An efficient synthesis of naphtha[1,2-e]oxazinone and 14-substituted-14H- dibenzo[a,j]xanthene derivatives promoted by zinc oxide nanoparticle under thermal and solvent-free conditions

Article abstract of DOI:10.1016/j.tetlet.2012.03.085

A general synthetic route to the synthesis of 1,2-dihydro-1-arylnaphtho[1, 2-e][1,3]oxazine-3-one and 14-substituted-14H-dibenzo[a,j]xanthenes derivatives has been developed using ZnO-NPs under thermal and solvent-free conditions. The union of 2-naphthol,

Full text of DOI:10.1016/j.tetlet.2012.03.085

Tetrahedron Letters 53 (2012) 2741–2744
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
An efficient synthesis of naphtha[1,2-e]oxazinone and
14-substituted-14H-dibenzo[a,j]xanthene derivatives promoted by zinc oxide
nanoparticle under thermal and solvent-free conditions
G.B. Dharma Rao a, M.P. Kaushik a, , A.K. Halve b
⇑
a Discovery Centre, Process Technology Development Division, Defence R&D Establishment, Jhansi Road, Gwalior 474 002, MP, India
b School of Studies of Chemistry, Jiwaji University, Gwalior 474 002, MP, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A general synthetic route to the synthesis of 1,2-dihydro-1-arylnaphtho[1,2-e][1,3]oxazine-3-one and
14-substituted-14H-dibenzo[a,j]xanthenes derivatives has been developed using ZnO-NPs under thermal
and solvent-free conditions. The union of 2-naphthol, aldehyde, urea enabling the synthesis of naph-
tho[1,2-e][1,3]oxazinone and 2-naphthol, aldehyde gave dibenzo[a,j]xanthenes in excellent yields. This
method provides several advantages like simple work-up, environmentally benign, and shorter reaction
times along with high yields.
Received 6 February 2012
Revised 20 March 2012
Accepted 22 March 2012
Available online 29 March 2012
Keywords:
Naphthoxazinone
Xanthene
Ó 2012 Elsevier Ltd. All rights reserved.
2-Naphthol
Aldehyde
Zinc oxide nanoparticles
Heterogeneous catalyst
Oxazinone, benzoxazinone, and their derivatives are an impor-
tant class of heterocyclic compounds. In recent years oxazinones
core containing heterocyclic derivatives have received considerable
attention, due to its biological activities.1,2 Naphthalene condensed
oxazinone derivatives have a broad spectrum of antibacterial
properties3 and the synthesis of 1,2-dihydro-1-arylnaphtho[1,
2-e][1,3]oxazine-3-one which involves a three-component conden-
sation reaction of 2-naphthol, arylaldehyde, and urea in one-pot
(Scheme 1, Path A). These compounds have also been used as a
precursor in the synthesis of chiral amino phosphine ligands for
asymmetric catalysis.4 Due to the pharmacological importance,
several protocols have been developed over a period of time. The
conventional method includes condensation of phenols, formalde-
hyde, and amines through Mannich reaction,5 additionally they
have also been synthesized by the reaction of amino alkylnaphthols
with phosgene6 and reaction with carbonyl di-imidazole.7 However,
these methods have some drawbacks like prolonged reaction time,
lack of easy availability/preparation of starting materials, and haz-
ardous reaction conditions. To overcome these drawbacks, several
methods are reported in the literature utilizing acidic and basic
catalysts8 each of these methods has their own advantages but also
suffer from some bottlenecks, such as modest yields and tedious
work-up procedure. Therefore, these drawbacks prompted us to
examine a new catalyst for the environmentally benign synthesis
of 1,2-dihydro-1-arylnaphtho[1,2-e][1,3]oxazine-3-one.
Nano-chemistry is an up growing research area due to their
unique properties.9 The usage of nanomaterials such as heteroge-
neous catalyst has gained significant role in organic synthesis
due to simple work-up procedure, environmentally benign nature,
reusability, low cost, and ease of isolation. Zinc oxide nanoparticles
(ZnO-NPs) are heterogeneous catalysts and widely used in cosmet-
ics, paints, and fibers. It can also play a role of Lewis acid in various
F
O
H
N
F
O
H
O
+
O
path A
path B
ZnO NPs
H2N
NH2
F
solvent-free
+
OH
O
Path A: aldehyde + urea + 2-naphthol sequence addition
Path B: aldehyde, urea, 2-naphthol rando maddition
⇑
Corresponding author. Tel.: +91 751 2343972; fax: +91 751 2340042.
E-mail address: mpkaushik@rediffmail.com (M.P. Kaushik).
