Synthesis of 14-aryl-14H-dibenzo[a,j]xanthene derivatives using Cu(CH 3CN)4PF6 as catalyst

Article abstract of DOI:10.2174/157017811797249399

A simple and expedient method for the synthesis of a series of 14-aryl-14H-dibenzo[a.j]xanthenes and bis (14-aryl-14H-dibenzo[a.j]xanthenes) is described through a one-pot condensation of β-naphthol with aryl aldehydes catalyzed by Cu(CH₃CN)

Full text of DOI:10.2174/157017811797249399

Letters in Organic Chemistry, 2011, 8, 573-576
573
Synthesis of 14-Aryl-14H-Dibenzo[a,j]xanthene Derivatives Using
Cu(CH3CN)4PF6 as Catalyst
Ebrahim Soleimani*,a, Mohsen Zainalia and Shahram Lotfib
aDepartment of Chemistry, Razi University, P.O. Box 67149-67346, Kermanshah, Iran
bDepartment of Chemistry, Payame Noor University (PNU), Iran
Received May 28, 2011: Revised June 06, 2011: Accepted June 15, 2011
Abstract: A simple and expedient method for the synthesis of a series of 14-aryl-14H-dibenzo[a.j]xanthenes and bis (14-
aryl-14H-dibenzo[a.j]xanthenes) is described through a one-pot condensation of ꢀ-naphthol with aryl aldehydes catalyzed
by Cu(CH3CN)4PF6 under solvent-free conditions. The novel synthesis method offers the advantages of high yields, short
reaction times, simplicity and easy workup compared to the conventional method of syntheses.
Keywords: 14-aryl-14H-dibenzo[a.j]xanthene, aldehyde, bis-14-aryl-14H-dibenzo[a.j]xanthene, Cu(CH3CN)4PF6, solvent-free,
ꢀ-naphthol.
INTRODUCTION
harmful organic solvents, requirement of excess of cata-
lyst/reagents, and harsh reaction conditions.
The synthesis of xanthenes, especially benzoxanthenes,
has emerged as a powerful tool in organic synthesis due to
their wide range of biological and therapeutic properties such
as antibacterial, antiviral and anti-inflammatory activities
[1], as well as in photodynamic therapy [2] and for antago-
nism of the paralyzing action of zoxazolamine [3]. Further-
more, due to their useful spectroscopic properties, they are
used as dyes [4], in laser technologies [5], and in fluorescent
materials for visualization of biomolecules [6].
In continuation of our work to develop new synthetic
methodologies and solvent-free protocols [22], herein we
report efficient, convenient and facile method for the synthe-
sis of some benzoxanthenes derivative 3 by the condensation
of ꢀ-naphthol 1 with various aromatic aldehydes 2 catalyzed
by Cu(CH3CN)4PF6 under solvent-free conditions at 80 ˚C
(Scheme 1).
R
R
CHO
2
+
Cu(CH3CN)4PF6(20% mol)
Solvent-free, 80 oC
O
OH
HO
1
3
1
Scheme 1.
The synthesis of benzoxanthenes has been achieved by
various methods [7]. Recently, the synthesis of benzoxan-
thenes has been achieved by the condensation of aldehydes
with ꢀ-naphthol by cyclodehydration in the presence of vari-
ous catalysts, such as AcOH–H2SO4 [8], p-TSA [9],
BF3.SiO2 [10], sulfamic acid [11], ionic liquid [12], iodine
[13], Dowex-50W [14], silica sulfuric acid [15], Amberlyst-
15 [16], cyanuric chloride [17], LiBr [18], Yb(OTf)3 [19],
InCl3 [20], and KAl(SO4)2.12H2O [21]. However, many of
these existing methodologies suffer from one or more disad-
vantages such as prolonged reaction times, low yields, use of
RESULTS AND DISCUSSION
To study the feasibility of the Cu(CH3CN)4PF6 catalyzed
in this reaction, the reaction of 4-nitrobenzaldehyde with ꢀ-
naphthol was selected as a model under solvent-free condi-
tions. We first studied the model reaction catalyzed by
Cu(CH3CN)4PF6 (20 mol%) at different temperatures. The
reaction rate was increased as the reaction temperature was
raised. When it was carried out at 80 ˚C, the maximum yield
was obtained in a short reaction period. Next, to evaluate the
effect of catalyst concentration, the model reaction was car-
ried out in the presence of different amounts of catalyst (5,
10, 15, 20 and 25 mol%) at 80 ˚C. The result showed that 20
mol% of catalyst was sufficient to achieve a fairly high yield
(Table 1).
*Address correspondence to this author at the Department of Chemistry,
Razi University, P.O. Box 67149-67346, Kermanshah, Iran; Fax: +98-
8314274559; E-mail: E_soleimanirazi@yahoo.com
1570-1786/11 $58.00+.00
© 2011 Bentham Science Publishers

