Microwave-assisted synthesis of 2-substituted naphtho[1,2-d][1,3]oxazoles by reacting 1-nitroso-2-naphthol with allyl bromides and benzyl bromides using FeCl3 as catalyst

Article abstract of DOI:10.14233/ajchem.2020.22745

Efficient and improved preparation of 2-substituted[1,2-d][1,3]oxazoles by the reaction of 1-nitroso-2-naphthol and allyl bromides, benzyl bromides under microwave condition utilizing FeCl3 as a catalyst with yield ranging from 32% to 72%. Reaction with bromo acetonitrile yields the corresponding 2-cyanonaphthoxazole with 58% yield.

Full text of DOI:10.14233/ajchem.2020.22745

Asian Journal of Chemistry; Vol. 32, No. 8 (2020), 2038-2042
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2020.22745
Microwave-assisted Synthesis of 2-Substituted Naphtho[1,2-d][1,3]oxazoles by Reacting
1-Nitroso-2-naphthol with Allyl Bromides and Benzyl Bromides using FeCl3 as Catalyst
1,*,
2,
3
4
N. ALJAAR
, S.M. FRAIHAT , A. ALOTHMAN and N.A. KHALAF
1Department of Chemistry, Hashemite University, P.O. Box 150459, Zarqa 13115, Jordan
2Department of Chemistry, School of Science, The University of Jordan, 11942, Amman, Jordan
3Department of Medical Laboratory Science, Faculty of Allied Medical Sciences, Al-Ahliyya Amman University, Amman 19328, Jordan
4Department of Pharmaceutical Science, Faculty of Pharmacy, Pharmacological and Diagnostic Research Center (PDRC),Al-AhliyyaAmman
University, Amman 19328, Jordan
*Corresponding author: E-mail: nayyef@hu.edu.jo
Received: 27 March 2020;
Accepted: 26 May 2020;
Published online: 27 July 2020;
AJC-19987
Efficient and improved preparation of 2-substituted[1,2-d][1,3]oxazoles by the reaction of 1-nitroso-2-naphthol and allyl bromides, benzyl
bromides under microwave condition utilizing FeCl3 as a catalyst with yield ranging from 32% to 72%. Reaction with bromo acetonitrile
yields the corresponding 2-cyanonaphthoxazole with 58% yield.
Keywords: Microwave, Allyl bromides, Benzyl bromides, 2-Substituted naphthoxazoles, 1-Nitroso-2-naphthol.
O
H
INTRODUCTION
R1
N
O
N
O
N
R2
Heterocyclic compounds containing oxygen and nitrogen
as heteroatoms, such as annulated oxazoles [1-3] form the key
unit in a wide variety of natural products and biologically active
compounds that have pharmacological properties [4]. Repre-
sentative examples include the anticancer agent NCS-693638
[5], the estrogen receptor-β agonist ERB-041 [6], the HIV
reverse transcriptase inhibitor L-697661 [7], the HT3 receptor
agonist [8], cathepsin S inhibitor [9], UK-1 [10], salvianen [11],
AJ9561 [12] and pseudopteroxazole [13]. Naphthoxazoles are
known for their significant interest in material sciences as they
are known for their exceptional fluorescent properties [14-17]
(Fig. 1).
R1 = NEt2, n-butyl,
R2 =CO2Bu CN, CO2H,
(Phenylamino)naphtho[1,2-d]oxazol-2-yl
2-((Furan-2-yl)ethyl)naphtho-
[1,2-d]oxazole
O
O
O
N
O
N
2-((Furan-2-yl)vinyl)naphtho-
2-(Furan-2-yl)naphtho[1,2-d]oxazole
[1,2-d]oxazole
Fig. 1 Synthetic naphthoxazoles with significant fluorescent properties
On that account, there is a great deal of effort in the develop-
ment of new synthetic approaches to the naphthoxazoles skeleton.
