Synthesis and liquid crystalline behavior of azulene-based liquid crystals with 6-hexadecyl substituents on each azulene ring

Article abstract of DOI:10.1016/j.tet.2010.08.012

Hexakis(6-hexadecyl-2-azulenyl)benzene (1b) has been synthesized by Co ₂(CO)₈-catalyzed cyclotrimerization reaction of bis(6-hexadecyl-2-azulenyl)acetylene (2b). The mesomorphic behaviors of 1b, 2b, and 6-hexadecyl-2-phenylazulene (3

Full text of DOI:10.1016/j.tet.2010.08.012

Tetrahedron 66 (2010) 8304e8312
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and liquid crystalline behavior of azulene-based liquid crystals
with 6-hexadecyl substituents on each azulene ring
,
b
Kosuke Nakagawa a, Takahiro Yokoyama a, Kozo Toyota a, Noboru Morita a, Shunji Ito b , Shota Tahata ,
*
Mao Ueda b, Jun Kawakami b, Miho Yokoyama c, Yoriko Kanai c, Kazuchika Ohta c
a Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
b Graduate School of Science and Technology, Hirosaki University, Hirosaki 036-8561, Japan
c Smart Materials Science and Technology, Department of Bioscience and Textile Technology, Interdisciplinary Graduate School of Science and Technology,
Shinshu University, Ueda 386-8567, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 June 2010
Received in revised form 30 July 2010
Accepted 5 August 2010
Available online 12 August 2010
Hexakis(6-hexadecyl-2-azulenyl)benzene (1b) has been synthesized by Co2(CO)8-catalyzed cyclo-
trimerization reaction of bis(6-hexadecyl-2-azulenyl)acetylene (2b). The mesomorphic behaviors of 1b,
2b, and 6-hexadecyl-2-phenylazulene (3b) were studied by differential scanning calorimetry (DSC),
polarizing optical microscopy (POM), and X-ray diffraction (XRD) techniques and their mesomorphic
properties were compared with those of their 6-octyl derivatives 1a, 2a, and 3a. Increase of the number
of carbon atoms in the peripheral side chains drops the isotropization temperatures of 1b, 2b, and 3b by
56.9 ꢀC, 33 ꢀC, and 23.6 ꢀC, respectively. Additionally, the phase-transition behavior varied with increase
of the number of the peripheral chains, as well as decrease of the crystallineemesophase transition
temperatures, except for compound 3b. As the results, spontaneous monodomain homeotropic molec-
ular alignment was revealed by compound 1b in its Colhd mesophase on non-treated glass substrate,
which would be attracted to the application for the device fabrication of molecular materials.
Ó 2010 Published by Elsevier Ltd.
Keywords:
Discotic liquid crystals
Homeotropic alignment
Azulenes
Cyclotrimerization
1. Introduction
For example, vibrational excitation is applied to the alignment con-
trol of the Colh mesophase for 2,3,6,7,10,11-hexaalkoxytriphenylene
Spontaneous or controllable alignment of molecules on a sub-
strate is an important factor for device fabrication of molecular
materials.1 Disk-like compounds with long alkyl chains have
attracted interest because of their ability to self-assemble to form
columnar mesophases.2 The stacking behavior of the disk-like
compounds as discotic liquid crystals (LCs) provides opportunities
for materials with one-dimensional transport processes, such as
energy migration, electric conductivity, and photoconductivity.3
Some discotic liquid crystalline semiconductors are recently found
to show very fast carrier mobility.4 However, both defects and
polydomain boundaries in the discotic LCs may prevent the charge
carrier transport in the liquid crystalline phase. To obtain better
functional performance requires appropriate large-area-uniformity
for the application to the device fabrication.5 Therefore, controlling
the alignment of discotic mesophases becomes a crucial point for the
molecular design of the discotic liquid crystalline semiconductors.
However, the conventional techniques applied to nematic phase are
not useful for the alignment control of highly ordered columnar LCs.
derivatives to induce homeotropic orientation; i.e., discs flat-on to
the surface or ‘horizontal’.6 However, discotic liquid crystalline ma-
terials have a chance to induce spontaneous homeotropic alignment
without domain boundaries and disclinations by their modification.
Indeed, by introduction of fluoroalkylated chains into the peripheral
parts, triphenylene mesogens lead to get a strong tendency of the
homeotropic alignment.7 Nevertheless, discotic LCs exhibiting
spontaneous homeotropic alignment without domain boundaries
and disclinations are very exceptional.8
Azulene (C10H8) has attracted the interest of many research
groups because of its unusual properties and its beautiful blue
color.9 Amphoteric redox properties of the azulene derivatives are
especially attractive to construct advanced materials for electronic
applications. However, to date, molecules with potentially useful
electronic properties constructed from azulene derivatives are
fairly scarce. Substituted azulene derivatives linked to nemato-
genic alkylcyclohexanes by an ester function have been reported in
the literatures to show nematic or smectic mesomorphisms.10
Recently, we have reported the synthesis of the first azulene de-
rivatives exhibiting discotic liquid crystalline behaviors.11 Novel
hexakis(6-octyl-2-azulenyl)benzene (1a) surrounding six octyl
groups exhibits the columnar mesophases, Colho, with unusually
* Corresponding author. Tel.: þ81 172 39 3568; fax: þ81 172 39 3541; e-mail
address: itsnj@cc.hirosaki-u.ac.jp (S. Ito).
0040-4020/$ e see front matter Ó 2010 Published by Elsevier Ltd.
doi:10.1016/j.tet.2010.08.012

K. Nakagawa et al. / Tetrahedron 66 (2010) 8304e8312
8305
alkyl chains to the hexakis(2-azulenyl)benzene core to increase the
flexibilityof theperipheralside chains, whichinduced a spontaneous
perfect homeotropic alignment without domain boundaries and
disclinationsforthefirsttimeinazulene-basedcolumnarLCs. Herein,
we report the comparative study of the mesomorphic properties of
hexakis(6-hexadecyl-2-azulenyl)benzene (1b), bis(6-hexadecyl-2-
azulenyl)acetylene (2b), and 6-hexadecyl-2-phenylazulene (3b)
with those of their 6-octyl derivatives 1a, 2a, and 3a12 to investigate
the influence of the peripheral side chains in length (Fig. 1).
2. Results and discussion
2.1. Synthesis
Preparation of hexakis(6-hexadecyl-2-azulenyl)benzene (1b)
surrounding bysix hexadecyl groups was accomplished by Co2(CO)8-
catalyzed cyclotrimerization reaction of bis(6-hexadecyl-2-azulenyl)
acetylene (2b), as similar to the synthesis of 1a by the reaction of 6,60-
dioctyl derivative 2a.12 Preparation of 1b via 2b commenced with
diethyl 6-bromo-2-methoxyazulene-1,3-dicarboxylate (4);12,14 it
is outlined in Schemes 1e3. Pd-catalyzed cross-coupling reaction of
4 with 1-hexadecyne under SonogashiraeHagihara conditions
afforded diethyl 6-(1-hexadecynyl)-2-methoxyazulene-1,3-dicar-
boxylate (5) in almost quantitative yield. Catalytic hydrogenation
of 5 utilizing PdeC catalyst produced reduced compound 6 in 94%
yield. After the two ester parts of 6 were hydrolyzed under basic
conditions to give 7, treatment of 7 with 100% H3PO4, which was
freshly prepared by dissolving phosphorous pentaoxide in 85%
phosphoric acid, afforded a mixture of 2-hydroxy and 2-methoxy
derivatives 8 and 9 in 71% and 10% yields, respectively (Scheme 1).
