One-pot reaction for the synthesis of N-substituted 2-aminobenzoxazoles using triphenylbismuth dichloride as cyclodesulfurization reagent

Article abstract of DOI:10.1016/j.jorganchem.2018.01.041

The treatment of various 2-aminophenols with isothiocyanates afforded thioureas, which were reacted in situ with triphenylbismuth dichloride in the presence of triethylamine to give the expected N-substituted benzoxazol-2-amines in good to excellent yields. Triphenylbismuth dichloride promoted the successful cyclodesulfurization of thioureas with short reaction times under mild reaction conditions. This reaction is the first example of the synthesis of heterocyclic rings using a pentavalent organobismuth reagent.

Full text of DOI:10.1016/j.jorganchem.2018.01.041

Journal of Organometallic Chemistry 859 (2018) 18e23
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
One-pot reaction for the synthesis of N-substituted
2-aminobenzoxazoles using triphenylbismuth dichloride as
cyclodesulfurization reagent
Yuki Murata a, Natsuho Matsumoto a, Maya Miyata a, Yuki Kitamura a, Naoki Kakusawa b,
,
*
Mio Matsumura a, Shuji Yasuike a
a School of Pharmaceutical Sciences, Aichi Gakuin University, 1-100 Kusumoto-cho, Chikusa-ku, Nagoya 464-8650, Japan
b Faculty of Pharmaceutical Sciences, Hokuriku University, Ho-3 Kanagawa-machi, Kanazawa 920-1181, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
The treatment of various 2-aminophenols with isothiocyanates afforded thioureas, which were reacted in
situ with triphenylbismuth dichloride in the presence of triethylamine to give the expected N-substituted
benzoxazol-2-amines in good to excellent yields. Triphenylbismuth dichloride promoted the successful
cyclodesulfurization of thioureas with short reaction times under mild reaction conditions. This reaction
is the first example of the synthesis of heterocyclic rings using a pentavalent organobismuth reagent.
© 2018 Elsevier B.V. All rights reserved.
Received 4 December 2017
Received in revised form
18 January 2018
Accepted 23 January 2018
Keywords:
One-pot reaction
Benzoxazole
Triphenylbismuth dichloride
Thioureas
Cyclodesulfurization
1. Introduction
[15], Brønsted acids such as CF3CO2H [16] and TfOH [17], and other
reagents such as TsCl/NaOH [18], LiOH/H2O2 [19], polymer-
Benzoxazoles are important heterocycles, serving as key func-
tional groups in many bioactive molecules and organic materials
[1e5]. Among these, N-substituted benzo[d]oxazol-2-amines (2-
aminobenzoxazoles) have attracted significant interest because of
their potential as biological and pharmaceutical therapeutic agents.
For instance, suvorexant I [6,7] has been recently approved as a
therapeutic drug for insomnia, compound II [8] is a potent inhibitor
of 5-lipoxygenase, compound III [9] behaves as a potent inhibitor of
p90 Ribosomal S6 kinases, and compound IV [10] displays potent
supported carbodiimides [20], hypervalent iodine (III) [21], and
1,10-(ethane-1,2-diyl)dipyridinium bistribromide (EDPBT) [22].
Phakhodee et al. recently reported a rapid ultrasound-assisted
synthesis of 2-aminobenzoxazoles using a Ph3PeI2 system [23].
However, these reagents have some disadvantages such as their
toxicity and the long reaction times or harsh conditions required:
moreover, the substrate scope and scalability for the synthesis of 2-
aminobenzoxazoles are a problem that also remain unsolved.
Organobismuth compounds are generally nontoxic, environ-
mentally benign, and useful synthetic reagents [24e28]. Among
them, the utility of triarylbismuth dichlorides (Ar3BiCl2) has
attracted much attention in recent years. These reagents are used as
arylating agents in the Ce and Oearylation of phenol derivatives
[29e31], the Nearylation of pyridin-2-ones [32,33], and the
inhibitory activity against
a-glucosidase (Fig. 1). Consequently,
many methods have been developed for the synthesis of 2-
aminobenzoxazoles. Among these methods, an efficient approach
involves the treatment of 2-aminophenols with isothiocyanates to
generate the corresponding thioureas, which subsequently un-
dergo cyclodesulfurization with the assistance of diverse desul-
furizing agents. Known desulfurization reagents include transition
metal reagents such as NiO [11], HgO [12], FeCl3 [13,14], and CuCl2
a
earylation of a,beunsaturated carbonyls [34] in the presence of a
base. They are also used in the Pd-catalyzed C(Ar)eC(Ar, sp2) bond
formation reaction with hypervalent iodium salts, organostananes,
and vinyl epoxides [35e37]. Furthermore, they can also be used for
the oxidation of alcohols and in the phosphine-catalyzed
* Corresponding author.
E-mail address: s-yasuik@dpc.agu.ac.jp (S. Yasuike).
aearylation of enones [38,39]. However, to be the best of our
https://doi.org/10.1016/j.jorganchem.2018.01.041
0022-328X/© 2018 Elsevier B.V. All rights reserved.

Y. Murata et al. / Journal of Organometallic Chemistry 859 (2018) 18e23
19
reagent for this cyclization, producing 90% of expected product 4a,
and side product triphenylbismuthane 2c in 91% yield (entry 1).
