Cucurbit[6]uril-OSO3H: A novel acidic nanocatalyst for the one-pot preparation of 14-aryl-14H-dibenzo[a,j]xanthenes and 1,8-dioxo-octahydro-xanthenes

Article abstract of DOI:10.1039/c6ra02255c

Cucurbit[6]uril-OSO₃H (CB[6]-OSO₃H) has been prepared and used as an efficient acidic nanocatalyst for the one-pot preparation of 14-aryl-14H-dibenzo[a,j]xanthenes and 1,8-dioxo-octahydro-xanthenes. The nanocatalyst was characterized

Full text of DOI:10.1039/c6ra02255c

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Cucurbit[6]uril-OSO H: A Novel Acidic Nanocatalyst for the one-pot
3
preparation of 14-aryl-14H-dibenzo[a,j]xanthenes and 1,8-dioxo-
octahydro-xanthenes
,
1
2
1
Seyyed Jafar Saghanezhad* , Yaser Nazari , and Fereshteh Davod
1
ACECRꢀProduction Technology Research Institute, Ahvaz, Iran
2
Kimia Kankash Jondishapur Research Co., Ahvaz, Iran
*
Corresponding Author Tel: (+98) 61ꢀ33364400, Email: jafar_saghanezhad@yahoo.com
Abstract: Cucurbit[6]urilꢀOSO
acidic nanocatalyst for the oneꢀpot preparation of 14ꢀarylꢀ14Hꢀdibenzo[a,j]xanthenes and
,8ꢀdioxoꢀoctahydroꢀxanthenes. The nanocatalyst was characterized by FTꢀIR, AFM, TEM,
and TGA analyses. This greener protocol is catalyzed by CB[6]ꢀOSO H, and proceeds
3 3
H (CB[6]ꢀOSO H) has been prepared and used as an efficient
1
3
efficiently in the absence of any organic solvent under optimized, mild, green and
environmentally benign reaction conditions in high yields and within short reaction time.
Keywords: Xanthenes, Nanocatalyst, Dimedone, βꢀnaphthol, Solventꢀfree, Cucurbit[6]urilꢀ
OSO H
3
1. Introduction
Quite recently chemists have been interested by cucurbit[n]urils (CBn) as new molecular
hosts and also nanovessels, while their first report in the literature goes back to 1905. CBn
have been the subject of extensive research by supramolecular chemists. Due to the great
growth of this field of research, several review articles have been published recently [1ꢀ6].
Most recently, the synthesis of functionalized derivatives has progressed, and among the
manifold applications, cucurbiturilꢀcatalyzed reactions are receiving increasing attention [1].
Meanwhile cucurbit[6]uril, (CB[6]) is a hexameric macrocyclic compound selfꢀassembled
from an acidꢀcatalyzed condensation reaction of glycoluril and formaldehyde. Although its
synthesis first appeared in the literature in 1905 by Behrend, its chemical nature and structure
had been unknown until 1981, when full characterization was reported by Mock and coꢀ
workers. The rigid structure and capability of forming stable complexes with molecules and
1

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ions also make CB[6] attractive as a building block for the construction of supramolecular
architectures [2].
Due to xanthenes’ applicability such as antibacterial [7], antiviral [8], and antiꢀinflammatory
[
9] activities, utilization as leucoꢀdyes [10], application in laser technology [11], and also as
sensitizers in photodynamic therapy [12]; their synthesis is of great importance in organic
synthesis. Although many catalysts have been developed for the preparation of biologically
important 14ꢀarylꢀ14Hꢀdibenzo[a,j]xanthenes [13ꢀ17] and 1,8ꢀdioxoꢀoctahydroꢀxanthene [18ꢀ
24] derivatives, However, most of these methods show varying degrees of success as well as
limitations such as unsatisfactory yields, expensive catalysts, prolonged reaction times, toxic
organic solvents, and harsh reaction conditions. Thus the development of an alternate milder
procedure is highly demanding which could overcome those limitations.
In continuation of our previous works on the applications of reusable acid catalysts in organic
synthesis [25,26] we decided to investigate the synthesis of 14ꢀarylꢀ14Hꢀ
3
dibenzo[a,j]xanthenes and 1,8ꢀdioxoꢀoctahydroꢀxanthenes in the presence of CB[6]ꢀOSO H
under solvent free conditions (Scheme 1).
<Scheme 1>
2. Results and Discussion
In the first step CB[6](OH)12 was prepared according to literature [27]. In the second
step CB[6]ꢀOSO H was prepared with dropwise addition of ClSO H to CB[6](OH)
12.
3
3
(Scheme 2).
<Scheme 2>
To be qualified as a nanocatalyst, CB[6]ꢀOSO H was characterized by FTꢀIR, AFM, TEM,
3
and TGA analyses. In order to confirm the successful functionalization of the CB[6](OH)12
with ClSO
and CB[6]ꢀOSO
found at 1680 and 1760 cm for CB[6] and at 1701 and 1766 cm for CB[6](OH)12. It should
be notified that the stretching vibration of C=O group for CB[6]ꢀOSO H was found at 1664
and 1770 cm and also a broad peak around 3400 cm which is attributed to absorbed water.
3
H, FTꢀIR was employed. The FTꢀIR spectra of Glycoluril, CB[6], CB[6](OH)12
,
3
H has been shown in Fig 1. The stretching vibration of C=O group was
ꢀ1
ꢀ1
3
ꢀ1
ꢀ1
ꢀ1
CB[6]ꢀOSO
3
H, shows peaks at 1020 and 1200 cm
H groups (Fig 1, d).
corresponding to S=O stretching
vibrations of –SO
3
2

