A novel and efficient one pot synthesis of 2,4-disubstituted thiazoles and oxazoles using phenyltrimethylammoniumtribromide in ionic liquid

Article abstract of DOI:10.1002/jhet.904

A novel and efficient one-pot procedure has been described for synthesis of 2,4-disubstituted thiazoles and oxazoles from substituted ketones using phenyltrimethylammoniumtribromide as in situ brominating agent followed by reaction with thioamide/thiourea and amides/ureas, respectively in [bmim][BF₄] ionicliquid. The advantages of the procedure include avoiding the handling of lacrymetric compounds, hazardous and toxic organic solvents along with good to excellent yield of the products.

Full text of DOI:10.1002/jhet.904

July 2012
A Novel and Efficient One Pot Synthesis of 2,4-Disubstituted
Thiazoles and Oxazoles Using
959
Phenyltrimethylammoniumtribromide in Ionic Liquid
*
Manoj Kumar Muthyala and Anil Kumar
Department of Chemistry, Birla Institute of Technology and Science, Pilani 333 031, India
*
E-mail: anilkadian@gmail.com
Received December 15, 2010
DOI 10.1002/jhet.904
View this article online at wileyonlinelibrary.com.
A novel and efficient one-pot procedure has been described for synthesis of 2,4-disubstituted thiazoles
and oxazoles from substituted ketones using phenyltrimethylammoniumtribromide as in situ brominating
agent followed by reaction with thioamide/thiourea and amides/ureas, respectively in [bmim][BF4]
ionicliquid. The advantages of the procedure include avoiding the handling of lacrymetric compounds,
hazardous and toxic organic solvents along with good to excellent yield of the products.
J. Heterocyclic Chem., 49, 959 (2012).
INTRODUCTION
been far fewer methods that describe the synthesis of
oxazoles starting directly from ketones. Thus, there is
a need for an economical, environmentally safe and
practical method for the synthesis of thiazoles and
oxazoles.
Ionic liquids have currently received much attention
as alternative reaction media for various chemical and
biochemical reactions [18]. In continuation of our
research work towards development of eco-friendly
reaction methodologies [19] and our interest in thiazoles
and oxazoles, herein we report a greener one-pot
synthesis of 2,4-disubstituted thiazoles and oxazoles
from ketones using phenyltrimethylammoniumtribromide
(PTT) as in-situ brominating agent in [bmim][BF4] ionic
liquid (Scheme 1). To the best of our knowledge this is
the first report on the synthesis of oxazoles in ionic liquid
using PTT as in-situ brominating agent.
Thiazoles and oxazoles are common structural motif
found in both natural products and pharmaceuticals with
broad spectrum of biological activities [1]. These mole-
cules are also synthetic intermediates for the synthesis
of large number of pharmaceutical compounds. Com-
pounds containing these motifs display antifungal [2],
antibacterial [2,3], anti-HIV [4], antiinflammatory [5],
antitubercular [6], histone deacetylase inhibition [7], and
are ligands for estrogen-receptors (ER) [8]. Occurrence
of these motifs in natural products and their diverse bio-
logical activities has inspired significant interest in their
synthesis [1b,9]. The well known method for synthesis
of thiazole and oxazole skeleton is Hantzsch’s method,
which involves condensation of a-haloketones with thioa-
mide/thiourea and amides/ureas, respectively. Many
other methods have been reported for the synthesis of
2,4-disubstituted thiazoles and oxazoles using b-cyclo-
dextrin in water [10], alkynyl(aryl)iodonium reagents
[11], ammonium-12-molybdophosphate [12], oxodiphos-
phonium salt [13], and microwave irradiation [14].
Owing to stress on development on green synthetic
methodologies, recently synthesis of thiazoles was also
achieved in alternative solvents such as water [15], ionic
liquid [16], and PEG [17]. However, many of these
methods suffer from one or more drawbacks that include
use of reactive or unsafe starting materials such as
a-haloketones, use of expensive and corrosive catalysts,
use of volatile organic solvents, tedious reaction work-
up, long reaction times, low yields, and harsh reaction
conditions. Furthermore, most of these procedure are for
the synthesis of 2,4-disubstituted thiazoles, there have
RESULT AND DISCUSSION
Initially, we tried reaction of p-chloroacetophenone and
thiourea in the presence of NBS or Br2 to yield 4-(40-
chlorophenyl)thiazol-2-amine (3b). The yield of 3b was
very low (<20%) with both NBS and Br2. With our
earlier experience with PTT as in situ brominating agent
in ionic liquid [19d], we replaced NBS or Br2 with PTT
in the above reaction and to our delight the yield of 3b
increased to 90%. The added advantage with PTT is that
it does not require any acidic conditions or radical
initiator like NBS and handling of PTT is very easy as
compare to other brominating agents. With PTT in-situ
bromination of p-chloroacetophenone was completed
© 2012 HeteroCorporation

960
M. K. Muthyala and A. Kumar
Vol 49
Scheme 1. Outline for synthesis of thiazoles and oxazoles.
