Synthesis of fluorescent trisubstituted oxazoles via a facile tandem Staudinger/aza-Wittig/isomerization reaction

Article abstract of DOI:10.1016/j.dyepig.2016.12.040

A new facile synthesis of trisubstituted oxazoles starting from azides was developed. The reactions of azides with triphenyl phosphine afforded the corresponding 2,4,5-trisubstituted oxazole derivatives via tandem Staudinger, aza-Wittig and isomerization reaction either thermally or under basic conditions. Properties of the oxazole derivatives were surveyed and some of the examples showed reasonable fluorescence. The greatest fluorescence intensity was observed when the 2- and the 5- substituents on the oxazole ring were aromatic groups (with ε?=?2.3–3.0?×?10⁴?mol^?1?dm³?cm^?1 and Φ?=?0.25–0.29 relative to quinine sulphate). However, the fluorescence intensity was diminished when either the 2- or the 5-substituent was H or alkyl.

Full text of DOI:10.1016/j.dyepig.2016.12.040

Dyes and Pigments 139 (2017) 440e447
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Synthesis of fluorescent trisubstituted oxazoles via a facile tandem
Staudinger/aza-Wittig/isomerization reaction
,
, *
Hai Xie a b, Yong Rao a, Ming-Wu Ding a
a Key Laboratory of Pesticide & Chemical Biology of Ministry of Education, Central China Normal University, Wuhan 430079, PR China
b College of Chemistry & Chemical Engineering, Shanxi Datong University, Shanxi 037009, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A new facile synthesis of trisubstituted oxazoles starting from azides was developed. The reactions of
azides with triphenyl phosphine afforded the corresponding 2,4,5-trisubstituted oxazole derivatives via
tandem Staudinger, aza-Wittig and isomerization reaction either thermally or under basic conditions.
Properties of the oxazole derivatives were surveyed and some of the examples showed reasonable
fluorescence. The greatest fluorescence intensity was observed when the 2- and the 5- substituents on
Received 14 December 2016
Accepted 17 December 2016
Available online 23 December 2016
Keywords:
Oxazole
Azide
Aza-Wittig reaction
Fluorescence property
Isomerization
the oxazole ring were aromatic groups (with ε ¼ 2.3e3.0 ꢀ 104 molꢁ1 dm3 cmꢁ1 and
F
¼ 0.25e0.29
relative to quinine sulphate). However, the fluorescence intensity was diminished when either the 2- or
the 5-substituent was H or alkyl.
© 2016 Published by Elsevier Ltd.
1. Introduction
by the reaction of aromatic ketones with nitriles in the presence of
molecular iodine and oxone [14]. Meanwhile, our group developed
Oxazoles, especially fully substituted oxazoles, have been the
focus of great interest because of their remarkable biological
properties. Some oxazole derivatives were recently found to be
good fatty acid amide hydrolase (FAAH) inhibitors [1], complement
C3a receptor agonists [2], potent and selective sphingosine-1-
phosphate agonists [3], anti-HIV agents [4], anti-tuberculotic
agents [5] and antifungal agents [6]. The oxazole nucleus is also
ubiquitous in natural products such as pyrronazol [7], ulapualides
[8], diazonamides [9], and rhizopodin [10]. In addition, oxazole
derivatives have exhibited a high potential as efficient lumino-
phores for liquid and fluorescent probes and markers in biological
or supramolecular systems [11]. Owing to the structural diversity
and complexity of these oxazoles, many new method have been
developed for their synthesis to deduce structure-activity re-
lationships and discover new analogues with improved properties
[12e19]. For example, Jiang et al. recently reported a palladium-
catalyzed sequential reaction to prepare oxazole derivatives from
amides and ketones [12]. N-Iodosuccinimide (NIS) mediated cycli-
zation of propargylamides was also used to synthesize the oxazole
derivatives in good yields [13]. Tojo et al. reported a one-pot
preparation of 2,5-disubstituted and 2,4,5-trisubstituted oxazoles
reaction sequences to prepare oxazoles from iminophosphoranes
[20]. In spite of the above advances, there is still a need for a
convenient synthesis of 2,4,5-trisubstituted oxazoles from readily
available starting materials.
The aza-Wittig reactions have received attention in synthetic
organic chemistry because of their ability to create structurally
diverse heterocyclic compounds from simple precursors in an
efficient manner [21]. Continuing our interest in the synthesis of N-
heterocycles via the aza-Wittig reaction [22], we wish to report
herein a facile synthesis of 2,4,5-trisubstituted oxazoles by a tan-
dem Staudinger/aza-Wittig/isomerization reaction starting from
easily accessible vinyl azides 3. We also surveyed their fluorescence
properties in order to test their possible use as fluorescent probes.
2. Results and discussion
Vinyl azide 1 was obtained easily either from the condensation
of the a-azidoketone with aromatic aldehydes in the presence of
piperidinium acetate, or from the reaction of dibromides with so-
dium azide according to literature reports [23,24]. Reduction of the
vinyl azides 1 with NaBH4 in methanol at 0 ꢂC gave the azides 2 in
good yields (81e92%, Scheme 1, Table 1). The reaction of azides 2
with various acyl chlorides in the presence of NEt3 produced the
azides 3 in 70e90% yields (Scheme 1, Table 2).
* Corresponding author.
E-mail address: mwding@mail.ccnu.edu.cn (M.-W. Ding).
When azides 3 were treated with triphenylphosphine in dry
http://dx.doi.org/10.1016/j.dyepig.2016.12.040
0143-7208/© 2016 Published by Elsevier Ltd.

H. Xie et al. / Dyes and Pigments 139 (2017) 440e447
441
spectrum of 6a shows a molecular ion peak at m/z 269 with 95%
abundance.
O
OH
R1
R3COCl
NEt3
NaBH4
R2
R1
R2
The fluorescence properties of compounds 6a, 6d, 6h, 6l, 6n, and
6p were studied in ethanol. These compounds present comparable
molar absorption coefficients with literature reported oxazoles
[11c,e]. The fluorescence spectra of these compounds are presented
in Fig. 1. The fluorescence intensity of the compounds 6d, 6h, 6l and
6n is far stronger than that of the compounds 6a and 6p. This im-
plies that stronger fluorescence intensity is resulted as both of R1
and R3 on oxazole ring are aromatic substituents (compounds 6d,
6h, 6l and 6n) which present a more extended aromatic system.
However, the fluorescence intensity is reduced when R1 or R3 is a
hydrogen or alkyl substituent (compounds 6a and 6p). The
maximum absorption (labs) and emission (lem) wavelengths, molar
absorption coefficients (ε), and quantum yield (Fs) of the oxazole
derivatives are presented in Table 3.
N3
N3
2
1
R1
O
O
R2
R2
O
Ph3P
R3
N
R1
Ph3P
N3
O
R3
4
3
3. Conclusion
O
R1
R3
O
R1
R2
R3
In summary, we have developed an efficient synthetic proced-
ure to access 2,4,5-trisubstituted oxazoles. Our method has a sig-
nificant implication for the synthesis of a variety of fully substituted
oxazole derivatives. In addition, these reactions have the advan-
tages of mild reaction conditions, easily accessible starting mate-
rials and good yields. Furthermore, the photophysical properties
carried out with some of the oxazole derivatives indicate that they
may be useful in future fluorescent probes.
N
N
or NaH
R2
6
5
Scheme 1. Preparation of vinyl azides 2, 3 and oxazoles 6.
Table 1
Preparation of vinyl azides 2.
4. Experimental
R1
R2
Yielda(%)
Column chromatography purifications were performed under
“flash” conditions using 400e630 mesh silica gel, except where
otherwise noted. Analytical thin-layer chromatography (TLC) was
carried out on silica gel 60 F254 plates, which were visualized by
exposure to ultraviolet light.
