1 Hz, 4H), 2.44 (t, J = 12.1 Hz, 1H), 2.11 (d, J = 12.5 Hz, 2H),
2.00 (m, 4H), 1.86 (d, J = 12.5 Hz, 2H), 1.61–1.50 (m, 2H), 1.37–1.15
Calcd (%) for: C20
Found: C, 69.12; H, 6.65; N, 4.04.
H
23
F
2
2
+
+
Trans-4-(trans-4-n-pentylcyclohexyl)cyclohexanecarboxylic
(m, 10H), 0.93 (m, 4H). MS (ESI) m/z: 344.44 (M + H ). Anal. Calcd
(%) for: C22 (343.50): C, 76.92; H, 9.68; N, 4.08. Found: C,
0
acid 4 -(3,3,4,4-tetrafluoropyrrolidin-1-yl) phenyl ester (5/2-4F).
8
2
H33NO
2
1
2% yield; white solid; H NMR (CDCl
H), 6.50 (d, J = 8.9 Hz, 2H), 3.80 (m, 4H), 2.43 (m, J = 1H), 2.13 (d,
3
)
d
(ppm): 6.99 (d, J = 8.9 Hz,
76.60; H, 9.58; N, 4.12.
J = 11.5 Hz, 2H), 1.95–1.75 (m, 4H), 1.71 (d, J = 13.4 Hz, 3H), 1.61–
Acknowledgments
1
9
1
.15 (m, 11H), 1.16 (s, 2H), 1.07 (m, 10H), 0.88 (t, J = 6.9 Hz, 6H).
NMR (CDCl
(ppm): ꢀ122.69 (m, 4F). MS (ESI) m/z: 498.30
M + H ). Anal. Calcd (%) for: C28 NO (497.29): C, 67.58; H,
.90; N, 2.81. Found: C, 67.55; H, 7.92; N, 2.84.
F
3
) d
The authors gratefully acknowledge the support of National
Natural Science Foundation of China (21272080), Department of
Science and Technology, Guangdong Province (2010A020507001-
76, 5300410, FIPL-05-003) and the Scientific Research Foundation
for the Returned Overseas Chinese Scholars, State Education
Ministry.
+
+
(
7
H
39
F
4
2
Trans-4-(trans-4-n-pentylcyclohexyl)cyclohexanecarboxylic
0
acid 4 -(3,4-difluoropyrrole-1-yl) phenyl ester (5/2-2F). 82% yield;
1
white solid; H NMR (CDCl
3
)
d
(ppm): 7.26 (d, J = 8.7 Hz, 2H), 7.08
(d, J = 8.7 Hz, 2H), 6.70 (s, 2H), 2.45 (m, J = 1H), 2.12 (d, J = 11.5 Hz,
2
1
d
H), 1.95–1.75 (m, 4H), 1.71 (d, J = 13.4 Hz, 3H), 1.60–1.14 (m,
Appendix A. Supplementary data
19
3
1H), 1.16 (s, 2H), 1.08(m, 10H), 0.89(t, J = 6.9 Hz. F NMR (CDCl )
+
+
(ppm): ꢀ177.34 (s, 2F). MS (ESI) m/z: 480.18 (M +Na ). Anal.
NO (457.28): C, 73.49; H, 8.15; N, 3.06.
Found: C, 73.31; H, 8.10; N, 3.07.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.jfluchem.
Calcd (%) for: C28
H
37
F
2
2
2
013.07.022.
0
Trans-4-n-pentylcyclohexanecarboxylic acid 4 -(3,3,4,4-tetra-
fluoropyrrolidin-1-yl) phenyl ester (5/1-4F). 80% yield; white solid;
1
H NMR (CDCl
H), 3.81 (t, J = 10.0 Hz, 4H), 2.45 (t, J = 12.2 Hz, 1H), 2.12 (d,
J = 12.2 Hz, 2H), 1.87 (d, J = 12.4 Hz, 2H), 1.56 (t, J = 11.6 Hz, 2H),
3
) d (ppm): 6.99 (d, J = 8.6 Hz, 2H), 6.51 (d, J = 8.6 Hz,
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