The effect of polar substituents on the heterocyclic benzoxazoles

Article abstract of DOI:10.1016/j.tet.2006.07.058

The synthesis, characterization, and mesomorphic properties of a new type of heterocyclic compounds 1, 2 derived from benzoxazole are reported. In order to understand the relationship between the structure and the mesomorphic behavior, compounds containin

Full text of DOI:10.1016/j.tet.2006.07.058

Tetrahedron 62 (2006) 9383–9392
The effect of polar substituents on the heterocyclic
benzoxazoles
Chung-Shu Wang,a I-Wen Wang,a Kung-Lung Chengb and Chung K. Laia,
*
aDepartment of Chemistry and Center for Nano Science Technology, National Central University, Chung-Li 320, Taiwan, ROC
bUnion Chemical Laboratories, Industrial Technology Research Institute, Hsinchu 300, Taiwan, ROC
Received 22 May 2006; revised 3 July 2006; accepted 20 July 2006
Available online 10 August 2006
Abstract—The synthesis, characterization, and mesomorphic properties of a new type of heterocyclic compounds 1, 2 derived from benz-
oxazole are reported. In order to understand the relationship between the structure and the mesomorphic behavior, compounds containing a
variety of polar substituents (i.e., X¼H, F, Cl, Br, CH3, CF3, OCH3, NO2, CN, OH, NMe2, COOCH3) on the terminal end were prepared. The
phase behavior of these mesogenic compounds was characterized and studied by differential scanning calorimetry (DSC) and polarization
optical microscopy. The formation of mesophases was strongly dependent on the electronic and/or the steric factors of the substituents. In
general, a mesophase was better induced by introduction of a polar substituent. Compounds (X¼H) formed a crystalline phase, however, other
compounds, except for X¼OH, exhibited nematic or smectic A phases. Interestingly all compounds with electron-donating substituents
(X¼CH3, OCH3, NMe2) exhibited nematic phases, however, other compounds with electron-withdrawing substituents (X¼F, Cl, Br, CF3,
NO2, CN, COOCH3) formed smectic A phases. Compounds (X¼NO2, CN, COOCH3) have higher clearing temperatures than those of other
homologues, and the higher Tcl was attributed to an enhanced conjugative interaction. However, no linear correlation between the clearing
temperature or the temperature range of mesophases with Hammett sp constants was found. The fluorescent properties of the compounds
were examined. All lmax peaks of the absorption and photoluminescence spectra of compounds occurred at ca. 348–381 and 389–478 nm,
respectively. Whereas, the quantum yields of some compounds were relatively low.
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
such heterocyclic rings also explained the preferred or better
mesomorphic properties. Materials with lower melting
temperatures, potential candidates for further applications,
are often generated by such compounds. It is well known
that the stability7 of the mesophase may be augmented by
an increase of the polarity or polarization along the meso-
genic core of the molecule. A substantial change of the
micro- as well as macro-polarizability in a specific structure
or molecule can be easily achieved by the introduction of
polar substituent along the preferred molecular direction.
The effect of polar substituents in a variety of mesogenic
systems8 has been studied and investigated during the past
years. Some predictions were successfully made in terms
of mesomorphic behavior. The transition temperature of
M/I has been correlated with the polarizability anisotropy
of bonds to the substituent in 4-(4-substituted phenylazo)-
phenyl-4-alkoxybenzoates.8d Previous studies7,8c alsoshowed
that compounds substituted with polar groups, such as –NO2,
–CN, might lead to a higher clearing temperature, which
has been attributed to the conjugative interaction increase
between the substituent and the ester moiety. On the other
hand, the effect of polar substituents on the mesogenic 1,3,4-
oxadiazoles-based materials was also studied. The meso-
phase and optical properties of these oxadiazole materials3a
were also found to be strongly influenced by the presence
of a terminal polar group.
A delicate balance of molecular interactions in a specific
state1 is crucially essential to the formation of a predesigned
structure. This is particularly important in liquid crystalline
materials, and liquid crystals form a state of matter inter-
mediate between the solid and the liquid. This type of molec-
ular interaction1c,d induced to form mesophases can be weak
dipole–dipole interaction, dispersion, H-bonding, coordina-
tive force, and others. Forces which are too strong or too
weak can lead to the formation of a solid or liquid state.
Numerous heterocyclic compounds2 derived from com-
pounds such as 1,3,4-oxadiazole,3 1,2,4-triazole,4 and benz-
oxazole5 exhibiting interesting mesophases have recently
been explored due to their varieties in structures and/or
known chemistry. Better mesomorphic behavior6 formed
by these heterocyclic structures was attributed to their
unsaturation and/or more polarizable nature. On the other
hand, a lower symmetry3 and/or non-planar structure caused
by nitrogen, oxygen, sulfur, or other atoms incorporated on
* Corresponding author. Tel.: +886 3 4259207; fax: +886 3 4277972;
e-mail: cklai@cc.ncu.edu.tw
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.07.058

9384
C.-S. Wang et al. / Tetrahedron 62 (2006) 9383–9392
C12H25
O
C12H25
O
C12H25
O
b
c
OR
X
RO
RO
Y
NO2
NH2
OH
OH
OH
d
N
N
O
a
O
O
O
O
Cu
X
H2n+1CnO
HO
OH
X = Me, OMe, F, Cl, CN, NO2
OR
NO2
NO2
C12H25
O
N
OH
Y
OR
X
e
OR
C12H25
O
C12H25O
R = C12H25; X = H, F;
Y = H, F, CF3, OCH3, NMe2
O
O
f
NH2
N
N
4
3
Benzoxazoles, as an important type of heterocyclic com-
pound, have been studied in a variety of research areas,
including non-linear optics (NLO),9 organic light-emitting
diodes (OLED),10 and polymeric materials.11 However, benz-
oxazole derivatives exhibiting mesophases5a,12 have been
less often reported. Nematic or/and smectic C mesophases
formed by these rod-like compounds were observed. Benzo-
thiazole-derived compounds were also found to have photo-
physical and fluorescent applications.13 In a previous paper,
the substituent effect on the columnar formation in b-di-
ketonate metallomesogens14 was investigated. A rectangular
columnar phase (Colr) was observed for substituents with
bulkier groups (i.e., X¼Me, Et), however, a hexagonal co-
lumnar phase (Colh) was observed for substituents with elec-
tron-withdrawing groups (i.e., X¼Cl, Br, I). Interestingly,
a satisfactory linear relationship with a correlation coeffi-
cient of 0.974 between the clearing temperatures and Ham-
mett sp constants was obtained for the copper complexes.
g
C12H25
O
O
N
N
X
1a-1l
X = H, F, Cl, Br, CH3, CF3, OCH3, NO2, CN, OH,
NMe2, COOCH3
Scheme 1. Reactions and reagents: (a) RBr (1.1 equiv), KHCO3 (1.3 equiv),
KI, refluxed in dry CH3COCH3, 48 h, 60 ꢀC; (b) HNO3 (1.2 equiv), NaNO2
(0.2 equiv), stirred at 0 ꢀC in CH2Cl2, 12 h, 25 ꢀC; (c) N2H4 (1.2 equiv),
Pd/C (0.1 equiv), refluxed in absolute C2H5OH, 6 h, 85 ꢀC; (d) 4-Nitrobenz-
aldehyde (1.0 equiv), CH3COOH (drops), refluxed in absolute C2H5OH,
12 h, 90 ꢀC; (e) Pb(OAc)4 (1.3 equiv), refluxed in CH2Cl2, 6 h, 85 ꢀC;
(f) N2H4 (1.2 equiv), Pd/C (0.1 equiv), refluxed in absolute ethanol, 6 h,
80%; (g) substituted benzaldehyde (1.0 equiv), CH3COOH (drops), refluxed
in absolute C2H5OH, 12 h, 68–90 ꢀC.