Most of them are based on the reaction of oximes with allyl
bromide, 4-nitrobenzyl bromide, dimethyl sulfate and ethyl
iodide [18], oxime or 5-N,N-diethylamino-2-nitrosophenol
with benzyl bromides [19], 1,2-naphthalenedione 1-oxime with
benzyl bromides in the presence of Et3N [20] and the reaction
of 1-nitroso-2-naphthols and α-functionalized ketones [21].
Other methods of preparation include the condensation of
1-amino-2-naphthol with aromatic aldehydes [22,23], Pd/C-
catalyzed reaction of 1-nitronaphthalen-2-yl benzoate with
a 1,4-dihydropyridine [24] and the decomposition of the
corresponding benzo- and naphthoxazinones with potassium
hydroxide [25]. In view of this, a new and straight-forward
approach for the synthesis of 2-substituted napthoxazoles
derivatives is divulged, which relied on the FeCl3 catalyzed
the reaction between 1-nitroso-2-naphthol with allyl bromides
and benzyl bromides under microwave condition.
This is an open access journal, and articles are distributed under the terms of the Attribution 4.0 International (CC BY 4.0) License. This
license lets others distribute, remix, tweak, and build upon your work, even commercially, as long as they credit the author for the original
creation. You must give appropriate credit, provide a link to the license, and indicate if changes were made.

Vol. 32, No. 8 (2020)
Microwave-Assisted Synthesis of 2-Substituted Naphtho[1,2-d][1,3]oxazoles using FeCl3 as Catalyst 2039
Hz, J = 8.1 Hz, 1H), 7.75 (d, J = 8.8 Hz, 1H), 7.82 (d, J = 8.8
Hz, 1H), 7.98 (d, J = 8.0 Hz, 1H), 8.30-8.38 (m, 2H), 8.60 (d,
J = 8.0 Hz, 1H); 13C NMR (75 MHz, CDCl3): δ 110.8, 122.3,
125.5, 126.0, 126.6, 126.9, 127.3, 127.5, 128.6, 128.9, 131.1,
131.2, 137.6, 148.1, 162.4.
2-(4-Cyanophenyl)naphtho[1,2-d][1,3]oxazole (3e):
White solid, 45% yield; m.p. 220-222 ºC (lit. m.p. 221-222
ºC) [Ref. 21]; Rf = 0.30 (cyclohexane/EtOAc = 5:1); 1H NMR
(300 MHz, CDCl3): δ 7.58 (ddd, J = 1.2 Hz, J = 7.9 Hz, J =
8.0 Hz, 1H), 7.70 (ddd, J = 1.0 Hz, J = 7.9 Hz, J = 7.9 Hz, 1H),
7.75 (d, J = 9.1 Hz, 2H), 7.80 (d, J = 8.7 Hz, 1H), 7.85 (d, J =
8.7 Hz, 1H), 7.98 (d, J = 8.0 Hz, 1H), 8.40 (d, J = 8.0 Hz, 2H),
8.56 (d, J = 8.3 Hz, 1H); 13C NMR (75 MHz, CDCl3): δ 110.7,
114.1, 118.2, 122.1, 125.7, 126.5, 127.2, 127.3, 127.5, 128.6,
131.31, 131.34, 132.6, 137.6, 148.3, 160.1.
2-(4-Fluorophenyl)naphtho[1,2-d][1,3]oxazole (3f):
White solid, 42% yield; m.p. 169-170 ºC (lit. m.p. 168-169
ºC) [Ref. 21]; Rf = 0.60 (cyclohexane/EtOAc = 5:1); 1H NMR
(300 MHz, CDCl3): δ 7.26-7.32 (m, 2H), 7.61 (ddd, J = 1.3
Hz, J = 7.1 Hz, J = 7.1 Hz, 1H), 7.72 (d, J = 7.4 Hz, 1H), 7.77
(d, J = 8.7 Hz, 1H), 7.86 (d, J = 8.7 Hz, 1H), 8.03 (d, J = 8.2
Hz, 1H), 8.33-8.42 (m, 2H), 8.63(d, J = 8.2 Hz, 1H); 13C NMR
(75 MHz, CDCl3): δ 110.7, 116.1 (d, 22.0 Hz), 122.1, 123.8
(d, 3.1 Hz), 125.4, 126.0, 126.5, 126.9, 128.5, 129.4 (d, 8.4
Hz), 131.2, 137.5, 148.0, 161.4, 164.6 (d, 251 Hz).
