Alternative two-step route to khellactone analogues using silica tungstic acid and sodium hydrogen phosphate

Article abstract of DOI:10.2478/s11696-013-0411-z

A series of coumarins was synthesised via the silica tungstic acid-catalysed Pechmann reaction; some of these were employed for known three-component reactions with aromatic aldehydes and malononitrile in the presence of sodium hydrogen phosphate (Na₂HPO₄) as a basic catalyst, affording a variety of potentially anti-HIV active khellactone analogues.

Full text of DOI:10.2478/s11696-013-0411-z

Chemical Papers
DOI: 10.2478/s11696-013-0411-z
SHORT COMMUNICATION
Alternative two-step route to khellactone analogues using silica
tungstic acid and sodium hydrogen phosphate
Bahador Karami*, Saeed Khodabakhshi, Khalil Eskandari
Department of Chemistry, Yasouj University, 75918-74831 Yasouj, P.O. Box 353, Iran
Received 26 November 2012; Revised 15 February 2013; Accepted 16 February 2013
A series of coumarins was synthesised via the silica tungstic acid-catalysed Pechmann reaction;
some of these were employed for known three-component reactions with aromatic aldehydes and
malononitrile in the presence of sodium hydrogen phosphate (Na2HPO4) as a basic catalyst, afford-
ing a variety of potentially anti-HIV active khellactone analogues.
c
ꢀ 2013 Institute of Chemistry, Slovak Academy of Sciences
Keywords: anti-HIV, khellactone, coumarins, Pechmann condensation, silica tungstic acid, sodium
hydrogen phosphate
Among heterocyclic compounds containing the
oxygen atom, coumarins (benzo-2-pyrones) are well
known due to their applications in the synthesis of
pharmaceuticals, fragrances, agrochemicals, and in-
secticides (Oyamada et al., 2002).
ual intercourse (Huang et al., 1994). Moreover, those
compounds with fused pyran and coumarin rings are
important as synthons for the synthesis of some phar-
macological agents (El-Agrody et al., 2001). Follow-
ing ongoing studies on the synthesis of dihydropy-
rano[c]chromene derivatives via MCRs by employ-
ing hydroxycoumarins (Mehrabi & Abusaidi, 2010),
the synthesis of some 5-hydroxycoumarin derivatives
via an eco-friendly method is described here. Subse-
quently, these coumarins were utilised in the one-pot
synthesis of fused pyrano[2,3-h]coumarin derivatives
as khellactone analogues.
All chemicals were purchased from Merck Co.
(Germany) and Sigma–Aldrich Co. (USA). The sil-
ica chloride and silica tungstic acid were prepared as
detailed in the previous paper (Karami et al., 2012b).
The reactions were monitored by TLC (silica gel 60
In recent years, multi-component reactions (MCRs)
have become valued tools for the generation of struc-
turally diverse chemical libraries of drug-like het-
erocycles (Gladkov et al., 2007). Among MCRs,
the three-component reactions have emerged as a
useful method, because the combination of three-
components to generate new products in a single
step is extremely economical (Karami et al., 2012a;
da Silva et al., 2012; Szakonyi et al., 2010; Shaa-
bani & Maleki, 2007; Yavari & Beheshti, 2011). It
is worth noting that the majority of polyhetero-
cyclic compounds containing the oxygen atom ex-
hibit biological activities. For example, 3ꢀ,4ꢀ-di-O-(S)-
(–)-camphanoyl-(3ꢀR,4ꢀR)(+)-cis-khellactone (DCK)
and 3ꢀ-O-acetyl-4ꢀ-O-isopentanoyl-(+)-cis-khellactone
(suksdorfin; isolated from the fruit of Lomatium suks-
dorfii) have been found to show anti-HIV activity (Xie
et al., 1999).
F
254). IR spectra (in KBr discs) were recorded on a
FTIR Shimadzu-470 spectrometer (Shimadzu, Japan)
1
in the scanning range of 400–4000 cm−1 and the H
NMR spectra (400 MHz) were obtained on a Bruker
DPX-400 Avance II instrument (Bruker, USA).