2.1. Mesomorphic properties
As part of our studies of heterocyclic mesogens, in this
paper, we describe the synthesis, characterization, and the
mesomorphic properties of a series of calamitic benzoxazole
derivatives with various substituents on the terminal phenyl
ring. Their fluorescent properties were also examined.
Nematic or smectic phases were observed depending on the
electronic nature of the substituents. However, the observed
optical properties were not sensitive to the substituents
except for the compound with an NMe2 group.
The mesomorphic behavior of compounds 1a–1l was char-
acterized and studied by differential scanning calorimetry
(DSC) and polarizing optical microscopy. The phase transi-
tions and thermodynamic data were summarized in Table 1.
In order to study the substituent effect on the formation of
the mesophases, a variety of compounds with a variety of
polar groups (i.e., X¼H, F, Cl, Br, CH3, CF3, OCH3, NO2,
CN, OH, NMe2, COOCH3) substituted on the opposite end
of the benzoxazole ring were studied. Among these polar
groups, some are known as strong p-acceptors (i.e.,
X¼CN, NO2) or p-donors (X¼Cl, Br, OH), and others are
known as intermediate (X¼Cl, COOCH3), besides being
classified as electron-donating or electron-withdrawing
groups. The results indicated that the formation of meso-
phases in this type of electron-deficient heterocyclic system
was strongly dependent on the electronic and/or the steric
factors of the substituents. Compound 1a (X¼H) was in
fact non-mesogenic. A transition of crystal-to-isotropic at
99.8 ꢀC was observed, and the lack of liquid crystallinity
of compound 1a can probably be attributed to the insufficient
dipole over the entire molecule. When a polar functional
group was substituted on the phenyl ring located on the
opposite side to the benzoxale core, the mesomorphic prop-
erties were improved. All compounds except for 1j (X¼OH)
were truly mesogenic, in which introducing a polar group
was used to enhance or/and induce the formation of the
mesophases. The results also indicated that compounds
(1e, 1g, 1k) with an electron-donating substituent (–CH3,
OCH3, NMe2) exhibited nematic (N) phases, however, other
2. Results and discussion
The synthetic procedures5a for the benzoxazole derivatives
1a–1l are summarized in Scheme 1. The majority of benz-
oxazole-based derivatives were prepared by the condensa-
tion of 2-aminophenols with benzaldehydes or benzoic acid
and subsequent intramolecular cyclization. The compounds
of 5-dodecyloxy-2-nitrophenol, 2-amino-5-dodecyloxy-
phenol, 5-dodecyloxy-2-[(4-nitrobenzylidene)amino]phenol,
6-dodecyloxy-2-(4-nitrophenyl)benzoxazole 3, and 4-(6-
dodecyloxybenzoxazol-2-yl)phenylamine 4 were prepared
by reported procedures.5a The final compounds, benzyl-
idene-4-(6-dodecyloxybenzoxazol-2-yl)phenylamine were
prepared by the condensation reaction of 4-(6-dodecyloxy-
benzoxazol-2-yl)phenylamine and appropriate aldehydes
in refluxing absolute ethanol with a yield ranging from
67–82%. 1H and 13C NMR spectroscopy, mass spectrometry,
and elemental analysis were used to characterize the inter-
mediates and the final products.

C.-S. Wang et al. / Tetrahedron 62 (2006) 9383–9392
Table 1. Phase transitions and enthalpies of compounds 1a–1l
9385
99.8 (60.1)
Cr
SmA
SmA
SmA
N
I
I
1a
1b
79.8 (60.8)
101.7 (59.2)
155.6 (4.25)
Cr
74.9 (56.7)
92.1 (45.3)
154.7 (4.12)
174.0 (4.24)
82.4 (2.03)
Cr2
Cr1
Cr1
I
I
I
I
I
1c
74.3 (10.3)
97.9 (59.9)
80.2 (13.1)
103.9 (55.4)
173.2 (3.28)
194.3 (6.42)
63.3 (14.6)
50.0 (25.5)
Cr2
Cr
1d
192.8 (6.36)
137.4 (0.38)
1e
137.0 (0.40)
180.9 (6.22)
86.7 (56.5)
90.8 (47.6)
Cr
SmA
N
1f
75.3 (50.4)
179.5 (6.11)
169.5 (0.49)
92.0 (4.61)
95.6 (2.28)
108.3 (51.6)
Cr2
Cr1
Cr1
Cr1
1g
76.3 (51.5)
169.2 (0.47)
224.8 (2.64)
224.2 (2.66)
219.1 (3.27)
129.3 (7.85)
SmA
SmA
Cr2
Cr2
I
I
1h
1i
127.0 (8.03)
120.7 (40.1)
88.1 (1.96)
102.9 (8.93)
86.3 (6.08)
102.7 (30.7)
217.3 (3.21)
130.7 (16.7)
1j
Cr
N
I
I
I
117.2 (16.4)
161.0 (0.60)
123.3 (34.6)
111.8 (33.8)
156.7 (0.29)
Cr1
Cr1
SmX
Cr2
1k
160.5 (0.53)
212.5 (5.68)
210.8 (5.54)
156.2 (0.23)
133.0 (51.6)
115.2 (12.7)
SmA
1l
103.1 (35.6)
Cr1, Cr2¼crystalline phases, SmX¼unidentified smectic phase, SmC¼smectic C phase, SmA¼Smectic A phase, N¼nematic phase, I¼isotropic phase.
compounds (1b, 1c, 1d, 1f, 1h, 1i, 1l) with an electron-
withdrawing substituent (–F, –Cl, –Br, –CF3, –NO2, –CN,
–COOCH3) formed smectic A (SmA) phases. The N and
SmA phases were observed and identified by optical texture,
as shown in Figure 1.
due to a more overall molecular planar structure may be
achieved in the solid and liquid crystal states. The tempera-
ture range of mesophases were relatively wide with these
three compounds, at ca. 79.5 ꢀC (1l)–98.4 ꢀC (1i). Among
these three substituents, the NO2 group is particularly
worthy to note. Compound 1h (X¼NO2) has the highest
clearing temperature in the whole series, and this is probably
due to NO2 group having the largest dipole. The range of
mesophase temperature is relatively high; 98.4 ꢀC (1i;
CN)>96.4 ꢀC (1d; Br)>95.5 ꢀC (1h; NO2). The effect of lat-
eral and terminal –NO2 as a substituent in achiral calamitic
liquid crystals has been reviewed.8e The results indicated
that substantial changes in clearing and/or melting tempera-
tures were obviously observed depending on the molecular
structures and the substituted position. A polar NO2 group
attached to the hydrocarbon moiety changes substantially
the electron affinity of the molecules, and the strong meso-
meric effect caused by the NO2 group induces a positive
charge on the nitrogen atom and increases the electro-
negativity of the group.8e,15 The transition enthalpies of
SmA/I in the whole series of the compounds, measured
with 2.64 kJ/mol (1h)–6.42 kJ/mol (1d), varied slightly
with the substituents. On the other hand, compounds 1e
and 1f, which are relatively equal in molecular size, ex-
hibited a different mesophase; N phase for 1e and SmA
phase for 1f, respectively. On the other hand, a higher Tcl
in compound 1f (180.9 ꢀC) over 1e (137.4 ꢀC) by ca.
43.4 ꢀC, as well as a wider mesophase range by DT¼56.6 ꢀC
Among them, compounds 1b, 1c , 1d formed SmA phases,
however, compound 1d containing a larger and/or more
polarized group (X¼Br) enhanced the SmA phase more
than compounds with a smaller and/or less polarized group
(X¼F, Cl). The clearing temperature of compound 1d
was higher than those of compounds 1b and 1c, i.e.,
194.3 ꢀC>174.0 ꢀC>155.6 ꢀC. This order in clearing tem-
peratures and the temperature of mesophase was parallel
to the increased polarizability in the order of Br>Cl>F.