within 2 h. After bromination, the condensation of insitu
generated a-bromo-p-chloroacetophenone with thiourea
was carried out in the same reaction media to give 4-(40-
chlorophenyl)thiazol-2-amine (3b).
corresponding thiazoles (3a–o). The results for these thia-
zoles are summarized in Table 2. The yields of the thia-
zoles are excellent (75–92%) and the synthetic strategy
allows synthesis of diverse thiazoles. As per the yields
of thiazoles (Table 2) it can be observed that
acetophenones containing both electron withdrawing
and electron releasing substituents were tolerated as good
substrate for this reaction under these conditions.
To understand the role of solvent the model reaction
was carried out in different solvents such as [bmim]
[BF4], [bmim][PF6], methanol, THF, DMF, DCM, tolu-
ene, and water. In DMF and toluene, no appreciable yield
of product was obtained whereas in other organic solvents
such as DCM, THF and methanol the yield of 3b was
between 65 and 80% (Table 1). Among two ionic liquids
screened, [bmim][BF4] was found to give the best yield
(90%) of 3b (Table 1). The results are in agreement
with previous report on the synthesis of thiazoles from
a-bromoketones in ionic liquid where [bmim][BF4] was
found to be better medium over [bmim][PF6] and other
ionic liquids [16]. The ionic liquid [bmim][BF4] was
selected as solvent of choice keeping in view of its non
volatile and environmentally benign nature. The role of
ionic liquid to enhance the rate of reaction may be in
terms of some Lewis/ Brønsted acidity of the imidazolium
cation leading to increased electropositive character of
carbonyl group of in situ generated a-bromoketone as
proposed earlier [16,19c]. The [bmim][BF4] also
enhances the rate of in-situ bromination of ketones by
PTT as reported earlier [19d]. The structure of 3b was
To explore the generality and increase the utility of
the protocol we extended it for the synthesis of 2,4-
disubstituted oxazoles (5a–f) from ketones. Initially, we
failed to achieve the desired 2-methyl-4-phenyloxazole
(5f) from the reaction of acetophenone and acetamide
using PTT in [bmim][BF4] at room temperature. After
exploring different reaction conditions the best yield of
5f was obtained when the reaction mixture was heated
at 80ꢁC in [bmim][BF4]. The lower reactivity at room
temperature can be attributed to the lower nucleophilicity
of oxygen in acetamide as compared to sulfur in
thioamides. The structure of oxazole 5f was confirmed
1
by IR, H-NMR, 13C-NMR, and HRMS data. In HRMS,
a peak at m/z 160.0431 was observed for [M+H]+ ion. In
Table 1
1
confirmed by IR, H-NMR, 13C-NMR, and HRMS data.
Solvent effect on the yield of 4-(40-chlorophenyl)thiazol-2-amine (3b).
In HRMS spectrum a peak appeared at m/z 210.9817
corresponding to [M+H]+ ion for C9H8ClN2S. In
1H-NMR characteristic peak at d 6.72 appeared for C5-
proton of the thiazole ring and in 13C-NMR characteristic
peak appeared at d 165.28 and 102.21 ppm for C2-carbon
and C4-carbon of the thiazole ring, respectively. The IR
spectrum showed two peaks at 3446 and 3216 cmꢀ1
corresponding to the NH2 group.
Sr. No.
Solvent
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
[bmim][BF4]
[bmim][PF6]
DCM
Methanol
THF
DMF
Toluene
Water
4
6
4
6
6
24
24
24
90
65
82
70
75
<10
–
–
After obtaining optimum reaction conditions, to study
the scope of the reaction different substituted ketones (1)
and thioamides/thiourea (2) were allowed to react to give
aIsolated yields.
bNo product observed on TLC.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

July 2012
A novel and Efficient One Pot Synthesis of 2,4-Disubstituted Thiazoles and Oxazoles
961
Using Phenyltrimethylammoniumtribromide in Ionic Liquid
Table 2
Synthesis of 2,4-disubstituted thiazoles in [bmim][BF4].