Triphenylbismuthane 2c was converted back to Ph3BiCl2 2a by
oxidative chlorination with SO2Cl2 for reuse. When antimony re-
agents 3a-d were employed instead of bismuth reagents, penta-
valent organoantimony compounds 3a and b were found to be
effective for this reaction (entries 5e8). However, the recovery of
renewable triphenylstibane 3c was low. A solvent screen showed
that the reaction took place effectively in DMF, DMSO, THF, CH3CN,
and CH3OH, among which DMF gave the highest yield of product 4a
(Table 1, entries 9e12). However, the reaction in CH2Cl2 did not
produce the desired product (Table 1, entry 13). This reaction was
found to be stoichiometric as decreasing the loading of Ph3BiCl2 2a
to either 0.5 or 0.3 equivalents significantly reduced the yield of 4a,
which was obtained in accordance to the amount of Ph3BiCl2 used
(entries 14, 15). When the reaction was carried out without trie-
thylamine, the yield of 4a remarkably decreased (entry 16). The
best result was obtained when 1a was treated with one equivalent
amount of Ph3BiCl2 2a in DMF at room temperature in the presence
of base. This cyclization could also be scaled up to 10 mmol and
desired product 4a was obtained in excellent yields of up to 75%,
generating up to 1.58 g of the product.
Fig. 1. Biologically active 2-aminobenzoxazoles.
knowledge, there are no reports of triarylbismuth dichloride-
promoted ring closure reactions for the synthesis of heterocycles.
Herein, we report a versatile synthesis of 2-aminobenzoxazoles via
the triphenylbismuth dichloride-assisted cyclodesulfurization of
thioureas generated from 2-aminophenols and isothiocyanates.
To investigate the scope of the reaction, we carried out the one-
2. Results and discussions
pot synthesis of 2-aminobenzoxazoles
4 from various 2-
aminophenols 5 (0.5 mmol) and isothiocyanates 6 (0.5 mmol) us-
ing Ph3BiCl2 (0.5 mmol) and triethylamine. The key intermediates 1
were prepared in situ from 5 and 6 at room temperature by a re-
ported method [40] and the formation of 1 was confirmed by thin
layer chromatography. DMF, which gave excellent results in the
cyclodesulfurization reaction, was selected as the solvent (Table 1,
entry 1). The results are summarized in Table 2. The reaction of 2-
aminophenol 5a with aryl isothiocyanates 6 containing electron-
donating or electron-withdrawing groups on the phenyl ring
afforded the corresponding products 4b-f in good to excellent
yields. The reaction of sterically hindered ortho-substituted iso-
thiocyanates with 5a gave the corresponding oxazoles 4g and 4h
without any difficulty. Moreover, the reaction of benzyl isothiocy-
anate and 5a afforded the corresponding product 4i. Next, we
treated various 2-aminophenol derivatives 5 with phenyl isothio-
cyanate 6a under the same reaction conditions. Substrates bearing
either electron-donating or electron-withdrawing groups at the 4-
position on the phenyl ring afforded the corresponding benzox-
azoles 4j-n in good to excellent yields. 2-Aminophenols with
methyl groups at the 3-, 5-, and 6-position gave products 4o, 4p,
and 4q, respectively, in satisfactory yields. The reaction of 3-amino-
2-naphthol with 6a gave tricyclic compound 4r. On the other hand,
the reaction with 3-amino-2-anthracenol generated a low yield of
tetracyclic compound 4s due to the low solubility of the thiourea.
This one-pot reaction could also be applied to the synthesis of 6-
and 7-membered heterocyclic rings 8 and 9 (Scheme 1).
At present, the mechanism of the cyclodesulfurization reaction
is unclear. We consider that the mechanism would be similar to
that of the reaction using a hypervalent iodine such as diacetox-
yiodobenzene proposed by Patel et al. [21]. Moreover, the reaction
of aniline (0.5 mmol) with phenyl isothiocyanate (0.5 mmol) in the
presence of Ph3BiCl2 (0.5 mmol) afforded N,N-diphenylcarbodii-
mide and triphenylbismuthane in 72% and 71% yields, respectively.
A possible mechanism for the present cyclodesulfurization reaction
is shown in Scheme 2. The initial step would be the generation of
intermediate A from the reaction of thiourea 1 and Ph3BiCl2
through the attack of the sulfur atom of 1 to the thiophilic bismuth
center [41,42]. The reductive elimination of A leads to the formation
of carbodiimide B, triphenylbismuthane, sulfur, and triethylamine
hydrochloride (Et3N$HCl) and finally B undergoes intramolecular
cyclization to give benzoxazole 4 (path A). Another potential route
We initially focused our attention on determining suitable
experimental conditions for the cyclodesulfurization of 1-(2-
hydroxyphenyl)-3-phenylthiourea 1a. Standard reaction condi-
tions used bismuth and antimony reagents 2 and 3 in the presence
of triethylamine as base at room temperature under aerobic con-
ditions. The screening results of active reagents and suitable sol-
vents for the reaction are summarized in Table 1. Initially, the
reaction of 1a and bismuth reagents 2a-d was performed in DMF at
room temperature in order to compare their reactivity (entries
1e4). Pentavalent organobismuth compounds 2a,
b and tri-
chlorobismuth 2d gave the expected 2-aminobenzoxazole 4a in
excellent yield. In terms of yield and reaction time, triphe-
nylbismuth dichloride (Ph3BiCl2) 2a was found to be the best
Table 1
a
Cyclodesulfurization of thiourea 1a using Bi and Sb reagents.
