The one-pot synthesis of 14-aryl or alkyl-14H-dibenzo[a,j]xanthenes catalyzed by P2O5/Al2O3 under microwave irradiation

Article abstract of DOI:10.1016/j.dyepig.2009.10.015

A convenient and efficient procedure for the synthesis of 14-aryl or alkyl-14H-dibenzo[a,j]xanthenes by condensation of 2-naphthol and aldehydes in the presence of P₂O₅/Al₂O₃ is described. Both aromatic and alip

Full text of DOI:10.1016/j.dyepig.2009.10.015

Dyes and Pigments 85 (2010) 133e138
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Short communication
The one-pot synthesis of 14-aryl or alkyl-14H-dibenzo[a,j]xanthenes
catalyzed by P2O5/Al2O3 under microwave irradiation
,
b
,
c,
Amin Zarei a , Abdol R. Hajipour d, Leila Khazdooz e
*
a Department of Science, Islamic Azad University, Fasa Branch, PO Box No. 364, Fasa 7461713591, Fars, Iran
b Fasa Higher Education Complex, Fasa, 7461781189, Fars, Iran
c Department of Pharmacology, University of Wisconsin, Medical School, 1300 University Avenue, Madison, WI 53706-1532, USA
d Pharmaceutical Research Laboratory, College of Chemistry, Isfahan University of Technology, Isfahan 84156, Iran
e Department of Science, Islamic Azad University, Khorasgan Branch, Isfahan 81595-158, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
A convenient and efficient procedure for the synthesis of 14-aryl or alkyl-14H-dibenzo[a,j]xanthenes by
condensation of 2-naphthol and aldehydes in the presence of P2O5/Al2O3 is described. Both aromatic and
aliphatic aldehydes react easily to afford the corresponding 14-aryl or alkyl-14H-dibenzo[a,j]xanthenes
under microwave irradiation. This reaction was studied under different conditions; several solvents were
examined for this conversion. In the terms of reaction time and yield, it was found that optimum results
were obtained when reaction was carried out under microwave irradiation.
Received 28 April 2009
Received in revised form
18 October 2009
Accepted 21 October 2009
Available online 28 October 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Dibenzoxanthene
P2O5/Al2O3
Catalyst
2-Naphthol
Aldehyde
Microwave irradiation
1. Introduction
The use of catalysts and reagents on solid supports has been
developed because such reagents not only simplify purification
Xanthenes, especially benzoxanthens, are important intermedi-
ates in organic synthesis due to their wide range of biological and
therapeutic properties such as antibacterial [1], antiviral [2], anti-
inflammatory activities [3] and sensitizers in photodynamic therapy
for destroying the tumor cells [4]. Moreover, these heterocyclic
compounds can be used as dyes [5], antagonists for the paralyzing
action of zoxazolamine [6], pH-sensitive fluorescent materials for
visualization of biomolecules [7] and in laser technology [8]. The
reported methods for the synthesis of 14-aryl or alkyl-14H-dibenzo[a,j]
xanthenes involve the mixing of 2-naphthol with aldehydes in the
presence of an acidic catalyst such as pTSA [9], LiBr [10], Amberlyst-
15 [11], silica sulfuric acid [12,13], molecular iodine [14,15], sulfamic
acid [16], heteropoly acid [17,18], Yb(OTf)3 [19], alum [20], BF3.SiO2
[21], Montmorillonite K-10 [22] and Ionic liquids [23e25].
processes but also help to prevent release of reaction residues
into the environment [26]. Although there are many reports using
phosphorus pentoxide as a reagent in organic reactions [27e29],
P2O5 is difficult to handle due to its moisture sensitivity at room
temperature. P2O5 on solid supports is easy to prepare and to handle
and can be removed from the reaction mixture by simple filtration
[30e35]. In continuation of our investigations on the applications of
P2O5 on solid supports in organic synthesis [30e35], herein we
report an efficient and convenient procedure for the synthesis of
14-aryl or alkyl-14H-dibenzo[a,j]xanthenes using catalytic amount
of P2O5/Al2O3 under microwave irradiation (Fig. 1).
2. Experimental
2.1. General
* Corresponding author. Department of Science, Islamic Azad University, Fasa
Branch, PO Box No. 364, Fasa 7461713591, Fars, Iran. Tel.: þ98 917 1302528; fax:
þ98 311 2289113.
All reagents were purchased from Merck and Aldrich and used
without further purification. P2O5/Al2O3 was prepared according
E-mail address: aj_zarei@yahoo.com (A. Zarei).
0143-7208/$ e see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2009.10.015