Scheme 1. General synthetic approach of naphtha[1,2-e]oxazinone.
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.03.085

2742
G. B. Dharma Rao et al. / Tetrahedron Letters 53 (2012) 2741–2744
organic transformations.10 Recently, Prasad et al. have reported the
crystalline sizes of ZnO-NPs prepared by the calcination of xerogel
at 500 °C, 900 °C, 1000 °C, 1100 °C, which were characterized by
TEM, XRD, N2 BET.11 They have also studied the photocatalytic
decontamination of sulfur mustered (CWA) on the surface of zinc
oxide nanoparticles. Inspired by the above catalytic activity of
ZnO-NPs, we examined the ZnO-NPs as a heterogeneous catalyst
in the synthesis of naphtha[1,2-e]oxazinone and dibenzoxanthenes
derivative.
Table 2
ZnO-NPs catalyzed synthesis of 14-substituted-14H-dibenzo[a,j]xanthenes deriva-
tives (5a–k)a
R
O
OH
ZnO NPs
+
H
R
2
solvent-free
O
1
5a-k
2
Entry
Aldehyde (R)
Product
Time (min)
Yieldb (%)
M.P.ref
In continuation of our studies on the synthesis of various bioac-
tive compounds12 herein, we report an efficient, facile, and conve-
nient procedure for the synthesis of naphtha[1,2-e]oxazinone
derivatives employed by the union of 2-naphthol, aldehyde, and
urea in the presence of catalytic amount of ZnO-NPs as an environ-
mentally benign and heterogeneous catalyst under thermal and
solvent-free conditions.
Initially we investigated the catalytic activity of ZnO-NPs for the
synthesis of naphtha[1,2-e]oxazinone derivatives. A set of control
experiments on 3-fluoro benzaldehyde, 2-naphthol, and urea were
carried out under solvent-free conditions. The utility of ZnO bulk in
the synthesis of naphtha[1,2-e]oxazinone shows that its efficiency
which is lower than ZnO-NPs. From the above observations, it was
revealed that the sequential addition of reactants had played a sig-
nificant role in the synthesis of target molecule. Any alternation in
the sequential addition or random addition of reactants led to the
formation of the new product (Scheme 1).
By the random addition of the 3-fluoro benzaldehyde, 2-naph-
thol, urea, and ZnO-NPs (Scheme 1, Path B), we observed xanthene
derivative (Table 2, entry 6) as a major product and there was no for-
mation of naphthoxazinone derivative. The sequential addition of
reactants like 3-fluoro benzaldehyde, urea, and catalyst followed
by 2-naphthol played a crucial role and influenced toward the
course of desired naphthoxazinone (Table 1, entry 4) product which
was observed as a major product (Scheme 1, Path A). The formation
of xanthene derivative as a major product in random addition might
be due to the highly reactive nature of benzaldehyde with 2-naph-
thol than urea. ZnO-NPs (0.3 equiv) was efficiently accelerated by
the reaction of arylbenzaldehyde (1.0 equiv), 2-naphthol (1.0 equiv)
and urea (2.0 equiv) toward the formation of desired product under
thermal and solvent-free conditions.22a Further, we extended the
optimized reaction conditions to various aldehydes and all the
results are appended in Table 1.
1
2
3
4
5
6
7
8
9
4-OCH3 -C6H5
4-OC2H5 -C6H5
4-Cl-C6H5
3-Cl-C6H5
4-F -C6H5
3-F -C6H5
4-C2H5-C6H5
3-C5H4N-
5a
5b
5c
5d
5e
5f
5g
5h
5i
60
60
40
60
50
45
70
60
80
60
55
82
88
92
90
85
90
88
85
86
80
86
202–20421a
172–174
288–29021a
210–21221c
240–24221a
258–26021d
186–188
202–20421b
156–15821a
182–18421a
310–31221a
(CH3)2CH-
C6H5
4-NO2-C6H5
10
11
5j
5k
a
Reaction conditions: 1 (1.0 equiv), 2 (2.0 equiv) and ZnO-NPs (0.3 equiv).
