Synthesis of non-symmetrically substituted 1,2,4-oxadiazole derived liquid crystals

Article abstract of DOI:10.1016/j.tet.2011.09.039

Non-symmetrically substituted 1,2,4-oxadiazole derived bent-core liquid crystals have been synthesized by a simple and straightforward synthetic method. All these compounds exhibit enantiotropic nematic phases over exceptionally wide temperature ranges.

Full text of DOI:10.1016/j.tet.2011.09.039

Tetrahedron 67 (2011) 8635e8638
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Synthesis of non-symmetrically substituted 1,2,4-oxadiazole derived liquid
crystals
*
Govindaswamy Shanker, Carsten Tschierske
Institute of Chemistry, Organic Chemistry, Martin-Luther-University Halle-Wittenberg, Kurt Mothes Str. 2, D-06120 Halle/Saale, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 29 July 2011
Received in revised form 12 September 2011
Accepted 13 September 2011
Available online 16 September 2011
Non-symmetrically substituted 1,2,4-oxadiazole derived bent-core liquid crystals have been synthesized
by a simple and straightforward synthetic method. All these compounds exhibit enantiotropic nematic
phases over exceptionally wide temperature ranges.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
1,2,4-Oxadiazole
Liquid crystal
Nematic mesophase
1. Introduction
structures, such as polymers and dendrimers etc.4 Therefore, the
target was to develop a straightforward route to prepare compound
Bent-core or banana-shaped molecules have developed to one
of the most important area of research in the field of liquid crystals
(LCs) since 1996, when macroscopic polar order (ferroelectricity
and antiferroelectricity) and spontaneous achiral symmetry
breaking with formation of chiral superstructures were observed
for some liquid crystalline phases of these molecules.1 Very re-
cently the first example of a new ferronematic phase was reported
for a special compound derived from the bent 3,5-diphenyl-1,2,4-
oxadiazole unit.2 However, the reported material has a relatively
high melting point and the nematic phase is replaced by a smectic
phase at lower temperature. In order to confirm these results and to
explore the application of such materials in devices it is necessary
to improve and optimize this class of compounds by reducing the
melting points and removing all undesired smectic LC phases, so
that in the ideal case the ferronematic phase is stable down below
room temperature. One way to achieve this is to substitute the 3,5-
diphenyl-1,2,4-oxadiazole moiety non-symmetrically, as reduced
molecular symmetry of bent-cores leads to lower melting tem-
peratures compared to the symmetric counter-parts.3 However,
molecules of this type have been not reported so far. Moreover,
such a molecular structure would allow the combination of the LC-
forming unit with additional functional units and this provides the
possibility to combine these units, for example, with photo-
responsive units or fullerenes and to incorporate them into larger
4 (Scheme 1) as a universal building block for unsymmetrically
substituted 1,2,4-oxadiazoles. In this compound one side already
represents one leg of the target bent-core mesogen and the phe-
nolic hydroxyl group at the other end provides the possibility to
attach different kinds of building blocks by esterification and
etherification procedures as shown with the examples reported
herein.
The most commonly used routes to construct the 1,2,4-
oxadiazole ring are 1,3-dipolar cycloaddition of nitrile oxides to
nitriles and cyclization of O-acylated amidoximes.5,6 However,
construction of functional materials based on 1,2,4-oxadiazole re-
mains still challenging, because the ring is quite sensitive to nu-
cleophilic attack7 and the ring oxygen can acts as a good internal
leaving group.6,8 Especially the presence of reactive ester groups in
the desired molecules 4e8 requires an efficient synthesis under
mild conditions. Activation of
amidoximes was recently reported by Braga et al. for the one pot-
synthesis of
-amino acid derived 1,2,4-oxadiazoles.9a
a-amino acids and their reaction with
a
2. Synthesis and characterization
Here we adopted this methodology for the synthesis of liquid
crystalline materials. Specifically, we report a simple and straight-
forward synthetic strategy to accomplish unsymmetrical
substituted 1,2,4-oxadiazole derivatives as described in Scheme 1.
Accordingly, 4-benzyloxybenzonitrile was treated with hydroxyl-
amine hydrochloride, which yielded the corresponding benzyl-
* Corresponding author. Tel.: þ49 (0) 345 55 25664; fax: þ49 (0) 345 55 27346;
e-mail address: carsten.tschierske@chemie.uni-halle.de (C. Tschierske).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.09.039

8636
G. Shanker, C. Tschierske / Tetrahedron 67 (2011) 8635e8638
of LC phases. Particularly, they exhibit broad regions of nematic
phases, as indicated by the typical textures observed by polarizing
microscopy (crossed polarizers, see Fig. 1).