The product 8 was transformed into 2-bromo derivative 10 by
the treatment with PBr3 in 80% yield. The Pd-catalyzed cross-cou-
pling reaction of 10 with trimethylsilylacetylene at 60 ꢀC afforded
6-hexadecynyl-2-(trimethylsilylethynyl)azulene (11) in 89% yield.
Treatment of 11 with potassium fluoride in dimethylformamide
(DMF) furnished 2-ethynyl-6-octylazulene (12) in 95% yield
(Scheme 2).
Since the cross-coupling reaction of 2-ethynylazulene with
2-bromoazulene using Pd(PPh3)4 as a catalyst affords a mixture of
di(2-azulenyl)acetylene and di(2-azulenyl)diacetylene, which may
be produced by the Pd-catalyzed oxidative coupling of 2-ethynyl-
azulene, the halogen exchange reaction of 10 was examined to give
the desired 2-iodo derivative 13. Although the halogen exchange
reaction of 10 with a mixture of copper(I) iodide and potassium
iodide in refluxing DMF should afford the desired 13 in 84% yield,
we encountered with the difficulties in the reproducibility of this
halogen exchange reaction (Scheme 2). The less effectiveness of the
halogen exchange reaction might be attributed to insufficient sol-
ubility of 10 by increase the number of carbon atoms in the alkyl
chain under these reaction conditions.
Figure 1. Azulene-based discotic liquid crystals.
large staking distances (h¼5.20e5.52 Å) owing to the propeller
conformation of the molecule (Fig. 1).12
The large size of the aromatic core of 1a might have advantage for
the preparation of the highly conductive materials, because the size
of the aromatic core of the discogen may set the upper limit on the
carrier mobility.13 However, in general, the ordered functional ma-
terials constructed by large
p-aromatic core would have high vis-
cosity, which may induce domain boundaries in their columnar
mesophases.8 In spite of the large discogen core, compound 1a may
sustain fluidity in the LC mesophases owing to the large staking
distances, which may reduce the interaction of the large p-aromatic
core. Lower viscosity resulting from the sterically hindered aromatic
core might induce the uniform alignment in the columnar meso-
phases. Therefore, we have investigated the introduction of longer
Scheme 1. Preparation of 6-hexadecyl-2-hydroxyazulene (8).

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K. Nakagawa et al. / Tetrahedron 66 (2010) 8304e8312
Scheme 2. Preparation of 2-ethynyl-6-hexadecylazulene (12) and 6-hexadecyl-2-iodoazulene (13).
temperatures and enthalpy changes determined by DSC for 1b, 2b,
and 3b are summarized. X-ray diffraction powder patterns were
also measured with Cu K radiation to distinguish between the
a
solid polymorphs in the compounds. The X-ray diffraction powder
patterns of these compounds are shown in the Supplementary data.
The assignments of X-ray reflections of each of the mesophases are
summarized in Table 2. For the comparison, the phase-transition
Scheme 3. Preparation of hexakis(6-hexadecyl-2-azulenyl)benzene (1b).
However, the cross-coupling reaction of 6-alkyl-2-ethynyl de-
rivative 12 readily proceeded with 2-bromo derivative 10 to give
the expected bis(6-hexadecyl-2-azulenyl)acetylene (2b) in 77%
yield under the ordinary reaction conditions. It is noteworthy that
the cross-coupling reaction proceeds readily utilizing the bromide
10 to give the presumed cross-coupling product in high yield. As
a matter of course, the Pd-catalyzed cross-coupling reaction of 12
with 2-iodo-6-hexadecylazulene (13) also afforded the expected bis
(6-hexadecyl-2-azulenyl)acetylene (2b) in 86% yield. Cyclo-
origomerization of 2b catalyzed by Co2(CO)8 gave the desired
benzene derivative 1b with high solubility in 78% yield, as similar to
that of 6,60-dioctyl derivative 2a (Scheme 3). For comparison of the
phase-transition behavior, 6-hexadecyl-2-phenylazulene (3b) was
also prepared by Pd-catalyzed MiyauraeSuzuki cross-coupling re-
action of 10 with phenylboronic acid in 85% yield (Scheme 4). The
spectral features of compounds 1b, 2b, and 3b are in agreement
with the structure of these compounds as summarized in the
Experimental section.
Table 1
Phase-transition temperature (T) and enthalpy changes (
DH) of compounds 1b, 2b,
and 3ba
TðꢀCÞ
HðkJ molꢁ1
Sample Phase [b]
Þꢂ Phase
½
D
96:7
#
143
1b
2b
KðvÞ
Colhd
½#6:80ꢂ I:L:
½147ꢂ
59:2
#
67:9
#
½13:5ꢂ
85:2
#
½7:32ꢂ
104
#
½24:8ꢂ
148
#
152
#
½3:66ꢂ
182
½#12:1ꢂ I:L:
44:5
/
½0:79ꢂ
K1ðvÞ
K2
K3
K4
K5
SX
SC
SA
½1:07ꢂ
½1:13ꢂ
118
#
157
½#19:7ꢂ I:L:
3b
KðvÞ
SE
½31:2ꢂ
a
Phase-transition temperature (T) and enthalpy change (DH) determined by DSC.
Phase nomenclature: K¼crystal; Colhd¼hexagonal disordered columnar meso-
b
phase; SE¼smectic E mesophase; SC¼smectic C mesophase; SA¼smectic A meso-
phase; SX¼unidentified smectic mesophase; I.L.¼isotropic liquid; (v)¼fresh virgin
state obtained by recrystallization from the solvent.
Table 2
X-ray diffraction data of the mesophase of compounds 1b, 2b, and 3b
Mesophase
Lattice constants/Å
Spacing/Å
Observed
Miller indices (hkl)
Sample
Calculated
1b
Colhd at 122 ꢀ
C
34.0
19.8
17.1
13.0
ca. 4.7
34.0
19.6
17.0
12.8
d
(100)
(110)
(200)
(210)
dc
a¼39.2 Å
Z¼1.25 for ¼1.00
r
Scheme 4. Preparation of 6-hexadecyl-2-phenylazulene (3b).
and h¼3.40 Åa
Mass spectrum of compound 1b measured by MALDI-TOF con-
ditions showed correct MþHþ ion peaks, which afford a criterion of
the trimerized structure of compound 1b. The absorption spectra of
these compounds are quite similar with those of their 6-octyl de-
rivatives 1a, 2a, and 3a. They show the characteristic weak absorp-
tion of the azulene system in the visible region. The bathochromic
shift of the longest absorption maxima of 1b (lmax¼570 nm) in the
visible region by 6 nm relative to that of 3b (lmax¼564 nm) exhibits
2b
SA at 167 ꢀ
c¼40.5 Å
C
C
40.5
20.3
13.5
ca. 4.3
40.5
20.3
13.5
d
(001)
(002)
(003)
dc
SC at 150 ꢀ
c¼40.0 Å
39.9
20.0
13.4
10.0
ca. 4.4
40.0
20.0
13.3
10.0
d
(001)
(002)
(003)
(004)
dc
the extension of the p-system. The longest absorption maximum of
3b
SE at 138 ꢀ
a¼9.40 Å
b¼4.50 Å
c¼33.8 Å
Z¼2.01 for
C
33.4
16.9
11.3
8.50
4.70
4.06
3.32
33.4
16.7
11.1
8.35
4.70
4.06
3.25
(001)
(002)
(003)
(004)
(100)
(110)
(210)
2b (lmax¼569 nm) in the visible region exhibits a slight red shift (by
5 nm) compared with that of 3b probably because of the electron-
withdrawing nature of the substituted triple bond.15
r
¼1.00b
2.2. Mesomorphic properties
a
Number of molecules in a slice calculated by the assumption of the density of the
Phase-transition behavior of 1b, 2b, and 3b was examined with
a polarizing microscope (POM) with a heating plate controlled by
a thermoregulator and measured with a differential scanning cal-
orimeter (DSC). The DSC thermograms of these compounds are
shown in the Supplementary data. In Table 1, phase-transition
mesophase (
r
¼1.00 g cmꢁ1) and the average of the stacking distances (h¼3.40 Å) in
the Colhd mesophase.
