Symmetrical dimer liquid crystals derived from benzoxazoles

Article abstract of DOI:10.1016/j.tet.2008.06.001

A series of dimeric twin liquid crystals derived from symmetric heterocyclic benzoxazoles 1a-1f exhibiting single smectic C phase are reported. All benzoxazoles were prepared by condensation of 2-aminophenols with benzaldehydes and then followed by subsequent intramolecular cyclization. The mesomorphic properties were investigated by DSC and POM, and the structure of the mesophases was confirmed as smectic C phases by powder XRD. The formation of mesophases was attributed to the weak dipole force induced by donor-acceptor interaction (D→A). A monolayer conformation was proposed based on the powder XRD data. A value of aspect ratio d/l=0.80-0.92 was calculated from d-spacings and the molecular lengths. By contrast, the odd-even effects by a value of entropy changes ΔS_SmC→I/R=2.00-6.50 showing odd-even effect for the transition of SmC→I phases were also associated in twin system.

Full text of DOI:10.1016/j.tet.2008.06.001

Tetrahedron 64 (2008) 7977–7985
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Symmetrical dimer liquid crystals derived from benzoxazoles
,
Cheng-Chung Liao a, Chung-Shu Wang a, Hwo-Shuenn Sheu b, Chung K. Lai a
*
a Department of Chemistry, National Central University and Center for Nano Science Technology, UST, Chung-Li 32054, Taiwan, ROC
b National Synchrotron Radiation Research Center, Hsinchu 30077, Taiwan, ROC
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of dimeric twin liquid crystals derived from symmetric heterocyclic benzoxazoles 1a–1f
exhibiting single smectic C phase are reported. All benzoxazoles were prepared by condensation of
2-aminophenols with benzaldehydes and then followed by subsequent intramolecular cyclization. The
mesomorphic properties were investigated by DSC and POM, and the structure of the mesophases was
confirmed as smectic C phases by powder XRD. The formation of mesophases was attributed to the weak
dipole force induced by donor–acceptor interaction (D/A). A monolayer conformation was proposed
based on the powder XRD data. A value of aspect ratio d/l¼0.80–0.92 was calculated from d-spacings and
Received 22 March 2008
Received in revised form 26 May 2008
Accepted 3 June 2008
Available online 6 June 2008
the molecular lengths. By contrast, the odd–even effects by a value of entropy changes
D
SSmC/I/R¼2.00–
6.50 showing odd–even effect for the transition of SmC/I phases were also associated in twin system.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
mesophase. The difference observed in phase behavior was mostly
attributed to the dependence of the average molecular shape and/
Liquid crystalline dimers1 (or also known as twins or bimes-
ogens) have attracted quite extensive attention during the past
decades. These dimers were particularly of appealing because of
their unique thermal behavior and structural features as model
compounds similar to polymeric liquid crystals. Mesogenic dimers
can be symmetric or unsymmetric2 in structure. The molecular
conformations1a and mesomorphic behavior were quite differential
from classical (or monomeric) mesogens. On the other hand, their
mesomorphic properties were significantly influenced by the
spacer length and also the linking group.2d,3 This type of molecules
is often made by linking either two identical or non-identical
moieties through a flexible central spacer. A variety of liquid
crystalline dimers made up of two rod-like mesogenic unit as well
as disc-like units have been prepared7 and studied by using
alkylene (–CH2–),3a,4 dioxyalkylene [–O(CH2)nO–]1e,5,6 or esters
[–COO(CH2)nOOC–]7 as central spacers. The mesomorphic proper-
ties were known to be critically dependent on the length and the
parity of the central spacer.8 Compared to the conventional rod-like
mesogens, the transitional properties produced by such dimeric
mesogens are in fact modified to a much larger extent by changes in
the length and parity of the alkyl chains. Some twin liquid crystals
showed a significant odd–even effect3a,5b,9 on mesomorphic be-
havior with spacer length or/and terminal length. The dimers with
an even spacer have generally more parallel orientations than those
of other dimers with an odd spacer, thus exhibiting a more stable
or geometry adopted on the parity1e,6,10b,10d of the central spacer
when considered in the all-trans conformation.
Most of the mesogenic twins formed smectic or nematic phases.
However, some dimeric1e,10b,10c,11 twins with a bent-core (BC) or
banana-shaped structure exhibited interesting banana phases. The
micro-segregations in layer SmA phases have been generated by
liquid crystalline dimers12 possessing an oligo(ethylene glycol)
spacer and two terminal alkyl chains. A few novel dimeric com-
pounds1c,13 with a chiral and a disulphide-bridged1f cyanobiphenyl
spacerall exhibiting a monotropic SmA phasewerereported. Known
examples including common Schiff bases, stilbenes,3c aromatics,
cholesterols,1c,14 and tolan moieties were reported.
Three subtypes of proposed structures in smectic layers or
phases; for example, monolayer,2,5b,14 interdigitated1d,10a or inter-
calated1b,1f,5a,7b,10c,12 conformations were already known depend-
ing on their spacing and/or molecular length. Shape effect caused by
odd or even carbon number15 in the spacer group often influence
overall molecular conformations, therefore, leading to different
phases formed. Benzoxazoles are often considered as fused electron
deficient structure (also as acceptor). A weak dipole generated from
the donor–acceptor (D–A) interaction might facilitate the formation
of mesophase in such heterocyclic compounds. Known examples of
mesogenic benzoxazoles16 were relatively rare. A few heterocyclic
benzoxazole derivatives17 exhibiting smectic or columnar phases
were prepared and studied previously in this group. As part of our
studies of heterocyclic mesogens, in this paper, we describe the
synthesis, characterization, and the mesomorphic properties of
a series of calamitic dimeric benzoxazole derivatives with various
spacer lengths. A single smectic C phase was observed along the
* Corresponding author. Tel.: þ886 3 4259207; fax: þ886 3 4277972.
E-mail address: cklai@cc.ncu.edu.tw (C.K. Lai).
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.06.001

7978
C.-C. Liao et al. / Tetrahedron 64 (2008) 7977–7985
series of compounds 1a–1f. A monolayer conformation in the SmC
phase was proposed based on XRD diffraction experiments.
benzoxazoles 1a, 1c, 1e, 1f were obtained by reactions of com-
pounds 2 with Pb(OAc)4 in refluxing chloroform and the yields
were relatively high in the range 64–77%. In contrast, all other
benzoxazoles 1b, 1d with an even carbon number (m¼4, 6) in
spacer length were obtained by procedures summarized in Scheme
2. The final benzoxazoles 1b, 1d were obtained by the reactions of
compound 4 and adipoyl chloride or suberoyl chloride in dried THF.
1H and 13C NMR spectroscopies were used to identify the interme-
diates and the final products. All compounds were characterized by
elemental analysis.
2. Results and discussion
2.1. Synthesis
OR
RO
N
N
O
O
O
m
O
2.2. Mesomorphic properties of compounds
O
O
R = (CH2)nH
The liquid crystalline behavior of compounds 1a–1f was char-
acterized and studied by differential scanning calorimetry and
polarized optical microscope. The phase transitions and thermo-
dynamic data are summarized in Table 1. Three derivatives; 1a
(m¼3; n¼6, 8) 1f (m¼11, n¼12) exhibited monotropic phases and
the mesophase was only obtained during the cooling process.