Entry
Reagent (eq)
Solvent
Time
Yield (%)b
4a
2c or 3c
1
2
3
4
5
6
7
8
2a: Ph3BiCl2 (1)
2b: Ph3Bi(OAc)2 (1)
2c: Ph3Bi (1)
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMSO
THF
CH3CN
CH3OH
CH2Cl2
DMF
DMF
DMF
10 min
22 h
24 h
4 h
10 min
10 min
24 h
24 h
4 h
5 h
5 h
5 h
24 h
6 h
90
83
0
84
85
86
0
2c: 91
2c: 46
2c: 93
e
2d: BiCl3 (1)
3a: Ph3SbCl2 (1)
3b: Ph3Sb(OAc)2 (1)
3c: Ph3Sb (1)
3c: 56
3c: 84
3c: 95
e
3d: SbCl3 (1)
0
9
2a: Ph3BiCl2 (1)
2a: Ph3BiCl2 (1)
2a: Ph3BiCl2 (1)
2a: Ph3BiCl2 (1)
2a: Ph3BiCl2 (1)
2a: Ph3BiCl2 (0.5)
2a: Ph3BiCl2 (0.3)
2a: Ph3BiCl2 (1)
83
79
75
73
0
44
27
38
2c: 91
2c: 69
2c: 37
2c: 58
2c: 94
2c: 89
2c: 91
2c: 45
10
11
12
13
14
15
16c
6 h
24 h
a
Reaction conditions: 1a (0.5 mmol), 2 or 3 (0.15e0.5 mmol), Et3N (1.0 mmol).
Isolated yield.
Without Et3N.
b
c

20
Y. Murata et al. / Journal of Organometallic Chemistry 859 (2018) 18e23
Table 2
One-pot synthesis of 2-animobenzoxazoles.a,b
4b: 75%
4c: 82%
4d: 58%
4e: 55%
4f: 57%
4g: 91%
4l: 66%
4q: 92%
4h: 87%
4m: 71%
4r: 80%
4i: 72%
4n: 57%
4sc: 24%
4j: 79%
4o: 76%
4k: 88%
4p: 83%
aReaction conditions: 5 (0.5 mmol), 6 (0.5 mmol), Ph3BiCl2 (0.5 mmol), Et3N (1.0 mmol).
bIsolated yield.
cCyclodesulfurization at 24 h.
to extend the applications of this type of cyclization to other het-
erocycles and for the synthesis of biologically active oxazoles are in
progress.
4. Experimental
4.1. General
Melting points were measured on a Yanagimoto micro melting
point hot stage apparatus and are uncorrected. Mass spectra (MS)
were recorded on a JEOL JMP-DX300 instrument. 1H NMR (CHCl3:
d:
7.26 ppm or DMSO:
d
: 2.50 ppm as an internal standard) and 13C
: 39.51 ppm as an internal
NMR (CHCl3: : 77.00 ppm or DMSO:
d
d
Scheme 1. Synthesis of 1,3-benzoxazine and dihydrobenzoxazepine.
standard) spectra were recorded on JEOL JNM-AL400 (400 MHz and
100 MHz) spectrometers in CDCl3 or DMSO-d6. Mass spectra were
obtained on a JEOL JMP-DX300 instrument (70 eV, 300 mA). GLC
would involve the direct intramolecular cyclization at the iminium
carbon in intermediate A (path B).
analyses were made using Shimazu GC-16A. Column chromatog-
raphy was performed on Silica Gel 60N (Kanto Chemical Co., Inc.).
Triphenylbismuth dichloride 2a (mp 151e153 ꢀC, lit [43].
149e150 ꢀC) were prepared according to the literature method. The
others were purchased from Wako Pure Chemical Industries, Ltd.
Japan, Tokyo Kasei Kogyo Co., LTD and SIGMA-ALDRICH Japan K.K.
and used without further purification.
3. Conclusion
In summary, N-substituted benzo[d]oxazol-2-amines were
synthesized in moderate to excellent yields via a simple one-pot
two-step reaction involving the reaction of 2-aminophenols with
isothiocyanates in the presence of Ph3BiCl2 and base under mild
4.2. General procedure for the preparation of N-aryl-2-
aminobenzoxazoles
reaction conditions. Triphenylbismuthane, obtained as
a by-
product, was converted back to triphenylbismuth dichloride by
oxidative chlorination with SO2Cl2 for reuse. Further investigations
To a solution of aryl isothiocyanate (0.5 mmol) in DMF (3.0 mL)

Y. Murata et al. / Journal of Organometallic Chemistry 859 (2018) 18e23
21
Scheme 2. Possible mechanism.
was added 2-aminophenol derivatives (0.5 mmol), and the reaction
mixture was stirred at room temperature for 3e24 h. After com-
plete conversion of 2-aminophenols to the corresponding o-
phenolic thioureas as indicated by TLC, Ph3BiCl2 (0.5 mmol) and
triethylamine (1.0 mmol) were added to the reaction mixture.
Conversion of o-phenolic thiourea to N-phenyl-benzoxazole was
observed with 10 min (monitored by TLC). The reaction mixture
was poured into water and extracted with AcOEt. The combined
organic layers were dried over MgSO4 and concentrated under
vacuum. The residue was purified by chromatography (4a‒q and 9:
n-hexane: EtOAc ¼ 6: 1, 4r, s, and 8: n-hexane: EtOAc ¼ 4:1) to give
N-aryl-2-aminobenzoxazole.
(q). FTIR (KBr): 3231, 3034, 1574, 1520, 1487, 1460, 1366, 1352, 1281,
1250, 1229, 1188, 1167, 1003, 972, 812, 752, 737, 507, 428 cmꢁ1
LRMS (EI) m/z: 224 (Mþ, 100), 91 (20). HRMS: m/z [M]þ calcd for
14H12N2O: 224.0950. Found: 224.0947.
.
