Synthesis of quinoxaline-benzoxale conjugates and mesomorphic properties

Article abstract of DOI:10.1016/j.tet.2010.11.014

A new series of non-discotic heterocyclic compounds 1a-e derived from quinoxaline was prepared and their mesomorphic properties investigated. The crystal and molecular structures of nonmesogenic 2,3-bis(3,4-didodecyloxyphenyl) quinoxaline-6-carboxylic aci

Full text of DOI:10.1016/j.tet.2010.11.014

Tetrahedron 67 (2011) 114e124
Contents lists available at ScienceDirect
Tetrahedron
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Synthesis of quinoxalineebenzoxale conjugates and mesomorphic properties
,
Chun-Jung Chen a, Yu-Che Wu a, Hwo-Shuenn Sheu b, Gene-Hsiang Lee c, Chung K. Lai a
*
a Department of Chemistry, National Central University, Chung-Li 32001, Taiwan
b National Synchrotron Radiation Research Center, Hsinchu 30077, Taiwan
c Instrumentation Center, National Taiwan University, Taipei 10660, Taiwan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 28 August 2010
Received in revised form 23 October 2010
Accepted 2 November 2010
Available online 6 November 2010
A new series of non-discotic heterocyclic compounds 1aee derived from quinoxaline was prepared and
their mesomorphic properties investigated. The crystal and molecular structures of nonmesogenic 2,3-
bis(3,4-didodecyloxyphenyl)quinoxaline-6-carboxylic acid 4-[(4-butoxy2-hydroxyphenylimino)methyl]
phenyl ester 2a (n¼4, m¼12) were determined by means of X-ray structural analysis. It crystallizes in
ꢀ
ꢀ
ꢀ
a monoclinic space group P2(1)/c, with a¼21.9193(13) A, b¼8.3693(4) A, c¼30.896(2) A, and Z¼4. The
molecule was considered as an elongated or tapered triangle. Both inter- and intra-molecular H-bonds
were observed in the crystal lattice, which was attributed to the formation of columnar mesophase in
compounds 2. The mesomorphic behavior of compounds 1e2 was studied by thermal analysis and
polarized optical microscopy. All compounds 1e2 exhibited hexagonal columnar phases (Colh), which
were also confirmed by powder XRD diffractometer. A Ncell and Rar value equal to 4.74 and 4.34 within
ꢀ
a slice of 9.0 A thick were obtained for 1b and 2b, indicating that a more disc-like correlated structure by
two molecules lying side-by-side was formed in Colh phases. The fluorescent properties of the com-
pounds 1e4 in CH3Cl were also examined.
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
Quinoxalines were long known as highly photoluminecent and/
or efficient electroluminescent materials1 and some of them have
More and more promising materials incorporating five- or six-
membered heterocyclic derivatives as a core or terminal moiety
have gained more impetus during the past years. Part of thus
exploring motives originates from their inherent features, such as
well-known chemistry/higher thermal stability, lower symmetry/
non-coplanarity, electro/photoluminescence, acceptor/electron-
deficiency and/or others. Quinoxalines, oxadiazoles or benzax-
azole are a few prevalent examples among them, and most of
these heterocyclic derivatives were often considered as electron-
deficient motifs. Heteroatoms therein incorporated, such as N, S
or O atom were often more polarized, therefore, a weak dipole
might be possibly induced. This dipole can be intramolecularly
induced within a structural moiety resulting from the other ac-
ceptor group located in two separated extremes. Similarly, an
intermolecular force (D/A) between the acceptor and other
donor of the neighboring molecule might be induced, giving
novel electroluminescent and mesogenic properties often ob-
served in these materials. The magnitude of the force is extre-
mely critical in the formation of mesophases: when they are
too weak or too strong the liquid crystalline behavior is then
lost.
been studied as light emitting dopants.2 Like oxadiazoles, they
were often used as electron-transporting (ETL) or hole-blocking
layers in organic light-emitting diodes (OLEDs). Quinoxalines were
recently also studied as dye-sensitizers used in photovoltaic or
heterojunction solar cells;3 they are relatively easy to prepare and
also thermally stable. Most of these quinoxalines constructed by
extended
p-conjugated structures with a donoreacceptor have
unique optical and electrical properties. In addition, a few lumi-
nescent iridium complexes4 with cyclometalated4a or orthometa-
lated4b quinoxaline ligands were reported. However, known
examples of mesogenic quinoxalines5a or structurally similar
derivatives5bee were relatively lesser. A series of discotic and el-
liptical molecules5e based on dibenzophenazine carboxylic acids
and their methyl ester analogs were prepared and N/colh/Colr
phases were observed. Interestingly, an enhanced mesophase range
for triphenyl-based mesogens by adding 1:1 ratio with hexakis(4-
nonylphenyl) dipyrazino[2,3-f:20,30-h]quinoxaline5d were obtained.
Two new fluorescent ethyl 3-aryl-1-methyl-8-oxo-8H-anthra[9,1-
gh]quinoline-2-carboxylates5a were synthesized, and such new
dyes have shown a very good orientation parameter (SA) in nematic
liquid crystals. In contrast, known mesogenic benzoxazoles were
somehow more. A few benzoxazoles6 with structures I, II, III
(Scheme 1) and some of their metal complexes were previously
prepared and studied in this group, and their mesomorphic
* Corresponding author. E-mail address: cklai@cc.ncu.edu.tw (C.K. Lai).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.11.014

C.-J. Chen et al. / Tetrahedron 67 (2011) 114e124
115
properties and optical properties investigated. All these related
benzoxazoles formed SmC, SmA and/or N phases, as expected for
rod-like molecules.
H2m+1CmO
OCnH2n+1
OCnH2n+1
N
O
Y
N
N
X
O
RO
O
N
N
2a-2e; X = H, Y = OH
2f; X = Y = H; m = n = 12
2g; X = OH, Y = H; m = n = 12
X
OCnH2n+1
OCnH2n+1
I
R1O
O
N
O
O
Pb(OAc)4
THF
OR2
H2m+1CmO
X
II; X = H, OH
O
X
OCnH2n+1
OCnH2n+1
N
O
N
N
R1O
O
N
O
O
OR2
X
O
OCnH2n+1
OCnH2n+1
1a-1e; X = H
III; X = H, OH
Scheme 1. The structures of mesogenic benzoxazoles I, II, and III.
Scheme 3. The synthetic preparation of compounds 1aee.
Discotic organic molecules, particularly for those molecules with
an extended p-conjugated structure have been extensively studied
both inter- and intra-molecular H-bonds were observed in the
crystal lattice, and two molecules werearrangedaboveand belowby
a head-to-tail style. A more correlated structure was organized by
these H-bonds and a mesophase was then better induced. All com-
pounds 2 have a wider temperature range of columnar phase than
those of compounds 1, which might be due to the existent H-bond in
compounds 2. Also indicated by single crystallographic data, this
type of molecules has a relatively lower symmetry element. Some of
these compounds, with a lower fluidity observed under polarized
optical microscope were considered as room temperature liquid
crystals.
due to their promising materials in optoelectronic devices,7 such as
organic field-effect transistors (OFETs),8 organic light-emitting di-
odes (OLEDs), and photovoltaic cells.9 In liquid crystals, columnar
phases could be generated by typical discotic or round molecules
with at least a total number of six or eight side chains. However,
many other types of non-discotic molecules could also form co-
lumnar phases. These are examples of half-disc, catenar/lathy,10
cone/bowlike and bent/banana-shaped11 molecules. In general,
these compounds were often constructed with a lesser number of
peripheral side chains attached around rigid core. Kinetically stable
columnar phase induced by a single molecule were not easily
approached by these non-discotic molecules due to their shape ef-
fect. On the other hand, lesser side chains are not able to stabilize the
rigid core. Thus tuning the intermolecular interaction or using
complementary shapes between molecules within the columns to
generatebettercorrelated organizationsbecomesatruechallengein
generating such non-classical columnar liquid crystals. Among them
2. Results and discussion
2.1. Synthesis and characterization
The synthetic procedures for final compounds 1 are summarized
in Scheme 4. 1,2-Bis(3,4-dialkoxyphenyl)-1,2-ethanediones 5 were
obtained by the reaction of 1,2-dialkoxy benzenes with oxalyl chlo-
ride in the presence of AlCl3 stirring in carbon disulfide at ice bath
temperature, which were then condensed with 3,4-diaminobenzoic
acid stirring in absolute ethanol to gave 2,3-bis-(3,4-dialkoxyphenyl)
quinoxaline-6-carboxylic acids 4. However, a characteristic broad
covalent H-bond and/or pep stacking interaction are used the most
to induce such correlated mesogens or metallomesogens.