Sr. No.
1
R
R0
H
R00
Product
Time (h)
4
Yield (%)
92
Mp ꢁC (Lit. Mp)
Ph
NH2
3a
3b
3c
148–150 (150) [15]
2
3
4-ClPh
H
H
NH2
NH2
4
4
90
86
163–165 (163–164) [16]
187–189 (188–190) [15]
3-NO2Ph
4
5
4-OCH3Ph
1-Naphthyl
H
H
NH2
NH2
3d
3e
4
4
87
80
204–207 (204–205) [15]
157–158
6
2-Naphthyl
H
NH2
3f
4
80
152–154 (152–153) [15]
7
8
4-CH3Ph
H
H
NH2
NH2
3g
3h
4
4
85
85
130 (125–126) [16]
209–212
6-OH, 2-BrPh
9
2-Thiazolyl
H
NH2
NH2
3i
3j
4
4
87
83
186–189
10
-CH2(CH2)2CH2-
-CH2(CH2)3CH2-
87–90 (88–90) [20]
11
NH2
3k
4
81
63–66
(Continues)
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

962
M. K. Muthyala and A. Kumar
Vol 49
Table 2
(Continued)
SrS. rN. oN.o.
R
R0
H
R00
Product
Time (h)
5
Yield (%)
81
Mp ꢁC (Lit. Mp)
112–115 (111–112) [16]
12
4-ClPh
CH3
3l
13
2-Naphthyl
3-NO2Ph
H
H
CH3
CH3
3m
3n
5
5
78
80
88–89
14
15
87–89
4-ClPh
H
Ph
3o
6
75
130–132
aAll the products gave satisfactory 1H-NMR, 13C-NMR, and mass data.
bIsolated yield.
EXPERIMENTAL
similarity with 3b, a characteristic peak for C3-proton of
oxazole ring was observed at d 8.36 ppm whereas a peak
appeared at d 2.40 for C2-methyl protons in H-NMR
1-Methylimidazole, n-butyl bromide, NaBF4, and KPF6 were
purchased from Sigma-Aldrich. All other reagents and solvents
were purchased from S. D. Fine, India and used without further
purification unless otherwise specified. Column chromatography
was carried out over silica gel (60–120 mesh, S. D. Fine, India).
NMR spectra were recorded on a Brucker Heaven Avance 11
400 spectrophotometer using CDCl3 and DMSO-d6 as solvent
and the chemical shifts were expressed in ppm. Mass spectra were
recorded on a QSTARW ELITE LX/MS/MS mass spectrometer
from applied biosystem. The purity of the products was
determined on silica-coated aluminium plates (Merck). The ionic
liquid, [bmim][BF4] and [bmim][PF6] were prepared from
1-methylimidazole by minor modification of literature procedure
[23].
1
spectrum. Two peaks appeared at d 167.73 and 125.42
ppm for C2-carbon and C4-carbon, respectively in 13C-
NMR spectrum. After obtaining the optimum reaction
conditions, the scope of protocol was examined for the
synthesis of diversified oxazoles by the reaction of dif-
ferent substituted ketones and amides/ureas in the pres-
ence of PTT in [bmim][BF4]. The results for different
oxazoles are summarized in Table 3. It was observed that
yields were lower for oxazoles (68–76%) and reaction
required longer time and high temperature as compared
to thiazoles. Like thiazoles, in the synthesis of oxazole
as well acetophenones containing both electron with-
drawing and electron releasing substituents were toler-
ated as good substrate for this reaction under these
conditions.
General procedure for synthesis of 2,4-disubstitutedthiazoles.
