Synthesis of 12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one catalyzed by silica sulfuric acid under solvent free condition

Article abstract of DOI:10.2174/157017812800221816

An efficient synthesis of 12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11- one derivatives via the threecomponent condensation of aromatic aldehyde, 2-naphthol and 5,5-dimethyl-1,3-cyclohexanedione was carried out in 72-85% yields at 80 °C under solvent fr

Full text of DOI:10.2174/157017812800221816

Letters in Organic Chemistry, 2012, 9, 145-149
145
Synthesis of 12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one Cataly-
zed by Silica Sulfuric Acid Under Solvent Free Condition
Ya-Li Song*,a, Zhi-Ping Linc, Guo-Feng Chenb, Quan-Lin Liub and Ji-Tai Li*,b
aKey Laboratory for Pharmaceutical Quality Control of Hebei Province, Key Laboratory of Medical Chemistry and
Molecular Diagnosis, Ministry of Education, College of Pharmaceutical Sciences, Hebei University, Baoding, 071002,
P. R. China
bKey Laboratory of Analytical Science and Technology of Hebei Province, College of Chemistry and Environmental
Science, Hebei University, Baoding 071002, P. R. China
cDepartment of Biology and Chemistry, Baoding University, Baoding 071002, P. R. China
Received August 23, 2011: Revised September 20, 2011: Accepted December 07, 2011
Abstract: An efficient synthesis of 12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one derivatives via the three-
component condensation of aromatic aldehyde, 2-naphthol and 5,5-dimethyl-1,3-cyclohexanedione was carried out in 72-
85% yields at 80 oC under solvent free condition using silica sulfuric acid (SSA) as catalyst.
Keywords: Silica sulfuric acid, three-component condensation, xanthene.
INTRODUCTION
Xanthenes and
easy production, insolubility in all organic solvent, reusable,
cheap and facile, SSA has been used as catalyst in some
organic reactions [22].
benzoxanthenes
are
important
biologically active heterocyclic compounds, which possess
antiviral [1], antibacterial [2] and anti-inflammatory
activities [3]. These compounds can be used as dyes [4, 5],
pH-sensitive fluorescent materials [6] and in laser
technology [7]. Synthesis of these compounds via three-
component condensation of aldehyde, 2-naphthol and cyclic
1,3-dicarbonyl compounds was carried out under different
conditions, such as solvent-free reaction catalyzed by
HBF4/SiO2 [8], I2 [9], p-TSA [10, 11], InCl3 or P2O5 [12],
Zr(HSO4)4 [13], H3PW12O40 [14], cyanuric chloride [15],
HClO4-SiO2 [16], CAN [17], and refluxing in 1,2-
dichloroethane catalyzed by Sr(OTf)2 [18] or NaHSO4·SiO2
[19]. However, in spite of their potential utility, some of the
reported methods suffer from some draw-backs, such as
longer reaction time, use of expensive transition metal
catalyst or hazardous solvent. Hence, the development of
new and simple synthetic methods for the preparation of
heterocyclic compounds containing xanthone fragment
remains an interesting challenge.
In continuation of our investigation on application of
SSA in organic synthesis [23, 24], we wish to report the one-
pot synthesis of 12-aryl-8,9,10,12-tetrahydrobenzo[a]
xanthen-11-one catalyzed by SSA under solvent free
condition (Scheme 1).
RESULTS AND DISCUSSION
To optimize the reaction conditions, the condensation of
benzaldehyde, 2-naphthol and 5,5-dimethyl-1,3-cyclo-
hexanedione was selected as the model under solvent free
condition catalyzed by SSA. A series of experiments at
varying temperature were carried out. As shown in Table 1,
when the reaction was carried out at 70 oC, it took 30 min to
obtain compound 4 in 80% yield (Entry 1), while when the
o
o
temperature was 80 C and 100 C, the reaction time was
shortened to 20 min and the yield was 81% (Entry 2) and
83% (Entry 3) respectively. It indicates that reaction
temperature had a little effect on the reaction.
