Alum (KAl(SO4)2·12H2O)-catalyzed, eco-friendly, and efficient one-pot synthesis of 2-arylbenzothiazoles and 2-arylbenzoxazole in aqueous medium

Article abstract of DOI:10.1071/CH08122

Alum (KAl(SO₄)₂12H₂O) performs as a novel catalyst for the synthesis of 2-arylbenzothiazoles and 2-arylbenzoxazole from o-aminothiophenol and o-aminophenol with various substituted aldehydes in good to excellent isolated yields (8595%) using water as a solvent at ambient temperature. Several solvents were examined for this reaction; however, in terms of reaction yield and time, water was found to be the optimum solvent. The remarkable advantages offered by this method are an inexpensive and easily available catalyst, a simple procedure, mild conditions, much faster (6090 min) reactions, and good to excellent yields of products.

Full text of DOI:10.1071/CH08122

Full Paper
CSIRO PUBLISHING
www.publish.csiro.au/journals/ajc
Aust. J. Chem. 2008, 61, 905–909
Alum (KAl(SO4)2·12H2O)-Catalyzed, Eco-Friendly,
and Efficient One-Pot Synthesis of 2-Arylbenzothiazoles
and 2-Arylbenzoxazole in Aqueous Medium
Shivaji S. Pawar,A Deepak V. Dekhane,A Murlidhar S. Shingare,B
and Shivaji N. ThoreA,C
ADepartment of Chemistry, Vinyakrao Patil Mahavidyala Vaijapur, Aurangabad-423 701,
Maharashtra, India.
BDepartment of Chemistry, Dr Babasaheb Ambedkar Marathwada University,
Aurangabad-431 004, Maharashtra, India.
CCorresponding author. Email: snthore@rediffmail.com
Alum (KAl(SO4)2·12H2O) performs as a novel catalyst for the synthesis of 2-arylbenzothiazoles and 2-arylbenzoxazole
from o-aminothiophenol and o-aminophenol with various substituted aldehydes in good to excellent isolated yields (85–
95%) using water as a solvent at ambient temperature. Several solvents were examined for this reaction; however, in terms
of reaction yield and time, water was found to be the optimum solvent. The remarkable advantages offered by this method
are an inexpensive and easily available catalyst, a simple procedure, mild conditions, much faster (60–90 min) reactions,
and good to excellent yields of products.
Manuscript received: 25 March 2008.
Final version: 16 September 2008.
Introduction
solvents, but also because water exhibits unique reactivity and
selectivity, which is different from those in conventional organic
solvents.[25] In this respect, the development of water-tolerant
catalysts has rapidly become an area of intense research. Sur-
prisingly, however, there are very few reports for synthesis
of benzothiazole and benzoxazole and its derivatives in aque-
ous media.[26] These findings prompted us to investigate the
synthesis of benzothiazole and benzoxazole in aqueous media.
Alum (KAl(SO4)2·12H2O) is an acid with extremely
wide applications such as in the synthesis of 14H-
dibenzo[a,j]xanthenes[27] and coumarins.[28] However, there are
no examples of the use of alum as a catalyst for the preparation
of benzothiazoles and benzoxazoles.