PTT (655 mg, 1.1 mmol) was added to a mixture of ketone
(1.0 mmol) in [bmim][BF4] (2.0 mL) and reaction mixture was
stirred vigorously at room temperature for 2 h then thioamide/
thiourea (1.2 mmol) was added to this reaction mixture and
stirred for additional 1 h at room temperature. Progress of the
reaction was monitored by thin layer chromatography (TLC),
after completion of reaction aqueous sodium bicarbonate wash
was given to reaction mixture and pH ꢂ9 was maintained. The
precipitation occurred, which was filtered and washed with
diethyl ether. The residue obtained after diethyl wash was
percolated through a band of silica gel (60–120 mesh) using
CONCLUSIONS
In conclusion, we have demonstrated a novel, highly ef-
ficient one-pot procedure for synthesis of 2,4-disubstituted
thiazoles and oxazoles from the reaction of ketones with
thioamides/thiourea and amides/urea using PTT as in-situ
brominating agent in ionic liquid [bmim][BF4]. The main
advantages of this procedure are avoiding the handling of
lacrymetric compounds, hazardous organic solvents, and
toxic catalysts. Further studies for the synthesis of 1,3-imi-
dazoles using this method is in progress in our laboratory.
hexane/ethyl acetate (9:
1 v/v) as an eluent to afford
corresponding compounds in 75–92% yield.
Spectral data for selected thiazoles. 4-(Napthalen-1-yl)
thiazol-2-amine (3e).
1H-NMR (500 MHz, DMSO-d6): d =
6.75 (s, 1H), 7.09 (s, 2H, NH2), 7.50 (d, J = 6.5 Hz, 3H), 7.62
(d, J = 7.1 Hz, 1H), 7.97–7.82 (m, 2H), 8.44 (d, J = 8.0 Hz,
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

July 2012
A novel and Efficient One Pot Synthesis of 2,4-Disubstituted Thiazoles and Oxazoles
963
Using Phenyltrimethylammoniumtribromide in Ionic Liquid
Table 3
Synthesis of 2,4-disubstituted oxazoles in [bmim][BF4].
Sr. No.
1
R
R0
H
R00
Product
Time (h)
8
Yield (%)
76
Mp (ꢁC) (Lit. Mp)
Ph
NH2
5a
5b
150–152 (151–152) [21]
2
3-NO2Ph
H
NH2
8
75
149–153
3
4
4-CH3OPh
3-NO2Ph
H
H
NH2
CH3
5c
8
9
74
70
179–181 (179–180) [21]
113–115
5d
5
6
2-Naphthyl
H
H
CH3
CH3
5e
5f
10
10
68
71
70–72
Ph
45 (45) [22]
aAll the products gave satisfactory 1H-NMR, 13C-NMR, and mass data.
bIsolated yield.
1H). 13C-NMR (126 MHz, DMSO-d6): d = 168.41, 150.49,
133.94, 133.91, 131.17, 128.56, 128.35, 127.01, 126.67,
126.31, 126.21, 125.85, and 105.41; HRMS: m/z calcd. for
C13H10N2S 226.0565, found: 227.0343 [M+H]+.
(brs, 2H, amine), 7.16 (s, 1H); 13C-NMR (126 MHz, DMSO-d6)
d = 169.16, 163.21, 144.51, 143.95, 120.15, and 104.50;
MS (ESI) m/z calcd. for C6H5N3S2 182.9925, found 183.8932
[M+H]+.
4-(Naphthalene-2yl)thiazol-2-amine (3f). 1H-NMR (500
MHz, DMSO-d6) d = 7.09 (s, 2H), 7.15 (s, 1H), 7.50–7.42
(m, 2H), 7.95–7.83 (m, 4H), 8.30 (s, 1H); 13C-NMR (126 MHz,
DMSO-d6) d = 168.68, 150.20, 133.63, 132.76, 132.72, 128.50,
128.32, 127.96, 126.77, 126.24, 124.47, 124.44, and 102.85;
HRMS: m/z calcd. for C13H10N2S 226.0565, found 227.0341
[M+H]+.
4,5,6,7-Tetrahydrobenzo(d)thiazol-2-amine (3j). 1H-NMR
(400 MHz, DMSO-d6) d = 5.06 (brs, 2H), 3.01–2.43 (m, 4H),
2.00–1.53 (m, 4H); 13C-NMR (101 MHz, DMSO-d6) d =
165.21, 145.23, 118.07, 26.50, 23.54, 23.17, and 22.95;
MS (ESI) m/z calcd. for C7H10N2S 154.0565, found 155.0235
[M+H]+.
5,6,7,8-Tetrahydro-4H-cyclohepta(d)thiazol-2-amine (3k).
1H-NMR (400 MHz, CDCl3) d = 4.88 (brs, 2H, NH2),
2.63–2.56 (m, 4H), 1.78–1.55 (m, 6H); 13C-NMR (101 MHz,
DMSO-d6) d = 163.18, 149.71, 121.12, 31.58, 31.29, 28.25,
26.60, and 26.02; MS (ESI) m/z calcd. for C8H12N2S
168.0721, found 169.0452 [M+H]+.