Monotropic behavior was often considered as kinetically unstable
and it occurred when aspect ratio of the molecule was not appro-
priate. All others formed enantiotropic phases regardless of the
alkoxy chain length. These compounds all exhibited a layer smectic
phase, as expected for the rod-like molecules. For the compounds
1a (m¼3; n¼6, 8, 10, 12, 14, 16) the clearing temperatures were
increased with the carbon numbers of the terminal alkyl chains, i.e.,
Tcl¼132.6 (n¼6)<142.5 (n¼12)<145.2 ꢀC (n¼16), however, the
melting temperatures remained at 126.1 (n¼10)–129.9 ꢀC (n¼16)
(Fig. 1). This increase in clearing temperatures was also true for the
series of compounds 1c (n¼8, 12, 16), i.e., Tcl¼118.7 (n¼8)<130.6
(n¼12)<133.4 ꢀC (n¼16). This may probably be attributed to an
enhanced dispersive interaction or van der Waals interaction be-
tween the terminal alkoxy chains. The phases were identified as
smectic C phases, and typical textures described as focal-conic or
Schlieren domains (Fig. 2) were easily observed under optical po-
larized microscope when cooling from isotropic liquid. These tex-
tures were not homeotropic, which were often observed in SmA
1a m = 3; n = 6, 8, 10, 12, 14,16
1b m = 4; n = 12
1c m = 5; n = 8, 12, 16
1d m = 6; n = 12
1e m = 7; n =12
1f m = 11; n = 12
All benzoxazoles with an odd carbon number (1a, 1c, 1e, and 1f;
m¼3, 5, 7, 11) in spacer length were prepared by procedures sum-
marized in Scheme 1. Most of known benzoxazoles reported in
the literatures were prepared by the condensation of 2-aminophe-
nols with benzaldehydes or benzoic acid and then followed by sub-
sequent intramolecular cyclization. All compounds in this work were
prepared by this synthetic route. The reactions of bis(4-formy-
lphenyl)alkanedioates 3 (m¼3, 5, 7, 11) and 2-amino-5-alkoxy-
phenols in refluxing absolute ethanol gave compounds 2 (m¼3, 5,
7, 11), bis(4-((E)-(4-alkyl-2-hydroxyphenylimino)methyl)phenyl)-
alkyldioates with a yield ranged from 69 to 73%. The final
OH
OR
O
O
m
OHC
OHC
RO
b
Cl
CI
OH
OH
OH
c
a
phases. A higher enthalpy (i.e.,
DH¼8.65–13.2 and 8.94–10.6 kJ/mol
on cooling cycle for compounds 1a and 1c, respectively) for the
transition of SmC/I phase was obtained. In contrast, both melting
temperatures and clearing temperatures have no apparent in-
creasing or decreasing effect on increasing the carbon length of the
spacer group with all terminal n¼12 considered. However, the
temperature range of the mesophase reached to maximum at
compound 1b (m¼4, n¼12) and then it started to lower to mini-
CHO
OR
OR
O
d
O
m
O2N
H2N
O
O
OH
N
OH
3
m = 3, 5, 7, 11
e
OR
mum at compound 1f (m¼11, n¼12), i.e.,
DTSmC¼19.4 (1a,
m¼3)<42.9 (1b, m¼4)>25.7 (1c, m¼5)>21.9 (1d, m¼6)>16.2 (1e,
m¼7)>7.9 ꢀC (1f, m¼11). On the other hand, the compound 1b with
spacer length m¼4 and terminal chain length n¼12 has the best
aspect ratio in forming the mesophase. In other mesogenic twin
systems, most compounds with lower terminal carbon chains often
formed nematic phases besides smectic C phase for higher terminal
carbon chains. In our system, SmC phase was only observed. This is
probably attributed to the weak dipole induced interaction or/and
produced by heterocyclic benzoxazoles. Benzoxazole is often con-
sidered as an electron deficient fused ring and molecules were
tilted in the layer structure in order to reduce the dipole–dipole
repulsion. The same mesomorphic behavior was observed in tro-
ponoid system.18
N
OH
OH
O
O
O
O
m
2 m = 3, 5, 7, 11
f
RO
OR
N
N
O
O
m
O
O
O
O
R = (CH2)nH
1a m = 3; n = 6, 8, 10, 12, 14, 16
1c m = 5; n = 8, 12, 16
1e m = 7; n =12
2.3. The odd–even effect
1f m = 11; n = 12
Scheme 1. Reactions and reagents: (a) DMAP (2.1 equiv), stirred in dry THF, rt, 8 h, 48–
72%; (b) RBr (1.1 equiv), KHCO3 (1.5 equiv), refluxing in acetone, 24 h, 60%; (c) HNO3
(1.2 equiv), NaNO2 (0.2 equiv), 0 ꢀC in CH2Cl2, 6 h, 25%; (d) H2NNH2 (1.2 equiv), Pd/C
(0.1 equiv), refluxed in C2H5OH, 24 h, 85%; (e) acetic acid (drops), refluxed in C2H5OH,
24 h, 69–73%; (f) Pd(OAc)4 (1.1 equiv), refluxed in CHCl3, 2 h, 64–77%.
The odd–even effect, quite common in dimeric twins was also
observed in this system. For all compounds 1a–1f with all n¼12, the
clearing temperatures of compounds 1b and 1d were much higher
than those of other compounds (1a, 1c, 1e, 1f), i.e., Tcl¼166.8

C.-C. Liao et al. / Tetrahedron 64 (2008) 7977–7985
7979
b
OR
OR
OH
HO
H3CCOO
H3CCOO
CHO
HO
HO
HO
a
c
CHO
H2N
HO
OR
O2N
d
e
OR
O
N
f
H3CCOO
O
OR
N
HO
5
6
g
OR
HO
N
4
h
OR
RO
N
N
O
O
O
m
O
O
O
R = (CH2)nH
1b m = 4; n = 12
1d m = 6; n = 12
Scheme 2. Reactions and reagents: (a) TEA (1.1 equiv), acetyl chloride, stirred in dry THF, rt, 8 h, 83%; (b) RBr (1.1 equiv), KHCO3 (1.5 equiv), refluxing in acetone, 24 h, 60%; (c) concd
HNO3 ( 1.2 equiv), NaNO2 (0.2 equiv), 0 ꢀC in CH2Cl2, 6 h, 25%; (d) H2NNH2 (1.2 equiv), Pd/C (0.1 equiv), refluxing in C2H5OH, 24 h, 85%; (e) acetic acid (drops), refluxing in C2H5OH,
24 h, 78%; (f) Pd(OAc)4 (1.1 equiv), refluxing in CHCl3, 2 h, 72%; (g) KOH (1.5 equiv), refluxing in 95% ethanol, 24 h, 93%; (h) DMAP (1.0 equiv), adipoyl chloride or suberoyl chloride
(0.50 equiv), refluxing in dry THF, 12 h, 51–72%.
(1b)>147.4 (1d)>142.5 (1a)>133.6 (1c)>122.7 (1e)>105.7 ꢀC (1f).
The relationship plot between the melting temperatures, clearing
temperatures, and the temperature range for all compounds 1a–1f
are shown in Figure 3. When compounds with even carbon spacer
and molecules were considered in all-trans conformations, the
overall molecules were more likely linear, resulting in a better
packing in mesophases. Therefore, their clearing temperatures
were often much higher than those of compounds with odd carbon
spacer, in which all molecules were considered as more bent-sha-
observed for SmC phases. For example, compound 1a (m¼3, n¼12)
showed two peaks at 45.91 Å and 22.96 Å, shown in Figure 5. An-
other very broad and very weak peak at 4.44–4.61 Å was also ob-
served, and this peak was assigned to the molten alkoxyl chains.