5,7-Dihydroxy-4-substituted coumarins (III ) were
prepared as in the published method (Karami et al.,
2012a) by the reaction of β-ketoester (I ) (1 mmol)
and phloroglucinol (II ) (1 mmol), using STA (0.25 g, 5
mole %) (Fig. 1) instead of 10 mole % of ZrOCl2 ·8H2O
Some khellactone-type compounds are also used in
preventing transmission of the HIV infection from an
HIV-infected pregnant woman to a foetus and in pre-
venting transmission of the HIV infection during sex-
*Corresponding author, e-mail: karami@mail.yu.ac.ir

ii
B. Karami et al./Chemical Papers
Fig. 1. STA-catalysed Pechmann condensation. Reaction conditions: i) STA (5 mole %), solvent-free, 80◦C, 20–90 min.
/SiO2 as a catalyst. They were characterised by NMR
and IR spectral data and compared with the data of
authentic samples (Karami & Kiani, 2011).
8-Amino-5-hydroxy-4-methyl-2-oxo-10-phenyl-
2H,10H-pyrano[2,3-h]chromene-9-carbonitrile
(IVa), 8-amino-10-(4-chlorophenyl)-5-
hydroxy-4-methyl-2-oxo-2H,10H-pyrano[2,3-
h]chromene-9-carbonitrile (IVb), 8-amino-5-
hydroxy-4-methyl-10-(3-nitrophenyl)-2-oxo-
2H,10H-pyrano[2,3-h]chromene-9-carbonitrile
(IVc), 8-amino-10-(3-bromophenyl)-5-
Fig. 2. Synthesis of khellactone analogues. Reaction condi-
tions: i) Na2HPO4 (20 mole %), MeOH, reflux.
hydroxy-4-methyl-2-oxo-2H,10H-pyrano[2,3-
h]chromene-9-carbonitrile (IVd), 8-amino-
5-hydroxy-4-methyl-10-(4-methylphenyl)-
2-oxo-2H,10H-pyrano[2,3-h]chromene-
9-carbonitrile (IVe), 8-amino-10-(2,4-
(0.2 mmol) (Fig. 2) instead of K2CO3 (0.1 mmol).
The characterisation and spectral data of compounds
IVb–IVl and IVn are summarised in Tables 1 and 2,
respectively.
dichlorophenyl)-5-hydroxy-4-methyl-2-oxo-
2H,10H-pyrano[2,3-h]chromene-9-carbonitrile
(IVf), 8-amino-5-hydroxy-4-methyl-10-(4-
methoxylphenyl)-2-oxo-2H,10H-pyrano[2,3-
h]chromene-9-carbonitrile (IVg), 8-amino-
10-(3-chlorophenyl)-5-hydroxy-4-methyl-
2-oxo-2H,10H-pyrano[2,3-h]chromene-9-
carbonitrile (IVh), 8-amino-5-hydroxy-4-
methyl-10-(2-methoxylphenyl)-2-oxo-2H,10H-
pyrano[2,3-h]chromene-9-carbonitrile (IVi),
8-amino-10-(2-chlorophenyl)-5-hydroxy-4-
methyl-2-oxo-2H,10H-pyrano[2,3-h]chromne-
9-carbonitrile (IVj), 8-amino-5-hydroxy-4-
methyl-10-(4-nitrophenyl)-2-oxo-2H,10H-
pyrano[2,3-h]chromene-9-carbonitrile
(IVk), 8-amino-(4-chloromethyl)-10-(2-
chlorophenyl)-5-hydroxy-2-oxo-2H,10H-
pyrano[2,3-h]chromene-9-carbonitrile (IVl),
8-amino-10-(2-chlorophenyl)-5-hydroxy-2-
oxo-4-phenyl-2H,10H-pyrano[2,3-h]chromene-
9-carbonitrile (IVm), 8-amino-5-hydroxy-
4-methyl-2-oxo-10-(thiophen-2-yl)-2H,10H-
pyrano[2,3-h]chromene-9-carbonitrile (IVn)
One of the simplest routes to coumarins is Pech-
mann condensation based on the reaction of phe-
nols with β-ketoesters under acidic conditions (von
Pechmann, 1884). Several conditions have been estab-
lished for modification of this reaction. For example,
synthesis of hymecromone on zeolites under thermal
or ultrasound irradiation (Gutiérrez-Sánchez et al.,
2009) and MOFs versus zeolites (Opanasenko et al.,
2013), catalysis with molecular iodine in toluene or
dichloromethane as solvent (Wu et al., 2006), use of
titanium (IV) chloride as catalyst in tetrahydrofuran
(Sheng et al., 2006), FeCl3-catalysis in ionic liquids
(Kumar et al., 2008), and use of ceric ammonium ni-
trate (CAN) under microwave irradiation. However,
some of these methods suffer from such disadvantages
as harsh conditions, extra tools, organic solvents, and
unrecyclable catalysts, long reaction times, cumber-
some work-up procedures and low yields.
