Silica supported perchloric acid: An efficient catalyst for the synthesis of 14-aryl-14h-dibenzo[a, i]xanthene-8, 13-diones

Article abstract of DOI:10.1590/S0103-50532010000500025

The condensation of β-naphthol with aromatic aldehydes and 2-hydroxynaphthalene-1, 4-dione in presence of silica supported perchloric acid under solvent-free media to afford the corresponding 14-aryl-14H-dibenzo[a, i]xanthene-8, 13-diones in excellent yields and short reaction times is described. The reaction work-up is very simple and the catalyst can be easily separated from the reaction mixture and reused several times in subsequent reactions.

Full text of DOI:10.1590/S0103-50532010000500025

J. Braz. Chem. Soc., Vol. 221, No. 5, 941-945, 2010.
Printed in Brazil - ©2010 Sociedade Brasileira de Química
0103 - 5053 $6.00+0.00
Silica Supported Perchloric Acid: An Efficient Catalyst for the Synthesis of
14-Aryl-14H-dibenzo[a,i]xanthene-8,13-diones
Li Qiang Wu,* Yan Fang Wu, Chun Guang Yang, Li Min Yang and Li Juan Yang
School of Pharmacy, Xinxiang Medical University, Xinxiang, Henan 453003, China
Este trabalho descreve a obtenção de 14-aril-14H-dibenzo[a,i]xanteno-8,13-dionas, com
excelentes rendimentos e em um curto tempo de reação, a partir da reação de condensação do
β-naftol com aldeídos aromáticos e 2-hidroxinaftaleno-1,4-dionas na presença de sílica suportada
em ácido perclórico em um meio livre de solvente. A reação é muito simples e o catalisador pode
ser separado facilmente da mistura reacional e, ainda, ser reutilizado por muitas vezes em reações
subseqüentes.
The condensation of β-naphthol with aromatic aldehydes and 2-hydroxynaphthalene-1,4-dione
in presence of silica supported perchloric acid under solvent-free media to afford the corresponding
14-aryl-14H-dibenzo[a,i]xanthene-8,13-diones in excellent yields and short reaction times is
described. The reaction work-up is very simple and the catalyst can be easily separated from the
reaction mixture and reused several times in subsequent reactions.
Keywords: dibenzo[a,i]xanthenes, β-naphthol, 2-hydroxynaphthalene-1,4-dione, silica
supported perchloric acid, solvent-free
Introduction
their homogeneous counterparts due to the prime advantage
that in most of the cases the catalyst can be recovered easily
and reused. Silica supported perchloric acid (HClO4-SiO2)
has been used as an efficient heterogeneous catalyst for
many organic transformations because of its low cost, ease
of preparation, catalyst recycling, and ease of handling.18
We now report a simple and efficient route to synthesis
of 14-aryl-14H-dibenzo[a,i]xanthene-8,13-diones using
HClO4-SiO2 as an efficient catalyst under solvent-free
conditions (Scheme 1).
Xanthenes and benzoxanthenes have been reported to
posses diverse biological and therapeutic properties such as
antibacterial,1 antiviral,2 and anti-inflammatory activities,3
as well as photodynamic therapy4 and for antagonism of
the paralyzing action of zoxazolamine.5 The other useful
applications of this heterocycles are as dyes,6 fluorescent
materials for visualization of biomolecules,7 and in laser
technologies.8 Many procedures have been developed for the
synthesis of xanthenes and benzoxanthenes, which include
trapping of benzynes by phenols,9 cyclocondensation
between 2-hydroxyaromatic aldehydes and 2-tetralone,10
cyclodehydrations,11 and intramolecular phenyl carbonyl
reaction of aldehydes with 5,5-dimethylcyclohexane-
1,3-dione12 or β-naphthol.13 Furthermore, the synthesis
of benzoxanthenes and their related products include
the reaction of β-naphthol with formamide,14 carbon
monoxide,15 2-naphthol-1-methanol,16 aldehydes and cyclic
1,3-dicarbonyl compounds.17
Results and Discussion
Initially, to optimize the amount of catalyst and
the reaction temperature, the reaction of β-naphthol,
benzaldehyde and 2-hydroxy-1,4-naphthoquinone was
studied under solvent-free conditions in the presence of
HClO4-SiO2 at different temperatures. The results were
summarized in Table 1, and showed that the reaction using
5 mol % HClO4-SiO2 at 110 °Cproceeded in highest yield.
Based on the optimized reaction conditions, several
syntheses of 14-aryl-14H-dibenzo[a,i]xanthene-
8,13-diones from the condensation of β-naphthol,
2-hydroxynaphthalene-1,4-dione, and a wide range of
aromatic aldehydes utilizing HClO4-SiO2 under solvent-free
In recent years, the use of heterogeneous catalysts
has received considerable interest in various disciplines
including organic synthesis. They are advantageous over
*e-mail: wliq870@163.com