Catalysts supported on inorganic substrates have received
increasing attention in recent years as a means to develop
more convenient or selective catalysts [20]. SSA is a good
proton source and an excellent candidate for sulfuric acid or
chlorosulfonic acid replacement in organic reactions without
any limitation such as destruction of acid sensitive functional
groups, use of rather toxic solvents and expensive reagents
or solvents [21]. Because of its advantages such as stable,
The effect of amount of SSA on the reaction was
studied. When the amount of SSA was 5 mol% and 10
mol%, the yield of 4i was 75% (Entry 4) and 81% (Entry 2)
respectively. While increasing the amount of silica sulfuric
acid to 15 mol% (Entry 5), no improvement was observed on
both the yield and the reaction time compared with that at 10
mol% (Entry 2).
The effect of molar ratio of reactants on reaction was
investigated. As shown in Table 1, when molar ratio of
*Address correspondence to these authors at the College of Pharmaceutical
Sciences, Hebei University, Wusi East Road No. 180, Baoding 071002, P.
R. China; Fax: +86-312-5096136; E-mail: yalisong@yahoo.com.cn
College of Chemistry and Environmental Science, Hebei University, Wusi
East Road No. 180, Baoding 071002, P. R. China; Fax: +86-312-5079628;
E-mail: lijitai@hbu.cn
benzaldehyde,
2-naphthol
and
5,5-dimethyl-1,3-
cyclohexanedione was 1:1:1, 1:1:1.2 and 1.2:1:1.2
respectively, the best yield of 9,9-dimethyl-12-phenyl-
8,9,10,12-tetrahydrobenzo[a]xanthen-11-one was achieved
1875-6255/12 $58.00+.00
© 2012 Bentham Science Publishers

146 Letters in Organic Chemistry, 2012, Vol. 9, No. 2
Song et al.
CHO
O
O
OH
SSA, solvent free
80 oC
O
O
R
R
3
4a-i
1a-i
2
Scheme 1. Synthesis of 12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one
Table 1． The Effect of Reaction Conditions on the Synthesis of 9,9-dimethyl-12-phenyl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-
one
Entry
Amount of SSA/mol%
Molar ratio of 1: 2: 3
Temperature/oC
Reaction time/min.
Isolated yield/%
1
2
3
4
5
10
10
10
5
1:1:1
1:1:1
1:1:1
1:1:1
1:1:1
70
80
30
20
20
20
20
80
81
83
75
81
100
80
15
80
6
7
10
10
1:1:1.2
80
80
20
40
81
86
1.2:1:1.2
(86%, Table 1, Entry 7) but with molar ratio of 1.2:1:1.2, the
reaction time increased to 40 min. Considering the amount of
benzaldehyde and 5,5-dimethyl-1,3-cyclohexanedione both
were increased by 20% while the yield was only increased by
5%, so the molar ratio of benzaldehyde, 2-naphthol and 5,5-
dimethyl-1,3-cyclohexanedione was chosen to 1:1:1.
From these results listed in Table 2, we can deduce that
the yields are in general, similar or a little lower than those
described in literatures [8-19, 25-26], but the reaction time
was greatly decreased. For example, in the previous report
[18], the condensation of 4-chlorobenzaldehyde, 2-naphthol
and 5,5-dimethyl-1,3-cyclohexanedione catalyzed by
Sr(OTf)2 at refluxing temperature in ClCH2CH2Cl for 5 h,
the yield of 4e was 85%; in the reaction catalyzed by
NaHSO4·SiO2 [19], the condensation of benzaldehyde, 2-
naphthol and 5,5-dimethyl-1,3-cyclohexanedione was carried
out in 87% yield under refluxing 1,2-dichloroethane for 4 h,
while present procedure needed only 20 min to afford target
product in 81% yield (Table 2, 4i).
From the results given in Table 1, the reaction conditions
we chose were as follows: aromatic aldehyde (1, 1 mmol), 2-
naphthol (2, 1 mmol), 5,5-dimethyl-1,3-cyclohexanedione
(3, 1 mmol), SSA (0.1 mmol), reaction temperature 80 oC.