Benzothiazoles and benzoxazoles constitute an important class
of compounds. They are widely found in bioorganic and medic-
inal chemistry, with applications in drug discovery such as
antitumour, anticonvulsant, and antiviral applications.[1–3] They
have also found applications in industry as antioxidants, vulcan-
ization accelerators, and as a dopant in light-emitting organic
electroluminescent devices.[4,5] There are few methods for the
synthesis of the title compounds. The most common ones
include the reaction of 2-aminothiophenol or 2-aminophenol
with a substituted carboxylic acid, aldehyde, or ester in the pres-
ence of polyphosphoric acid (PPA),[6] polyphosphate ester,[7]
a
mixture of methanesulfonic acid and phosphorus pentoxide,[8]
or oxidative cyclization of phenolic Schiff bases using−vari-
ous oxidants such as Pb(OAc)4,[9] Mn(OAc)3,[10] Th+ClO4 ,[11]
PhI(OAc)2,[12] and Dess–Martin periodane.[13]
Result and Discussion
As a continuation of our research devoted to the development of
green organic chemistry by performing organic transformations
with water as the reaction medium,[29] herein, we have devel-
oped an efficient and green methodology for the synthesis of
2-substituted benzothiazoles and benzoxazoles by condensation
of 2-aminothiophenol and 2-aminophenol respectively with vari-
ousaromaticaldehydesusingalum(25 mol-%)asaninexpensive
catalyst in water, which makes use of milder conditions over the
reported procedure as depicted in Scheme 1; the methodology
developed is simple with good to excellent yields of products.
We first compared the catalyst effect on different sol-
vents for the synthesis of 2-phenylbenzothiazole as summa-
rized in Table 1. In a typical experiment, the reaction of
2-aminothiophenol 1 and aldehydes 2 in water was carried out
in the presence of alum (KAl(SO4)2·12H2O) to afford the corre-
sponding 2-phenylbenzothiazole 3a in 95% yield. The reaction
proceeded rapidly at ambient temperature with 25 mol-% of
Several microwave-assisted[14] procedures for the synthe-
sis of benzothiazoles and benzoxazoles have been developed
over the past few years in the presence of p-toluenesulfonic
acid (p-TsOH),[15] Lawesson’s reagent,[16] ionic liquid,[17]
SiO2,[18] SiO2 and nitrobenzene,[19] carboxylic acid[20] or
acid chloride,[21] and iodine.[22] Some palladium-catalyzed
reagents were used for condensation of 2-aminothiophenol
or 2-aminophenol with aryl halides followed by dehydrative
cyclization,[23] also reported was the ligand-promoted copper-
catalyzed cyclization of benzoxazole and benzothiazol from
ortho-halobenzanilides.[24] However, there still remains the need
for a simple and efficient process for the synthesis benzothia-
zoles and benzoxazoles.
Organic reactions in aqueous media have attracted much
attention in synthetic organic chemistry, not only because water
is one of the most abundant, cheap, and environmentally friendly
© CSIRO 2008
10.1071/CH08122
0004-9425/08/110905

906
S. S. Pawar et al.
NH2
ϩ
N
X
Alum (25 mol-%)
R
R
ArCHO
Ar
Water, room temp.,
60–90 min
XH
2
1
3
R ϭ H, Cl, Me, F
X ϭ S, O
Where X ϭ S, 3a–k
X ϭ O, 3l–q
ϩ
H
N
R
Ar
X
4
Not formed
Scheme 1.
Table 1. Solvent effects on the reaction of benzaldehyde and 2-amino-
thiophenol in the presence of alum (KAl(SO4)2·12H2O)
Standard conditions: 1 mmol 2-aminothiophenol, 1.1 mmol benzaldehyde,
25 mol-% catalyst, solvent, room temp. Isolated yields based on starting
2-aminothiophenol
Table 2. Alum (KAl(SO4)2·12H2O)-catalyzed synthesis of 2-aryl-