b
Number of molecules in a 2D lattice calculated by the assumption of the density
of the mesophase (
r
¼1.00 g cmꢁ1).
c
Halo of the molten alkyl chains.

K. Nakagawa et al. / Tetrahedron 66 (2010) 8304e8312
8307
Figure 2. Graphical representation of the phase-transition temperatures of 1a, 1b, 2a, 2b, 3a, and 3b.
temperatures of 1b, 2b, and 3b are represented schematically with
those of 6-octyl derivatives 1a, 2a, and 3a in Figure 2. The detailed
thermal behaviors of these compounds are described below.
Compound1bshowedmesomorphismsassummarizedinTable1.
These state changes were observed in both the DSC measurements
andthemicroscopicobservations(Fig.3).Recrystallizationof1bfrom
a solvent (CH2Cl2) at room temperature produced a crystalline phase,
which was denoted as K(v) in Table 1. The K(v) crystals transformed
into a mesophase at 96.7 ꢀC, followed by an isotropic liquid (I.L.) at
143 ꢀC. As expected, the isotropization temperature of compound 1b
drops by 56.9 ꢀC with increasing the number of carbon atoms in the
peripheral side chain. The crystallineemesophase transition tem-
perature is also decreased by 18.8 ꢀC relative to that of 6-octyl de-
rivative 1a (115.5 ꢀC). The phase transition enthalpy change was
147 kJ molꢁ1, which is rather larger than that of a phase transition
from a crystal to a columnar mesophase of 6-octyl derivative 1a
(21 kJ molꢁ1). The enthalpy difference may have resulted from the
length of the peripheral alkyl groups in these compounds. Therefore,
the length of the mesogenic alkyl chains can markedly influence the
phase-transition temperatures.
a completely dark area between crossed polarizers (Fig. 3a). Upon
holding at this temperature, the perfect homeotropic alignment
grew within a minute as represented in Figures 3b and c. This is the
first example to exhibit ‘spontaneous uniform homeotropic align-
ment’ in a discotic liquid crystalline azulene derivatives, so far as we
know. The molecular difference between 1a and 1b consists only of
the length of the alkyl chains in the surrounding. Therefore, it may
be concluded that the longer alkyl chains induce the strong in-
termolecular interaction of the flexible large
p-aromatic core to
decrease the stacking distance and perfect homeotropic alignment
on the non-treated glass substrate in these examples.
As expected, the 6-hexadecyl derivative 2b also lowered iso-
tropization temperature and varied with the mesomorphic be-
haviors. As can be seen from Table 1, compound 2b exhibited
mesomorphisms with crystalline polymorphs as similar with those
of compound 2a. Crystalline phase of 2b obtained by re-
crystallization (hexane) was denoted as K1(v) in Table 1. When the
virgin crystals, K1(v), were heated from room temperature, they
exhibited subsequent solidesolid transitions at 44.5, 59.2, 67.9, and
85.2 ꢀC to give the K2, K3, K4, and K5 crystals, respectively. On fur-
ther heating, the K5 crystals melted into a mesophase at 104 ꢀC
The X-ray diffraction experiments of the mesophase at 122 ꢀC
exhibited a diffuse band around 2
q
¼20ꢀ in the wide-angle region,
(
D
H¼24.8 kJ molꢁ1). As expected, the crystallineemesophase
which corresponds to the melt of the 6-hexadecyl chains. Com-
pound 1b also gave sharp four reflections corresponding to the
spacing, 34.0, 19.8, 17.1, and 13.0 Å, in the small-angle region, which
is characteristic of a Colh mesophase. However, the Colh mesophase
did not give an additional reflection owing to the stacking distance
(h) between disks in the column. Therefore, the phase was de-
scribed as a disordered hexagonal columnar mesophase (Colhd) in
Table 2. The lattice constant (a) of the Colhd mesophase of com-
pound 1b became significantly longer than that of compound 1a
owing to the increase of the number of the carbon atoms in the
peripheral side chain. The number of molecules (Z¼1.25) in a slice
presented in Table 2 was calculated by assuming the stacking dis-
tance h¼3.40 Å (typical van der Waals radius of aromatic com-
transition temperature was also decreased by 14.8 ꢀC relative to
that of 6-octyl derivative 2a (118.8 ꢀC). The X-ray diffraction ex-
periments of the mesophase at 126 ꢀC exhibited reflections in the
small-angle region characteristic for a smectic mesophase. The
mosaic texture at 126 ꢀC (Fig. 4d) should consist with a smectic
mesophase, such as a smectic E (SE) or a smectic B (SB) mesophase.
However, the X-ray diffraction experiments of the mesophase did
not afford characteristic reflections such as SE mesophase in the
wide-angle region around 2
patterns did not allow us to unequivocal analysis of the lowest-
temperature state, which was denoted as SX in Table 1.
q
¼20ꢀ. Therefore, the X-ray diffraction
Upon further heating, the unidentified SX mesophase trans-
formed into
a
smectic
C
(SC) mesophase at 148 ꢀC
pounds) and the density
r
¼1.00 g cmꢁ3. The Z value for compound
(D
H¼1.13 kJ molꢁ1) followed by a smectic A (SA) mesophase at
1b is comparable with the usual number (Z¼1) for the Colh meso-
phase. Therefore, the face-to-face stacking in the Colhd mesophase
could be concluded to be much more attractive compared with that
of the 6-octyl derivative 1a. The reason may be attributed to the
strong intermolecular interaction of the peripheral 6-hexadecyl
substituents, which may induce the aggregation of the aromatic
core to reduce the face-to-face stacking distance (h) of compound
1b for the Colhd mesophase. Rather short stacking distance of
compound 1b in the Colhd mesophase should be attributable to the
decreasing of the tilt angle of the 2-azulenyl groups.
