Efficient, solvent-free method for the one-pot condensation of-naphthol, Aromatic aldehydes, and cyclic 1,3-dicarbonyl compounds catalyzed by silica sulfuric acid

Article abstract of DOI:10.1080/00397911.2010.520832

Silica sulfuric acid as a reusable and efficient catalyst has been used for the preparation of 12-aryl-8,9,10,12-tetrhydro benzo[a]xanthene-11-one derivatives from the one-pot multicomponent reaction of aromatic aldehydes,-naphthol, and a cyclic diketone under solvent-free conditions. Good yields, simple procedure, easy workup, short reaction times, and mild conditions are the advantages of this methodology.

Full text of DOI:10.1080/00397911.2010.520832

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Efficient, Solvent-Free Method for the
One-Pot Condensation of β-Naphthol,
Aromatic Aldehydes, and Cyclic 1,3-
Dicarbonyl Compounds Catalyzed by
Silica Sulfuric Acid
Firouzeh Nemati a , Maryam Arghan a & Ali Amoozadeh a
a Department of Chemistry, Faculty of Science, Semnan University,
Semnan, Iran
Accepted author version posted online: 27 Jun 2011. Version of
record first published: 14 Sep 2011
To cite this article: Firouzeh Nemati, Maryam Arghan & Ali Amoozadeh (2012): Efficient, Solvent-Free
Method for the One-Pot Condensation of β-Naphthol, Aromatic Aldehydes, and Cyclic 1,3-Dicarbonyl
Compounds Catalyzed by Silica Sulfuric Acid, Synthetic Communications: An International Journal for
Rapid Communication of Synthetic Organic Chemistry, 42:1, 33-39
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Synthetic Communications1, 42: 33–39, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.520832
EFFICIENT, SOLVENT-FREE METHOD FOR
THE ONE-POT CONDENSATION OF b-NAPHTHOL,
AROMATIC ALDEHYDES, AND CYCLIC
1,3-DICARBONYL COMPOUNDS CATALYZED BY SILICA
SULFURIC ACID
Firouzeh Nemati, Maryam Arghan, and Ali Amoozadeh
Department of Chemistry, Faculty of Science, Semnan University,
Semnan, Iran
GRAPHICAL ABSTRACT
Abstract Silica sulfuric acid as a reusable and efficient catalyst has been used for the prep-
aration of 12-aryl-8,9,10,12-tetrhydro benzo[a]xanthene-11-one derivatives from the one-pot
multicomponent reaction of aromatic aldehydes, b-naphthol, and a cyclic diketone under
solvent-free conditions. Good yields, simple procedure, easy workup, short reaction times,
and mild conditions are the advantages of this methodology.
Keywords Benzoxanthene; multicomponent reaction; one-pot synthesis; silica sulfuric
acid
INTRODUCTION
Xanthenes and benzoxanthenes have attracted considerable interest because of
their biological activities such as anti-inflammatory, antibacterial, and antiviral
activities.[1–3] These are being utilized as antagonists for the paralyzing action of
zoxazolamine[4] and in photodynamic therapy.[5] Furthermore, these compounds
can be used as dyes, as pH-sensitive fluorescent materials for the visualization of
biomolecular assemblies, and in laser technologies.[6,7] Thus, the synthesis of
xanthene derivatives is of great importance.
A number of methods for the synthesis of tetrahydrobenzo[a]xanthen-11-ones
have been reported. Generally they are synthesized by three-component conden-
sation of cyclic 1,3-diketones with an aldehyde and b-naphthol, which entails the
Received July 2, 2010.
Address correspondence to Firouzeh Nemati, Department of Chemistry, Faculty of Science,
Semnan University, Semnan, Iran. E-mail: fnemati_1350@yahoo.com; fnemati@semnan.ac.ir
33

