Clean synthesis of 1,8-dioxooctahydroxanthenes promoted by DABCO-bromine in aqueous media

Article abstract of DOI:10.1016/j.cclet.2010.05.018

An efficient procedure is reported for the synthesis of 3,3,6,6-tetramethyl-9-aryl-1,8-dioxooctahydroxanthenes using a one-pot condensation of arylaldehydes and 5,5-dimethyl-1,3-cyclohexandione in the presence of DABCO-bromine (TDB) as an acid catalyst. To the best of our knowledge this is the first time that DABCO-bromine is used as an acid catalyst in aqueous media for this type of reaction. This method provides several advantages such as use of water as solvent, easy and clean synthesis, simple work up and versatility.

Full text of DOI:10.1016/j.cclet.2010.05.018

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Chinese Chemical Letters 21 (2010) 1180–1182
www.elsevier.com/locate/cclet
Clean synthesis of 1,8-dioxooctahydroxanthenes promoted by
DABCO-bromine in aqueous media
Mohammadali Bigdeli
Faculty of Chemistry, Tarbiat Moallem University, No. 49, Mofateh Ave., Tehran, Iran
Received 24 February 2010
Abstract
An efficient procedure is reported for the synthesis of 3,3,6,6-tetramethyl-9-aryl-1,8-dioxooctahydroxanthenes using a one-pot
condensation of arylaldehydes and 5,5-dimethyl-1,3-cyclohexandione in the presence of DABCO-bromine (TDB) as an acid
catalyst. To the best of our knowledge this is the first time that DABCO-bromine is used as an acid catalyst in aqueous media for this
type of reaction. This method provides several advantages such as use of water as solvent, easy and clean synthesis, simple work up
and versatility.
# 2010 Mohammadali Bigdeli. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: 1,4-Diazabicyclo[2,2,2]octane; (DABCO)-bromine; Octahydroxyxanthene; Aqueous media; Arylaldehyde; Dimedone
Xanthenes and benzoxanthenes are important classes of compounds that find use as dyes, as fluorescent
materials for visualization of biomolecules and laser technologies due to their useful spectroscopic properties
[1,2]. Xanthene-based compounds have also been investigated for agricultural bactericide activity, photodynamic
therapy [3], anti-inflammatory effect [4], and antiviral activity [5]. Various reports are available on synthesis
of xanthenes including palladium catalyzed cyclization of polycyclic aryltriflate esters [6], intramolecular
trapping of benzynes by phenols [7,8] and reaction of aryloxymagnesium halides with triethylorthoformate
[9,10].
These methodologies, however, have drawbacks such as low yields, lack of availability or tedious preparation of the
starting materials, prolonged reaction times and use of toxic organic solvents. Excessive use of catalyst and use of
special apparatus and harsh reaction conditions are further disadvantage of such procedures.
1. Experimental
General procedure: A mixture of an aldehyde (1.0 mmol) 5,5-dimethyl-1,3-cyclohexandione (2.0 mmol) and
DABCO-bromine (0.015 g, 0.01 mmol) in H2O (10 mL) was stirred while refluxing for 1–2.5 h. The progress of the
reaction was monitored by TLC. After completion of the reaction, the mixture was cooled and filtered. The filtrate was
washed with H2O and purified by recrystallization from EtOH. The products were characterized by comparison of
1
their spectra (IR, H NMR) and melting points with those reported in literature (Table 1).
E-mail address: mabig397@yahoo.com.
1001-8417/$ – see front matter # 2010 Mohammadali Bigdeli. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2010.05.018