In this work, a new type of non-discotic heterocyclic compounds
1e2 derived from quinoxalines and benzoxales linked with an ester
spacer group was prepared and their mesomorphic properties in-
vestigated. Both compounds 1bed (Scheme 2) and 2beg (Scheme 3)
formed hexagonal columnar phases (Colh), which were character-
ized and identified by DSC and POM and also confirmed by powder
XRD. Single crystallographic data of 2a (n¼4, m¼12) indicated that
peak12 often appeared at
d ∼13.50 assigned for -COOH was not ob-
served for acids 4 due to rapid exchange. This peak in other similar
structures5e was also not observed. Then the reactions of compounds
4 with 4-hydroxybenzaldehyde with DCC and DMAP in refluxing
dried THF/absolute ethanol gave 2,3-bis(3,4-dialkoxyphenyl) qui-
noxaline-6-carboxylic acid 4-formyl phenyl esters 3. The condensa-
tion of compounds 3 and 2-amino-5-alkoxyphenols in refluxing
ethanol led to 2,3-bis(3,4-dialkoxyphenyl) quinoxaline-6-carboxylic
acid 4-[(4-alkoxy-2-hydroxyphenylimino)methyl]phenyl esters 2.
The final compounds 1; 2,3-bis(3,4-dialkoxyphenyl)quinoxaline-6-
carboxylic acid 4-(6-alkoxybenzoxazol-2-yl)phenyl esters were
obtained by the reactions of compounds 2 and lead acetate, Pb(OAc)4
in refluxing THF with a yield ranged from 68 to 73%. 1H and 13C NMR
spectroscopy were used to characterize all intermediates. For in-
H2m+1CmO
O
OCnH2n+1
OCnH2n+1
N
O
N
N
O
1a; n = 4, m = 12
1b; n = 8, m = 12
1c; n = 12, m = 4
1d; n = 12, m = 8
1e; n = 12, m = 12
stance, a characteristic singlet peak occurred at d 8.62e8.64, assigned
OCnH2n+1
OCnH2n+1
for imine-H (eCH]N) of compounds 2 disappeared upon formation
of final products 1. Elemental analysis was used to confirm the purity
of the compounds 1e2.
Scheme 2. The structures of compounds 1aee.

116
C.-J. Chen et al. / Tetrahedron 67 (2011) 114e124
OCnH2n+1
OCnH2n+1
OCnH2n+1
O
OCnH2n+1
OCnH2n+1
O
O
N
H2m+1CmO
b
HO
OCnH2n+1
OCnH2n+1
a
N
4
OH
OCnH2n+1
OCnH2n+1
OCnH2n+1
d
c
5
O
OCnH2n+1
O
H2m+1CmO
H2m+1CmO
N
N
e
O
OCnH2n+1
OCnH2n+1
NH2
NO2
OH
OH
3
OCnH2n+1
f
H2m+1CmO
H2m+1CmO
O
OCnH2n+1
OCnH2n+1
OCnH2n+1
N
O
N
O
OH
N
N
g
N
N
O
OCnH2n+1
OCnH2n+1
O
2a-2e
OCnH2n+1
OCnH2n+1
OCnH2n+1
1a-1e
Scheme 4. Reagents and conditions. (a) Oxalyl chloride (0.5 equiv), AlCl3, stirred in CS2 at 0 ꢀC 24 h; (b) 3.4-diamino benzoic acid (1.0 equiv), AcOH (drops) stirred in EtOH, 12 h; (c)
4-hydroxybenzaldehyde (1.1 equiv), DCC (1.2 equiv), DMAP (1.2 equiv), stirred in dried THF at rt; (d) HNO3 (1.1 equiv), NaNO2 (0.5 equiv), refluxed in CH2Cl2, 24 h; (e) Pd/C
(1.1 equiv), N2H4 (1.1 equiv), refluxed in EtOH, 24 h; (f) refluxed in abs EtOH, 8 h; (g) Pb(OAc)4 (1.2 equiv), refluxed in THF, 2 h.
2.2. Single crystal structure of 2,3-bis(3,4-didodecyloxyphenyl)
quinoxaline-6-carboxylic acid 4-[(4-butoxy2-hydroxy
phenylimino)methyl]phenyl ester 2a (n[4, m[12)
atoms) were coplanar, however, two other benzene rings (C34eC39
and C49eC54 atoms) attached to quinoxaline ring were not co-
planar, each with a dihedral angle of 35ꢀ and 46ꢀ. Four molecules
were paced in a single unit cell.
A single crystal of the nonmesogenic compound 2a suitable for
crystallographic analysis was obtained by slow vaporization from
CH2Cl2 at room temperature and its structure resolved. Fig. 1 shows
its molecular structure with the atomic numbering schemes. Table 1
lists its crystallographic and structural refinement data for the
molecule. It crystallizes in a monoclinic space group P2(1)/c with
a Z¼4. The overall molecular shape of crystal 2awas considered as an
elongated or tapered triangle with quinoxaline ring as its base. The
Unsurprisingly, both intra-molecular and inter-molecular H-
bonds were observed in the crystal lattice. Two molecules lying
above and below plane were arranged in an antiparallel head-to-
tail into a layer structure. An inter-molecular H-bond of H(3A)eN1
ꢀ
with a bond length of 2.284 A was observed, while other H-bond
lengths induced by H(3A)eO(8) and O(3)eH(3A) atoms were
ꢀ
ꢀ
measured as d ∼2.79 A and 2.30 A, respectively (Fig. 2). These inter-
molecular H-bonds have apparently enhanced the molecular in-
teraction between the layers. Also two pep interactions as point to
ꢀ
triangle has a molecular length of ca. ∼39.07 A (C32eC58 atoms) and
ꢀ
a basal length of ca. ∼13.16 A (C43eC60 atoms). Two phenyl rings of
face were observed; one is H7A to central phenyl ring (C2eC7) with
ꢀ
benzylideneamineephenol (defined by C15eC20 and C8eC13
a distance of 2.9932 A and the other one is H8 to phenyl ring with
Fig. 1. An ORTEP plot for compound 2a with the numbering scheme, and the thermal ellipsoids of the non-hydrogen atoms are drawn at the 50% probability level.

C.-J. Chen et al. / Tetrahedron 67 (2011) 114e124
117
Table 1
were formed by such elliptical-shaped molecules. A dimeric
structure induced by inter-molecular H-bond was attributed to the
formation of mesophases in such acid derivatives.
Crystallographic and experimental data for compound 2a
Compd
2a (n¼4, m¼12)
The phase transitions and thermodynamic data for compounds
1e2 are summarized in Table 2. Compounds 2beg formed columnar
phases based on observation under polarized microscope. Under
POM, a typically pseudo focal-conic or more dendritic texture (see
Fig. 3) with linear birefringent defects on slowly cooling from the
isotropic liquids was clearly observed. These observed textures often
accompanied by a large area of homeotropic domain are often char-
acteristic for hexagonal columnar phases. As indicated in Table 1, all
derivatives 2 exhibited enantiotropic columnar phases (Col), inwhich
two typical transitions of crystal-to-columnar and columnar-to-iso-
tropic (Cr/Colh/I) were appeared on DSC thermographs. A few
transition temperatures from Cr/Colh or Colh/Cr phases for com-
pounds 2b, 2d, 2e, and 2g were obtained from POM due to their rel-
ativelysmallerenthalpies. The melting and the isotropic temperatures
were ranged from Tmp¼33.0e50.2 ꢀC and Tcl¼71.6e104.7 ꢀC on
heatingprocess,andthetemperaturerangesofcolumnarphaseswere
Empirical formula
Formula weight
T/K
C62H79N3O8
994.28
150(2)
Monoclinic
P2(1)/c
21.9193(13)
8.3693(4)
30.896(2)
90
97.016(2)
90
5625.4(6)
4
2144
1.174
Crystal system
Space group
ꢀ
a/A
ꢀ
b/A
ꢀ
c/A
ꢀ
ꢀ
a
/
b
/
ꢀ
g
/
3
ꢀ
U/A
Z
F(000)
Dc/Mg mꢁ3
Crystal size/mm3
Range for data collection/0
Reflection collected
Data, restraints, parameters
Independent reflection
Final R1, wR2
0.40ꢂ0.07ꢂ0.03
1.33e25.00
19259
9688/4/62
9688 [R(int)¼0.1336]
0.0818, 0.1484
ranged from
D
Tcol¼31.8e54.9 ꢀC. Compound 2e has a slightly wider
temperature of mesophase, i.e.,
D
Tcol¼54.0>46.0>31.8 ꢀC than those
of compounds 2f and 2g, respectively. The reason for this smaller
range of decreasing mesophase temperatures was uncertain, and it
might be probably attributed to the intermolecular or/and intra-mo-
lecular H-bonded interaction (eOH/O). On the other hand, there
might exist H-bonds in compound 2e and 2g, whereas no such
H-bond was possible in compound 2f.
