A simple and efficient one-pot bis-bromine-1,4-diazabicyclo [2.2.2]octane (Br2-DABCO) catalyzed synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes under solvent-free conditions

Article abstract of DOI:10.1515/HC.2011.020

Bis-bromine-1,4-diazabicyclo[2.2.2]octane (Br₂-DABCO) is an efficient, readily available, and reusable catalyst for the synthesis of 14-aryl-14 H-dibenzo[a,j]xanthenes 3 by condensation of β-naphthol 2 and aldehydes 1. This reaction under solve

Full text of DOI:10.1515/HC.2011.020

Heterocycl. Commun., Vol. 17(1-2), pp. 83–85, 2011 • Copyright © by Walter de Gruyter • Berlin • Boston. DOI 10.1515/HC.2011.020
A simple and efficient one-pot bis-bromine-1,4-diazabicyclo
[2.2.2]octane (Br2-DABCO) catalyzed synthesis of 14-aryl-14H-
dibenzo[a,j]xanthenes under solvent-free conditions
Hassan Ghasemnejad-Bosra1,* and Mehdi Forouzani2
1 Department of Chemistry, Islamic Azad University-Babol
al., 2005) as a robust and efficient catalyst in the one-pot synthe-
sis of the 14-aryl-14H-dibenzo[a,j]xanthenes derivatives 3a– o
by reaction of β-naphthol with different aromatic aldehydes
Branch, P.O. Box 755, Babol 47188-33348, Iran
in excellent yields (88–97%) under solvent-free conditions
2 Department of Chemistry, Payamenoor University,
(Scheme 1, Table 1). As shown in Table 1, the reactions occur
19395-4697, Tehran, I.R. of Iran
within 48–73 min under solvent-free conditions. The experi-
*Corresponding author
e-mail: h_ghasem2000@yahoo.com
mental results indicate that the most effective conversions occur
when a molar ratio 1:0.17 of substrate/Br2-DABCO is used.
Longer reaction times are required when lower amounts of Br2-
DABCO are employed. It is important to note that no 14-aryl-
14H-dibenzo[a,j]xanthenes derivatives were afforded when the
reactions were performed in the absence of Br2-DABCO.
The proposed mechanism for these reactions is shown in
Scheme 2. As can be seen, the reaction likely proceeds via
initial formation of an intermediate product 4. The oxonium
species 5 is then formed by reaction with β-naphthol, which
then undergoes dehydration to afford the desired product 3.
The advantages of the method described in this paper in
comparison with other previously reported methods are as
follows: the yields of products are higher than the previ-
ously reported yields. In addition, the catalyst Br2-DABCO is
inexpensive, without any moisture sensitivity, and no special
efforts are required for the reaction.
Abstract
Bis-bromine-1,4-diazabicyclo[2.2.2]octane (Br2-DABCO) is
an efficient, readily available, and reusable catalyst for the
synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes 3 by conden-
sation of β-naphthol 2 and aldehydes 1. This reaction under
solvent-free conditions is very simple, affording good to
excellent yields of products.
Keywords: 14-aryl-14H-dibenzo[a,j]xanthenes;
bis-bromine-1,4-diazabicyclo[2.2.2]octane; one-pot
synthesis; solvent-free.
Introduction
Conclusion
Xanthenes and benzoxanthenes are biologically important
drug intermediates. They are cited in the literature as oxygen
heterocycles possessing antibacterial (El-Brashy et al., 2004),
anti-inflammatory (Chibale et al., 2003), and antiviral proper-
ties (Jamison et al., 1990). The synthesis of xanthene deriva-
tives is currently of much interest, and various methods have
been reported (Wang and Harvey, 2002; Khoramabadi-zad et
al., 2005; Khosropour et al., 2005; Rajitha et al., 2005; Ko and
Yao, 2006; Mohamed and Vaderapura, 2007; Mozhdeh et al.,
2008). However, the existing methods suffer from long reac-
tion times, unsatisfactory yields, harsh reaction conditions
and excessive use of reagents and catalysts. It is therefore
important to find more convenient methods for the prepara-
tion of these compounds.
We described herein bis-bromine-1,4-diazabicyclo[2.2.2]
octane (Br2-DABCO) catalyzed highly efficient, one-pot, pro-
tocol for the synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes
by the condensation of an aldehyde and 2-naphthol under sol-
vent-free conditions in excellent yields. The main advantages
of the presented protocol are mild, clean and environmentally
benign reaction conditions, low costs of the reagents, and
high yields of the products.
Experimental section
The employed chemicals were obtained from either Merck or
Fluka. The infrared spectroscopy (IR) spectra were recorded using a
R
CHO
Results and discussion
OH
Br2-DABCO