2a
2b
2c
2d
2e
H
Ph
Ph
4-ClC6H4
Ph
Ph
4-ClC6H4
Ph
Ph
92
84
87
90
81
Instrumentation: Melting points were determined using a X-4
model apparatus and were uncorrected. IR spectra were recorded
on a PE-983 infrared spectrometer as KBr pellets with absorption in
cmꢁ1. MS were measured on a Finnigan Trace MS spectrometer. 1H
NMR spectra were recorded in CDCl3 on a Varian Mercury Plus 600
O
2f
CH3
Ph
89
a
Isolated yields based on azides 1.
(600 MHz) spectrometer and chemical shifts (
using (CH3)4Si as an internal reference (
were taken on a Vario EL III elementary analysis instrument.
d) were given in ppm
¼ 0). Elemental analyses
d
toluene at room temperature, and then at reflux for 4e10 h, the
oxazole derivatives 6c-6o were isolated directly in good yields in
most cases (61e85%, Scheme 1, Table 2, entry 2e15). Though a
mixture of 5 and 6 often resulted, in other cases (Scheme 1, Table 2,
entry 1e2 and entry 16e19), compounds 6a-6b and 6p-6s could be
obtained in 71e84% overall yields by further treating the reaction
mixture with sodium hydride at room temperature. The tandem
formation of oxazoles 6 can be viewed as an initial Staudinger re-
action between the azide 5 and triphenylphosphine to create the
iminophosphorane intermediate 4. Further intramolecular aza-
Wittig reaction of 4 produces dihydrooxazoles 5, in which an
isomerization reaction takes place to give the aromatized oxazoles
6 under either heating or basic conditions. It's noteworthy that the
reaction proceeds under mild conditions to give various 2,4,5-
trisubstituted oxazoles 6, and the overall transformation is run in
a simple one-pot procedure from azides 3 in good overall yields.
4.1. Synthetic details
4.1.1. Preparation of azides 2
A methanol (20 mL) solution of vinyl azides 1 (8 mmol) was
cooled to 0 ꢂC and NaBH4 (0.15 g, 4 mmol) was added. Vigorous gas
evolution occurred. After stirred for 10 min at 0 ꢂC, the reaction
mixture was poured into 1 N HCl (30 mL) and extracted with ethyl
acetate (20 mL ꢀ 3). The combined organic layer was washed with
brine (20 mL) and dried over anhydrous Na2SO4. The solution was
concentrated in vacuo and the residue was purified by chroma-
tography eluting with EtOAc/petroleum ether (1:1) to give com-
pounds 2.
The structure of the 2,4,5-trisubstituted oxazoles
6 was
4.1.1.1. 2-Azido-3-phenylprop-2-en-1-ol (2a). light yellow solid
(1.29 g, 92%). mp. 39e41 ꢂC. IR (KBr): 3386, 2106, 1644, 1491,
confirmed from their spectroscopic data. For example, the 1H NMR
spectral data of 6a shows a singlet at 3.93 ppm due to the hydrogen
of CH2. The signals attributable to the protons of the aromatic ring
are found at 7.94e7.24 ppm as multiplets. The 13C NMR spectrum
data in 6a show the signals of the C-2 carbon of the oxazole at
160.7 ppm. The signals of CH2 are found at 33.0 ppm. The mass
1261 cmꢁ1. 1H NMR (CDCl3, 600 MHz):
d
¼ 7.62 (d, J ¼ 5.4 Hz, 2H, Ar-
H), 7.33e7.23 (m, 3H, Ar-H), 5.81 (s, 1H, ¼CH), 4.47 (s, 2H, CH2), 1.91
(br, 1H, OH). 13C NMR (CDCl3, 150 MHz):
d
¼ 134.3, 134.1, 128.8,
128.1, 127.3, 116.3, 64.6. Elemental Anal. Calcd for C9H9N3O: C,
61.70; H, 5.18; N, 23.99. Found: C, 61.93; H, 5.38; N, 23.81.

442
H. Xie et al. / Dyes and Pigments 139 (2017) 440e447
Table 2
Preparation of vinyl azides 3 and oxazoles 6.
Entry
R1
R2
R3
Compd
Yielda (%)
Compd
Yieldb (%)
1
2
3
4
5
6
7
8
H
H
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
4-ClC6H4
4-ClC6H4
4-ClC6H4
Ph
Ph
Ph
Ph
Ph
Ph
Ph
4-ClC6H4
4-ClC6H4
4-ClC6H4
Ph
Ph
Ph
4-ClC6H4
4-NO2C6H4
Ph
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
85
90
87
83
82
80
86
88
90
89
85
89
81
70
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
6m
6n
74
82
69
78
69
71
85
78
72
68
83
76
72
69
4-ClC6H4
4-NO2C6H4
4-CH3C6H4
2-ClC6H4
4-ClC6H4
2-ClC6H4
4-NO2C6H4
4-NO2C6H4
4-ClC6H4
2-ClC6H4
4-ClC6H4
9
10
11
12
13
14
Ph
O
15
Ph
4-NO2C6H4
3o
73
6o
61
O
16
17
18
19
Ph
4-ClC6H4
Ph
Ph
Ph
Ph
Ph
CH3
CH3
n-Pr
Ph
3p
3q
3r
3s
72
76
79
87
6p
6q
6r
6s
74
71
79
84
CH3
a
Isolated yields based on azides 2.
Isolated yields based on azides 3.
b
4.1.1.2. 2-Azido-1,3-diphenylprop-2-en-1-ol (2b). yellow oil (1.69 g,
600 MHz):
d
¼ 7.62 (d, J ¼ 7.2 Hz, 2H, Ar-H), 7.48 (d, J ¼ 7.2 Hz, 2H,
84%). IR (KBr): 3373, 2107, 1638, 1492, 1259 cmꢁ1. 1H NMR (CDCl3,
Ar-H), 7.38e7.19 (m, 6H, Ar-H), 5.87 (s, 1H, ¼CH), 5.48 (s, 1H, OCH),
2.76 (br, 1H, OH). 13C NMR (CDCl3, 150 MHz):
d
¼ 139.2, 136.0, 134.3,
129.0, 128.9, 128.8, 128.6, 128.3, 128.1, 127.4, 126.3, 116.3, 76.3.
Elemental Anal. Calcd for C15H13N3O: C, 71.70; H, 5.21; N, 16.72.
Found: C, 71.75; H, 5.45; N, 16.81.
4.1.1.3. 2-Azido-3-(4-chlorophenyl)-1-phenylprop-2-en-1-ol
light yellow oil (1.98 g, 87%). IR (KBr): 3359, 2109, 1638, 1490,
1282 cmꢁ1. 1H NMR (CDCl3, 600 MHz):
(2c).
d
¼ 7.63 (d, J ¼ 7.8 Hz, 2H, Ar-
H), 7.47 (d, J ¼ 7.8 Hz, 2H, Ar-H), 7.38e7.23 (m, 5H, Ar-H), 5.90 (s,
1H, ¼CH), 5.54 (s, 1H, OCH), 2.56 (s, 1H, OH). 13C NMR (CDCl3,
150 MHz):
d
¼ 139.1, 136.6, 132.8, 130.2, 128.8, 128.5, 128.3, 126.4,
114.9, 76.1. Elemental Anal. Calcd for C15H12ClN3O: C, 63.05; H, 4.23;
N, 14.71. Found: C, 63.27; H, 4.34; N, 14.64.
4.1.1.4. 2-Azido-1-(4-chlorophenyl)-3-phenylprop-2-en-1-ol
light yellow solid (2.05 g, 90%). mp. 97e99 ꢂC. IR (KBr): 3451, 2103,
1630, 1490, 1281 cmꢁ1 1H NMR (CDCl3, 600 MHz):
(2d).
