The efficient synthesis of 14-alkyl or aryl 14H-dibenzo[a,j]xanthenes catalyzed by bismuth(III) chloride under solvent-free conditions

Article abstract of DOI:10.1016/j.cclet.2011.01.012

An efficient method for the synthesis of 14-alkyl or aryl 14H-dibenzo[a,j]xanthene derivatives by the reaction of β-naphthol, and aldehydes in the presence of a catalytic amount of bismuth(III) chloride (BiCl₃) under solvent-free conditions at

Full text of DOI:10.1016/j.cclet.2011.01.012

Available online at www.sciencedirect.com
Chinese Chemical Letters 22 (2011) 927–930
www.elsevier.com/locate/cclet
The efficient synthesis of 14-alkyl or aryl 14H-
dibenzo[a,j]xanthenes catalyzed by bismuth(III)
chloride under solvent-free conditions
*
Ebrahim Soleimani , Mohammad Mehdi Khodaei,
Afsaneh Taheri Kal Koshvandi
Department of Chemistry, Razi University, Kermanshah 67149, Iran
Received 9 November 2010
Available online 18 May 2011
Abstract
An efficient method for the synthesis of 14-alkyl or aryl 14H-dibenzo[a,j]xanthene derivatives by the reaction of b-naphthol, and
aldehydes in the presence of a catalytic amount of bismuth(III) chloride (BiCl3) under solvent-free conditions at 110 8C is
described. Aliphatic and aromatic aldehydes were used in the reaction and in all cases the desired products were synthesized
successfully. This reaction was studied under different temperatures; the maximum yield was obtained in a short reaction period at
110 8C. The method offers the advantages of high yields, short reaction times, simplicity and easy workup compared to the
conventional method of syntheses.
# 2011 Ebrahim Soleimani. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Bismuth(III) chloride; 14H-Dibenzo[a,j]xanthenes; b-Naphthol
Xanthenes and benzoxanthenes have received much attention because of their wide range of therapeutic and
biological properties, such as antibacterial, antiviral, and anti-inflammatory activities [1]. Further, these compounds
are very important class of compounds widely used as leuco-dye [2], pH-sensitive fluorescent materials for
visualization of biomolecules [3] and in laser technology [4]. Several methods have been reported for the synthesis of
xanthenes and benzoxanthenes, which include the cycloacylation of carbamates [5], trapping of benzynes by phenol
[6], cyclocondensation between 2-hydroxy aromatic aldehydes and 2-tetralone [7], cyclodehydrations [8] and
intramolecular phenyl carbonyl reaction of aldehydes with b-naphthol by dehydration [9]. Other routes for the
synthesis of benzoxanthenes and related products include the reaction of b-naphthol with formamide [10], carbon
monoxide [11] and 2-hydoxynaphth-1-ylmethanol [12]. However, these methods have many disadvantages, such as
the use of toxic solvents, prolonged reaction times, excess reagents, low yields and harsh reaction conditions. The
synthesis of xanthenes has been improved by condensing b-naphthol with aldehydes in the presence of an acid catalyst
such as sulfamic acid [13], SelectfluorTM [14], molecular iodine [15], p-toluene sulfonic acid [16], cation-exchange
resins [17], and Dowex-50W [18] as catalysts. However, many of these existing methodologies suffer from one or
* Corresponding author.
E-mail address: e_soleimanirazi@yahoo.com (E. Soleimani).
1001-8417/$ – see front matter # 2011 Ebrahim Soleimani. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2011.01.012