The d-spacings of four compounds were all well correlated with the
central spacer length.
Two possible structures in such layer mesophases were often
proposed in symmetric twins; intercalated and non-intercalated
(or monolayer). In intercalated phase the d-spacing value was
equal to a half of molecular length dw(1/2)L whereas d-spacing
was equal to molecular length d¼L in non-intercalated structure.
Interdigitated layer structures were not considered in our system.
In many mesogenic twin systems, most dimeric molecules
exhibiting either SmA or SmC phase will adopt intercalated ar-
rangements. In contrast, the dimeric molecules will form mono-
layer arrangement when d/lw1.0. The molecular length (L) in our
system was estimated when the most extended conformations
were considered. All d/l values of four compounds are given in
Table 2 and all values were ranged from d/l¼0.80 (1a) to 0.92
(1f). Therefore, monolayer structure in mesophase was proposed,
as shown in Figure 6.
ped. A ratio of
D
S/R often used to evaluate the odd–even effect was
SN/I/R),
also calculated in twin systems. The transition entropy (
D
showing the orientational order was generally measured from
nematic to isotropic state. However, a SmA phase was not observed,
then a value of
in our system. This transition entropy ranged from
to 6.5. This entropy change was not correlated with carbon length
in spacer group, shown in Figure 4. A value of
SN/I/R¼0.5–2.0 was
observed on other dimeric twins. The value of SSmC/I/R for
D
SSmC/I/R (R¼gas constant in J/mol) was evaluated
D
SSmC/I/R¼2.01
D
D
compounds 1f was particularly large (i.e., w6.50) due to mono-
tropic transitions.
2.4. Powder X-ray diffraction experiments
The powder X-ray diffraction experiments of four compounds
1a (m¼3, n¼12), 1c (m¼5, n¼12), 1e (m¼7, n¼12), and 1f (m¼11,
n¼12) were performed to confirm the structure of the smectic C
phases. The X-ray diffraction data are summarized in Table 2. As can
be seen, they all displayed a similar diffraction pattern with one
strong peak and one very weak at lower angle region, and also
a very weak and broad diffraction peak at wider angle. These two
diffraction peaks at lower angle were assigned as 001 and 002. This
diffraction pattern was typically characteristic of layer structures
3. Conclusions
A new series of heterocyclic twin mesogenic benzoxazoles with
different spacer lengths was prepared and studied. All the com-
pounds 1a–1f exhibited liquid crystalline smectic C phase and
a strong odd–even effect in the isotropization temperatures. A
monolayer structure in this type of dimeric twin liquid crystals was
proposed.

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C.-C. Liao et al. / Tetrahedron 64 (2008) 7977–7985
Table 1
Phase transitionsa and temperatures of compounds 1a–1f
132.6 (40.9)
1a; m¼3
n¼6
n¼8
Cr
Cr
I
SmC
SmC
SmC
123.5b
125.0b
137.5 (44.7)
I
121.7 (31.3)
131.6 (6.40)
126.1 (46.3)
120.6 (33.5)
139.8 (11.0)
n¼10
n¼12
n¼14
n¼16
n¼12
n¼8
Cr
Cr
Cr
Cr
Cr
Cr
Cr
I
137.5 (10.6)
142.5 (13.0)
125.9 (55.8)
122.3 (34.9)
I
SmC
SmC
SmC
SmC
SmC
141.7 (12.7)
144.3 (13.2)
126.5 (63.5)
122.3 (34.9)
I
143.2 (12.8)
129.9 (49.7)
117.7 (53.3)
145.2 (8.65)
I
140.2 (8.29)
166.8 (15.4)
124.4 (43.0)
122.1 (42.9)
1b; m¼4
1c; m¼5
I
165.0 (13.7)
118.7 (8.94)
110.6 (38.6)
98.3 (42.5)
I
117.5 (9.34)
130.6 (10.4)
116.2 (45.7)
103.1 (46.0)
n¼12
I
SmC
128.8 (10.3)
118.2 (52.5)
108.7 (54.5)
133.4 (10.6)
SmC
SmC
SmC
n¼16
n¼12
n¼12
n¼12
Cr
Cr
Cr
Cr
I
129.4 (10.4)
125.4 (23.5)
121.6 (23.8)
147.4 (7.04)
1d; m¼6
1e; m¼7
I
143.5 (6.93)
106.8 (49.1)
105.2 (49.3)
122.7 (16.2)
I
121.4 (16.2)
105.6 (97.6)
1f; m¼11
I
SmC
95.2 (77.85)
103.1 (20.0)
a
m
and
n
are the spacer length and terminal carbon length. Cr¼crystal,
SmC¼smectic C, and I¼isotropic phase.
b
Observed by optical microscope.
Cr
SmC
160
140
120
100
80
Figure 2. The optical textures observed in compounds 1a (m¼4, n¼12; top plate) at
139.0 ꢀC, 1b (m¼4, n¼12) at 145.0 ꢀC, and 1c (m¼5, n¼12; bottom plate) at 120.0 ꢀC.
4. Experimental
4.1. General
1H and 13C NMR spectra were measured on a Bruker DRS-200.
DSC thermographs were carried out on a Mettler DSC 822. All phase
transitions are determined by a scan rate of 10.0 ꢀC/min. Optical
polarized microscope was carried out on Zeiss Axioplan 2 equipped
with a hot stage system of Mettler FP90/FP82HT. Elemental analysis
for carbon, hydrogen, and nitrogen were conducted at In-
strumentation Center, National Taiwan University on a Heraeus
CHN-O-Rapid elemental analyzer (Table 3). The powder X-ray dif-
fraction data were collected from the Wiggler-A beam line of the
National Synchrotron Radiation Research Center with a wavelength
of 1.3305 Å. All compounds of 3-alkoxyphenols, 5-alkoxy-2-
6
3
8
3
10 12 14 16 12
8
5
12 16 12 12 12
11
n =
3
3
3
3
4
5
5
6
7
m =
Figure 1. Bar graphs showing the phase behavior of compounds 1a–1f. All tempera-
tures were taken from cooling process.

C.-C. Liao et al. / Tetrahedron 64 (2008) 7977–7985
7981
175
165
155
145
135
125
115
105
95
4.3. 5-Dodecyloxy-2-nitrophenol
Yellow solid, yield 25%. 1H NMR (CDCl3):
d
0.86 (t, 3H, –CH3,
J¼6.88 Hz), 1.24–1.44 (m, 18H, –CH2), 1.75–1.81 (m, 2H, –CH2), 3.99
(t, 2H, –OCH2, J¼6.53 Hz), 6.47–6.49 (m, 2H, Ar–H), 8.00 (d, 1H, Ar–
l
H, J¼10.1 Hz), 11.02 (s, 1H, Ar–OH). 13C NMR (CDCl3):
d 14.12, 22.69,
25.87, 28.83, 29.27, 29.35, 29.41, 29.52, 29.57, 29.63, 29.64, 29.71,
31.92, 69.15, 101.80, 109.83, 126.91, 127.54, 158.01, 166.74.