Following our previous studies on the develop-
ment of various catalysts in synthesis of organic com-
pounds (Karami et al., 2011, 2012b, 2012c, 2012d),
silica tungstic acid (STA) was used as a powerful and
re-usable catalyst for the solvent-free synthesis of sub-
stituted coumarins (III ) via Pechmann condensation
of β-ketoester (I) with phloroglucinol (II) (Fig. 1).
In the next step, 4,5,7-trisubstituted coumarins
(III ) were transformed to khellactone analogues by
the one-pot, three-component reaction with malonon-
Pyrano[2,3-h]coumarin derivatives IVa–IVn were
prepared following the published method (Karami et
al., 2012a) by the reaction of substituted benzaldehyde
(1 mmol), malononitrile (1 mmol), and substituted
coumarin III (1 mmol) in MeOH, using Na2HPO4

B. Karami et al./Chemical Papers
Table 1. Characterisation data of pyrano[2,3-h]coumarin derivatives
iii
wi(calc.)/%
wi(found)/%
Timeb Yieldc M.p.d
Compounda
R1
Ar
Formula
Appearance
C
H
N
min
80
%
95
90
85
98
90
97
85
85
90
97
75
90
◦C
IVb
IVc
IVd
IVe
IVf
IVg
IVh
IVi
IVj
IVk
IVl
CH3
CH3
CH3
CH3
4-chlorophenyl
3-nitrophenyl
3-bromophenyl
4-methylphenyl
C20H13ClN2O4 63.08
63.28
3.44
3.50
7.36
7.49
255–256 pale yellow
242–244 pale yellow
293–295 pale yellow
C20H13N3O6
61.38
61.45
3.35
3.12
10.74
10.93
65
C20H13BrN2O4 56.49
56.12
3.08
3.29
6.59
6.90
80
C21H16N2O4
69.99
69.65
4.48
4.32
7.77
8.03
120
90
295–296
225–226
white
white
CH3 2,4-dichlorophenyl C20H12Cl2N2O4 57.85
57.75
2.91
3.11
6.75
6.42
CH3
4-methoxyphenyl
3-chlorophenyl
2-methoxyphenyl
2-chlorophenyl
4-nitrophenyl
C21H16N2O5
67.02
67.16
4.28
4.25
7.44
7.22
70
322–324 pale yellow
CH3
C20H13ClN2O4 63.08
62.98
3.44
3.58
7.36
7.56
70
265–266
208–210
white
white
CH3
C21H16N2O5
67.02
67.26
4.28
4.16
7.44
7.33
65
CH3
C20H13ClN2O4 63.08
63.20
3.44
3.63
7.36
7.27
60
303–305 pale yellow
320–322 pale yellow
CH3
C20H13N3O6
61.38
61.30
3.35
3.31
10.74
10.52
50
CH2Cl
CH3
2-chlorophenyl
thiophen-2-yl
C20H12Cl2N2O4 57.85
57.68
2.91
3.01
6.75
6.65
110
100
245–247
250–252
white
IVn
C18H12N2O4S 61.35
61.76
3.43
3.23
7.95
8.10
yellow
a) Characterisation data of compounds IVa (R1 = CH3, Ar = phenyl) and IVm (R1 = phenyl, Ar = 2-chlorophenyl) were already
published (Karami et al., 2012a); b) heating under reflux; c) isolated yield; d) in accord with published m.p. data (Karami et al.,
2012a).