benzothiazoles and 2-arylbenzoxazoles in water
Standard conditions: 1 mmol 2-aminothiophenol or 2-aminophenol,
1.1 mmol ArCHO, 25 mol-% catalyst (alum), water, room temp. Isolated
yields based on starting 2-aminothiophenol and 2-aminophenol
Entry
Solvent
Catalyst [mol-%]
Time [min]
Yield [%]
Entry
R
Ar
X
Product
Time
[min]
Yield
[%]
1
2
3
4
5
6
7
8
CH2Cl2
CH3CN
THF
CHCl3
DMSO
DMF
MeOH
EtOH
Dioxan
H2O
25
25
25
25
25
25
25
25
25
25
10
15
20
30
180
150
120
150
120
130
90
60
90
60
90
35
45
40
50
45
45
30
35
45
95
45
47
65
95
1
2
3
4
5
6
7
8
H
H
H
H
H
H
5-Cl
5-Cl
5-Cl
5-Cl
5-Cl
H
H
H
H
5-Me
5-F
Ph
S
S
S
S
S
S
S
S
S
S
S
O
O
O
O
O
O
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3q
60
65
90
70
65
75
70
70
75
90
80
85
75
70
80
80
85
95
90
92
88
85
89
92
94
87
88
91
93
92
87
85
92
93
4-OCH3C6H4
4-toluene
4-CNC6H4
3,4,5-tri-OCH3C6H2
4-ClC6H4
Ph
4-OCH3C6H4
3-OCH3C6H4
4-FC6H4
4-ClC6H4
Ph
9
10
11
12
13
14
9
H2O
H2O
H2O
H2O
10
11
12
13
14
15
16
17
90
90
90
4-CNC6H4
4-OCH3C6H4
3,4,-di-ClC6H3
Ph
Ph
catalyst (which is highly water soluble) and was complete within
60 min (Table 1, entry 10). We kept the catalyst constant and
used different solvents; CH2Cl2, CH3CN, THF, CHCl3, DMSO,
DMF, MeOH, EtOH, and dioxan all afforded a very low yield
of product (Table 1, entries 1–9). Varying the amount of cata-
lyst did not improve the yield (Table 1, entries 11–14). These
results suggest that water is the best solvent for the synthesis of
2-phenylbenzothiazole; it may be due to the greater solubility of
the catalyst in water compared with organic solvent.
With optimal conditions in hand, we reacted various sub-
stituted 2-aminothiophenols 1 and aldehydes 2 to give the
corresponding substituted 2-arylbenzothiazole products 3a–n in
good to excellent yields (Table 2, entries 1–11).
We also examined the scope of this methodology on 2-
aminophenol 1 with aldehydes 2, and the results are summarized
in Table 2 (entries 12–17). We found that the condensation of 2-
aminophenol with various aldehydes also worked, with the same
reactivityof2-aminothiophenolaffordingthedesiredproductsin
good yields. All the reactions were complete within 60–90 min.
The obtained yields of benzothiazole and benzoxazole were 85–
95%.The structures of the products were confirmed by 1H NMR,
13C NMR, mass spectrometry, and elemental analysis.
To emphasize the effect of the catalyst, 2-aminothiophenol 1
and aldehydes 2 were subjected to reaction in the presence of
different acidic catalysts (25 mol-%) under the same conditions.
As can be seen inTable 3, satisfactory results were obtained only
with alum (entry 10).
Conclusions
Alum (KAl(SO4)2·12H2O) as a catalyst provides an efficient
methodology for the selective synthesis of 2-substituted
benzothiazole and benzoxazole derivatives from various aro-
matic aldehydes with 2-aminothiophenol and aminophenol. The
remarkable advantages offered by this method are the use of
a stable and inexpensive catalyst, a simple procedure, mild
conditions, and good to excellent yields of products.

Synthesis of 2-Arylbenzothiazoles and 2-Arylbenzoxazole in H2O
907
Table 3. Effect of acidic catalyst on the reaction of 2-aminothiophenol
and benzaldehyde in water at ambient temperature
1H, ArH), 8.02 (t, J 7.42, 1H, ArH), 8.12 (d, J 7.38, 1H, ArH).
δC (CDCl3, 100 MHz) 120.8, 121.1, 124.9, 124.9, 127.1, 128.6,
129.8, 129.8, 133.1, 133.8, 154.9, 167.1. m/z (electron impact
(EI), 70 eV) 212 (M + H)+. Calc. for C13H9NS: C 73.9, H 4.3,
N 6.6, S 15.4. Found: C 73.7, H 4.3, N 6.3, S 15.1%.