O
O
N OH
NH2
HO
C6H13
BnO
O
i
2
Table 1
1
Phase transition temperatures (T/ꢁC) of compounds (5aed) and (6a, b)a
O
O
N O
N O
NH2
C6H13
O
O
m
BnO
N
H
O
O
O
C6H13
H2n+1Cn
H
O
N
O
O
N
Compd
m
n
Phase transitions
Tcr
BnO
O
5a
5b
5c
5d
6a
6b
0
0
0
0
1
1
3
4
5
7
3
5
Cr 149 N 305 Iso
Cr 120 N 293 Iso
Cr 129 N 296 Iso
Cr 124 N 283 Iso
Cr 127 N 250 Iso
Cr 123 N 245 Iso
85
95
112
98
100
99
3
ii
C6H13
O
N
N
a
Phase transition temperatures were obtained from DSC heating curved
(10 K minꢀ1) and confirmed by polarizing microscopy; Abbreviations: Cr¼crystal-
line solid; N¼nematic phase; Iso¼isotropic liquid; Tcr¼crystallization temperature
on cooling (DSC, 10 K minꢀ1).
O
iv
HO
4
C6H13
O
OH
Table 2
H2n+1Cn
Phase transition temperatures (T/ꢁC) of compounds (7a, b) and (8a, b)a
iii
OH
O
Br
H
O
N
H2n+1Cn
n
O
N
H2n+1Cn
X
H
O
O
8
5, 6, 7
Scheme 1. Synthesis of compounds 3e8; reagent and conditions: (i) DCC, 1,4-dioxane,
reflux, 8 h, (75%); (ii) THF/EtOAc (3:7), 10% Pd/C, 100 kPa, 6 h (65%); (iii) DCC, DMAP,
CH2Cl2, 12 h, (65e71%); (iv) K2CO3, butanone, 10 h, (73, 68%).
C6H13
H2n+1Cn
Compd
X
n
Phase transitions
Tcr
7a
7b
8a
8b
CO
CO
CH2
CH2
4
5
3
7
Cr 146 N 294 Iso
Cr 154 N 285 Iso
Cr 105 N 241 Iso
Cr 99 N 211 Iso
126
118
89
protected 4-hydroxybenzamidoxime 1.10 Activation of the 4-(4-n-
hexylbenzoyloxy)benzoic acid 211 with N,N0-dicyclohex-
ylcarbodiimide (DCC) and O-acylation of the amidoxime 1 in dry
dioxane as a solvent furnished the intermediate O-acylamidoxime,
which was not isolated and immediately undergoes a cyclo-
dehydration reaction on refluxing for 8 h, delivering the 4-[3-(4-
benzyloxyphenyl)-1,2,4-oxadiazol-5-yl]phenyl 4-hexylbenzoate 3.
84
a
See foot note of Table 1.
The peaks at
d
¼174.76 and 168.68 ppm in the 13C NMR spectrum
(see Experimental section) confirms the formation of 1,2,4-
oxadiazole ring and the ester group (
d
¼164.66 ppm) was not af-
fected under these conditions.9
Deprotection of 3 was initially tried using numerous procedure
reported in literature,12 but was unsuccessful with all these
methods; also the acidolytic deprotection, as reported previously3c,f
was not possible due to the presence of the ester group in the
molecule. Finally we were successful by using a carefully controlled
hydrogenation procedure described in the Experimental section to
afford the desired compound 4-[3-(4-hydroxyphenyl)-1,2,4-
oxadiazol-5-yl]phenyl 4-hexylbenzoate 4 in about 65% yield. It is
essential to exactly keep the optimized conditions (T, p, t) given
there, as otherwise the oxadiazole ring is cleaved hydrogenolyti-
cally. First examples of liquid crystalline target compounds (5e7)
were obtained by O-acylation of the phenol 4 with appropriate
4-alkylbenzoic acids, trans-4-alkylcyclohexanecarboxylic acids or
trans-4-alkylcyclohexylpropionic acids using DCC as condensation
8 were synthesized by Williamson
etherification with 1-bromomethyl-4-n-alkylbenzenes using K2CO3
as base (see Experimental section for details).
The LC phases and transition temperatures of the obtained LC
materials are summarized in Tables 1 and 2. It is apparent from
these tables that all synthesized compounds display broad regions
Fig. 1. Microphotograph (crossed polarizers) of representative textures of the nematic
phase of compound 5a: (a) nematic droplets as observed after cooling from the iso-
tropic liquid at 305 ꢁC (dark areas are residues of the isotropic liquid), (b) complete
texture after cooling further to T¼240 ꢁC.