itrile and arylaldehydes in the presence of a catalytic
amount of sodium hydrogen phosphate (Na2HPO4)
(Fig. 2), which is recognised as a cheap and effi-
cient catalyst for the synthesis of such organic com-
pounds as 2-aminochromenes (Meng et al., 2011),
isonucleosides (Sanki et al., 2008), exo-methylene bu-
tyrolactones (Ballini et al., 2001), and corn starch
fatty acid esters with high DS values (Junistia et
al., 2008). To overcome the reaction progress prob-
lems, a careful selection of starting coumarin III needs
to be considered. It was found that coumarins with-
out the hydroxyl group in position 5 were not ac-
tive in Pechmann condensation, indicating the effect
of the electron-donating group on the benzene ring
of coumarin. It is possible that the activity of 5,7-
dihydroxy-4-methylcoumarins is related with the OH
group in meta position to another OH group on the
benzene ring of coumarin, which activates the benzene
ring for nucleophilic attack.
was successful with 2-thiophenecarbaldehyde, to af-
ford pyrano[2,3-h]coumarin derivative IVn, while 2-
furaldehyde was inactive.
For spectral assignment, compound IVe was chosen
1
as a model. Its H NMR spectrum exhibited a singlet
at δ = 10.95 attributed to the OH group, two doublets
(δ = 7.08–7.10, δ = 7.02–7.04) of the phenyl protons.
Five sharp singlets correspond to the NH2 (δ = 6.99),
a methine (C-6 position, δ = 6.51), an olefinic (C-3
position, δ = 6.09), methine (pyran ring, δ = 4.59),
methyl (C-4 position of coumarin ring, δ = 2.62), and
methyl (at phenyl ring, δ = 2.24) protons.
The 1H NMR spectrum of IVn exhibited a dou-
blet (δ = 7.26–7.27) and a multiplet (δ = 6.93–6.91)
identified as the protons of the phenyl group. A sharp
singlet (δ = 7.05) corresponded to the NH2 protons.
Four sharp singlets were identified as a methine (H-6,
δ = 6.24), an olefinic (H-3, δ = 5.79), methine (H-6,
δ = 5.00), and methyl (δ = 2.54) protons.
After determining the suitable reaction conditions,
the scope of this MCR was examined using var-
ious starting aldehydes under standard conditions.
It was found that both electron-rich and electron-
deficient aldehydes reacted well (Table 1). Using
heteroaromatic aldehydes, the condensation reaction
In summary, a green strategy was presented for the
synthesis of some substituted coumarins as precursors
of khellactons using recyclable silica tungstic acid un-
der solvent-free conditions. In addition, the reaction of
5,7-dihydroxycoumarins, aromatic aldehydes and mal-
ononitrile in the presence of Na2HPO4, as an efficient

iv
B. Karami et al./Chemical Papers
Table 2. Spectral data of pyrano[2,3-h]coumarin derivatives
Compounda
Spectral data
IVb
IVc
IVd
IVe
IVf
IVg
IVh
IVi
IVj
IVk
FTIR, ν˜/cm−1: 3402, 2196, 1730, 1665, 1391, 841
1H NMR (400 MHz, DMSO-d6), δ: 11.02 (s, 1H), 7.35 (d, 2H, J = 8.4 Hz), 7.18 (d, 2H, J = 8.4 Hz), 7.06 (s, 2H),
6.51 (s, 1H), 6.08 (s, 1H), 4.66 (s, 1H), 2.62 (s, 3H)
13C NMR (100 MHz, DMSO-d6), δ: 160.01, 159.81, 157.94, 154.95, 153.76, 147.95, 144.66, 131.62, 129.44, 128.85,
120.41, 112.02, 108.43, 102.39, 99.07, 57.50, 36.29, 24.49
FTIR, ν˜/cm−1: 3401, 2198, 1731, 1660, 1527,1349, 1399, 1095
1H NMR (400 MHz, DMSO-d6), δ: 11.57 (s, 1H), 8.11–8.09 (m, 1H), 8.02 (s, 1H), 7.67–7.60 (m, 2H), 7.19 (s, 1H),
6.51 (s, 1H), 6.12 (s, 1H), 4.88 (s, 1H), 2.63 (s, 3H)
13C NMR (100 MHz, DMSO-d6), δ: 160.23, 159.75, 157.92, 155.14, 153.77, 148.23, 147.97, 147.79, 134.53, 130.66,
122.33, 122.03, 120.22, 112.17, 107.78, 102.50, 99.15, 56.74, 36.56, 24.49
FTIR, ν˜/cm−1: 3423, 3346, 3205, 2187, 1690, 1647, 1382, 852
1H NMR (400 MHz, DMSO-d6), δ: 11.06 (s, 1H), 7.40 (d, 1H, J = 7.6 Hz), 7.34 (s, 1H), 7.27 (t, 1H, J = 7.6 H),
7.17 (d, 1H, J = 8 Hz), 7.09 (s, 2H), 6.50 (s, 1H), 6.08 (s, 1H), 4.76 (s, 1H), 2.62 (s, 3H)
13C NMR (100 MHz, DMSO-d6), δ: 160.10, 159.79, 157.93, 155.01, 153.78, 148.37, 147.97, 131.22, 130.21, 130.03,
126.78, 122.05, 120.37, 112.05, 108.16, 102.44, 99.11, 57.27, 36.55, 24.51
FTIR, ν˜/cm−1: 3402, 2200, 1731, 1663, 1397, 1097
1H NMR (400 MHz, DMSO-d6), δ: 10.95 (s, 1 H), 7.09 (d, 2H, J = 8 Hz), 7.03 (d, 2H, J = 8 Hz), 6.99 (s, 2H), 6.51
(s, 1H), 4.59 (s, 1H), 2.62 (s, 3H), 2.24 (s, 3H)
13C NMR (100 MHz, DMSO-d6), δ: 160.06, 159.78, 157.95, 154.77, 153.83, 148.03, 142.71, 136.14, 129.41, 127.40,
120.59, 111.96, 109.24, 102.37, 99.02, 58.12, 36.37, 24.48, 21.06
FTIR, ν˜/cm−1: 3404, 2194, 1730, 1666, 1391, 1092
1H NMR (400 MHz, DMSO-d6), δ: 11.00 (s, 1H), 7.55 (s, 1H), 7.33–7.31 (m, 1H), 7.11–7.07 (m, 3H), 6.45 (s, 1H),
6.09 (s, 1H), 5.15 (s, 1H), 2.62 (s, 3H)
13C NMR (100 MHz, DMSO-d6), δ: 159.83, 159.78, 158.05, 155.14, 153.86, 148.22, 142.16, 133.30, 132.19, 131.98,
129.00, 128.32, 119.90, 112.02, 107.31, 102.22, 98.91, 56.02, 33.54, 24.52
FTIR, ν˜/cm−1: 3400, 3335, 2931, 2190, 1706, 1664, 1387, 1155
1H NMR (400 MHz, DMSO-d6), δ: 11.16 (s, 1H), 7.07 (d, 2H, J = 8.4 Hz), 7.97 (s, 2H), 6.84 (d, 2H, J = 8.4 Hz),
6.47 (s, 1 H), 6.07 (s, 1H), 4.58 (s, 1H), 3.71 (s, 3H), 2.62 (s, 3H)
13C NMR (100 MHz, DMSO-d6), δ: 160.08, 159.90, 158.41, 158.17, 154.77, 153.83, 147.94, 137.79, 128.56, 120.66,
114.23, 111.83, 109.47, 102.25, 99.04, 58.27, 55.49, 35.95, 24.48
FTIR, ν˜/cm−1: 3401, 2194, 1728, 1661, 1390, 1095
1H NMR (400 MHz, DMSO-d6), δ: 11.06 (s, 1H), 7.36-7.26 (m, 2H), 7.19 (s, 1H), 7.13-7.10 (m, 3H), 6.51 (s, 1H),
6.10 (s, 1H), 4.68 (s, 1H), 2.62 (s, 3H)