Entry
Catalyst
Time [min]
Yield [%]A
1
2
3
4
5
6
7
8
p-TsOH
NH4Cl
(NH4)2HPO4
Silica sulfuric acid
H2SO4
NaHSO3
NaHSO4
TiCl4
180
150
120
150
120
130
90
55
35
Trace
65
40
45
2-(4-Methoxyphenyl)benzothiazole 3b
Yellow solid, mp 199–200◦C. δH (CDCl3, 400 MHz) 3.92 (s,
3H, OCH3), 7.12–7.41 (m, 4H, ArH), 7.07 (d, J 7.75, 2H, ArH),
8.05 (d, J 8.22, 1H, ArH), 8.19 (d, J 8.22, 1H, ArH). δC (CDCl3,
100 MHz) 55.7, 112.5, 117.9, 120.8, 121.1, 123.9, 125.9, 127.1,
130.1, 135.6, 154.9, 160.2, 167.9. m/z (EI, 70 eV) 242 (M + H)+.
Calc. for C14H11NOS: C 69.7, H 4.6, N 5.8, S 13.3. Found:
C 69.8, H 4.4, N 5.6, S 13.5%.
45
55
60
9
I2
90
55
10
Alum
60
95
AIsolated yields based on starting 2-aminothiophenol.
2-(4-Methylphenyl)benzothiazole 3c
Yellow solid, mp 83◦C. δH (CDCl3, 400 MHz) 2.45 (s, 3H,
CH3), 7.26 (d, J 8.12, 2H,ArH), 7.30 (t, J 7.38, 1H,ArH), 7.41 (t,
J 7.38, 1H,ArH), 7.92–8.10 (m, 3H,ArH). δC (CDCl3, 100 MHz)
21.8, 121.7, 123.4, 125.4, 126.4, 127.9, 130.1, 131.3, 135.2,
141.9, 154.6, 168.5. m/z (EI, 70 eV) 226 (M + H)+. Calc. for
C14H11NS: C 74.6, H 4.9, N 6.2, S 14.2. Found: C 74.7, H 4.8,
N 6.4, S 14.4%.
Experimental
Reactions were monitored by TLC (silica, 80:20 ethyl
acetate/hexane). 1H NMR spectra were recorded on a 400 MHz
Varian–Mercury Plus spectrometer and are reported as parts
per million (ppm) downfield from tetramethylsilane as inter-
nal standard. 13C NMR spectra were recorded on a 100 MHz
Varian–Mercury Plus spectrometer and are reported as ppm
downfield from tetramethylsilane as internal standard. The fol-
lowing abbreviations are used: singlet (s), doublet (d), triplet (t),
multiplet (m), and broad (br). Mass spectra were taken with a
Waters Micromass-Quattro-II mass spectrometer. All chemicals
were obtained from commercial suppliers and were used without
purification.
2-(4-Cyanophenyl)benzothiazole 3d
Brownish solid, mp 100–102◦C. δH (CDCl3, 400 MHz) 7.61
(dd, J 7.55, 7.75, 2H, ArH), 7.85 (d, J 8.15, 2H, ArH), 8.05 (dd,
J 2.42, 7.55, 2H, ArH), 8.09 (d, J 8.15, 2H, ArH). δC (CDCl3,
100 MHz) 112.4, 117.2, 122.2, 125.1, 127.3, 127.9, 132.4, 132.5,
133.6, 140.1, 169.9. m/z (EI, 70 eV) 237 (M + H)+. Calc. for
C14H8N2S: C 71.2, H 3.4, N 11.9, S 13.6. Found: C 71.2, H 3.5,
N 11.8, S 13.5%.
General Procedure for the Preparation of 3a–k
2-Aminothiophenol (1 mmol), aromatic aldehyde (1.1 mmol),
and water (5 mL) were mixed in a 25-mL single-neck round-
bottom flask, and to this alum (KAl(SO4)2·12H2O; 25 mol-%)
was added. The reaction mixture was stirred at room temper-
ature for the appropriate time (Table 2, entries 1–11), and the
progress of the reaction was monitored by TLC. After comple-
tion of the reaction, the mixture was extracted with ethyl acetate
(2 × 10 mL). The combined organic layer was dried over anhy-
drous Na2SO4 and evaporated under reduced pressure; the crude
material was purified by column chromatography over silica gel
to afford products 3a–k with high purity.