942
Silica Supported Perchloric Acid
J. Braz. Chem. Soc.
O
R
O
O
HO
OH
HClO4-SiO2
neat, 110 oC
+
RCHO
+
O
O
1
2
3
4
Scheme 1.
Table 2. Preparation of 14-aryl-14H-dibenzo[a,i]xanthene-8,13-diones
conditions at 110 °C were examined. All reactions were
complete with in 1-2 h, as indicated in Table 2; in all cases
the reactions afforded the desired products in excellent
yields. When this reaction was carried out with aliphatic
aldehyde such as butanal or pentanal, TLC and 1H NMR
spectra of the reaction mixture showed a combination of
starting materials and numerous products, the yield of the
expected product was very poor.
catalyzed by HClO4-SiO2a
Entry
R
time / h
Product
4a
Yield / %b
1
2
3
4
5
6
7
8
9
C6H5
1
1
92
94
89
90
89
88
87
92
88
4-Cl-C6H4
4-MeO-C6H4
4-Me-C6H4
4-NO2-C6H4
3-NO2-C6H4
2,4-Cl2-C6H3
3,4-Cl2-C6H3
2-Cl-C6H4
4b
1
4c
1
4d
1.5
2
4e
Table 1. Amounts of catalyst and temperature optimization for the
synthesis of 14-phenyl-14H-dibenzo[a,i]xanthene-8,13-dionea
4f
1.5
1.5
2
4g
4h
Entry
1
HClO4-SiO2 / mol % Temp. / °C time / h Yield / %b
4i
5
5
5
5
0
1
2
3
4
5
6
7
5
5
50
3
2
49
64
72
82
0
aReaction conditions: β-naphthol (1 mmol); aldehyde (1 mmol);
2-hydroxynaphthalene-1,4-dione (1 mmol); HClO4-SiO2 (0.05 mmol);
110°C; neat. bIsolated yield.
2
80
3
90
1.5
1
4
100
110
110
110
110
110
110
110
110
120
130
Table 3. Effect of reusability of HClO4-SiO2 catalyst on 14-phenyl-14H-
dibenzo[a,i]xanthene-8,13-dione synthesisa
5
5
6
2
52
61
74
82
92
92
91
90
91
Yield / %b
7
2
Run
1
Cycle
8
1.5
1
0
1
2
3
92
91
89
88
9
2
10
11
12
13
14
1
3
1
4
aReaction conditions: β-naphthol (1 mmol); benzaldehyde (1 mmol);
2-hydroxynaphthalene-1,4-dione (1 mmol); HClO4-SiO2 (0.05 mmol);
110°C; neat. bIsolated yield.
1
1
0.5
aReaction conditions: β-naphthol (1 mmol); benzaldehyde (1 mmol);
that the reaction proceeded via a reaction sequence of
condensation, addition, cyclization and dehydration. First,
the condensation of aldehyde (2) and β-naphthol (1) gave
the intermediate ortho-quinone methide (5). The addition
of 2-hydroxynaphthalene-1,4-dione (3) to (5) leading to
the formation of (6), which on intermolecular cyclization
gave rise to (7). In the last step, the intermediate product (7)
undergoes dehydration to afford the desired product (4). In
β-naphthol the electron density at the benzylic C-1 position
(whichisinconjugationwiththearomaticring)ishigherthan
that at the C-3 position. Thus the regioselective formation of
the ortho-quinone methide from this compound involving
the C-1 and C-2 positions is favored. In simple phenolic
compounds and a-naphthol (which are weaker nucleophiles
2-hydroxynaphthalene-1,4-dione (1 mmol); neat. bIsolated yield.
The reusability of the catalyst was checked by
separating HClO4-SiO2 from the reaction mixture by simple
filtration, washing with CHCl3, and drying in a vaccum oven
at 60 °C for 10 h prior to reuse in subsequent reactions. The
recovered catalyst can be reused at least three additional
times in subsequent reactions without significant loss in
product yield (Table 3).
Although the detailed mechanism of the above reaction
remains to be fully clarified, the formation of 14-aryl-14H-
dibenzo[a,i]xanthene-8,13-diones could be explained by
a reaction sequence presented in Scheme 2. We proposed