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<
Fig 1>
To ensure the particle size of the catalyst, TEM image was applied. It can be recognized that
the particles are under 25 nm in size (Fig 2). This finding is also supported by AFM image.
<
Fig 2>
AFM was utilized to view the particle size as well as size distribution of the nanoparticles. As
it can be seen in Fig 3, the mean size of the particles in a 5 µm × 5 µm square is 17.8 nm.
<
Fig 3>
Heat stability of CB[6]ꢀOSO
3
H was evaluated via TGA analysis. TGA diagram of the
3
catalyst indicates that decomposition occurs at 300°C. Thus CB[6]ꢀOSO H can be utilized in
the reaction, under 300°C without any danger of decomposition.
<
Fig 4>
In order to evaluate the catalytic activity of CB[6]ꢀOSO
3
H in the preparation of 14ꢀ
arylꢀ14Hꢀdibenzo[a,j]xanthenes derivatives, the reaction of 2 mmol of βꢀnaphthol and 1
mmol of benzaldehyde under solventꢀfree conditions at 110°C in the absence and presence of
CB[6]ꢀOSO
3
H were examined. It was found that in the absence of solid acid catalyst only
trace amount of the desired product was produced even after 5 h of heating (Table 1). When
3
the reaction was performed in the presence of CB[6]ꢀOSO H, we were fortunate to obtain the
desired product.
<
Table 1>
In order to evaluate the appropriate catalyst loading, a model reaction was carried out
using 0.01 to 0.03 g of the catalyst, at different temperatures under solventꢀfree conditions
(Table 1). It was found that 0.02 g of the catalyst shows maximum yield in minimum time.
Higher percentage of loading of the catalyst (0.03 g) lowers the conversion time but the
product’s yield is also decreased.
Delighted with these results, we decided to investigate the feasibility of this synthetic
procedure for the synthesis of xanthene derivatives. We extended the reaction of βꢀnaphthol
with a range of aromatic aldehydes under optimized reaction conditions. The respective 14ꢀ
arylꢀ14Hꢀdibenzo[a,j]xanthenes derivatives in high to excellent yields were isolated. The
optimized results are summarized in Table 2. This method has the ability to tolerate a variety
3

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of functional groups such as chloro, nitro, methoxy and methyl. The products were
1
13
characterized by FTꢀIR, H & C NMR. Physical and spectral data of known compounds are
in agreement with those reported in the literature.
<
Table 2>
As seen from Table 2, electron withdrawing as well as electron donating substituents
have the same effect on the reaction rate. It seems steric effects are dominated more than
electronic effects.
After the success of CB[6]ꢀOSO
dibenzo[a,j]xanthenes, we decided to explore the catalytic activity of CB[6]ꢀOSO
preparation of 1,8ꢀdioxoꢀoctahydroꢀxanthenes. Subsequently, the condensation of various
aromatic aldehydes with dimedone was carried out using CB[6]ꢀOSO H as the solid acid
catalyst under the above optimized reaction conditions (Scheme 1, Table 3).
3
H in the preparation of 14ꢀ arylꢀ14Hꢀ
3
H in the
3
<
Table 3>
A postulated mechanism is outlined in scheme 3. In the first step, the nucleophilic
attack of βꢀnaphthol or dimedone takes place on the carbonyl carbon of aromatic aldehyde in
a Knoevenagel condensation manner. In the second step, a Michael addition occurs. In the
last step, acid catalyzed cyclization happens with the subsequent dehydration to prepare 14ꢀ
arylꢀ14Hꢀdibenzo[a,j]xanthene or 1,8ꢀdioxoꢀoctahydroꢀxanthene derivatives.
<Scheme 3>
According to increasing interest in human health and environmental concerns, more
attention is being paid to green chemistry. With this view we studied the recyclability and
3
reusability of the catalyst. After completion of the reaction the separated CB[6]ꢀOSO H was
washed with hot ethanol and dichloromethane and dried. The catalyst was used for two more
subsequent cycles. To our surprise consistent performance of the catalyst is observed in all
the cycles Fig 5.
<
Fig 5>
3
. Experimental
.1 General
3
4