C
4.2.4. N‒(4‒bromophenyl)‒1,3‒benzoxazol‒2‒amine (4d) [17]
Colorless powder (92.5 mg, 58%), m.p. 219e220 ꢀC (from AcOEt‒
Hexane), 1H NMR (400 MHz, DMSO‒d6):
d 10.78 (brs, 1H, NH), 7.73
(d, J ¼ 9.3 Hz, 2H, Ar‒H), 7.55 (d, J ¼ 8.8 Hz, 2H, Ar‒H), 7.50 (d,
J ¼ 7.3 Hz, 1H, Ar‒H), 7.46 (d, J ¼ 6.8 Hz, 1H, Ar‒H), 7.22 (dt, J ¼ 7.6,
1.1 Hz, 1H, Ar‒H), 7.14 (dt, J ¼ 7.8, 1.0 Hz, 1H, Ar‒H). 13C NMR
(100 MHz, DMSO‒d6): d 157.6 (s), 146.9 (s), 142.2 (s), 138.1 (s), 131.7
(d), 124.1 (d), 121.9 (d), 119.4 (d), 116.7 (d), 113.5 (s), 109.0 (d). FTIR
(KBr): 3163, 3030, 2928, 1665, 1591, 1491, 1460, 1366, 1248, 1233,
822, 752, 739 cmꢁ1. LRMS (EI) m/z: 290 (Mþ, 100), 209 (30), 167
(20), 105 (30). HRMS: m/z [M]þ calcd for C13H9BrN2O: 287.9898.
Found: 287.9892.
4.2.1. N‒Phenyl‒1,3‒benzoxazol‒2‒amine (4a) [8]
Colorless needles (95.7 mg, 90%), m.p. 172e174 ꢀC (from MeOH),
1H NMR (400 MHz, CDCl3):
d
7.61 (d, J ¼ 8.3 Hz, 2H, Ar‒H), 7.50 (d,
J ¼ 7.8 Hz, 1H, Ar‒H), 7.41 (t, J ¼ 8.0 Hz, 2H, Ar‒H), 7.36 (d, J ¼ 8.3 Hz,
1H, Ar‒H), 7.25 (t, J ¼ 7.6 Hz, 1H, Ar‒H), 7.16e7.11 (m, 2H, Ar‒H).13
C
NMR (100 MHz, CDCl3):
d 158.4 (s), 147.8 (s), 141.8 (s), 137.7 (s),
129.4 (d), 124.4 (d), 123.4 (d), 121.9 (d), 118.6 (d), 116.9 (d), 109.2 (d).
FTIR (KBr): 3381, 3048, 1659, 1574, 1503, 1458, 1375, 1281, 1250,
1225, 1005, 972, 687, 637, 505, 430 cmꢁ1. LRMS (EI) m/z: 210 (Mþ,
100), 209 (40), 149 (20). HRMS: m/z [M]þ calcd for C13H10N2O:
210.0793. Found: 210.0796.
4.2.5. N‒[4‒(trifluoromethyl)phenyl]‒1,3‒benzoxazol‒2‒amine
(4e)
Colorless prisms (93.2 mg, 55%), m.p. 176e177 ꢀC (from MeOH),
1H NMR (400 MHz, CDCl3):
d
7.75 (d, J ¼ 8.8 Hz, 2H, Ar‒H), 7.65 (d,
J ¼ 8.8 Hz, 2H, Ar‒H), 7.51 (d, J ¼ 7.8 Hz, 1H, Ar‒H), 7.40 (d,
J ¼ 8.3 Hz, 1H, Ar‒H), 7.29 (td, J ¼ 7.6, 1.0 Hz, 1H, Ar‒H), 7.19 (td,
J ¼ 7.8, 1.3 Hz, 1H, Ar‒H). 13C NMR (100 MHz, CDCl3):
d 157.3 (s),
4.2.2. N‒(4‒methoxyphenyl)‒1,3‒benzoxazol‒2‒amine (4b) [44]
Colorless prisms (90.1 mg, 75%), m.p. 125e127 ꢀC (from Hexane‒
3
147.7 (s), 141.2 (s), 140.7 (s), 126.7 (d, JCF ¼ 4.1 Hz), 125.2 (s,
2JCF ¼ 32 Hz), 124.7 (d), 124.2 (s, 1JCF ¼ 271 Hz), 122.6 (d), 117.9 (d),
117.3 (d), 109.4 (d). FTIR (KBr): 3395, 3046, 1672, 1618, 1582, 1495,
1460, 1370, 1329, 1236, 1196, 1163, 1113, 1071, 1017, 976, 831, 754,
743 cmꢁ1. LRMS (EI) m/z: 278 (Mþ, 82), 277 (35), 83 (100). HRMS:
m/z [M]þ calcd for C14H9F3N2O: 278.0667. Found: 278.0663.
AcOEt), 1H NMR (400 MHz, CDCl3):
d
7.50 (dd, J ¼ 6.3, 2.2 Hz, 2H, Ar‒
H), 7.43 (d, J ¼ 7.8 Hz, 1H, Ar‒H), 7.33 (d, J ¼ 7.8 Hz, 1H, Ar‒H), 7.22
(td, J ¼ 7.8, 1.0 Hz, 1H, Ar‒H), 7.10 (td, J ¼ 7.8, 1.0 Hz, 1H, Ar‒H), 6.94
(dd, J ¼ 6.8, 2.4 Hz, 2H, Ar‒H), 3.82 (s, 3H, OCH3). 13C NMR
(100 MHz, CDCl3): d 159.2 (s), 156.2 (s), 147.9 (s), 142.0 (s), 130.9 (s),
124.2 (d), 121.5 (d), 121.0 (d), 116.6 (d), 114.6 (d), 109.1 (d), 55.6 (q).