ꢀ
a distance of 2.669 A. The dihedral angle between above mentioned
phenyl rings was 44.71ꢀ.
The formation of columnar phases was often sensitive to the
side-chain density, i.e., the larger size or the more rigid is the core
group, and more side-chain density is necessarily required. The
overall molecular shape of compounds 2 and 1 is considered as an
elongated triangular shape, therefore, two molecules arranged
side-by-side to adopt an overall correlated disc molecule were then
proposed (see later discussion). Similar mesomorphic behavior for
compounds 1 was also observed. Compound 1a was not mesogenic,
and a higher clearing temperature by 22.1 ꢀC than that of 2a was
2.3. Mesomorphic properties
The mesomorphic behavior of compounds 1e2 was studied and
characterized by differential scanning calorimetry (DSC) and po-
larizing optical microscopy (POM). A series of similar structures
with compounds 4, dibenzophenazine carboxylic acids5e and their
methyl ester analogs have been prepared and studied, and an or-
dered hexagonal phase and an ordered rectangular/nematic phase
Fig. 2. Inter-molecular H-bonds in unit cell.

118
C.-J. Chen et al. / Tetrahedron 67 (2011) 114e124
Table 2
The phase temperatures and enthalpiesa of compounds 1 and 2
64.1 (10.9)
71.1 (17.4)
32.2b
85.1 (1.63)
Cr1
Cr2
2a n = 4, m = 12
I
44.5b
33.9b
2b
2c
2d
Cr
Cr
8
12
4
Colh
I
I
79.7 (1.47)
98.6 (3.98)
51.4 (17.0)
12
12
Colh
Colh
Colh
30.1 (11.3)
95.3 (3.87)
104.7 (3.62)
50.2b
8
Cr
Cr
I
I
38.2b
49.5b
35.1b
101.8 (3.56)
104.4 (3.78)
2e
12
12
101.6 (3.71)
79.3 (1.81)
33.3 (7.15)
Cr
Cr
Colh
Colh
Cr
I
I
I
2f
2g
1a
12
12
4
12
12
12
23.9 (6.49)
39.8b
30.6b
75.4 (1.68)
71.6 (1.75)
62.5 (1.44)
93.2b
64.2b
47.8 (1.62)
46.6b
79.2 (6.63)
I
I
1b
1c
1d
8
12
4
Cr
Cr
Colh
Colh
37.0 (1.11)
45.7b
12
12
37.4b
75.9 (6.58)
83.9 (4.65)
42.1b
8
I
I
Colh
Colh
Cr
Cr
33.9b
45.8b
40.3b
80.4 (4.48)
77.1 (3.89)
1e
12
12
73.6 (3.82)
bObserved by polarized microscope.
a
Cr¼crystal, Colh¼hexagonal columnar, I¼isotropic phase. The temperatures (ꢀC) and enthalpies (kJ/mol) were determined by DSC at a scan rate of 10.0 ꢀC/min.
Fig. 3. Optical textures observed by compounds; 2e at 70.0 ꢀC (top left), 2f at 65 ꢀC (top right), 2g at 50.0 ꢀC (bottom left), and 1d at 75.0 ꢀC (bottom right).

C.-J. Chen et al. / Tetrahedron 67 (2011) 114e124
119
obtained. All other compounds 1bee have lower melting and
clearing temperatures than those of compounds 2bee. The tem-
perature range of mesophase for 1bee was narrower than those of
2bee. Similar optical textures for 2 were also characterized under
POM, and the mesophases were identified as columnar phases.
(a2dꢁa1d), which might be due to a less interdigitation of alkoxy
chains in compounds 1. A few XRD diffractions of compounds 2f, 2g,
and 1b were shown in Fig. 4. The XRD data were also consistent
with single crystallographic analysis. The molecular length was
ꢀ
measured as ca. 39.07 A, which was quite close to the d-spacing of
ꢀ
ꢀ
38.08 A and 36.10 A obtained by powder XRD diffraction experi-
ment for compound 2b and 1b, respectively. Therefore, alkoxy side
2.4. Variable-temperature powder XRD data
Variable-temperature powder XRD diffraction experiments
were conducted to confirm the structure of the mesophases of
compounds 1e2. A summary of the diffraction peaks and lattice
constants for compounds 1e2 is listed in Table 3. For derivatives
2beg, a typical diffraction pattern of a two-dimensional hexagonal
lattice with one very strong diffraction peak at lower angle and two
much weaker diffraction peaks was all observed. These are the
characteristic of hexagonal columnar phases with a d-spacing ratio
of 1, (1/3)1/2, and (1/4)1/2, corresponding to Miller indices; 100, 110,
and 200, respectively. For example, a diffraction pattern at 90 ꢀC
ꢀ
ꢀ
ꢀ
with a d-spacing at 35.66 A, 20.62 A, 17.84 A and a broad diffuse
ꢀ
peak (4.61 A) at wide-angle region was observed for compound 2e
and this diffraction pattern corresponded to a hexagonal columnar
arrangement (see Fig. 5a). This diffraction pattern corresponds to
an intercolumnar distance or lattice constant (i.e., a parameter of
ꢀ
the hexagonal lattice) of 41.18 A. On the other hand, a lattice con-
ꢀ
stant of 38.08e41.10 A for mesogenic 2bee were all close to the
ꢀ
molecular length (ca. disc diameter) ∼38.01 A of nonmesogenic 2a.
The lack of any relatively peaks at wide angles excluded a more
regular periodicity along the columns. However, liquid-like corre-
lations between the rigid cores occurred at wide angle regions of
ꢀ
4.43e4.61 A. The hexagonal lattices were correlated quite well with
increasing side-chain alkoxy carbon lengths.
Unsurprisingly, all compounds 1b, 1d, and 1e gave similar XRD
diffraction patters as compounds 2b, 2d, and 2f due to their similar
structures. The lattice constants of compounds 1 were slightly
ꢀ
ꢀ
smaller than that of compounds 2 by ca. 1.58 A (a2e, ꢁa1e)ꢁ3.01 A
Table 3
Variable-temperature XRD diffraction data for compounds 1e2
ꢀ
ꢀ
Compd Mesophase/temp Lattice const./A d-Spacing/A obs Miller indices
2b
2d
2e
2f
Colh (70 ꢀC)
Colh (90 ꢀC)
Colh (90 ꢀC)
Colh (65 ꢀC)
Colh (41 ꢀC)
Colh (70 ꢀC)
Colh (76 ꢀC)
Colh (68 ꢀC)
a¼38.08
a¼41.20
a¼41.18
a¼42.45
a¼36.10
a¼36.49
a¼38.19
a¼39.60
32.98 (32.98)
19.17 (19.04)
16.68 (16.50)
4.55 (br)
35.68 (35.68)
20.56 (20.60)
17.75 (17.84)
4.60 (br)
35.66 (35.66)
20.62 (20.59)
17.84 (17.83)
4.61 (br)
36.76 (36.76)
21.17 (21.22)
18.35 (18.38)
4.47 (br)
31.26 (31.26)
18.15 (18.05)
15.71 (15.63)
4.48 (br)
31.60 (32.42)
18.30 (18.24)
15.88 (15.80)
4.53 (br)
33.07 (33.07)
18.98 (19.09)
16.50 (16.53)
4.58 (br)
34.29 (34.29)
17.19 (17.15)
4.57 (br)
100
110
200
halo
100
110
200
halo
100
110
200
halo
100
110
200
halo
100
110
200
halo
100
110
200
halo
100
110
200
halo
100
110
halo
1b
1c
1d
1e
Fig. 4. The powder X-ray diffraction plots of compound 2e at 90 ꢀC (top), 2f at 65.0 ꢀC,
and 1b at 41.0 ꢀC (bottom).

120
C.-J. Chen et al. / Tetrahedron 67 (2011) 114e124
ꢀ
chains were probably not or slightly interdigitated both in the
crystal phase and the mesophase when lower carbon considered.
16.98 A, respectively. These two Rar values were approximately half
ꢀ
of the 38.01 A as molecular length of 2a. On the other hand, an av-
erage number of 4e5 molecules for 1b and 2b were packed within
ꢀ
a height of 9.0 A in the columnar phases. A distance ranged ca.
2.5. Packing study of compounds 2b and 1b in hexagonal
columnar phases
ꢀ
3.2e3.5 A between the molecules within a column was often ob-
served in columnar phases. However, compounds 1b and 2b were
not perfectly round molecules, but triangular-shaped molecules.