Using this reaction system, a series of experiments for the
synthesis of 4a-i were carried out. The results were
summarized in Table 2. As shown in Table 2, all reactions
can be finished in 30 min except 4-hydroxybenzaldehyde (65
min) to give the products in 72-85% yields. In the present
procedure, aromatic aldehydes with electron-donating
substituents or electron-withdrawing substituents have a
little effect on the yield.
The recycling performance of catalyst in the same model
condensation reaction was also investigated. After
completion of the reaction, the reaction mixture was
dissolved in dicholoromethane to precipitate the catalyst.
The organic layer was separated and the catalyst was used
Table 2． Synthesis of 4a-i catalyzed by SSA at 80 oC Under Solvent Free
Entry
R
Reaction time/min
Product
Isolated yield/%
m. p. /oC (Ref.)
a
b
c
d
e
f
3-NO2
4-NO2
2-Cl
20
20
20
30
20
30
30
65
20
4a
4b
4c
4d
4e
4f
78
168-169 (168–170) [25]
179-180 (178-180) [24]
178-179 (179-180) [24]
180-181 (180-181) [26]
183-184 (182-183) [27]
180-181 (176-177) [28]
209-210 (208-209) [29]
212-213 (213-214) [27]
152-153 (152-153) [27]
81
82
3-Cl
85
4-Cl
80
4-CH3
4-OCH3
4-OH
H
72
g
h
ia
4g
4h
4i
73
74
81, 75, 72, 72
aCatalyst was reused three times.

Synthesis of 12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one
Letters in Organic Chemistry, 2012, Vol. 9, No. 2
147
r.t.
SiO2
SiO2
OH
OSO3H
HCl
ClSO3H
Scheme 2. Preparation of silica sulfuric acid.
directly for next run after removing the residual solvent. The
catalyst at least can be reused three times without significant
decrease in activity. Yields remained practically constant
(72-75%, Table 2, 4i) over three catalyst cycling
experiments.
9,9-Dimethyl-12-(3-nitrophenyl)-8,9,10,12-tetrahydrobenzo
[a]xanthen-11-one (4a)
1
White solid, HNMR: ꢀH 0.95 (s, 3H, CH3), 1.13 (s, 3H,
CH3), 2.24 (d, J = 16.3 Hz, 1H, CH2), 2.33 (d, J = 16.3 Hz,
1H, CH2), 2.61 (s, 2H, CH2), 5.82 (s, 1H, CH), 7.35-7.46 (m,
4H, Ph-H), 7.79-7.82 (m, 3H, Ph-H), 7.86 (d, J = 8.2 Hz, 1H,
Ph-H), 7.92-7.94 (m, 1H, Ph-H), 8.11 (s, 1H, Ph-H).
In conclusion, the SSA can catalyze three-component
one-pot synthesis of 12-aryl-8,9,10,12-tetrahydrobenzo
[a]xanthen-11-one via the condensation of aromatic
aldehyde, 2-naphthol and 5,5-dimethyl-1,3-cyclohexane-
dione under solvent free condition to offer a moderate yield.
9,9-Dimethyl-12-(4-nitrophenyl)-8,9,10,12-tetrahydrobenzo
[a]xanthen-11-one (4b)
White solid, 1H NMR: ꢀH 0.94 (s, 3H, CH3), 1.13 (s, 3H,
CH3), 2.24 (d, J = 16.3 Hz, 1H, CH2), 2.32 (d, J = 16.3 Hz,
1H, CH2), 2.57 (d, J = 17.6 Hz, 1H, CH2), 2.61 (d, J = 17.6
Hz, 1H, CH2), 5.81 (s, 1H, CH), 7.35 (d, J = 8.9 Hz, 1H, Ph-
H), 7.38-7.41 (m, 1H, Ph-H), 7.42-7.45 (m, 1H, Ph-H), 7.50-
7.52 (m, 2H, Ph-H), 7.79-7.83 (m, 3H, Ph-H), 8.02-8.04 (m,
2H, Ph-H).
EXPERIMENTAL
Melting points were determined with a SGW X-4
microscopic melting point apparatus (Shanghai Precision &
Scientific Instrument Co., Ltd, P. R. China) in open
1
capillaries and are uncorrected. The H NMR spectra were
recorded on Bruker AVANCE III 600 (600 MHz)
spectrometer using TMS as internal standard and CDCl3 as
solvent.