152 ꢀC (
D
H¼3.66 kJ molꢁ1). Generally, the enthalpy changes could
not be observed at the SCeSA phase transition. However, in some
cases, it is also reported the small enthalpy changes at the SCeSA
phase transition.16 The SCeSA phase transition of 2b exhibits rather
large enthalpy change in the DSC measurements. The enthalpy
changes of fusion depend on the length of the chains. The rather
large enthalpy change at the SCeSA phase transition of 2b might be
attributed to the two long C-16 alkyl chains substituted. Upon
further heating, the SA mesophase clears to an I.L. at 182 ꢀC. The
crystallineemesophase transition and isotropization temperatures
of compound 2b (cf. 2a, 118.8 ꢀC and 215.0 ꢀC, respectively) drop-
ped by 14.8 ꢀC and 33 ꢀC, respectively, with increasing the number
of carbon atoms in the peripheral side chains. On the cooling
When the isotropic liquid transformed into the Colhd meso-
phase, spontaneous homeotropic alignment could be observed on
the non-treated glass plates, in which the development of

8308
K. Nakagawa et al. / Tetrahedron 66 (2010) 8304e8312
Figure 3. Microscopy images of the mesophase of compound 1b; (a) Textures of
compound 1b obtained by cooling from the isotropic liquid at 135.5 ꢀC; (b) Textures of
compound 1b obtained by standing at 135.5 ꢀC; (c) Textures of compound 1b obtained
by further standing at 135.5 ꢀC.
process from the I.L. phase, the development of batonnets was first
observed at 167 ꢀC. The appearance of the batonnets (Fig. 4a)
should correspond to a smectic mesophase of compound 2b. The
batonnets coalesced and built up fan-shaped texture of the SA
mesophase (Fig. 4b) by standing the sample at that temperature,
where the X-ray diffraction showed a typical pattern for smectic
mesophase of c¼40.5 Å. Compound 2b had schlieren texture for
the SC mesophase (Fig. 4c), where the X-ray diffraction showed
Figure 4. Textures of the mesophase of compound 2b; (a) Batonnets observed at first
by cooling from the isotropic liquid at 167 ꢀC; (b) Fan-shaped texture of the SA
mesophase obtained when the sample stood at 167 ꢀC; (c) Schlieren texture of the SC
mesophase at 150 ꢀC; (d) Mosaic texture of the SX mesophase at 126 ꢀC.

K. Nakagawa et al. / Tetrahedron 66 (2010) 8304e8312
8309
a typical pattern for smectic mesophase of c¼40.0 Å. The schlieren
texture gives the unequivocal evidence of the SC mesophase of 2b.
Compound 3b exhibited smectic mesomorphism as similar to
that of compound 3a (Table 1). Upon heating the sample, the K(v)
crystals obtained by recrystallization of 3b (hexane) transformed
believed to force the system to minimize contact with polar sub-
strates such as non-treated glass, which results in an ‘edge-on’
alignment of the molecules.17 However, successful perfect homeo-
tropic alignment of all-hydrocarbon compound 1b should open
a novel molecular design for the alignment controls of the discotic
mesophases.
The homeotropic alignment is significant to increase the mo-
bility of discotic LCs for practical usage such as photovoltaic di-
odes.18 According to the Colhd mesophase of compound 1b easily
self-organizes in columns perpendicular to the substrate when
cooled from the isotropic liquid phase. Therefore, the present
compound 1b might exhibit excellent paths for charge carrier
transportation and may become an intrinsic candidate for the fu-
ture applications to a semiconductor owing the amphoteric redox
properties of azulene derivatives.
into the SE mesophase at 118 ꢀC (
D
H¼31.2 kJ molꢁ1). Upon further
heating, the SE mesophase cleared to an isotropic liquid (I.L.) at
157 ꢀC (
D
H¼19.7 kJ molꢁ1). On the cooling process from the I.L.
phase, compound 3b developed grandjean terrace texture charac-
teristic for the SE mesophase (Fig. 5). The X-ray diffraction pattern
of the mesophase at 138 ꢀC showed a typical pattern for the SE
structure (Table 2). It showed two narrow reflections in the small-
angle region which correspond to the (001) and (002) planes; the
interlayer distance of 33.8 Å. It also had three reflections in the
wide-angle region which correspond to (100), (110), and (210) in
a two-dimensional rectangular lattice (lattice constants a¼9.40 Å
and b¼4.50 Å). By assuming a specific gravity of 1.00 g cmꢁ3, we can
estimate the average number of molecules per unit cell to be 2.01
molecules with the interlayer distance of 33.8 Å. The reflections
arisen from the two-dimensional rectangular lattice, the average
number of molecules per unit cell, and also the grandjean terrace
texture at the mesophase represent the evidence of the SE meso-
phase of 3b.
4. Experimental section
4.1. General
Melting points were determined on a Yanagimoto micro melting
apparatus MP-S3 and are uncorrected. Mass spectra were obtained
with a Hitachi M-2500 or a Bruker APEX II instrument. IR and UV
spectra were measured on a Shimadzu FTIR-8100M and a Hitachi
U-3410 spectrophotometers, respectively. 1H NMR spectra (13
C
NMR spectra) were recorded on a JEOL GSX 400 spectrometer at
400 MHz (100 MHz). Gel permeation chromatography (GPC) puri-
fication was performed on a BIO-RAD Bio-BeadsÒ S-X3 with CH2Cl2
as an eluent. Elemental analyses were performed at the Research
and Analytical Center for Giant Molecules, Graduate School of Sci-
ence, Tohoku University.
4.1.1. Diethyl 6-(1-hexadecynyl)-2-methoxyazulene-1,3-dicarboxylate
(5). To a degassed solution of diethyl 6-bromo-2-methoxyazulene-
1,3-dicarboxylate (4) (5.01 g, 13.1 mmol), 1-hexadecyne (5.85 g,
26.3 mmol), CuI (250 mg, 1.31 mmol), triethylamine (27 mL) in dry
toluene (200 mL) was added tetrakis(triphenylphosphine)palla-
dium(0) [Pd(PPh3)4] (765 mg, 0.662 mmol). The resulting mixture
was stirred at room temperature for 1 h under an Ar atmosphere.
The reaction mixture was washed successively with a 5% NH4Cl
solution and brine, dried over MgSO4, and concentrated under re-
duced pressure. The residue was purified by column chromatog-
raphy on silica gel with 20% ethyl acetate/hexane to afford 5 (6.79 g,
99%). Purple needles; mp 57.2e57.7 ꢀC (MeOH); 1H NMR (400 MHz,
Figure 5. Grandjean terrace texture of the SE mesophase of compound 3b obtained by
cooling from the isotropic liquid at 153 ꢀC.
The isotropization temperature of compound 3b (cf. 3a,
180.6 ꢀC) dropped by 23.6 ꢀC with increasing the number of carbon
atoms in the alkyl chain as similar to those of 1b and 2b. However,
the crystallineemesophase transition temperature was increased
by 8.4 ꢀC relative to that of 6-octyl derivative 3a (109.6 ꢀC). Thus,
the temperature range of the SE mesophase becomes narrow with
increasing the number of carbon atoms in the alkyl chain.