2-(4-Chlorophenyl)naphtho[1,2-d][1,3]oxazole (3g):
White solid, 40% yield, m.p. 188-190 ºC (lit. m.p. 189-190
ºC) [Ref. 21] Rf = 0.46 (cyclohexane/EtOAc = 5:1); 1H NMR
(300 MHz, CDCl3): δ 7.51 (d, J = 8.2 Hz, 2H), 7.57 (dd, J =
1.3 Hz J = 7.6 Hz, 1H), 7.67 (d, J = 7.4 Hz, 1H), 7.72 (d, J =
9.1 Hz, 1H), 7.82 (d, J = 9.1 Hz, 1H), 7.98 (d, J = 8.6 Hz, 1H),
8.26 (d, J = 8.2 Hz, 2H), 8.57 (d, J = 8.2 Hz, 1H); 13C NMR (75
MHz, CDCl3): δ 110.7, 122.1, 125.4, 126.0, 126.2, 126.5, 127.0,
128.4, 128.5, 129.2, 131.2, 137.1, 137.6, 148.2, 161.3.
2-(3-Bromophenyl)naphtho[1,2-d][1,3]oxazole (3h):
White solid, 39% yield; m.p. 197-199 ºC (lit. m.p. 199 ºC)
[Ref. 22]; Rf = 0.43 (cyclohexane/EtOAc = 5:1); 1H NMR (300
MHz, CDCl3): δ 7.42 (t, J = 7.9 Hz, 1H), 7.57 (ddd, J = 1.2
Hz, J = 7.5 Hz, J = 7.5 Hz, 1H), 7.62-7.70 (m, 2H), 7.73 (d, J
= 8.9 Hz, 1H), 7.83 (d, J = 9.3 Hz, 1H), 7.98 (d, J = 7.8 Hz,
1H), 8.27 (d, J = 7.8 Hz, 1H ), 8.48 (s, 1H ), 8.58 (d, J = 8.4 Hz,
1H); 13C NMR (75 MHz, CDCl3): δ 110.7, 122.2, 123.0, 125.5,
125.7, 126.52, 126.56, 127.1, 128.6, 129.4, 130.1, 130.4,
131.2, 133.9, 137.5, 148.1, 160.7.
EXPERIMENTAL
All the starting materials and reagents are available commer-
cially and used as received. Glassware was dried for 24 h at
100 ºC. Solvents used in reactions were distilled over suitable
drying agents prior to use. Microwave-assisted reactions were
performed using a Biotage single-mode cavity microwave
synthesizer producing continuous microwave irradiation at
2450 MHz. Compounds were visualized with UV light (λ =
254 nm). Products were purified by flash chromatography on
silica gel 0.04-0.063 mm. Melting points were obtained on a
melting point apparatus with open capillary tubes and are
uncorrected. 1H (13C) NMR spectra were recorded at 300 (75)
and 400 (100) MHz using CDCl3 as the solvent. The 1H and 13C
chemical shifts were referenced to residual solvent signals at
δH/C 7.26/77.0 (CDCl3). Coupling constants J [Hz] were directly
taken from the spectra and are not averaged.
General procedure: A mixture of 1-nitroso-2-naphthol
(1a) (1 mmol), allyl bromides or benzyl bromides 2 (1 mmol),
15 mol% FeCl3 (24 mg) and o-dichlorobenzene (2 mL) was
sealed in a 10 mL septum reaction vial and irradiated with micro-
waves (Biotage, 2450 MHz, 200 W, 100 ºC) for 10 min. After
cooling to room temperature the reaction mixture was poured
into water (25 mL) and extracted with CH2Cl2 (3 × 20 ml). The
combined organic layers were dried over anhydrous MgSO4
and concentrated in a vacuum. The residue was purified by
flash chromatography on silica gel (cyclohexane/EtOAc =
15:1) to give the desired product [21].