Isolated yields.
b
Xanthenes have active oxygen atom and they are widely used as
a leuco-dye13 in laser technologies14 and in fluorescent materials
for the visualization of bio-molecule15 cascades due to their useful
spectroscopic properties. Xanthenes have also received significant
attention from organic chemists essentially because of the wide
range of their pharmaceutical properties.16–18 Also these com-
pounds have been utilized as antagonists for the paralyzing action
of zoxazolamine19 and in photodynamic therapy.20 In recent years,
several attempts have been made for the synthesis of xanthenes
derivatives to increase the yield.21
In order to demonstrate the catalytic activity of this ZnO-NPs,
the same procedure was extended for one-pot synthesis of 14-
substituted-14H-dibenzo[a,j]xanthenes class of compounds by
using 2-naphthol and aldehyde under the same reaction condi-
tions22b and all the results are depicted in Table 2. We observed
that ZnO-NPs promoted the reaction of 2-naphthol as well as 2-
naphthol and urea smoothly with aryl aldehyde bearing electron-
releasing or electron-withdrawing substituents.
From the green chemistry point of view, efficient recovery and
reuse of the catalyst are highly desirable, thus the recovery and
reusability of ZnO-NPs were investigated. After the reaction was
completed, ethylacetate was added until the solid crude product
was dissolved. Then, ZnO-NPs as the catalysts were isolated from
the mixture of reaction by simple filtration and reused again after
washing with ethylacetate. The reusability of ZnO-NPs was exam-
ined efficiently (without any activation) by using 3-fluoro benzal-
Table 1
Synthesis of 1,2-dihydro-1-arylnaphtho[1,2-e][1,3]oxazine-3-one (4a–j) using ZnO-
NPsa
R
O
H
N
O
OH
+
O
H
ZnO NPs
dehyde as
a model substrate. The recovered ZnO-NPs were
R
+
O
H2N
NH2
solvent-free
reused directly for four consecutive cycles and all the results are
tabulated in Table 3.
On the basis of the above observations and the literature reports,
a plausible reaction pathway for the formation of naphthoxazinone
3
2
1
4a-j
M.P.ref
Entry
Aldehyde (R)
Product
Time (min)
Yieldb (%)
1
2
3
4
5
6
7
8
9
10
4-CH3-C6H5
4-OCH3-C6H5
4-F-C6H5
3-F-C6H5
4-Cl-C6H5
4a
4b
4c
4d
4e
4f
4g
4h
4i
90
90
60
50
60
60
80
50
45
120
85
82
92
92
90
88
80
94
90
76
164–1668a
188–1908a
198–2008a
218–220
Table 3
Recyclability of the catalyst for the synthesis of 4da
210–2128a
194–1968c
216–218
Entry
Cycle
Time (min)
Yieldb (%)
3-Cl-C6H5
1
2
3
4
Cycle 1
Cycle 2
Cycle 3
Cycle 4
50
60
75
90
92
87
78
68
4-OC2H5-C6H5
4-CF3-C6H5
4-OCF3-C6H5
4-(CH3)3C-C6H5
234–236
168–170
4j
180–1828b
a
a
Reaction conditions: 2-naphthol (1.0 equiv), 3-fluoro benzaldehyde (1.0 equiv),
Reaction condition: 1 (1.0 equiv), 2 (1.0 equiv), 3 (2.0 equiv) and ZnO-NPs
(0.3 equiv).
urea (2.0 equiv) and ZnO-NPs (0.3 equiv).
b
b
Isolated yields.
Isolated yield.

G. B. Dharma Rao et al. / Tetrahedron Letters 53 (2012) 2741–2744
2743
(i)
O
OH
N
OH
N
R
R
OH
O
H2N
O
NH2
O
O
N
H
NH2
NH2
NH2
Zn2+
Zn2+
R
R
Zn2+
Zn2+
R
R
R
H2N
O
H
N
H
N
NH Zn2+
O
O
O
NH2
Zn2+
Zn2+
O
-NH 3
OH
(ii)
Zn2+
O
OH
OH OH
OH
R
R
H
OH
+
OH
R
Zn2+
R
R
R
H
Zn2+
-H2O
O
O
O
OH
OH
Zn2+
Zn2+
Scheme 2. Proposed mechanism for naphthoxazinone (i) and dibenzoxanthene (ii).
is depicted in Scheme 2. (i) The interaction of aryl aldehyde with the
catalyst surface generated the more electrophilic carbon center
followed by the nucleophilic attack of urea to give reactive acylim-
ine intermediate. The resulting acylimine intermediate undergoes a
cyclization with 2-naphthol affording the corresponding desired
naphtha[1,2-e]oxazinone followed by the elimination of ammonia.
(ii) The more electrophilic carbon center generated by catalytic sur-
face was attacked by the nucleophilic 2-naphthol. Aryl- or alkyl-
methane bisnaphthol was formed by the attack of 2-naphthol in
second step. Elimination of water molecule take place from bis-
naphthol to form final desired product 14-substituted-14H-
dibenzo[a,j]xanthenes.