3
3
CDCl3):
d
¼9.31 (d, JH,H¼11.3 Hz, 2H, 4,8-H), 7.73 (d, JH,H¼11.3 Hz,
2H, 5,7-H), 4.46 (q, 3JH,H¼7.1 Hz, 4H, 1,3-CO2Et), 4.14 (s, 3H, 2-OMe),
2.49 (t, 3JH,H¼7.2 Hz, 2H, 30-H), 1.65 (tt, 3JH,H¼7.2, 7.2 Hz, 2H, 40-H),
3
1.46 (t, JH,H¼7.1 Hz, 6H, 1,3-CO2Et), 1.40e1.20 (m, 22H, 50e150-H),
0.88 (t, JH,H¼6.8 Hz, 3H, 160-H); 13C NMR (100 MHz, CDCl3):
3
3. Conclusions
d
¼170.27, 164.61, 141.45, 134.80, 134.67, 133.93, 108.07, 96.48, 84.30,
62.96, 60.19, 31.88, 29.65, 29.63, 29.49, 29.32, 29.10, 28.97, 28.43,
22.65, 19.73, 14.42, 14.07; IR (KBr disk): nmax¼2990 (w), 2982 (w),
2921 (s), 2851 (s), 2226 (w, C^C), 1688 (w), 1678 (s, C]O), 1580
(w), 1566 (w), 1541 (w), 1487 (s), 1474 (w), 1429 (s), 1389 (s), 1331
(w), 1287 (s), 1246 (m), 1225 (m), 1200 (s), 1125 (w), 1111 (w), 1069
(w), 1038 (m), 999 (m), 880 (w), 860 (w), 797 (w), 789 (w), 720 (w),
Hexakis(6-hexadecyl-2-azulenyl)benzene (1b) was successfully
synthesized by Co2(CO)8-catalyzed cyclotrimerization reaction of
2b. The mesomorphic behaviors of 1b, 2b, and 3b have been clar-
ified and were compared with those of 6-octyl derivatives 1a, 2a,
and 3a. Introduction of 6-hexadecyl chains as the peripheral tails
provided a spontaneous perfect homeotropic alignment of a Colhd
mesophase in 1b on the non-treated glass substrate. Therefore, the
chain length is very important for the alignment controls of the
discotic mesophases in these cases.
In general, the surface affinity of the molecules is modified by
changing the chemical nature of the aromatic core or side chains.
The examples of homeotropic alignment are of triphenylenes and
phthalocyanines bearing heteroatoms in the side chains, which
imply a strong influence of the substituents on the arrangement of
the molecules. The long, flexible, hydrophobic alkyl chains are
710 (w), 695 (w), 604 (w), 567 (w), 534 (w), 480 (w), 430 (w) cmꢁ1
UVevis (CH2Cl2): lmax (log
;
3
)¼238 (4.43), 271 sh (4.17), 329 (4.92),
372 (4.24), 395 sh (3.89), 493 (2.73) nm; HRMS (ESI positive): calcd
for C33H45O5þNaþ 545.3237; found 545.3237. Anal. Calcd for
C33H46O5: C, 75.83; H, 8.87; found: C, 75.63; H, 8.72.
4.1.2. Diethyl 6-hexadecyl-2-methoxyazulene-1,3-dicarboxylate (6). A
mixture of diethyl 6-(1-hexadecynyl)-2-methoxyazulene-1,3-
dicarboxylate (5) (3.58 g, 6.85 mmol) and 10% PdeC (384 mg) in
ethanol (74 mL) and THF (44 mL) was stirred at room temperature

8310
K. Nakagawa et al. / Tetrahedron 66 (2010) 8304e8312
3
for 6 h under an H2 atmosphere. After the Pd catalyst was removed
by filtration, the solvent was removed under reduced pressure. The
residue was purified by column chromatography on silica gel with
10% ethyl acetate/hexane to afford 6 (3.40 g, 94%). Orange crystals;
20-H), 1.37e1.21 (m, 26H, 30e150-H), 0.88 (t, JH,H¼6.8 Hz, 3H, 160-
H); 13C NMR (100 MHz, CDCl3):
d
¼168.50, 148.53, 138.54, 131.46,
125.50, 100.95, 57.47, 42.00, 32.88, 31.93, 29.70, 29.67, 29.58,
29.54, 29.37, 29.33, 22.70, 14.11; IR (KBr disk): nmax¼3092 (w),
3015 (w), 2953 (w), 2917 (s), 2849 (s), 1584 (w), 1549 (m), 1526 (s),
1472 (m), 1464 (m), 1431 (m), 1410 (m), 1342 (w), 1293 (w), 1233
(w), 1204 (m), 1165 (w), 1144 (m), 1026 (m), 961 (w), 951 (w), 833
(m), 820 (w), 789 (w), 783 (m), 772 (w), 727 (w), 720 (w), 650 (w),
mp 56.1e56.3 ꢀC (MeOH); 1H NMR (400 MHz, CDCl3):
d
¼9.41
3
3
(d, JH,H¼10.8 Hz, 2H, 4,8-H), 7.58 (d, JH,H¼10.8 Hz, 2H, 5,7-H),
3
4.46 (q, JH,H¼7.2 Hz, 4H, 1,3-CO2Et), 4.13 (s, 3H, 2-OMe), 2.88
3
3
(t, JH,H¼7.6 Hz, 2H, 10-H), 1.72 (tt, JH,H¼7.6, 7.6 Hz, 2H, 20-H), 1.46
3
(t, JH,H¼7.2 Hz, 6H, 1,3-CO2Et), 1.33e1.22 (m, 26H, 30e150-H),
604 (w), 411 (w) cmꢁ1; UVevis (CH2Cl2): lmax (log
3
)¼283 (4.87),
0.87 (t, JH,H¼7.0 Hz, 3H, 160-H); 13C NMR (100 MHz, CDCl3):
292 (4.98), 320 (3.88), 344 (3.69), 360 (3.85), 376 (3.86), 510
(2.29), 540 sh (2.22), 589 sh (1.73) nm; HRMS (ESI positive): calcd
for C27H42OþNaþ 405.3128; found 405.3126. HRMS (ESI positive):
calcd for C27H42OþHþ 383.3308; found 383.3307. Anal. Calcd for
C27H42O: C, 84.75; H, 11.06; found: C, 84.48; H, 11.15.
3
d
¼169.79, 164.83, 155.46, 140.89, 136.13, 132.29, 107.37, 62.96,
60.05, 41.71, 32.56, 31.90, 29.67, 29.63, 29.60, 29.50, 29.44, 29.33,
29.20, 22.67, 14.47, 14.09; IR (KBr disk): nmax¼2979 (w), 2953 (w),
2919 (s), 2853 (m), 1682 (s, C¼O), 1582 (w), 1545 (w), 1495 (s), 1474
(m), 1460 (w), 1431 (s), 1416 (m), 1393 (m), 1377 (w), 1339 (w), 1300
(w),1285 (m),1279 (m),1242 (m),1231 (w),1204 (m),1154 (w),1111
(w), 1084 (w), 1038 (m), 1032 (m), 1001 (m), 924 (w), 903 (w), 841
(w), 814 (w), 789 (w), 733 (w), 716 (w), 569 (w) cmꢁ1; UVevis
4.1.4. 2-Bromo-6-hexadecylazulene (10). To a solution of 6-hexa-
decyl-2-hydroxyazulene (8) (1.67 g, 4.53 mmol) in dry toluene
(187 mL) was added PBr3 (3.81 g, 14.1 mmol). The resulting mix-
ture was heated at 90 ꢀC for 50 min. The reaction mixture was
poured into water (1.5 L) and extracted with toluene. The organic
layer was washed with water, dried over MgSO4, and concen-
trated under reduced pressure. The residue was purified by col-
umn chromatography on silica gel with hexane to afford 10
(CH2Cl2): lmax (log
3
)¼270 (4.36), 314 (4.81), 348 (3.98), 370 sh
(3.79), 463 (2.75) nm; HRMS (ESI positive): calcd for C33H50O5þNaþ
549.3550; found 549.3548. Anal. Calcd for C33H50O5: C, 75.25; H,
9.57; found: C, 75.18; H, 9.57.