SmC
4.4. 2-Amino-5-dodecyloxyphenol
White solid, yield 85%. 1H NMR (CDCl3):
d 0.86 (t, 3H, –CH3,
J¼6.91 Hz), 1.24–1.41 (m, 18H, –CH2), 1.68–1.73 (m, 2H, –CH2), 3.84
Cr
(t, 2H, –OCH2, J¼6.61 Hz), 6.32 (d, 1H, Ar–H, J¼8.58 Hz), 6.41 (s, 1H,
85
Ar–H), 6.75 (d, 1H, Ar–H, J¼8.57 Hz). 13C NMR (CDCl3):
d 13.94,
1a
1b
1c
1d
1e
1f
22.59, 26.02, 29.25, 29.34, 29.51, 29.53, 29.56, 29.58, 31.85, 68.67,
102.72, 106.75, 120.85, 125.58, 148.06, 154.94.
Figure 3. Dependence of melting and clearing temperatures on the number of
methylene groups in the spacer of compounds 1a–1f (all with terminal n¼12).
4.5. Bis(4-formylphenyl)glutarate 3 (m[3)
8
7
6
5
4
3
2
1
Under nitrogen atmosphere the mixture of 4-hydroxy-
benzaldehyde (2.00 g, 0.016 mol) and DMAP (2.10 g, 0.017 mol) was
dissolved in 25 ml of dry THF. To the solution, a solution of glutaryl
chloride (1.38 g, 0.0082 mol) dissolved in 15 ml of dry THF was
dropwise added and the solution was stirred for 4 h. The solution
was filtered off and the filtrate was concentrated to dryness. The
product isolated as white solids were obtained after re-
crystallization from CH2Cl2/MeOH. Yield 72%. 1H NMR (CDCl3):
d
2.15–2.22 (m, 2H, –CH2), 2.76 (t, 4H, –OCOCH2, J¼8.47 Hz), 7.26 (d,
4H, Ar–H, J¼8.63 Hz), 7.90 (d, 4H, Ar–H, J¼6.74 Hz), 9.97 (s, 2H,
–CHO). 13C NMR (CDCl3):
155.02, 170.52, 190.78.
d 19.53, 32.97, 122.17, 131.10, 133.89,
1a
1b
1c
1d
1e
1f
Figure 4. The dependence of the entropy change (
D
S/R, unitless) for transition of
4.6. Bis(4-formylphenyl)heptanedioate 3 (m[5)
White solid, yield 48%. 1H NMR (CDCl3):
SmC/I phase on the carbon length m in spacer chains in compounds 1a–1f with all
terminal n¼12. R is gas constant in J Kꢁ1 molꢁ1
.
d
1.25–1.32 (m, 2H,
–CH2), 162–1.69 (m, 4H, –CH2), 2.47–2.60 (m, 4H, –OCOCH2), 7.26
nitrophenols, 2-amino-5-aloxyphenols were followed by the
literatures.17
(d, 4H, Ar–H, J¼8.39 Hz), 7.90 (d, 4H, Ar–H, J¼8.73 Hz), 9.95 (s, 2H,
–CHO). 13C NMR (CDCl3):
153.82, 171.59, 191.01.
d 25.79, 29.31, 32.41,121.38,129.86,133.51,
4.2. 3-Dodecyloxyphenol
4.7. Bis(4-formylphenyl)tridecanedioate 3 (m[11)
Yellow solid, yield 60%. 1H NMR (CDCl3):
d 1.24–1.33 (m, 14H,
White solid, yield 60%. 1H NMR (CDCl3):
d 0.87 (t, 3H, –CH3,
J¼6.91 Hz), 1.25–1.43 (m, 18H, –CH2), 1.72–1.77 (m, 2H, –CH2), 3.90
(t, 2H, –OCH2, J¼6.62 Hz), 6.39–6.40 (m, 2H, Ar–H), 6.46–6.48 (m,
–CH2), 1.66–1.77 (m, 4H, –CH2), 2.48–2.60 (m, 4H, –OCOCH2), 7.25
1H, Ar–H), 7.10 (t, 1H, Ar–H, J¼8.48 Hz). 13C NMR (CDCl3):
d
14.14,
(d, 4H, Ar–H, J¼6.86 Hz), 7.89 (d, 4H, Ar–H, J¼8.49 Hz), 9.95 (s, 2H,
22.71, 26.05, 29.23, 29.37, 29.42, 29.60, 29.63, 29.66, 29.68, 31.94,
68.10, 102.08, 107.10, 107.59, 130.10, 156.68, 160.51.
–CHO). 13C NMR (CDCl3):
d 25.33, 29.29, 29.41, 29.96, 32.17, 122.03,
130.63, 133.81, 154.20, 170.89, 191.08.
Table 2
The powder X-ray diffraction data of the compounds 1a, 1c, 1e, and 1fa
Compounds
Phase
SmC
Temp (ꢀC)
126.0
d-Spacing (Å)
Miller indices (Å)
Length (Å)
Aspect ratio (d/l)
1a (m¼3; n¼12)
45.91 (45.91)
22.93 (22.96)
4.51
49.82 (49.82)
24.75 (24.91)
4.48
56.43 (56.43)
28.19 (28.22)
4.44
60.83 (60.83)
30.19 (30.42)
4.61
001
002
Halo
001
002
Halo
001
002
Halo
001
002
Halo
57.68
59.12
62.28
66.11
0.80
1c (m¼5; n¼12)
1e (m¼7; n¼12)
1f (m¼11; n¼12)
SmC
SmC
SmC
120.0
109.0
105.0
0.84
0.91
0.92
a
The molecular length (l) was obtained by MM2 model when considered all-trans conformation.

7982
C.-C. Liao et al. / Tetrahedron 64 (2008) 7977–7985
(a)
1a (m= 3, n= 12)
7000
d 45.91
6000
5000
4000
3000
2000
1000
0
d 22.93
200
2.5
3.0
3.5
2 theta
4.0
4.5
10
20
30
30
30
2 theta
(b)
4500
4000
3500
3000
2500
2000
1500
1000
500
1c (m= 5, n= 12)
d 49.82
d 24.75
100
Figure 6. The proposed monolayer arrangements in SmC phase for compounds 1c
(m¼5, n¼12) with a ratio of d/l (49.82/59.12¼0.84)<1.0. The terminal alkoxyl chains
might be slightly interdigitated.
80
hexadecyloxyphenol (0.36 g, 0.0012 mol) dissolved in 50 ml of
absolute ethanol with a few drops of glacial acetic acid added was
slowly added under nitrogen atmosphere. The solution was
refluxed for 8 h. The yellow solids were collected. The product
isolated as white solids were obtained after recrystallization from
60
2.5
3.0
3.5
2 theta
CH2Cl2/MeOH. Yield 73%. 1H NMR (CDCl3):
d 0.86 (t, 6H, –CH3,
0
J¼6.88 Hz), 1.24–1.45 (m, 36H, –CH2), 1.73–1.78 (m, 4H, –OCH2CH2),
2.20–2.23 (m, 2H, –CH2), 2.76 (t, 4H, –OCOCH2, J¼7.22 Hz), 3.94 (t,
4H, –OCH2, J¼6.58 Hz), 6.44 (d, 2H, Ar–H, J¼11.48 Hz), 6.55 (s, 2H,
Ar–H), 7.19 (d, 4H, Ar–H, J¼8.57 Hz), 7.25 (d, 2H, Ar–H, J¼8.94 Hz),
7.47 (s, 2H, –OH), 7.88 (d, 4H, Ar–H, J¼8.61 Hz), 8.60 (s, 2H, –NCH).