2-(3,4,5-Trimethoxyphenyl)benzothiazole 3e
Colourless oil. δH (CDCl3, 400 MHz) 3.61 (s, 9H, OCH3),
6.57 (d, J 2.42, 2H, ArH), 7.45 (dd, J 2.42, 7.55, 2H, ArH), 8.22
(t, 1H,ArH), 8.31 (t, 1H,ArH). δC (CDCl3, 100 MHz) 56.3, 56.7,
104.5, 121.9, 122.1, 125.3, 125.9, 127.9, 135.6, 139.2, 151.5,
166.7. m/z (EI, 70 eV) 302 (M + H)+. Calc. for C16H15NO3S: C
63.8, H 5.0, N 4.7, S 10.6. Found: C 63.8, H 5.0, N 4.6, S 10.5%.
2-(4-Chlorophenyl)benzothiazole 3f
White solid, mp 114 –115◦C. δH (CDCl3, 400 MHz) 7.16 (d,
J 8.22, 2H, ArH), 7.30 (t, J 7.6, 1H, ArH), 7.41 (t, J 7.6, 1H,
ArH), 7.8 (d, J 7.3, 1H, ArH) 8.05 (d, J 8.4, 2H, ArH), 8.15 (d, J
7.3, 1H,ArH). δC (CDCl3, 100 MHz) 121.7, 121.7, 125.4, 126.1,
128.9, 129.9, 131.3, 134.2, 135.9, 154.6, 166.9. m/z (EI, 70 eV)
246 (M + H)+. Calc. for C13H8ClNS: C 63.5, H 3.3, Cl 14.4,
N 5.7, S 13.1. Found: C 63.4, H 3.2, Cl 14.5, N 5.4, S 13.2%.
General Procedure for the Preparation of 3l–q
2-Aminophenol (1 mmol), aromatic aldehyde (1.1 mmol), and
water (5 mL) were mixed in a 25-mL single-neck round-bottom
flask, and to this alum (KAl(SO4)2·12H2O; 25 mol-%) was
added. The reaction mixture was stirred at room temperature for
the appropriate time (Table 2, entries 12–17), and the progress of
thereaction wasmonitoredbyTLC.After completion of the reac-
tion, the mixture was extracted with ethyl acetate (2 × 10 mL).
The combined organic layer was dried over anhydrous Na2SO4
and evaporated under reduced pressure; the crude material was
purified by column chromatography over silica gel to afford
products 3l–q with high purity.
6-Chloro-2-phenylbenzothiazole 3g
Yellow solid, mp 104–105◦C. δH (CDCl3, 400 MHz) 7.16 (m,
1H, ArH), 7.36 (t, J 7.61, 2H, ArH), 7.56 (dd, J 7.61, 2.17, 2H,
ArH), 8.13 (d, J 2.12, 1H, ArH), 8.19 (d, J 8.3, 1H, ArH). δC
(CDCl3, 100 MHz) 121.5, 123.3, 125.7, 127.6, 128.9, 129.3,
129.7, 133.4, 137.3, 152.6, 166.7. m/z (EI, 70 eV) 246 (M + H)+.
Calc. for C13H8ClNS: C 63.5, H 3.3, Cl 14.4, N 5.7, S 13.1.
Found: C 63.4, H 3.2, Cl 14.5, N 5.5, S 13.2%.