Therefore, a more disc-like correlated structure constructed by two
molecules lying roughly side-by-side was then generated within the
column. The possible molecular arrangement in columnar phases
was then proposed in Fig. 5.
A simple model10a,13 often used to calculate the number of mol-
ecules within a portion of height h has been developed, and this
model has been able to correlate the possible molecular arrange-
ment in columnar phases. In order to get more insight the molecular
organizations in columnar phases, two important parameters, Ncel
Fig. 5. A schematic representation of molecular organization in columnar phase for compounds 2b and 1b. Two tapered-shaped molecules lying side-by-side to generate a more
disc correlated molecule was packed within a column. In a typical calculation10a,13a a value of 9.0 A (2h¼9.0 A) has been assumed for most discotic molecules corresponding to the
ꢀ
ꢀ
board signal seen in the XRD diffraction patterns.
and Rar were calculated from XRD diffraction data combined with
single crystallographic data for compounds 2b and 1b. In this ap-
proach, a columnar structure is often considered to be constructed
by columnar cross section (Scol) and the stacking periodicity along
2.6. Optical properties
The UVevis absorption and PL spectra of the compounds 1e4
measured in CHCl3 solution at room temperature are presented in
Fig. 6. The lmax peaks of UVevis absorption and PL spectra were
listed in Table 4. The absorption lmax peaks occurred at ca.
the columns (h, portion of height), according toVcell¼hScol¼NcellVmol
.
Vcell is the volume of the repeat unit (per cell), and Vmol is the mo-
lecular volume of one molecule. Ncell is the number of molecules
within a column. Scol can be calculated from lattice parameters of X-
ray diffraction. In addition, Vmol is composed by two components,
the rigid part Var and the flexible chains, Vch by the equation,
Vmol¼VarþVch. Another parameter to be considered is Rar, defined as
the diameter of the aromatic or hard columnar part, which can be
379e397 nm, which were attributed to a
pep transition arising
*
from quinoxalines. For compounds 1e there appeared a strong ab-
sorption peak occurred at ∼316 nm, which was attributed to ben-
zoxazole ring. The lmax peaks of UVevis absorption and PL spectra of
benzoxazole derivatives often occurred at 313e319 nm and
348e381 nm.6 Whereas, the conjugation linked by two heterocyclic
rings of quinoxaline and benzoxazole was interrupted by the con-
necting ester spacer. The PL spectra of all compounds showed one
intense peak occurred at lmax¼522e525 nm, and this photo-
luminescent emission originated from heterocyclic quinoxaline.
calculated by Rar¼(4Sar/
p)
1/2. By use of the theory approach, the Ncell
and Rar parameter for two similar compounds 2b and 1b were
ꢀ
ꢀ
ꢀ
obtained. An Ncell for compound 1b at 70 C and 2b at 41 C is 4.74 A
ꢀ
ꢀ
and 4.34 A, whereas a Rar for compound 1b and 2b is 17.77 A and

C.-J. Chen et al. / Tetrahedron 67 (2011) 114e124
121
Incorporation of a benzoxazole moiety to the quinoxaline would not
hexagonal columnar phases, identified by DSC, POM, and XRD. Pack-
ing studies indicated that two molecules lay side-by-side to generate
a more disc-like correlated structure in the columnar phases. These
materials are potentially excellent candidates for electronic devices.
shift their lmax. An apparent red shift was often observed when an
electron-donating group1a
, such as triphenylamine was in-
corporated. A relatively lower quantum yield ranged in 0.16e0.26 is
obtained and the lower yields might be due to the effect of the lone
pair on the nitrogen atom. The PL data of compounds 1e and 2e
measured as a thin film at room temperature were also performed.
The lmax for compound 1e and 2e are 522 and 524 nm, which were
slightly blue-shifted by 20 nm and 19 nm, respectively (Table 4).
4. Experimental section
4.1. General
All chemicals and solvents were reagent grade from Aldrich
Chemical Co., and all solvents were dried by standard techniques.1H
and 13C NMR spectra were measured on a Bruker DRS-200. DSC
thermographs were carried out on a Mettler DSC 822 and calibrated
with a pure indium sample. All phase transitions are determined by
a scan rate of 10.0 ꢀC/min. Optical polarized microscopy was carried
out on Zeiss Axioplan 2 equipped with a hot stage system of Mettler
FP90/FP82HT. The UVevis absorption and fluorescence spectrawere
obtained using a Jasco V-530 and Hitachi F-4500 spectrometer. All
spectra were measured in CHCl3 at room temperature, and the ex-
citation wavelength of the fluorescent spectra was 397 nm. Ele-
mental analyses were performed on a Heraeus CHNeOeRapid
elemental analyzer, and their mass spectra were also measured. The
powderdiffractiondatawerecollected fromtheWiggler-A beamline
of the National Synchrotron Radiation Research Center (NSRRC)
4
0.4
0.3
0.2
0.1
0.0
3
2e
2f
2g
1e
ꢀ
with the wavelength of 1.3263 A. Diffraction patterns were recorded
in
q
/2
q
geometry with step scans normally 0.02ꢀ in 2
q
¼1∼10ꢀ
250
300
350
400
450
500
stepꢁ1 sꢁ1 and 0.05ꢀ in 2
q
¼10e5ꢀ stepꢁ1 sꢁ1 and a gas flow heater
wavelength
was used to control the temperature. The powder samples were
charged in Lindemann capillary tubes from Charles Supper Co. with
an inner diameter of 1.0 mm. The compounds of 1,2-dialkoxy ben-
zenes, 3-alkoxyphenols, 4-alkoxy-2-nitrophenols, and 4-alkoxy-3-
aminophenols were followed by literatures’ procedures.6
180
160
140
120
100
80
4
3
1a
1b
1c
1d
1e
2e
4.1.1. 3-Dodeclyoxyphenol (n¼12). White solid; yield 42%. 1H NMR
(CDCl3): 0.86 (t, J¼6.7 Hz, eCH3, 3H), 1.17e1.45 (m, eCH2, 18H),
1.67e1.81 (m, eCH2, 2H), 3.90 (t, J¼6.6 Hz, eOCH2, 2H), 6.36e6.39
(d, J¼6.6 Hz, eArH, 2H), 6.49 (s, eArH, 1H), 7.10 (t, J¼8.4 Hz, eArH,
1H). 13C NMR (CDCl3): 14.09, 22.66, 29.20, 29.37, 29.58, 29.61, 29.64,
31.90, 68.06, 102.05, 107.03, 107.58, 130.04, 156.69, 160.47.
60
40
4.1.2. 5-Dodecyloxy-2-nitrophenol (m¼12). Yellow solid; yield 42%.
1H NMR (CDCl3): 0.86 (t, J¼6.7 Hz, eCH3, 3H), 1.24e1.38 (m, eCH2,
18H), 1.74e1.82 (m, eCH2, 2H), 3.99 (t, J¼6.4 Hz, eOCH2, 2H),
6.45e6.48 (d, J¼6.7 Hz, eArH, 2H), 8.00 (s, eArH,1H), 11.03 (s, eOH,
1H). 13C NMR (CDCl3): 14.10, 22.66, 28.81, 29.25, 29.26, 29.32, 29.49,
29.54, 29.6, 31.90, 69.12,101.76,109.82,126.89,127.51,157.98,166.72.
20
0
400
450
500
550
600
650
700
wavelength
Fig. 6. Absorption (top) and fluorescent spectra (bottom) of the compounds 1e4.
4.1.3. 2-Amino-5-dodecyloxyphenol (m¼12). White solid; yield
86%. 1H NMR (CDCl3): 0.86 (t, J¼6.7 Hz, eCH3, 3H), 1.24e1.38 (m,
eCH2, 18H), 1.67e1.71 (m, eOCH2, 2H), 3.84 (t, J¼6.5 Hz, eOCH2,
2H), 6.42e6.45 (d, J¼7.6 Hz, eArH, 2H), 6.74 (s, eArH, 1H), 11.03(s,
eOH, 1H). 13C NMR (CDCl3): 14.10, 23.12, 28.81, 29.25, 29.26, 29.32,
29.5, 29.49, 29.61, 31.91, 72.28, 102.17, 107.60, 117.23, 125.64, 144.53,
162.17.
Table 4
Absorption and emission dataa of compounds 1e4
Compds
Absorption lmax (nm)
Emission lmax (nm)
Ff
4 (n¼12)
395
397
379
397
397
397
397
397
522
525
0.26
0.22
0.16
0.24
0.26
0.26
0.26
0.26
3 (n¼12)
2e
1a
1b
1c
1d
1e
524 (505)b
522
4.1.4. 4-Dodecyloxy-nitrobenzene. 1H NMR (CDCl3): 0.85 (t, eCH3,
3H), 1.25e1.79 (m, eCH2, 20H), 4.01 (t, eOCH2, 2H), 6.89 (d,
J¼8.0 Hz, eArH, 2H), 8.13 (d, J¼8.0 Hz, eArH, 2H). 13C NMR (CDCl3):
14.11, 22.69, 25.91, 28.98, 29.32, 29.35, 29.54, 29.58, 29.64, 29.65,
31.92, 68.91, 114.39, 125.87, 141.29, 164.27.
522
522
522
522 (502)b
a
Measured in CHCl3 at rt.
Measured as a thin film at rt.
b
4.1.5. 1,2-Bis(3,4-didodecyloxyhenyl)-1,2-ethanedione (5, m¼12).
The solution of 1, 2-didodecyloxybenzene (3.2 g, 7.18 mmol) dis-
solved in 30 mL carbon disulfide was added aluminum chloride
(1.01 g, 7.53 mmol) under nitrogen atmosphere. The solution was
vigorously stirred for a minute and the oxalyl chloride (0.35 mL,
3. Conclusions
A series of quinoxaline-based derivatives 1 and 2 were prepared,
and theirmesomorphicand opticalproperties studied.Theyexhibited

122
C.-J. Chen et al. / Tetrahedron 67 (2011) 114e124
3.95 mmol) dissolved in 20 mL of carbon disulfide was dropwise
added at ice bath temperature. The solution was stirred for 8 h. The
solution was concentrated under reduced pressure, and the residue
was extracted with H2O/CH2Cl2 (5/1). The organic layers were
collected and dried over MgSO4. The product isolated as milky
white solids was obtained after recrystallization from CH2Cl2/
150.42, 154.47, 155.34, 157.45, 163.18, 163.48, 195.44. IR (neat): 2954
(CeH), 2920 (CeH), 2871 (CeH), 2850 (CeH),1744 (C]O),1659 (C]
O), 1621(C]N), 1600 (C]N), 1583 (C]N).
4.1.9. 2,3-Bis(3,4-didodecyloxyphenyl)quinoxaline-6-carboxylic acid
4-[(4-dodecyloxy-2-hydroxyphenylimino)methyl]phenyl ester 2e.
The mixture of 2,3-bis-(3,4-didodecyloxyphenyl)quinoxaline-6-
carboxylic acid 4-formyl phenyl ester (0.30 g, 0.26 mmol) and 2-
amino-5-dodecyloxyphenol (0.08 g, 0.28 mmol) was refluxed in
20 mL of absolute ethanol for 3 h. The solution was cooled and the
yellow solids were collected. The products isolated as bright yellow
solids were obtained after recrystallization from THF. Yield 89%. 1H
CH3OH. Yield 82%. 1H NMR (CDCl3):
1.24e1.83 (m, eCH2, 80H), 4.03 (t, CH2, 8H), 6.85 (d, eArH, 2H), 7.39
(d, eArH, 2H), 7.55 (s, eArH, 1H). 13C NMR (CDCl3):
14.06, 22.64,
d 0.87 (m, eCH3, 12H),
d
25.87, 25.94, 28.87, 29.04, 29.28, 29.30, 31.72, 31.85, 53.37, 69.06,
69.18, 111.58, 112.28, 126.05, 126.16, 149.25, 154.94, 193.73.
4.1.6. 2,3-Bis-(3,4-didodecyloxyphenyl)quinoxaline-6-carboxylic acid
(4, m¼12). The solution of 1,2-bis(3,4-didodecyloxyphenyl)-1,2-
ethanedione (3.0 g, 3.17 mmol) was dissolved in 30 mL of absolute
ethanol and 50 mL of dried THF under nitrogen atmosphere. The
solution was added 0.5 mL of glacial acetic acid and 3,4-dia-
minobenzoic acid (0.579 g, 3.80 mmol), and then refluxed for 12 h.
The solution was concentrated to give a brown solid, which was
purified by column chromatography using hexane/ethyl acetate (1/
1) as eluent. The product isolated as light yellow solids was
obtained after recrystallization from acetone. Yield 90%. 1H NMR
NMR (CDCl3): d 0.84e0.88 (m, eCH3, 15H), 1.25e1.82 (m, eCH2,
100H), 3.81e3.83 (m, eOCH2, 4H), 3.93e4.00 (m, eOCH2, 6H), 6.46
(dd, J¼2.8 , 8.7 Hz, eArH, 1H), 6.57 (d, J¼2.6 Hz, eArH, 1H), 6.83 (d,
J¼8.2 Hz, eArH, 2H), 7.09e7.15 (m, eArH, 4H), 7.29 (d, J¼8.9 Hz,
eArH, 1H), 7.40 (d, J¼8.6, eArH, 2H), 7.97 (d, J¼8.6, eArH, 2H), 8.21
(d, J¼8.7 Hz, eArH, 1H), 8.42 (dd, J¼1.8 , 8.7 Hz, eArH, 1H), 8.65
(s, eCHN, 1H), 9.03 (d, J¼1.6 Hz, eArH, 1H). 13C NMR (CDCl3):
d
14.09, 22.68, 26.02, 29.14, 29.20, 29.34, 29.38, 29.42, 29.45, 29.57,
29.59, 29.64, 29.66, 29.69, 29.74, 31.92, 68.29, 69.17, 69.22, 100.52,
107.19, 113.04, 113.08, 115.20, 115.28, 116.20, 122.11, 122.90, 123.09,
128.24, 129.20, 129.51, 129.58, 129.72, 131.12, 131.18, 132.60, 134.16,
140.12,143.40, 148.75, 150.25,150.43,152.22,152.98,153.85,154.43,
160.42, 164.21. IR (neat): 3445 (OeH), 2953 (CeH), 2921 (CeH),
2869 (CeH), 2851 (CeH), 1735 (C]O), 1624 (C]N), 1601 (C]N),
1582 (C]N). Anal. Calcd for C94H143N3O8: C, 78.23; H, 9.99. Found:
C, 78.13; H, 10.06. MS (FAB, m/z): 1444.0 (Mþ).
(CDCl3):
d 0.83e0.89 (m, eCH3, 12H), 1.24e1.84 (m, eCH2, 80H),
3.82 (t, J¼4.6 Hz, eOCH2, 4H), 3.99 (t, J¼6.5 Hz, eOCH2, 4H), 6.83 (d,
J¼8.3 Hz, eArH, 2H), 7.10e7.16(m, eArH, 4H), 8.17 (d, J¼8.7 Hz,
eArH, 1H), 8.34 (dd, J¼1.6, 8.8 Hz, eArH, 1H), 8.94 (d, J¼1.5 Hz,
eArH, 1H). 13C NMR (CDCl3):
d 14.09, 22.67, 26.01, 29.12, 29.19,
29.37, 29.42, 29.66, 31.92, 69.17, 113.04, 115.24, 122.26, 130.00,
131.11, 131.17, 132.64, 148.73, 150.17, 150.33, 154.29, 155.11, 170.99. IR
(neat): 2953 (CeH), 2924 (CeH), 2870 (CeH), 2854 (CeH), 2572
(OeH), 1688 (C]O), 1599 (C]N), 1582 (C]N).
4.1.10. 2,3-Bis(3,4-didodecyloxyphenyl)quinoxaline-6-carboxylic acid
4-[(4-butoxy-2-hydroxy phenylimino)methyl]phenyl ester 2a. 1H
NMR (CDCl3):
d 0.86e1.00 (m, eCH3, 15H), 1.25e1.81 (m, eCH2,
4.1.7. 2,3-Bis-(3,4-didodecyloxyphenyl)quinoxaline-6-carboxylic acid
4-formyl phenyl ester (3, m¼12). Under nitrogen atmosphere the
mixture of 2,3-bis-(3,4-bis-didodecyloxyphenyl)-quinoxaline-6-
carboxylic acid 4 (2.50 g, 2.39 mmol) and 4-hydroxybenzoaldyhide
(0.35 g, 2.87 mmol) dissolved in 50 mL of CHCl3 was added 4-
dimethylaminopyridine (0.38 g, 3.10 mmol) at ice bath tempera-
ture. The solution was stirred for 30 min. The ice bath was removed
and the solution was slowly added N,N0-dicyclohexylcarbodiimide
(0.64 g, 3.10 mmol). The solution was stirred for 12 h at room
temperature. The solids were filtered off, and the solution was
concentrated as light brown solids. The product isolated as yellow
was obtained after recrystallization twice from acetone. Yield 71%.
36H), 3.83 (t, J¼6.6 Hz, eOCH2, 4H), 3.91e4.04 (m, eOCH2, 6H), 6.46
(d, J¼2.6 , 8.8 Hz, eArH, 1H), 6.56 (d, J¼2.6 Hz, eArH, 1H), 6.84 (d,
J¼8.4 Hz, eArH, 2H), 7.09e7.18 (m, eArH, 4H), 7.29 (d, J¼9.0 Hz,
eArH, 1H), 7.40 (d, J¼8.6 Hz, eArH, 2H), 7.96 (d, J¼8.6 Hz, eArH,
2H), 8.21 (d, J¼8.8 Hz, eArH, 1H), 8.43 (dd, J¼1.9 , 8.8 Hz, eArH, 1H),
8.64 (s, eCHN, 1H), 9.03 (d, J¼1.6 Hz, eArH, 1H). 13C NMR (CDCl3):
d
13.78, 13.85, 14.11, 19.15, 19.19, 22.67, 26.00, 29.18, 29.33, 29.37,
29.58, 29.62, 31.07, 31.18, 31.90, 68.27, 68.78, 68.83, 100.48, 107.17,
112.98, 115.20, 116.20, 122.10, 123.05, 128.22, 129.50, 129.58, 129.70,
131.07, 131.14, 132.58, 134.13, 140.10, 143.37, 148.70, 150.21, 150.39,
152.20, 152.95, 153.83, 154.40, 155.23, 160.39,164.20. Anal. Calcd for
C62H79N3O8: C, 74.89; H, 8.01. Found: C, 74.78; H, 8.11. MS (FAB, m/
z): 995.6 (Mþ).
1H NMR (CDCl3):
d 0.82e0.88 (m, eCH3, 12H), 1.25e1.82 (m, eCH2,
80H), 3.82 (t, J¼6.2 Hz, eOCH2, 4H), 3.99 (t, J¼6.4 Hz, eOCH2, 4H),
6.83 (d, J¼8.3 Hz, eArH, 2H), 7.10e7.18 (m, eArH, 4H), 7.48(d,
J¼8.5 Hz, eArH, 2H), 8.00 (d, J¼8.6 Hz, eArH, 2H), 8.21(d, J¼8.8 Hz,
eArH, 1H), 8.41 (dd, J¼1.9 , 8.8 Hz, eArH, 1H), 9.02 (d, J¼1.8 Hz,
4.1.11. 2,3-Bis(3,4-didodecyloxyphenyl)quinoxaline-6-carboxylic acid
4-[(4-butoxy-2-hydroxy phenylimino)methyl]phenyl ester 2b. 1H
NMR (CDCl3):
d 0.83e0.89 (m, eCH3, 15H), 1.25e1.85 (m, eCH2,
eArH, 1H), 10.03 (s, eCHO, 1H). 13C NMR (CDCl3):
d
14.14, 22.71,
36H), 3.83 (t, J¼6.7 Hz, eOCH2, 4H), 3.91e4.03 (m, eOCH2, 6H), 6.46
(dd, J¼2.7 , 8.8 Hz, eArH, 1H), 6.56 (d, J¼2.6 Hz, eArH, 1H), 6.83 (d,
J¼8.2 Hz, eArH, 2H), 7.10e7.18 (m, eArH, 4H), 7.29 (d, J¼9.0 Hz,
eArH, 1H), 7.40 (d, J¼8.6 Hz, eArH, 2H), 7.97 (d, J¼8.7 Hz, eArH,
2H), 8.21 (d, J¼8.7 Hz, eArH, 1H), 8.43 (dd, J¼1.9 , 8.8 Hz, eArH, 1H),
8.64 (s, eCHN, 1H), 9.03 (d, J¼1.8 Hz, eArH, 1H). 13C NMR (CDCl3):
26.44, 29.13, 29.21, 29.41, 29.70, 31.95, 69.16, 112.92, 115.19, 122.43,
122.88, 123.09, 129.12, 129.30, 129.60, 131.02, 131.10, 131.32, 132.32,
134.17, 140.07, 143.47, 148.69, 150.25, 150.43, 154.51, 155.36, 155.57,
163.83, 190.84. IR (neat): 2955 (CeH), 2920 (CeH), 2870 (CeH),
2850 (CeH), 1740 (C]O), 1700 (C]O), 1598 (C]N), 1581 (C]N).
d
14.08, 22.67, 25.99, 29.11, 29.17, 29.26, 29.34, 29.57, 29.61, 31.81,
4.1.8. 2,3-Bis-(3,4-didodecyloxyphenyl)quinoxaline-6-carboxylic acid
31.89, 68.25, 69.17, 100.49, 107.15, 112.96, 115.13, 116.19, 122.08,
122.89, 123.07, 128.20, 129.56, 129.68, 131.08, 131.14, 132.58, 134.12,
140.08, 143.37, 148.71, 150.21, 150.38, 152.18, 152.94, 153.83, 154.41,
155.23, 160.38, 164.17. Anal. Calcd for C78H111N3O8: C, 76.87; H, 9.18.
Found: C, 76.89; H, 9.26. MS (FAB, m/z): 1219.9 (Mþ).
4-formyl-3-hydroxy phenyl ester. 1H NMR (CDCl3):
d 0.82e0.88 (m,
eCH3,12H),1.25e1.85 (m, eCH2, 80H), 3.82 (t, J¼6.4 Hz, eOCH2, 4H),
3.99 (t, J¼6.4 Hz, eOCH2, 4H), 6.83 (d, J¼8.4 Hz, eArH, 2H), 6.96e7.01
(m, eArH, 2H), 7.09e7.18 (m, eArH, 4H), 7.64 (d, J¼8.0, eArH, 1H),
8.20 (d, J¼8.8 Hz, eArH, 1H), 8.39 (dd, J¼2.0, 8.8 Hz, eArH, 1H), 8.99
(d, J¼1.8 Hz,eArH,1H), 9.90(s, eCHO,1H),11.27(s, eOH,1H).13CNMR
4.1.12. 2,3-Bis(3,4-didodecyloxyphenyl)quinoxaline-6-carboxylic acid
(CDCl3):
d
14.07, 22.65, 25.99, 29.10, 29.16, 29.35, 29.39, 29.66, 31.89,
4-[(4-butoxy-2-hydroxy phenylimino)methyl]phenyl ester 2c. 1H
69.16, 110.75, 112.99, 113.84, 115.21, 118.78,122.86, 123.06, 129.09,
129.18, 129.58, 130.99, 131.09, 132.70, 136.01, 140.02, 148.69, 150.23,
NMR (CDCl3):
d 0.83e1.00 (m, eCH3, 15H), 1.25e1.82 (m, eCH2,
84H), 3.82 (t, J¼6.6 Hz, eOCH2, 4H), 3.92e4.02 (m, eOCH2, 6H),

C.-J. Chen et al. / Tetrahedron 67 (2011) 114e124
123
6.46(d, J¼2.6 , 8.8 Hz, eArH, 1H), 6.57 (d, J¼2.6 Hz, eArH, 1H), 6.83
(d, J¼8.3 Hz, eArH, 2H), 7.10e7.18 (m, eArH, 4H), 7.29 (d, J¼8.9 Hz,
eArH, 1H), 7.40 (d, J¼8.6 Hz, eArH, 2H), 7.97 (d, J¼8.6 Hz, eArH,
2H), 8.21 (d, J¼8.7 Hz, eArH, 1H), 8.43 (dd, J¼1.8 , 8.8 Hz, eArH, 1H),
8.64 (s, eCHN, 1H), 9.03 (d, J¼1.7 Hz, eArH, 1H). 13C NMR (CDCl3):
acid 4-[(4-dodecyloxy-2-hydroxyphenylimino)methyl]phenyl ester
(0.30 g, 0.21 mmol) dissolved in 10 mL of CHCl3 was added Pb
(OAc)4 (0.11 g, 0.25 mmol) under nitrogen atmosphere. The solu-
tion was gently refluxed for 2 h. The solution was extracted twice
with 100 mL of CH2Cl2/H2O (1/4) each, and the organic layers were
combined and dried over MgSO4. The solution was concentrated to
give light brown solids. The product isolated as light yellow solids
was obtained after recrystallization from acetone. Yield 75%. 1H
d
13.81, 14.08, 19.21, 22.66, 26.00, 29.11, 29.19, 29.36, 29.41, 29.67,
31.22, 31.91, 67.92, 69.18, 100.49, 107.14, 113.00, 115.18, 116.19,
122.08, 122.88, 123.06, 128.22, 129.19, 129.56, 129.69, 131.09, 131.16,
132.58, 134.12, 140.09, 143.37, 148.72, 150.22, 150.40, 152.19, 152.95,
153.83, 154.40, 155.23, 160.38, 164.17. Anal. Calcd for C86H127NO8: C,
77.61; H, 9.62. Found: C, 77.40; H, 9.33. MS (FAB, m/z): 1331.9 (Mþ).
NMR (CDCl3):
d 0.85e0.88 (m, eCH3, 15H), 1.25e1.84 (m, eCH2,
100H), 3.81e3.84 (m, eOCH2, 4H), 3.98e4.02 (m, eOCH2, 6H), 6.83
(d, J¼8.3 Hz, eArH, 2H), 6.95 (dd, J¼2.3 , 8.8 Hz, eArH, 1H),
7.09e7.17 (m, eArH, 5H), 7.45 (d, J¼8.5 Hz, eArH, 2H), 7.62 (d,
J¼8.7 Hz, eArH, 1H), 8.21 (d, J¼8.7 Hz, eArH, 1H), 8.29 (d, J¼8.5 Hz,
eArH, 2H), 8.41 (dd, J¼1.9 , 8.8 Hz, eArH, 1H), 9.02 (d, J¼1.4 Hz,
4.1.13. 2,3-Bis(3,4-didodecyloxyphenyl)quinoxaline-6-carboxylic acid
4-[(4-octloxy-2-hydroxy phenylimino)methyl]phenyl ester 2d. 1H
NMR (CDCl3):
d
0.83e0.88 (m, eCH3, 15H), 1.25e1.82 (m, eCH2,
eArH, 1H). 13C NMR (CDCl3):
d 14.09, 22.68, 26.02, 26.04, 29.14,
92H), 3.82 (t, J¼6.2 Hz, eOCH2, 4H), 3.91e4.03 (m, eOCH2, 6H), 6.46
(d, J¼2.6 , 9.0 Hz, eArH, 1H), 6.57 (d, J¼2.5 Hz, eArH, 1H), 6.83 (d,
J¼8.3 Hz, eArH, 2H), 7.10e7.18 (m, eArH, 4H), 7.29 (d, J¼8.9 Hz,
eArH, 1H), 7.40 (d, J¼8.5 Hz, eArH, 2H), 7.97 (d, J¼8.6 Hz, eArH,
2H), 8.21 (d, J¼8.8, eArH, 1H), 8.40 (dd, J¼1.7 , 8.8 Hz, eArH, 1H),
8.64 (s, eCHN, 1H), 9.03 (d, J¼1.7 Hz, eArH, 1H). 13C NMR (CDCl3):
29.22, 29.36, 29.38, 29.42, 29.45, 29.59, 29.64, 29.66, 29.69, 29.74,
31.92, 68.90, 69.18, 69.23, 96.08, 113.07, 113.10, 113.50, 115.24,
115.32, 119.97, 122.21, 122.91, 123.09, 125.31, 128.61, 129.18, 129.53,
129.65, 131.14, 131.20, 132.64, 140.13, 143.40, 148.77, 148.79, 150.24,
150.41, 151.71, 153.04, 154.43, 155.26, 157.92, 161.37, 164.14. Anal.
Calcd for C94H141N3O8: C, 78.34; H, 9.86. Found: C, 78.12; H, 9.88.
MS (FAB, m/z): 1442.0 (Mþ).
d
14.09, 22.67, 26.02, 29.13, 29.21, 29.36, 29.42, 29.66, 31.80, 31.97,
68.28, 69.20, 100.51, 107.17, 113.05, 115.19, 116.20, 122.10, 122.90,
128.23, 129.20, 129.58, 129.71, 131.11, 131.18, 132.60, 134.14, 140.11,
143.39, 148.76, 150.24, 150.42, 152.21, 152.97, 153.84, 154.42, 155.25,
160.40,164.19. Anal. Calcd for C90H135N3O8: C, 77.93; H, 9.81. Found:
C, 77.79; H, 9.90. MS (FAB, m/z): 1388.0 (Mþ).
4.1.17. 2,3-Bis(3,4-dibutoxyphenyl)quinoxaline-6-carboxylic acid 4-
(6-dodecyloxy benzoxazol-2-yl)phenyl ester 1a. 1H NMR (CDCl3):
d
0.84e1.00 (m, eCH3, 15H), 1.25e1.84 (m, eCH2, 36H), 3.83 (t,
J¼5.6 Hz, eOCH2, 4H), 3.97e4.04 (m, eOCH2, 6H), 6.84 (d, J¼8.4 Hz,
eArH, 2H), 6.94 (dd, J¼2.1 , 8.8 Hz, eArH, 1H), 7.09e7.17 (m, eArH,
5H), 7.45 (d, J¼8.8 Hz, eArH, 2H), 7.62(d, J¼8.7, eArH, 1H), 8.21 (d,
J¼8.8 Hz, eArH, 1H), 8.28 (d, J¼8.8 Hz, eArH, 2H), 8.42 (dd, J¼1.9 ,
8.8 Hz, eArH, 1H), 9.03 (d, J¼1.7 Hz, eArH, 1H). 13C NMR (CDCl3):
4.1.14. 2,3-Bis(3,4-didodecyloxyphenyl)quinoxaline-6-carboxylic acid
4-[(4-dodecyloxyphenyl imino)methyl]phenyl ester 2f. Yellow solids;
yield 80%. 1H NMR (CDCl3):
d 0.85e0.87 (m, eCH3, 15H), 1.25e1.82
(m, eCH2, 100H), 3.81e3.83 (m, eOCH2, 4H), 3.95e4.00 (m, eOCH2,
6H), 6.82 (d, J¼1.5 Hz, eArH, 2H), 6.40 (d, J¼1.5 Hz, eArH, 1H)
7.10e7.14 (m, eArH, 4H), 7.22 (s, eArH, 2H), 7.39 (d, J¼8.5 Hz, eArH,
2H), 7.98 (d, J¼8.5 Hz, eArH, 2H), 8.21 (d, J¼8.7 Hz, eArH, 1H), 8.42
(dd, J¼1.4 , 8.7 Hz, eArH, 1H), 8.49 (s, eCHN, 1H), 9.02 (d, J¼1.5 Hz,
d 13.77, 13.84, 14.09, 19.15, 19.19, 22.66, 26.04, 29.21, 29.32, 29.57,
29.61, 31.08, 31.19, 31.89, 68.80, 68.84, 96.05, 113.01, 113.43, 115.17,
119.95, 122.20, 122.87, 123.05, 125.29, 128.59, 129.52, 129.63, 131.09,
131.15, 132.62, 135.69, 140.11, 143.41, 148.72, 150.23, 150.41, 151.70,
153.00, 154.42, 155.20, 157.90, 161.35, 164.14. Anal. Calcd for
C62H77N3O8: C, 75.04; H, 7.82. Found: C, 75.05; H, 7.94. MS (FAB, m/
z): 993.3 (Mþ).
eArH, 1H). 13C NMR (CDCl3):
d 14.08, 22.67, 26.02, 29.14, 29.21,
29.36, 29.40, 29.42, 29.45, 29.57, 29.59, 29.63, 29.66, 29.68, 29.74,
31.91, 68.30, 69.17, 69.22, 113.07, 115.01, 115.23, 115.31, 121.97,
122.18, 122.90, 123.08, 129.48, 129.80, 131.16, 132.58, 134.44, 140.12,
143.38,144.57,148.75,148.78,150.25,150.42,152.93,154.39,156.79,
158.00, 164.20. IR (neat): 2956 (CeH), 2920 (CeH), 2871 (CeH),
2851 (CeH), 1735 (C]O), 1624 (C]N), 1600 (C]N), 1581 (C]N).
Anal. Calcd for C94H143N3O7: C, 79.1; H, 10.10. Found: C, 79.43; H,
10.11. MS (FAB, m/z): 1427.9 (Mþ).
4.1.18. 2,3-Bis-(3,4-dioctloxyphenyl)quinoxaline-6-carboxylic acid 4-
(6-dodecyloxy benzoxazol-2-yl)phenyl ester 1b. 1H NMR (CDCl3):
d
0.84e0.87 (m, eCH3, 15H), 1.26e1.85 (m, eCH2, 68H), 3.83 (t,
J¼6.3 Hz, eOCH2, 4H), 3.97e4.02 (m, eOCH2, 6H), 6.83 (d,
J¼8.2 Hz, eArH, 2H), 6.94 (dd, J¼2.1 , 8.8 Hz, eArH, 1H) 7.11e7.18
(m, eArH, 5H), 7.45 (d, J¼8.7, eArH, 2H), 7.62 (d, J¼8.7 Hz, eArH,
1H), 8.21(d, J¼8.8, eArH, 1H), 8.28 (d, J¼8.6 Hz, eArH, 2H) 8.42
(dd, J¼1.7 , 8.8 Hz, eArH, 1H), 9.02 (d, J¼1.6 Hz, eArH, 1H). 13C
4.1.15. 2,3-Bis(3,4-didodecyloxyphenyl)quinoxaline-6-carboxylic acid
4-[(4-dodecyloxyphenyl imino)methyl]-3-hydroxyphenyl ester 2g. 1H
NMR (CDCl3): d 14.05, 22.63, 25.97, 29.10, 29.16, 29.23, 29.32
NMR (CDCl3)
d
0.86 (m, eCH3, 15H), 1.25e1.81 (m, eCH2, 100H),
29.35, 29.55, 31.56, 31.78, 31.87, 68.81, 69.14, 95.99, 112.95, 113.43,
115.13, 119.91, 122.16, 122.87, 123.05, 125.23, 128.54, 129.47,129.58,
131.06, 131.12, 132.58, 135.64, 140.06, 143.36, 148.68, 150.20,
150.37, 151.66, 152.99, 154.37, 155.20, 157.86, 161.31, 164.07. Anal.