10
20
2 theta
(c)
1800
1600
1400
1200
1000
800
1e (m= 7, n= 12)
13C NMR (CDCl3):
d 14.13, 19.90, 22.70, 26.03, 29.21, 29.37, 29.40,
d 56.43
29.58, 29.61, 29.67, 29.70, 31.94, 33.24, 68.31, 100.52, 107.20, 116.20,
122.03, 128.22, 129.50, 134.03, 152.21, 152.63, 153.83, 160.42, 171.03.
100
95
90
85
80
75
70
4.9. Bis(4-((E)-(4-(dodecyloxy)-2-hydroxyphenylimino)-
methyl)phenyl)heptanedioate 2 (m[5, n[12)
d 28.19
Yellow solid, yield 69%. 1H NMR (CDCl3):
d 0.86 (t, 6H, –CH3,
J¼6.32 Hz), 1.25–1.59 (m, 38H, –CH2), 1.73–1.91 (m, 8H, –CH2), 2.62
600
2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6
2 theta
400
Table 3
Elemental analysis data of compounds 1a–1f
200
1a; m¼3
n¼6
72.20 (71.85)
72.69 (72.84)
73.97 (73.71)
74.65 (74.46)
75.45 (75.13)
76.01 (75.72)
74.98 (74.64)
73.54 (73.29)
75.09 (74.80)
76.21 (75.99)
75.16 (74.97)
75.64 (75.13)
75.48 (75.72)
6.33 (6.45)
7.12 (7.02)
7.58 (7.52)
8.09 (7.95)
8.23 (8.33)
8.69 (8.67)
8.11 (8.05)
7.29 (7.28)
7.99 (8.15)
8.86 (8.83)
8.29 (8.24)
8.47 (8.33)
8.59 (8.67)
n¼8
n¼10
n¼12
n¼14
n¼16
n¼12
n¼8
10
20
2 theta
Figure 5. The powder X-ray diffraction patterns for compounds 1a (m¼3, n¼12) at
126.0 ꢀC, 1c (m¼5, n¼12) at 120.0 ꢀC, and 1e (m¼7, n¼12) at 109.0 ꢀC.
1b; m¼4
1c; m¼5
n¼12
n¼16
n¼12
n¼12
n¼12
4.8. Bis(4-((E)-(4-(dodecyloxy)-2-hydroxyphenylimino)-
methyl)phenyl)glutarate 2 (m[3, n[12)
1d; m¼6
1e; m¼7
1f; m¼11
Bis(4-formylphenyl)glutarate (0.20 g, 0.00059 mol) was dis-
solved in 50 ml of warm absolute ethanol and 2-amino-5-
Calcd value in parentheses.

C.-C. Liao et al. / Tetrahedron 64 (2008) 7977–7985
7983
(t, 4H, –OCOCH2, J¼7.25 Hz), 3.93 (t, 4H, –OCH2, J¼6.52 Hz), 6.43 (d,
4.14. Bis(4-(6-(decyloxy)benzo[d]oxazol-2-yl)phenyl)glutarate
1a (m[3, n[10)
2H, Ar–H, J¼11.41 Hz), 6.55 (s, 2H, Ar–H), 7.17 (d, 4H, Ar–H,
J¼8.53 Hz), 7.25 (d, 2H, Ar–H, J¼8.75 Hz), 7.49 (s, 2H, –OH), 7.88 (d,
4H, Ar–H, J¼8.57 Hz), 8.58 (s, 2H, –NCH). 13C NMR (CDCl3):
d
14.12,
White solid, yield 69%. 1H NMR (CDCl3):
d
0.86 (t, 6H, –CH3,
22.68, 24.42, 26.00, 28.40, 28.51, 29.02, 29.17, 29.34, 29.58, 29.63,
29.67, 31.90, 34.09, 68.25, 100.54, 107.17, 116.37, 122.06, 128.40,
129.58, 133.67, 152.42, 152.84, 153.72, 160.38, 171.63.
J¼6.76 Hz),1.26–1.47 (m, 28H, –CH2),1.79–1.83 (m, 4H, –CH2), 2.20–
2.25 (m, 2H, –CH2), 2.77 (t, 4H, –OCOCH2, J¼7.17 Hz), 3.99 (t, 4H,
–OCH2, J¼6.49 Hz), 6.93 (d, 2H, Ar–H, J¼10.76 Hz), 7.07 (s, 2H, Ar–H),
7.24 (d, 4H, Ar–H, J¼8.06 Hz), 7.59 (d, 2H, Ar–H, J¼8.66 Hz), 8.20 (d,
4.10. Bis(4-((E)-(4-(dodecyloxy)-2-hydroxyphenylimino)-
methyl)phenyl)tridecanedioate 2 (m[11, n[12)
4H, Ar–H, J¼8.54 Hz). 13C NMR (CDCl3):
d 14.11, 19.90, 22.69, 26.06,
29.24, 29.33, 29.40, 29.57, 29.58, 31.90, 33.24, 68.91, 96.09, 113.50,
119.95, 122.13, 125.18, 128.52, 135.68, 151.72, 152.69, 157.93, 161.38,
170.94. MS (FAB): calcd for MHþ C51H62N2O8: 831.1, found: 831.0.
Yellow solid, yield 70%. 1H NMR (CDCl3):
d 0.86 (t, 6H, –CH3,
J¼6.39 Hz), 1.25–1.59 (m, 50H, –CH2), 1.73–1.91 (m, 8H, –CH2), 2.57
(t, 4H, –OCOCH2, J¼7.05 Hz), 3.92 (t, 4H, –OCH2, J¼6.34 Hz), 6.44 (d,
2H, Ar–H, J¼8.80 Hz), 6.55 (s, 2H, Ar–H), 7.16 (d, 4H, Ar–H,
J¼8.25 Hz), 7.25 (d, 2H, Ar–H, J¼8.80 Hz), 7.47 (s, 2H, –OH), 7.86 (d,
4.15. Bis(4-(6-(tetradecyloxy)benzo[d]oxazol-2-yl)phenyl)-
glutarate 1a (m[3, n[14)
4H, Ar–H, J¼8.23 Hz), 8.57 (s, 2H, –NCH). 13C NMR (CDCl3):
d
14.11,
White solid, yield 66%. 1H NMR (CDCl3):
d 0.87 (t, 6H, –CH3,
22.67, 24.83, 26.20, 28.59, 28.73, 28.92, 29.05, 29.19, 29.36, 29.41,
29.58, 29.64, 31.90, 34.63, 68.22, 100.45, 107.09, 116.20, 122.04,
128.13, 129.45, 133.72, 152.30, 152.82, 153.74, 160.30, 171.95.