FTIR (KBr): 3044, 1674, 1582, 1512, 1460, 1370, 1348, 1285, 1269,
1248, 1233, 1175, 1165, 1032, 968, 822, 752, 743 cmꢁ1. LRMS (EI) m/
z: 240 (Mþ, 95), 225 (100). HRMS: m/z [M]þ calcd for C14H12N2O2:
240.0899. Found: 240.0896.
4.2.6. N‒(4‒nitrophenyl)‒1,3‒benzoxazol‒2‒amine (4f) [17]
Yellow powder (72.7 mg, 57%), m.p. 225e227 ꢀC (from Hexane‒
CH2Cl2). 1H NMR (400 MHz, DMSO‒d6):
d 11.42 (s, 1H, NH), 8.30 (d,
J ¼ 7.2 Hz, 2H, Ar‒H), 7.97 (d, J ¼ 8.8 Hz, 2H, Ar‒H), 7.56 (d,
J ¼ 5.2 Hz, 1H, Ar‒H), 7.54 (d, J ¼ 5.6 Hz, 1H, Ar‒H), 7.28 (t, J ¼ 7.2 Hz,
1H, Ar‒H), 7.21 (t, J ¼ 7.6 Hz, 1H, Ar‒H). 13C NMR (100 MHz, DMSO‒
4.2.3. N‒(4‒methylphenyl)‒1,3‒benzoxazol‒2‒amine (4c) [17]
Colorless powder (91.9 mg, 82%), m.p. 168e169 ꢀC (from AcOEt‒
Hexane), 1H NMR (400 MHz, DMSO‒d6):
d
10.51 (brs, 1H, NH), 7.65
d6): d 156.8 (s), 147.0 (s), 144.9 (s), 141.6 (s), 141.3 (s), 125.4 (d), 124.4
(d, J ¼ 8.3 Hz, 2H, Ar‒H), 7.48e7.43 (m, 2H, Ar‒H), 7.23e7.17 (m, 3H,
(d), 122.7 (d), 117.3 (d), 117.3 (d), 109.4 (d). FTIR (KBr): 3032, 1589,
1521, 1458, 1332, 1240, 732 cmꢁ1. LRMS (EI): m/z 255 (Mþ, 100), 225
(29), 167 (14). HRMS: m/z [M]þ calcd for C13H9N3O3: 255.0644.
Found: 255.0648.
Ar‒H), 7.12 (t, J ¼ 7.6 Hz, 1H, Ar‒H), 2.28 (s, 3H, CH3). 13C NMR
(100 MHz, DMSO‒d6): d 158.1 (s), 147.0 (s), 142.5 (s), 136.2 (s), 130.9
(s), 129.3 (d), 123.9 (d), 121.4 (d), 117.6 (d), 116.4 (d), 108.8 (d), 20.3

22
Y. Murata et al. / Journal of Organometallic Chemistry 859 (2018) 18e23
4.2.7. N‒(2‒methylphenyl)‒1,3‒benzoxazol‒2‒amine (4g) [10]
Yellow oil (102.0 mg, 91%), 1H NMR (400 MHz, DMSO‒d6):
J ¼ 8.0 Hz, 1H, Ar‒H), 7.37 (t, J ¼ 7.2 Hz, 2H, Ar‒H), 7.28 (dd, J ¼ 8.4,
2.0 Hz, 1H, Ar‒H), 7.05 (t, J ¼ 7.2 Hz, 1H, Ar‒H). 13C NMR (100 MHz,
d
9.67
(brs, 1H, NH), 7.82 (d, J ¼ 8.8 Hz, 1H, Ar‒H), 7.45 (d, J ¼ 7.8 Hz, 1H,
Ar‒H), 7.36 (d, J ¼ 7.8 Hz, 1H, Ar‒H), 7.27e7.21 (m, 2H, Ar‒H), 7.19 (t,
J ¼ 7.8 Hz, 1H, Ar‒H), 7.09 (t, J ¼ 7.8 Hz, 2H, Ar‒H), 2.31 (s, 3H, CH3).
DMSO‒d6): d 158.9 (s), 146.2 (s), 144.5 (s), 138.3 (s), 129.0 (d), 124.0
(d),122.5 (d), 119.1 (d), 117.8 (s), 115.9 (d), 110.6 (d). FTIR (KBr): 3037,
1678, 1572, 1498, 1458, 1442, 1230 cmꢁ1. LRMS (EI): m/z 289
([MþH]þ, 100), 209 (35), 118 (10). HRMS: m/z [M]þ calcd for
13C NMR (100 MHz, DMSO‒d6):
d 159.5 (s), 147.5 (s), 142.5 (s), 136.6
(s), 130.5 (d), 130.2 (s), 126.4 (d), 124.4 (d), 123.9 (d), 122.7 (d), 121.2
(d), 116.2 (d), 108.8 (d), 17.8 (q). FTIR (neat): 3231, 3053, 2251, 2124,
1651, 1591, 1574, 1489, 1460, 1236, 1053, 1028, 1007, 822, 758,
746 cmꢁ1. LRMS (EI) m/z: 224 (Mþ, 100), 207 (55), 117 (75). HRMS:
m/z [M]þ calcd for C14H12N2O: 224.0950. Found: 224.0946.
C13H8BrN2O: 287.9898. Found: 287.9891.
4.2.13. N‒Phenyl‒5‒trifluoromethy‒1,3‒benzoxazol‒2‒amine (4m)
Colorless powder (98.8 mg, 71%), m.p.198e200 ꢀC (from MeOH).