4.1.3. 6-Hexadecyl-2-hydroxyazulene (8) and 6-hexadecyl-2-methoxy-
azulene (9). Diethyl 6-hexadecyl-2-methoxyazulene-1,3-dicarbox-
ylate (6) (2.80 g, 5.32 mmol) was dissolved in a solution of KOH
(17.4 g, 0.310 mol) in water (70 mL) and ethanol (70 mL). The
resulting mixture was refluxed for 4 h. After cooling the reaction
mixture, water (500 mL) was added to the mixture and the com-
bined mixture was acidified with 2 M HCl. The precipitated crystals
were collected by filtration and dissolved in CHCl3. The organic
layer was dried over MgSO4 and concentrated under reduced
pressure to afford 6-hexadecyl-2-methoxyazulene-1,3-dicarboxylic
diacid (7), which was utilized to the next reaction without further
purification.
(1.56 g, 80%). Purple crystals; mp 82.8e83.2 ꢀC (EtOH); 1H NMR
3
(400 MHz, CDCl3):
d
¼8.13 (d, JH,H¼10.4 Hz, 2H, 4,8-H), 7.53
3
(s, 2H, 1,3-H), 7.12 (d, JH,H¼10.4 Hz, 2H, 5,7-H), 2.77 (t,
3JH,H¼7.6 Hz, 2H, 10-H), 1.70 (tt, JH,H¼7.6, 7.6 Hz, 2H, 20-H),
3
1.40e1.21 (m, 26H, 30e150-H), 0.88 (t, 3JH,H¼6.8 Hz, 3H, 160-H); 13C
NMR (100 MHz, CDCl3):
d
¼154.18, 138.55, 134.66, 125.76, 118.43,
42.43, 32.55, 31.93, 29.69, 29.66, 29.62, 29.53, 29.48, 29.36, 29.31,
22.69, 14.11; IR (KBr disk): nmax¼2951 (m), 2919 (s), 2851 (s), 2361
(w), 2342 (m), 1584 (w), 1545 (m), 1470 (w), 1441 (m), 1404 (w),
1235 (w), 1157 (w), 1073 (w), 974 (w), 916 (w), 862 (w), 839 (m),
791 (w), 768 (w), 720 (w), 691 (w), 669 (w), 596 (w), 440 (w)
cmꢁ1; UVevis (CH2Cl2): lmax (log
3
)¼285 (4.90), 294 (4.89), 326
A mixture of 7 and freshly prepared 100% phosphoric acid
(120 mL) was heated at 100 ꢀC for 30 min with occasional stirring
with a glass rod. After cooling the reaction mixture, the mixture was
poured into ice-water (1.5 L) and extracted with toluene. The or-
ganic layer was washed with water, dried over MgSO4, and con-
centrated under reduced pressure. The residue was purified by
column chromatography on silica gel with 20% ethyl acetate/hexane
to afford 8 (1.38 g, 71%) and 9 (203 mg, 10%).
sh (3.65), 336 (3.79), 350 (3.85), 364 (3.86), 537 (2.65), 572 sh
(2.60), 625 sh (2.18) nm; HRMS (ESI positive): calcd for
C26H39BrþHþ 431.2308; found 431.2346. Anal. Calcd for C26H39Br:
C, 72.37; H, 9.11; found: C, 72.18; H, 9.21.
4.1.5. 6-Hexadecyl-2-(trimethylsilyl)ethynylazulene (11). Trime-
thylsilylacetylene (551 mg, 5.61 mmol) was added to a solution of
2-bromo-6-hexadecylazulene (10) (806 mg, 1.87 mmol), CuI
(36 mg, 0.19 mmol), and tetrakis(triphenylphosphine)palladium(0)
[Pd(PPh3)4] (108 mg, 0.0934 mmol) in triethylamine (9 mL) and dry
toluene (47 mL). The resulting mixture was stirred at 60 ꢀC for
30 min under an Ar atmosphere. The reaction mixture was poured
into a 10% NH4Cl solution and extracted with toluene. The organic
layer was washed with brine, dried over MgSO4, and concentrated
under reduced pressure. The residue was purified by column
chromatography on silica gel with hexane to afford 11 (747 mg,
89%). Blue crystals; mp 37.0e37.5 ꢀC (EtOH); 1H NMR (400 MHz,
Compound 8: Reddish brown crystals; mp 88.0e88.5 ꢀC (MeOH);
1H NMR (400 MHz, acetone-d6):
d
¼9.49 (s, 1H, 2-OH), 7.95 (d,
3JH,H¼10.4 Hz, 2H, 4,8-H), 7.11 (d, 3JH,H¼10.4 Hz, 2H, 5,7-H), 6.70 (s,
2H, 1,3-H), 2.77 (t, 3JH,H¼7.6 Hz, 2H, 10-H), 1.70 (tt, 3JH,H¼7.6, 7.6 Hz,
3
2H, 20-H), 1.39e1.25 (m, 26H, 30e150-H), 0.88 (t, JH,H¼7.0 Hz, 3H,
160-H); 13C NMR (100 MHz, acetone-d6):
d¼167.58, 148.09, 140.15,
131.12, 126.00, 103.77, 42.41, 33.71, 32.64, 30.37, 30.31, 30.07, 23.33,
14.35 (Several signals in aliphatic region could not be determined by
overlapping with signals from acetone-d6); IR (KBr disk):
nmax¼2955 (w), 2917 (s), 2849 (s),1657 (m),1630 (w),1580 (w),1549
(m),1538 (m),1518 (m),1472 (m),1464 (m),1437 (w),1406 (w),1366
(w), 1291 (w), 1262 (w), 1231 (w), 1169 (w), 1142 (w), 978 (w), 957
(w), 860 (w), 831 (m), 820 (w), 795 (w), 720 (w), 652 (w), 550 (w),
CDCl3):
d
¼8.11 (d, 3JH,H¼10.3 Hz, 2H, 4,8-H), 7.34 (s, 2H, 1,3-H), 7.06
(d, 3JH,H¼10.3 Hz, 2H, 5,7-H), 2.76 (t, 3JH,H¼7.6 Hz, 2H, 10-H), 1.69 (tt,
3JH,H¼7.6, 7.6 Hz, 2H, 20-H), 1.40e1.21 (m, 26H, 30e150-H), 0.88 (t,
3JH,H¼7.0 Hz, 3H, 160-H), 0.29 (s, 9H, TMS); 13C NMR (100 MHz,
438 (w), 411 (w) cmꢁ1; UVevis (CH2Cl2): lmax (log
3)¼281 (4.52),
CDCl3):
d
¼154.72, 138.70, 136.19, 128.67, 125.16, 120.88, 103.36,
290 (4.60), 322 sh (3.72), 362 sh (4.11), 373 (4.14), 393 sh (3.92), 444
sh (3.10), 474 sh (2.91), 516 sh (2.56) nm; HRMS (ESI positive) calcd
for C26H40OþNaþ 391.2971; found 391.2970. HRMS (ESI positive)
calcd for C26H40OþHþ 369.3152; found 369.3150. Anal. Calcd for
C26H40O: C, 84.72; H, 10.94; found: C, 84.60; H, 10.65.