Vol. 21, No. 5, 2010
Wu et al.
943
compared to β-naphthol) the electron density at the ortho
position of the hydroxyl group is not sufficient for the
reaction of these compounds with the aldehydes leading to
the formation of the corresponding ortho-quinone methides.
Preparation of HClO4-SiO2 catalyst
HClO4 (1.8 g, 12.5 mmol, as 70% aqueous solution)
was added to a suspension of SiO2 (230-400 mesh, 23.7 g)
in Et2O (70.0 mL). The mixture was concentrated and the
residue was heated at 100 °C for 72 h under vacuum to
furnish HClO4-SiO2 (0.5 mmol g−1) as a free flowing powder
(50 mg = 0.025 mmol of HClO4).
Conclusions
In conclusion, we have developed a simple and efficient
protocol for the synthesis of 14-aryl-14H-dibenzo[a,i]
xanthene-8,13-diones using HClO4-SiO2 under solvent-
free conditions. Short reaction times, simple work-up in
isolation of the products in high yields with high purity,
mild reaction conditions and recyclability of supported
catalyst are features of this procedure.
General procedure for the preparation of 14-aryl-14H-
dibenzo[a,i]xanthene-8,13-diones
A mixture of β-naphthol (1 mmol), aldehyde (1 mmol),
2-hydroxynaphthalene-1,4-dione (1 mmol) and HClO4-SiO2
(100 mg, 0.05 mmol) was heated at 110 °C for an
appropriate time and monitored by TLC until the final
conversion.After cooling, the reaction mixture was washed
with CHCl3 and filtered to recover the catalyst. Solvent
was evaporated and the crude product puried by silica gel
column chromatography using CHCl3 as eluent to afford
the pure product.
Experimental
NMR spectra were determined on Bruker AV-400
spectrometer at room temperature using TMS as internal
standard. Chemical shifts (d) are given in ppm and coupling
constants (J) in Hz. Mass spectra were recorded on a
Finnigan LCQ Advantage mass spectrometer. Elemental
analysis were performed by a Vario-III elemental analyzer.
Melting points were determined on a XT-4 binocular
microscope and were uncorrected. Commercially available
reagents were used throughout without further purification
unless otherwise stated.
14-Phenyl-14H-dibenzo[a,i]xanthene-8,13-dione
(4a): Yellow powder, mp 319-320 °C; H NMR (CDCl3,
400 MHz) d 8.17 (d, 1H, J 7.6 Hz), 8.12 (d, 1H, J 7.6 Hz),
7.99 (d, 1H, J 8.4 Hz), 7.91-7.77 (m, 3H), 7.61-7.41 (m,
6H), 7.20 (t, 2H, J 8.0 Hz), 7.12-7.09 (m, 1H), 5.95 (s, 1H);
1
R
OH
OH
R
OH
O
RCHO
H
-H2O
5
1
O
HO
3
O
O
O
O
-H2O
-H
H
R
O
O
R
R
O
OH2
OH
O
O
OH
4
7
6
Scheme 2.