Spectroscopic Data for Compounds
2-Phenylbenzothiazole 3a
White solid, mp 112–114◦C. δH (CDCl3, 400 MHz) 7.19–
7.25 (m, 3H, ArH), 7.33–7.39 (m, 3H, ArH), 7.65 (t, J 7.42,
6-Chloro-2-(4-methoxyphenyl)benzothiazole 3h
Yellow solid, mp 132–136◦C. δH (CDCl3, 400 MHz) 3.87 (s,
3H, OMe), 7.06 (d, J 8.61, 2H, ArH), 7.46 (s, 1H, ArH), 7.40

908
S. S. Pawar et al.
(d, J 7.8, 1H, ArH), 7.80 (d, J 7.8, 1H, ArH), 8.11 (d, J 8.8, 2H,
ArH). δC (CDCl3, 100 MHz) 55.7, 114.5, 122.6, 123.2, 125.6,
126.5, 129.3, 132.7, 133.4, 155.3, 162.7. m/z (EI, 70 eV) 276
(M + H)+. Calc. for C14H10ClNOS: C 61.0, H 3.7, Cl 12.9,
N 5.1, S 11.6. Found: C 61.0, H 3.7, Cl 12.8, N 5.2, S 12.7%.
ArH), 8.19 (dd, J 8.2, 1.8, 1H, ArH), 8.37 (d, J 1.8, 1H, ArH).
δC (CDCl3, 100 MHz) 110.5, 120.1, 125.1, 125.7, 126.2, 127.1,
129.2, 131.2, 133.4, 136.0, 142.1, 150.8, 170.0. m/z (EI, 70 eV)
264 (M + H)+. Calc. for C13H7Cl2NO: C 59.1, H 2.7, Cl 26.9,
N 5.3. Found: C 59.1, H 2.7, Cl 26.8, N 5.3%.
6-Methyl-2-phenylbenzoxazole 3p
6-Chloro-2-(3-methoxyphenyl)benzothiazole 3i
Off-white solid, mp 95◦C. δH (CDCl3, 400 MHz) 2.51 (s,
3H, CH3), 7.09 (ddd, J 8.0, 1.5, 0.6, 1H, ArH), 7.35 (t, J 0.6,
1H, ArH), 7.55–7.62 (m, 3H, ArH), 7.70 (d, J 8.2, 1H, ArH),
8.26–8.39 (m, 2H, ArH). δC (CDCl3, 100 MHz) 21.9, 110.6,
119.2, 126.0, 127.8, 131.2, 131.7, 135.9, 140.2, 151.7, 162.9. m/z
(EI, 70 eV) 210 (M + H)+. Calc. for C14H11NO: C 80.4, H 5.3,
N 6.7. Found: C 80.2, H 5.5, N 5.3%.
Yellow solid, mp 72–74◦C. δH (CDCl3, 400 MHz) 3.91 (s,
3H, OMe), 7.16 (dd, J 2.5, 7.8, 1H, ArH), 7.32–7.50 (m, 2H,
ArH), 7.60–7.70 (m, 2H, ArH), 7.77 (d, J 7.7, 1H, ArH), 7.99 (d,
J 2.5, 2.5, 1H, ArH). δC (CDCl3, 100 MHz) 112.4, 117.9, 120.2,
122.4, 123.6, 126.1, 130.2, 132.9, 133.5, 135.0, 155.5, 166.7.
m/z (EI, 70 eV) 276 (M + H)+. Calc. for C14H10ClNOS: C 61.0,
H 3.7, Cl 12.9, N 5.1, S 11.6. Found: C 61.0, H 3.7, Cl 12.8,
N 5.2, S 12.8%.
6-Fluoro-2-phenylbenzoxazole 3q
White solid, mp 108–111◦C. δH (CDCl3, 400 MHz) 7.11 (td,
J 8.8, 2.3, 1H, ArH), 7.29 (dd, 1H, J 8.0, 2.3, 1H, ArH), 7.52–
7.61 (m, 3H, ArH), 7.79 (dd, J 8.8, 4.9, 1H, ArH), 8.20–8.28
(m, 2H, ArH). δC (CDCl3, 100 MHz) 98.6, 112.3, 120.6, 127.1,
127.9, 130.2, 131.8, 138.7, 150.9, 161.0, 163.4. m/z (EI, 70 eV)
214 (M + H)+. Calc. for C13H8FNO: C 73.2, H 3.8, F 8.9,
N 6.6. Found: C 73.2, H 3.8, F 8.7, N 6.4%.