On the other hand, the temperature range of the mesophase
was also wider for compound 1d than those of compounds
1a and 1b, i.e., 96.4 ꢀC>81.9 ꢀC>53.9 ꢀC on heating. Inter-
estingly, among these electron-withdrawing substituents,
compounds 1h, 1i, 1l (X¼NO2, CN, COOCH3) appeared
to have clearing temperatures higher than those of other
homologues, which ranged from 212.5 and 224.8 ꢀC. These
polar groups are also known as good p-acceptors, and have
a more planar structure (i.e., sp or sp2 hybrid orbital). The
increase in Tcl might be attributed to two factors. Electroni-
cally, a conjugative interaction over the entire molecule was
better achieved between the polar substituent and the other
side of benzoxazole, and also a better packing arrangement

9386
C.-S. Wang et al. / Tetrahedron 62 (2006) 9383–9392
250
200
150
100
50
N
SmA
SmX
Cr
0
1a 1b 1c 1d 1e 1f 1g 1h 1i 1j 1k 1l
compds
Figure 2. Bar graph showing the phase behavior of compounds 1a–1l.
a transition of crystal-to-isotropic at 130.7 ꢀC was observed.
The lack of mesomorphic properties might result from the
intermolecular H-bonds formed, which can lead to a stronger
molecular interaction between the molecules. Figure 2
showed the bar graph of the transition temperatures of com-
pounds 1a–1l. The relationship between the melting temper-
atures, the clearing temperatures or the temperature ranges
of the mesophases with the electronic properties of the
substituents was plotted. However, no linear correlation
between the clearing temperature or the temperature range
of mesophases with Hammett sp constants for the substitu-
ents was found in this system (Fig. 3).
In order to understand the effect of terminal carbon chain
length on the formation of mesophase, the compounds 2a
(X¼OCH3) and 2b (X¼CN) with a carbon chain length of
n¼8 and 16 were also prepared and studied. The phase tran-
sitions and thermodynamic data are summarized in Table 2.
The mesomorphic properties exhibited by three compounds
2a and 1g with different carbon chain length (n¼8, 12, 16)
were compared. Compounds 2a (n¼8) and 1g (n¼12) ex-
hibited nematic phases, however, the compound 2a with
a longer carbon chain length (n¼16) formed a N phase and
a SmA phase. This phase behavior is expected for rod-like
molecules. The melting temperature increased slightly
with the carbon chain length, i.e., Tmp: 106.1 ꢀC (n¼8)<
108.3 ꢀC (n¼12)<112.5 ꢀC (n¼16), however, the clearing
temperatures decreased with the carbon chain length, i.e.,
Tcl: 186.0 ꢀC (n¼8)>169.5 ꢀC (n¼12)>158.1 ꢀC (n¼16).
The temperature range of the mesophase increased with
carbon chain length, DT¼82.9 ꢀC (n¼8)>61.2 ꢀC>45.6 ꢀC
(n¼16) (Fig. 4). Elongation of the overall molecular length
by increasing the carbon length on the other side of terminal
chains led to the formation of more ordered SmA phases
beside for N phase at higher temperature. This can probably
Figure 1. Optical textures observed by 1e (X¼CH3) at 119.0 ꢀC (top plate),
1f (X¼CF3) at 165.0 ꢀC (middle plate), and 1l (X¼COOCH3) at 175.0 ꢀC
(bottom plate).
240
(i.e., 90.1 ꢀC for 1f vs 33.5 ꢀC for 1e) might be attributed to
a better or larger dipole on 1f (CF3) over 1e (CH3). The elec-
tronic factor of the substituent, but not the steric factor,
might have played a more important role in forming or
inducing the phase. Heterocyclic benzoxazole is known as
an electron-deficient moiety, and polarization or electron
distribution by an electron-donating group, such as –CH3,
is better achieved by compound 1f than by compound 1e.
Compound 1g formed a N phase.
NO
2
220
200
180
160
140
120
100
CN
COOCH
CF
3
2
Br
Cl
R
= 0.6882
3
OCH
2
3
NMe
F
CH
3
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
σp
The transition enthalpies of N/I, measured with 0.38 kJ/
mol (1e)–0.60 kJ/mol (1k), were insensitive to the substitu-
ents. Compound 1j (X¼OH) was non-mesogenic, and only
Figure 3. The plot of clearing temperature (ꢀC) with Hammett sp constants
of substituents in 1a–1l.

C.-S. Wang et al. / Tetrahedron 62 (2006) 9383–9392
Table 2. Phase transitions and enthalpies of compounds 1g, 1i, 2a, and 2b
9387
106.1 (43.6)
78.0 (42.2)
108.3 (51.6)
76.3 (51.5)
154.8 (0.43)
186.0 (0.47)
185.3 (0.46)
169.5 (0.49)
I
2a;
1g;
2a;
2b;
n = 8
12
Cr
N
N
N
92.0 (4.61)
Cr2
Cr1
Cr
I
I
169.2 (0.47)
158.1 (0.63)
112.5 (63.4)
SmA
16
157.0 (0.63)
233.0 (0.45)
88.3 (67.6)
153.7 (0.42)
195.0a
187.0a
126.3 (31.9)
8
I
I
I
Cr
SmA
Cr2
Cr
N
106.2 (27.3)
102.9 (8.93)
232.2 (0.41)
219.1 (3.27)
120.7 (40.1)
SmA
SmA
Cr1
1i; 12
2b; 16
217.3 (3.21)
213.7 (6.16)
211.9 (6.09)
102.7 (30.7)
120.9 (12.2)
86.3 (6.08)
100.7 (78.8)
Cr1, Cr2¼crystalline phases, SmA¼Smectic A phase, N¼nematic phase, I¼isotropic phase.
a
Determined by optical microscope.
spectra of all compounds 1a–1l were very similar in shape
because of their structural similarity. The highest absorption
peaks of all compounds were found to be insensitive to the
substituents. Interestingly, they all occurred at ca. 348–
365 nm except for two compounds 1h and 1k, for which
230
180
130
80
N
SmA
Cr2
Cr1
0.6
1a
30
1b
0.5
1c
-20
1d
2a(n=8) 1g(n=12) 2a(n=16) 2b(n=8) 1i(n=12) 2b(n=16)
1f
0.4
compds
1h
1i
Figure 4. Bar graph showing the phase behavior of compounds 2a, 2b.
1l
0.3
be attributed to an enhanced dispersive interaction between
the terminal alkoxy chains. Similar mesomorphic behavior
was also observed in compounds 2b (n¼8, 16) and 1i
(n¼12), and compounds 2b with longer carbon chain length
(n¼12, 16) favored the formation of the more ordered SmA
over N phase.
0.2
0.1
0.0
300
350
400
450
500
wavelength (nm)
H2n+1CnO
O
0.6
0.5
0.4
0.3
0.2
0.1
0.0
N
N
X
1a
1e
1g
1j
n = 12
1g; X = OCH3
1h; X = NO2
1i; X = CN
1a; X = H
1b; X = F
1c; X = Cl
1d; X = Br
1e; X = CH3
1f; X = CF3
1k
1j; X = OH
1k; X = NMe2
1l; X = COOCH3
n = 8, 16
2a; X = OCH3
2b; X = CN
2.2. Optical properties
300
350
400
450
500
The UV–vis absorption and PL spectra of the compounds
1a–1l in CH2Cl2 solution are presented in Figures 5 and 6.
The data of lmax peaks of UV–vis absorption and PL spectra
in CH2Cl2 are listed in Table 3. The absorption and emission
wavelength (nm)
Figure 5. Normalized absorption spectra of compounds with electron-with-
drawing (top) and electron-donating substituents (bottom) in CH2Cl2.