944
Silica Supported Perchloric Acid
J. Braz. Chem. Soc.
13C NMR (CDCl3, 100 MHz) d 178.3, 157.2, 147.3, 143.1,
135.1, 131.9, 131.2, 131.0, 130.9, 130.0, 129.5, 129.4,
128.6, 127.5, 126.8, 125.5, 124.5, 123.8, 116.9, 116.8,
116.6, 35.2; MS (ESI): m/z 389 [M+H]+; Anal. Calc. for
C27H16O3:C, 83.49; H, 4.15. Found: C, 83.25; H, 4.12%.
14-(3- Nitrophenyl)-14H-dibenzo[a,i]xanthene-
8,13-dione (4f): Yellow powder, mp 304-305 °C;
1H NMR (CDCl3, 400 MHz) d 8.22 (d, 1H, J 8.0 Hz),
8.15 (d, 1H, J 8.0 Hz), 8.12 (s, 1H), 8.00-7.82 (m, 6H),
7.66-7.61 (m, 2H), 7.52-7.41 (m, 3H), 6.06 (s, 1H);
13C NMR (CDCl3, 100 MHz) d 178.1, 178.0, 157.7,
148.6, 147.3, 145.1, 135.3, 135.1, 132.0, 131.7, 130.6,
130.4, 130.1, 129.6, 129.4, 128.9, 127.8, 125.9, 124.9,
123.3, 122.1, 117.0, 115.3, 115.2, 35.2; MS (ESI):
m/z 434 [M+H]+; Anal. Calc. for C27H15NO5: C, 74.82;
H, 3.49; N, 3.23. Found: C, 74.76; H, 3.56; N, 3.25%.
14-(4-Chlorophenyl)-14H-dibenzo[a,i]xanthene-8,13-
1
dione (4b): Yellow powder, mp 305-306 °C; H NMR
(CDCl3, 400 MHz) d 8.16 (d, 1H, J 7.6 Hz), 8.13 (d, 1H,
J 7.6 Hz), 7.92-7.77 (m, 4H), 7.62-7.44 (m, 4H), 7.34 (d,
2H, J 8.4 Hz), 7.15 (d, 2H, J 8.4 Hz), 5.90 (s, 1H); 13C NMR
(CDCl3, 100 MHz) d 178.2, 157.3, 147.2, 141.6, 135.2,
132.7, 131.9, 131.4, 130.8, 130.7, 130.0, 120.0, 129.8,
129.5, 128.7, 127.6, 125.7, 124.6, 123.6, 116.8, 116.3,
116.0, 34.6; MS (ESI): m/z 423 [M+H]+; Anal. Calc. for
C27H15ClO3: C, 76.69; H, 3.58. Found: C, 76.48; H, 3.62%.
14-(2,4-Dichlorophenyl)-14H-dibenzo[a,i]xanthene-
8,13-dione (4g): Yellow powder, mp 301-302 °C;
1H NMR (CDCl3, 400 MHz) d 8.20 (d, 1H, J 8.4 Hz),
8.16-8.11 (m, 2H), 7.89-7.80 (m, 3H), 7.65-7.45 (m,
4H), 7.31-7.27 (m, 2H), 7.07-7.05 (m, 1H), 6.14 (s,
1H); 13C NMR (CDCl3, 100 MHz) d 178.1, 157.6,
147.1, 139.2, 135.2, 134.0, 133.1, 132.6, 131.8, 131.5,
131.1, 130.6, 130.1, 130.0, 129.8, 129.5, 128.7, 127.7,
127.5, 125.7, 124.7, 123.7, 116.8, 33.2; MS (ESI): m/z
457 [M+H]+; Anal. Calc. for C27H14Cl2O3: C, 70.91;
H, 3.09. Found: C, 70.82; H, 3.11%.
14-(4-Methoxylphenyl)-14H-dibenzo[a,i]xanthene-
8,13-dione (4c):Yellow powder, mp 279-280 °C; 1H NMR
(CDCl3, 400 MHz) d 8.16 (d, 1H, J 8.0 Hz), 8.12 (d, 1H, J
7.6 Hz), 7.98 (d, 1H, J 8.4 Hz), 7.89-7.76 (m, 4H), 7.60-7.43
(m, 5H), 7.31 (d, 2H, J 8.4 Hz), 5.90 (s, 1H), 3.69 (s, 3H);
13C NMR (CDCl3, 100 MHz) d 178.4, 158.3, 157.0, 147.2,
135.5, 135.1, 131.9, 131.2, 131.0, 130.0, 129.6, 129.4,
128.5, 127.4, 125.5, 124.5, 123.8, 117.1, 116.8, 113.9, 55.1,