2-Prenylnaphtho[1,2-d][1,3]oxazole (3a): Pale yellow
oil, 72% yield [Ref. 21]; Rf = 0.32 (cyclohexane-EtOAc = 5:1);
1H NMR (300 MHz, CDCl3): δ 2.07 (s, 3H), 2.43 (s, 3H), 6.37
(s, 1H), 7.52 (ddd, J = 1.2 Hz, J = 8.1 Hz, J = 8.2 Hz, 1H),
7.61-7.66 (m, 2H), 7.75 (d, J = 9.1 Hz, 1H), 7.95 (d, J = 8.0
Hz, 1H), 8.51 (d, J = 8.2 Hz, 1H);13C NMR (75 MHz, CDCl3):
δ 20.9, 27.6, 110.0, 112.0, 122.1, 125.1, 125.2, 126.3, 126.7,
128.4, 131.0, 137.2, 146.8, 149.1, 162.2.
2-Cyanonaphtho[1,2-d][1,3]oxazole (3b): White solid,
58% yield; Rf = 0.39 (cyclohexane-EtOAc = 5:1); m.p. 164-
165 ºC (lit. m.p. 163-164 ºC) [Ref. 21]; 1H NMR (300 MHz,
CDCl3): δ 7.66 (ddd, J = 1.5 Hz, J = 7.3 Hz, J = 7.4 Hz, 1H),
7.72 (d, J = 9.0 Hz, 1H), 7.78 (ddd, J = 1.0 Hz, J = 7.0 Hz, J =
8.2 Hz, 1H), 7.99-8.05 (m, 2H), 8.52 (d, J = 8.2 Hz, 1H); 13C
NMR (75 MHz, CDCl3): δ 109.4, 110.5, 122.2, 126.3, 126.9,
128.5, 128.8, 130.7, 131.6, 135.7, 136.1, 148.7.
2-Vinylnaphtho[1,2-d][1,3]oxazole (3c): Colourless oil
, 50% yield [Ref. 18]; Rf = 0.32 (cyclohexane-EtOAc = 4:1);
1H NMR (300 MHz, CDCl3): δ 5.84 (dd, J = 11.1 Hz, J = 1.0
Hz, 1H), 6.49 (dd, J = 17.6 Hz, J = 1.0 Hz, 1H), 6.85 (dd, J =
17.6 Hz, J = 11.2 Hz, 1H ), 7.54 (ddd, J = 1.0 Hz, J = 7.3 Hz,
J = 8.0 Hz, 1H), 7.62-7.69 (m, 2H), 7.78 (d, J = 8.7 Hz, 1H),
7.96 (d, J = 8.1 Hz, 1H), 8.50 (d, J = 8.1 Hz, 1H); 13C NMR
(75 MHz, CDCl3): δ 110.7, 122.0, 123.9, 124.1, 125.4, 126.4,
127.1, 128.5, 131.1, 137.2, 147.6, 161.4.
2-(4-Methoxyphenyl)naphtho[1,2-d][1,3]oxazole
(3i):White solid, 37% yield, m.p. 117-118 ºC (lit. m.p. 116-
118 ºC) [Ref. 22]; Rf = 0.31 (cyclohexane/EtOAc = 5:1); 1H
NMR (300 MHz, CDCl3): δ 3.90 (s, 3H), 7.01-7.09 (m, 2H),
7.53 (ddd, J = 1.4 Hz, J = 7.1 Hz, J = 7.2 Hz, 1H), 7.65-7.69
(m, 1H), 7.70 (d, J = 8.7 Hz, 1H), 7.77 (d, J = 8.8 Hz, 1H),
7.97 (d, J = 8.1 Hz, 1H), 8.23-8.30 (m, 2H), 8.59 (d, J = 8.1 Hz,
1H ); 13C NMR (75 MHz, CDCl3): δ 55.4, 110.7, 114.3, 120.1,
122.2, 125.1, 125.3, 126.4, 126.7, 128.5, 129.0, 131.1, 137.6,
147.8, 161.9, 162.4.