1H NMR (400 MHz, DMSO‒d6):
d 10.90 (brs, 1H, NH), 7.77 (s, 1H, Ar‒
H), 7.75 (d, J ¼ 8.4 Hz, 2H, Ar‒H), 7.68 (d, J ¼ 8.0 Hz, 1H, Ar‒H), 7.48
4.2.8. N‒(naphthalen-1-yl)‒1,3‒benzoxazol‒2‒amine (4h) [23]
Gray powder (113.2 mg, 87%), m.p. 157e159 ꢀC (from AcOEt‒
(d, J ¼ 8.0 Hz, 1H, Ar‒H), 7.38 (t, J ¼ 8.4 Hz, 2H, Ar‒H), 7.06 (t,
J ¼ 7.2 Hz, 1H, Ar‒H).13C NMR (100 MHz, DMSO‒d6):
d 159.4 (s),
Hexane), 1H NMR (400 MHz, CDCl3):
d
8.13 (m, 1H, Ar‒H), 8.06 (d,
149.3 (s), 143.1 (s), 138.2 (s), 129.0 (d), 124.6 (s, 1JCF ¼ 270 Hz), 125.1
(s, 2JCF ¼ 33 Hz), 122.7 (d), 118.9 (d, 3JCF ¼ 4.1 Hz), 117.9 (d), 113.0 (d,
3JCF ¼ 4.3 Hz), 109.6 (d). FTIR (KBr): 3061, 1681, 1583, 1494, 1438,
1359, 1321, 1165, 1122, 1111 cmꢁ1. LRMS (EI): m/z 278 (Mþ, 100), 259
(8), 208 (5), 181 (15). HRMS: m/z [M]þ calcd for C14H9F3N2O:
278.0667. Found: 278.0662.
J ¼ 7.3 Hz, 1H, Ar‒H), 7.93 (dd, J ¼ 5.9, 2.9 Hz, 1H, Ar‒H), 7.75 (d,
J ¼ 8.3 Hz, 1H, Ar‒H), 7.59e7.55 (m, 3H, Ar‒H), 7.34e7.29 (m, 2H,
Ar‒H), 7.18 (t, J ¼ 7.6 Hz, 1H, Ar‒H), 7.11 (t, J ¼ 7.6 Hz, 1H, Ar‒H). 13
C
NMR (100 MHz, CDCl3):
d 159.7 (s), 147.9 (s), 141.7 (s), 134.3 (s),
132.8 (s), 128.7 (d), 127.0 (s), 126.5 (d), 126.3 (d), 125.9 (d), 125.3 (d),
124.3 (d), 121.9 (d), 121.1 (d), 118.8 (d), 116.9 (d), 109.2 (d). FTIR
(KBr): 2897, 1655, 1622, 1574, 1516, 1479, 1460, 1402, 1360, 1333,
1275, 1240, 963, 922, 849, 804, 793, 770, 754, 739 cmꢁ1. LRMS (EI)
m/z: 260 (Mþ, 100), 127 (20). HRMS: m/z [M]þ calcd for C17H12N2O:
260.0950. Found: 260.0956.
4.2.14. 5‒Nitro‒N‒phenyl‒1,3‒benzoxazol‒2‒amine (4n)
Yellow powder (72.7 mg, 57%), m.p. 163e166 ꢀC (from MeOH).
1H NMR (400 MHz, DMSO‒d6):
d 11.01 (brs, 1H, NH), 8.20 (d,
J ¼ 4.0 Hz, 1H, Ar‒H), 8.07 (dd, J ¼ 8.0 Hz, 1H, Ar‒H), 7.75e7.71 (m,
3H, Ar‒H), 7.40 (t, J ¼ 8.0 Hz, 2H, Ar‒H), 7.08 (t, J ¼ 8.0 Hz,1H, Ar‒H).
4.2.9. N‒benzyl‒1,3‒benzoxazol‒2‒amine (4i) [44]
13C NMR (100 MHz, DMSO‒d6):
d 160.0 (s), 151.3 (s), 144.6 (s), 143.4
Brown powder (80.7 mg, 72%), m.p. 101e104 ꢀC (from Hexane‒
(s), 137.9 (s), 129.0 (d), 122.9 (d), 118.1 ꢂ 2 (d), 111.5 (d), 109.2 (d).
FTIR (KBr): 3049, 1693, 1531, 1498, 1344, 1265, 734 cmꢁ1. LRMS (EI):
m/z 255 (Mþ, 100), 209 (30), 104 (18). HRMS: m/z [M]þ calcd for
CH2Cl2). 1H NMR (400 MHz, CDCl3):
d
7.41e7.25 (m, 7H, Ar‒H), 7.18
(t, J ¼ 8.0 Hz, 1H, Ar‒H), 7.06 (t, J ¼ 4.0 Hz, 1H, Ar‒H), 4.69 (s, 2H,
CH2). 13C NMR (100 MHz, CDCl3):
161.9 (s), 148.5 (s), 142.7 (s),
d
C13H9N3O3: 255.0644. Found: 255.0647.
137.6 (s), 128.8 (d), 127.9 (d), 127.6 (d), 124.0 (d), 121.0 (d), 116.4 (d),
108.8 (d), 47.1 (t). FTIR (KBr): 3146, 1668, 1589, 1460, 1348, 1246,
744, 738, 721, 692 cmꢁ1. LRMS (EI): m/z 224 (Mþ, 70), 133 (5), 91
(100), 65 (10) HRMS: m/z [M]þ calcd for C14H12N2O: 224.0950.
Found: 224.0953.