Representative textures of the liquid crystalline phases are
shown in Fig. 1 for compound 5a as example. Typically, nematic
droplets occur at the Iso-N transition (Fig. 1a), which coalesce to
schlieren textures (Fig. 1b) and also marbled textures on further
cooling. This indicates nematic LC phases,14 which were observed in
the whole LC temperature range down to the crystallization tem-
perature (Tcr, see Tables 1 and 2) without formation of any addi-
tional smectic phase. Also calorimetric investigations are in line
with the optical investigations; the transition enthalpies for the
transition N-Iso are in the range between 1 and 2 kJ molꢀ1 for all
compounds, which is in the typical range as usually observed for
these phase transitions of bent-core molecules.
agent,13 and compounds

G. Shanker, C. Tschierske / Tetrahedron 67 (2011) 8635e8638
8637
3. Conclusions
chromatographed using CH2Cl2/EtOAc (9:1) to afford the desired
compound. Colourless solid; yield 680 mg, 1.54 mmol, 65%; phase
transitions: Cr 155 ꢁC N 192 ꢁC Iso; IR (cmꢀ1): 3345, 2921, 2856,1741,
Non-symmetric
substituted
3,5-diphenyl-1,2,4-oxadiazole
based bent-core liquid crystals have been synthesized by a simple
and straightforward synthetic strategy. The obtained compounds
represent first examples of non-symmetrically substituted 1,2,4-
oxadiazole bent-core mesogens and have promising properties.
Most compounds exhibit lower melting temperature in comparison
to their symmetric counter part and exclusively nematic phase
were observed over broad temperature ranges, i.e., undesirable
smectic phases were suppressed by appropriate choice of the chain
length attached to the used carboxylic acids. The nematic phases of
these compounds are presently under more detailed investigation
by X-ray diffraction (XRD), electro-optical methods and dielectric
spectroscopy to investigate the detailed structure of these nematic
phases, to check for ferroelectricity and phase biaxiality, and to
explore the application potentials of these new materials.15
1069; 1H NMR (400 MHz, CDCl3):
d
8.26 (d, J¼8.8 Hz, 2H, Ar), 8.12 (d,
J¼8.4 Hz, 2H, Ar), 8.06 (d, J¼8.4 Hz, 2H, Ar), 7.41 (d, J¼8.8 Hz, 2H, Ar),
7.32 (d, J¼8.0 Hz, 2H, Ar), 6.94 (d, J¼8.8 Hz, 2H, Ar), 2.72 (t, J¼7.6 Hz,
2H, CH2), 1.66e1.24 (m, 8H, 4ꢂ CH2), 0.89 (m, 3H, CH3); 13C NMR
(100 MHz, CDCl3):
d 174.66, 168.60, 165.05, 158.35, 154.36, 150.02,
130.41, 129.67, 129.31, 128.81, 126.26, 122.64, 121.97, 119.31, 115.81,
36.12, 31.64, 31.05, 28.89, 22.56, 14.05; EA, calcd for C27H26N2O4,
442.51 g/mol: C 73.28, H 5.92, N 6.33, found: C 73.12, H 5.74, N 6.25.
4.4. General procedure for the synthesis of compounds 5e7
Compound (4) (0.45 mmol), the appropriate carboxylic acid,
either trans-4-alkylcyclohexanecarboxylic acid or trans-4-
alkylcyclohexylpropionic acid or 4-alkylbenzoic acid (0.45 mmol,
1 equiv), and 4-dimethylamino pyridine (DMAP) (1 mg,
0.006 mmol) were dissolved in dry CH2Cl2 (20 mL) under an argon
atmosphere. A solution of N,N0-dicyclohexylcarbodiimide (DCC)
(140 mg, 0.68 mmol, 1.5 equiv) in CH2Cl2 (10 mL) was added to
above mixture and the mixture was stirred at room temperature for
additional 12 h. The precipitate N,N0-dicyclohexylurea was filtered
off and the filtrate was concentrated, the residue was purified by
column chromatography on silica gel using CH2Cl2/hexane (3/7) as
eluent to afford the product as a colourless solid.