34
F. NEMATI, M. ARGHAN, AND A. AMOOZADEH
use of para-toluenesulfornic acid (p-TSA) in ionic liquid,[8] perchloric acid adsorbed
on silica gel,[9] dodecatungstophosphoric acid,[10] indium(III) chloride,[11] strontium
triflate,[12] cyanuric chloride,[13] iodine,[14] and tetrabutyl ammonium fluoride.[15]
Recently, silica sulfuric acid (SSA) has drawn much interest in numerous
organic transformations[16–20] because of its environmental compatibility, greater
selectivity, experimental simplicity, ease of handling, noncorrosive nature and ease
of isolation.
RESULTS AND DISCUSSION
In continuation of our studies to develop of green methods for the synthesis of
organic compounds,[21] we report herein the results of the preparation of 12-aryl-8,9,
10,12-tetrhydro benzo[a]xanthene-11-one derivatives catalyzed by SSA under
solvent-free conditions at 100 ꢀC (Scheme 1). To the best of our knowledge, there
has been no report on the use of SSA as a catalyst in preparation of these compounds.
At first, the amount of catalyst required for the reaction of b-naphthol
(1 mmol), dimedone (1 mmol), and benzaldehyde (1 mmol) was investigated under
solvent-free condition at 100 ꢀC. The results are summarized in Table 1. As shown
from Table 1, this transformation does not take place in the absence of catalyst.
The best result was obtained when using 0.10 g (0.26 mmol) of catalyst.
As the synthesis of 12-aryl-8,9,10,12-tetrhydrobenzo[a]xanthene-11-one deriva-
tives was reported using 1.1–1.2 mmol of dimedone,[8–13] the optimum amount of
dimedone was also examined. As it can be seen from Table 2, it was possible to
achieve the reaction with less dimedone than in other studies.
Further experimentation revealed that the reaction was completed in 30 min by
heating the reaction mixture in an oil bath maintained at 100 ꢀC in solvent-free
condition. Lower yield was obtained when the reaction was carried out in different
solvents (Table 3).
To broaden the scope of this new protocol, we used several aromatic aldehydes,
including both electron-withdrawing and electron-donating groups, b-naphthol, and
cyclic 1,3-diketones in the presence of 0.1 g SSA under solvent-free conditions at
100 ꢀC. The results are summarized in Table 4.
The reaction proceeds efficiently with various kinds of aromatic aldehydes in
good to excellent yields within short reaction time (30–45 min). As indicated in
Table 4, the yield of the reaction with ortho-substituted aldehydes was less
(Table 4, entries 4 and 7). In addition, aldehydes bearing electron-donating groups
need longer reaction times as compared to aldehydes containing electron-
withdrawing groups.
Scheme 1. Synthesis of 12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one derivatives.

CLEAN SYNTHESIS OF BENZOXANTHENES
35
Table 1. Optimization of silica sulfuric acid in condensation of b-naphthol,
dimedone, and benzaldehyde in solvent-free conditions at 100 ꢀC
Entry
SSA (g)
Time (min)
Yield (%)
1
2
3
4
5
0.0
30
30
30
30
30
0.0
40
65
95
95
0.05
0.08
0.10
0.15
Table 2. Optimization of dimedone in synthesis of
12-phenyl-8,9,10,12-tetrahydrobenzo[a]xanthene-11-one
in solvent-free conditions at 100 ꢀC
Entry
Dimedone (mmol)
Yield (%)
1
2
3
1.2
1.1
1
85
95
95
Table 3. Optimization of temperature and medium of reaction in synthesis of
12-phenyl-8,9,10,12-tetrahydrobenzo[a]xanthene-11-one
Entry
Temp. (ꢀC)
Condition
Time (min)
Yield (%)
1
2
3
4
5
6
7
80
100
Neat
Neat
30
30
30
30
30
30
30
60
95
120
Neat
EtOH
95
Reflux
Reflux
Reflux
Reflux
Trace
Trace
Trace
20
H2O
CH3CN
ClCH2CH2Cl
Table 4. Synthesis of 12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one derivatives
Entry
ArCHO
R1 and R2
Time (min)
Yield (%)a
Mp (ꢀC)
1
2
PhCHO
Me
Me
30
45
45
35
30
30
40
30
30
35
30
35
30
95
80
80
75
90
95
75
90
95
85
95
80
85
149–151[14]
174–176[14]
210–211[15]
179–180[11]
167–169[9]
177–178[14]
223–225[11]
167–168[11]
185–187[13]
230–232[15]
184–186[15]
118–124
4-MeC6H4CHO
4-OMeC6H4CHO
2-ClC6H4CHO
4-ClC6H4CHO
4-NO2C6H4CHO
2-NO2C6H4CHO
3-NO2C6H4CHO
4-BrC6H4CHO
2-Naphthaldehyde
4-FC6H4CHO
PhCHO
3
Me
Me
4
5
Me
Me
6
7
Me
Me
8
9
Me
Me
10
11
12
13
Me
H, Ph
H, Ph
4-ClC6H4CHO
181–183
aIsolated yields.