4.2.15. 4-Methyl‒N‒phenyl‒1,3‒benzoxazol‒2‒amine (4o) [45]
Colorless powder (85.2 mg, 76%), m.p. 120e123 ꢀC (from Hex-
ane‒CH2Cl2). 1H NMR (400 MHz, CDCl3):
d
7.63 (dd, J ¼ 8.8, 0.8 Hz,
2H, Ar‒H), 7.40 (t, J ¼ 7.3 Hz, 2H, Ar‒H), 7.20 (dd, J ¼ 6.8 Hz, 2.4 Hz,
1H, Ar‒H), 7.11 (t, J ¼ 7.2 Hz, 1H, Ar‒H), 7.08e7.03 (m, 2H, Ar‒H),
4.2.10. 5‒Methoxy‒N‒phenyl‒1,3‒benzoxazol‒2‒amine (4j) [8]
Colorless powder (94.8 mg, 79%), m.p. 158e161 ꢀC (from
2.58 (s, 3H, CH3). 13C NMR (100 MHz, CDCl3):
d 157.4 (s), 147.5 (s),
141.0 (s), 137.8 (s), 129.3 (d), 127.5 (s), 125.0 (d), 123.2 (d), 121.6 (d),
118.2 (d), 106.5 (d), 16.4 (q). FTIR (KBr): 3184, 1647, 1643, 1639, 1622,
1604, 1573, 1498, 1483, 746 cmꢁ1. LRMS (EI): m/z 224 (Mþ, 100), 195
(4), 132 (8). HRMS: m/z [M]þ calcd for C14H12N2O: 224.0950. Found:
224.0952.
CH2Cl2‒Hexane). 1H NMR (400 MHz, CDCl3):
d
7.58 (d, J ¼ 7.6 Hz,
2H, Ar‒H), 7.40 (t, J ¼ 8.0 Hz, 2H, Ar‒H), 7.23 (d, J ¼ 8.8 Hz, 1H, Ar‒
H), 7.13 (t, J ¼ 7.2 Hz,1H, Ar‒H), 7.04 (s, 1H, Ar‒H), 6.72 (d, J ¼ 6.4 Hz,
1H, Ar‒H), 3.84 (s, 3H, CH3). 13C NMR (100 MHz, CDCl3):
d 159.0 (s),
157.3 (s), 142.9 (s), 142.3 (s), 137.7 (s), 129.3 (d), 123.4 (d), 118.4 (d),
109.1 (d), 108.8 (d), 102.0 (d), 55.9 (q). FTIR (KBr): 3037, 1685, 1602,
1583, 1498, 1483, 1444, 1197, 1155, 729 cmꢁ1. LRMS (EI): m/z 240
(Mþ, 100), 197 (18), 163 (5), 104 (9). HRMS: m/z [M]þ calcd for
4.2.16. 6‒Methyl‒N‒phenyl‒1,3‒benzoxazol‒2‒amine (4p)
Brown powder (93.1 mg, 83%), m.p. 108e110 ꢀC (from Hexane‒
CH2Cl2). 1H NMR (400 MHz, CDCl3):
d
7.59 (d, J ¼ 8.4 Hz, 2H, Ar‒H),
C
14H12N2O2: 240.0899. Found: 240.0894.
7.41e7.36 (m, 3H, Ar‒H), 7.18 (s, 1H, Ar‒H), 7.11 (t, J ¼ 8.0 Hz, 1H, Ar‒
H), 7.07 (d, J ¼ 8.0 Hz, 1H, Ar‒H), 2.44 (s, 3H, CH3). 13C NMR
4.2.11. 5‒Methyl‒N‒phenyl‒1,3‒benzoxazol‒2‒amine (4k) [8]
Colorless powder (98.6 mg, 88%), m.p. 200e202 ꢀC (from
(100 MHz, CDCl3): d 157.9 (s), 148.0 (s), 139.5 (s), 137.9 (s), 132.1 (s),
129.3 (d), 125.1 (d), 123.2 (d), 118.3 (d), 116.4 (d), 109.6 (d), 14.2 (q).
FTIR (KBr): 3041, 1668, 1602, 1577, 1496, 1458, 1446, 1431, 1251,
754 cmꢁ1. LRMS (EI): m/z 224 (Mþ, 100), 195 (8), 141 (5), 104 (32).
HRMS: m/z [M]þ calcd for C14H12N2O: 224.0950. Found: 224.0946.
MeOH). 1H NMR (400 MHz, DMSO‒d6):
d 10.53 (brs, 1H, NH), 7.73
(d, J ¼ 8.0 Hz, 2H, Ar‒H), 7.37e7.32 (m, 3H, Ar‒H), 7.25 (s, 1H, Ar‒H),
7.01 (t, J ¼ 8.0 Hz, 1H, Ar‒H), 6.92 (d, J ¼ 8.8 Hz, 1H, Ar‒H), 2.36 (s,
3H, CH3). 13C NMR (100 MHz, DMSO‒d6):
d 158.1 (s), 145.1 (s), 142.5
(s), 138.7 (s), 133.1 (s), 128.9 (d), 122.2 (d), 122.0 (d), 117.5 (d), 116.8
(d), 108.3 (d), 21.0 (q). FTIR (KBr): 3053, 1660, 1639, 1600, 1579,
1570, 1500, 1492 cmꢁ1. LRMS (EI): m/z 224 (Mþ, 100), 195 (6), 132
(3), 104 (10). HRMS: m/z [M]þ calcd for C14H12N2O: 224.0950.
Found: 224.0954.