13C NMR (100 MHz, DMSO-d6), δ: 160.11, 159.80, 157.91, 155.00, 153.81, 148.11, 148.00, 133.39, 130.89, 127.33,
126.37, 120.36, 112.05, 108.16, 102.46, 99.10, 57.25, 36.56, 24.49
FTIR, ν˜/cm−1: 3414, 3322, 3202, 2190, 1691, 1661, 1385, 1159
1H NMR (400 MHz, DMSO-d6), δ: 10.80 (s, 1H), 7.17 (t, 1H, J = 7.6 Hz), 6.97 (d, 1H, J = 8.4 Hz), 6.88–6.81 (m,
4H), 6.48 (s, 1H), 6.10 (s, 1H), 4.96 (s, 1H), 3.74 (s, 3H), 2.64 (s, 3H)
13C NMR (100 MHz, DMSO-d6), δ: 160.53, 159.95, 157.95, 157.21, 154.68, 153.91, 148.87, 133.31, 128.91, 128.28,
120.90, 120.66, 112.05, 111.82, 108.43, 102.12, 98.79, 57.05, 56.09, 31.49, 24.53
FTIR, ν˜/cm−1: 3397, 2929, 2201, 1733, 1664, 1394, 1096
1H NMR (400 MHz, DMSO-d6), δ: 10.94 (s, 1H), 7.39 (dd, 1H, J = 7.6 Hz, 1.2 Hz), 7.26–7.18 (m, 2H), 7.07 (dd,
1H, J = 7.2 Hz, 1.6 Hz), 7.00 (s, 2H), 6.45 (s, 1H), 6.08 ( s, 1H), 5.18 (s, 1H), 2.64 (s, 3H)
13C NMR (100 MHz, DMSO-d6), δ: 159.89, 159.82, 158.09, 155.04, 153.86, 148.30, 143.03, 132.38, 130.55, 129.68,
128.59, 128.08, 120.05, 111.94, 107.89, 128.08, 98.89, 56.63, 33.78, 24.54
FTIR, ν˜/cm−1: 3402, 2194, 1728, 1663, 1572, 1349, 1096
1H NMR (400 MHz, DMSO-d6), δ: 11.10 (s, 1H), 8.18 (d, 2H, J = 8.8 Hz), 7.44 (d, 2H, J = 8.4 Hz), 7.17 (s, 2H),
6.51 (s, 1H), 6.12 (s, 1H), 4.82 (s, 1H), 2.63 (s, 3H)
13C NMR (100 MHz, DMSO-d6), δ: 160.02, 159.76, 157.97, 155.17, 153.76, 153.10, 147.99, 146.72, 128.92, 124.29,
120.17, 112.12, 107.55, 102.46, 99.11, 56.64, 36.81, 24.49
MS (m/z): 391.1 [M]+
IVl
FTIR, ν˜/cm−1: 3400, 2972, 1723, 1657, 1373, 1119
1H NMR (400 MHz, DMSO-d6), δ: 11.09 (s, 1H), 7.44–7.38 (m, 1H), 7.24–7.21 (m, 2H), 7.13 (s, 2H), 7.09–7.07 (m,
1H), 6.49 (s, 1H), 5.87 (s. 1H), 5.25–5.19 (m, 2H), 5.15 (s, 1H)
13C NMR (100 MHz, DMSO-d6), δ: 159.85, 158.48, 155.11, 152.68, 151.02, 147.61, 142.81, 132.39, 130.58, 129.75,
128.71, 119.98, 111.91, 108.14, 106.93, 99.89, 98.10, 56.41, 46.22, 33.74
IVn
FTIR, ν˜/cm−1: 3323, 3176, 2198, 1686, 1660, 1396, 1095
1H NMR (400 MHz, DMSO-d6), δ: 7.26 (d, 1H, J = 4.4 Hz), 7.05 (s, 2H), 6.93–6.91 (m, 2H), 6.24 (s, 1H), 5.79 (s,
1H), 5.00 (s, 1H), 2.54 (s, 3H)
13C NMR (100 MHz, DMSO-d6), δ: 165.01, 161.50, 160.59, 155.92, 153.94, 150.75, 147.88, 127.03, 124.37, 123.85,
120.96, 110.67, 108.26, 99.60, 98.81, 57.63, 31.87, 24.40
a) Spectral data of compounds IVa (R1 = CH3, Ar = phenyl) and IVm (R1 = phenyl, Ar = 2-chlorophenyl) were published
previously (Karami et al., 2012a).

B. Karami et al./Chemical Papers
v
and safe catalyst, provides a simple one-pot entry for
the high-yielding synthesis of khellactone analogues of
potential synthetic and pharmaceutical interest.
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