134
A. Zarei et al. / Dyes and Pigments 85 (2010) 133e138
Table 1
The reaction between 2-naphthol and 4-chlorobenzaldehyde using catalytic amount
of P2O5/Al2O3 under different conditions.a
O
C
OH
P2O5/Al2O3 (18 mol%)
MW,10-15 min
Entry
Solvent
Conditions
Time
Yield (%)
+
2
R
O
R
H
1b
2b
3b
4b
5
THF
Reflux
Reflux
Reflux
Reflux
60 ꢁC
5 h
0
CH3CN
CH2Cl2
ClCH2CH2Cl
Neat
5 h
5 h
5 h
Trace
Trace
20
3 h
30
6
Neat
80 ꢁC
3 h
46
Fig. 1. . An efficient and convenient procedure for the synthesis of 14-aryl or alkyl-
14H-dibenzo[a,j]xanthenes using catalytic amount of P2O5/Al2O3 under microwave
irradiation.
7
Neat
Neat
MW, neat
MW, neat
100 ꢁC
125 ꢁC
900 W
900 W
3 h
65
8
1.5 h
10 min
10 min
90
92
15
9c
10c
,d
a
The yields refer to the isolated pure products.
The reaction was carried out in 5 mL of solvent.
The reaction was irradiated by using microwave laboratory system (micro-
b
c
to the previous work [33,35]. The reactions were irradiated
by using microwave laboratory system (microsynth), model;
Milestone. Melting points were measured with a Gallenkamp
Apparatus and were uncorrected. IR spectra were obtained using
a JASCO FT-IR-680 PLUS spectrometer. The 1H NMR spectra were
recorded on a Bruker 500 MHz spectrometer at 500 MHz with
synth), model; Milestone.
d
The reaction was carried out in the absence of P2O5/Al2O3.
After optimization of the reaction conditions, we studied
the generality of these conditions to other substrates. Using this
method, different kinds of aromatic and aliphatic aldehydes
were reacted with 2-naphtol to produce the corresponding 14-aryl
or alkyl-14H-dibenzo[a,j]xanthenes under microwave irradiation
(Table 2). Several aromatic aldehydes with different functional
groups were subjected to the condensation reaction and the desire
products were synthesized in good to high yields and short reaction
time. The use of 18 mol% of P2O5/Al2O3 was sufficient to progress the
reaction and an increase of the amount of catalyst did not improve
the yield.
The substituted functional groups on the aromatic ring of the
aldehyde affected on the yield and reaction time. In comparison with
electron with-drawing groups on the aryl aldehydes, we found that
the presence of electron donating groups on the aryl aldehydes
decreased both the reaction rate and yield of product (Table 2, entries
3e5). We also studied the reaction between terephthaldialdehyde
(1 mmol) and excess amount of 2-naphtol (4 mmol), we expected
that both of the formyl groups on the aromatic ring of tereph-
thaldialdehyde would react with 2-naphtol. However, we observed
that one of the formyl groups was condensed with 2-naphtol and
another group was intact because of steric effects between o-hydro-
gens of benzene ring and the xanthene ring [22] (Fig. 2).
To evaluate the role of Al2O3, we studied the reaction of benzal-
dehyde, 4-nitrobenzaldehyde, 4-methoxybenzaldehyde and butyr-
aldehyde in the absence of Al2O3 using P2O5 alone. It was found that
theyields by using P2O5/Al2O3, were greater (average,12%) than those
with P2O5 alone under the same conditions. In our previous work,
we described the structure of P2O5/Al2O3 [35]. It was found that P2O5
reacted with Al2O3 and bonded on the surface of alumina. This
structure has Brꢀnsted and Lewis acidic sites dispersed on the surface
of alumina. Furthermore, Al2O3 as a support mayalso minimize cross-
contamination between the product and H3PO4 generated during the
course of the reaction [26,35]. We think that these reasons can lead to
significant improvements in its reactivity.
chemical shift (
d) values reported in ppm relative to an internal
standard (TMS).
2.2. General procedure for the synthesis of aryl
or alkyl-14H-dibenzo[a,j]xanthenes
A mixture of 2-naphthol (2 mmol), aldehyde (1 mmol), and P2O5/
Al2O3 (0.05 g, 18 mol%) was taken in a sealed teflon vessel and
irradiated (900 W) for 10e15 min. The progress of the reaction was
monitored by TLC. After completion of the reaction, the product was
extracted with chloroform and the crude product was recrystallized
from ethanol to afford the pure 14-aryl or alkyl-14H-dibenzo[a,j]
xanthene derivatives.
2.3. The spectral data of new products
Table 2, entry 17: 1H NMR (400 MHz, CDCl3)
d
¼ 8.39
(d, J ¼ 8.40 Hz, 2 H), 7.20 (m, 4 H), 7.58 (m, 2 H), 7.48 (d, J ¼ 8.80 Hz,
2 H), 7.42 (m, 4 H), 6.68 (d, J ¼ 8.40 Hz, 2 H), 6.46 (s, 1 H). 13C NMR
(100 MHz, CDCl3)
d
¼ 157.85, 148.68, 137.36, 131.41, 131.07, 129.14,
128.79,128.71,126.74,124.20,122.68,117.99,117.53,113.84, 37.09. IR
(KBr): 3060, 1591, 1509, 1457, 1430, 1399, 1249, 1177, 1029, 961, 830,
808, 742 cmꢀ1. Anal. Calcd for C26H17NO: C, 86.90; H, 4.73; N, 3.90.
Found: C, 86.81; H, 4.84; N, 3.82.
Table 2, entry 18: 1H NMR (400 MHz, CDCl3)
d
¼ 8.68
(d, J ¼ 8.40 Hz, 2 H), 8.54 (d, J ¼ 4.80 Hz,1 H), 7.83 (d, J ¼ 8.80 Hz, 4 H),
7.58 (t, J ¼ 7.60 Hz, 2 H), 7.48 (d, J ¼ 8.80 Hz, 2 H), 7.41 (t, J ¼ 7.60 Hz,
2 H), 7.34 (m,1 H), 7.14 (d, J ¼ 8.00 Hz,1 H), 6.91 (m,1 H), 6.76 (s,1 H).
13C NMR (100 MHz, CDCl3)
d
¼ 164.70, 148.20, 147.74, 137.10, 131.92,
130.90, 129.18, 128.39, 126.92, 124.38, 123.99, 123.84, 121.23, 117.90,
116.00, 41.93. IR (KBr): 3044,1620,1588,1513,1458,1429,1407,1255,
1244,1147, 967, 831, 805, 773, 754 cmꢀ1. Anal. Calcd for C26H17NO: C,
86.90; H, 4.73; N, 3.90. Found: C, 86.82; H, 4.82; N, 3.84.
3. Results and discussion
4. Conclusion
Initially, to optimize the reaction conditions, we studied the
reaction between 2-naphthol (2 mmol) and 4-chlorobenzaldehyde
(1 mmol) as a simple model using catalytic amount of P2O5/Al2O3
(0.05 g, 18 mol%) under different conditions (Table 1). We found
that the best result was obtained when the reaction was carried
out under microwave irradiation (Table 1, entry 9). In the absence of
P2O5/Al2O3, the reaction was carried out in low yield under the
same conditions (Table 1, entry 10).
P2O5/Al2O3 is an inexpensive, easily available, non-corrosive and
environmentally benign compound. A convenient and efficient
procedure for the preparation of 14-aryl or alkyl-14H-dibenzo[a,j]
xanthenes in good yields and short reaction times was reported in
this work. The notable advantages of this methodology are opera-
tional simplicity, generality, availability of reactants, short reaction
times and easy work-up.