4. Experimental sections
4.1. General
All the starting materials were obtained from Aldrich Company
and used as received. Solvents were purified and dried by standard
methods prior to use. The crude samples were purified by column
chromatographic technique using silica gel (230e400 mesh) has
a stationary phase. Thin layer chromatography (TLC) was per-
formed on aluminium sheets pre-coated with silica gel (Merck,
Kieselgel 60, F254). Investigation of the LC properties was carried
out by polarizing microscopy (Optiphot-2, Nikon) on a hot stage (FP
82 HAT, Mettler). Phase transition temperatures were recorded by
differential scanning calorimetry (DSC-7, PerkineElmer) at
10 K minꢀ1 on heating/cooling (Tcr).
4.4.1. 4-{3-[4-(trans-4-n-Propylcyclohexylcarbonyloxy)phenyl]-
1,2,4-oxadiazol-5-yl}phenyl 4-hexylbenzoate (5a). Colourless solid;
yield 70% (after crystallization from CH2Cl2/EtOH 2:8); 1H NMR
(400 MHz, CDCl3):
d
8.28 (d, J¼8.4 Hz, 2H, Ar), 8.19 (d, J¼8.8 Hz, 2H,
Ar), 8.11 (d, J¼8.4 Hz, 2H, Ar), 7.42 (d, J¼8.8 Hz, 2H, Ar), 7.33 (d,
J¼8.0 Hz, 2H, Ar), 7.22 (d, J¼8.8 Hz, 2H, Ar), 2.71 (t, J¼7.6 Hz, 2H,
CH2), 2.52 (m, 1H, CHCOO), 2.16 (m, 2H, CH2CHCOO(cy)), 1.90 (m,
2H, CH2CHCOO(cy)), 1.65e0.86 (m, 23H, 1ꢂ CH, 8ꢂ CH2, 2ꢂ CH3);
EA, calcd for C37H42N2O5, 594.74 g/mol: C 74.72, H 7.12, N 4.71,
found: C 74.47, H 7.04, N 4.70.
4.2. Procedure for the synthesis of compound 3
4-[3-(4-Benzyloxyphenyl)-1,2,4-oxadiazol-5-yl]phenyl
4-
hexylbenzoate (3). 4-Benzyloxyphenylamidoxime (1)10 (2.0 g,
8.25 mmol, 1 equiv) and 4-(4-n-hexylbenzoyloxy)benzoic acid (2)11
(2.9 g, 9.08 mmol, 1 equiv) were dissolved in dry 1,4-dioxane
(15 mL) and to the above reaction mixture, a solution of N,N0-
dicyclohexylcarbodiimide (DCC) (1.9 g, 9.08 mmol, 1.1 equiv) in
dioxane (10 mL) was added and stirred for a hour at 25 ꢁC. A white
precipitate forms in the solution, which was then refluxed for 8 h,
after this the solvent was removed under vacuum and the residue
was purified by flash chromatography (EtOAc/hexane 3:7). Col-
ourless solid; yield 2.7 g, 2.33 mmol, 75% (after crystallization
CH2Cl2/EtOH 3:7); phase transitions: Cr 136 ꢁC N 205 ꢁC Iso; 1H
4.4.2. 4-{3-[4-(trans-4-n-Butylcyclohexylcarbonyloxy)phenyl]-1,2,4-
oxadiazol-5-yl}phenyl 4-hexylbenzoate (5b). Colourless solid; yield
65% (after crystallization from CH2Cl2/EtOH 2:8); 1H NMR
(400 MHz, CDCl3):
d
8.28 (d, J¼8.8 Hz, 2H, Ar), 8.18 (d, J¼8.8 Hz, 2H,
Ar), 8.12 (d, J¼8.0 Hz, 2H, Ar), 7.42 (d, J¼8.8 Hz, 2H, Ar), 7.33 (d,
J¼8.4 Hz, 2H, Ar), 7.22 (d, J¼8.4 Hz, 2H, Ar), 2.72 (t, J¼7.6 Hz, 2H,
CH2), 2.53 (m, 1H, CHCOO), 2.17 (m, 2H, CH2CHCOO(cy)), 1.90 (m,
2H, CH2CHCOO(cy)), 1.65e0.87 (m, 25H, 1ꢂ CH, 9ꢂ CH2, 2ꢂ CH3);
EA, calcd for C38H44N2O5, 608.77 g/mol: C 74.97, H 7.29, N 4.60,
found: C 74.73, H 7.14, N 4.47.