[()TD$FIG]
928
E. Soleimani et al. / Chinese Chemical Letters 22 (2011) 927–930
R
OH
O
BiCl3
solvent-free, 110 oC
+
R
H
O
1
2
3
Scheme 1.
more disadvantages such as prolonged reaction times, low yields, use of harmful organic solvents, and requirement of
excess of catalyst and reagents, and harsh reaction conditions.
In recent years, BiCl3 has attracted much attention because of its diverse applicability as catalysts in organic synthesis
[19]. Compared with transition-metal complexes, bismuth(III) salts are stable in air, relatively nontoxic and inexpensive.
Herein, inourcontinuedinterest forthe synthesis of finechemicalsand heterocyclic compoundsof biologicalimportance
[20], wereportarapid, efficientandhigh-yieldingmethodforthesynthesisofbenzoxanthenes3bythecondensationofb-
naphthol 1 with aldehydes 2 catalyzed by BiCl3 under solvent-free conditions at 110 8C (Scheme 1).
We first investigated the catalytic activities of various catalysts, which promoted the model reaction of b-naphthol
(2 mmol) and 3-nitrobenzaldehyde (1 mmol) under solvent-free condition. In the course of this study, we found that
BiCl3 was the most effective catalyst producing benzoxanthenes in higher yields than other catalysts. We also studied
the model reaction catalyzed by BiCl3 (20 mol%) at different temperatures. The reaction rate was increased as the
reaction temperature was raised. When it was carried out at 110 8C, the maximum yield was obtained in a short
reaction period (Table 1, entry 4). To evaluate the effect of catalyst concentration, the model reaction was carried out in
the presence of different amounts of catalyst (5, 10, 15, 20 and 25 mol%) at 110 8C. The result showed that 20 mol% of
catalyst was sufficient to achieve a fairly high yield (Table 1, entry 4). With 5 mol% of BiCl3, a lower yield was
observed under the same reaction period (Table 1, entry 1). This encouraged us to study the scope of the reaction under
the optimized reaction parameters in the presence of 20 mol% of catalyst under solvent-free condition at 110 8C. The
results of using BiCl3 as a catalyst in the reaction of b-naphthol and various aldehydes are summarized in Table 2.
Various functionalities present in the aryl aldehydes, such as halogen, methoxy, methyl, and nitro groups were
tolerated. In all these cases, the corresponding benzoxanthenes were obtained in good to excellent yields. Similar
results were also obtained in the case of aliphatic aldehydes in good yields in long time reaction than aromatic
aldehyde (Table 2, entries 12 and 13).
In order to show the merit of BiCl3 in comparison with other reported catalysts, we summarized some of the results
for the synthesis of 14-aryl-14H-dibenzo[a,j]xanthene obtained by other workers. It is clear from Table 3 that the
current method is simpler, more efficient and less time-consuming for the synthesis of 14-aryl-14H-
dibenzo[a,j]xanthene derivatives.
Table 1
Catalytic activity of various catalysts for the reaction of b-naphthol, and 3-nitrobenzaldehyde.
Entry
Catalyst
Temperature/8C
Time/min
Yield
1
2
BiCl3 (5 mol%)
110
110
110
110
110
25
45
30
20
6
70
83
85
98
98
50
60
74
85
98
80
25
35
45
30
BiCl3 (10 mol%)
3
BiCl3 (15 mol%)
4
BiCl3 (20 mol%)
5
BiCl3 (25 mol%)
5
6
BiCl3 (20 mol%)
60
60
20
10
6
7
BiCl3 (20 mol%)
50
8
BiCl3 (20 mol%)
80
9
BiCl3 (20 mol%)
100
120
110
110
110
110
110
10
11
12
13
14
15
BiCl3 (20 mol%)
Cu(OAc)2Á6H2O (20 mol%)
Bi(NO3)2Á5H2O (20 mol%)
Bi5O(OH)9(NO3)4 (20 mol%)
LaN3O9Á6H2O (20 mol%)
CuCO3 (20 mol%)
180
240
240
240
240

E. Soleimani et al. / Chinese Chemical Letters 22 (2011) 927–930
929
Table 2
BiCl3-promoted synthesis of benzoxanthene derivatives under solvent-free condition at 110 8C.
Entry
R
Product
Time/min
Yield
Mp/8C
Found
Reported
1
2
4-ClC6H4
3a
3b
3c
3d
3e
3f
8
5
98
98
98
97
93
88
85
98
93
96
83
74
290
311
227
296
214
293
260
210
217
184
112
152
289 [16]
310 [16]
229 [16]
297 [16]
215 [16]
293 [16]
260 [16]
211 [16]
217 [22]
185 [16]
113 [16]
152 [16]
4-NO2C6H4
4-CH3C6H4
4-BrC6H4
2-ClC6H4
3
3
4
6
5
8
6
2-NO2C6H4
2-OCH3C6H4
3-NO2C6H4
2-naphtyl
15
10
6
7
3g
3h
3i
9
10
11
12
13
10
7
phenyl
3j
(CH3)2CHCH2
CH3CH2
3k
3m
180
180
Table 3
Comparison of the efficiencies of various catalysts used in the synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes.
Catalyst
Conditions/T/8C
Time/h
Yield/%
Reference
Montmorillonite K10
SelectfluorTM
p-Toluenesulfonic acid
I2
Solvent-free/120
Solvent-free/125
Solvent-free/125
Solvent-free/90
Solvent-free/125
Solvent-free/125
Solvent-free/100
Solvent-free/110
2–4
6–12
2.5–6
2–5
75–89
90–95
80–96
85–95
90–95
80–94
78–91
85–99
[21]
[14]
[16]
[15]
Sulfamic acid
Amberlyst-15
Dowex-50W
BiCl3
6–12
0.5–2
1–2
[13]
[23]
[18]
8–15 min
This work
In conclusion, we have developed a simple method for the synthesis of 14-alkyl or aryl-14H-dibenzo[a,j]xanthenes
by condensation reaction of aldehydes and 2-naphthol in the presence of BiCl3 under solvent-free conditions. This
method offers some advantages in terms of simplicity of performance, low reaction times, solvent-free condition, good
to excellent yields, and it follows along the line of green chemistry. The catalyst is readily available and inexpensive
and can conveniently be handled and removed from the reaction mixture. Further applications of BiCl3 in organic
transformation are currently in progress in our laboratories.
General procedure: A mixture of the aldehyde (1 mmol) and b-naphthol (2 mmol) was well stirred with BiCl3
(0.2 mmol) at 110 8C for the appropriate time according to table. After completion of the reaction, the reaction mixture
was cooled to ambient temperature, dichloromethane (3 mL) was added, and BiCl3 was filtered off. The filtrate was
concentrated to dryness, and the crude solid product was crystallized from EtOH to afford the pure 14-alkyl or aryl-
14H-dibenzo[a,j]xanthene.
All the products are known compounds, which were characterized by IR and 1H NMR spectral data and their mp’s
compared with literature reports.
Acknowledgment
We gratefully acknowledge financial support from the Research Council of Razi University.
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