100.18, 42.49, 32.58, 31.92, 29.69, 29.66, 29.54, 29.49, 29.35, 22.68,
14.11, 0.04; IR (KBr disk): nmax¼2955 (m), 2917 (s), 2849 (s), 2147
(w), 1580 (m), 1485 (w), 1472 (m), 1455 (w), 1406 (m), 1375 (w),
1252 (m), 1015 (w), 972 (w), 901 (w), 857 (m), 837 (s), 808 (w), 758
(w), 729 (w), 718 (w), 698 (w), 668 (w), 646 (w), 436 (w), 409 (w)
Compound 9: Purple needles; mp 78.8e79.5 ꢀC (hexane); 1H
cmꢁ1; UVevis (CH2Cl2): lmax (log
3
)¼238 (4.14), 245 sh (4.08), 271
3
NMR (400 MHz, CDCl3):
d
¼7.99 (d, JH,H¼10.6 Hz, 2H, 4,8-H), 7.10
(4.38), 278 sh (4.37), 296 (4.80), 307 (4.88), 338 sh (3.60), 352
(3.78), 369 (4.13), 388 (4.33), 432 sh (1.64), 568 (2.61), 601 (2.61),
658 sh (2.26) nm; MS (70 eV): m/z (%)¼448 (100) [Mþ], 433 (6)
3
(d, JH,H¼10.6 Hz, 2H, 5,7-H), 6.76 (br s, 2H, 1,3-H), 4.02 (s, 2H, 2-
OMe), 2.76 (t, 3JH,H¼7.6 Hz, 2H, 10-H), 1.68 (tt, 3JH,H¼7.6, 7.6 Hz, 2H,

K. Nakagawa et al. / Tetrahedron 66 (2010) 8304e8312
8311
[MþꢁCH3], 377 (1) [MþꢁTMS]. Anal. Calcd for C31H48Si: C, 82.96; H,
42.51, 32.60, 31.92, 29.69, 29.65, 29.55, 29.51, 29.36, 22.69, 14.11; IR
(KBr disk): nmax¼2953 (w), 2917 (s), 2849 (s), 1578 (w), 1545 (w),
1471 (w), 1464 (w), 1410 (w), 837 (m), 720 (w), 642 (w), 417 (w)
10.78; found: C, 82.94; H, 10.69.
4.1.6. 2-Ethynyl-6-hexadecylazulene (12). A solution of KF (195 mg,
3.36 mmol) inwater (11 mL) was added to a solution of 6-hexadecyl-
2-(trimethylsilyl)ethynylazulene (11) (747 mg, 1.66 mmol) in DMF
(54 mL). After stirring the mixture at room temperature for 3 h, the
reaction mixture was poured into water (500 mL) and extracted
with toluene. The organic layer was washed with water, dried over
MgSO4, and concentrated under reduced pressure. The residue was
purified by column chromatography on silica gel with hexane to
afford 12 (598 mg, 95%). Blue crystals; mp 63.5e63.9 ꢀC (EtOH); 1H
cmꢁ1; UVevis (CH2Cl2): lmax (log
3
)¼276 (4.58), 312 sh (4.96), 320
(5.05), 395 sh (4.50), 411 sh (4.68), 421 (4.75), 448 (4.92), 530 sh
(3.03), 569 (3.13), 609 sh (3.07), 665 sh (2.67) nm; MS (70 eV): m/z
(%)¼727 (100) [Mþ], 529 (3), 515 (3). Anal. Calcd for C54
H78$1/2H2O:
C, 88.10; H, 10.82; found: C, 88.32; H, 10.72.
4.1.9. Hexakis(6-hexadecyl-2-azulenyl)benzene (1b). Co2(CO)8 (21 mg,
0.061 mmol) was added to a solution of bis(6-hexadecyl-2-azulenyl)
acetylene (2b) (209 mg, 0.287 mmol) in 1,4-dioxane (73 mL).
The mixture was refluxed for 20 h under an Ar atmosphere. After
removing the solvent under reduced pressure, the residue was puri-
fied by column chromatography on silica gel with CH2Cl2 and Bio-
BeadsÒ S-X3 with CH2Cl2 to afford 1b (164 mg, 78%). Green crystals;
NMR (400 MHz, CDCl3):
d
¼8.14 (d, 3JH,H¼10.4 Hz, 2H, 4,8-H), 7.37 (s,
2H, 1,3-H), 7.08 (d, 3JH,H¼10.4 Hz, 2H, 5,7-H), 3.43 (s, 1H, 2-C^CH),
3
3
2.77 (t, JH,H¼7.6 Hz, 2H, 10-H), 1.70 (tt, JH,H¼7.6, 7.6 Hz, 2H, 20-H),
1.38e1.22 (m, 26H, 30e150-H), 0.88 (t, JH,H¼7.0 Hz, 3H, 160-H); 13C
3
NMR (100 MHz, CDCl3):
d¼155.15, 138.60, 136.46, 127.57, 125.27,
mp 141.0 ꢀC (CH2Cl2); 1H NMR (400 MHz, CDCl3):
d
¼7.50 (d,
3
120.88, 82.20, 82.05, 42.50, 32.56, 31.93, 29.69, 29.66, 29.54, 29.48,
29.35, 29.33, 22.69, 14.11; IR (KBr disk): nmax¼3316 (m), 2953 (w),
2919 (s), 2851 (s),1580 (m),1466 (m),1410 (w),1184(w), 976 (w), 839
(m), 822 (w), 804 (w), 720 (w), 644 (w), 629 (m), 592 (m), 552 (w),
3JH,H¼10.4 Hz, 2H, 4,8-H), 6.62 (d, JH,H¼10.4 Hz, 2H, 5,7-H), 6.56 (s,
2H, 1,3-H), 2.57 (t, 3JH,H¼7.2 Hz, 2H, 10-H), 1.57 (tt, 3JH,H¼7.2 Hz, 2H, 20-
H), 1.41e1.20 (m, 26H, 30e150-H), 0.88 (t, 3JH,H¼7.2 Hz, 3H, 160-H); 13C
NMR (100 MHz, CDCl3):
d
¼151.18, 149.85, 137.85, 137.74, 134.57,
459 (w), 448 (w), 421 (w) cmꢁ1: UVevis (CH2Cl2): lmax (log
3
)¼238
122.93, 121.24, 42.27, 32.62, 31.93, 30.91, 29.71, 29.68, 29.60, 29.54,
29.50, 29.37, 22.69, 14.11; IR (KBr disk): nmax¼2919 (s), 2851 (s), 1576
(m),1545 (w),1508 (w),1468 (m),1414 (w),1396 (m), 837 (m), 722 (w),
(4.18), 268 (4.37), 292 (4.87), 303 (4.91), 333 sh (3.51), 348 (3.73), 362
(3.99), 370 sh (3.88), 380 (4.26), 568 (2.69), 602 (2.69), 660 sh (2.34)
nm; MS (70 eV): m/z (%)¼376 (100) [Mþ], 347 (6) [MþꢁC2H5], 333 (6)
[MþꢁC3H7], 319 (5) [MþꢁC4H9], 305 (4) [MþꢁC5H11]. Anal. Calcd
for C28H40: C, 89.29; H, 10.71; found: C, 89.21; H, 10.84.
669 (w) cmꢁ1; UVevis (CH2Cl2): lmax (log
3)¼288 (5.59), 317 sh (5.27),
384 sh (4.75), 570 (3.28), 608 sh (3.24), 671 sh (2.86) nm; MS (MALDI-
TOF): m/z (%)¼2180.8 (96) [MþHþ], 1865.4 (100) [MþꢁC23H38]. Anal.
Calcd for C162H234: C, 89.19; H, 10.81; found: C, 89.11; H, 10.66.