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All commercially available chemicals were purchased from Merck company and used
without further purification. CB[6] and CB[6](OH)12 was prepared according to literature
[
27]. IR spectra were recorded on a BOMEM MBꢀSeries 1998 FTꢀIR spectrophotometer
−1
1
13
using KBr pellets for the samples and the catalyst in the range of 4000–400 cm . H and C
NMR spectra were recorded in CDCl on a Bruker Advanced DPX 400 MHz spectrometer
3
using TMS as internal standard. Reaction monitoring was accomplished by TLC on silica gel
polygram SILG/UV 254 plates. Thermal stability of the supported catalyst was examined by
ꢀ1
BÄHR, SPA 503 Thermoꢀgravimetric Analyzer (TGA) at heating rate of 10 °C min over the
temperature range of 40–600 °C.
3
.2 Typical procedure for the preparation of CB[6]ꢀOSO H
3
A 50 mL RBF was equipped with a constant pressure dropping funnel. The gas outlet was
connected to a vacuum system through an adsorbing solution of alkali trap. CB[6](OH)12 (1
g, 0.84 mmol) together with 20 ml of CH Cl was added to the flask and sonicated for 30
2
2
2 2
minutes. Chlorosulfonic acid (ca. 0.7 mL, 10.1 mmol) in CH Cl (10 mL) was added
dropwise over a period of 30 min at room temperature. After completion of the addition, the
mixture was stirred for 2 h, while the residual HCl was eliminated by suction. Then the
2 2
mixture was washed with excess CH Cl . Finally, a white solid powder was obtained.
3.3 Typical procedure for the preparation of 14ꢀarylꢀ14Hꢀdibenzo[a,j]xanthenes/1,8ꢀdioxoꢀ
octahydroꢀxanthenes derivatives
In a test tube, aromatic aldehyde (1.0 mmol), βꢀnaphthol or dimedone (2.0 mmol), and
o
CB[6]ꢀOSO
3
H (0.02 g) was heated at 110 C. Completion of the reaction was indicated by
TLC [TLC ethyl acetate/nꢀhexane (2:5)]. After completion of the reaction (According to
Table 2 and 3) the insoluble crude product was dissolved in hot ethanol or CH Cl and
CB[6]ꢀOSO H was filtered. The filtrate was concentrated to dryness, and the crude product
was recrystallized in ethanol.
2
2
3
3.4 Determination of the acidity of CB[6]ꢀOSO
3
H
For evaluation of acidity of the catalyst, in a 25 mL aqueous solution of NaCl (1 M, pH =
6
.35), CB[6]ꢀOSO
3
H (40 mg) was added and the resulted mixture was stirred for 2 hours and
+
the pH of solution decreased to 2.18. This is equal to 4.13 mmol H /g of the catalyst.
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4. Conclusion
Cucurbit[6]urilꢀOSO
nanocatalyst for the oneꢀpot preparation of 14ꢀarylꢀ14Hꢀdibenzo[a,j]xanthenes and 1,8ꢀdioxoꢀ
octahydroꢀxanthenes. This greener protocol is catalyzed by CB[6]ꢀOSO H, and proceeds
3 3
H (CB[6]ꢀOSO H) has been prepared and used as an efficient acidic
3
efficiently in the absence of any organic solvent under optimized, mild, green and
environmentally benign reaction conditions in high yields and within short reaction time.
Acknowledgements. We gratefully acknowledge the support of this work by Production
Technology Research Institute of ACECR Research Council.
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R
2
OH
O
14ꢀ arylꢀ14Hꢀdibenzo[a,j]xanthenes
R
3
a-h
CB[6]ꢀOSO H
3
solventꢀfree 110oC
CHO
R
O
2
O
O
O
O
1,8ꢀdioxoꢀoctahydroꢀxanthenes
5a-h
Scheme 1. Oneꢀpot preparation of 14ꢀ arylꢀ14Hꢀdibenzo[a,j]xanthenes (3a-h) and 1,8ꢀdioxoꢀ
octahydroꢀxanthenes (5a-h)
8