Table 2
Synthesis of 14-aryl or alkyl-14H-dibenzo[a,j]xanthenes using catalytic amount of P2O5/Al2O3 under microwave irradiation.
Entry
Aldehyde
Product
Time (min)
Yield (%)a
Mp (ꢁC)
Found
Reported
1
12
85
183e185
226e228
258e259
183e184 [21]
2
12
83
227e228 [21]
3
15
77
258e259 [21]
4
5
15
15
80
75
202e204
203e205 [21]
141e143
140 [13]
6
7
8
9
10
10
12
10
90
92
90
95
298e300
289e291
213e215
209e210
297e298 [21]
289e290 [21]
214e216 [21]
209e211 [21]
(continued on next page)

136
A. Zarei et al. / Dyes and Pigments 85 (2010) 133e138
Table 2 (continued)
Entry Aldehyde
Product
Time (min)
Yield (%)a
Mp (ꢁC)
Found
Reported
10
10
90
238e240
250e252
310e312
293e295
210e211
238e240 [20]
11
12b
13
14
12
12
10
10
87
87
89
93
249e250 [24]
308e312 [22]
291e292 [19]
210e211 [21]
15
16
17
10
10
15
91
95
65
213e215
310e312
200e202
214e215 [21]
311e312 [21]
e
18
15
60
236e237
e

A. Zarei et al. / Dyes and Pigments 85 (2010) 133e138
137
Table 2 (continued)
Entry Aldehyde
Product
Time (min)
Yield (%)a
Mp (ꢁC)
Found
Reported
19
10
80
154e156
155e157 [21]
20
10
83
152e154
152e154 [21]
a
The yields refer to the isolated pure products which were characterized from their spectral data and were compared with authentic samples.
The molar ratio of terephthaldialdehyde/2-naphtol is 1/4.
b
O
O
OH
P2O5/Al2O3 (18 mol%)
(0%)
OHC
CHO
+
MW, neat conditions, 12 min
1 mmol
4 mmol
O
O
CH
(87%)
Fig. 2. . Reaction between terephthaldialdehyde and excess amount of 2-naphtol.
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Acknowledgements
We gratefully acknowledge the funding support received for this
project from the Islamic Azad University of Fasa and the Isfahan
University of Technology (IUT).
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