.
d
¼ 7.60 (d,
J ¼ 7.8 Hz, 2H, Ar-H), 7.39 (d, J ¼ 8.4 Hz, 2H, Ar-H), 7.32e7.20 (m, 5H,
Ar-H), 5.81 (s, 1H, ¼CH), 5.42 (s, 1H, OCH), 2.88 (s, 1H, OH). 13C NMR
(CDCl3, 150 MHz):
d
¼ 137.5, 135.5, 134.0, 129.0, 128.9, 128.7, 128.3,
Fig. 1. Fluorescence spectra at 25 ꢂC of solution (2 ꢀ 10ꢁ5 mol dmꢁ3) of compound 6a,
6p 6d, 6h, 6l, and 6n in ethanol.
128.1, 127.9, 127.7, 127.4, 116.7, 75.9. Elemental Anal. Calcd for
15H12ClN3O: C, 63.05; H, 4.23; N, 14.71. Found: C, 62.84; H, 4.41; N,
C
14.78.
Table 3
Luminescent properties of 6 in ethanol.
4.1.1.5. 2-Azido-3-(furan-2-yl)-1-phenylprop-2-en-1-ol
light yellow oil (1.56 g, 81%). IR (KBr): 3370, 2105, 1643, 1483,
(2e).
Entry
Comp
ε (104 molꢁ1 dm3 cmꢁ1
)
labs (nm)
lem (nm)
Fc
1261 cmꢁ1. 1H NMR (CDCl3, 600 MHz):
d
¼ 7.49 (d, J ¼ 7.2 Hz, 2H, Ar-
1
2
3
4
5
6
6aa
6db
6hb
6lb
2.3
2.3
3.0
2.4
2.9
2.1
292
327
330
325
325
277
344
380
380
377
383
325
0.28
0.27
0.29
0.25
0.26
0.10
H), 7.42e7.35 (m, 4H, Ar-H), 6.77e6.44 (m, 2H, Ar-H), 5.87 (s,
1H, ¼CH), 5.56 (s, 1H, OCH), 2.48 (s, 1H, OH). 13C NMR (CDCl3,
150 MHz):
d
¼ 150.0,141.5, 141.2, 139.0, 134.5, 128.8, 128.6, 126.6,
6nb
6pa
126.4,111.8, 110.1, 105.6, 75.2. Elemental Anal. Calcd for C13H11N3O2:
C, 64.72; H, 4.60; N, 17.42. Found: C, 64.57; H, 4.85; N, 17.53.
a
Excitation at 276 nm, relative to phenol (
F
¼ 0.14 at 25 ꢂC) for 6a, 6p.
b
Excitation at 351 nm, relative to quinine sulphate (0.1 M Lꢁ1
,
F
¼ 0.577 at 25 ꢂC)
4.1.1.6. 3-Azido-4-phenylbut-3-en-2-ol (2f). yellow oil (1.35 g, 89%).
for 6d, 6h, 6l, 6n.
Error about 10%.
IR (KBr): 3379, 2110, 1641, 1491, 1320, 1066 cmꢁ1. 1H NMR (CDCl3,
c

H. Xie et al. / Dyes and Pigments 139 (2017) 440e447
443
600 MHz):
d
¼ 7.62 (d, J ¼ 7.2 Hz, 2H, Ar-H), 7.34e7.21 (m, 3H, Ar-H),
4.1.2.6. 2-Azido-1,3-diphenylallyl 4-methylbenzoate (3f). light yel-
low solid (1.47 g, 80%). mp. 45e47 ꢂC. IR (KBr): 2105, 1726, 1612,
5.82 (s, 1H, ¼CH), 4.68e4.64 (m, 1H, OCH), 1.94 (s, 1H, OH), 1.57 (d,
J ¼ 6.0 Hz, 3H, CH3). 13C NMR (CDCl3, 150 MHz):
d
¼ 137.8, 134.4,
1493, 1262, 1089 cmꢁ1
.
1H NMR (CDCl3, 600 MHz):
d
¼ 8.08 (d,
129.0, 128.8, 128.3, 128.2, 127.3, 127.2, 114.0, 70.3, 22.3. Elemental
Anal. Calcd for C10H11N3O: C, 63.48; H, 5.86; N, 22.21. Found: C,
63.59; H, 5.68; N, 22.34.
J ¼ 8.4 Hz, 2H, Ar-H), 7.67 (d, J ¼ 7.8 Hz, 2H, Ar-H), 7.54 (d, J ¼ 7.2 Hz,
2H, Ar-H), 7.44e7.23 (m, 8H, Ar-H), 6.92 (s, 1H, ¼CH), 6.06 (s, 1H,
CH), 2.44 (s, 3H, CH3). 13C NMR (CDCl3, 150 MHz):
d
¼ 165.1, 144.4,
136.3, 134.0, 132.4, 130.0, 129.9, 129.5, 129.4, 129.3, 129.2, 129.0,
128.9, 128.7, 128.3, 128.1, 126.6, 126.5, 126.3, 119.4, 119.2, 60.7, 21.8.
Elemental Anal. Calcd for C23H19N3O2: C, 74.78; H, 5.18; N, 11.37.
Found: C, 74.70; H, 4.95; N, 11.57.
4.1.2. Preparation of azides 3
A solution of azido alcohol 2 (5 mmol) in dry methylene chloride
(20 mL) was added dropwise under nitrogen to a solution of acyl
chloride (5 mmol) and triethylamine (10 mmol) in dry methylene
chloride (10 mL) at 0 ꢂC. After the stirring was continued for 0.5 h,
the reaction mixture was slowly warmed to room temperature
while the stirring was continued until the reaction completed
based on TLC monitoring. The solution was concentrated in vacuo
and the residue was purified by chromatography eluting with
EtOAc/petroleum ether (1:3) to give compounds 3.
4.1.2.7. 2-Azido-1,3-diphenylallyl 2-chlorobenzoate (3g). light yel-
low solid (1.67 g, 86%). mp. 80e82 ꢂC. IR (KBr): 2118, 1733, 1642,
1450, 1247, 1110 cmꢁ1
.
1H NMR (CDCl3, 600 MHz):
d
¼ 8.02 (d,
J ¼ 7.8 Hz,1H, Ar-H), 7.66 (d, J ¼ 7.8 Hz, 2H, Ar-H), 7.56e7.25 (m,11H,
Ar-H), 6.91 (s, 1H, ¼CH), 6.09 (s, 1H, CH). 13C NMR (CDCl3, 150 MHz):
d
¼ 163.8, 135.8, 134.2, 133.8, 131.9, 131.7, 131.4, 131.2, 129.2, 129.1,
128.8, 128.7, 128.6, 128.3, 128.1, 126.8, 126.6, 126.5, 119.5, 77.7.
Elemental Anal. Calcd for C22H16ClN3O2: C, 67.78; H, 4.14; N, 10.78.
Found: C, 68.06; H, 4.20; N, 10.95.
4.1.2.1. 2-Azido-3-phenylallyl 4-chlorobenzoate (3a). white solid
(1.33 g, 85%). mp. 102e103 ꢂC. IR (KBr): 2111, 1722, 1645, 1289,
1119 cmꢁ1. 1H NMR (CDCl3, 600 MHz):
d
¼ 8.02 (d, J ¼ 8.4 Hz, 2H, Ar-
H), 7.66 (d, J ¼ 7.8 Hz, 2H, Ar-H), 7.45e7.26 (m, 5H, Ar-H), 6.00 (s,
4.1.2.8. 2-Azido-1-(4-chlorophenyl)-3-phenylallyl 4-chlorobenzoate
(3h). light yellow solid (1.86 g, 88%). mp. 87e89 ꢂC. IR (KBr):
2107, 1732, 1641, 1492, 1262, 1092 cmꢁ1. 1H NMR (CDCl3, 600 MHz):
1H, ¼CH), 5.14 (s, 2H, CH2). 13C NMR (CDCl3, 150 MHz):
d
¼ 164.5,
134.0, 132.9, 131.6, 131.3, 131.1, 129.2, 128.3, 128.1, 126.7, 120.4, 66.2.