M. Bigdeli / Chinese Chemical Letters 21 (2010) 1180–1182
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Table 1
Synthesis of 1,8-dioxo-octahydroxanthene by DABCO-bromine in water.
[TD$INLINE]
Entry
Ar
Time (h)
Isolated yield (%)
Mp (8C)
Reference
1
2
C6H5
1
90
85
85
80
83
85
80
85
85
85
85
201–203
216–219
242–245
228–230
221–223
167–170
225–228
185–187
229–232
172–175
219–220
201–203 [11]
216–218 [11]
241–243 [11]
231–233 [11]
222 [12]
4-CH3C6H4
4-CH3OC6H4
4-ClC6H4
2
3
2
4
2.5
2.5
2.5
2.5
2
5
4-NO2C6H4
3-NO2C6H4
2-ClC6H4
6
168–170 [12]
226–228 [16]
187–188 [17]
228–231 [11]
175–177 [16]
220–222 [17]
7
8
2-CH3OC6H4
4-BrC6H4
9
2.5
2
10
11
C6H4CH CH2
4-Me2NC6H4
2
Isolated product: products were confirmed by IR and 1H NMR.
[(Scheme_1)TD$FIG]
Scheme 1.
2. Results and discussion
The preparation of xanthenes in water is desirable due to environmental considerations. There are limited numbers
of reports on synthesis of xanthenes in aqueous media [11,12]. These reports, however, suffer from long reaction times
and complicated catalyst preparations.
Tetrameric DABCO-bromine (TDB) has been used in a number of oxidation and bromination reactions of organic
compounds [13,14]. The use of TDB as an acid catalyst in aqueous media for the synthesis of 1,8-dioxo-
octahydroxanthene and their derivatives, however, has not been reported. TDB complex is a homogeneous non-
hygroscopic solid, which is stable at room temperature and is not affected by exposure to light, air or water. It has no
offensive odor of bromine or amine. It could be readily prepared by adding a solution of bromine in dichloromethane to
a solution of DABCO in the same solvent (Scheme 1).
The crystal structure of DABCO-bromine has been already reported [15]. In this manuscript, we wish to report a
general a highly efficient route to the synthesis of 1,8-dioxooctahydroxanthene and their derivatives using DABCO-
bromine in aqueous media.
In a general experimental procedure, a solution of an aromatic aldehyde and 5,5-dimethyl-1,3-cyclohexandione
(dimedone) was heated under reflux in water in the presence of catalytic amount of DABCO-bromine for a period of
time (1–2.5 h), which resulted in the formation of the corresponding 1,8-dioxo-octahydroxanthene. The results are
summarized in Table 1. The optimum amount of catalyst was found to be 0.015 g (0.01 mmol) for 80–95% yields.
Increasing the ratio of DABCO-bromine did not improve the yields.
Benzaldehyde and other aromatic aldehydes containing electron-withdrawing or electron-donating groups were
employed and gave the corresponding 1,8-dioxooctahydroxanthenes in excellent yields. These results indicate that the
use of DABCO-bromine overcomes the substituent effects observed in previous reports. Table 2 compares the
efficiency of our method with the efficiency of other works in the synthesis of 1,8-dioxooctahydroxanthenes.

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M. Bigdeli / Chinese Chemical Letters 21 (2010) 1180–1182
Table 2
Comparison of results using DABCO-bromine with those reported previously.
Catalyst
Conditions
Time (h)
Yield (%)
Ref.
DABCO-bromine
DBSAa
H2O/reflux
1
6
90
89
75
92
52
90
95
–
H2O/reflux
[12]
[11]
[18]
[19]
[16]
[20]
PANI-PTSAb
H2O/reflux
6
Amberlyst-15
c
PPA-SiO2
CH3CN/reflux
CH3CN/reflux
H2O/25–30 8C
[bmim]BF4/808
5
10
6.5
5
Ultra sound
InCl3Á4H2O
a
p-Dodecylbenzenesulfonic acid.
b
Polyaniline-p-toluenesulfonate salt.
c
Polyphosphoric acid supported on silica.
In conclusion, we wish to report the use of DABCO-bromine as an excellent homogenous catalyst in preparation of
all types of 1,8-dioxooctahydroxanthenes.
Acknowledgment
We wish to thank Teacher Training University for supporting this work.
References
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