NMR (400 MHz, CDCl3):
d
8.27 (d, J¼8.8 Hz, 2H, Ar), 8.12 (dd,
J1¼8.8 Hz, J2¼9.2 Hz, 4H, Ar), 7.44 (m, 5H, Ar), 7.37 (m, 4H, Ar); 7.08
(d, J¼8.8 Hz, 2H, Ar), 5.13 (s, 2H, CH2), 2.72 (t, J¼7.2 Hz, 2H, CH2),
1.68e1.31 (m, 8H, 4ꢂ CH2), 0.87 (t, J¼6.4 Hz, 3H, CH3); 13C NMR
4.4.3. 4-{3-[4-(trans-4-n-Pentylcyclohexylcarbonyloxy)phenyl]-
1,2,4-oxadiazol-5-yl}phenyl 4-hexylbenzoate (5c). Colourless solid;
yield 68% (after crystallization from CH2Cl2/EtOH 2:8); 1H NMR
(100 MHz, CDCl3):
d
174.76, 168.68, 164.66, 164.64, 161.13, 154.46,
(400 MHz, CDCl3):
d
8.28 (d, J¼8.4 Hz, 2H, Ar), 8.19 (d, J¼8.8 Hz, 2H,
149.87, 149.68, 136.47, 134.34, 129.63, 129.17, 128.77, 128.71, 128.28,
127.49, 126.55, 126.39, 122.03, 119.64, 115.15, 70.09, 36.10, 36.08,
31.63, 31.05, 28.89, 26.20, 22.55, 14.04; EA, calcd for C34H32N2O4,
532.63 g/mol: C 76.67, H 6.06, N 5.26, found: C 76.39, H 5.80, N 5.27.
Ar), 8.12 (d, J¼7.6 Hz, 2H, Ar), 7.42 (d, J¼8.4 Hz, 2H, Ar), 7.33 (d,
J¼8.4 Hz, 2H, Ar), 7.22 (d, J¼8.8 Hz, 2H, Ar), 2.72 (t, J¼6.8 Hz, 2H,
CH2), 2.49 (m, 1H, CHCOO), 2.15 (m, 2H, CH2CHCOO(cy)), 1.89 (m,
2H, CH2CHCOO(cy)), 1.65e0.88 (m, 27H, 1ꢂ CH, 10ꢂ CH2, 2ꢂ CH3);
EA, calcd for C39H46N2O5, 622.79 g/mol: C 75.21, H 7.44, N 4.50,
found: C 75.09, H 7.38, N 4.40.
4.3. Procedure for the synthesis of compound 4
4-[3-(4-Hydroxyphenyl)-1,2,4-oxadiazol-5-yl]phenyl 4-hexyl-
benzoate (4). 10% Pd/C (ALDRICH, 100 mg) was added to com-
pound (3) (1 g, 4.12 mmol) taken in a mixture of THF/EtOAc (3:7)
solution (20 mL) and was hydrogenated at 20 ꢁC for a period of 6 h at
100 kPa in a Parr hydrogenation apparatus. The suspension was fil-
tered through Celite and evaporated, the residue was
4.4.4. 4-{3-[4-(trans-4-n-Heptylcyclohexylcarbonyloxy)phenyl]-
1,2,4-oxadiazol-5-yl}phenyl 4-hexylbenzoate (5d). Colourless solid;
yield 67% (after crystallization from CH2Cl2/EtOH 2:8); 1H NMR
(400 MHz, CDCl3):
d
8.28 (d, J¼8.4 Hz, 2H, Ar), 8.19 (d, J¼8.0 Hz, 2H,
Ar), 8.12 (d, J¼8.4 Hz, 2H, Ar), 7.42 (d, J¼8.8 Hz, 2H, Ar), 7.33 (d,
J¼8.4 Hz, 2H, Ar), 7.22 (d, J¼8.8 Hz, 2H, Ar), 2.72 (t, J¼7.6 Hz, 2H,

8638
G. Shanker, C. Tschierske / Tetrahedron 67 (2011) 8635e8638
CH2), 2.50 (m, 1H, CHCOO), 2.16 (m, 2H, CH2CHCOO(cy)), 1.90 (m,
2H, CH2CHCOO(cy)), 1.65e0.86 (m, 31H, 1ꢂ CH, 12ꢂ CH2, 2ꢂ CH3);
d 8.25 (m, 2H, Ar), 8.12 (m, 4H, Ar), 7.42 (m, 2H, Ar), 7.33 (m, 4H, Ar),
7.20 (m, 2H, Ar), 7.09 (m, 2H, Ar), 5.01 (m, 2H, CH2), 2.71 (t, J¼7.2 Hz,
2H, CH2), 2.60 (t, J¼7.2 Hz, 2H, CH2), 1.68e0.86 (m, 16H, 5ꢂ CH2, 2ꢂ
CH3); EA, calcd for C37H38N2O4, 574.71 g/mol: C 77.33, H 6.66, N
4.87, found: C 77.06, H 6.43, N 4.61.
13C NMR (100 MHz, CDCl3):
d 175.01, 174.14, 168.31, 164.52, 154.54,
153.19,149.81,130.33,129.65,128.79,128.75, 126.40,124.36, 122.66,
122.10, 121.80, 43.85, 37.31, 37.09, 36.25, 32.42, 32.03, 31.78, 31.18,
30.04, 29.47, 29.17, 29.04, 27.01, 22.83, 22.71, 14.24, 14.19; EA, calcd
for C41H50N2O5, 650.85 g/mol: C 75.66, H 7.74, N 4.30, found: C
75.46, H 7.60, N 4.23.