2
+
R
In continuation of our research on various transformations by
halogenating agents (Azarifar and Ghasemnejad-Bosra, 2006;
Azarifar et al., 2006; Ghasemnejad-Bosra et al., 2008a,b;
Habibzadeh et al., 2011), herein is reported the use of bis-bro-
mine-1,4-diazabicyclo[2.2.2]octane (Br2-DABCO) (Heravi et
110°C - Solvent free
O
2
3
1
Scheme 1 Synthesis of xanthenes with Br2-DABCO under solvent-
free conditions.
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84 H. Ghasemnejad-Bosra and M. Forouzani
Table 1 Br2-DABCO catalyzed synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes.
Entry
Product
R
Time (min)
Yields (%)a
M.p. (°C)b
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
H
4-Cl
2-Cl
4-Br
50
61
67
53
60
66
71
61
49
50
48
52
73
50
62
96
94
92
91
93
89
88
90
95
96
96
97
92
94
93
181 (183)
288 (287)
214 (215)
298 (296)
191 (190)
309 (312)
292 (293)
214 (213)
227 (228)
206 (205)
199 (197)
95 (93)
2-Br
4-NO2
2-NO2
3-NO2
4-Me
3-Me
4-OMe
2-OMe
3-F
258 (259)
210 (209)
238 (239)
2-F
4-F
aYields of isolated products.
bAll products are known, characterized by IR, NMR and melting points, and compared with authentic samples. The literature melting points
are given in parentheses (Wang and Harvey, 2002; Khosropour et al., 2005).
N
N+
-
Br
N
+
Br-Br
N
Br
+
N
N+
O
-
OBr
N
Br
+
+
Ar
H
Ar
H
N
-
Br
1
..
OH
H
N
Ar
-
N+
Ar
2
Br
Ar
OBr
OH
OH
+
O+
Br
H
Br
OH
.O.H
-HOBr
Ar
N
..
+
N
-
Ar
O+
OH
Ar
H
OH
+
4
OH
HO
OH
+
H
5
- H+
Ar
Ar
Ar
H
H
H
+ H+
O
O
O
OH2
OH2
+
OH
+
(HOBr)
Ar
O
N
-
Br
+
N+
Br
3
Scheme 2 Possible mechanism for the synthesis of xanthenes.
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Synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes 85
Shimadzu 435-U-04 spectrophotometer (KBr pellets) and the nuclear
magnetic resonance (NMR) spectra were obtained in CDCl3 using a
90 MHz JEOL FT NMR spectrometer. All melting points were deter-
mined on a Büchi 530 melting point apparatus and are uncorrected.
Ghasemnejad-Bosra, H.; Haghdadi, M.; Gholampour-Azizi, I.
N-Bromosuccinimide (NBS) as promoter for acylation of syd-
nones in the presence of acetic anhydride under neutral condi-
tions. Heterocycles 2008a, 75, 391–395.
Ghasemnejad-Bosra, H.; Haghdadi, M.; Khanmohamadi, O.;
Gholipour, M.; Asghari, G. Bis-bromine-1,4-diazabicyclo[2.2.2]
octane (Br2-DABCO) as an efficient promoter for one-pot con-
version of N-arylglycines to N-arylsydnones in the presence
of NaNO2/Ac2O under neutral conditions. J. Chin. Chem. Soc.
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Habibzadeh, S.; Ghasemnejad, H.; Faraji, M. Efficient one-pot
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General procedure for the synthesis of 14-aryl-14H-
dibenzo[a,j]xanthenes
To a mixture of aldehyde 1 (1 mmol) and β-naphthol 2 (2 mmol), bis-
bromine-1,4-diazabicyclo[2.2.2]octane (Br2-DABCO) (0.17 mmol,
0.2 mg) was added and the mixture was placed in an oil bath and
heated at 110°C for the period of time shown in Table 1. Completion
of the reaction was indicated by thin layer chromatography (TLC).
After the reaction was completed, EtOH was added and the mixture
was heated until the solid crude product was dissolved. Then, the het-
erogeneous catalyst wasremoved from the mixture by simple filtration
and the EtOH solution was concentrated. A 15% mixture of ethanol
and water was added to the crude product, the precipitate was filtered
and then crystallized twice from the 15% aqueous ethanol. The prod-
ucts were characterized on the basis of their physical and spectral
analysis (Table 1) and by direct comparison with literature data.
Khoramabadi-zad, A.; Akbari, S. A.; Shiri, A.; Veisi, H. One-pot syn-
thesis of 14H-dibenzo[a,j]xanthene and its 14-substituted deriva-
tives. J. Chem. Res. (S) 2005, 5, 277–279.
Acknowledgements
Khosropour, A. R.; Khodaei, M. M.; Moghannian, H. A facile, sim-
ple and convenient method for the synthesis of 14-alkyl or aryl-
14H-dibenzo[a,j]xanthenes catalyzed by pTSA in solution and
solvent-free conditions. Synlett 2005, 6, 955–958.
We wish to thank the Islamic Azad University, Babol-Branch Iran,
for financial support.
Ko, S.; Yao, C. F. Amberlyst-15 catalyzes the synthesis of 14-substi-
tuted-14H-dibenzo[a,j]xanthenes under solvent-free conditions.
Tetrahedron Lett. 2006, 47, 8827–8829.
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Received April 26, 2011; accepted June 14, 2011
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