34.3; MS (ESI): m/z 419 [M+H]+;Anal. Calc. for C28H18O4:
C, 80.37; H, 4.34. Found: C, 80.50; H, 4.27%.
14-(3,4-Dichlorophenyl)-14H-dibenzo[a,i]xanthene-
8,13-dione (4h): Yellow powder, mp 260-261 °C;
1H NMR (CDCl3, 400 MHz) d 8.19 (d, 1H, J 7.6 Hz),
8.16 (d, 1H, J 7.6 Hz), 7.95-7.82 (m, 4H), 7.65-7.43
(m, 5H), 7.31-7.30 (m, 2H), 5.92 (s, 1H); 13C NMR
(CDCl3, 100 MHz) d 178.2, 178.0, 157.6, 147.3, 143.2,
135.2, 132.7, 132.0, 131.6, 131.1, 130.7, 130.5, 130.4,
130.1, 129.6, 128.8, 128.2, 127.8, 125.8, 124.7, 123.4,
116.8, 115.6, 115.4, 34.6; MS (ESI): m/z 457 [M+H]+;
Anal. Calc. for C27H14Cl2O3: C, 70.91; H, 3.09. Found:
C, 70.95; H, 3.02%.
14-(4-Methylphenyl)-14H-dibenzo[a,i]xanthene-
8,13-dione (4d): Yellow powder; mp 255-256 °C;
1H NMR (CDCl3, 400 MHz) d 8.16 (d, 1H, J 8.0 Hz),
8.11 (d, 1H, J 7.6 Hz), 7.99 (d, 1H, J 8.0 Hz), 7.89-7.76
(m, 3H), 7.60-7.42 (m, 4H), 7.29 (d, 2H, J 8.0 Hz), 7.00
(d, 2H, J 7.6 Hz), 5.90 (s, 1H), 2.21 (s, 3H); 13C NMR
(CDCl3, 100 MHz) d 178.3, 178.2, 157.1, 147.2, 140.3,
136.5, 135.1, 131.9, 131.2, 131.0, 130.9, 120.0, 129.4,
129.3, 129.2, 128.5, 128.4, 127.4, 125.5, 124.5, 123.8,
117.0, 116.8, 116.7, 34.7, 21.0; MS (ESI): m/z 403
[M+H]+; Anal. Calc. for C28H18O3: C, 83.57; H, 4.51.
Found: C, 83.49; H, 4.63%.
14-(2-Chlorophenyl)-14H-dibenzo[a,i]xanthene-8,13-
1
dione (4i): Yellow powder, mp 281-282 °C; H NMR
(CDCl3, 400 MHz) d 8.25-8.22 (m, 2H), 8.14 (d, 1H, J 7.2
Hz), 7.89-7.83 (m, 3H), 7.65-7.29 (m, 6H), 7.08-7.04 (m,
2H), 6.22 (s, 1H); 13C NMR (CDCl3, 100 MHz) d 178.2,
178.1, 157.4, 147.1, 135.2, 133.3, 131.8, 131.4, 131.3,
130.8, 130.2, 130.1, 129.8, 129.4, 128.6, 128.2, 127.6,
127.1, 125.6, 124.7, 124.0, 116.8, 116.7, 115.6, 33.5;
MS (ESI): m/z 423 [M+H]+; Anal. Calc. for C27H15ClO3:
C, 76.69; H, 3.58. Found: C, 76.79; H, 3.41%.
14-(4-Nitrophenyl)-14H-dibenzo[a,i]xanthene-8,13-
1
dione (4e): Yellow powder, mp 332-333 °C; H NMR
(CDCl3, 400 MHz) d 8.20 (d, 1H, J 7.6 Hz), 8.15 (d, 1H,
J 7.6 Hz), 8.06 (d, 2H, J 8.8 Hz), 7.97-7.81 (m, 4H), 7.66-
7.49 (m, 6H), 6.06 (s, 1H); 13C NMR (CDCl3, 100 MHz)
d 178.2, 178.0, 157.8, 150.0, 147.3, 146.7, 135.3, 132.0,
131.7, 130.7, 130.4, 130.3, 130.0, 129.6, 128.8, 127.9,
125.9, 124.8, 123.9, 123.3, 116.8, 115.4, 115.0, 35.3; MS
(ESI): m/z 434 [M+H]+; Anal. Calc. for C27H15NO5: C,
74.82; H, 3.49; N, 3.23. Found: C, 74.91; H, 3.38; N, 3.29%.
Supplementary Information
1H NMR, 13C NMR spectra of compounds 4a-i are
available free of charge at http://jbcs.sbq.org.br, as pdf file.