4.5.2. 4-{3-[4-(4-n-Heptylbenzyloxy)phenyl]-1,2,4-oxadiazol-5-yl}
phenyl 4-hexylbenzoate (8b). Colourless solid; yield 68% (after
crystallization from CH2Cl2/EtOH 2:8); 1H NMR (400 MHz, CDCl3):
4.4.5. 4-{3-[4-(trans-4-n-Propylcyclohexylpropanoyloxy)-phenyl]-
1,2,4-oxadiazol-5-yl}phenyl 4-hexylbenzoate (6a). Colourless solid;
yield 65% (after crystallization from CH2Cl2/EtOH 2:8); 1H NMR
d 8.29 (m, 2H, Ar), 8.12 (m, 4H, Ar), 7.41 (m, 2H, Ar), 7.35 (m, 4H, Ar),
7.21 (m, 2H, Ar), 7.10 (m, 2H, Ar), 5.09 (m, 2H, CH2), 2.72 (t, J¼7.6 Hz,
2H, CH2), 2.62 (t, J¼7.2 Hz, 2H, CH2), 1.67e0.85 (m, 24H, 9ꢂ CH2, 2ꢂ
CH3); EA, calcd for C41H46N2O4, 630.81 g/mol: C 78.06, H 7.35, N
4.44, found: C 77.78, H 7.16, N 4.34.
(400 MHz, CDCl3):
d
8.29 (d, J¼6.8 Hz, 2H, Ar), 8.19 (d, J¼6.8 Hz, 2H,
Ar), 8.12 (d, J¼6.4 Hz, 2H, Ar), 7.42 (d, J¼6.8 Hz, 2H, Ar), 7.33 (d,
J¼6.4 Hz, 2H, Ar), 7.22 (d, J¼6.8 Hz, 2H, Ar), 2.71 (t, J¼6.0 Hz, 2H, CH2),
2.60 (m, 2H, CH2COO), 1.78e0.85 (m, 30H, 2ꢂ CH, 11ꢂ CH2, 2ꢂ CH3);
Acknowledgements
13C NMR (125 MHz, CDCl3):
d 175.08, 172.17, 168.35, 164.61, 154.57,
153.06, 149.87, 130.34, 129.67, 128.83, 128.76, 126.35, 124.41, 122.67,
122.11, 121.75, 39.67, 37.44, 37.37, 36.09, 33.06, 32.91, 32.20, 32.14,
31.62,31.04, 28.88,22.54,19.98,14.36,14.03;EA, calcd forC39H46N2O5,
622.79 g/mol: C 75.21, H 7.44, N 4.50, found: C 75.08, H 7.32, N 4.43.
This work supported by the EU with in the FP7 funded Collab-
orative Project BIND (grant No 216025).
References and notes
4.4.6. 4-{3-[4-(trans-4-n-Pentylcyclohexylpropanoyloxy)-phenyl]-
1,2,4-oxadiazol-5-yl}phenyl 4-hexylbenzoate (6b). Colourless solid;
yield 69% (after crystallization from CH2Cl2/EtOH 2:8); 1H NMR
1. (a) Niori, T.; Sekine, T.; Watanabe, J.; Furukawa, T.; Takezoe, H. J. Mater. Chem.
1996, 6, 1231e1233; (b) Reddy, R. A.; Tschierske, C. J. Mater. Chem. 2006, 16,
907e961; (c) Link, D. R.; Natale, G.; Shao, R.; Maclennan, J. E.; Clark, N. A.;
€
Korblova, E.; Walba, D. M. Science 1997, 278, 1924e1927; (d) Hough, L. E.;
(400 MHz, CDCl3):
d
8.28 (d, J¼6.8 Hz, 2H, Ar), 8.19 (d, J¼6.8 Hz, 2H,
Spannuth, M.; Nakata, M.; Coleman, D. A.; Jones, C. D.; Dantlgraber, G.;
Ar), 8.12 (d, J¼6.4 Hz, 2H, Ar), 7.42 (d, J¼6.8 Hz, 2H, Ar), 7.33 (d,
J¼6.4 Hz, 2H, Ar), 7.23 (d, J¼6.8 Hz, 2H, Ar), 2.71 (t, J¼6.0 Hz, 2H,
CH2), 2.60 (m, 2H, CH2COO),1.80e0.85 (m, 34H, 2ꢂ CH,13ꢂ CH2, 2ꢂ
CH3); EA, calcd for C41H50N2O5, 650.85 g/mol: C 75.66, H 7.74, N
4.30, found: C 75.63, H 7.68, N 4.20.