Acknowledgments
The authors are thankful to Dr. G. K. Prasad for providing the
zinc oxide nanoparticles and express special thanks to Director,
DRDE, Gwalior for his keen interest and encouragement.
References and notes
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environmentally benign one-pot procedure for the synthesis
of 1,2-dihydro-1-arylnaphtho[1,2-e][1,3]oxazine-3-one and 14-
substituted-14H-dibenzo[a,j]xanthenes derivatives by using cata-
lytic amount of ZnO-NPs under thermal and solvent-free conditions.
Salient features of this method are mild reaction conditions, envi-
ronmental compatibility, ease of isolation of product, and excellent
reusability of the catalyst. ZnO-NPs make the reaction inexpensive
and the procedure an attractive alternative to the existing method-
ologies for the synthesis naphthoxazinone and 14-substituted-14H-
dibenzo[a,j]xanthenes derivatives. The present procedure gave the
products in good to excellent yields at reduced reaction time, which
might be due to the increased reactivity of the reactants on high sur-
face area of ZnO-nanoparticles.

2744
G. B. Dharma Rao et al. / Tetrahedron Letters 53 (2012) 2741–2744
13. Banerjee, A.; Mukherjee, A. K. Stain Technol. 1981, 56, 83.
(400 MHz, DMSO-d6) d = 5.932 (s, 1H), 6.082 (s, 1H), 6.965 (m, 2H), 7.119 (m,
1H), 7.337–7.359 (m, 2H), 7.427–7.451 (m, 2H), 7.519 (s, 1H), 7.880–7.903 (m,
2H). 13C NMR (DMSO-d6) d = 53.170, 113.410, 113.860, 114.077, 114.738,
114.945, 116.837, 122.833, 122.858, 122.983, 125.119, 127.450, 128.846,
130.430, 131.105, 145.427, 147.557, 149.204, 160.954, 163.388. ESI-MS: m/
z = 294.671 [M+1].
14. (a) Sirkeeioglu, O.; Talinli, N.; Akar, A. J. Chem. Res. (S) 1995, 502; (b) Ahmad,
M.; King, T. A.; Ko, D.-K.; Cha, B. H.; Lee, J. J. Phys. D: Appl. Phys. 2002, 35, 1473.
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G.; Lacroix, R. Eur. J. Med. Chem. 1978, 13, 67.
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45, 833–845.
21. (a) Bigdeli, M. A.; Heravi, M. M.; Mahdavinia, G. H. Catal. Commun. 2007, 8,
1595; (b) Maleki, B.; Gholizadeh, M.; Sepehr, Z. Bull. Korean Chem. Soc. 2011, 32,
1697–1702; (c) Mirjalili, B. B. F.; Bamoniri, A.; Akbari, A. Tetrahedron Lett. 2008,
49, 6454–6456; (d) Rajitha, B.; Kumar, B. S.; Reddy, Y. T.; Reddy, P. N.;
Sreenivasulu, N. Tetrahedron Lett. 2005, 46, 8691.
1-(4-Ethoxyphenyl)-1H-naphtho[1,2-e][1,3]oxazin-3(2H)-one 4g: mp 216–218,
IR (m
Max): 812, 921, 1178, 1223, 1400, 1513, 1722, 2977, 3128, 3240. 1H NMR
(400 MHz, CDCl3) d = 1.363 (t, J = 7.2 Hz, 3H), 3.926 (q, J = 7.2 Hz, 2H), 6.025 (s,
1H), 6.644 (s, 1H), 6.780–6.802 (m, 2H), 7.146–7.175 (m, 2H), 7.257–7.853 (m,
6H). 13C NMR (CDCl3) d = 14.721, 55.393, 63.438, 112.910, 115.130, 117.051,
122.955, 125.132, 127.366, 128.236, 128.742, 129.394, 130.376, 131.001,
133.862, 147.522, 150.625, 159.011. ESI-MS: m/z = 320.216 [M+1].
1-(4-(Trifluoromethyl)phenyl)-1H-naphtho[1,2-e][1,3]oxazin-3(2H)-one 4h: mp
234–236, IR (m
Max): 814, 1068, 1120, 1325, 1516, 1727, 1760, 3151, 3234. 1H
NMR (400 MHz, CDCl3) d = 6.154 (s, 1H), 6.798 (s, 1H), 7.343–7.912 (m, 10H).
13C NMR (CDCl3) d = 55.279, 111.717, 117.043, 122.346, 122.471, 125.051,
125.439, 126.394, 126.430, 126.467, 127.458, 127.750, 128.973, 129.083,
130.663, 131.007, 131.032, 145.247, 147.717, 150.474. ESI-MS: m/z = 344.08
[M+1].