2-Phenylnaphtho[1,2-d][1,3]oxazole (3d): White solid,
35% yield; m.p.: 133-134 ºC (lit.m.p. 133-135 °C) [Ref. 22];
2-(4-Methylphenyl)naphtho[1,2-d][1,3]oxazole (3j):
White solid, 34% yield; m.p. 168-169 ºC (lit. m.p. 168-170
ºC) [Ref. 22]; Rf = 0.54 (cyclohexane/EtOAc = 5:1); 1H NMR
1
Rf = 0.52 (cyclohexane/EtOAc = 5:1); H NMR (300 MHz,
CDCl3): δ 7.50-7.60 (m, 4H), 7.68 (ddd, J = 1.3 Hz, J = 8.5

2040 Aljaar et al.
Asian J. Chem.
(300 MHz, CDCl3): δ 2.45 (s, 3H) , 7.35 (d, J = 7.9 Hz, 2H),
7.54 (ddd, J = 1.2 Hz, J = 7.6 Hz, J = 7.7 Hz, 1H), 7.67 (ddd, J
= 1.4 Hz, J = 7.4 Hz, J = 7.4 Hz, 1H), 7.75 (d, J = 8.9 Hz, 1H),
7.82 (d, J = 8.8 Hz, 1H), 7.98 (d, J = 7.9 Hz, 1H), 8.22 (d, J =
8.4 Hz, 2H), 8.57 (d, J = 8.8 Hz, 1H); 13C NMR (75 MHz,
CDCl3): δ 21.7, 110.7, 122.2, 124.7, 125.2, 125.7, 126.5, 126.8,
127.3, 128.5, 129.6, 131.1, 137.6, 141.5, 147.8, 162.5.
2-(Naphth-2-yl)naphtho[1,2-d][1,3]oxazole (3k):White
solid, 32% yield; m.p. 154-155 °C (lit. m.p. 154 ºC) [Ref. 21];
increased to 45% by increasing the amount of catalyst to 15
mol% (Table-1, entry 2). Increasing the amount of catalyst to
20 mol% and 30 mol% lead to a decrease in the yield to 40%
and 34%, respectively (Table-1, entries 3-4). Next, the influence
of different solvents, such as dichloroethene, dichloromethane,
o-dichlorobenzene, DMF, toluene and [bmin]BF4 on the outcome
of the model reaction was investigated (Table-1, entries 5-10).
These experiments showed that the reaction can be performed
with halogenated solvents with good yield (Table-1, entries
5-7). With DMF and toluene the yield dropped to 5% and 20%,
respectively (Table-1, entries 8-9). It must be mentioned that
the reaction could be performed in an ionic solvent such as
[bmin]BF4 with moderate yield (Table-1, entry 10). Without
any Fe-catalyst, the formation of product 3a didn't take place
at all (Table-1, entry 11).
Over the last decades, vast progress has been made in using
microwave irradiation in synthetic organic chemistry [26,27].