Elemental Anal. Calcd for C16H12ClN3O2: C, 61.25; H, 3.86; N, 13.39.
Found: C, 61.41; H, 4.06; N, 13.32.
d
¼ 8.10 (d, J ¼ 8.4 Hz, 2H, Ar-H), 7.66 (d, J ¼ 7.8 Hz, 2H, Ar-H),
7.50e7.26 (m, 9H, Ar-H), 6.86 (s, 1H, ¼CH), 6.05 (s, 1H, CH). 13C
NMR (CDCl3, 150 MHz):
d
¼ 164.1, 140.3, 134.8, 134.6, 133.6, 131.7,
4.1.2.2. 2-Azido-3-phenylallyl 4-nitrobenzoate (3b). yellow solid
(1.46 g, 90%). mp. 105e107 ꢂC. IR (KBr): 2110, 1722, 1645, 1271,
131.2, 129.3, 129.2, 129.0, 128.4, 128.2, 127.9, 127.7, 119.8, 76.8.
Elemental Anal. Calcd for C22H15Cl2N3O2: C, 62.28; H, 3.56; N, 9.90.
Found: C, 62.46; H, 3.78; N, 9.95.
1073 cmꢁ1. 1H NMR (CDCl3, 600 MHz):
d
¼ 8.33 (d, J ¼ 8.4 Hz, 2H,
Ar-H), 8.27 (d, J ¼ 9.0 Hz, 2H, Ar-H), 7.67 (d, J ¼ 7.8 Hz, 2H, Ar-H),
7.37e7.26 (m, 3H, Ar-H), 6.04 (s, 1H, ¼CH), 5.21 (s, 2H, CH2). 13C
4.1.2.9. 2-Azido-1-(4-chlorophenyl)-3-phenylallyl 2-chlorobenzoate
NMR (CDCl3, 150 MHz):
d
¼ 163.9, 150.7, 134.7, 133.6, 131.0, 130.8,
(3i). light yellow solid (1.90 g, 90%). mp. 48e50 ꢂC. IR (KBr): 2111,
129.3, 129.1, 128.2, 123.6, 120.9, 66.9. Elemental Anal. Calcd for
16H12N4O4: C, 59.26; H, 3.73; N, 17.28. Found: C, 59.39; H, 3.92; N,
1723, 1643, 1489, 1272, 1094 cmꢁ1 1H NMR (CDCl3, 600 MHz):
.
C
d
¼ 8.01 (d, J ¼ 7.8 Hz, 1H, Ar-H), 7.66 (d, J ¼ 7.8 Hz, 2H, Ar-H),
17.55.
7.53e7.25 (m, 10H, Ar-H), 6.86 (s, 1H, ¼CH), 6.09 (s, 1H, CH). 13C
NMR (CDCl3, 150 MHz):
131.8, 131.6, 129.3, 129.2, 129.0, 128.7, 128.4, 128.3, 128.2, 128.1,
126.9, 126.7, 119.9, 119.7, 77.3. Elemental Anal. Calcd for
d
¼ 163.9, 134.8, 134.5, 134.4, 133.7, 133.4,
4.1.2.3. 2-Azido-1,3-diphenylallyl benzoate (3c). yellow solid (1.54 g,
87%). mp. 95e96 ꢂC. IR (KBr): 2100, 1734, 1634, 1448, 1262 cmꢁ1. 1H
NMR (CDCl3, 600 MHz):
d
¼ 8.21e7.24 (m, 15H, Ar-H), 6.94 (s,
C22H15Cl2N3O2: C, 62.28; H, 3.56; N, 9.90. Found: C, 62.57; H, 3.43;
N, 10.11.
1H, ¼CH), 6.08 (s, 1H, CH). 13C NMR (CDCl3, 150 MHz):
d
¼ 165.0,
136.2, 133.9, 133.5, 132.3, 130.0, 129.8, 129.3, 129.2, 129.1, 128.9,
128.7, 128.5, 128.3, 128.1, 127.9, 127.6, 126.4, 119.5, 119.3, 76.8.
Elemental Anal. Calcd for C22H17N3O2: C, 74.35; H, 4.82; N, 11.82.
Found: C, 74.12; H, 4.66; N, 11.97.
4.1.2.10. 2-Azido-1-(4-chlorophenyl)-3-phenylallyl 4-nitrobenzoate
(3j). yellow solid (1.93 g, 89%). mp. 58e60 ꢂC. IR (KBr): 2108,
1738, 1641, 1492, 1291, 1110 cmꢁ1 1H NMR (CDCl3, 600 MHz):
.
d
¼ 8.36 (d, J ¼ 9.0 Hz, 2H, Ar-H), 8.33 (d, J ¼ 9.0 Hz, 2H, Ar-H), 7.66
(d, J ¼ 7.8 Hz, 2H, Ar-H), 7.48e7.26 (m, 7H, Ar-H), 6.90 (s, 1H, ¼CH),
6.08 (s, 1H, CH). 13C NMR (CDCl3, 150 MHz):
4.1.2.4. 2-Azido-1,3-diphenylallyl 4-chlorobenzoate (3d). light yel-
low solid (1.61 g, 83%). mp. 96e97 ꢂC. IR (KBr): 2108, 1728, 1632,
d
¼ 163.2, 150.9, 135.0,
1448, 1264, 1100 cmꢁ1
.
1H NMR (CDCl3, 600 MHz):
d
¼ 8.12 (d,
134.4, 134.1, 133.4, 131.2, 131.1, 130.9, 130.7, 129.3, 129.2, 129.1, 128.4,
128.2, 127.9, 127.7, 123.9, 120.4, 78.0. Elemental Anal. Calcd for
J ¼ 7.8 Hz, 2H, Ar-H), 7.67 (d, J ¼ 7.8 Hz, 2H, Ar-H), 7.53e7.25 (m,
10H, Ar-H), 6.91 (s, 1H, ¼CH), 6.06 (s, 1H, CH). 13C NMR (CDCl3,
C22H15ClN4O4: C, 60.77; H, 3.48; N, 12.88. Found: C, 60.94; H, 3.62;
150 MHz):
d
¼ 164.2, 140.1, 136.0, 133.8, 132.0, 131.3, 131.2, 129.3,
N, 13.14.
129.2, 129.1, 128.9, 128.8, 128.3, 128.1, 127.9, 127.8, 126.4, 126.2,
119.7, 119.5, 77.8. Elemental Anal. Calcd for C22H16ClN3O2: C, 67.78;
H, 4.14; N, 10.78. Found: C, 68.03; H, 4.30; N, 10.74.
4.1.2.11. 2-Azido-3-(4-chlorophenyl)-1-phenylallyl 4-nitrobenzoate
(3k). yellow solid (1.84 g, 85%). mp. 116e118 ꢂC. IR (KBr): 2099,
1735, 1640, 1491, 1260, 1093 cmꢁ1 1H NMR (CDCl3, 600 MHz):
.
4.1.2.5. 2-Azido-1,3-diphenylallyl 4-nitrobenzoate (3e). yellow solid
(1.64 g, 82%). mp. 52e54 ꢂC. IR (KBr): 2106, 1732, 1640, 1494, 1261,
d
¼ 8.35 (s, 4H, Ar-H), 7.61 (d, J ¼ 8.4 Hz, 2H, Ar-H), 7.53e7.29 (m,
7H, Ar-H), 6.93 (s, 1H, ¼CH), 6.00 (s, 1H, CH). 13C NMR (CDCl3,
1097 cmꢁ1. 1H NMR (CDCl3, 600 MHz):
d
¼ 8.36 (s, 4H, Ar-H), 7.67 (d,
J ¼ 7.2 Hz, 2H, Ar-H), 7.54e7.26 (m, 8H, Ar-H), 6.94 (s,1H, ¼CH), 6.08
(s, 1H, CH). 13C NMR (CDCl3, 150 MHz):
150 MHz):
d
¼ 163.1, 150.7, 135.3, 134.4, 133.4, 132.2, 132.1, 130.9,
130.4, 129.0, 128.3, 126.3, 123.7, 118.5, 118.4, 78.3. Elemental Anal.