6-Chloro-2-(4-fluorophenyl)benzothiazole 3j
Pale yellow solid, mp 150–152◦C. δH (CDCl3, 400 MHz)
7.16–7.32 (m, 2H, ArH), 7.32 (dd, J 2.3, 7.8, 1H, ArH), 7.81
(d, J 7.8, 1H, ArH), 8.10–8.15 (m, 3H, ArH). δC (CDCl3,
100 MHz) 116.1, 116.5, 122.2, 123.4, 126.0, 129.2, 130.2, 133.2,
133.9, 155.7, 168.5. m/z (EI, 70 eV) 264 (M + H)+. Calc. for
C13H7ClFNS: C 59.2, H 2.7, Cl 13.4, N 5.3, S 12.2. Found:
C 59.1, H 2.7, Cl 13.3, N 5.4, S 12.2%.
Acknowledgements
6-Chloro-2-(4-chlorophenyl)benzothiazole 3k
The authors are thankful to the Head, Department of Chemistry, Vinyakrao
Patil Mahavidyala Vaijapur-423 701 (MS), India, for partial support of the
present work.
White solid, mp 140–142◦C. δH (CDCl3, 400 MHz) 7.32 (d,
J 8.1, 2H, ArH), 7.41 (d, J 8.1, 2H, ArH), 7.56 (dt, J 7.9, 2.2,
1H, ArH), 8.13 (d, J 2.2, 1H, ArH), 8.17 (d, J 7.9, 1H, ArH).
δC (CDCl3, 100 MHz) 121.2, 123.0, 125.6, 128.9, 129.3, 129.8,
131.5, 134.2, 137.0, 155.5, 166.5. m/z (EI, 70 eV) 280 (M + H)+.
Calc. for C13H7Cl2NS: C 55.7, H 2.5, Cl 25.3, N 5.0, S 11.4.
Found: C 55.6, H 2.7, Cl 25.4, N 5.2, S 11.3%.
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2-Phenylbenzoxazole 3l
White solid, mp 101–102◦C. δH (CDCl3, 400 MHz) 7.36–
7.44 (m, 2H, ArH), 7.53–7.67 (m, 4H, ArH), 7.79–7.86 (m, 1H,
ArH), 8.32 (dd, J 5.6, 2.1, 2H, ArH). δC (CDCl3, 100 MHz)
110.6, 120.2, 124.4, 125.1, 127.4, 127.7, 129.0, 131.4, 142.4,
150.7, 163.2. m/z(EI, 70 eV)196(M + H)+. Calc. forC13H9NO:
C 80.0, H 4.1, N 7.2. Found: C 79.9, H 4.6, N 7.3%.
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White solid, mp 201–204◦C. δH (CDCl3, 400 MHz) 7.31–
7.49 (m, 2H, ArH), 7.51 (m, 1H, ArH), 7.81–7.97 (m, 3H, ArH),
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2-(4-Methoxyphenyl)benzoxazole 3n
Off-white solid, mp 98◦C. δH (CDCl3, 400 MHz) 3.89 (d,
J 0.9, 3H, ArH), 7.16 (d, J 8.2, 2H, ArH), 7.37–7.42 (m, 2H),
7.61 (m, 1H, ArH), 7.85 (m, 1H, ArH), 8.22 (d, J 8.2, 2H, ArH).
δC (CDCl3, 100 MHz) 55.5, 110.2, 114.4, 119.6, 119.5, 124.4,
129.2, 142.1, 150.5, 162.1, 163.4. m/z (EI, 70 eV) 226 (M + H)+.
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White solid, mp 142–144◦C. δH (CDCl3, 400 MHz) 7.40–
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