The highly effective uniform heating source in microwave leads
to accelerate the reaction rate, provide better yields, greater
reproducibility of reactions, help in developing cleaner synth-
etic methods and reduce reaction times. Due to these benefits
of microwave, the model reaction was performed using a sealed
vial and microwave irradiation at 100 ºC (Table-2, entries 1 and
2). Remarkably enough, the yield could be increased to 68%
in a sealed vial and 72% in the microwave. In summary, the
best results were achieved when 1 mmol of 1-nitroso-2-naphthol
1
Rf = 0.49 (cyclohexane/EtOAc = 5:1); H NMR (400 MHz,
CDCl3): δ 7.52-7.62 (m, 3H), 7.71 (ddd, J = 1.1 Hz, J = 7.3
Hz, J = 7.2 Hz, 1H), 7.77 (d, J = 8.8 Hz, 1H), 7.83 (d, J = 8.8
Hz, 1H), 7.87-7.94 (m, 1H), 7.95-8.06 (m, 4H), 8.42 (dd, J =
1.9 Hz, J = 8.5 Hz, 1H), 8.64 (d, J = 8.3 Hz, 1H), 8.83 (s, 1H);
13C NMR (100 MHz, CDCl3): δ110.3, 122.2, 123.9, 124.8, 125.4,
126.1, 126.5, 126.8, 127.0, 127.56, 127.57, 127.9, 128.6, 128.7,
128.9, 131.2, 133.1, 134.5, 137.7, 148.1, 162.5.
RESULTS AND DISCUSSION
Initial experiment between 1-nitroso-2-naphthol (1a) with
prenyl bromide (2a) using 10 mol% FeCl3 as a catalyst and
CH3CN as a solvent under reflux for 3 h produced 3a with
25% yield (Table-1, entry 1). Inspired by this result, we optimized
this reaction using different solvents, temperature and amount
of catalyst (Table-1). The yield of product 3a could easily be
TABLE-1
OPTIMIZATION OF THE MODEL REACTION UNDER DIFFERENT AMOUNT OF CATALYST, SOLVENTS AND TEMPERATUREa
O
OH
N
Br
NO
1a
2a
3a
Yield 3a (%)b
Entry
FeCl3 (mol%)
Solvent
Temp. (°C)
1
2
3
4
5
6
7
8
9
10
15
20
30
15
15
15
15
15
15
–
CH3CN
CH3CN
CH3CN
CH3CN
CH2ClCH2Cl
CH2Cl2
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
100
100
100
100
100
25
45
40
34
61
48
64
5
o-Dichlorobenzene
DMF
Toluene
[bmin]BF4
o-Dichlorobenzene
20
42
–
10
11
aAll reactions were carried using 1 mmol 1a and 1 mmol 2a; bIsolated Yield.
TABLE-2
OPTIMIZATION OF THE MODEL REACTION UNDER DIFFERENT CONDITIONSa
15% FeCl3
O
o-dichlorobenzene
OH
NO
N
Br
1a
2a
3a
Entry
Condition
Temp. (°C)
Time
3 h
10 min
Yield 3a (%)
1
Sealed tube
Microwave
100
100
68
72
2b
aAll reactions were carried using 1 mmol 1a and 1 mmol 2a; bThe reactions were performed using a microwave apparatus (200 W).

Vol. 32, No. 8 (2020)
Microwave-Assisted Synthesis of 2-Substituted Naphtho[1,2-d][1,3]oxazoles using FeCl3 as Catalyst 2041
(1a) and 1 mmol of prenyl bromide (2a) in the presence of 15
mol% FeCl3 in o-dichlorobenzene under microwave at 100 ºC
for 10 min.
med with a number of benzyl bromides (2d-j) having different
substituents on the phenyl group with yield ranging from 34
to 45% (Table-3, entries 3-9). Several substituents could be
employed such as cyano, fluoro, chloro, bromo, methoxy and
methyl groups. It seems that the influence of the nature of the
substituent on the phenyl group of 2 is only small. The yields
with electron-withdrawing groups are comparable to electron-
donating groups. In addition to allyl brmides and benzyl brmides
the reaction was also performed with 2-(bromomethyl)naphth-
alene (2k) to yield 2-(naphth-2-yl)naphtho[1,2-d][1,3]oxazole
(3k) with yield 32% (Table-3, entry 10).