Calcd for C78H109N3O8: C, 77.00; H, 9.03. Found: C, 77.02; H, 9.31.
MS (FAB, m/z): 1217.8 (Mþ).
3.80e3.84 (m, eOCH2, 4H), 3.97e3.99 (m, eOCH2, 6H), 6.82e6.95
(m, eArH, 6H), 7.10e7.15 (m, eArH, 4H), 7.26(d, J¼8.4 Hz, eArH,
2H), 7.42 (d, J¼8.3 Hz, eArH, 1H), 8.20 (d, J¼8.6 Hz, eArH, 1H), 8.41
(d, J¼8.6 Hz, eArH, 1H), 8.62 (s, eCHN, 1H), 9.00 (s, eArH, 1H). 13C
NMR (CDCl3): d 14.08, 22.67, 29.13, 29.20, 29.37, 29.42, 29.45, 29.56,
29.60, 29.64, 29.66, 29.69, 29.74, 31.91, 68.36, 69.17, 69.21, 110.40,
112.63, 113.06, 113.09, 115.22, 115.29, 117.60, 122.25, 122.90, 123.07,
129.23, 129.45, 129.79, 131.16, 131.21, 132.59, 132.83, 140.12, 140.79,
143.37, 158.75, 148.77, 150.22, 150.40, 154.14, 154.37, 155.20, 158.56,
159.27, 162.50, 164.01. IR (neat): 2955 (CeH), 2919 (CeH), 2870
(CeH), 2851(CeH),1736 (C]O),1617 (C]N),1598 (C]N),1578 (C]
N). Anal. Calcd for C94H143N3O8: C, 78.23; H, 9.99. Found: C, 78.17;
H, 10.10. MS (FAB, m/z): 1444.0 (Mþ).
4.1.19. 2,3-Bis-(3,4-didodecyloxyphenyl)quinoxaline-6-carboxylic
acid 4-(6-butoxy benzoxazol-2-yl)phenyl ester 1c. 1H NMR (CDCl3):
d
0.86e1.02 (m, eCH3, 15H), 1.25e1.85 (m, eCH2, 84H), 3.82 (t,
J¼6.5 Hz, eOCH2, 4H), 3.96e4.05 (m, eOCH2, 6H), 6.83 (d, J¼8.3 Hz,
eArH, 2H), 6.95 (dd, J¼2.3, 8.8 Hz, eArH, 1H), 7.10e7.18 (m, eArH,
5H), 7.45 (d, J¼8.7 Hz, eArH, 2H), 7.62 (d, J¼8.7 Hz, eArH, 1H), 8.21
(d, J¼8.7 Hz, eArH, 1H), 8.29 (d, J¼8.7 Hz, eArH, 2H), 8.41 (dd,
J¼1.8 , 8.8 Hz, eArH, 1H), 9.03 (d, J¼1.6 Hz, eArH, 1H). 13C NMR
4.1.16. 2,3-Bis(3,4-didodecyloxyphenyl)quinoxaline-6-carboxylic acid
4-(6-dodecyloxy benzoxazol-2-yl)phenyl ester 1e. The solution of
2,3-bis-(3,4-bis-didodecyloxyphenyl)-quinoxaline-6-carboxylic
(CDCl3): d 14.09, 22.65, 25.99, 29.10, 29.17, 29.35, 29.39 29.42, 29.64,
31.89, 68.48, 69.10, 95.98, 112.96, 113.43, 115.21, 119.91, 122.16,
122.90, 123.05, 125.31, 128.56, 129.13, 129.58, 131.06, 131.12, 132.58,

124
C.-J. Chen et al. / Tetrahedron 67 (2011) 114e124
3. Velusamy, M.; Huang, J. H.; Hsu, Y. C.; Chou, H. H.; Ho, K. C.; Wu, P. L.; Chang, W.
H.; Lin, J. T.; Chu, C. W. Org. Lett. 2009, 11, 4898e4901.
135.66, 140.06, 143.36, 148.68, 150.20, 150.37, 151.66, 152.97, 154.37,
155.20, 157.66, 161.31, 164.06. Anal. Calcd for C86H125N3O8: C, 77.73;
H, 9.48. Found: C, 77.83; H, 9.70. MS (FAB, m/z): 1329.9 (Mþ).
4. (a) Zhang, K. Y.; Li, S. P. Y.; Zhu, N.; Or, I. W. S.; Cheung, M. S. H.; Lam, Y. W.; Lo,
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Williams, V. E. J. Mater. Chem. 2005, 15, 4062e4068.
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7977e7985; (b) Wang, H. C.; Wang, Y. J.; Hu, H. M.; Lee, G. H.; Lai, C. K. Tet-
rahedron 2008, 64, 4939e4948; (c) Wang, C. S.; Wang, I. W.; Lai, C. K. Tetra-
hedron 2006, 62, 9383e9392; (d) Lai, C. K.; Liu, H. C.; Li, F. J.; Cheng, K. L.; Sheu,
H. S. Liq. Cryst. 2005, 32, 85e94.
4.1.20. 2,3-Bis-(3,4-didodecyloxyphenyl)quinoxaline-6-carboxylic
acid 4-(6-octloxy benzoxazol-2-yl)phenyl ester 1d. 1H NMR (CDCl3):
d
0.86e0.88 (m, eCH3, 15H), 1.25e1.85 (m, eCH2, 92H), 3.82 (t,
J¼6.5 Hz, eOCH2, 4H), 3.96e4.03 (m, eOCH2, 6H), 6.83 (d, J¼8.3 Hz,
eArH, 2H), 6.95 (dd, J¼2.3 , 8.8 Hz, eArH, 1H) 7.10e7.19 (m, eArH,
5H), 7.45 (d, J¼8.7 Hz, eArH, 2H), 7.62 (d, J¼8.8, eArH, 1H), 8.21 (d,
J¼8.8 Hz, eArH, 1H), 8.28 (d, J¼8.7 Hz, eArH, 2H), 8.41 (dd, J¼1.9 ,
8.8 Hz, eArH, 1H), 9.03 (d, J¼1.4 Hz, eArH, 1H). 13C NMR (CDCl3):
d
14.09, 22.67, 26.02, 29.13, 29.22, 29.36, 29.44, 29.67, 31.80, 31.91,
68.88, 69.20, 96.06, 113.03, 113.94, 115.18, 119.95, 122.90, 123.07,
125.29, 128.60, 129.18, 129.63, 131.10, 131.16, 132.63, 135.70, 140.11,
143.40, 148.74, 150.24, 150.41, 151.71, 153.02, 154.43, 155.26, 157.37,
161.37,164.14. Anal. Calcd for C90H133N3O8: C, 78.05; H, 9.68. Found:
C, 78.62; H, 9.79. MS (FAB, m/z): 1386.9 (Mþ).x
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Acknowledgements
9. (a) Leng, S.; Chan, L. H.; Jing, J.; Hu, J.; Moustafa, R. M.; Van Horn, R. M.; Graham, M.
J.; Sun, B.; Zhu, M.; Jeong, K. U.; Kaafarani, B. R.; Zhang, W.; Harrisa, F. W.; Cheng, F.
Z. D. Soft Mater. 2010, 6,100e112; (b) Venkataraman, D.; Yurt, S.; Venkatraman, B.
H.; Gavvalapalli, N. J. Phys. Chem. Lett. 2010, 1, 947e958; (c) Lee, J. Y.; Shin, W. S.;
Haw, J. R.; Moon, D. K. J. Mater. Chem. 2009, 19, 4938e4945; (d) Fischer, M. K. R.;
We thank the National Science Council of Taiwan, ROC (NSC 98-
2113-M-008-003-MY2) in generous support of this work.
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