22. Typical experimental procedure:
(a) A 25 ml round bottom flask was charged with benzaldehyde (1.0 equiv),
urea (2.0 equiv) and catalytic amount of ZnO-NPs (0.3 equiv). The reactants are
finely powdered and mixed together and allowed to stir for 30 min at room
temperature. The 2-naphthol (1.0 equiv) was added to the above mixture and
the resulting reaction mixture was heated at 150 °C (oil bath) with constant
stirring till the reaction was complete. After completion of reaction as
indicated on TLC, the reaction mixture was cooled to room temperature and
the crude reaction mixture was dissolved in ethylacetate and the catalyst was
separated out by simple filtration. The reaction mixture in ethylacetate was
washed with water and excess of solvent was removed under reduced
pressure. The solid mass was washed with cold diethylether (20 ml  2) and
dried. The pure product was obtained in 76–94% yield. (b) A mixture of
1-(4-(Trifluoromethoxy)phenyl)-1H-naphtho[1,2-e][1,3]oxazin-3(2H)-one 4i: mp
168–170, IR (mMax): 816, 923, 1175, 1224, 1262, 1512, 1739, 2968, 3140, 3226.
1H NMR (400 MHz, CDCl3) d = 6.117 (s, 1H), 6.865 (s, 1H), 7.139–7.160 (m, 2H),
7.259–7.515 (m, 6H), 7.846–7.898 (m, 2H). 13C NMR (CDCl3) d = 54.945,
112.154, 117.051, 119.072, 121.656, 122.645, 125.413, 127.699, 128.608,
128.946, 129.202, 130.876, 131.074, 140.196, 147.702, 149.179, 149.192,
150.765. ESI-MS: m/z = 360.481 [M+1].
14-(4-Ethoxyphenyl)-14H-dibenzo[a,j]xanthenes 5b: mp 172–174 °C, IR (mMax):
2976, 2905, 1591, 1510, 1397, 1244, 1044, 806. 1H NMR (400 MHz, CDCl3)
d = 1.255 (t, J = 6.8 Hz, 3H), 3.808 (q, J = 6.8 Hz, 2H), 6.418 (s, 1H), 6.645 (d,
J = 8.8 Hz, 2H), 7.404–7.367 (m, 4H), 7.465 (d, J = 8.8 Hz, 2H), 7.558–7.534 (m,
2H), 7.812–7.745 (m, 4H), 8.372 (d, 2H). 13C NMR (CDCl3) d = 14.643, 37.025,
63.034, 114.266, 117.479, 117.880, 122.650, 124.084, 126.609, 128.593,
128.676, 129.047, 130.987, 131.358, 137.111, 148.562, 157.167.
aldehyde (1.0 equiv) and 2-naphthol (2.0 equiv) was charged in
a round
bottom flask. A catalytic amount of ZnO-NPs (0.3 equiv) was added and the
reaction was heated at 120 °C (oil bath) with constant stirring under solvent-
free condition for certain period of time as required. The progress of the
reaction was monitored by TLC. After completion of reaction, the reaction
mixture was cooled to room temperature. The reaction mixture was dissolved
in ethylacetate and the catalyst was separated out by simple filtration. Excess
of solvent was removed under reduced pressure and the crude product was
recrystallized with ethanol to afford the pure product in 80–92% yield. The
spectral data for some selected compounds are given below.
14-(4-Ethylphenyl)-14H-dibenzo[a,j]xanthenes 5g: mp 186–188 °C, IR (mMax):
2961, 2927, 1592, 1513, 1399, 1244, 961, 806. 1H NMR (400 MHz, CDCl3)
d = 1.045 (t, J = 7.6 Hz, 3H), 2.411 (q, J = 7.6 Hz, 2H), 6.428 (s, 1H), 6.947 (d,
J = 8.0 Hz, 2H), 7.350–7.390 (m, 4H), 7.411 (d, J = 8.0 Hz, 2H), 7.439–7.561 (m,
2H), 7.793–7.730 (m, 4H), 8.381 (d, 2H). 13C NMR (CDCl3) d = 15.021, 28.136,
37.532, 117.468, 117.908, 122.679, 124.086, 126.622, 127.845, 128.027,
128.630, 128.671, 130.993, 131.421, 141.986, 142.216, 148.656.
1-(3-Fluorophenyl)-1H-naphtho[1,2-e][1,3]oxazin-3(2H)-one 4d: mp 218–220, IR
(m
Max): 794, 929, 1184, 1226, 1397, 1487, 1756, 2966, 3132, 3216. 1H NMR