J¼6.85 Hz), 1.26–1.50 (m, 44H, –CH2), 1.79–1.82 (m, 4H, –OCH2CH2),
2.21–2.24 (m, 2H, –CH2), 2.76 (t, 4H, –OCOCH2, J¼7.18 Hz), 4.00 (t,
4H, –OCH2, J¼6.52 Hz), 6.93 (d, 2H, Ar–H, J¼8.71 Hz), 7.07 (s, 2H,
Ar–H), 7.25 (d, 4H, Ar–H, J¼8.78 Hz), 7.59 (d, 2H, Ar–H, J¼8.72 Hz),
4.11. Bis(4-(6-(dodecyloxy)benzo[d]oxazol-2-yl)phenyl)-
glutarate 1a (m[3, n[12)
8.20 (d, 4H, Ar–H, J¼8.68 Hz). 13C NMR (CDCl3):
d 13.95, 19.98,
22.59, 26.02, 29.24, 29.26, 29.33, 29.51, 29.53, 29.58, 29.60, 29.62,
31.86, 33.30, 69.05, 96.28, 113.51, 119.95, 122.00, 125.26, 128.50,
135.89, 151.77, 152.79, 158.00, 161.39, 170.72. MS (FAB): calcd for
MHþ C59H78N2O8: 943.3, found: 943.0.
The
mixture
of
bis(4-((E)-(4-(dodecyloxy)-2-hydroxy-
phenylimino)methyl)phenyl)glutarate (0.20 g, 0.22 mmol) and
lead acetate Pb(OAc)4 (0.12 g, 0.26 mmol) dissolved in 20 ml of
CHCl3 was refluxed for 2 h. The solution was filtered and the filtrate
was extracted with CH2Cl2/H2O. The organic layers were collected
and dried (MgSO4). The product isolated as white solids were
obtained after recrystallization from CH2Cl2/MeOH. Yield 70%. 1H
4.16. Bis(4-(6-(hexadecyloxy)benzo[d]oxazol-2-yl)phenyl)-
glutarate 1a (m[3, n[16)
White solid, yield 77%. 1H NMR (CDCl3):
d 0.87 (t, 6H, –CH3,
NMR (CDCl3):
d
0.85 (t, 6H, –CH3, J¼7.09 Hz), 1.26–1.50 (m, 36H,
J¼6.88 Hz), 1.26–1.49 (m, 52H, –CH2), 1.80–1.82 (m, 4H, –OCH2CH2),
2.22–2.24 (m, 2H, –CH2), 2.77 (t, 4H, –OCOCH2, J¼7.21 Hz), 4.01 (t,
4H, –OCH2, J¼6.55 Hz), 6.93 (d, 2H, Ar–H, J¼8.74 Hz), 7.07 (s, 2H,
Ar–H), 7.25 (d, 4H, Ar–H, J¼8.78 Hz), 7.59 (d, 2H, Ar–H, J¼8.72 Hz),
–CH2), 1.78–1.84 (m, 4H, –CH2), 2.21–2.24 (m, 2H, –CH2), 2.77 (t, 4H,
–OCOCH2, J¼7.20 Hz), 4.00 (t, 4H, –OCH2, J¼6.55 Hz), 6.94 (d, 2H,
Ar–H, J¼8.71 Hz), 7.07 (s, 2H, Ar–H), 7.26 (d, 4H, Ar–H, J¼7.31 Hz),
7.60 (d, 2H, Ar–H, J¼8.73 Hz), 8.21 (d, 4H, Ar–H, J¼8.67 Hz). 13C
8.20 (d, 4H, Ar–H, J¼8.68 Hz). 13C NMR (CDCl3):
d 13.94, 19.98,
NMR (CDCl3):
d
14.12, 19.88, 22.70, 26.06, 29.23, 29.36, 29.40, 29.58,
22.59, 26.02, 29.24, 29.27, 29.33, 29.51, 29.53, 29.58, 29.62, 31.86,
33.30, 69.05, 96.28, 113.51, 119.95, 122.00, 125.26, 128.50, 135.89,
151.77, 152.79, 158.00, 161.39, 170.72. MS (FAB): calcd for MHþ
C63H86N2O8: 999.4, found: 999.1.
29.61, 29.65, 29.67, 31.93, 33.24, 68.91, 96.09, 113.56, 119.91, 122.15,
125.06, 128.57, 135.49, 151.68, 152.73, 157.96, 161.37, 170.95. MS
(FAB): calcd for MHþ C55H70N2O8: 887.2, found: 887.0.
4.12. Bis(4-(6-(hexyloxy)benzo[d]oxazol-2-yl)phenyl)-
glutarate 1a (m[3, n[6)
4.17. Bis(4-(6-(octyloxy)benzo[d]oxazol-2-yl)phenyl)-
heptanedioate 1c (m[5, n[8)
White solid, yield 65%. 1H NMR (CDCl3):
d
0.89 (t, 6H, –CH3,
White solid, yield 64%. 1H NMR (CDCl3):
d 0.87 (t, 6H, –CH3,
J¼7.14 Hz), 1.33–1.49 (m, 12H, –CH2), 1.78–1.83 (m, 4H, –CH2), 2.20–
2.23 (m, 2H, –CH2), 2.77 (t, 4H, –OCOCH2, J¼7.21 Hz), 4.00 (t, 4H,
–OCH2, J¼6.54 Hz), 6.93 (d, 2H, Ar–H, J¼8.72 Hz), 7.07 (s, 2H, Ar–H),
7.25 (d, 4H, Ar–H, J¼7.56 Hz), 7.59 (d, 2H, Ar–H, J¼8.72 Hz), 8.20 (d,
J¼6.51 Hz), 1.28–1.57 (m, 22H, –CH2), 1.79–1.85 (m, 8H, –CH2), 2.63
(t, 4H, –OCOCH2, J¼7.32 Hz), 3.98 (t, 4H, –OCH2, J¼6.51 Hz), 6.92 (d,
2H, Ar–H, J¼8.68 Hz), 7.05 (s, 2H, Ar–H), 7.22 (d, 4H, Ar–H,
J¼8.51 Hz), 7.58 (d, 2H, Ar–H, J¼8.71 Hz), 8.18 (d, 4H, Ar–H,
4H, Ar–H, J¼8.66 Hz). 13C NMR (CDCl3):
d
14.05, 19.89, 22.62, 25.74,
J¼8.50 Hz). 13C NMR (CDCl3):
d 14.11, 22.67, 24.47, 26.07, 28.45,
29.20, 31.60, 33.24, 68.89, 96.07, 113.49, 119.96, 122.13, 125.18,
128.52, 135.69, 151.70, 152.67, 157.91, 161.37, 170.97. MS (FAB): calcd
for MHþ C43H46N2O8: 718.8, found: 719.0.
29.25, 29.38, 31.83, 34.12, 68.88, 96.05, 113.46, 119.93, 122.15,
125.04, 128.49, 135.68, 151.68, 152.81, 157.89, 161.41, 171.58. MS
(FAB): calcd for MHþ C49H58N2O8: 803.0, found: 803.0.