36
F. NEMATI, M. ARGHAN, AND A. AMOOZADEH
Table 5. Comparison of results using silica sulfuric acid with results obtained by other workers for the
synthesis of 9,10-dihydro-9,9-dimethyl-12-phenyl-8H-benzo[a]xanthen-11(12H)-one
Entry
Catalyst
Conditions
Time (min) Yield (%) Ref.
1
2
3
4
5
6
7
8
9
p-TSAa
HClO4-SiO2
[bmim]BF4=neat
80 ꢀC=neat
180
72
90
89
86
84
85
90
99
91
95
8
9
Dodecatungsto phosphoric acid 60 ꢀC=neat
70
30
10
11
12
13
15
23
—
InCl3
Sr(OTf)2
120 ꢀC=neat
1,2-Dichloroethane=80 ꢀC
80 ꢀC=neat
H2O=reflux
300
50
TCT
TBAFb
540
300
30
NaHSO4=SiO2
Silica sulfuric acid
CH2Cl2=reflux
100 ꢀC=neat
ap-Toluenesulfonic acid.
bTetrabutyl ammonium fluoride.
As an aspect of green chemistry, the recyclability of the catalyst was tested. The
catalyst was separated from the reaction mixture, washed with ethyl acetate, and
dried at 100 ꢀC for 24 h to give recycled SSA. The reaction of 4-bromobenzaldehyde,
b-naphthol, and dimedone was repeated with recycled catalyst, and the yields were
found to remain in the range of 85% for three runs.
In Table 5 the efficiency of our method for the synthesis of 12-aryl-8,9,10,12-
tetrhydro benzo[a]xanthene-11-one is compared with some other published studies.
Each of these methods have their own advantages, but they often suffer from some
disadvantages, including expensive reagent or catalyst, use of corrosive reagent, long
reaction time, and nonrecyclable catalyst.
In conclusion, we have shown that the silica-based solid acid catalyst, which
can be easily prepared from commercially available starting materials, efficiently
catalyzes the synthesis of 12-aryl-8,9,10,12-tetrhydrobenzo[a]xanthene-11-one
derivatives through the condensation of aromatic aldehydes and b-naphthol with
1,3-dicarbonyl compounds. The low cost, recyclability, and easy preparation of this
catalyst may allow of these compounds on a large scale.
EXPERIMENTAL
Chemicals were purchased from the Fluka, Merck, and Aldrich chemical
companies. Melting points were determined on an Electrothermal 9100 instrument
and are not corrected. Thin-layer chromatography (TLC) on commercial aluminum-
backed plates of silica gel 60 F254 was used to monitor the progress of reactions. 1H
NMR and 13C NMR spectra were recorded on Bruker Avance 300-MHz spectro-
meters with 7- to 10 mM solutions in CDCl3 in the presence of tetramethylsilane
as internal standard. Infrared (IR) spectra were recorded using a Perkin-Elmer
843 spectrometer with KBr plates. Elemental analyses were performed on a
Perkin-Elmer CHN analyzer, 2400 series II.
Preparation and Recycling of Silica Sulfuric Acid
SSA was prepared according to the Zolfigol procedure.[22] The catalyst was
separated from the reaction mixture, washed with ethyl acetate, and dried at 100 ꢀC