With the optimized reaction conditions, 2-substituted
naphtho[1,2-d][1,3]oxazoles (3b-k) were synthesized with
yields ranging from 32% to 58% by reacting 1-nitroso-2-naphthol
(1a) with a number of allyl bromides and benzyl bromides
(2b-k) (Table-3). The reaction with bromo acetonitrile (2b)
and allyl bromide (2c) delivered 2-cyanonaphthoxazole, 2-
vinyl naphthoxazole with yield 58% and 50%, respectively
(Table-3, entries 1 and 2). A conversion could also be perfor-
TABLE-3
PREPARATION OF SEVERAL 2-SUBSTITUTEDNAPHTHA[1,2-d]OXAZOLES (3)a
15 mol% FeCl3
O
OH
o-dichlorobenzene
R2
Br
R2
N
MW, 100 °C,10 min
NO
1a
2
3
Entry
1
Substrate
Product
Yield (%)b
58
O
Br
NC
2b
2c
N
N
CN
3b
3c
O
Br
2
3
50
35
Br
O
N
3d
2d
O
Br
4
5
45
42
2e
N
3e
3f
NC
F
CN
F
O
Br
2f
N
O
O
Br
Br
6
7
8
40
39
37
2g
2h
N
N
3g
3h
Cl
Cl
Br
Br
O
Br
2i
N
3i
H3CO
OCH3

2042 Aljaar et al.
Asian J. Chem.
O
O
Br
Br
9
34
2j
N
N
3j
H3C
CH3
10
32
3k
2k
aAll reactions were carried using 1 mmol 1 and 1 mmol 2; bIsolated yield
10. M. Ueki, K. Ueno, S. Miyadoh, K. Abe, K. Shibata, M. Taniguchi and
S. Oi, J. Antibiot. (Tokyo), 46, 1089 (1993);
https://doi.org/10.7164/antibiotics.46.1089
11. M.-J. Don, C.-C. Shen, Y.-L. Lin, W.-J. Syu, Y.-H. Ding and C.-M.
Sun, J. Nat. Prod., 68, 1066 (2005);
https://doi.org/10.1021/np0500934
12. S. Sato, T. Kajiura, M. Noguchi, K. Takehana, T. Kobayashi and T. Tsuji,
J. Antibiot. (Tokyo), 54, 102 (2001);
https://doi.org/10.7164/antibiotics.54.102
13. A.D. Rodríguez, C. Ramírez, I.I. Rodríguez and E. González, Org. Lett.,
1, 527 (1999);
Conclusion
In conclusion, a simple and highly efficient method for
the synthesis of 2-substituted naphtho[1,2-d][1,3]oxazoles has
been developed. Best results were accomplished when 1 mmol
of compound 1a was reacted with 1 mmol of compound 2 in
the presence of 15 mol% FeCl3 in o-dichlorobenzene solvent.
Using microwave condition the time for the synthesis of 2-
substituted naphthoxazoles (3a-k) was reduced from 3 h to 10
min with increased yield.
https://doi.org/10.1021/ol9907116
14. Y. Ooyama, Y. Kagawa, H. Fukuoka, G. Ito and Y. Harima, Eur. J. Org.
Chem., 5321 (2009);
ACKNOWLEDGEMENTS
https://doi.org/10.1002/ejoc.200900758
15. Y. Ooyama, H. Egawa and K.Yoshida, Eur. J. Org. Chem., 5239 (2008);
https://doi.org/10.1002/ejoc.200800606
16. K. Tanaka, T. Kumagai, H.Aoki, M. Deguchi and S. Iwata, J. Org. Chem.,
66, 7328 (2001);
One of the authors, NA gratefully acknowledges the finan-
cial and research support from the Department of Chemistry,
Hashemite University, Zarqa, Jordan.
https://doi.org/10.1021/jo010462a
CONFLICT OF INTEREST
17. R. Ruiz-González, R. Zanocco, Y. Gidi, A.L. Zanocco, S. Nonell and
E. Lemp, Photochem. Photobiol., 89, 1427 (2013);
https://doi.org/10.1111/php.12106
18. A.R. Katritzky, Z. Wang, C.D. Hall, N.G.Akhmedov, A.A. Shestopalov
and P.J. Steel, J. Org. Chem., 68, 9093 (2003);
https://doi.org/10.1021/jo026771y
The authors declare that there is no conflict of interests
regarding the publication of this article.