4.13. Bis(4-(6-(octyloxy)benzo[d]oxazol-2-yl)phenyl)glutarate
1a (m[3, n[8)
4.18. Bis(4-(6-(dodecyloxy)benzo[d]oxazol-2-yl)phenyl)-
heptanedioate 1c (m[5, n[12)
White solid, yield 65%. 1H NMR (CDCl3):
d
0.87 (t, 6H, –CH3,
White solid, yield 64%. 1H NMR (CDCl3):
d 0.86 (t, 6H, –CH3,
J¼6.87 Hz), 1.28–1.47 (m, 20H, –CH2), 1.79–1.82 (m, 4H, –CH2),
2.22–2.23 (m, 2H, –CH2), 2.77 (t, 4H, –OCOCH2, J¼7.20 Hz), 3.99 (t,
4H, –OCH2, J¼6.57 Hz), 6.93 (d, 2H, Ar–H, J¼8.73 Hz), 7.07 (s, 2H,
Ar–H), 7.25 (d, 4H, Ar–H, J¼8.70 Hz), 7.59 (d, 2H, Ar–H, J¼8.74 Hz),
J¼6.90 Hz),1.25–1.48 (m, 38H, –CH2),1.79–1.86(m, 8H, –CH2), 2.63 (t,
4H, –OCOCH2, J¼7.38 Hz), 3.98 (t, 4H, –OCH2, J¼6.57 Hz), 6.92 (d, 2H,
Ar–H, J¼8.72 Hz), 7.05 (s, 2H, Ar–H), 7.22 (d, 4H, Ar–H, J¼8.70 Hz),
7.58 (d, 2H, Ar–H, J¼8.72 Hz), 8.19 (d, 4H, Ar–H, J¼8.70 Hz). 13C NMR
8.20 (d, 4H, Ar–H, J¼8.72 Hz). 13C NMR (CDCl3):
d
14.12, 19.89, 22.67,
(CDCl3): d 14.13, 22.70, 24.47, 26.07, 28.45, 29.24, 29.36, 29.41, 29.59,
26.07, 29.24, 29.25, 29.37, 31.83, 33.23, 68.90, 96.06, 113.49, 119.95,
122.13, 125.18, 128.52, 135.68, 151.70, 152.67, 157.91, 161.37, 170.97.
MS (FAB): calcd for MHþ C47H54N2O8: 774.9, found: 775.0.
29.62, 29.65, 29.67, 31.93, 34.13, 68.88, 96.05, 113.47, 119.93, 122.16,
125.04,128.50,135.67,151.68,152.81,157.89,161.41,171.59. MS (FAB):
calcd for MHþ C57H74N2O8: 915.2, found: 915.1.

7984
C.-C. Liao et al. / Tetrahedron 64 (2008) 7977–7985
4.19. Bis(4-(6-(hexadecyloxy)benzo[d]oxazol-2-yl)phenyl)-
heptanedioate 1c (m[5, n[16)
4.24. 4-(6-(Dodecyloxy)benzo[d]oxazol-2-yl)phenyl acetate 5
White solid, yield 72%. 1H NMR (CDCl3):
d
0.86 (t, 3H, –CH3,
White solid, yield 66%. 1H NMR (CDCl3):
d
0.87 (t, 6H, –CH3,
J¼6.44 Hz), 1.24–1.44 (m, 18H, –CH2), 1.76–1.88 (m, 2H, –CH2), 2.30
(s, 3H, –OCOCH3), 3.97 (t, 2H, –OCH2, J¼6.39 Hz), 6.92 (d, 1H, Ar–H,
J¼8.73 Hz), 6.95 (s, 1H, Ar–H), 7.21 (d, 2H, Ar–H, J¼8.33 Hz), 7.58 (d,
1H, Ar–H, J¼8.74 Hz), 8.18 (d, 2H, Ar–H, J¼8.23 Hz). 13C NMR
J¼6.73 Hz), 1.26–1.51 (m, 54H, –CH2), 1.79–1.87 (m, 8H, –CH2), 2.62
(t, 4H, –OCOCH2, J¼7.27 Hz), 4.00 (t, 4H, –OCH2, J¼6.48 Hz), 6.93 (d,
2H, Ar–H, J¼8.67 Hz), 7.06 (s, 2H, Ar–H), 7.23 (d, 4H, Ar–H,
J¼8.90 Hz), 7.58 (d, 2H, Ar–H, J¼8.69 Hz), 8.19 (d, 4H, Ar–H,
(CDCl3): d 14.08, 21.10, 22.65, 26.00, 29.17, 29.31, 29.35, 29.55, 29.61,
J¼8.56 Hz). 13C NMR (CDCl3):
d
13.94, 22.59, 24.44, 26.03, 28.44,
31.87, 68.77, 95.94, 113.38, 119.85, 122.10, 124.97, 128.41, 135.57,
151.60, 152.70, 157.81, 160.30, 168.96.
29.25, 29.26, 29.34, 29.51, 29.53, 29.58, 29.62, 31.86, 34.12, 69.04,
96.27, 113.48, 119.93, 122.02, 125.12, 128.47, 135.89, 151.76, 152.93,
157.97, 161.44, 171.32. MS (FAB): calcd for MHþ C65H90N2O8: 1027.4,
found: 1027.1.
4.25. 4-(6-(Dodecyloxy)benzo[d]oxazol-2-yl)phenol 4
The mixture of 4-(6-(dodecyloxy)benzo[d]oxazol-2-yl)phenyl
acetate 5 (0.9 g, 0.0021 mol) and KOH (0.18 g, 0.0032 mol) dis-
solved in 100 ml 95% C2H5OH was refluxed for 24 h. The solution
was neutralized with dilute aqueous HCl and the white solids were
collected. The product isolated as white solid were obtained after
recrystallization from CH2Cl2/CH3OH. Yield 93%. 1H NMR (CDCl3):
4.20. Bis(4-(6-(dodecyloxy)benzo[d]oxazol-2-yl)phenyl)-
heptanedioate 1e (m[7, n[12)
White solid, yield 68%. 1H NMR (CDCl3):
d 0.85 (t, 6H, –CH3,
J¼7.03 Hz), 1.23–1.45 (m, 42H, –CH2), 1.78–1.82 (m, 8H, –CH2), 2.58
(t, 4H, –OCOCH2, J¼7.36 Hz), 3.98 (t, 4H, –OCH2, J¼6.42 Hz), 6.92 (d,
2H, Ar–H, J¼8.20 Hz), 7.03 (s, 2H, Ar–H), 7.22 (d, 4H, Ar–H,
J¼8.33 Hz), 7.59 (d, 2H, Ar–H, J¼8.59 Hz), 8.20 (d, 4H, Ar–H,
d
0.87 (t, 3H, –CH3, J¼6.69 Hz), 1.26–1.50 (m, 18H, –CH2), 1.77–1.83
(m, 2H, –CH2), 4.00 (t, 2H, –OCH2, J¼6.49 Hz), 6.91–6.96 (m, 3H, Ar–
H), 7.07 (s, 1H, Ar–H), 7.56 (d, 1H, Ar–H, J¼8.67 Hz), 8.06 (d, 2H, Ar–
J¼8.21 Hz). 13C NMR (CDCl3):
d
14.46, 23.02, 25.08, 26.38, 29.18,
H, J¼8.35 Hz). 13C NMR (CDCl3):
d 14.38, 23.02, 26.44, 29.66, 29.69,
29.55, 29.70, 29.73, 29.91, 29.94, 30.00, 30.03, 32.26, 34.66, 69.20,
96.38, 113.86, 120.18, 122.53, 125.10, 128.87, 135.68, 151.95, 153.28,
158.25, 161.73, 172.09. MS (FAB): calcd for MHþ C59H78N2O8: 943.3,
found: 942.9.
29.76, 29.93, 29.95, 29.99, 30.01, 32.28, 69.51, 96.83, 113.78, 116.54,
119.64, 119.74, 129.79, 135.54, 151.84, 158.15, 159.66, 163.01.
