Tris(hydrogensulfato) boron as a solid heterogeneous catalyst for the rapid synthesis of α,α′-benzylidene bis(4-hydroxycoumarin) derivatives

Article abstract of DOI:10.1016/j.cclet.2012.05.003

α,α′-Benzylidene bis(4-hydroxycoumarin) derivatives were readily prepared in a few minutes with good yields through the reaction of an aromatic aldehyde and 4-hydroxycoumarin in aqueous media in the presence of catalytic tris(hydrogensulfato) boron [B(HSO

Full text of DOI:10.1016/j.cclet.2012.05.003

Available online at www.sciencedirect.com
Chinese Chemical Letters 23 (2012) 781–784
www.elsevier.com/locate/cclet
Tris(hydrogensulfato) boron as a solid heterogeneous
catalyst for the rapid synthesis of a,a0-benzylidene
bis(4-hydroxycoumarin) derivatives
*
Zahed Karimi-Jaberi , Mohammad Reza Nazarifar, Baharak Pooladian
Department of Chemistry, Firoozabad Branch, Islamic Azad University, P.O. Box 74715-117 Firoozabad, Fars, Iran
Received 5 March 2012
Available online 9 June 2012
Abstract
a,a0-Benzylidene bis(4-hydroxycoumarin) derivatives were readily prepared in a few minutes with good yields through the
reaction of an aromatic aldehyde and 4-hydroxycoumarin in aqueous media in the presence of catalytic tris(hydrogensulfato) boron
[B(HSO4)3].
# 2012 Zahed Karimi-Jaberi. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Biscoumarin; 4-Hydroxycoumarin; Tris(hydrogensulfato)boron; Heterogeneous catalyst
Due to special reactivity of 4-hydroxycoumarin, the synthesis of new coumarin derivatives of dimer and tetramer
type has been carried out. Coumarins and their derivatives exhibit pharmacological properties such as antibacterial,
antifungal, pharmacological, anti-cancer and anticoagulant activity [1–5]. Biscoumarins derivatives are effective
urease inhibitors [6]. Also, a number of coumarin derivatives were shown HIV inhibitory activity [1].
The most direct procedure for the preparation of bis-coumarins includes condensation of an aldehyde with 4-
hydroxycoumarin in the presence of hazardous catalysts, such as glacial acetic acid and acetic anhydride [7],
ethylenediammonium diacetate [8], and piperidine [6]. However, some of these protocols require long reaction times,
harsh reaction conditions and expensive reagents [9–11]. Thus, the introduction of milder, faster and more eco-
friendly methods is still in great demand.
From the environmental acceptability, recently inorganic acidic salts have widely used in organic synthesis because
of minimized wastes, simplicity in handling and decreased reactor corrosion problems [12].
In continuation of our studies on the synthesis of heterocyclic compounds [13–16], we wish to report the results that
led to an extremely convenient method for the preparation a,a0-benzylidene bis(4-hydroxycoumarin) from aromatic
aldehydes and 4-hydroxycoumarin in the presence of tris(hydrogensulfato)boron [B(HSO4))3] in excellent yield
(Scheme 1).
Tris(hydrogensulfato) boron was easily prepared by addition of chlorosulfonic acid to boric acid at room
temperature. It must be noted that the preparation method is simple, clean, and without work-up procedure, because
* Corresponding author.
E-mail address: z.karimi@iauf.ac.ir (Z. Karimi-Jaberi).
1001-8417/$ – see front matter # 2012 Zahed Karimi-Jaberi. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2012.05.003