574 Letters in Organic Chemistry, 2011, Vol. 8, No. 8
Soleimani et al.
Table 1. Optimization Amount of Cu(CH3CN)4PF6 Catalyst
NO2
CHO
Cu(CH3CN)4PF6
Solvent-free, 80 oC
+
2
OH
O
NO2
1
3b
2
Entry
Cu(CH3CN)4PF6 (mol%)
Time (min)
Yield (%)
1
2
3
4
5
6
0
180
120
65
0
5
27
50
70
90
91
10
15
20
25
50
25
25
With the optimized condition established above, we next
attempted to extend the process to ꢀ-naphthol and various
types of aromatic aldehydes. The results have been summa-
rized in Table 2. In all cases, 14-aryl-14H-dibenzo[a,j] xan-
thenes were obtained in good yields, whatever the nature of
the substituent present on the aldehyde (electron-donating or
electron-withdrawing).
amount of ꢀ-naphthol (4 mmol) was similar reaction between
terephthaldialdehyde and ꢀ-naphthol (Table 2, entry 9).
The efficiency of Cu(CH3CN)4PF6 (time, yield, reaction
conditions) was compared with the efficiencies of other cata-
lysts used in synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes,
the results are presented in Table 3. It is clear that the pre-
sented method is simpler, more efficient and less time con-
suming compared with other methods except for that em-
ploying Cu(CH3CN)4PF6 having disadvantages already men-
tioned.
We also studied the reaction between terephthaldialde-
hyde (1 mmol) and excess amount of ꢀ-naphthol (4 mmol),
we expected that both of the formyl groups on the aromatic
ring of terephthaldialdehyde would react with ꢀ-naphthol
and produced bis-14-aryl-14H-dibenzo[a,j]xanthene. How-
ever, we observed that one of the formyl groups was con-
densed with ꢀ-naphthol and another group was intact be-
cause of steric effects between o-hydrogen’s of tere-
phthaldialdehyde and the xanthene ring and steric interaction
between two xanthene ring (Table 2, entry 8) (Scheme 2).
Reaction between isophthalaldehyde (1 mmol) and excess
CONCLUSION
In conclusion, we have developed a simple and efficient
synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes and bis (14-
aryl-14H-dibenzo[a,j]xanthenes) using Cu(CH3CN)4PF6 cata-
lyst under solvent-free conditions. This method offers some
advantages in terms of simplicity of performance, low reac-
Table 2. Preparation of 14-aryl or alkyl-14H-dibenzo[a,j]xanthenes
Mp/˚C
Entry
R
Time (min)
Yield (%)
Product
Found
Reported
1
2
3
4
5
6
7
8
9
H
120
25
83
90
93
89
92
94
94
84
86
3a
3b
3c
3d
3e
3f
182-185
312-315
211-214
214-217
287-289
143-145
225-228
310-313
>160(dec)
181-183 [23]
311-312 [23]
211-212 [23]
215-216 [23]
288-289 [23]
141-143 [24]
228-229 [23]
4-NO2
3-NO2
2-Cl
40
120
60
4-Cl
4-OH
4-Me
4-CHO
3-CHO
55
50
3g
3h
3i
36
310-312 [24]
-
30

Synthesis of 14-Aryl-14H-Dibenzo[a,j]xanthene
Letters in Organic Chemistry, 2011, Vol. 8, No. 8
575
O
CHO
OH
+
O
Cu(CH3CN)4PF6(20% mol)
Solvent-free, 80 oC
(0%)
CHO
CHO
(4 mmol)
(1 mmol)
O
(84%)
Scheme 2.
Table 3. Comparison of the Efficiencies of Various Catalysts Used in the Synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes
Catalyst
Conditions/T/ꢀC
Time/h
Yield/%
Reference
Montmorillonite K10
SelectfluorTM
Solvent-free/120
Solvent-free/125
Solvent-free/125
Solvent-free/90
Solvent-free/125
Solvent-free/125
Solvent-free/100
Solvent-free/80
2–4
6–12
2.5–6
2–5
75–89
90–95
80–96
85–95
90–95
80–94
78–91
83-94
26
25
p-Toluenesulfonic acid
I2
9
13
11
Sulfamic acid
Amberlyst-15
Dowex-50W
6–12
0.5–2
1–2
16
14
Cu(CH3CN)4PF6
0.5-2
This work
tion times, good yields, solvent-free condition, and it follows
along the line of green chemistry. This protocol could serve
as a valuable alternative to known reaction systems.
3-(14H-Dibenzo[a,j]xanthene-14-yl)benzaldehyde: (3i)
White crystals; yield 0.33 g (86%); M.p. 260>˚C (dec.);
IR (KBr, cm-1): 1691, 1590, 1245; MS (70 eV): m/z = 386
(M+), 282, 281, 252, 141; 1H NMR (200 MHz, DMSO-d6, ꢁ,
ppm): 6.22 (1H, s, CH), 6.63-8.00 (14H, m, H-Ar), 8.67 (2H,
d, J=8.2 Hz, H-Ar), 9.88 (1H, s, CHO); 13C NMR (50 MHz,
DMSO-d6, ꢁ, ppm): ꢁ = 37.6, 117.1, 118.16, 123.5, 124.7,
125.2, 126.6, 127.9, 128.2, 129.8, 131.0, 132.0, 147.0, 148.4,
153.1, 155.5, 161.8, 195.4.
EXPERIMENTAL SECTION
General Procedure for the Synthesis of Bicyclic Phos-
phonates 4a-i
To a mixture of ꢀ-naphthol (2 mmol) and aldehydes (1
mmol), Cu(CH3CN)4PF6 (0.074 g, 0.2 mmol) was added and
the reaction mixture was heated at 80 ˚C. for the appropriate
time (Table 2). After completion reaction indicated by TLC,
the mixture was cooled to 25 ˚C, dichloromethane was added
and the mixture stirred for 5 min. Products were filtered and
recrystallized from aqueous ethanol.
ACKNOWLEDGMENTS
We gratefully acknowledge financial support from the
Iran National Science Foundation (INSF) and Research
Council of Razi University.
All the products (except 3i) are known compounds,
1
which were characterized by IR and H-NMR spectral data
and their mp’s compared with literature reports.
DISCLOSURES
It should be noted that the synthesis of 14-alkyl or aryl
14H-dibenzo[a.j]xanthene derivatives were published by

576 Letters in Organic Chemistry, 2011, Vol. 8, No. 8
Soleimani et al.
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