12-(2-Chlorophenyl)-9,9-dimethyl-8,9,10,12-tetrahydro-
benzo[a]xanthen-11-one (4c)
White solid, 1H NMR: ꢀH 1.00 (s, 3H, CH3), 1.14 (s, 3H,
CH3), 2.26 (d, J = 16.3 Hz, 1H, CH2), 2.31 (d, J = 16.3 Hz,
1H, CH2), 2.59 (d, J = 17.4 Hz, 1H, CH2), 2.62 (d, J = 17.4
Hz, 1H, CH2), 5.99 (s, 1H, CH), 6.97-7.00 (m, 1H, Ph-H),
7.05 (t, J = 7.1 Hz, 1H, Ph-H), 7.26-7.30 (m, 3H, Ph-H), 7.38
(t, J = 7.2 Hz, 1H, Ph-H), 7.48 (t, J = 7.1 Hz, 1H, Ph-H),
7.75 (t, J = 9.1 Hz, 2H, Ph-H), 8.22 (d, J = 8.5 Hz, 1H, Ph-
H).
SSA was prepared according to the method reported in
literature [30].
A 500 mL suction flask was used. It was equipped with a
constant-pressure dropping funnel containing chlorosulfonic
acid (23.3 g, 0.2 mol) and gas inlet tube for conducting HCl
gas over an adsorbing solution i.e. water. Into it were
charged 60.0 g of silica gel. Cholorosulfonic acid was added
dropwise over a period of 30 min at room temperature. HCl
gas evolved from the reaction vessel immediately (Scheme
2). After the addition was complete the mixture was shaken
for 30 min. A white solid (silica sulfuric acid) of 76.0 g was
obtained.
12-(3-Chlorophenyl)-9,9-dimethyl-8,9,10,12-tetrahydro-
benzo[a]xanthen-11-one (4d)
White solid, 1H NMR: ꢀH 0.98 (s, 3H, CH3), 1.12 (s, 3H,
CH3), 2.26 (d, J = 16.3 Hz, 1H, CH2), 2.31 (d, J = 16.3 Hz,
1H, CH2), 2.56 (d, J =17.4 Hz, 1H, CH2 ), 2.59 (d, J = 17.6
Hz, 1H, CH2), 5.69 (s, 1H, CH), 7.02-7.04 (m, 1H, Ph-H),
7.11 (t, J = 7.9 Hz, 1H, Ph-H), 7.25-7.29 (m, 2H, Ph-H), 7.33
(d, J = 8.9Hz, 1H, Ph-H), 7.38-7.40 (m, 1H, Ph-H), 7.44-
7.46 (m, 1H, Ph-H), 7.79 (t, J = 7.7 Hz, 2H, Ph-H), 7.92 (d, J
= 8.5 Hz, 1H, Ph-H).
General Procedure for the Synthesis of title Compound
4a-i
A 5 mL flask was charged with aromatic aldehydes (1, 1
mmol), 2-naphthol (2,
1
mmol), 5,5-dimethyl-1,3-
cyclohexanedione (3, 1 mmol) and silica sulfuric acid (0.1
12-(4-Chlorophenyl)-9,9-dimethyl-8,9,10,12-tetrahydro-
benzo[a]xanthen-11-one (4e)
o
mmol). The reaction mixture was stirred at 80 C for the
period of time as indicated in Table 2. The reaction was
monitored by TLC. After completion of the reaction, the
reaction mixture was diluted with dicholoromethane to
precipitate the catalyst, which was used directly for next run
after removing the residual solvent. The organic layer was
separated and dried over anhydrous sodium sulfate, filtered
and evaporated to dryness in vacuo to give the crude
product, which was separated by column chromatography on
silica gel (200-300 mesh), eluted with petroleum ether (bp
White solid, 1H NMR: ꢀH 0.96 (s, 3H, CH3), 1.11 (s, 3H,
CH3), 2.24 (d, J = 16.3 Hz, 1H, CH2), 2.30 (d, J = 16.3 Hz,
1H, CH2), 2.56 (s, 2H, CH2), 5.68 (s, 1H, CH), 7.12-7.14 (m,
2H, Ph-H), 7.26-7.28 (m, 2H, Ph-H), 7.31 (d, J = 8.9 Hz, 1H,
Ph-H), 7.37-7.39 (m, 1H, Ph-H), 7.42-7.44 (m, 1H, Ph-H),
7.77 (t, J = 8.6 Hz, 2H, Ph-H), 7.90 (d, J = 8.5 Hz, 1H, Ph-
H).