CLEAN SYNTHESIS OF BENZOXANTHENES
37
for 24 h to give recycled SSA. The reaction of 4-bromobenzaldehyde, b-naphthol, and
dimedone was repeated with recycled catalyst, and the yields were found to remain in
the range of 85% for three runs.
General Procedure for the Synthesis of 12-Aryl-8,9,10,12-
tetrahydrobenzo[a]xanthen-11-one Derivatives
Aldehyde (1.0 mmol), b-naphthol (1.0 mmol), 5,5-dimethyl-1,3-cyclohexane
dione or 5-phenyl-1,3-cyclohexane dione (1.0 mmol), and SSA (0.1 g, 0.26 mmol)
were taken in a 10-ml round-bottomed flask. The mixture was stirred at 100 ꢀC
for an appropriate time as mentioned in Table 4. After completion of the reaction
as monitored by TLC, the mixture was quenched with water (ꢁ10 mL) and filtered
off. The solid was washed with ethyl acetate (10 mL) and filtered to recover the
catalyst. The solvent was evaporated, and the crude product was recrystallized from
EtOH.
The known compounds were identified by comparison of melting points with
literature reports.
1
Spectral (IR, H NMR, and 13C NMR) and Analytical Data of New
Compounds
9,10-Dihydro-9,12-diphenyl-8H-benzo[a]xanthen-11(12H)-one (Table 4,
Entry 12). Mp 118–124 ꢀC; IR (KBr): n max=cmꢂ1: 1700, 1400, 1200, 700. 1H
NMR (300 MHz, CDCl3, Me4Si) as a mixture of diastereomers: d 7.40–7.17 (m,
32H), 4.91 (s, 1H), 4.92 (s, 1H), 3.49 (quintet, J ¼ 5.57 Hz, 1H), 3.34 (quintet,
J ¼ 4.95, 1H), 3.00–2.81 (m, 4H), 2.74–2.53 (m, 4H); 13C NMR (75 MHz, CDCl3)
as a mixture of diastereomers: d 31.77, 31.94, 34.62, 34.75, 38.22, 38.76, 43.70,
44.02, 195.65, 195.51, 163.36, 163.21, 162.54, 162.43, 143.81, 142.10, 142.01,
128.88, 128.80, 128.72, 128.59, 128.51, 128.39, 128.30, 128.14, 127.99, 127.25,
127.16, 127.02, 126.72, 126.63, 126.57. Anal. calc. for C29H22O2: C, 86.56; H, 5.47.
Found: C, 86.00; H, 6.01.
12-(4-Chlorophenyl)-9,10-dihydro-9-phenyl-8H-benzo[a]xanthen-11-
(12H)-one (Table 4, Entry 13). Mp 181–183 ꢀC, IR (KBr): n max=cmꢂ1: 1700,
1550, 1450, 1300. 1H NMR (300 MHz, CDCl3, Me4Si) as a mixture of diastereomers:
d 7.93–7.77 (m, 6H), 7.45–7.12 (m, 24 H), 5.78 (s, 1H), 5.76 (s, 1H), 3.52–3.49 (m,
1H), 3.35–3.33 (m, 1H), 3.00–2.81 (m, 4H), 2.79–2.54 (m, 4H); 13C NMR
(75 MHz, CDCl3) as a mixture of diastereomers: d 34.24, 34.34, 35.12, 35.26,
38.29, 38.93, 43.98, 43.76, 114.91, 116.98, 123.51, 126.62, 126.70, 127.05, 127.17,
127.19, 128.35, 128.52, 128.54, 128.73, 128.87, 128.93, 129.20, 129.88, 129.95,
141.86, 142.32, 142.91, 147.70, 162.71, 163.52, 164.11, 165.09, 195.56, 196.06. Anal.
calc. for C29H21ClO2: C, 79.72; H, 4.81; Found: C, 78.43; H, 4.79.
ACKNOWLEDGMENT
We thank the Department of Chemistry and Office of Gifted Students at
Semnan University for financial support.

38
F. NEMATI, M. ARGHAN, AND A. AMOOZADEH
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