4.1.7. 6-Hexadecyl-2-iodoazulene (13). A solution of 2-bromo-6-
hexadecylazulene (10) (1.07 g, 2.48 mmol), CuI (5.74 g, 30.1 mmol),
KI (9.43 g, 56.8 mmol) in DMF (50 mL) was refluxed for 16 h. The
reaction mixture was poured into water (300 mL) and extracted
with toluene. The organic layer was washed with water, dried over
MgSO4, and concentrated under reduced pressure. The residue was
purified by column chromatography on silica gel with hexane to
afford 13 (995 mg, 84%). Purple plates; mp 88.8e89.2 ꢀC (EtOH); 1H
4.1.10. 6-Hexadecyl-2-phenylazulene (3b). A solution of 2-bromo-6-
hexadecylazulene (10) (200 mg, 0.464 mmol), phenylboronic acid
(114 mg, 0.935 mmol), Cs2CO3 (433 mg, 1.33 mmol), tetrakis(triphe-
nylphosphine)palladium(0) [Pd(PPh3)4] (27 mg, 0.023 mmol) in di-
oxane (11 mL) was refluxed for 2 h under an Ar atmosphere. The
reaction mixture was poured into water (200 mL) and extracted with
CH2Cl2. The organic layer was washed with brine, dried over MgSO4,
and concentrated under reduced pressure. The residue was purified
by column chromatography on silica gel with hexane to afford 3b
NMR (400 MHz, CDCl3):
d
¼8.14 (d, 3JH,H¼10.5 Hz, 2H, 4,8-H), 7.41 (s,
3
3
2H, 1,3-H), 7.10 (d, JH,H¼10.5 Hz, 2H, 5,7-H), 2.76 (t, JH,H¼7.6 Hz,
3
2H, 10-H), 1.70 (tt, JH,H¼7.6, 7.6 Hz, 2H, 20-H), 1.36e1.22 (m, 26H,
(169 mg, 85%). Blue plates; mp 154.1e154.5 ꢀC (hexane); 1H NMR
3
3
30e150-H), 0.88 (t, JH,H¼6.8 Hz, 3H, 160-H); 13C NMR (100 MHz,
(400 MHz, CDCl3):
d
¼8.18 (d, JH,H¼10.4 Hz, 2H, 4,8-H), 7.94 (d,
3
CDCl3):
d
¼154.64, 139.24, 134.16, 125.51, 124.41, 96.38, 42.52, 32.49,
3JH,H¼7.6 Hz, 2H, 20,60-H), 7.60 (s, 2H, 1,3-H), 7.45 (dd, JH,H¼7.6,
3
31.92, 29.68, 29.65, 29.52, 29.47, 29.35, 29.29, 22.68, 14.11; IR (KBr
disk): nmax¼2951 (m), 2919 (s), 2851 (s), 1582 (m), 1466 (m), 1399
(m), 1233 (w), 974 (w), 912 (w), 839 (m), 820 (w), 791 (w), 720 (w),
7.6 Hz, 2H, 30,50-H), 7.33 (t, JH,H¼7.6 Hz, 1H, 40-H), 7.06 (d,
3JH,H¼10.4 Hz, 2H, 5,7-H), 2.77 (t, JH,H¼7.2 Hz, 2H, 100-H), 1.71 (tt,
3
3JH,H¼7.2, 7.2 Hz, 2H, 200-H), 1.41e1.20 (m, 26H, 300e1500-H), 0.88 (t,
615 (w), 590 (w) cmꢁ1; UVevis (CH2Cl2): lmax (log
3
)¼238 (4.12),
3JH,H¼7.2 Hz, 3H, 1600-H); 13C NMR (100 MHz, CDCl3):
d¼153.10,
291 (4.83), 302 (4.90), 329 sh (3.63), 343 (3.79), 356 (3.85), 372
(4.01), 399 (2.46), 544 (2.65), 576 sh (2.61), 633 sh (2.18) nm; MS
(70 eV): m/z (%)¼478 (100) [Mþ], 351 (18) [MþꢁI]. Anal. Calcd for
C26H39I: C, 65.26; H, 8.22; found: C, 65.26; H, 8.11.
148.57, 139.93, 136.72, 135.41, 128.84, 127.87, 127.45, 124.97, 114.24,
42.39, 32.62, 31.92, 29.69, 29.65, 29.55, 29.51, 29.35, 22.68, 14.11; IR
(KBr disk): nmax¼2951 (w), 2917 (s), 2849 (s), 1578 (m), 1549 (w),
1471 (m),1441 (w), 1415 (w),1026 (w), 908 (w), 837 (m), 756 (s), 720
(w), 687 (m), 450 (w) cmꢁ1; UVevis (CH2Cl2): lmax (log
3)¼300
4.1.8. Bis(6-hexadecyl-2-azulenyl)acetylene (2b). To a degassed so-
lution of 2-ethynyl-6-hexadecylazulene (12) (400 mg, 1.06 mmol),
2-bromo-6-hexadecylazulene (10) (457 mg, 1.06 mmol), and CuI
(23 mg, 0.12 mmol) in triethylamine (5 mL) and toluene (27 mL)
was added tetrakis(triphenylphosphine)palladium(0) [Pd(PPh3)4]
(63 mg, 0.054 mmol). The resulting mixture was stirred at 60 ꢀC for
1.5 h under an Ar atmosphere. The reaction mixture was poured into
a 10% NH4Cl solution and extracted with toluene. The organic layer
was washed with brine, dried over MgSO4, and concentrated under
reduced pressure. The residue was purified by recrystallization from
hexane to afford 2b (592 mg, 77%). Green plates; mp 184.5 ꢀC
(4.90), 311 (4.96), 359 sh (3.92), 377 (4.22), 396 (4.29), 564 (2.63),
597 (2.61), 650 sh (2.25) nm; MS (70 eV): m/z (%)¼428 (100) [Mþ],
231 (11), 217 (15). Anal. Calcd for C32H44: C, 89.65; H,10.35; found: C,
89.44; H, 10.23.
Acknowledgements
The present work was supported by the Ministry of Education,
Culture, Sports, Science, and Technology, Japan by a Grant-in-Aid
for Scientific Research (Grant 21550031 to S.I.).
(hexane); 1H NMR (400 MHz, CDCl3):
d
¼8.16 (d, 3JH,H¼10.4 Hz, 2H,
Supplementary data
4,8-H), 7.46 (s, 2H, 1,3-H), 7.09 (d, 3JH,H¼10.4 Hz, 2H, 5,7-H), 2.78 (t,
3JH,H¼7.2 Hz, 2H, 10-H), 1.71 (t, 3JH,H¼7.2 Hz, 2H, 20-H), 1.41e1.20 (m,
26H, 30e150-H), 0.88 (t, 3JH,H¼6.8 Hz, 3H,160-H); 13C NMR (100 MHz,
DSC thermograms of compounds 1b, 2b, and 3b; X-ray diffrac-
tion powder patterns of compounds 1b, 2b, and 3b. Supplementary
data associated with this article can be found in online version at
CDCl3):
d¼154.49, 138.98, 135.95, 129.22, 125.25, 120.64, 93.86,

8312
K. Nakagawa et al. / Tetrahedron 66 (2010) 8304e8312
781e787; (c) Nekelson, F.; Monobe, H.; Shimizu, Y. Mol. Cryst. Liq. Cryst. 2007,
479, 205e211.
doi:10.1016/j.tet.2010.08.012. These data include MOL files and
InChIKeys of the most important compounds described in this
article.
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