782
Z. Karimi-Jaberi et al. / Chinese Chemical Letters 23 (2012) 781–784
Ar
OH
O
OH
O
OH
O
B(HSO4)3
+
ArCHO
H2O:EtOH (1:1), 70 0
C
O
O
O
1
2
3
Scheme 1. Synthesis of a,a0-benzylidene bis(4-hydroxycoumarin).
HCl gas is evolved from the reaction vessel immediately (Scheme 2). This catalyst is safe and easy to handle and has
been successfully applied in various organic transformations [17].
To optimize the amount of catalyst, effect of solvent and effect of temperature, reaction of benzaldehyde and 4-
hydroxycoumarin was selected as the model reaction to afford 3,30-(benzylidene)-bis-(4-hydroxycoumarin). The
optimized reactant ratios were found to be 1.0 equiv. benzaldehyde and 2.0 equiv. 4-hydroxycoumarin in the presence
of B(HSO4)3 (0.3 equiv.) in 5 mL aqueous ethanol (1:1, H2O–EtOH). The expected a,a0-benzylidene bis(4-
hydroxycoumarin) was produced in 86% yield after 6 min at 70 8C.
To ascertain the scope and limitation of the present reaction, several aldehydes were examined and the results of
their reaction with 4-hydroxycoumarin are summarized in Table 1. Aromatic aldehydes both with activating and
deactivating groups underwent smooth transformation to the corresponding bis-coumarins, without the formation of
any side products, in high to excellent yields and in very short reaction times. However, the synthesis could not be
achieved in the absence of the catalyst.
The reaction proceeds via condensation of 1 equiv. of aldehyde with 2 equiv. of 4-hydroxycoumarin to form the
corresponding product as has been suggested earlier [20]. The reaction pathway is shown in Scheme 3.
As shown in Table 2, we compared results of 3-methyl-1-(4-sulfonic acid)butylimidazolium hydrogen sulfate
[MIM(CH2)4SO3H] [18], sodium dodecyl sulfate (SDS) [19], phosphotungstic acid [20], H14[NaP5W30O110])–SiO2
[21], piperidine [6], HBF4 and tetrabutylammonium bromide (TBAB) [9], [bmim]BF4 [22], in the synthesis of a,a0-
benzylidene bis(4-hydroxycoumarin) derivatives with present method and demonstrated that B(HSO4)3 can act as an
effective catalyst. Thus, the present work using B(HSO4)3 as a catalyst is an efficient route for production of a,a0-
benzylidene bis(4-hydroxycoumarin) derivatives.
In conclusion, we have demonstrated that B(HSO4)3 is a efficient catalyst for synthesis of a,a0-benzylidene bis(4-
hydroxycoumarin). The notable advantages of this method are high catalytic activity, short reaction times, good yields,
simple workup, reusable catalyst, and environmental benignancy.
HO3SO
OSO3H
HO
OH
B
B
3 ClSO3H
3 HCl
+
+
OSO3H
OH
Scheme 2. Synthesis of tris(hydrogensulfato) boron.
Table 1
Synthesis of a,a0-benzylidene bis(4-hydroxycoumarin).
Entry
Aldehyde
Product
Time (min)
Yield (%)
m.p. (8C)
Found
Reported [9,19,20,23]
1
2
Benzaldehyde
3a
3b
3c
3d
3e
3f
6
4
5
4
3
4
4
5
4
5
4
86
98
82
86
88
92
81
83
95
87
88
230–232
232–234
229–231
242–244
211–212
256–258
238–240
246–248
264–266
266–268
269–270
233–234
238–239
234–236
240–242
213–215
258–259
238
4-Nitrobenzaldehyde
3-Nitrobenzaldehyde
4-Cyanobenzaldehyde
4-Fluorobenzaldehyde
4-Chlorobenzaldehyde
3-Methoxybenzaldehyde
4-Methoxybenzaldehyde
4-Bromobenzaldehyde
4-Methylbenzaldehyde
4-Choloro-3-nitrobenzaldehyde
3
4
5
6
7
3g
3h
3i
8
249–250
265–267
269–270
–
9
10
11
3j
3k

Z. Karimi-Jaberi et al. / Chinese Chemical Letters 23 (2012) 781–784
783
OH
O
Ar
O
B(HSO4)3
Ar
H
O
O
O
O
Ar
OH
OH
O
OH
O
Ar
O
B(HSO4)3
O
O
O
O
O
O
Scheme 3. Proposed mechanism.
1. Experimental
1.1. Preparation of tris(hydrogensulfato)boron (B(HSO4)3)
A 50 mL suction flask was equipped with a constant pressure dropping funnel. The gas outlet was connected to a
vacuum system through an adsorbing solution (water) and an alkali trap. Boric acid (1.55 g, 25 mmol) was charged in
the flask and chlorosulfonic acid (8.74 g, ca. 5 mL, 75 mmol) was added dropwise over a period of 1 h at room
temperature. HCl evolved immediately. After completion of the addition, the mixture was shaken for 1 h, while the
residual HCl was eliminated by suction. Then the mixture was washed with diethyl ether to remove the unreacted
chlorosulfonic acid. Finally, a grayish solid material was obtained in 93% yield (7.0 g) and then, in a mortar mixed
with silica gel (1:4).
1.2. Representative procedure for synthesis of a,a0-benzylidene bis(4-hydroxycoumarin) derivatives
A solution of aromatic aldehyde (1 mmol), 4-hydroxycoumarin (2 mmol), and B(HSO4)3 (0.018 g) in 5.0 mL
aqueous ethanol (50%) was stirred at 70 8C for the appropriate times (Table 1). Upon completion of the reaction,
monitored by TLC, the reaction mixture was allowed to cool to room temperature. The solid was filtered off and
washed with water (2 ꢀ 20 mL) and purified by recrystalization from ethanol. The structures of all products 3a–k were
1
confirmed by IR, HNMR, 13CNMR, and elemental analysis.
3,30-(3-Nitrobenzylidene)-bis-(4-hydroxycoumarin)(entry 3): IR(KBr): 3424, 2925, 1655, 1616, 1564, 1494, 1450,
1347, 762 cmꢁ1; 1H NMR (400 MHz, DMSO-d6): d 6.39 (s, 1H, CH), 7.28–8.04 (m, 12H, ArH), 8.04–9.52 (m, 2H,
OH).
3,30-(4-Cholorobenzylidene)-bis-(4-hydroxycoumarin)(entry 6): IR(KBr): 3420, 2923, 1668, 1606, 1563, 1490,
1451, 1351, 765 cmꢁ1; 1H NMR (400 MHz, DMSO-d6): d 6.63 (s, 1H, CH), 7.16–7.90 (m, 12H, ArH), 7.90–9 (m, 2H,
OH).
3,30-(4-Methoxybenzylidene)-bis-(4-hydroxycoumarin)(entry 8): IR(KBr): 3443, 2926, 1668, 1606, 1563, 1510,
1452, 1352, 767 cmꢁ1; 1H NMR (400 MHz, DMSO-d6): d 3.71 (s, 3H, CH3O), 6.31 (s, 1H, CH), 6.80–7.93 (m, 12H,
ArH), 8.16–8.78 (m, 2H, OH).
Table 2
Comparison results of B(HSO4)3 with other catalysts reported in the literature.
Entry
Conditions
Catalyst
Time (min)
25–30
Yield (%)
1
2
3
4
5
6
7
8
9
Solvent-free, 80 8C
H2O, 60 8C
H2O, 80 8C
EtOH, 25 8C
EtOH, r.t.
[MIM(CH2)4SO3H] (20 mol%)
SDS (20 mol%)
86–96
80–96
90–98
90–98
89–97
55–70
82–95
77–91
81–98
2.5–3 h
Phosphotungstic acid (15 mol%)
H14[NaP5W30O110])–SiO2 (0.3 mol%)
Piperidine
14–25
20–30
4 h
H2O, 25 8C
H2O, reflux
HBF4 (10 mol%)
10–12 h
25–40
2–3 h
3–6
TBAB (10 mol %)
Solvent-free, 60–70 8C
H2O:EtOH (1:1), 70 8C
[bmim]BF4 (4 mmol)
B(HSO4)3 (0.3 mmol)

784
Z. Karimi-Jaberi et al. / Chinese Chemical Letters 23 (2012) 781–784
3,30-(4-Choloro-3-nitrobenzylidene)-bis-(4-hydroxycoumarin)(entry 11): IR(KBr): 3423, 2920, 1665, 1613, 1558,
1536, 1450, 1348, 765 cmꢁ1; 1H NMR (400 MHz, DMSO-d6): d 6.28 (s, 1H, CH), 7.26–7.85 (m, 11H, ArH), 8.15–
8.56 (m, 2H, OH); 13C NMR (DMSO-d6): d 36.42, 103.23, 116.24, 119.31, 121.99, 123.81, 124.03, 124.51, 131.39,
132.07, 132.89, 143.87, 147.94, 152.90, 164.70, 167.34. Anal. Calcd. for C25H14ClNO8: C, 60.80; H, 3.27; N, 2.84;
Found: C, 60.89; H, 3.25; N, 2.90.
References
[1] R.D.R.S. Manian, J. Jayashankaran, R. Raghunathan, Tetrahedron Lett. 48 (2007) 1385.
[2] I. Kostova, G. Momekov, M. Zaharieva, et al. Eur. J. Med. Chem. 40 (2005) 542.
[3] J.H. Lee, H.B. Bang, S.Y. Han, et al. Tetrahedron Lett. 48 (2007) 2889.
[4] H. Zhao, N. Neamati, H. Hong, et al. J. Med. Chem. 40 (1997) 242.
[5] G.K. Maria, E. Marian, J. Med. Pharm. Chem. 3 (1961) 583.
[6] K.M. Khan, S. Iqbal, M.A. Lodhi, et al. Bioorg. Med. Chem. 12 (2004) 1963.
[7] M. Ilia, M.M. Caecilia, D. Nicolay, Eur. J. Med. Chem. 41 (2006) 882.
[8] G. Appendino, G. Cravotto, S. Tagliapietra, et al. Helv. Chim. Acta (1991) 1451.
[9] J.M. Khurana, S. Kumar, Tetrahedron Lett. 50 (2009) 4125.
[10] J. Wang, D.Q. Shi, Q.Y. Zhuang, et al. Chin. J. Org. Chem. 25 (2005) 926.
[11] K. Mazaahir, V. Bansal, P. Mothsra, et al. J. Mol. Catal. A: Chem. 268 (2007) 76.
[12] P. Salehi, M.A. Zolfigol, F. Shirini, et al. Curr. Org. Chem. 10 (2006) 2171.
[13] Z. Karimi-Jaberi, M.M. ReyazoShams, Heterocycl. Commun. 17 (2011) 177.
[14] Z. Karimi-Jaberi, M. Keshavarzi, Chin. Chem. Lett. 21 (2010) 547.
[15] Z. Karimi-Jaberi, R. Arjmandi, Monatsh. Chem. 142 (2011) 631.
[16] Z. Karimi-Jaberi, L. Zarei, S. Afr, J. Chem. 65 (2012) 36.
[17] A.R. Kiasat, M. Fallah-Mehrjardi, J. Braz. Chem. Soc. 19 (2008) 1595.
[18] N. Tavakoli-Hoseini, M.M. Heravi, F.F. Bamoharram, et al. J. Mol. Liq. 163 (2011) 122.
[19] H. Mehrabi, H. Abusaidi, J. Iran. Chem. Soc. 7 (2010) 890.
[20] P. Singh, P. Kumar, A. Katyal, et al. Catal. Lett. 134 (2010) 303.
[21] M.M. Heravi, F. Nahavandi, S. Sadjadi, et al. Synth. Commun. 40 (2010) 498.
[22] J.M. Khurana, S. Kumar, Monatsh. Chem. 141 (2010) 561.
[23] K. Tabatabaeian, H. Heidari, A. Khorshidi, et al. J. Serb. Chem. Soc. 76 (2011) 1.