9388
300
C.-S. Wang et al. / Tetrahedron 62 (2006) 9383–9392
quantum yields of some compounds in CH2Cl2 estimated
1a
1b
1c
1d
1f
with anthracene as a standard (4f¼0.27 in hexane) were rel-
atively low. For example, the yields were all ranged between
0.05 and 0.07%.
250
200
150
100
50
1h
1i
3. Conclusions
1l
The effect of polar substituents on a series of heterocyclic
benzoxazoles was systematically studied, and the formation
of mesophases was observed depending on the electronic
and/or the steric factors of the substituents. In general, the
mesophase observed was improved by introducing a polar
group. Most compounds (except 1j) exhibited nematic or
smectic A phases. Compounds with electron-donating sub-
stituents favored nematic phases, however, compounds
with electron-withdrawing substituents formed smectic A
phases. However, no linear correlation between the clearing
temperature or the temperature range of mesophases with
Hammett sp constants was found.
0
400
450
500
550
wavelength (nm)
1a
1e
1g
1j
150
125
100
75
1k
4. Experimental section
4.1. General
50
All chemicals and solvents were reagent grades from
Lancaster or Aldrich. Solvents were dried by standard
25
1
techniques. H and 13C NMR spectra were measured on
a Bruker AM-300. FTIR spectra were performed on Nicolet
Magna-IR 550 spectrometer. DSC thermographs were
carried out on a Mettler DSC 821 and calibrated with a pure
indium sample (mp¼156.60 ꢀC, 28.45 J/K), and all phase
transitions are determined by a scan rate of 10.0ꢀ/min. Opti-
cal polarized microscopy was carried out on an Zeiss Axia-
Plan equipped with a hot stage system of Mettler FP90/
FP82HT. The UV–vis absorption and fluorescence spectra
were obtained using HITACHI F-4500 or JASCO V-530
spectrometer, and all spectra were recorded at room temper-
ature. Elemental analysis for carbon, hydrogen, and nitrogen
were conducted on a Heraeus Vario EL-III elemental ana-
lyzer at National Taiwan University.
0
400
450
500
550
wavelength (nm)
Figure 6. Normalized PL spectra of compounds with electron-withdrawing
(top) and electron-donating substituents (bottom) in CH2Cl2.
the lmax were all shifted to longer wavelength, by ca. 31 and
33 nm, respectively. The electronic properties of the substit-
uents might not play an important role in the UV absorption
spectra. The photoluminescence spectra measured in
CH2Cl2 of compounds 1a–1l are also shown in Figure 6. A
similar trend was also observed in the photoluminescence
spectra. The emission peaks occurred at 386–409 nm except
for compounds 1k, which the lmax were slightly shifted to
longer wavelength, by ca. 80 nm. The dependence of PL
spectra is more sensitive to the electronic factor than that
of UV-absorption. However, it is worth noting that the
3-Alkoxyphenols, 5-alkoxy-2-nitrophenols, 2-amino-5-
alkoxyphenols, 5-alkoxy-2-[(4-nitro-benzylidene)amino]-
phenols, 6-alkoxy-2-(4-nitrophenyl)benzoxazoles, 4-(6-al-
koxybenzoxazol-2-yl)phenylamines were prepared by
similar procedures.5a
4.1.1. 3-Dodecyloxyphenol5a (n¼12). White solid, yield
1
Table 3. A summary of UV and PL peaks for compounds 1a–1l
60%. H NMR (CDCl3): d 0.87 (t, 3H, –CH3, J¼6.9 Hz),
1.25–1.43 (m, 18H, –CH2), 1.72–1.77 (m, 2H, –OCH2CH2),
3.90 (t, 2H, –OCH2, J¼6.6 Hz), 6.39–6.40 (m, 2H, Ar-H),
6.46–6.48 (m, 1H, Ar-H), 7.10 (t, 1H, Ar-H, J¼8.5 Hz).
13C NMR (CDCl3): d 14.14, 22.71, 26.05, 29.23, 29.37,
29.42, 29.60, 29.63, 29.66, 29.68, 31.94, 68.10, 102.08,
107.10, 107.59, 130.10, 156.68, 160.51.
Compounds sp
UV (nm)
PL (nm)
1a
1b
1c
1d
1f
0
273, 313 (sh), 348
0.15 273, 313 (sh), 348
0.24 277, 313 (sh), 348
0.26 277, 313, 352
382, 398
382, 398
387, 397
392
372, 389
0.53 267, 313, 356
1h
1i
1l
0.81 283 (sh), 309, 379
0.71 273, 309, 365
0.44 273, 309, 362
391 (sh), 409, 425 (sh)
391 (sh), 409, 425
372, 389
4.1.2. 5-Dodecyloxy-2-nitrophenol5a (n¼12). Yellow solid,
yield 25%. 1H NMR (CDCl3): d 0.86 (t, 3H, –CH3,
J¼6.9 Hz), 1.24–1.44 (m, 18H, –CH2), 1.75–1.80 (m, 2H,
–CH2), 3.99 (t, 2H, –OCH2, J¼6.5 Hz), 6.47–6.49 (m,
2H, Ar-H), 8.00 (d, 1H, Ar-H, J¼10.1 Hz), 11.02 (s, 1H,
1e
1j
1g
1k
ꢁ0.14 280, 313 (sh), 348
382, 398
ꢁ0.22 280 (sh), 313 (sh), 348 372, 386
ꢁ0.25 284 (sh), 313 (sh), 348 382, 398
ꢁ0.32 319 (sh), 381
478

C.-S. Wang et al. / Tetrahedron 62 (2006) 9383–9392
9389
Ar-OH). 13C NMR (CDCl3): d 14.12, 22.69, 25.87, 28.83,
29.27, 29.35, 29.41, 29.52, 29.57, 29.63, 29.64, 29.71,
31.92, 69.15, 101.80, 109.83, 126.91, 127.54, 158.01,
166.74.
(CDCl3): d 14.15, 22.71, 26.08, 29.28, 29.37, 29.43, 29.60,
29.62, 29.66, 29.68, 31.94, 68.88, 96.13, 112.74, 114.70,
117.27, 119.17, 128.93, 135.96, 149.26, 151.35, 157.19,
162.94.
4.1.3. 2-Amino-5-dodecyloxyphenol5a (n¼12). White
4.1.7. Benzylidene-4-(6-dodecyloxybenzoxazol-2-yl)phe-
nylamine (1a; n¼12, X¼H). A mixture of benzaldehyde
(0.10 mL, 0.001 mol) and 4-(6-dodecyloxybenzoxazol-2-
yl)phenylamine (0.4 g, 0.001 mol) was dissolved in
100 mL of absolute ethanol under nitrogen atmosphere.
The solution was refluxed for 10 min, and 0.5 mL of acetic
acid was slowly added. The solution was refluxed for 12 h.
The brown solids were then collected. The products isolated
as light yellow solids were obtained after recrystallization
1
solid, yield 85%. H NMR (CDCl3): d 0.86 (t, 3H, –CH3,
J¼6.9 Hz), 1.24–1.41 (m, 18H, –CH2), 1.68–1.73 (m, 2H,
–CH2), 3.84 (t, 2H, –OCH2, J¼6.6 Hz), 6.32 (dd, 1H, Ar-
H, J¼2.6 Hz, 8.6 Hz), 6.41 (d, 1H, Ar-H, J¼2.7 Hz), 6.75
(d, 1H, Ar-H, J¼8.6 Hz). 13C NMR (CDCl3): d 13.94,
22.59, 26.02, 29.25, 29.34, 29.51, 29.53, 29.56, 29.58,
31.85, 68.67, 102.72, 106.75, 120.85, 125.58, 148.06,
154.94.