4-p-Tolylthiazol-2-amine (3g). 1H-NMR (500 MHz, DMSO-
d6) d = 7.70 (d, J = 7.9 Hz, 2H, ArH), 7.14 (d, J = 7.8 Hz, 2H,
ArH), 6.99 (brs, 2H, NH2), 6.89 (s, 1H), 2.27 (s, 3H, CH3);
13C-NMR (126 MHz, DMSO-d6) d = 168.52, 150.30, 136.80,
132.70, 129.45, 125.91, 100.99, and 21.22; HRMS: m/z calcd. for
C10H10N2S 190.0565, found 191.0347 [M+H]+.
4-(40-Chlorophenyl)-2-methylthiazole (3l). 1H-NMR (300
MHz, CDCl3) d = 7.82–7.79 (d, J = 8.4 Hz, 2H), 7.39–7.29 (m,
2H), 7.26 (s, 1H), 2.76 (s, 3H); 13C-NMR (75 MHz, CDCl3) d
= 169.32, 150.36, 138.06, 133.03, 128.88, 127.57, 112.61, and
19.33; HRMS: m/z calcd. for C10H8ClNS 209.0066, found
209.9316 [M+H]+.
2-(2-Aminothiazol-4-yl)-3-bromophenol (3h). 1H-NMR
(500 MHz, DMSO-d6) d = 11.93 (s, 1H, OH), 7.92–7.90 (m,
1H, ArH), 7.45–7.39 (m, 2H, ArH), 7.24 (brs, 2H, NH2),
7.16 (s, 1H); 13C-NMR (126 MHz, DMSO-d6) d = 168.62,
155.10, 145.95, 131.51, 129.14, 121.23, 119.46, 110.60, and
103.09; HRMS: m/z calcd. for C9H7BrN2OS 269.9462, found
270.9342 [M+H]+.
2-Methyl-4-(naphthalene-20-yl)thiazole (3m).
1H-NMR
(300 MHz, CDCl3) d = 8.41 (s, 1H), 7.94–7.81 (m, 4H), 7.47–
7.42 (m, 3H), 2.80 (s, 3H); 13C-NMR (75 MHz, CDCl3) d =
163.76, 152.80, 131.37, 130.80, 129.52, 126.14, 126.10,
1
4-(Thiazol-2-yl)thiazol-2-amine (3i). H-NMR (500 MHz,
DMSO-d6) d = 7.83–7.74 (m, 1H), 7.68–7.58 (m, 1H), 7.28
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

964
M. K. Muthyala and A. Kumar
Vol 49
125.39, 124.04, 123.78, 123.00, 121.98, 110.4, and 17.12; HRMS:
m/z calcd. for C14H11NS 225.0612, found 226.0389 [M+H]+.
2-Methyl-(40-nitrophenyl)thiazole (3n). 1H-NMR (300 MHz,
CDCl3) d = 8.72 (s, 1H), 8.23–8.15 (m, 2H), 7.61–7.55 (t, J =
8.1 Hz, 1H), 7.48 (s, 1H), 2.79 (s, 3H); 13C-NMR (75MHz,
CDCl3) d = 166.71, 152.59, 148.72, 136.14, 132.08, 129.68,
122.52, 121.14, 114.43, and 19.33; HRMS: m/z calcd. for
C10H8N2O2S 220.0306, found 221.0278 [M+H]+.
125.42, and 13.86; HRMS: m/z calcd. for C10H9NO 159.0684,
found 160.0431 [M+H]+.
Acknowledgments. This work was supported by Council of
Scientific and Industrial Research (CSIR), New Delhi (01(2214)/
08/EMR-II). The author MMK is thankful to CSIR, New Delhi
for junior research fellowship.
4-(40-Chlorophenyl)-2-phenylthiazole (3o). 1H-NMR (500
MHz, DMSO-d6) d = 8.24 (s, 1H), 8.12–8.05 (m, 3H), 8.05–7.96
(m, 2H), 7.62–7.45 (m, 4H); 13C-NMR (126 MHz, DMSO-d6) d
= 167.73, 154.32, 133.30, 133.27, 133.17, 130.94, 129.75,
129.31, 128.30, 126.69, and 115.84; HRMS: m/z calcd. for
C15H10ClNS 271.0222, found 272.0103 [M+H]+.
