Trityl bromide versus nano-magnetic catalyst in the synthesis of henna-based xanthenes and bis-coumarins

Article abstract of DOI:10.1007/s13738-017-1155-4

Abstract: In this work, trityl bromide (TrBr) as a new, efficient, mild and neutral catalyst was used for the synthesis of henna-based xanthenes (aryl-5H-dibenzo[b,i]xanthene-5,7,12,14(13H)-tetraones) and bis-coumarins by in situ generation of trityl carb

Full text of DOI:10.1007/s13738-017-1155-4

J IRAN CHEM SOC
DOI 10.1007/s13738-017-1155-4
ORIGINAL PAPER
Trityl bromide versus nano‑magnetic catalyst in the synthesis
of henna‑based xanthenes and bis‑coumarins
Mahmoud Zarei1 · Mohammad Ali Zolfgol1 · Ahmad Reza Moosavi‑Zare2 ·
Ehsan Noroozizadeh1
Received: 28 December 2016 / Accepted: 12 June 2017
© Iranian Chemical Society 2017
Abstract In this work, trityl bromide (TrBr) as a new, eff-
cient, mild and neutral catalyst was used for the synthesis
of henna-based xanthenes (aryl-5H-dibenzo[b,i]xanthene-
5,7,12,14(13H)-tetraones) and bis-coumarins by in situ
generation of trityl carbocation under solvent-free condi-
tions in comparison with [Fe3O4@SiO2@(CH2)3-Im-SO3H]
Cl as an acidic and reusable catalyst for the frst time.
Graphical Abstract
Electronic supplementary material The online version of this
article (doi:10.1007/s13738-017-1155-4) contains supplementary
material, which is available to authorized users.
* Mahmoud Zarei
mahmoud8103@yahoo.com
* Mohammad Ali Zolfgol
zolf@basu.ac.ir; mzolfgol@yahoo.com
* Ahmad Reza Moosavi-Zare
moosavizare@yahoo.com
1
Department of Organic Chemistry, Faculty of Chemistry,
Bu-Ali Sina University, Hamedan 6517838683, Iran
2
Sayyed Jamaleddin Asadabadi University,
Asadabad 6541835583, Iran
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J IRAN CHEM SOC
Keywords Trityl bromide · [Fe3O4@SiO2@(CH2)3-
Im-SO3H]Cl · Bis-coumarin · Henna-based xanthene ·
Organocatalyst
bis-coumarins through the Domino Knoevenagel–Michael
condensation reactions of aldehydes with two equivalents
of 4-hydroxycoumarin. This reaction can be catalyzed by
both acidic and basic catalysts such as silica-supported
Preyssler nanoparticles [28], CuO–CeO2 nano-composite
[29], basic ionic liquid tetramethylguanidinium acetate
[30], poly(4-vinylpyridine) and 1,4-butanesultone) [31],
propane-1,2,3-triyl tris(hydrogen sulfate) [32], silica-
supported perchloric acid nanoparticles [33], RuCl3·nH2O
[34], SO3H-functionalized ionic liquids based on benzimi-
dazolium cation [35], sodium dodecyl sulfate (SDS) [36]
and tetrabutylammonium bromide [37]. Most of these cata-
lytic systems have acidic or basic nature and often suffer
from high reaction temperature, low yield, long reaction
time and necessary refuxing in volatile organic solvents.
Thus, a great demand is needed to develop neutral catalytic
systems which can effciently catalyze this type of reac-
tions under mild reaction conditions.
With this issue in our mind and in our continuous
research on the use of trityl chloride [38–46] and magnetic
nanoparticles (MNPs) [47–54] as catalysts in the organic
synthesis, we have reported the frst catalytic application of
trityl bromide as an organocatalyst versus nano-magnetic
particles catalyst of [Fe3O4@SiO2@(CH2)3-Im-SO3H]
Cl (Scheme 1) in the synthesis of aryl-5H-dibenzo[b,i]
xanthene-5,7,12,14(13H)-tetraone leuco-dye and bis-cou-
marins by the condensation reaction of 2-hydroxynaphtha-
lene-1,4-dione (2 mmol) or 4-hydroxy cumarin (2 mmol)
with various aldehyde(1 mmol) under solvent-free condi-
tions (Schemes 2, 3).
Introduction
Among catalysts, organocatalysts can be used as a power-
ful synthetic paradigm which could be replaced with metal
to catalyze chemical transformations. Also, in comparison
with transition-metal catalysts, the cost and toxicity of
organocatalysts are low [1]. Therefore, making new organo-
catalysts is useful to prepare pharmaceutical intermedi-
ates and biological products [2]. Recently, comprehensive
reviews have covered the recent development in designing,
improvement and validation of more effcient organocata-
lytic domino, tandem and cascade strategies as effective
alternative tools for the creation of at least one chiral center
[3–5]. Biological-based organocatalysts such as urea- or
thiourea-based catalysts [6], chitosan, chemically modifed
chitosan, blended chitosan, or other biopolymers, such as
alginate with its carboxylic groups or carrageenan with its
sulfonate groups, have been emerged that are tightly con-
nected to green and sustainable chemistry [7]. On the other
hand, limitations in the recyclability and reusability of
organocatalysts are the major drawback for their applica-
tions in chemical processes: chemists design, synthesis and
development of magnetic nanoparticles (MNPs) and their
derivatives as a reusable catalysts for solving the above
mentioned limitation of organocatalysts. Moreover, appli-
cations of MNPs, as versatile inorganic support for organic
and inorganic materials, have appeared as a potent branch
in the feld of green chemistry. Utilizing MNPs as supports
for immobilization of organocatalysts can add various mer-
its to homogeneous nature of them and make them pow-
erful and easy recoverable heterogeneous active catalysts
[8–18].
Henna (2-hydroxynaphthalene-1,4-dione) refers to the
dye which is derived from the henna plant. It has been used
for various purposes such as dyeing of skin, hair, fnger-
nails, fabrics, silk, wool and leather. 2-Hydroxynaphtha-
lene-1,4-dione has been also used in the synthesis of azo
dyes and their copper complexes [19, 20], leuco-dye [21–
23], spiro[dibenzo[b,i]xanthene-13,30-indoline]-pentaones
and 5H-dibenzo[b,i]xanthene-tetraones [24].
Bis-coumarins, as an important kind of vitamin K antag-
onists, have various biological activities such as anti-HIV,
anti-bacterial, antioxidant, anticancer, and anticoagulant
activities [25]. Recently, Li and coworkers have reported
a good range of bis-coumarin derivatives which success-
fully show anti-tumor and anti-bacterial activities [25–27].
Several methods have been reported for the synthesis of
Experimental
General
Melting points were measured on an Electrothermal
9100 apparatus and are uncorrected. 1H NMR spectra
were recorded by a Bruker BioSpin GmbH spectrometer
at 400 MHz and 13C NMR spectrometer at 100 MHz. IR
spectra were recorded by a Bomem MB-Series FTIR spec-
trophotometer. All chemicals used in this work were pur-
chased from Merck chemical company.
General procedure for the preparation
of [nano‑Fe3O4@SiO2@(CH2)3‑Im‑SO3H]Cl
as a heterogeneous acidic catalyst
At frst magnetic nanoparticles of Fe3O4 and Fe3O4@SiO2
were synthesized according to the previous reported litera-
ture. Then, a mixture of Fe3O4@SiO2 (1 mmol), (3-chlo-
ropropyl) triethoxysilane (0.806 g, 3.3 mmol) and 30 mL
of dry toluene was added in a 50-mL round-bottomed
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J IRAN CHEM SOC
Scheme 1 Preparation of [nano-Fe3O4@SiO2@(CH2)3-Im-SO3H]Cl (NMPs)
Scheme 2 The preparation
of henna-based xanthenes
(aryl-5H-dibenzo[b,i]xanthene-
5,7,12,14(13H)-tetraones)
catalyzed by TrBr or [Fe3O4@
SiO2@(CH2)3-Im-SO3H]Cl
Scheme 3 The preparation
of bis-coumarins catalyzed by
TrBr or [Fe3O4@SiO2@(CH2)3-
Im-SO3H]Cl
fask connected to a refux condenser and refuxed under
nitrogen for 12 h. The obtained Fe3O4@SiO2@(CH2)3Cl
(grafted with chloropropyl group) was fltered, washed
twice with dry toluene and anhydrous diethyl ether and
dried at 80 °C for 6 h under vacuum. In the next step,
imidazole (0.491 g, 7 mmol) in 50 mL of dry toluene
was added to the Fe3O4@SiO2@(CH2)3Cl and the pre-
pared mixture was refuxed for 12 h. The obtained solid
was fltered, washed and dried according to same proce-
dure to create Fe3O4@SiO2@(CH2)3-Im. Finally, a solu-
tion of chloro sulfonic acid (0.456 mL, 1.165 g, 7 mmol)
in dry dichloromethane (10 mL) was added dropwise
to the suspension of {Fe3O4@SiO2@(CH2)3-Im}, and
the reaction mixture was stirred for 6 h, then fltered and
washed to give [nano-Fe3O4@SiO2@(CH2)3-Im-SO3H]Cl
(Scheme 1).
Typical procedure for the preparation
of 13‑aryl‑5H‑dibenzo [b,i]
xanthene‑5,7,12,14(13H)‑tetraone in the presence
of TrBr (A) and [Fe3O4@SiO2@(CH2)3‑Im‑SO3H]Cl (B)
Method A A mixture of 2-hydroxynaphthalene-1,4-dione
(0.348 g, 2 mmol), aldehyde (1 mmol) and TrBr ((0.0483 g,
15 mol%), in a 10-mL round-bottomed fask connected to
a refux condenser was heated and stirred at 100 °C in the
absence of solvent. The reaction was monitored by TLC.
After the completion of the reaction as monitored by TLC,
the reaction mixture was washed with petroleum ether
(15 mL) and fltered to separate the catalyst (the catalyst
was soluble in petroleum ether and the product was not sol-
uble in this solvent). The residue was recrystallized from
EtOH to afford the pure product (Scheme 2).
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J IRAN CHEM SOC
Method B A mixture of 2-hydroxynaphthalene-1,4-dione
(0.348 g, 2 mmol), aldehyde (1 mmol) and [Fe3O4@
SiO2@(CH2)3-Im-SO3H]Cl (8 mg), in a 10-mL round-
bottomed fask connected to a refux condenser, was
heated and stirred at 100 °C in the absence of solvent.
After the completion of the reaction as monitored by
TLC, the reaction mixture was dissolved in hot EtOH
Method B A mixture of 4-hydroxycoumarin (0.324 g,
2 mmol), aldehyde (1 mmol) and [Fe3O4@SiO2@(CH2)3-Im-
SO3H]Cl (7 mg) in a 10-mL round-bottomed fask connected
to a refux condenser, was heated and stirred at 100 °C in the
absence of solvent. After the completion of the reaction as
monitored by TLC, the reaction mixture was dissolved in hot
EtOH and [Fe3O4@SiO2@(CH2)3-Im-SO3H]Cl catalyst was
recovered magnetically. The crude product was recrystallized
from ethanol to afford the pure product (Scheme 3).
and
[Fe3O4@SiO2@(CH2)3-Im-SO3H]Cl
catalyst
was recovered magnetically. The crude product was
recrystallized from ethanol to afford the pure product
(Scheme 2).
Selected spectra of compounds
3,3′‑((4‑chlorophenyl)methylene)bis(4‑hydroxychro‑
man‑2‑one) White powder; Mp 260–262 °C; H NMR
Selected spectra of compounds
1
(400 MHz, DMSO-d6): δ (ppm): 6.38 (s, 1H), 7.20–7.23
(d, m, 2H), 7.28–7.4 (m, 6H), 7.59–7.63 (m, 2H), 7.93–7.96
(m, 2H); 13C NMR (100 MHz, DMSO-d6): 35.6, 104.6,
116.0, 117.2, 123.8, 123.9, 128.0, 128.7, 130.3, 132.2,
138.3, 152.1, 164.5, 164.7.
13‑Phenyl‑5H‑dibenzo[b,i]xanthene‑5,7,12,14(13H)‑
tetraone Red powder; Mp 304–306 °C; 1H NMR
(400 MHz, DMSO-d6): δ (ppm): 5.17 (s, 1H), 7.21–7.27
(m, 1H), 7.30–7.34 (m, 2H), 7.52 (d, J = 7.2 Hz, 2H),
7.79 (s, 1H), 7.93–7.96 (m, 2H), 8.00–8.05 (m, 2H),
8.01 (d, J = 4.8 Hz, 1H), 8.15–8.19 (m, 2H); 13C NMR
(100 MHz, DMSO-d6): δ (ppm): 33.05, 115.22, 123.16,
124.17, 125.98, 126.16, 127.11, 128.3, 128.69, 129.08,
129.31, 130.4, 130.66, 131.07, 131.71, 134.38, 134.69,
135.15, 141.38, 148.76, 155.04, 176.66, 176.83, 177.69,
182.69.
3,3′‑(pyridin‑4‑ylmethylene)bis(4‑hydroxychroman‑
2‑one) White powder; Mp: 270–274 °C; 1H NMR
(400 MHz, DMSO-d6): δ (ppm): 6.45 (s, 1H), 7.24–7.33
(m, 4H), 7.56 (t, J = 7.2 Hz, 2H), 7.81 (t, J = 8 Hz, 4H),
8.68 (d, J = 8 Hz, 2H); 13C NMR (100 MHz, DMSO-
d6): 37.7, 101.2, 115.7, 119.2, 123.2, 124.1, 125.2, 131.6,
140.7, 152.6, 164.0, 164.8, 168.0.
13‑(4‑Fluorophenyl)‑5H‑dibenzo[b,i]xanthene‑5,7,12,14
(13H)‑tetraone Yellow powder; Mp 268–270 °C; 1H
NMR (400 MHz, DMSO-d6): δ (ppm): 5.3 (s, 1H), 7.27
(t, J = 8 Hz, 2H), 7.69–7.70 (m, 2H), 7.99–8.20 (m, 8H);
13C NMR (100 MHz, DMSO-d6): δ (ppm): 33.05, 115.22,
123.16, 124.17, 125.98, 126.16, 127.11, 128.3, 128.69,
129.08, 129.31, 130.4, 130.66, 131.07, 131.71, 134.38,
134.69, 135.15, 141.38, 148.76, 155.04, 176.66, 176.83,
177.69, 182.69.
Results and discussion
At frst, to optimize the reaction conditions, the reaction
between 4-chloro benzaldehyde and 2-hydroxynaphtha-
lene-1,4-dione was selected as a model reaction and various
Table 1 Optimization reaction between 4-chloro benzaldehyde and
2-hydroxynaphthalene-1,4-dione using TrBr under solvent-free con-
dition
Entry Catalyst (mol%) Temperature °C Time (min) Yielda (%)
Typical procedure for the preparation of bis‑coumarin
in the presence of TrBr (A) and [Fe3O4@SiO2@
(CH2)3‑Im‑SO3H]Cl (B)
1
5
7
100
100
100
100
100
100
100
90
120
90
35
54
65
82
90
90
90
78
60
45
Trace
–
2
3
10
12
15
17
20
15
15
15
15
75
Method A A mixture of 4-hydroxycoumarin (0.324 g,
2 mmol), aldehyde (1 mmol) and TrBr ((0.0483 g,
15 mol %)), in a 10-mL round-bottomed fask connected
to a refux condenser, was heated and stirred at 100 °C
in the absence of solvent. After the completion of the
reaction as monitored by TLC, the reaction mixture was
washed with petroleum ether (15 mL) and fltered to sep-
arate the catalyst (the catalyst was soluble in petroleum
ether and the product was not soluble in this solvent).
The residue was recrystallized from EtOH to afford the
pure product. (Scheme 3)
4
60
5
45
6
45
7
45
8
65
9
70
80
10
11
12
50
90
rt
120
120
–
100
a
Isolated yield
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J IRAN CHEM SOC
Table 2 Optimization reaction between 4-chloro benzaldehyde and
2-hydroxynaphthalene-1,4-dione using [Fe3O4@SiO2@(CH2)3-Im-
SO3H]Cl under solvent-free condition
100 °C (Table 2, entry 4). No improvement was obtained
in the yield and reaction time using increasing the amount
of the catalyst (Table 1, entries 6, 7, Table 2, entries 5, 6).
Table 1 clearly shows that in the absence of catalyst, the
product was produced with low yield (Table 1, entry 12).
The acidic content of [Fe3O4@SiO2@(CH2)3-Im-SO3H]
Cl was characterized by the determination of its H+ of the
catalyst, through the titration with NaOH (0.01 mol/L).
For this purpose, 8 g of catalyst titrated by 1 mL of NaOH
(0.01 mol/L) and amounts of H+ in catalyst was obtained
0.01 mmol.
To compare the effect of the solution in comparison with
solvent-free condition, a mixture of 4-chloro benzaldehyde
and 2-hydroxynaphthalene-1,4-dione, as model reaction,
was tested using 15 mol% of TrBr, as a neutral organo-
catalyst or [Fe3O4@SiO2@(CH2)3-Im-SO3H]Cl in several
solvents such as H2O, C2H5OH, CH2Cl2, CHCl3 and tolu-
ene under refux condition. The results are summarized in
Table 3. The results displayed that solvent-free condition
was the best condition for this reaction (Table 3, entry 6).
To optimize the reaction conditions, the reaction
between benzaldehyde and 4-hydroxycoumarin (Scheme 3)
was chosen as a model reaction and various amounts of
TrBr as a neutral organocatalyst and [Fe3O4@SiO2@
(CH2)3-Im-SO3H]Cl as a heterogeneous nano-catalyst were
investigated in this reaction at different temperatures up to
Entry
Catalyst (mg) Temperature °C Time (min) Yielda (%)
1
1
3
100
100
100
100
100
100
70
50
35
28
12
11
11
24
30
60
60
35
54
65
92
92
92
73
61
21
70
2
3
6
4
8
5
10
12
8
6
7
8
8
50
9
10b
8
rt
8
100
a
b
Isolated yield. This reaction was carried out in the presence of
Fe3O4 in comparison with [Fe3O4@SiO2@(CH2)3-Im-SO3H]Cl
amounts of TrBr as a neutral organocatalyst and [Fe3O4@
SiO2@(CH2)3-Im-SO3H]Cl as a heterogeneous nano-cata-
lyst were investigated on this reaction at different tempera-
tures up to 100 °C under solvent-free conditions (Tables 1,
2). The worthy results were attained when the reaction was
achieved in the presence of 15 mol% of TrBr (Table 1,
entry 5) or 8 mg of [Fe3O4@SiO2@(CH2)3-Im-SO3H]Cl at
Table 3 The reaction of
Entry
Solvent
A: Catalyst (mol%)/B: (mg)
Temperature °C
Time (min) A/B
Yielda (%)
2-hydroxynaphthalene-1,4-
dione and 4-chlorobenzaldehyde
using TrBr (15 mol%) (method
A) and [Fe3O4@SiO2@(CH2)3-
Im-SO3H]Cl (8 mg) (method
B) in different solvents under
refux conditions
1
2
3
4
5
6
Ethanol
H2O
15/8
15/8
15/8
15/8
15/8
15/8
Refux
Refux
Refux
Refux
Refux
100
120/60
120/60
120/60
120/60
120/60
45/12
40/78
50/81
30/54
35/59
62/82
90/92
CH2Cl2
CHCl3
Toluene
–
a
Isolated yield
Table 4 Effect of different
amounts of the catalysts and
temperatures on the reaction
between 4-hydroxycoumarin
and benzaldehyde
Entry
A: Catalyst (mol%)/B: (mg)
Temperature °C
Time (min) A/B
Yielda (%)
1
2
–
80
80
80
80
80
90
70
50
rt
120
25
5/2
35/30
30/22
27/18
20/12
19/12
20/12
30/32
60/60
20/12
54/47
65/68
82/80
92/93
92/93
92/93
70/72
Trace
92/93
3
10/4
12/5
15/7
15/7
15/7
15/7
15/7
20/10
4
5
6
7
8
9
10
70
a
Isolated yield
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J IRAN CHEM SOC
Table 5 The preparation of
aryl-5H-dibenzo[b,i]xanthene-
5,7,12,14(13H)-tetraone by
using TrBr (method A) and
[Fe3O4@SiO2@(CH2)3-Im-
SO3H]Cl (method B)
Product
Time (min)
Method A/B
Yielda (%)
Method A/B
Mp. °C (Lit.)
50/15
85/87
304–306 (305–307) [21]
45/12
90/92
329–331 (330–332) [21]
50/10
85/92
350–353 (354–356) [36]
35/15
80/86
268–270 (270–272) [21]
40/14
55/10
60/18
86/88
80/89
90/91
330–333 (333–335) [21]
338–341 (340–342) [21]
243–246
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Table 5 continued
Product
Time (min)
Method A/B
Yielda (%)
Method A/B
Mp. °C (Lit.)
262–265
60/15
90/91
55/14
84/90
303–306 (304–307) [21]
60/15
75/86
307–309 (307–309) [36]
55/17
78/84
248–251
50/17
82/86
265–268
60/15
83/85
238–240
a
Isolated yield
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J IRAN CHEM SOC
Table 6 The preparation of bis-
coumarins using TrBr (method
A) and [Fe3O4@SiO2@(CH2)3-
Im-SO3H]Cl (method B)
Product
Time (min)
Method A/B
Yielda (%)
Method A/B
M p. °C (Lit.)
20/12
92/93
231–233 (230–232) [25]
O
O
O
O
OH
HO
18/10
91/94
259–261 (256–258) [25]
O
O
O
O
OH
HO
Cl
19/11
92/94
232–234 (232–234) [25]
O
O
O
O
OH
HO
O2N
22/14
89/91
260–262 (260–262) [25]
O
O
O
O
OH
HO
NC
28/18
85/87
205–207 (200–202) [25]
O
O
O
O
OH
HO
NO2
30/22
78/81
270–274 [25]
O
O
N
O
O
OH
HO
1 3

J IRAN CHEM SOC
Table 6 continued
Product
Time (min)
Method A/B
Yielda (%)
Method A/B
M p. °C (Lit.)
28/19
82/85
132–136 (133) [25]
O
O
O
O
OH
OH
NH
35/22
85/86
188–191 (190) [25]
HO
OH
O
O
O
O
O
40/27
76/79
188–191 [25]
O
O
O
OH
OH
HO
OH
O
O
O
O
a
Isolated yield
100 °C under solvent-free conditions (Table 4). As shown
in Table 4, the worthy results were obtained when the reac-
tion was carried out in the presence of 15 mol% of TrBr
or 7 mg of [Fe3O4@SiO2@(CH2)3-Im-SO3H]Cl at 70 °C
(Table 4, entry 7). No improvement was shown in the yield
and reaction time using increasing the amount of catalyst
and temperature (Table 4, entry 10). Table 4 clearly shows
that in the absence of catalyst, the product was produced
with low yield (Table 4, entry 1).
To explore the generality, scope and effciency of the
catalyst, we extended our study using TrBr (15 mol %)
and [Fe3O4@SiO2@(CH2)3-Im-SO3H]Cl (8 mg) with
different aromatic aldehydes under solvent-free condi-
tions to prepare a series of aryl-5H-dibenzo[b,i]xanthene-
5,7,12,14(13H)-tetraone derivatives (Table 5) and of bis-
coumarin derivatives (Table 6). Various aromatic aldehydes
containing electron withdrawing substituents, electron-
releasing substituents, halogens and hetero-aromatic alde-
hydes on their aromatic rings were utilized successfully in
the reaction and gave the corresponding products in high
yields and in short reaction times (Tables 5, 6). The struc-
tures of the desired obtained products were confrmed by
the IR, 1H and 13C NMR.
In a plausible mechanism (Scheme 4), aldehyde was
activated by the trityl bromide catalysts. Two resonance
forms of activated aldehyde could be produced and con-
verted together in a reversible reaction. To prove the for-
mation of I and II, 4-chlorobenzaldehyde was reacted with
trityl bromide at room temperature. Then, UV spectra of
the 4-chlorobenzaldehyde, trityl bromide and activated
4-chlorobenzaldehyde with trityl bromide were recorded
and maximum absorptions of them were appeared at
263, 235 and 314 nm, respectively (Fig. 1). I and II were
introduced by Oikawa et al. as cationic intermediates for
the frst time [38–46]. 2-Hydroxynaphthalene-1,4-dione
reacted with the carbonyl group of the aldehyde, which
was activated by trityl carbocation to afford intermediate
III and IV, respectively. In the next step, intermediate IV,
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J IRAN CHEM SOC
Scheme 4 The plausible mechanism for the reaction of 2-hydroxynaphthalene-1,4-dione with 4-chlorobenzaldehyde catalyzed by TrBr
carbonyl group, 13-(4-chlorophenyl)-5H-dibenzo[b,i]xan-
thene-5,7,12,14(13H)-tetraone was prepared (Scheme 4).
To confrm that TrBr cannot convert to TrOH and HBr by
very few water present in the reaction medium from envi-
ronment and consequently HBr is not the real catalyst of
the process, the model reaction was tested in the presence
of pyridine as a base besides TrBr as a catalyst in which no
changes in the reaction were observed. The preparation of
bis-coumarins was catalyzed using TrBr by similar mecha-
nism as given in Scheme 4.
Recyclability of [Fe3O4@SiO2@(CH2)3-Im-SO3H]Cl
was tested on the synthesis of 13-(4-Chlorophenyl)-5H-
dibenzo[b,i]xanthene-5,7,12,14(13H)-tetraone and (phe-
nylmethylene) bis (4-hydroxy-2H-chromen-2-one). Cata-
lytic activity of the catalyst was restored within the limits
of the experimental errors for 7 successive recycle runs
(Fig. 2).
Fig. 1 UV spectra of TrBr, 4-chlorobenzaldehyde and mixture of
4-chlorobenzaldehyde with TrBr
as a Michael acceptor, reacted with another molecule of
2-hydroxynaphthalene-1,4-dione to give intermediate V.
Finally, by intra molecular nucleophilic addition reaction to
In order to compare the catalytic activity of tri-
tyl chloride and trityl bromide in the synthesis of
1 3

J IRAN CHEM SOC
Fig. 2 Recycled [Fe3O4@
SiO2@(CH2)3-Im-SO3H]Cl
catalyst in the synthesis of
aryl-5H-dibenzo[b,i]xanthene-
5,7,12,14(13H)-tetraone and
(phenylmethylene) bis(4-
hydroxy-2H-chromen-2-one).
a13-(4-Chlorophenyl)-5H-
dibenzo[b,i]xanthene-
5,7,12,14(13H)-tetraone.
b(Phenylmethylene) bis
(4-hydroxy-2H-chromen-2-one)
activity of TrBr was more than that of TrCl in the men-
tioned reactions.
Table 7 Comparison of TrBr and TrCl in the synthesis of aryl-5H-
dibenzo[b,i]xanthene-5,7,12,14(13H)-tetraone and (phenylmethylene)
bis(4-hydroxy-2H-chromen-2-one)
Catalyst
Time (min)a
Yield (%)a
Time (min)b
Yield (%)b
Conclusions
TrBr
TrCl
45
65
90
70
20
35
92
85
In summary, we have developed new catalytic methods for
the preparation of biological henna-based xanthenes (aryl-5H-
dibenzo[b,i]xanthene-5,7,12,14(13H)-tetraone) and bis-cou-
marin derivatives via the reaction between 2-hydroxynaphtha-
lene-1,4-dione (henna) or 4-hydroxycoumarin with aromatic
aldehydes in the presence of trityl bromide as a homogenous
and neutral organocatalyst or [Fe3O4@SiO2@(CH2)3-Im-
SO3H]Cl as a heterogeneous, acidic and nano-magnetic
catalyst under solvent-free conditions. The advantages of the
described method are effciency, generality, high yields, short
reaction times, cleaner reaction profle and simplicity.
a
13-(4-Chlorophenyl)-5H-dibenzo[b,i]xanthene-5,7,12,14(13H)-
tetraone
b
(Phenylmethylene) bis (4-hydroxy-2H-chromen-2-one)
13-(4-chlorophenyl)-5H-dibenzo[b,i]xanthene-
5,7,12,14(13H)-tetraone and 3,3′(phenylmethylene)
bis(4-hydroxy-2H-chromen-2-one), 15 mol% of these
catalysts were used for the synthesis of these products
(Table 7) (Scheme 5). Table 7 indicates that the catalytic
Scheme 5 Incorporation of
TrBr and TrCl as catalysts
in the synthesis of aryl-
5H-dibenzo[b,i]xanthene-
5,7,12,14(13H)-tetraone and
(phenylmethylene) bis(4-
hydroxy-2H-chromen-2-one)
O
O
O
O
O
Ar
H
HO
O
OH
O
O
HO
OH
Ar
TrBr 15 mol%
O
TrBr 15 mol%
TrCl 15 mol%
O
O
TrCl 15 mol%
O O
Ar
O
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J IRAN CHEM SOC
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