€
Tschierske, C.; Watanabe, J.; Korblova, E.; Walba, D. M.; Maclennan, J. E.; Glaser,
M. A.; Clark, N. A. Science 2009, 325, 452e456.
2. Francescangeli, O.; Stanic, V.; Torgova, S. I.; Strigazzi, A.; Scaramuzza, N.; Fer-
rero, C.; Dolbnya, I. P.; Weiss, T. M.; Berardi, R.; Muccioli, L.; Orlandi, S.; Zannoni,
C. Adv. Funct. Mater. 2009, 19, 2592e2600.
3. (a) Karamysheva, L. A.; Torgova, S. I.; Agafonova, I. F.; Petrov, V. F. Liq. Cryst.
2000, 27, 393e405; (b) Gallerdo, H.; Begini, I. M. Mol. Cryst. Liq. Cryst. 1995, 258,
85e94; (c) Parra, M. L.; Hidalgo, P. I.; Elgueta, E. Y. Liq. Cryst. 2008, 35, 823e832;
(d) Gallardo, H.; Cristiano, R.; Vieira, A. A.; Neves, F.; Ricardo, A. W.; Srivastava,
R. M. Synthesis 2008, 605e609; (e) Gallardo, H.; Cristiano, R.; Vieira, A. A.;
Neves, F.; Ricardo, A. W.; Srivastava, R. M.; Bechtold, I. H. Liq. Cryst. 2008, 35,
857e863; (f) Parra, M. L.; Hidalgo, P. I.; Soto-Bustamante, E. A.; Barbera, J.;
Elgueta, E. Y.; Rrujillo-Rojo, V. H. Liq. Cryst. 2008, 35, 1251e1262; (g) Torgova, S.
I.; Geivandova, T. A.; Francescangeli, O.; Strigazzi, A. Pramana 2003, 61,
239e248; (h) Torgova, S. I.; Karamysheva, L. A.; Geivandova, T. A.; Strigazzi, A.
Mol. Cryst. Liq. Cryst. 2001, 365, 99e106; (i) Karamysheva, L. A.; Agafonova, I. F.;
Torgova, S. I. Mol. Cryst. Liq. Cryst. 1999, 332, 407e411; (j) Karamysheva, L. A.;
Torgova, S. I.; Agafonova, I. F.; Shitkov, N. M. Mol. Cryst. Liq. Cryst. 1995, 260,
217e225; (k) Karamysheva, L. A.; Agafonova, I. F.; Torgova, S. I.; Torgov, V. I. Mol.
Cryst. Liq. Cryst. 2000, 352, 327e334; (l) Torgova, S. I.; Karamysheva, L. A.;
Strigazzi, A. Braz. J. Phys. 2002, 32, 593e601.
4.4.7. 4-{3-[4-(4-n-Butylbenzoyloxy)phenyl]-1,2,4-oxadiazol-5-yl}
phenyl 4-hexylbenzoate (7a). Colourless solid; yield 68% (after
crystallization from CH2Cl2/EtOH 2:8); 1H NMR (400 MHz, CDCl3):
d
8.30 (d, J¼8.8 Hz, 2H, Ar), 8.25 (d, J¼8.8 Hz, 2H, Ar), 8.12 (dd,
J1¼8.4 Hz, J2¼8.0 Hz, 4H, Ar), 7.43 (d, J¼8.8 Hz, 2H, Ar), 7.38 (d,
J¼8.8 Hz, 2H, Ar), 7.33 (d, J¼1.6 Hz, 2H, Ar), 7.11 (d, J¼1.6 Hz, 2H, Ar),
2.72 (t, J¼7.2 Hz, 4H, 2ꢂ CH2), 1.64e1.31 (m, 12H, 6ꢂ CH2), 0.96 (m,
6H, 2ꢂ CH3); EA, calcd for C38H38N2O5, 602.78 g/mol: C 75.72, H
6.35, N 4.65, found: C 75.54, H 6.15, N 4.57.
4.4.8. 4-{3-[4-(4-n-Pentylbenzoyloxy)phenyl]-1,2,4-oxadiazol-5-yl}
phenyl 4-hexylbenzoate (7b). Colourless solid; yield 71% (after
crystallization from CH2Cl2/EtOH 2:8); 1H NMR (400 MHz, CDCl3):
4. Donnio, B.; Buathong, S.; Bury, I.; Guillon, D. Chem. Soc. Rev. 2007, 36,
1495e1513.
5. Pace, A.; Pierro, P. Org. Biomol. Chem. 2009, 7, 4337e4348.
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Ramsden, C. A., Scriven, E. E. V., Taylor, R. J. K., Eds.; Elsevier: Oxford, 2008;
Vol. 5, pp 243e314.