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[23] (a) Chauhan, S. M. S.; Kumar, A.; Srinivas, K. A. Chem
Commun (Cambridge, UK) 2003, 2348; (b) Srinivas, K. A.; Kumar, A.;
Chauhan, S. M. S. Chem Commun (Cambridge, UK) 2002, 2456.
General procedure for synthesis of 2,4-disubstituted
oxazoles. PTT (655 mg, 1.1 mmol) was added portion wise to
a mixture of ketone (1.0 mmol) in [bmim][BF4] (2.0 mL) and
the reaction was stirred vigorously at room temperature for 2 h
then acetamide/urea (1.2 mmol) was added to the reaction
mixture and stirred it for additional 7–10 h at 80ꢁC. Progress
of the reaction was monitored by TLC. After completion of
reaction aqueous sodium bicarbonate wash was given to the
reaction mixture to maintain pH ꢂ9. The compound was
extracted using ethyl acetate (3 ꢃ 3 mL). The combined
organic layer was dried with anhydrous sodium sulphate and
concentrated under reduced pressure. The crude product
obtained was purified by column chromatography on silica gel
(60–120 mesh) using hexane/ethyl acetate (9: 1 v/v) as eluent
to afford corresponding compounds in 71–85% yield.
Spectral data for selected oxazoles. 4-Phenyloxazol-2-amine
(5a). 1H-NMR (500 MHz, DMSO-d6) d = 7.29–7.24 (m, 1H,
ArH), 7.40–7.33 (m, 2H, ArH), 7.70 (d, J = 8.2 Hz, 2H, ArH),
8.36 (s, 1H); 13C-NMR (126 MHz, DMSO-d6) d = 161.99,
139.43, 132.49, 128.91, 127.66, 127.57, and 125.10; HRMS: m/z
calcd. for C9H8N2O 160.0637, found 161.0345 [M+H]+.
4-(30-Nitrophenyl)oxazol-2-amine (5b). 1H-NMR (500 MHz,
DMSO-d6) d = 8.34 (s, 1H), 8.03–7.96 (m, 3H), 7.57 (s, 1H),
6.79 (br, 2H, NH2); 13C-NMR (126 MHz, DMSO-d6) d =
164.45, 150.85, 139.81, 136.45, 133.45, 132.76, 131.71,
124.30, and 121.55; HRMS: m/z calcd. for C9H7N3O3
205.0487, found 206.0038 [M+H]+.
2-Methyl-4-(30-nitrophenyl)oxazole (5d). 1H-NMR (300 MHz,
CDCl3) d = 8.54 (s, 1H), 8.16–8.13 (d, J = 8.4 Hz, 1H), 8.05–8.03
(d, J = 7.5 Hz, 1H), 8.02–7.94 (m, 1H), 7.57–7.54 (d, J = 8.1 Hz,
1H), 2.55 (s, 3H); 13C-NMR (75 MHz, CDCl3) d = 162.46, 151.03,
146.32, 138.87, 134.42, 131.14, 129.73, 122.50, 120.27, and
13.95; HRMS: m/z calcd. for C10H8N2O 204.0535, found
205.0437 [M+H]+.
2-Methyl-(napthalen-20-yl)oxazole (5e). 1H-NMR (300 MHz,
CDCl3) d = 8.26 (s, 1H), 7.91–7.88 (m, 2H), 7.83–7.81 (m, 2H),
7.74–7.71 (m, 1H), 7.50–7.43 (m, 2H), 2.56 (s, 3H); 13C-NMR
(75 MHz, CDCl3) d = 163.0, 153.22, 141.70, 134.55, 134.01,
129.37, 129.18, 128.67, 127.37, 126.98, 125.11, 124.37,
118.31, and 15.01; HRMS: m/z calcd. for C14H11NO 209.0841,
found 210.0734 [M+H]+.
2-Methyl-4-phenyloxazole (5f). 1H-NMR (500 MHz, DMSO-d6)
d = 2.40 (s, 3H, CH3), 7.27 (s, 1H), 7.46–7.35 (m, 3H, ArH), 7.70 (d,
J = 8.2 Hz, 2H, ArH), 8.36 (s, 1H, ArH); 13C-NMR (126 MHz,
DMSO-d6) d = 162.10, 139.99, 134.96, 131.28, 129.20, 128.24,
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet