Convenient synthesis of 14-Aryl-14-H-dibenzo[a, j]xanthenes catalyzed by acyclic bro*?nsted acidic ionic liquid [H-NMP]+ [HSO 4]- under microwave irradiation

Article abstract of DOI:10.1002/jccs.201300019

Efficient method for direct preparation of 14-aryl-14-H-dibenzo[a, j]xanthenes through condensation of-naphthol with various aromatic aldehydes in the presence of the catalytic amount of [H-NMP]+[HSO4]- under microwave irradiation was described. This meth

Full text of DOI:10.1002/jccs.201300019

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
Convenient Synthesis of 14-Aryl-14-H-dibenzo[a,j]xanthenes Catalyzed by Acyclic
Brønsted Acidic Ionic Liquid [H–NMP]+[HSO4]- under Microwave Irradiation
Hossein Naeimi* and Zahra Sadat Nazifi
Department of Organic Chemistry, Faculty of Chemistry, University of Kashan, Kashan 87317, I.R. Iran
(Received: Jan. 7, 2013; Accepted: Apr. 1, 2013; Published Online: ??; DOI: 10.1002/jccs.201300019)
Efficient method for direct preparation of 14-aryl-14-H-dibenzo[a,j]xanthenes through condensation of
b-naphthol with various aromatic aldehydes in the presence of the catalytic amount of [H–NMP]+[HSO4]-
under microwave irradiation was described. This method has the advantages such as; very easy reaction
workup, absolute separation of catalyst from the reaction mixture and smooth recyclability of catalyst. In
this reaction 14-aryl-14-H-dibenzo[a,j]xanthenes were obtained as desired products in excellent yields
and short reaction times via green and one-pot procedure.
Keywords: b-Naphthol; Aromatic aldehyde; Ionic liquid; Microwave irradiation; Xanthene.
INTRODUCTION
Microwave-assisted organic synthesis (MAOS) has
hydes in the presence of p-toluenesulfonic acid,19,20 molec-
ular iodine,21 K5CoW12O40.3H2O/silica-gel/MW,22 LiBr/
MW,23 amberlyst-15,24 a-iodoacetates from alkenes/am-
monium acetate/I2,25 cation exchange resins26 as catalyst
isonitriles,27 silicasulfuric acid.28 The synthesis of hetero-
cycles under microwave irradiation has attracted much at-
tention in synthetic organic chemistry. However, many of
these methods suffer a drawback, including prolonged re-
action times, low yield, harsh reaction conditions, toxic
organic solvents and excess amount of catalysts.
been known since 1986.1 This “non-conventional” syn-
thetic method has shown broad applications as a very con-
venient way to accelerate the course of many organic reac-
tions, producing high yields and short reaction times, lower
quantities of side products and easier work-up and forma-
tion of cleaner products. MAOS is considered as a “green”
technology, principally since many organic reactions can
be carrying out in solvent-free conditions.2-3 Xanthenes es-
pecially benzoxanthenes, has emerged as a powerful tool in
organic synthesis due to their wide range of useful pharma-
cological activity such as antibacterial,4 anti-inflamma-
tory,5 antiviral properties.6 Furthermore, these heterocyclic
compounds are used as photodynamic therapy7 and also
utilized for antagonism of the paralyzing action of zoxazol-
amine. Benzoxanthenes are used as dyes,8 laser technol-
ogy,9 and in fluorescent materials for visualization of
biomolecules.10 These compounds have been synthesized
by many procedures. Some of the important methods are
include, trapping of benzynes by phenol,11 intermolecular
phenyl carbonyl coupling reactions of aldehydes and
b-naphthol,12 cyclodehydrations,13 carbon monoxide.14
Furthermore, the reaction of aryloxymagnesium halides
with triethylorthoformate,15 intra molecular phenyl car-
bonyl coupling reactions of benzaldehydes and acetophen-
ones,16 cyclization of polycyclic aryltriflate esters,17 and
2-tetralone.18
In this research, we hope to develop a simple, effi-
cient method for synthesis of 14-aryl-14-H-dibenzo[a,j]
xanthenes by treatment of b-naphthol and aromatic alde-
hydes in the presence of an ionic liquid as homogeneous
catalyst under mild conditions.
RESULTS AND DISCUSSION
In this research, in order to optimization of reaction
conditions, it was carried out the reaction of b-naphthol
and 3-nitrobezaldehyde in a 2:1 ratio as a model substrate
in the presence of various catalytic amounts of [H-
NMP]+[HSO4]- as a homogeneous catalyst under micro-
wave irradiation at different powers (Scheme I).
The obtained results from the reaction of determining
the optimum power are presented in Table 1. As it can be
seen in this reaction, the best results were obtained using
power of 450 W. After optimization of the different pow-
ers, the reaction of b-naphthol with several aldehydes was
carried out in various solvents. The best results were ob-
tained using ethanol solution (Table 2, entry 4).
The most common synthesis of xanthenes are in-
cluded the preparation of 14-H-dibenzo[a,j]xanthene has
been reported by condensation of b-naphthol and alde-
After optimization of the reaction conditions, in order
* Corresponding author. Fax: +983615552935; Email: naeimi@kashanu.ac.ir
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1

Article
Naeimi and Nazifi
Table 1. The synthesis of 3g under microwave at different
Reaction of b-naphthol and 3-nitrobezalde-
Scheme I
powers in ethanol
hyde
Entry
Power
Time (min)
Yielda (%)
1
2
3
4
100
180
300
450
20
10
6
30
50
65
95
4
[a] Isolated yields.
to develop this protocol the reaction of b-naphthol with
several aldehydes was carried out in according to the gen-
eral experimental procedure. The corresponding products
are summarized in Table 3. As it can be seen in this Table,
the best activity of aromatic aldehyde was shown in the
presence of an electron-withdrawing substituent (such as
–NO2) in the para position. The presence of electron-donat-
ing substituent (such as –OH) was decreased both the reac-
tion rate and the yield of product (Table 3, entry 11).
In this study, 14-aryl-14-H-dibenzo[a,j]xanthenes as
products in a new method were prepared using the model
reaction of b-naphthol and various aromatic aldehyhes in
the presence of the homogeneous catalytic amount of
[H–NMP]+[HSO4]- (20 mol %) at 450 W microwave irradi-
ation in ethanol. After the separation of the product, the cat-
alyst as a by-product is removable by washing with water,
and easily recycled to catalyze the preparation of 14-aryl-
14-H-dibenzo[a,j]xanthenes with excellent yields.
Table 2. The synthesis of 3g in different solvents under micro-
wave irradiation (450 W)
Entry
Solvent
Time (min)
Yielda (%)
1
2
3
4
H2O
CH2Cl2
DMF
11
9
10
50
30
95
8
EtOH
4
[a] Isolated yields.
Table 3. One-pot synthesis of various 14-aryl-14-H-dibenzo[a,j]
xanthenes using the catalytic amount of [H–NMP]+
[HSO4]- as catalyst under microwave irradiation at 450
W
Entry
Aldehyde
Product Time (min)
Yielda
1
C6H5
o–Cl.C6H4
3a
3b
3c
3d
3e
3f
4
5
93
87
96
92
90
86
95
97
95
90
78
88
85
86
83
2
3
p–Cl.C6H4
3.5
4.5
4
4
2,4–Cl2.C6H4
2,3–Cl2.C6H4
o–NO2.C6H4
m–NO2.C6H4
p–NO2.C6H4
4–Cl–3–NO2.C6H3
m–OH.C6H4
p–OH.C6H4
m–Me.C6H4
p–Me.C6H4
The reusability of catalyst was studied through the
completely separation of solid products (3g) with water.
Then, the water containing Brønsted acidic ionic liquid
(BAILs is soluble in water) was evaporated under vacuum
and the catalyst was recycled for several times without any
decrease in catalytic activity; the yields ranged from 95%
to 86% (Fig. 1).
5
6
4
7
3g
3h
3i
3.5
3
8
9
3.5
6
10
11
12
13
14
15
3j
3k
3l
7
5.5
5.5
6.5
6
3m
3n
3o
The structures of products were confirmed by spec-
troscopic and physical data such as; IR, 1H NMR, 13C NMR
m–OMe.C6H4
p–OMe.C6H4
[a] Isolated yields.
and UV-vis. The infrared spectra of the 14-(phenyl)-14-
H-dibenzo[a,j]xanthene exhibit a band at 1248 cm-1 as-
signed to u (C–O). In the 1H NMR spectra the signal around
d = 6.98-8.41 ppm is assigned to the protons of the aromatic
rings u (CH=CH), the signal of the aliphatic rings u (CH) is
shown at 6.5 ppm and the 13C NMR spectrum, the signal
around d = 117.34-148.74 ppm is assigned to the carbons of
the aromatic rings (CH=CH) and the signal of the aliphatic
rings u (CH) is shown at 38.07 ppm.
Fig. 1. Reusability of the catalyst in the synthesis of
3g.
2
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Synthesis of 14-Aryl-14-H-dibenzo[a,j]xanthenes
The proposed reaction mechanism
purity determination of the substrates and reaction monitoring
were accomplished by TLC on silica-gel polygram SILG/UV 254
plates (from Merck Company).
A plausible mechanism in the formation of 14-aryl-
14-H-dibenzo[a,j]xanthenes is presented in Scheme II. As
it can be seen, the reaction likely proceeds via initial forma-
tion of carbocation (1). Then, the oxonium species (2) is
formed in the reaction with b-naphthol, which undergoes
dehydration to afford the desired product (3).
General procedure for the synthesis of [H–NMP]+[HSO4]-.
1-Methyl-2-pyrolidone (0.2 mol) was charged into a 250 mL three
necked flask with a magnetic stirrer. Then equimolar concen-
trated sulfuric acid (98 wt %) was added drop wise slowly into the
flask at 80 °C for 12 h. The mixture was washed by diethyl ether
three times to remove non-ionic residues and dried in the vacuum
by a rotary evaporator to obtain the viscous clear [H–NMP]+
[HSO4]-.29
Scheme II Proposed reaction mechanism
General procedure for the synthesis of 14-aryl-14-H-di-
benzo[a,j]xanthenes. To a mixture of an aldehyde (1 mmol),
b-naphthol (2 mmol, 0.288 g), [H–NMP]+[HSO4]- (20 mol %),
EtOH as solvent was added and the mixture was inserted in a mi-
crowave oven and heated at 450 W for the appropriate time (Table
1) to yield the desired products. The progress of the reactions was
monitored by TLC (ethyl acetate/petroleum ether 3/7).
14-(Phenyl)-14H-dibenzo[a,j]xanthene (3a). Pale yellow
solid, m.p = 183-184 oC, (m.p = 182-183 oC),30 Uv-vis (CH2Cl2)
lmax: 244, 230; 1H NMR (CDCl3, 400 MHz) d: 6.5 (s, 1H, CH),
6.98-7.01 (t, 1H, J = 7.6 Hz, Ar), 7.13-7.17 (t, 2H, J = 7.6 Hz, Ar),
7.40-7.43 (t, 2H, J = 7.6 Hz, Ar), 7.48-7.54 (m, 4H, Ar), 7.56-7.60
(t, 2H, J = 7.2 Hz, Ar), 7.92-7.81 (d, 2H, J = 8.8 Hz, Ar), 7.82-
CONCLUSIONS
7.84 (d, 2H, J = 8.0 Hz, Ar), 8.39-8.41 (d, 2H, J = 8.8 Hz, Ar); 13
C
In this paper, we have described the synthesis of 14-
aryl-14-H-dibenzo[a,j]xanthenes using b-naphthol with
substituted aromatic aldehydes. This reaction was per-
formed in the presence of catalytic amount of [H–
NMP]+[HSO4]- as an efficient, inexpensive, non-toxic,
easy work-up and reusable catalyst make the present proce-
dure eco-friendly and economically acceptable.
NMR (CDCl3, 100 MHz) d: 148.74, 145.03, 131,48, 131.07,
128.88, 128.82, 128.5, 128.29, 126.81, 126.41, 124.26, 122.72,
118.04, 117.34, 38.07; IR (KBr) u (cm–1): 3061, 1624, 1592,
1513, 1458, 1410, 1248, 1078, 962, 805, 744. 14-(2-Chlorophen-
yl)-14H-dibenzo[a,j]xanthene (3b). White solid, m.p = 212-213
oC, (m.p = 214-215 oC)30, UV–vis (CH2Cl2) lmax: 246, 230; 1H
NMR (CDCl3, 400 MHz) d: 6.81 (s, 1H, CH), 6.92 (m, 2H, Ar),
7.40-7.44 (m, 3H, Ar), 7.48-7.51 (d, 2H, J = 8.8 Hz, Ar), 7.61-
7.64 (m, 5H, Ar), 8.74-8.76 (d, 2H, J = 8.4 Hz, Ar); 13C NMR
(CDCl3, 100 MHz) d: 148.95, 143.59, 131.83, 130.91, 130.15,
129.61, 129.06, 128.67, 127.95, 127.88, 126.94, 124.45, 123.49,
118.12, 118.01, 34.65; IR (KBr) u (cm–1): 3059, 1625, 1592,
1461, 1400, 1243, 1032, 959, 808. 14-(4-Chlorophenyl)-14H-di-
benzo[a,j]xanthene (3c). Yellow solid, m.p = 289-290 oC, (m.p =
287-288 oC),30 UV–vis (CH2Cl2) lmax: 244, 230; 1H NMR
(CDCl3, 400 MHz) d: 6.48 (s, 1H, CH), 7.10-7.12 (d, 2H, J = 8.4
Hz, Ar), 7. 41-7.47 (m, 4H, Ar), 7.48-7.50 (d, 2H, J = 8.8 Hz, Ar),
7.57-7.61 (t, 2H, J = 7.6 Hz, Ar), 7.80-7.82 (d, 2H, J = 8.8 Hz, Ar),
7.84-7.86 (d, 2H, J = 8.0 Hz, Ar), 8.32-8.34 (d, 2H, J = 8.4 Hz,
Ar); 13C NMR (CDCl3, 100 MHz) d: 148.51, 145.01, 131.39,
131.31, 131.20, 130.18, 129.83, 129.19, 128.91, 127.60, 125.14,
123.77, 118.21, 117.50, 39.87; IR (KBr) u (cm–1): 3067, 1624,
EXPERIMENTAL
Materials. All commercially available reagents were used
without further purification and purchased from the Merck Chem-
ical Company in high purity. The used solvents were purified by
standard procedure.
Apparatus. IR spectra were obtained as KBr pellets on a
Perkin–Elmer 781 spectrophotometer and on an impact 400
Nicolet FT–IR spectrophotometer. 1H NMR and 13C NMR were
recorded in CDCl3 solvents on a Bruker DRX-400 spectrometer
with tetramethylsilane as internal reference. Uv–vis spectra were
obtained with a Perkin–Elmer 550 was recorded in CDCl3 sol-
vents. Melting points were obtained with a Yanagimoto micro
melting point apparatus are uncorrected. Microwave irradiations
were carried out in microwave oven specially designed for or-
ganic synthesis (Milestone LAVIS 1000 Basic Microwave). The
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Naeimi and Nazifi
o
dibenzo[a,j]xanthene (3i). Yellow solid, m.p = 232-234 C,
1591, 1514, 1585, 1431, 1243, 1085, 961, 808, 743. 14-(2,4-Di-
chlorophenyl)-14H-dibenzo[a.j]xanthene (3d). Pale yellow
solid, m.p = 229-230 oC, (m.p = 227-228 oC),30 UV–vis (CH2Cl2)
lmax: 248, 230; 1H NMR (CDCl3, 400 MHz d: 6.77 (s, 1H, CH),
6.90-6.92 (d, 1H, Ar), 7.28-7.32 (m, 2H, Ar), 7.43-7.50 (m, 4H,
Ar), 7.61-7.65 (t, 2H, J = 7.6 Hz, Ar), 7.81-7.85 (t, 4H, J = 9.0 Hz,
Ar), 8.65-8.67 (d, 2H, J = 8.0 Hz, Ar); 13C NMR/ (CDCl3, 100
MHz) d: 148.9, 142.25, 132.8, 132.71, 132.6, 130.92, 130.59,
129.3, 128.78, 128.41, 127.06, 124.57, 123.17, 118.11, 117.46,
34.24; IR (KBr) u (cm–1): 3061, 1622, 1591, 1514, 1464, 1430,
1401, 1247, 1103, 1072, 960, 864, 836, 807, 743. 14-(2,3-Di-
chlorophenyl)-14H-dibenzo[a,j]xanthene (3e). White solid,
UV–vis (CH2Cl2) lmax: 246, 232; 1H NMR (CDCl3, 400 MHz) d:
7.27 (s, 1H, CH), 7.29-7.31 (d, 1H, J = 8.4 Hz, Ar), 7.45-7.52 (m,
4H, Ar), 7.62-7.65 (m, 3H, Ar), 7.84-7.89 (t, 4H, J = 9.2 Hz, Ar),
8.03-8.04 (d, 1H, J = 2.0 Hz, Ar), 8.24-8.26 (d, 2H, J = 8.4 Hz,
Ar); IR (KBr) u (cm–1): 3054, 1623, 1592, 1530, 1462, 1350,
1246, 952, 812, 742. 14-(4-Hydroxyphenyl)-14H-dibenzo[a,j]
o
xanthene (3k). Pink solid, m.p = 137-138 C, (m.p = 138-140
oC),32 1H NMR (CDCl3, 400 MHz) d: 4.97 (br s, 1H, OH), 6.43 (s,
1H, CH), 6.55-8.36 (m, 16H, Ar); 13C NMR (CDCl3, 100 MHz) d:
37.41, 115.70, 118.00, 118.39, 123.10, 124.62, 127.23, 129.11,
129.20, 129.78, 131.53, 131.81, 137.90, 149.11, 154.24; IR (KBr)
u (cm–1): 3404,1592, 1511, 1401, 1250, 1242, 816. 14-(4-Meth-
yl)-14H-dibenzo[a,j]xanthene (3m). Pale yellow solid, m.p =
228-230 oC, (m.p = 227-228 oC),30 UV–vis (CH2Cl2) lmax: 247,
232; 1H NMR (CDCl3, 400 MHz) d: 6.46 (s, 1H, CH), 6.95-6.97
(d, 2H, J = 8.0 Hz, Ar), 7.39-7.43 (m, 4H, Ar), 7.47-7.50 (d, 2H, J
= 9.2 Hz, Ar), 7.56-7.6 (t, 2H, J = 9.2 Hz, Ar), 7.78-7.80 (d, 2H, J
= 8.8 Hz, Ar), 7.82-8.84 (d, 2H, J = 8.0 Hz, Ar), 8.39-8.41 (d, 2H,
J = 8.8 Hz, Ar); 13C NMR (CDCl3, 100) d: 20.91, 37.64, 117.46,
118.02, 122.72, 124.22, 126.77, 128.11, 128.77, 128.79, 129.19,
131.08, 131.46, 135.91, 142.14, 148.68; IR (KBr) u (cm–1): 3069,
1623, 1591, 1531, 1458, 1399, 1244, 961, 810, 741
1
m.p = 250-253 oC, UV–vis (CH2Cl2) lmax: 248, 230; H NMR
(CDCl3, 400 MHz) d: 6.85 (s, 1H, CH), 6.87-6.89 (d, 1H, J = 8.0
Hz, Ar); 7.09-7.11 (d, 2H, J = 8.8 Hz, Ar), 7.32-7.35 (d, 1H, J =
9.0 Hz, Ar), 7.44-7.51 (m, 4H, Ar), 7.62-7.85 (t, 4H, J = 9.2 Hz,
Ar), 8.69-8.67 (d, 2H, J = 8.40 Hz, Ar); IR (KBr) u (cm–1): 3057,
1625, 1593, 1514, 1459, 1405, 1401, 1251, 1107, 1070, 962, 869,
813, 807, 746. 14-(2-Nitrophenyl)-14H-dibenzo[a,j]xanthene
o
o
(3f). Yellow solid, m.p = 213-214 C, (m.p = 214-215 C),30
UV–vis (CH2Cl2) lmax: 244, 230; 1H NMR (CDCl3, 400 MHz) d:
7.08 (t, 1H, J = 8.0 Hz, CH), 7.23-7.27 (t, 1H, J = 7.2 Hz, Ar),
7.42-7.46 (t, 2H, J = 7.2 Hz, Ar), 7.42-7.49 (m, 3H, Ar), 7.57-7.63
(m, 3H, Ar), 7.81-7.84 (m, 4H, Ar), 8.53-8.55 (d, 2H, J = 8.4 Hz,
Ar); 13C NMR (CDCl3, 100 MHz) d: 149.4, 147.03, 140.87,
134.14, 132.26, 131.72, 130.97, 129.47, 128.73, 127.59, 127.41,
124,92, 124,67, 122.58, 118.03, 117.58; IR (KBr) u (cm–1): 3057,
1625, 1593, 1500, 1397, 1346, 1305, 817, 750. 14-(3-Nitrophen-
yl)-14H-dibenzo[a,j]xanthene (3g). Yellow solid, m.p = 212-
213 oC, (m.p = 210-211 oC),30 UV–vis (CH2Cl2) lmax: 246, 228;
1H NMR (CDCl3, 400 MHz) d: 6.62 (s, 1H, CH), 7.28-7.32 (t, 1H,
J = 7.6 Hz, Ar), 7.43-7.47 (t, 2H, J = 7.6 Hz, Ar), 7.51-7.53 (d, 2H,
J = 8.8 Hz, Ar), 7.60-7.64 (t, 2H, J = 7.2 Hz, Ar), 7.81-7.87 (m,
ACKNOWLEDGEMENTS
The authors are grateful to University of Kashan for
supporting this work by Grant No. 159148/14.
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