1
from C2H5OH, yield 78%. H NMR (CDCl3): d 0.86 (t,
4.1.4. 5-Dodecyloxy-2-[(4-nitrobenzylidene)amino]phe-
3H, –CH3, J¼6.8 Hz), 1.25–1.47 (m, 18H, –CH2), 1.80–
1.83 (m, 2H, –CH2), 4.00 (t, 2H, –OCH2, J¼6.6 Hz), 6.94
(dd, 1H, Ar-H, J¼2.3 Hz, 8.7 Hz), 7.09 (d, 1H, Ar-H,
J¼2.3 Hz), 7.31 (d, 2H, Ar-H, J¼8.4 Hz), 7.47–7.50 (m,
3H, Ar-H), 7.60 (d, 1H, Ar-H, J¼8.7 Hz), 7.91–7.92 (m,
2H, Ar-H), 8.21 (d, 2H, Ar-H, J¼8.5 Hz), 8.49 (s, 1H,
–CHN). 13C NMR (CDCl3): d 14.13, 22.70, 26.08, 29.26,
29.36, 29.42, 29.60, 29.62, 29.66, 29.68, 31.94, 68.90,
96.08, 113.33, 119.81, 121.44, 124.88, 128.29, 128.87,
129.04, 131.81, 135.86, 135.94, 151.67, 154.42, 157.78,
161.20, 162.04. IR (KBr): 2919, 2848, 1625, 1614, 1505,
1496, 1490, 1467, 1281, 1226, 1150, 1053, 1004, 968,
861, 840, 800 cmꢁ1. MS (FAB): calcd for C32H39N2O2:
482.3, found: 483.4 [M+H]+. Anal. Calcd for C32H38N2O2:
C, 79.61; H, 7.79; N, 5.42. Found: C, 79.63; H, 7.94; N, 5.80.
1
nol5a (n¼12). Orange solid, yield 90%. H NMR (CDCl3):
d 0.86 (t, 3H, –CH3, J¼6.8 Hz), 1.25–1.44 (m, 18H,
–CH2), 1.74–1.79 (m, 2H, –CH2), 3.94 (t, 2H, –OCH2,
J¼6.5 Hz), 6.47 (dd, 1H, Ar-H, J¼2.4 Hz, 8.9 Hz), 6.55
(d, 1H, Ar-H, J¼2.5 Hz), 7.31 (d, 1H, Ar-H, J¼8.9 Hz),
7.40 (s, 1H, Ar-OH), 7.99 (d, 2H, Ar-H, J¼8.6 Hz), 8.29
(d, 2H, Ar-H, J¼8.6 Hz), 8.66 (s, 1H, Ar–CH]N–Ar).
13C NMR (CDCl3): d 14.12, 22.70, 26.02, 29.16, 29.36,
29.38, 29.58, 29.60, 29.65, 29.67, 31.93, 68.39, 100.57,
107.84, 116.45, 124.11, 127.46, 128.73, 141.71, 148.90,
149.83, 154.66, 161.56.
4.1.5. 6-Dodecyloxy-2-(4-nitrophenyl)benzoxazole5a (3;
n¼12). The mixture of 5-dodecyloxy-2-[(4-nitrobenzyli-
dene)amino]phenol (3.2 g, 0.007 mol) dissolved in 125 mL
of CH2Cl2 and Pb(OAc)4 (4.32 g, 0.01 mol) was refluxed
for 4 h. The solution was extracted with 100 mL of
CH2Cl2/H2O (1/2), and the organic layers were combined
and dried over MgSO4. The solution was concentrated and
the brown solids were recrystallized from C2H5OH. The
4.1.8. 4-(6-Dodecyloxybenzoxazol-2-yl)phenyl-(4-fluoro-
benzylidene)amine (1b; n¼12, X¼F). Light yellow solid,
yield 81%. 1H NMR (CDCl3): d 0.86 (t, 3H, –CH3,
J¼6.9 Hz), 1.25–1.48 (m, 18H, –CH2), 1.79–1.82 (m, 2H,
–CH2), 3.99 (t, 2H, –OCH2, J¼6.7 Hz), 6.93 (dd, 1H, Ar-
H, J¼2.3 Hz, 8.70 Hz), 7.07 (d, 1H, Ar-H, J¼2.2 Hz), 7.16
(t, 2H, Ar-H, J¼8.6 Hz), 7.29 (d, 2H, Ar-H, J¼8.5 Hz),
7.60 (d, 1H, Ar-H, J¼8.7 Hz), 7.91 (dd, 2H, Ar-H, J¼5.6,
8.6 Hz), 8.20 (d, 2H, Ar-H, J¼8.5 Hz), 8.44 (s, 1H,
–CHN). 13C NMR (CDCl3): d 14.13, 22.70, 26.07, 29.25,
29.36, 29.42, 29.59, 29.61, 29.65, 29.67, 31.93, 68.91,
96.09, 113.35, 115.99, 116.16, 119.81, 121.41, 124.96,
128.30, 131.02, 131.09, 132.31, 132.33, 135.85, 151.67,
154.15, 157.81, 159.58, 161.98, 163.95, 165.97. MS
(FAB): calcd for C32H38FN2O2: 500.3, found: 501.4
[M+H]+. Anal. Calcd for C32H37FN2O2: C, 76.77; H, 7.45;
N, 5.60. Found: C, 76.48; H, 7.59; N, 5.45.
1
light yellow solids were isolated with a yield of 85%. H
NMR (CDCl3): d 0.86 (t, 3H, –CH3, J¼6.9 Hz), 1.25–1.49
(m, 18H, –CH2), 1.74–1.84 (m, 2H, –CH2), 4.01 (t, 2H,
–OCH2, J¼6.5 Hz), 6.99 (dd, 1H, Ar-H, J¼2.28, 8.8 Hz),
7.09 (d, 1H, Ar-H, J¼2.2 Hz), 7.65 (d, 1H, Ar-H,
J¼8.8 Hz), 8.34 (m, 4H, Ar-H). 13C NMR (CDCl3):
d 14.12, 22.69, 26.05, 29.18, 29.35, 29.39, 29.58,
29.60, 29.64, 29.66, 31.92, 68.95, 95.92, 114.39, 120.67,
124.21, 127.82, 133.04, 135.61, 149.01, 152.07, 158.79,
159.70.
4.1.6. 4-(6-Dodecyloxybenzoxazol-2-yl)phenylamine5a
(4; n¼12). To a solution of 6-dodecyloxy-2-(4-nitrophenyl)-
benzoxazole (2.54 g, 0.006 mol) dissolved in absolute
C2H5OH (100 mL) was added powdered Pd/C (0.1 g,
0.001 mol) under nitrogen atmosphere. The solution was
gently refluxed for 10 min and then N2H4 (0.36 g,
0.007 mol) was added. The mixture was refluxed for 6 h.