4.26. Bis(4-(6-(dodecyloxy)benzo[d]oxazol-2-yl)phenyl)-
butanedioate 1b (m[4, n[12)
4.21. Bis(4-(6-(octyloxy)benzo[d]oxazol-2-yl)phenyl)-
tridecanedioate 1f (m[11, n[8)
The mixture of 4-(6-(dodecyloxy)benzo[d]oxazol-2-yl)phenol 4
(0.15 g, 0.38 mmol) and DMAP (0.046 g, 0.38 mmol) dissolved in
25 ml of dry THF was refluxed for 10 min under nitrogen atmo-
sphere. To the solution, a dilute solution of adipoyl chloride
(0.035 g, 0.19 mmol) dissolved in 5.0 ml of dry THF was slowly
added. The solution was stirred at room temperature for 4 h. The
solution was concentrated under reduce pressure and the product
isolated as white solids were obtained after recrystallization from
White solid, yield 77%. 1H NMR (CDCl3):
d 0.86 (t, 6H, –CH3,
J¼6.85 Hz), 1.26–1.45 (m, 34H, –CH2), 1.73–1.80 (m, 8H, –CH2),
2.656 (t, 4H, –OCOCH2, J¼7.50 Hz), 3.97 (t, 4H, –OCH2, J¼6.55 Hz),
6.92 (d, 2H, Ar–H, J¼8.70 Hz), 7.05 (s, 2H, Ar–H), 7.26 (d, 4H, Ar–H,
J¼7.05 Hz), 7.59 (d, 2H, Ar–H, J¼8.75 Hz), 8.19 (d, 4H, Ar–H,
J¼8.70 Hz). 13C NMR (CDCl3):
d 14.44, 22.99, 25.19, 26.38, 29.40,
29.57, 29.69, 29.72, 29.81, 32.14, 34.73, 69.19, 96.36, 113.86, 120.16,
122.54, 125.04, 128.85, 135.64, 151.93, 153.31, 158.24, 161.74, 172.22.
MS (FAB): calcd for MHþ C55H70N2O8: 887.2, found: 887.0.
CH2Cl2/MeOH. Yield 72%. 1H NMR (CDCl3):
d 0.86 (t, 6H, –CH3,
J¼6.94 Hz), 1.24–1.47 (m, 36H, –CH2), 1.79–1.80 (m, 8H, –CH2), 2.67
(t, 4H, –OCOCH2, J¼7.30 Hz), 3.99 (t, 4H, –OCH2, J¼6.38 Hz), 6.94 (d,
2H, Ar–H, J¼7.93 Hz), 7.07 (s, 2H, Ar–H), 7.24 (d, 4H, Ar–H,
J¼5.36 Hz), 7.61 (d, 2H, Ar–H, J¼8.44 Hz), 8.22 (d, 4H, Ar–H,
4.22. Bis(4-(6-(dodecyloxy)benzo[d]oxazol-2-yl)phenyl)-
tridecanedioate 1f (m[11, n[12)
J¼7.88 Hz). 13C NMR (CDCl3):
d 14.48, 23.04, 24.53, 26.40, 29.56,
29.71, 29.74, 29.93, 29.95, 30.01, 30.04, 32.27, 34.33, 69.24, 96.41,
113.97, 120.19, 122.56, 125.14, 128.98, 135.52, 151.95, 153.23, 158.32,
161.72, 171.64. MS (FAB): calcd for MHþ C56H72N2O8: 901.2, found:
900.9.
White solid, yield 70%. 1H NMR (CDCl3):
d 0.86 (t, 6H, –CH3,
J¼6.46 Hz), 1.24–1.46 (m, 50H, –CH2), 1.74–1.81 (m, 8H, –CH2), 2.57
(t, 4H, –OCOCH2, J¼7.47 Hz), 3.98 (t, 4H, –OCH2, J¼6.53 Hz), 6.93 (d,
2H, Ar–H, J¼8.71 Hz), 7.07 (s, 2H, Ar–H), 7.22 (d, 4H, Ar–H,
J¼8.65 Hz), 7.60 (d, 2H, Ar–H, J¼8.72 Hz), 8.20 (d, 4H, Ar–H,
4.27. Bis(4-(6-(dodecyloxy)benzo[d]oxazol-2-yl)phenyl)-
hexanedioate 1d (m[6, n[12)
J¼8.65 Hz). 13C NMR (CDCl3):
d 14.47, 23.03, 25.20, 26.39, 29.41,
29.56, 29.70, 29.74, 29.82, 29.92, 29.94, 29.98, 30.00, 30.04, 32.26,
34.74, 69.21, 96.38, 113.86, 120.18, 122.55, 125.09, 128.86, 135.70,
151.95, 153.32, 158.25, 161.76, 172.24. MS (FAB): calcd for MHþ
C63H86N2O8: 999.4, found: 998.9.
White solid, yield 51%. 1H NMR (CDCl3):
d 0.86 (t, 6H, –CH3,
J¼7.06 Hz), 1.24–1.46 (m, 40H, –CH2), 1.79–1.80 (m, 8H, –CH2), 2.60
(t, 4H, –OCOCH2, J¼7.40 Hz), 3.99 (t, 4H, –OCH2, J¼6.56 Hz), 6.93 (d,
2H, Ar–H, J¼8.71 Hz), 7.07 (s, 2H, Ar–H), 7.23 (d, 4H, Ar–H,
J¼9.45 Hz), 7.60 (d, 2H, Ar–H, J¼8.73 Hz), 8.21 (d, 4H, Ar–H,
4.23. 4-((E)-(4-(Dodecyloxy)-2-hydroxyphenylimino)-
methyl)phenyl acetate 6
J¼8.60 Hz). 13C NMR (CDCl3):
d 14.46, 23.04, 24.97, 26.40, 29.05,
29.57, 29.71, 29.74, 29.93, 29.95, 30.01, 30.04, 32.27, 34.62, 69.25,
96.42, 113.92, 120.18, 122.55, 125.10, 128.92, 135.62, 151.96, 153.31,
158.30, 161.75, 172.04. MS (FAB): calcd for MHþ C58H76N2O8: 929.2,
found: 928.9.
1H NMR (CDCl3):
d
0.87 (t, 3H, –CH3, J¼6.30 Hz), 1.26–1.42 (m,
18H, –CH2), 1.69–1.80 (m, 2H, –OCH2CH2), 2.31 (s, 3H, –OCOCH3),
3.93 (t, 2H, –OCH2, J¼6.52 Hz), 6.44 (d, 1H, Ar–H, J¼6.15 Hz), 6.55 (s,
1H, Ar–H), 7.15–7.27 (m, 3H, Ar–H), 7.44 (s, 1H, Ar–OH), 7.86 (d, 2H,
Ar–H, J¼8.58 Hz), 8.56 (s, 1H, –NCH). 13C NMR (CDCl3):
d
14.09,
Acknowledgements
21.09, 22.65, 26.00, 29.14, 29.31, 29.34, 29.55, 29.60, 31.87, 68.19,
100.42, 107.06, 116.16, 121.99, 128.12, 129.41, 133.83, 152.18, 152.65,
153.74, 160.29, 169.06.
We thank the National Science Council of Taiwan, ROC (NSC-94-
2738-M-008-001) in generous support of this work.

C.-C. Liao et al. / Tetrahedron 64 (2008) 7977–7985
7985
38, 1427–1443; (c) Attard, G. S.; Date, R. W.; Imrie, C. T.; Luckhurst, G. R.;
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D.; Pisipati, V. G. K. M. Cryst. Res. Technol. 2002, 37, 881–889.
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