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O
O
O
K S O
ClSO H
O
2
2
8
3
O, 85oC
N
N
N CH2
H
2
N
N
N CH2
OH
N
N
N CH2
H
H
HO
HO SO
OSO H
3
3
N CH2
N CH2
N CH2
O
O
6
6
6
CB[6]
CB[6](OH)12
CB[6]-OSO H
3
3
Scheme 2. Preparation of CB[6]ꢀOSO H
9

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a)
b)
c)
d)
3
Fig 1. IR spectra of a) Glycoluril, b) CB[6], c) CB[6](OH)12, d) CB[6]ꢀOSO H
1
0

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3
Fig 2. TEM of CB[6]ꢀOSO H
1
1

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3
Fig 3. AFM image of CB[6]ꢀOSO H
1
2

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3
Fig 4. TGA of CB[6]ꢀOSO H
1
3

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Fig 5. The reusability of CB[6]ꢀOSO H in reaction of βꢀnaphthol (2 mmol) and
3
benzaldehyde (1.0 mmol)
1
4

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Table 1. Optimum conditions for the reaction of βꢀnaphthol (2 mmol) and benzaldehyde (1.0
mmol) under thermal solventꢀfree conditions.
Entry
Catalyst (g)
Temp.(°C)
80
Time(min)
Yield(%)
<10
<10
45
1
2
3
4
5
6
7
0
0
300
300
55
45
35
110
100
110
110
110
110
0.01
0.01
0.02
0.03
0.05
52
96
95
83
30
30
1
5

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Table 2. Oneꢀpot preparation of 14ꢀ arylꢀ14Hꢀdibenzo[a,j]xanthenes promoted by CB[6]ꢀ
OSO H under solventꢀfree conditions at 110˚C.
3
Entry
R
Product
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
H
3a
3b
3c
3d
3e
3f
30
35
35
45
30
30
45
40
96
92
94
95
89
92
87
82
4ꢀNO
3ꢀNO
2ꢀCl
2
2
4ꢀCH
3
4ꢀCl
2ꢀNO
2
3g
3h
4ꢀOMe
1
6

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3
Table 3. Oneꢀpot preparation of 1,8ꢀdioxoꢀoctahydroꢀxanthenes promoted by CB[6]ꢀOSO H
under solventꢀfree conditions at 110˚C.
Entry
R
Product
Time (min)
Yield (%)
H
20
25
25
40
25
30
20
35
98
92
93
95
90
88
91
92
1
2
3
4
5
6
7
8
5a
5b
5c
5d
5e
5f
4
3
2
4
ꢀNO
2
ꢀNO2
ꢀNO2
ꢀCH3
4
ꢀOMe
ꢀCl
ꢀCN
2
5g
5h
4
1
7

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O H
A
O
H
H
O
O
H
R
O H
H
R
HO
R
O
O
O
CB[6]-OSO H = HA
3
H
HA
O
HA
R
O
O
H
H
R
HO
HO
O HO
R
R
O
O
H
HA
H
HA
O
O
1
,8ꢀdioxoꢀoctahydroꢀxanthenes
14ꢀarylꢀ14Hꢀdibenzo[a, j]xanthenes
3
Scheme 3. The postulated mechanism for the CB[6]ꢀOSO H catalyzed preparation of xanthenes
1
8

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Cucurbit[6]uril-OSO H: A Novel Acidic Nanocatalyst for the one-pot preparation of 14-
3
aryl-14H-dibenzo[a,j]xanthenes and 1,8-dioxo-octahydro-xanthenes
,
1
2
1
Seyyed Jafar Saghanezhad* , Yaser Nazari , and Fereshteh Davod
1
ACECR-Production Technology Research Institute, Ahvaz, Iran
2
Kimia Kankash Jondishapur Research Co., Ahvaz, Iran
*
Corresponding Author Tel: (+98) 61-33364400, Email: jafar_saghanezhad@yahoo.com
R
2
OH
O
14- aryl-14H-dibenzo[a,j]xanthenes
R
3a-h
CB[6]-OSO H
3
solvent-free 110oC
CHO
R
O
2
O
O
O
O
1
,8-dioxo-octahydro-xanthenes
5a-h
One-pot preparation of 14- aryl-14H-dibenzo[a,j]xanthenes (3a-h) and 1,8-dioxo-octahydro-
xanthenes (5a-h)