The solution was filtered while hot. The filtrate was concen-
trated to give off-white solids. The products isolated as white
solids were obtained after recrystallization from C2H5OH,
yield 80%. 1H NMR (CDCl3): d 0.86 (t, 3H, –CH3,
J¼6.9 Hz), 1.22–1.46 (m, 18H, –CH2), 1.78–1.81 (m, 2H,
–CH2), 3.98 (t, 2H, –OCH2, J¼6.6 Hz), 6.73 (dd, 2H, Ar-
H, J¼1.57, 6.9 Hz), 6.88 (dd, 1H, Ar-H, J¼2.31, 8.7 Hz),
7.04 (d, 1H, Ar-H, J¼2.3 Hz), 7.53 (d, 1H, Ar-H,
J¼8.7 Hz), 7.97 (d, 2H, Ar-H, J¼8.6 Hz). 13C NMR
4.1.9. 4-Chlorobenzylidene-4-(6-dodecyloxybenzoxazol-
2-yl)phenylamine (1c; n¼12, X¼Cl). Light yellow solid,
yield 84%. 1H NMR (CDCl3): d 0.86 (t, 3H, –CH3,
J¼6.8 Hz), 1.25–1.48 (m, 18H, –CH2), 1.79–1.82 (m, 2H,
–CH2), 4.00 (t, 2H, –OCH2, J¼6.6 Hz), 6.94 (dd, 1H, Ar-
H, J¼2.29, 8.7 Hz), 7.08 (d, 1H, Ar-H, J¼2.2 Hz), 7.30 (t,
2H, Ar-H, J¼8.5 Hz), 7.45 (d, 2H, Ar-H, J¼8.4 Hz), 7.60
(d, 1H, Ar-H, J¼8.7 Hz), 7.85 (d, 2H, Ar-H, J¼8.4 Hz),
8.21 (d, 2H, Ar-H, J¼8.4 Hz), 8.45 (s, 1H, –CHN). 13C
NMR (CDCl3): d 14.13, 22.70, 26.07, 29.25, 29.36, 29.42,
29.59, 29.62, 29.65, 29.68, 31.93, 68.90, 96.08, 113.37,
114.69, 119.83, 121.43, 125.12, 128.30, 128.92, 129.19,
130.16, 134.43, 135.84, 137.86, 151.68, 153.96, 157.82,
159.60, 161.93. IR (KBr): 2918, 2852, 1612, 1503, 1489,

9390
C.-S. Wang et al. / Tetrahedron 62 (2006) 9383–9392
1472, 1361, 1321, 1230, 1223, 1148, 1052, 1011, 973, 852,
for C33H37F3N2O2: C, 71.78; H, 6.59; N, 4.82. Found: C,
71.98; H, 6.77; N, 5.09.
815 cmꢁ1
.
MS (FAB): calcd for C32H38ClN2O2:
516.3, found: 517.3 [M+H]+. Anal. Calcd for
C32H37ClN2O2: C, 74.33; H, 7.21; N, 5.42. Found: C,
74.35; H, 7.40; N, 5.31.
4.1.13. 4-(6-Dodecyloxybenzoxazol-2-yl)phenyl-(4-meth-
oxybenzylidene)amine (1g; n¼12, X¼OCH3). Light
1
yellow solid, yield 82%. H NMR (CDCl3): d 0.86 (t, 3H,
4.1.10. 4-Bromobenzylidene-4-(6-dodecyloxybenzoxazol-
2-yl)phenylamine (1d; n¼12, X¼Br). Light yellow solid,
yield 83%. 1H NMR (CDCl3): d 0.86 (t, 3H, –CH3,
J¼6.9 Hz), 1.25–1.48 (m, 18H, –CH2), 1.79–1.84 (m, 2H,
–CH2), 4.00 (t, 2H, –OCH2, J¼6.6 Hz), 6.94 (dd, 1H, Ar-
H, J¼2.3, 8.7 Hz), 7.07 (d, 1H, Ar-H, J¼2.3 Hz), 7.30 (d,
2H, Ar-H, J¼8.5 Hz), 7.59–7.62 (m, 3H, Ar-H), 7.78 (d,
2H, Ar-H, J¼8.4 Hz), 8.21 (d, 2H, Ar-H, J¼8.5 Hz), 8.43
(s, 1H, –CHN). 13C NMR (CDCl3): d 14.13, 22.70, 26.07,
29.25, 29.36, 29.41, 29.59, 29.61, 29.65, 29.67, 31.93,
68.91, 96.08, 119.83, 121.42, 125.15, 126.41, 128.31,
130.34, 132.16, 134.83, 135.84, 151.68, 153.94, 157.83,
159.73, 161.93. IR (KBr): 2915, 2848, 1625, 1612, 1583,
1566, 1487, 1470, 1397, 1320, 1299, 1219, 1147, 1114,
1068, 1054, 1009, 847, 820 cmꢁ1. MS (FAB): calcd for
C32H38BrN2O2: 560.2, found: 561.2 [M+H]+. Anal. Calcd
for C32H37BrN2O2: C, 68.44; H, 6.64; N, 4.99. Found: C,
68.67; H, 6.63; N, 4.73.
–CH3, J¼6.9 Hz), 1.25–1.48 (m, 18H, –CH2), 1.77–1.83
(m, 2H, –CH2), 3.86 (s, 3H, Ar-OCH3), 3.99 (t, 2H,
–OCH2, J¼6.5 Hz), 6.93 (dd, 1H, Ar-H, J¼2.4, 8.7 Hz),
6.98 (d, 2H, Ar-H, J¼8.8 Hz), 7.07 (d, 1H, Ar-H,
J¼2.3 Hz), 7.28 (d, 2H, Ar-H, J¼7.0 Hz), 7.59 (d, 1H,
Ar-H, J¼8.70 Hz), 7.85 (d, 2H, Ar-H, J¼8.73 Hz), 8.19
(d, 2H, Ar-H, J¼8.53 Hz), 8.40 (s, 1H, –CHN). 13C NMR
(CDCl3): d 14.13, 22.70, 26.08, 29.26, 29.36, 29.42, 29.60,
29.62, 29.66, 29.68, 31.93, 55.47, 68.90, 96.08, 113.28,
114.30, 119.75, 121.46, 124.48, 128.27, 128.99, 130.82,
135.88, 151.66, 154.74, 157.73, 160.43, 162.15, 162.61.
IR (KBr): 2920, 2852, 1607, 1591, 1574, 1511, 1488,
1470, 1320, 1301, 1256, 1223, 1172, 1148, 1052, 1029,
1005, 860, 836, 815 cmꢁ1
. MS (FAB): calcd for
C33H41N2O3: 512.3, found: 513.4 [M+H]+. Anal. Calcd for
C33H40N2O3: C, 77.14; H, 7.59; N, 5.20. Found: C, 77.31;
H, 7.86; N, 5.46.
4.1.14. [4-(6-Dodecyloxybenzoxazol-2-yl)phenyl]-(4-ni-
trobenzylidene)amine (1h; n¼12, X¼NO2). Bright yellow
4.1.11. 4-(6-Dodecyloxybenzoxazol-2-yl)phenyl-(4-meth-
ylbenzylidene)amine (1e; n¼12, X¼CH3). Light yellow
1
solid, yield 85%. H NMR (CDCl3): d 0.86 (t, 3H, –CH3,
1
solid, yield 82%. H NMR (CDCl3): d 0.86 (t, 3H, –CH3,
J¼6.9 Hz), 1.25–1.48 (m, 18H, –CH2), 1.79–1.86 (m, 2H,
–CH2), 4.00 (t, 2H, –OCH2–, J¼6.6 Hz), 6.94 (dd, 1H, Ar-
H, J¼2.3, 8.7 Hz), 7.07 (d, 1H, Ar-H, J¼2.3 Hz), 7.35 (d,
2H, Ar-H, J¼8.5 Hz), 7.61 (d, 1H, Ar-H, J¼8.7 Hz), 8.08
(d, 2H, Ar-H, J¼8.8 Hz), 8.24 (d, 2H, Ar-H, J¼8.5 Hz),
8.33 (d, 2H, Ar-H, J¼8.7 Hz), 8.58 (s, 1H, –CHN). 13C
NMR (CDCl3): d 14.12, 22.70, 26.07, 29.24, 29.36, 29.41,
29.59, 29.61, 29.65, 29.67, 31.93, 68.92, 96.08, 113.49,
119.93, 121.54, 124.10, 125.95, 128.37, 129.63, 135.79,
141.22, 149.53, 151.72, 153.09, 157.95, 158.24, 161.68.
IR (KBr): 2925, 2848, 1714, 1680, 1623, 1611, 1583,
1574, 1551, 1488, 1471, 1362, 1345, 1323, 1284, 1221,
1150, 1113, 1004, 971, 858, 846, 828 cmꢁ1. MS (FAB):
calcd for C32H38N3O4: 527.3, found: 528.3 [M+H]+. Anal.
Calcd for C32H37N3O4: C, 72.84; H, 7.07; N, 7.96. Found:
C, 73.01; H, 6.99; N, 7.81.