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62, 1158e1164; (b) Trifonov, R. E.; Volovodenko, A. P.; Vergizov, S. N.; Shir-
inbekov, N. I.; Gindin, V. A.; Koren, A. O.; Ostrovskii, V. A. Helv. Chim. Acta 2005,
88, 1790e1797.
d
8.29 (d, J¼8.4 Hz, 2H, Ar), 8.25 (d, J¼8.8 Hz, 2H, Ar), 8.13 (dd,
J1¼8.4 Hz, J2¼8.4 Hz, 4H, Ar), 7.43 (d, J¼8.8 Hz, 2H, Ar), 7.38 (d,
J¼8.8 Hz, 2H, Ar), 7.33 (d, J¼2.0 Hz, 2H, Ar), 7.31 (d, J¼2.0 Hz, 2H,
Ar), 2.72 (t, J¼6.8 Hz, 4H, 2ꢂ CH2), 1.66e1.32 (m, 14H, 7ꢂ CH2), 0.96
(m, 6H, 2ꢂ CH3); EA, calcd for C39H40N2O5, 616.75 g/mol: C 75.95, H
6.54, N 4.54, found: C 75.80, H 6.40, N 4.48.
8. Cosimelli, B.; Guernelli, S.; Spinelli, D.; Buscemi, S.; Frenna, V.; Macaluso, G. J.
Org. Chem. 2001, 66, 6124e6129.
€
9. (a) Braga, A. L.; Ludtke, D. S.; Alberto, E. E.; Dornelles, L.; Filho, W. A. S.; Cor-
4.5. General procedure for the synthesis of compounds 8aeb
bellini, V. A.; Rosa, D. M.; Schwab, R. S. Synthesis 2004, 10, 1589e1594; (b) Ono,
M.; Haratake, M.; Saji, H.; Nakayama, M. Bioorg. Med. Chem. 2008, 16,
6867e6872; (c) Braga, V. M. L.; de Melo, S. J.; Srivastava, R. M.; da Falcao, E. P. S.
~
A
mixture of compound (4) (0.52 mmol, 1 equiv) and
J. Braz. Chem. Soc. 2004, 15, 603e607.
1-bromomethyl-4-n-alkylbenzene (0.52 mmol, 1 equiv) dissolved
in dry butanone under argon atmosphere followed by anhydrous
K2CO3 (1.1 mmol, 2 equiv) and the reaction mixture was refluxed
for 10 h. The solvent was evaporated and obtained solid residue
poured into water, extracted with CH2Cl2, concentrated and puri-
fied by column chromatography on silica gel using CH2Cl2/hexanes
(2/8) as eluent to afford the product as a colourless solid.
10. (a) Parra, M.; Hidalgo, P.; Alderete, J. Liq. Cryst. 2005, 32, 449e455; (b) Parra, M.;
Hidalgo, P.; Carrasco, E.; Barbera, J.; Silvino, L. Liq. Cryst. 2006, 33, 875e882.
11. (a) Shen, D.; Pegenau, A.; Diele, S.; Wirth, I.; Tschierske, C. J. Am. Chem. Soc.
2000, 122, 1593e1601; (b) Achten, R.; Cuypers, R.; Giesbers, M.; Koudijs, A.;
€
Marcelis, A. T. M.; Sudholter, E. J. R. Liq. Cryst. 2004, 31, 1167e1174.
12. (a) Katkevichs, M.; Korchagova, E.; Ivanova, T.; Slavinska, V.; Lukevics, E. Chem.
Heterocycl. Compd. 2004, 40, 872e874; (b) Weissman, S. A.; Zewge, D. Synthesis
2005, 61, 7833e7863 and cited reference 94e98 therein.
13. (a) Neises, B.; Steglich, W. Angew. Chem., Int. Ed. Engl. 1978, 17, 522e524; (b)
Sheehan, J. C.; Hlavka, J. J. J. Org. Chem. 1956, 21, 439e441; (c) Tschierske, C.;
Zaschke, H. J. Prakt. Chem. 1989, 331, 365e366.
14. Dirking, I. Textures of Liquid Crystals; Wiley-VCH: Weinheim, 2003.
15. Shanker, G.; Nagaraj, M.; Vij, J. K.; Prehm, M.; Tschierske, C. Adv. Funct. Mater.
submitted for publication.
4.5.1. 4-{3-[4-(4-n-Propylbenzyloxy)phenyl]-1,2,4-oxadiazol-5-yl}
phenyl 4-hexylbenzoate (8a). Colourless solid; yield 73% (after
crystallization from CH2Cl2/EtOH 2:8); 1H NMR (400 MHz, CDCl3):