Vol. 21, No. 5, 2010
Wu et al.
945
Acknowledgment
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We are pleased to acknowledge the financial support
from Xinxiang Medical University.
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Received: October 6, 2009
Web Release Date: March 11, 2010

J. Braz. Chem. Soc., Vol. 00, No. 00, S1-S10, 2010.
Printed in Brazil - ©2010 Sociedade Brasileira de Química
0103 - 5053 $6.00+0.00
Silica Supported Perchloric Acid: An Efficient Catalyst for the Synthesis of
14-Aryl-14H-dibenzo[a,i]xanthene-8,13-diones
Li Qiang Wu,* Yan Fang Wu, Chun Guang Yang, Li Min Yang and Li Juan Yang
School of Pharmacy, Xinxiang Medical University, Xinxiang, Henan 453003, China
Figure S1a. 1H NMR of 4a (400 MHz, CDCl3).
*e-mail: wliq870@163.com

2
Silica Supported Perchloric Acid
J. Braz. Chem. Soc.
Figure S1b. 13C NMR of 4a (400 MHz, CDCl3).
Figure S2a. 1H NMR of 4b (400 MHz, CDCl3).

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Figure S2b. 13C NMR of 4b (400 MHz, CDCl3).
Figure S3a. 1H NMR of 4c (400 MHz, CDCl3).

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Silica Supported Perchloric Acid
J. Braz. Chem. Soc.
Figure S3b. 13C NMR of 4c (400 MHz, CDCl3).
Figure S4a. 1H NMR of 4d (400 MHz, CDCl3).

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Figure S4b. 13C NMR of 4d (400 MHz, CDCl3).
Figure S5a. 1H NMR of 4e (400 MHz, CDCl3).

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Silica Supported Perchloric Acid
J. Braz. Chem. Soc.
Figure S5b. 13C NMR of 4e (400 MHz, CDCl3).
Figure S6a. 1H NMR of 4f (400 MHz, CDCl3).

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Figure S6b. 13C NMR of 4f (400 MHz, CDCl3).
Figure S7a. 1H NMR of 4g (400 MHz, CDCl3).

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Silica Supported Perchloric Acid
J. Braz. Chem. Soc.
Figure S7b. 13C NMR of 4g (400 MHz, CDCl3).
Figure S8a. 1H NMR of 4h (400 MHz, CDCl3).

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Figure S8b. 13C NMR of 4h (400 MHz, CDCl3).
Figure S9a. 1H NMR of 4i (400 MHz, CDCl3).

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Silica Supported Perchloric Acid
J. Braz. Chem. Soc.
Figure S9b. 13C NMR of 4i (400 MHz, CDCl3).