REFERENCES
19. W. Yao and D. Huang, Org. Lett., 12, 736 (2010);
https://doi.org/10.1021/ol902812q
20. P. Astolfi, P. Carloni, R. Castagna, L. Greci, P. Stipa and C. Rizzoli, J.
Heterocycl. Chem., 41, 971 (2004);
https://doi.org/10.1002/jhet.5570410618
21. N. Aljaar, C.C. Malakar, J. Conrad, W. Frey and U. Beifuss, J. Org. Chem.,
78, 10829 (2013);
https://doi.org/10.1021/acs.joc.5b02000
22. H. Li, K. Wei and Y.-J. Wu, Chin. J. Chem., 25, 1704 (2007);
https://doi.org/10.1002/cjoc.200790315
23. A.-M. Osman and I. Bassiouni, J. Org. Chem., 27, 558 (1962);
https://doi.org/10.1021/jo01049a051
24. R.-G. Xing, Y.-N. Li, Q. Liu, Q.-Y. Meng, J. Li, X.-X. Shen, Z. Liu, B.
Zhou, X. Yao and Z.-L. Liu, Eur. J. Org. Chem., 6627 (2010);
https://doi.org/10.1002/ejoc.201000985
1. R.V. Kumar, Asian J. Chem., 14, 1241 (2004).
2. G.V. Boyd, ed.: E. Schaumann, Product Class 12: Oxazoles, Category 2,
Hetarenes and Related Ring Systems, In: Science of Synthesis, Stuttgart:
Germany, vol. 11, p. 481 (2001).
3. W. Frederick and J. Hartner, ed.: A.R. Katritzky, C.W. Rees and E.F. V.
Scriven, Comprehensive Heterocyclic Chemistry II, Pergamon: Oxford,
vol. 3, p. 261 (1996).
4. V.S.C. Yeh, Tetrahedron, 60, 11995 (2004);
https://doi.org/10.1016/j.tet.2004.10.001
5. J. Easmon, G. Pürstinger, K.-S. Thies, G. Heinisch and J. Hofmann, J.
Med. Chem., 49, 6343 (2006);
https://doi.org/10.1021/jm060232u
6. L. Leventhal, M.R. Brandt, T.A. Cummons, M.J. Piesla, K.E. Rogers
and H.A. Harris, Eur. J. Pharmacol., 553, 146 (2006);
https://doi.org/10.1016/j.ejphar.2006.09.033
7. J.A. Grobler, G. Dornadula, R.M. Rice, A.L. Simcoe, D.J. Hazuda and
M.D. Miller, J. Biol. Chem., 282, 8005 (2007);
https://doi.org/10.1074/jbc.M608274200
8. S. Yoshida, S. Shiokawa, K. Kawano, T. Ito, H. Murakami, H. Suzuki
and Y. Sato, J. Med. Chem., 48, 7075 (2005);
25. C. Saitz, H. Rodríguez, A. Márquez, A. Cañete, C. Jullian and A.
Zanocco, Synth. Commun., 31, 135 (2001);
https://doi.org/10.1081/SCC-100000190
26. M. Gaba and N. Dhingra, Ind. J. Pharm. Educ. Res., 45, 175 (2011).
27. P. Lidström, J. Tierney, B. Wathey and J. Westman, Tetrahedron, 57,
9225 (2001);
https://doi.org/10.1021/jm050209t
https://doi.org/10.1016/S0040-4020(01)00906-1
9. D.C. Tully, H. Liu, P.B. Alper, A.K. Chatterjee, R. Epple, M.J. Roberts,
J.A. Williams, K.T. Nguyen, D.H. Woodmansee, C. Tumanut, J. Li, G.
Spraggon, J. Chang, T. Tuntland, J.L. Harris and D.S. Karanewsky,
Bioorg. Med. Chem. Lett., 16, 1975 (2006);
https://doi.org/10.1016/j.bmcl.2005.12.095