4.2.17. 7‒Methyl‒N‒phenyl‒1,3‒benzoxazol‒2‒amine (4q)
Pale brown powder (103.2 mg, 92%), m.p. 163e166 ꢀC (from
Hexane‒CH2Cl2). 1H NMR (400 MHz, CDCl3):
2H, Ar‒H), 7.42e7.32 (m, 3H, Ar‒H), 7.17e7.10 (m, 2H, Ar‒H), 6.96
(d, J ¼ 7.6 Hz, 1H, Ar‒H), 2.47 (s, 3H, CH3). 13C NMR (100 MHz,
d
7.60 (d, J ¼ 8.0 Hz,
CDCl3):
d 158.0 (s), 146.8 (s), 141.4 (s), 137.9 (s), 129.4 (d), 124.2 (d),
4.2.12. 5‒Bromo‒N‒phenyl‒1,3‒benzoxazol‒2‒amine (4l)
123.4 (d), 123.2 (d), 119.6 (s), 118.3 (d), 114.5 (d), 15.0 (q). FTIR (KBr):
3049, 1622, 1647, 1600, 1573, 1504, 1271, 746 cmꢁ1. LRMS (EI): m/z
224 (Mþ, 100), 208 (5), 127 (5). HRMS: m/z [M]þ calcd for
Colorless powder (95.4 mg, 66%), m.p. 190e192 ꢀC (from MeOH).
1H NMR (400 MHz, DMSO‒d6):
d
10.77 (brs, 1H, NH), 7.72 (d,
J ¼ 8.0 Hz, 2H, Ar‒H), 7.63 (d, J ¼ 2.0 Hz, 1H, Ar‒H), 7.46 (d,
C14H12N2O: 224.0950. Found: 224.0954.

Y. Murata et al. / Journal of Organometallic Chemistry 859 (2018) 18e23
23
4.2.18. N‒Phenylnaphtho[2,3‒d]oxazol‒2‒amine (4r)
Yellow powder (86.0 mg, 80%), m.p. 231e233 ꢀC (from Hexane‒
CH2Cl2). 1H NMR (400 MHz, DMSO‒d6):
10.84 (brs, 1H, NH),
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7.94e7.92 (m, 3H, Ar‒H), 7.85 (s, 1H, Ar‒H), 7.79 (d, J ¼ 8.0 Hz, 2H,
Ar‒H), 7.44e7.38 (m, 4H, Ar‒H), 7.21 (dd, J ¼ 7.2, 6.4 Hz 1H, Ar‒H).
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225 (29), 167 (14). HRMS: m/z [M]þ calcd for C17H12N2O: 260.0950.
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Yellow powder (37.2 mg, 24%), m.p. 278e281 ꢀC (from Hexane‒
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d 10.95 (brs, 1H, NH), 8.59 (d,
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d 159.7 (s),
147.5 (s), 143.7 (s), 138.2 (s), 130.3 (s), 130.2 (s), 129.9 (s), 129.0 (d),
128.7 (s), 127.6 (d), 127.5 (d), 125.5 (d), 125.1 (d), 124.9 (d), 124.7 (d),
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ꢀ
ꢀ
C
21H14N2O: 310.1106. Found: 311.1109.
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d
7.44 (d, J ¼ 8.0 Hz, 2H, Ar‒H),
7.30 (t, J ¼ 8.0 Hz, 2H, Ar‒H), 7.24 (t, J ¼ 8.0 Hz, 1H, Ar‒H), 7.07e6.97
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d
(s), 140.9 (s), 139.2 (s), 129.1 (d), 128.9 ꢂ 2 (d), 123.7 (d), 123.11 (d),
123.07 (d), 120.8 (s), 120.2 (d), 67.7 (t). FTIR (KBr): 3057, 1693, 1600,
1595, 1496, 1406, 1205, 1028, 786, 748, 690 cmꢁ1. LRMS (EI): m/z
224 (Mþ, 58), 180 (8), 132 (100), 104 (20). HRMS: m/z [M]þ calcd for
C
14H12N2O: 224.0950. Found: 224.0947.
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Colorless needles (85.8 mg, 72%), m.p. 135e137 ꢀC (from Hex-
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d
7.47 (d, J ¼ 8.0 Hz, 2H,
Ar‒H), 7.30 (t, J ¼ 8.0 Hz, 2H, Ar‒H), 7.20e7.18 (m, 2H, Ar‒H),
7.04e6.98 (m, 2H, Ar‒H), 6.97 (t, J ¼ 4.0 Hz, 1H, Ar‒H), 4.54 (t,
J ¼ 4.0 Hz, 2H, CH2), 3.16 (t, J ¼ 4.0 Hz, 2H, CH2). 13C NMR (100 MHz,
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CDCl3):
d
147.3 (s), 143.1 (s), 139.9 (s), 132.5 (s), 128.8 ꢂ 2 (d), 127.5
(d), 126.8 (d), 122.7 (d), 122.4 (d), 119.4 (d), 71.5 (t), 35.9 (t). FTIR
(KBr): 3196, 1674, 1593, 1583, 1508, 1462, 1406, 1371, 1340, 1238,
1091, 1037, 775, 748, 698 cmꢁ1. LRMS (EI): m/z 238 (Mþ, 82), 194
(17), 118 (100). HRMS: m/z [M]þ calcd for C15H14N2O: 238.1106.
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Acknowledgments
This research was supported by a research grant from Institute
of Pharmaceutical Life Sciences, Aichi Gakuin University and
Hokuriku University.
Appendix A. Supplementary data
Supplementary data related to this article can be found at
https://doi.org/10.1016/j.jorganchem.2018.01.041.
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