J¼6.7 Hz), 1.25–1.48 (m, 18H, –CH2), 1.79–1.82 (m, 2H,
–OCH2CH2), 2.41 (s, 3H, Ar-CH3), 3.99 (t, 2H, –OCH2,
J¼6.5 Hz), 6.93 (dd, 1H, Ar-H, J¼2.0, 8.65 Hz), 7.07 (d,
1H, Ar-H, J¼1.9 Hz), 7.27–7.30 (m, 4H, Ar-H), 7.60 (d,
2H, Ar-H, J¼8.7 Hz), 7.80 (d, 2H, Ar-H, J¼7.9 Hz), 8.20
(d, 2H, Ar-H, J¼8.4 Hz), 8.44 (s, 1H, –CHN). 13C NMR
(CDCl3): d 14.14, 21.70, 22.71, 26.08, 29.26, 29.37, 29.42,
29.60, 29.62, 29.66, 29.68, 31.94, 68.89, 96.07, 113.30,
119.78, 121.46, 124.67, 128.27, 129.05, 129.62, 133.40,
135.86, 142.42, 151.66, 154.62, 157.75, 161.14, 162.10.
IR (KBr): 2919, 2848, 1628, 1507, 1489, 1466, 1347,
1282, 1227, 1152, 1137, 1052, 1008, 969, 861, 844, 810,
800 cmꢁ1. MS (FAB): calcd for C32H41N2O2: 496.3,
found: 497.3 [M+H]+. Anal. Calcd for C32H40N2O2:
C, 79.80; H, 8.12; N, 5.64. Found: C, 79.84; H, 8.57;
N, 5.30.
4.1.15. 4-{[4-(6-Dodecyloxybenzoxazol-2-yl)phenyl-
imino]methyl}benzonitrile (1i; n¼12, X¼CN). Light
yellow solid, yield 86%. 1H NMR (CDCl3): d 0.86 (t,
3H, –CH3, J¼6.9 Hz), 1.25–1.48 (m, 18H, –CH2), 1.80–
1.83 (m, 2H, –CH2), 4.00 (t, 2H, –OCH2, J¼6.6 Hz),
6.93 (dd, 1H, Ar-H, J¼2.3, 8.7 Hz), 7.08 (d, 1H, Ar-H,
J¼2.3 Hz), 7.29 (d, 2H, Ar-H, J¼9.6 Hz), 7.59–7.62 (m,
3H, Ar-H), 7.77 (d, 2H, Ar-H, J¼8.4 Hz), 8.21 (d, 2H,
Ar-H, J¼8.5 Hz), 8.43 (s, 1H, –CHN). 13C NMR
(CDCl3): d 14.13, 22.70, 26.07, 29.24, 29.36, 29.41,
29.59, 29.61, 29.65, 29.67, 31.93, 68.92, 96.08, 113.47,
114.82, 118.35, 119.91, 121.50, 125.81, 128.36, 129.30,
132.62, 135.80, 139.63, 151.71, 153.21, 157.93, 158.73,
161.72. IR (KBr): 2921, 2849, 1714, 1681, 1626, 1613,
1495, 1488, 1467, 1361, 1281, 1223, 1152, 1135, 1050,
1010, 971, 861, 847, 799 cmꢁ1. MS (FAB): calcd for
C33H38N3O2: 507.3, found: 508.3 [M+H]+. Anal. Calcd
for C33H37N3O2: C, 78.07; H, 7.35; N, 8.28. Found: C,
78.04; H, 7.23; N, 8.27.
4.1.12. 4-(6-Dodecyloxybenzoxazol-2-yl)phenyl-(4-tri-
fluoromethylbenzylidene)amine (1f; n¼12, X¼CF3).
1
Light yellow solid, yield 85%. H NMR (CDCl3): d 0.86
(t, 3H, –CH3, J¼6.9 Hz), 1.25–1.48 (m, 18H, –CH2),
1.79–1.82 (m, 2H, –CH2), 3.99 (t, 2H, –OCH2, J¼6.5 Hz),
6.94 (dd, 1H, Ar-H, J¼2.20, 8.7 Hz), 7.07 (d, 1H, Ar-H,
J¼2.1 Hz), 7.32 (d, 2H, Ar-H, J¼8.4 Hz), 7.60 (d, 1H, Ar-
H, J¼8.7 Hz), 7.73 (d, 2H, Ar-H, J¼8.1 Hz), 8.02 (d, 2H,
Ar-H, J¼8.0 Hz), 8.22 (d, 2H, Ar-H, J¼8.5 Hz), 8.52 (s,
1H, –CHN). 13C NMR (CDCl3): d 14.13, 22.70, 26.07,
29.25, 29.37, 29.42, 29.60, 29.62, 29.66, 29.68, 31.94,
68.89, 96.05, 113.41, 119.87, 121.47, 122.75, 124.91,
125.48, 125.80, 125.83, 128.32, 129.17, 132.97, 133.23,
135.80, 138.95, 151.69, 153.57, 157.87, 159.37, 161.82.
IR (KBr): 2918, 2849, 1623, 1610, 1575, 1487, 1470,
1361, 1332, 1299, 1225, 1178, 1169, 1148, 1131, 1106,
1069, 1014, 860, 842, 816 cmꢁ1. MS (FAB): calcd for
C33H38F3N2O2: 550.3, found: 551.3 [M+H]+. Anal. Calcd

C.-S. Wang et al. / Tetrahedron 62 (2006) 9383–9392
9391
4.1.16. [4-(6-Dodecyloxybenzoxazol-2-yl)phenyl]-(4-di-
methylaminebenzylidene)amine (1k; n¼12, X¼NMe2).
–OCH2, J¼6.6 Hz), 6.93 (dd, 1H, Ar-H, J¼2.3, 8.71 Hz),
6.98 (d, 2H, Ar-H, J¼8.7 Hz), 7.08 (d, 1H, Ar-H,
J¼2.3 Hz), 7.29 (d, 2H, Ar-H, J¼8.5 Hz), 7.60 (d, 1H, Ar-
H, J¼8.7 Hz), 7.86 (d, 2H, Ar-H, J¼8.7 Hz), 8.19 (d, 2H,
Ar-H, J¼8.9 Hz), 8.41 (s, 1H, –CHN). 13C NMR (CDCl3):
d 14.13, 22.70, 26.08, 29.26, 29.37, 29.42, 29.60, 29.62,
29.68, 29.71, 31.94, 55.47, 68.89, 96.08, 113.28, 114.31,
119.76, 121.46, 124.51, 128.27, 128.92, 130.85, 135.89,
151.66, 157.73, 160.41, 162.14. Anal. Calcd for
C37H48N2O3: C, 78.13; H, 8.51; N, 4.93. Found: C, 76.80;
H, 8.99; N, 4.73.
1
Yellow solid, yield 85%. H NMR (CDCl3): d 0.86 (t, 3H,
–CH3, J¼6.9 Hz), 1.25–1.48 (m, 18H, –CH2), 1.79–1.82
(m, 2H, –CH2), 3.05 (s, 6H, –NMe2), 3.99 (t, 2H, –OCH2,
J¼6.6 Hz), 6.72 (d, 2H, Ar-H, J¼8.9 Hz), 6.92 (dd, 1H,
Ar-H, J¼2.3, 8.70 Hz), 7.07 (d, 1H, Ar-H, J¼2.3 Hz), 7.28
(d, 2H, Ar-H, J¼8.4 Hz), 7.59 (d, 1H, Ar-H, J¼8.7 Hz),
7.77 (d, 2H, Ar-H, J¼8.5 Hz), 8.18 (d, 2H, Ar-H,
J¼8.5 Hz), 8.34 (s, 1H, –CHN). 13C NMR (CDCl3):
d 14.14, 22.71, 26.08, 29.27, 29.37, 29.43, 29.60, 29.62,
29.66, 29.68, 31.94, 40.16, 68.89, 96.08, 111.56, 113.19,
119.68, 121.54, 123.86, 124.04, 128.24, 130.84, 135.94,
151.64, 152.79, 155.36, 157.64, 160.84, 162.36. IR (KBr):
2920, 2846, 1626, 1609, 1583, 1552, 1527, 1489, 1470,
1434, 1415, 1361, 1283, 1225, 1178, 1164, 1152, 1131,
1045, 1018, 1008, 941, 862, 839, 816 cmꢁ1. MS (FAB):
calcd for C34H44N3O2: 525.3, found: 526.4 [M+H]+. Anal.