Calcd for C22H15ClN4O4: C, 60.77; H, 3.48; N, 12.88. Found: C, 60.81;
H, 3.25; N, 12.82.
d
¼ 163.2, 150.8, 135.5, 134.7,
133.6, 131.6, 131.1, 129.3, 129.2, 129.1, 128.9, 128.4, 128.2, 126.4,
126.3, 123.9, 123.6, 120.1, 119.9, 78.6. Elemental Anal. Calcd for
C
22H16N4O4: C, 66.00; H, 4.03; N, 13.99. Found: C, 66.21; H, 4.16; N,
4.1.2.12. 2-Azido-3-(4-chlorophenyl)-1-phenylallyl-4-chlorobenzoate
(3l). light yellow solid (1.88 g, 89%). mp. 98e100 ꢂC. IR (KBr): 2102,
14.22.

444
H. Xie et al. / Dyes and Pigments 139 (2017) 440e447
1726, 1637, 1489, 1260, 1094 cmꢁ1
.
1H NMR (CDCl3, 600 MHz):
N, 13.08. Found: C, 71.23; H, 6.13; N, 13.36.
d
¼ 8.11 (d, J ¼ 8.4 Hz, 2H, Ar-H), 7.60 (d, J ¼ 8.4 Hz, 2H, Ar-H),
7.51e7.25 (m, 9H, Ar-H), 6.89 (s, 1H, ¼CH), 5.98 (s, 1H, CH). 13C
4.1.2.19. 3-Azido-4-phenylbut-3-en-2-yl benzoate (3s). light yellow
NMR (CDCl3, 150 MHz):
d
¼ 164.2, 140.2, 135.8, 133.4, 132.7, 132.3,
oil (1.27 g, 87%). IR (KBr): 2107, 1722, 1642, 1450, 1266, 1095 cmꢁ1
.
131.2, 130.5, 129.0, 128.9, 128.4, 127.7, 126.3, 118.2, 118.1, 77.7.
Elemental Anal. Calcd for C22H15Cl2N3O2: C, 62.28; H, 3.56; N, 9.90.
Found: C, 62.45; H, 3.70; N, 10.14.
1H NMR (CDCl3, 600 MHz):
d
¼ 8.10 (d, J ¼ 7.2 Hz, 2H, Ar-H),
7.65e7.23 (m, 8H, Ar-H), 5.98 (s, 1H, ¼CH), 5.92 (q, J ¼ 7.2 Hz, 1H,
CH), 1.73 (d, J ¼ 6.6 Hz, 3H, CH3). 13C NMR (CDCl3, 150 MHz):
d
¼ 165.2, 134.0, 133.9, 133.3, 129.9, 129.6, 129.1, 128.5, 128.4, 128.3,
4.1.2.13. 2-Azido-3-(4-chlorophenyl)-1-phenylallyl-2-chlorobenzoate
128.1, 127.6, 117.3, 73.1, 19.3. Elemental Anal. Calcd for C17H15N3O2:
C, 69.61; H, 5.15; N, 14.33. Found: C, 69.74; H, 5.32; N, 14.49.
(3m). light yellow solid (1.71 g, 81%). mp. 87e89 ꢂC. IR (KBr): 2101,
1745, 1638, 1490, 1282, 1096 cmꢁ1 1H NMR (CDCl3, 600 MHz):
.
d
¼ 8.01 (d, J ¼ 7.2 Hz, 1H, Ar-H), 7.61e7.25 (m, 12H, Ar-H), 6.90 (s,
4.1.3. Preparation of oxazoles 6
1H, ¼CH), 6.02 (s, 1H, CH). 13C NMR (CDCl3, 150 MHz):
d
¼ 163.8,
To a solution of triphenyl phosphine (0.52 g, 2 mmol) in dry
toluene (10 mL) was added dropwise azide 3 (2 mmol) at room
temperature. The reaction mixture was stirred for further 2 h, and
then heated at refluxing temperature for 4e10 h (6 h for com-
pounds 6d-6j; 4 h for compounds 6k-6m; 10 h for 6n-6o). For the
preparation of compounds 6a-6b and 6p-6s, NaH (0.005 g,
0.2 mmol) was added and the reaction mixture was stirred for
1e2 h at room temperature. The solvent was removed under
reduced pressure and the residue was chromatographed on a silica
gel column, eluting with petroleum ether (60e90 ꢂC)/ethyl acetate
(7:1), to afford 6.
135.6, 134.3, 133.2, 132.6, 132.4, 131.7, 131.4, 130.5, 128.9, 128.7,
128.3, 126.8, 126.6, 118.0, 117.9, 77.6. Elemental Anal. Calcd for
C
22H15Cl2N3O2: C, 62.28; H, 3.56; N, 9.90. Found: C, 62.53; H, 3.79;
N, 9.73.
4.1.2.14. 2-Azido-3-(furan-2-yl)-1-phenylallyl 4-chlorobenzoate (3n).
light yellow solid (1.33 g, 70%). mp. 66e68 ꢂC. IR (KBr): 2108, 1741,
1643, 1492, 1261, 1089 cmꢁ1 1H NMR (CDCl3, 600 MHz):
.
d
¼ 8.36e8.32 (m, 4H, Ar-H), 7.51e7.39 (m, 6H, Ar-H), 6.89 (s,
1H, ¼CH), 6.83e6.46 (m, 2H, Ar-H), 6.00 (s, 1H, CH). 13C NMR
(CDCl3, 150 MHz):
d
¼ 164.2, 149.5, 141.8, 135.8, 132.6, 131.3, 130.9,
130.5, 129.1, 128.9, 127.7, 126.5, 111.1, 110.9, 108.6, 108.4, 61.2.
Elemental Anal. Calcd for C20H14ClN3O3: C, 63.25; H, 3.72; N, 11.06.
Found: C, 63.54; H, 3.91; N, 11.17.
4.1.3.1. 4-Benzyl-2-(4-chlorophenyl)oxazole (6a). light yellow solid
(0.40 g, 74%). mp. 69e70 ꢂC. 1H NMR (CDCl3, 600 MHz):
d
¼ 7.94 (d,
J ¼ 8.4 Hz, 2H, Ar-H), 7.40 (d, J ¼ 8.4 Hz, 2H, Ar-H), 7.34e7.24 (m, 6H,
Ar-H), 3.93 (s, 2H, CH2). 13C NMR (CDCl3, 150 MHz):
d
¼ 160.7, 142.1,
4.1.2.15. 2-Azido-3-(furan-2-yl)-1-phenylallyl 4-nitrobenzoate (3o).
yellow solid (1.42 g, 73%). mp. 80e82 ꢂC. IR (KBr): 2110, 1739, 1637,
138.1, 136.2, 135.3, 135.0, 129.1, 129.0, 128.8, 128.7, 128.4, 127.6,
127.5, 33.0. MS: m/z (%) ¼ 269 (95, Mþ), 240(8), 139 (100), 103 (31),
91 (29), 77 (19). Elemental Anal. Calcd for C16H12ClNO: C, 71.25; H,
4.48; N, 5.19. Found: C, 71.49; H, 4.36; N, 5.40.
1492, 1282, 1110 cmꢁ1
.
1H NMR (CDCl3, 600 MHz):
d
¼ 8.01 (d,
J ¼ 8.4 Hz, 2H, Ar-H), 7.50e7.37 (m, 8H, Ar-H), 6.86 (s,1H, ¼CH), 6.86
(s, 1H, ¼CH), 6.81e6.45 (m, 2H, ArH), 5.98 (s, 1H, CH). 13C NMR
(CDCl3, 150 MHz):
d
¼ 163.2, 150.8, 149.4, 141.9, 135.3, 134.6, 131.1,
4.1.3.2. 4-Benzyl-2-(4-nitrophenyl)oxazole
(6b). yellow
solid
¼ 8.29
130.0, 129.1, 126.5, 123.9, 123.3, 112.0, 111.4, 108.8, 61.9. Elemental
Anal. Calcd for C20H14N4O5: C, 61.54; H, 3.62; N, 14.35. Found: C,
61.59; H, 3.79; N, 14.59.
(0.46 g, 82%). mp. 104e106 ꢂC. 1H NMR (CDCl3, 600 MHz):
d
(d, J ¼ 8.4 Hz, 2H, Ar-H), 8.18 (d, J ¼ 8.4 Hz, 2H, Ar-H), 7.41e7.23 (m,
6H, Ar-H, ¼CH), 3.97 (s, 2H, CH2). 13C NMR (CDCl3, 150 MHz):
d
¼ 159.4, 148.3, 142.9, 137.8, 136.3, 132.7, 128.7, 128.5, 126.8, 126.6,
4.1.2.16. 2-Azido-1,3-diphenylallyl acetate (3p). light yellow oil
(1.05 g, 72%). mp. 60e63 ꢂC. IR (KBr): 2107, 1752, 1641, 1494, 1293,
123.9, 32.8. MS: m/z (%) ¼ 280 (100, Mþ), 150 (53), 131 (23), 103
(22), 91 (25), 77 (15). Elemental Anal. Calcd for C16H12N2O3: C,
68.56; H, 4.32; N, 9.99. Found: C, 68.61; H, 4.56; N, 9.85.
1222, 1023 cmꢁ1. 1H NMR (CDCl3, 600 MHz):
d
¼ 7.63 (d, J ¼ 7.2 Hz,
2H, Ar-H), 7.46e7.24 (m, 8H, Ar-H), 6.64 (s, 1H, ¼CH), 5.93 (s, 1H,
CH), 2.25 (s, 3H, CH3). 13C NMR (CDCl3, 150 MHz):
d
¼ 169.4, 136.2,
4.1.3.3. 4-Benzyl-2,5-diphenyloxazole (6c). light yellow solid
(0.43 g, 69%). mp. 94e95 ꢂC. 1H NMR (CDCl3, 600 MHz):
133.9, 132.4, 129.2, 129.1, 128.9, 128.8, 128.7, 128.3, 128.1, 126.7,
126.5, 119.0, 118.8, 76.5, 21.0. Elemental Anal. Calcd for C17H15N3O2:
C, 69.61; H, 5.15; N, 14.33. Found: C, 69.69; H, 5.37; N, 14.54.
d
¼ 8.11e7.22 (m, 15H, Ar-H), 4.22 (s, 2H, CH2). 13C NMR (CDCl3,
150 MHz):
d
¼ 159.8, 146.4, 138.5, 135.6, 132.0, 131.9, 130.2, 128.8,
128.6, 128.5, 128.3, 127.9, 127.4, 126.3, 125.5, 33.0. MS: m/z (%) ¼ 311
(100, Mþ), 207 (31), 165 (20), 105 (49), 77 (59). Elemental Anal.
Calcd for C22H17NO: C, 84.86; H, 5.50; N, 4.50. Found: C, 85.01; H,
4.76; N, 4.55.
4.1.2.17. 2-Azido-3-(4-chlorophenyl)-1-phenylallyl acetate (3q).
light yellow oil (1.24 g, 76%). mp. 88e90 ꢂC. IR (KBr): 2109, 1756,
1641, 1490, 1291, 1222,1087 cmꢁ1 1H NMR (CDCl3, 600 MHz):
.
d
¼ 7.57 (d, J ¼ 8.4 Hz, 2H, Ar-H), 7.45e7.25 (m, 7H, Ar-H), 6.62 (s,
1H, ¼CH), 5.85 (s, 1H, CH), 2.25 (s, 3H, CH3). 13C NMR (CDCl3,
4.1.3.4. 4-Benzyl-2-(4-chlorophenyl)-5-phenyloxazole
white solid (0.54 g, 78%). mp. 133e134 ꢂC. 1H NMR (CDCl3,
600 MHz):
¼ 8.04 (d, J ¼ 7.2 Hz, 2H, Ar-H), 7.66 (d, J ¼ 6.6 Hz, 2H,
Ar-H), 7.45e7.23 (m, 10H, Ar-H), 4.21 (s, 2H, CH2). 13C NMR (CDCl3,
150 MHz):
128.9, 128.6, 128.5, 128.4, 128.2, 127.6, 126.4, 125.9, 125.6, 33.0. MS:
m/z (%) ¼ 345 (100, Mþ), 207 (39), 179 (11), 139 (46), 77 (76).
Elemental Anal. Calcd for C22H16ClNO: C, 76.41; H, 4.66; N, 4.05.
Found: C, 76.22; H, 4.84; N, 4.14.
(6d).
150 MHz):
d
¼ 169.3, 135.9, 133.1, 133.0, 132.4, 130.4, 128.8, 128.3,
126.5, 117.4, 117.3, 76.5, 21.0. Elemental Anal. Calcd for
17H14ClN3O2: C, 62.30; H, 4.31; N,12.82. Found: C, 62.17; H, 4.37; N,
d
C
12.65.
d
¼ 158.9, 146.8, 138.4, 136.3, 135.8, 131.8, 129.3, 129.0,
4.1.2.18. 2-Azido-1,3-diphenylallyl butyrate (3r). light yellow oil
(1.27 g, 79%). IR (KBr): 2108, 1745, 1641, 1494, 1294, 1161, 1079 cmꢁ1
.
1H NMR (CDCl3, 600 MHz):
d
¼ 7.63 (d, J ¼ 8.4 Hz, 2H, Ar-H),
7.46e7.24 (m, 8H, Ar-H), 6.66 (s, 1H, ¼CH), 5.93 (s, 1H, CH), 2.49
(t, J ¼ 7.2 Hz, 2H, CH2), 1.78e1.74 (m, 2H, CH2), 1.00 (t, J ¼ 7.2 Hz, 3H,
4.1.3.5. 4-Benzyl-2-(4-nitrophenyl)-5-phenyloxazole
yellow solid (0.49 g, 69%). mp. 174e176 ꢂC. 1H NMR (CDCl3,
600 MHz):
¼ 8.32e8.26 (m, 4H, Ar-H), 7.68e7.25 (m, 10H, Ar-H),
4.23 (s, 2H, CH2). 13C NMR (CDCl3, 150 MHz):
¼ 157.5, 148.3, 148.0,
(6e).
CH3). 13C NMR (CDCl3, 150 MHz):
d
¼ 172.0, 136.4, 134.0, 132.6,
129.2, 129.1, 128.6, 128.3, 128.1, 127.8, 126.7, 126.5, 119.0, 76.3, 36.3,
18.3, 13.5. Elemental Anal. Calcd for C19H19N3O2: C, 71.01; H, 5.96;
d
d

H. Xie et al. / Dyes and Pigments 139 (2017) 440e447
445
138.1, 136.8, 132.7, 128.9, 128.6, 128.3, 127.9, 126.8, 126.5, 125.8,
124.1, 33.0. MS: m/z (%) ¼ 356 (20, Mþ), 249 (20), 207 (56), 179 (43),
105 (65), 77 (100). Elemental Anal. Calcd for C22H16N2O3: C, 74.15;
H, 4.53; N, 7.86. Found: C, 74.31; H, 4.65; N, 8.05.
4.1.3.12. 4-(4-Chlorobenzyl)-2-(2-chlorophenyl)-5-phenyloxazole
(6l). white solid (0.58 g, 76%). mp. 124e125 ꢂC. 1H NMR (CDCl3,
600 MHz):
Ar-H), 7.53e7.26 (m, 10H, Ar-H), 4.20 (s, 2H, CH2). 13C NMR (CDCl3,
150 MHz):
d
¼ 8.08 (d, J ¼ 9.0 Hz, 1H, Ar-H), 7.65 (d, J ¼ 7.8 Hz, 2H,
d
¼ 158.0, 147.1, 136.9, 134.9, 132.3, 132.2, 131.2, 130.9,
129.8, 128.9, 128.6, 128.3, 128.2, 126.8, 126.1, 125.6, 32.5. MS: m/z
(%) ¼ 379 (37, Mþ), 207 (17), 178 (31), 165 (38), 105 (53), 77 (90).
Elemental Anal. Calcd for C22H15Cl2NO:C, 69.49; H, 3.98; N, 3.68.
Found: C, 69.22; H, 3.77; N, 3.64.
4.1.3.6. 4-Benzyl-5-phenyl-2-p-tolyloxazole (6f). white solid (0.46 g,
71%). mp. 108e109 ꢂC. 1H NMR (CDCl3, 600 MHz):
d
¼ 8.00 (d,
J ¼ 8.4 Hz, 2H, Ar-H), 7.66 (d, J ¼ 7.8 Hz, 2H, Ar-H), 7.43e7.23 (m,
10H, Ar-H), 4.21 (s, 2H, CH2), 2.41 (s, 3H, CH3). 13C NMR (CDCl3,
150 MHz):
d
¼ 160.1, 146.1, 140.5, 138.6, 135.5, 129.4, 128.8, 128.5,
4.1.3.13. 4-(4-Chlorobenzyl)-2-(4-nitrophenyl)-5-phenyloxazole
128.4, 127.8, 126.3, 125.5, 124.7, 33.1, 21.5. MS: m/z (%) ¼ 325 (100,
Mþ), 207 (25), 165 (16), 119 (28), 105 (19), 77 (43). Elemental Anal.
Calcd for C23H19NO: calcd. C, 84.89; H, 5.89; N, 4.30. Found: C,
84.72; H, 6.09; N, 4.28.
(6m). yellow solid (0.56 g, 72%). mp. 184e185 ꢂC. 1H NMR (CDCl3,
600 MHz):
Ar-H), 7.66 (d, J ¼ 7.8 Hz, 2H, Ar-H), 7.49e7.26 (m, 7H, Ar-H), 4.19 (s,
2H, CH2). 13C NMR (CDCl3, 150 MHz):
d
¼ 8.33 (d, J ¼ 8.4 Hz, 2H, Ar-H), 8.26 (d, J ¼ 8.4 Hz, 2H,
d
¼ 157.7, 148.4, 148.1, 136.6,
136.3, 132.6, 132.4, 129.7, 129.0, 128.8, 128.7, 127.8, 126.9, 125.8,
124.1, 32.4. MS: m/z (%) ¼ 390 (100, Mþ), 207 (25),178 (21),105 (27),
77 (62). Elemental Anal. Calcd for C22H15ClN2O3: C, 67.61; H, 3.87;
N, 7.17. Found: C, 67.82; H, 3.99; N, 6.98.
4.1.3.7. 4-Benzyl-2-(2-chlorophenyl)-5-phenyloxazole
white solid (0.59 g, 85%). mp. 85e86 ꢂC. 1H NMR (CDCl3, 600 MHz):
¼ 8.10 (d, J ¼ 7.8 Hz, 1H, Ar-H), 7.69 (d, J ¼ 7.2 Hz, 2H, Ar-H),
7.52e7.22 (m, 11H, Ar-H), 4.25 (s, 2H, CH2). 13C NMR (CDCl3,
150 MHz):
(6g).
d
d
¼ 157.9, 147.1, 138.5, 135.5, 132.3, 131.2, 131.0, 130.9,
4.1.3.14. 2-(4-Chlorophenyl)-4-(furan-2-ylmethyl)-5-phenyloxazole
128.8, 128.5, 128.4, 128.1, 126.7, 126.4, 126.3, 125.6, 33.1. MS: m/z
(%) ¼ 345 (51, Mþ), 207 (49), 165 (33), 139 (35), 105 (42), 77 (100).
Elemental Anal. Calcd for C22H16ClNO: calcd. C, 76.41; H, 4.66; N,
4.05. Found: C, 76.55; H, 4.82; N, 4.32.
(6n). light yellow solid (0.46 g, 69%). mp. 144e145 ꢂC. 1H NMR
(CDCl3, 600 MHz):
d
¼ 8.03 (d, J ¼ 7.8 Hz, 2H, Ar-H), 7.70 (d,
J ¼ 7.8 Hz, 2H, Ar-H), 7.48e6.15 (m, 8H, Ar-H), 4.17 (s, 2H, CH2). 13
C
NMR (CDCl3, 150 MHz):
d
¼ 158.9, 151.9, 146.9, 141.6, 136.3, 133.4,
129.0, 128.9, 128.3, 128.2, 127.6, 127.4, 125.8, 110.4, 106.5, 26.7. MS:
m/z (%) ¼ 335 (62, Mþ), 306 (29), 230 (14), 139 (47), 105 (100), 77
(82). Elemental Anal. Calcd for C20H14ClNO2: C, 71.54; H, 4.20; N
4.17. Found: C, 71.25; H, 4.14; N, 4.39.
4.1.3.8. 4-Benzyl-2,5-bis(4-chlorophenyl)oxazole (6h). white solid
(0.59 g, 78%). mp. 157e158 ꢂC. 1H NMR (CDCl3, 600 MHz):
d
¼ 8.03
(d, J ¼ 8.4 Hz, 2H, Ar-H), 7.57 (d, J ¼ 7.8 Hz, 2H, Ar-H), 7.45e7.23 (m,
9H, Ar-H), 4.18 (s, 2H, CH2). 13C NMR (CDCl3, 150 MHz):
d
¼ 159.1,
145.8, 138.1, 136.4, 136.3, 134.0, 129.1, 129.0, 128.7, 128.3, 127.6,
126.9, 126.7, 126.5, 125.7, 33.1. MS: m/z (%) ¼ 379 (100, Mþ), 241
(22), 207 (30), 139 (75), 111 (25). Elemental Anal. Calcd for
4.1.3.15. 4-(Furan-2-ylmethyl)-2-(4-nitrophenyl)-5-phenyloxazole
(6o). yellow solid (0.42 g, 61%). mp. 158e160 ꢂC. 1H NMR (CDCl3,
600 MHz):
Ar-H), 7.74 (d, J ¼ 6.6 Hz, 2H, Ar-H), 7.50e6.17 (m, 8H, Ar-H, ¼CH),
4.20 (s, 2H, CH2). 13C NMR (CDCl3, 150 MHz):
d
¼ 8.32 (d, J ¼ 7.8 Hz, 2H, Ar-H), 8.26 (d, J ¼ 7.8 Hz, 2H,
C
22H15Cl2NO: C, 69.49; H, 3.98; N, 3.68. Found: C, 69.72; H, 4.91; N,
3.79.
d
¼ 157.6, 151.6, 148.4,
148.3, 141.8, 141.7, 134.3, 132.7, 128.9, 128.6, 127.8, 126.9, 126.1, 124.1,
110.4, 106.7, 26.7. MS: m/z (%) ¼ 346 (100, Mþ), 316 (43), 271 (15),
141 (14), 105 (59), 77 (59). Elemental Anal. Calcd for C20H14N2O4:C,
69.36; H, 4.07; N, 8.09. Found: C, 69.44; H, 4.33; N, 7.91.
4.1.3.9. 4-Benzyl-5-(4-chlorophenyl)-2-(4-nitrophenyl)oxazole (6i).
yellow solid (0.56 g, 72%). mp. 207e209 ꢂC. 1H NMR (CDCl3,
600 MHz):
Ar-H), 7.43 (d, J ¼ 7.8 Hz, 2H, Ar-H), 7.44e7.24 (m, 7H, Ar-H), 4.21 (s,
2H, CH2). 13C NMR (CDCl3, 150 MHz):
137.2, 134.6, 132.6, 129.7, 129.3, 128.7, 128.3, 127.0, 126.7, 126.5,
124.2, 33.1. MS: m/z (%) ¼ 390 (100, Mþ), 241 (29), 207 (47), 178
(46), 139 (48), 103 (47). Elemental Anal. Calcd for C22H15ClN2O3: C,
67.61; H, 3.87; N, 7.17. Found: C, 67.82; H, 4.11; N, 7.35.
d
¼ 8.33 (d, J ¼ 7.8 Hz, 2H, Ar-H), 8.26 (d, J ¼ 7.8 Hz, 2H,
d
¼ 157.8, 148.5, 147.1, 137.8,
4.1.3.16. 4-Benzyl-2-methyl-5-phenyloxazole (6p). light yellow oil
(0.37 g, 74%). 1H NMR (CDCl3, 600 MHz):
d
¼ 7.57 (d, J ¼ 6.0 Hz, 2H,
Ar-H), 7.38e7.19 (m, 8H, Ar-H), 4.08 (s, 2H, CH2), 2.47 (s, 3H, CH3).
13C NMR (CDCl3, 150 MHz):
d
¼ 159.9, 146.0, 138.6, 134.1, 128.7,
128.5, 128.3, 127.7, 126.3, 125.4, 125.3, 32.9, 14.4. MS: m/z (%) ¼ 249
(100, Mþ), 207 (61), 179 (26), 131 (10), 103 (17), 77 (30). Elemental
Anal. Calcd for C17H15NO: C, 81.90; H, 6.06; N, 5.62. Found: C, 81.64;
H, 6.26; N, 5.69.
4.1.3.10. 4-Benzyl-2-(2-chlorophenyl)-5-(4-chlorophenyl)oxazole
(6j). white solid (0.52 g, 68%). mp. 116e118 ꢂC. 1H NMR (CDCl3,
600 MHz):
Ar-H), 7.52e7.23 (m, 10H, Ar-H), 4.22 (s, 2H, CH2). 13C NMR (CDCl3,
150 MHz):
129.0, 128.6, 128.3, 126.9, 126.7, 126.6, 126.4, 125.9, 33.1. MS: m/z
(%) ¼ 379 (42, Mþ), 241(26), 207 (26), 178 (38), 139 (100), 110 (57).
Elemental Anal. Calcd for C22H15Cl2NO: C, 69.49; H, 3.98; N, 3.68.
Found: C, 69.42; H, 4.17; N, 3.62.
d
¼ 8.09 (d, J ¼ 6.6 Hz, 1H, Ar-H), 7.60 (d, J ¼ 8.4 Hz, 2H,
4.1.3.17. 4-(4-Chlorobenzyl)-2-methyl-5-phenyloxazole
(6q).
¼ 7.54 (d,
light yellow oil (0.40 g, 71%). 1H NMR (CDCl3, 600 MHz):
d
d
¼ 158.0, 146.0, 138.1, 135.8, 133.8, 132.2, 131.1, 130.9,
J ¼ 6.6 Hz, 2H, Ar-H), 7.40 (d, J ¼ 6.0 Hz, 2H, Ar-H), 7.32e7.19 (m, 9H,
Ar-H), 4.04 (s, 2H, CH2), 2.49 (s, 3H, CH3). 13C NMR (CDCl3,
150 MHz):
d
¼ 160.0, 146.1, 137.1, 133.6, 132.1, 129.7, 128.8, 128.7,
128.5, 127.9, 125.2, 32.2, 13.9. MS: m/z (%) ¼ 283 (100, Mþ), 241 (31),
207 (21), 178 (26), 105 (28), 77 (37). Elemental Anal. Calcd for
4.1.3.11. 4-(4-Chlorobenzyl)-2-(4-chlorophenyl)-5-phenyloxazole
C17H14ClNO: C, 71.96; H, 4.97; N, 4.94. Found: C, 71.78; H, 5.02; N,
5.17.
(6k). white solid (0.63 g, 83%). mp. 142e143 ꢂC. 1H NMR (CDCl3,
600 MHz):
Ar-H), 7.63e7.25 (m, 10H, Ar-H), 4.16 (s, 2H, CH2). 13C NMR (CDCl3,
150 MHz):
129.7, 129.0, 128.7, 128.3, 127.6, 125.8, 125.6, 32.4. MS: m/z (%) ¼ 379
(100, Mþ), 207 (14), 178 (17), 165 (26), 139 (77), 77 (74). Elemental
Anal. Calcd for C22H15Cl2NO: C, 69.49; H, 3.98; N, 3.68. Found: C,
69.63; H, 4.05; N, 3.85.
d
¼ 8.08 (d, J ¼ 8.4 Hz, 1H, Ar-H), 8.03 (d, J ¼ 8.4 Hz, 2H,
4.1.3.18. 4-Benzyl-5-phenyl-2-propyloxazole (6r). light yellow oil
d
¼ 159.0, 146.8, 141.4, 136.9, 136.4, 135.3, 132.2, 131.8,
(0.44 g, 79%). 1H NMR (CDCl3, 600 MHz):
d
¼ 7.56 (d, J ¼ 7.2 Hz, 2H,
Ar-H), 7.42e7.20 (m, 8H, Ar-H), 4.11 (s, 2H, CH2), 2.78 (t, J ¼ 7.2 Hz,
2H, CH2), 1.86e1.82 (m, 2H, CH2), 1.02 (t, J ¼ 7.2 Hz, 2H, CH3). 13
C
NMR (CDCl3, 150 MHz):
d
¼ 163.3, 145.9, 138.7, 133.9, 128.9, 128.7,
128.5, 128.3, 127.6, 126.2, 125.3, 32.9, 30.1, 20.6, 13.4. MS: m/z

446
H. Xie et al. / Dyes and Pigments 139 (2017) 440e447
(%) ¼ 277 (100, Mþ), 249 (61), 207 (50), 179 (20), 103 (50), 77 (37).
Elemental Anal. Calcd for C19H19NO: C, 82.28; H, 6.90; N, 5.05.
Found: C, 82.43; H, 6.81; N, 5.16.
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4.1.3.19. 4-Benzyl-5-methyl-2-phenyloxazole
(6s). white
solid
(0.42 g, 84%). mp. 67e68 ꢂC. 1H NMR (CDCl3, 600 MHz):
d
¼ 7.98 (d,
J ¼ 6.6 Hz, 2H, Ar-H) 7.41e7.19 (m, 8H, Ar-H), 3.88 (s, 2H, CH2), 2.26
(s, 3H, CH3). 13C NMR (CDCl3, 150 MHz):
d
¼ 159.1, 139.0, 134.8,
129.4, 128.5, 128.4, 128.3, 127.6, 126.0, 125.8, 125.7, 32.0, 10.5. MS:
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Found: C, 81.79; H, 6.45; N, 5.54.
4.2. Spectroscopic measurements
All the solutions were prepared using spectroscopic grade sol-
vents. Absorption spectra were recorded using a Scinco S-3100 UV-
spectrophotometer. Fluorescence measurements were performed
using a Fluoro Max-3-P spectrofluorimeter, equipped with double
monochromators in both excitation and emission and a tempera-
ture controlled cuvette holder. Fluorescence spectra were corrected
for the instrumental response of the system. The absorption and
fluorescence spectra were recorded at 25 ꢂC.
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standard method (Eq. (1))
FsArn2S
fs ¼ fr
(1)
FrAsn2S
where A is the absorbance at the excitation wavelength, F is the
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F
¼ 0.14 at 25 ꢂC) for 6a, 6p, and on
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F
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Acknowledgements
We gratefully acknowledge financial support of this work by the
National Natural Science Foundation of China (No. 21572075 and
21172085).
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Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.dyepig.2016.12.040.
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ꢀ
a
adducts of
a,
b