9,9-Dimethyl-12-(4-methylphenyl)-8,9,10,12-tetrahydro-
benzo[a]xanthen-11-one (4f)
White solid, 1H NMR: ꢀH 0.97 (s, 3H, CH3), 1.11 (s, 3H,
CH3), 2.19 (s, 3H, CH3), 2.24 (d, J = 16.2 Hz, 1H, CH2), 2.30
(d, J = 16.2 Hz, 1H, CH2), 2.56 (s, 2H, CH2), 5.66 (s, 1H,
CH), 6.96 (d, J = 7.9 Hz, 2H, Ph-H), 7.21-7.22 (m, 2H, Ph-
o
60-90 C) or a mixture of petroleum ether and ethyl acetate
to offer product 4a-i. These products were known
1
compounds, which was established by H NMR and their
melting point compared with that reported in the literatures.

148 Letters in Organic Chemistry, 2012, Vol. 9, No. 2
Song et al.
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7.41-7.44 (m, 1H, Ph-H), 7.74 (d, J = 8.9 Hz, 1H, Ph-H),
7.76 (d, J = 7.9 Hz, 1H, Ph-H), 8.0 (d, J = 8.5 Hz, 1H, Ph-
H).
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White solid, 1H NMR: ꢀH 0.97 (s, 3H, CH3), 1.11 (s, 3H,
CH3), 2.24 (d, J = 16.3 Hz, 1H, CH2), 2.30 (d, J = 16.3 Hz,
1H, CH2), 2.55 (s, 2H, CH2), 3.68 (s, 3H, CH3), 5.65 (s, 1H,
CH), 6.69-6.71 (m, 2H, Ph-H), 7.23-7.25 (m, 2H, Ph-H),
7.30 (d, J = 8.9 Hz, 1H, Ph-H), 7.35-7.37 (m, 1H, Ph-H),
7.41-7.44 (m, 1H, Ph-H), 7.74 (d, J = 8.9 Hz, 1H, Ph-H),
7.76 (d, J = 7.9 Hz, 1H, Ph-H), 7.98 (d, J = 8.5 Hz, 1H, Ph-
H).
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CH3), 2.26 (d, J = 16.3 Hz, 1H, CH2), 2.31 (d, J = 16.3 Hz,
1H, CH2), 2.56 (s, 2H, CH2), 5.63 (s, 1H, CH), 6.14 (s, 1H,
OH), 6.59 (d, J = 8.6 Hz, 2H, Ph-H), 7.15-7.43 (m, 5H, Ph-
H), 7.74 (d, J = 8.9 Hz, 1H, Ph-H), 7.77 (d, J = 7.9 Hz, 1H,
Ph-H), 7.97 (d, J = 8.4 Hz, 1H, Ph-H).
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CH3), 2.24 (d, J = 16.3 Hz, 1H, CH2), 2.30 (d, J = 16.3 Hz,
1H, CH2), 2.56 (s, 2H, CH2), 5.70 (s, 1H, CH), 7.03-7.06 (m,
1H, Ph-H), 7.15-7.17 (m, 2H, Ph-H), 7.31-7.34 (m, 4H, Ph-
H), 7.40-7.43 (m, 1H, Ph-H), 7.76 (t, J = 9.2 Hz, 2H, Ph-H),
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ACKNOWLEDGEMENTS
We gratefully acknowledge of Hebei University Natural
Science Foundation (2010-194), the Reasearch Project of
Science Technology Ministry of Hebei Province (11276434)
and Natural Science Foundation of Hebei Province
(B2011201072) for financial assistance.
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[20]
[21]
[22]
CONFLICT OF INTEREST
Declared none.
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