Calcd for C34H43N3O2: C, 77.68; H, 8.24; N, 7.99. Found:
C, 77.63; H, 8.39; N, 8.31.
4.1.20. 4-{[4-(6-Octyloxybenzoxazol-2-yl)phenylimino]-
methyl}benzonitrile (2b; n¼8, X¼CN). Light yellow solid,
yield 80%. 1H NMR (CDCl3): d 0.88 (t, 3H, –CH3,
J¼6.9 Hz), 1.28–1.49 (m, 10H, –CH2), 1.78–1.83 (m, 2H,
–OCH2), 4.00 (t, 2H, –OCH2, J¼6.6 Hz), 6.94 (dd, 1H,
Ar-H, J¼2.3, 8.7 Hz), 7.08 (d, 1H, Ar-H, J¼2.3 Hz), 7.33
(d, 2H, Ar-H, J¼6.1 Hz), 7.61 (d, 1H, Ar-H, J¼8.7 Hz),
7.77 (d, 2H, Ar-H, J¼8.3 Hz), 8.02 (d, 2H, Ar-H,
J¼8.3 Hz), 8.23 (d, 2H, Ar-H, J¼8.8 Hz), 8.53 (s, 1H,
–CHN). 13C NMR (CDCl3): d 14.11, 22.67, 26.08, 29.25,
29.37, 31.83, 68.92, 96.07, 113.47, 114.70, 114.83,
118.36, 119.91, 121.50, 125.81, 128.36, 129.30, 129.89,
132.63, 132.91, 135.80, 139.63, 151.72, 153.22, 157.93,
158.73, 161.72. Anal. Calcd for C29H29N3O2: C, 77.13; H,
6.47; N, 9.31. Found: C, 77.01; H, 6.45; N, 9.15.
4.1.17. 4-{[4-(6-Dodecyloxybenzoxazol-2-yl)phenyl-
imino]methyl}benzoic acid methyl ester (1l; n¼12,
1
X¼COOCH3). Light yellow solid, yield 78%. H NMR
(CDCl3): d 0.86 (t, 3H, –CH3, J¼6.9 Hz), 1.25–1.46 (m,
18H, –CH2), 1.79–1.82 (m, 2H, –CH2), 3.93 (s, 3H, Ar–
COOCH3–), 3.99 (t, 2H, –OCH2, J¼6.6 Hz), 6.93 (dd, 1H,
Ar-H, J¼2.3, 8.7 Hz), 7.07 (d, 1H, Ar-H, J¼2.3 Hz), 7.32
(d, 2H, Ar-H, J¼8.5 Hz), 7.60 (d, 1H, Ar-H, J¼8.7 Hz),
7.97 (d, 2H, Ar-H, J¼8.3 Hz), 8.13 (d, 2H, Ar-H,
J¼8.3 Hz), 8.21 (d, 2H, Ar-H, J¼8.5 Hz), 8.53 (s, 1H,
–CHN). 13C NMR (CDCl3): d 14.14, 22.70, 26.07, 29.25,
29.37, 29.42, 29.60, 29.62, 29.66, 29.68, 31.93, 52.39,
68.89, 96.05, 113.40, 119.86, 121.49, 125.39, 128.85,
130.05, 132.68, 135.81, 139.66, 151.68, 153.76, 157.85,
159.92, 161.86, 166.51. IR (KBr): 2954, 2919, 2847, 1717,
1626, 1489, 1466, 1434, 1347, 1285, 1226, 1152, 1136,
1115, 1052, 1010, 968, 957, 854, 841, 800 cmꢁ1. MS
(FAB): calcd for C34H41N2O4: 540.3, found: 541.3
[M+H]+. Anal. Calcd for C34H40N2O4: C, 75.53; H, 7.46;
N, 5.18. Found: C, 75.36; H, 7.35; N, 4.90.
4.1.21. 4-{[4-(6-Hexadecyloxybenzoxazol-2-yl)phenyl-
imino]methyl}benzonitrile (2b; n¼16, X¼CN). Light
1
yellow solid, yield 87%. H NMR (CDCl3): d 0.86 (t, 3H,
–CH3, J¼6.9 Hz), 1.24–1.48 (m, 26H, –CH2), 1.79–1.82
(m, 2H, –OCH2), 3.99 (t, 2H, –OCH2, J¼6.5 Hz), 6.93
(dd, 1H, Ar-H, J¼2.3, 8.7 Hz), 7.07 (d, 1H, Ar-H,
J¼2.2 Hz), 7.32 (d, 2H, Ar-H, J¼8.5 Hz), 7.60 (d, 1H, Ar-
H, J¼8.7 Hz), 7.75 (d, 2H, Ar-H, J¼8.2 Hz), 8.00 (d, 2H,
Ar-H, J¼8.3 Hz), 8.22 (d, 2H, Ar-H, J¼8.5 Hz), 8.50 (s,
1H, Ar-CHN). 13C NMR (CDCl3): d 14.13, 22.70, 26.07,
29.25, 29.37, 29.42, 29.59, 29.62, 29.67, 29.71, 31.94,
68.90, 96.06, 113.46, 114.79, 118.34, 119.90, 121.50,
125.79, 128.34, 129.29, 132.60, 135.78, 139.61, 151.70,
153.17, 157.92, 158.69, 161.70. Anal. Calcd for
C37H45N3O2: C, 78.83; H, 8.05; N, 7.45. Found: C, 78.83;
H, 8.16; N, 7.34.
4.1.18. (4-Methoxybenzylidene)-[4-(6-octyloxybenzoxa-
zol-2-yl)phenyl]amine (2a; n¼8, X¼OCH3). Light yellow
1
solid, yield 77%. H NMR (CDCl3): d 0.87 (t, 3H, –CH3,
J¼6.9 Hz), 1.28–1.47 (m, 10H, –CH2), 1.79–1.82 (m, 2H,
–CH2), 3.86 (s, 3H, Ar-OCH3), 3.99 (t, 2H, –OCH2,
J¼6.5 Hz), 6.93 (dd, 1H, Ar-H, J¼2.3, 8.7 Hz), 6.98 (d,
2H, Ar-H, J¼8.7 Hz), 7.07 (d, 1H, Ar-H, J¼2.3 Hz), 7.28
(d, 2H, Ar-H, J¼6.7 Hz), 7.59 (d, 1H, Ar-H, J¼8.7 Hz),
7.85 (d, 2H, Ar-H, J¼8.7 Hz), 8.19 (d, 2H, Ar-H,
J¼8.5 Hz), 8.40 (s, 1H, –CHN). 13C NMR (CDCl3):
d 14.12, 22.67, 26.08, 29.26, 29.38, 31.83, 55.47, 68.90,
96.08, 113.28, 114.30, 119.75, 121.47, 124.48, 128.27,
128.98, 130.82, 135.88, 151.66, 154.74, 157.73, 160.44,
162.15, 162.62. Anal. Calcd for C29H32N2O3: C, 76.29; H,
7.06; N, 6.14. Found: C, 75.94; H, 7.20; N, 5.91.
Acknowledgements
We thank the National Science Council of Taiwan, ROC and
the UST for funding (NSC-94-2113-M-008-011) in gener-
ous support of this work.
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