Phosphinite ionic liquid (IL-OPPh2) as a recyclable reagent for the efficient synthesis of coumarins under microwave irradiation conditions

Article abstract of DOI:10.1007/BF03245917

Task-specific phosphinite ionic liquid (IL-OPPh₂) was used as a reagent for the efficient synthesis of 4-substituted coumarins via the reaction of di(methyl or ethyl) acetylenedicarboxylate with phenolic compounds under microwave irradiation co

Full text of DOI:10.1007/BF03245917

J. Iran. Chem. Soc., Vol. 8, No. 3, September 2011, pp. 862-871.
JOURIrNaAnLiaOnF THE
Chemical Society
Phosphinite Ionic Liquid (IL-OPPh2) as a Recyclable Reagent for the Efficient
Synthesis of Coumarins under Microwave Irradiation Conditions
H. Valizadeh*, H. Gholipour and M. Mahmoudian
Department of Chemistry, Faculty of Sciences, Azarbaijan University of Tarbiat Moallem, Tabriz, Iran
(Received 26 September 2010, Accepted 28 January 2011)
Task-specific phosphinite ionic liquid (IL-OPPh2) was used as a reagent for the efficient synthesis of 4-substituted coumarins
via the reaction of di(methyl or ethyl) acetylenedicarboxylate with phenolic compounds under microwave irradiation conditions.
The effects of parameters such as the amount of the phosphinite ionic liquid, reaction temperature and reaction time on this
procedure were investigated. Products were obtained in good yields using this mild and one-pot methodology under solvent-free
conditions. In addition, the ionic liquid recycling test showed that it could be reused for three times without loss of its activity.
Keywords: Coumarin, Microwave, Phosphinite ionic liquid, Solvent-free, Task-specific ionic liquid
INTRODUCTION
presence of in situ prepared ionic liquids [8]. We used task-
specific phosphinite ionic liquid as solvent and catalyst/
reagent for the synthesis of some heterocyclic compounds and
nitrones [9-12]. Very recently, we reported the dizotization of
aniline derivatives using nitrite ionic liquid (IL-ONO) [13].
Coumarins are biologically and synthetically important
heterocycles which exist in a large number of natural products.
These compounds are widely used as additives in food,
cosmetics, pharmaceuticals [14], as optical brighteners [15],
dispersed fluorescent and laser dyes [16]. So, the synthesis of
coumarins and their derivatives is of increasing interest.
Several routes have been reported for the synthesis of
coumarins such as Pechmann [17], Perkin [18], Knoevenage 1
[19], Reformatsky [20] and Wittig [21] reactions. Many
studies on the synthesis of coumarin derivatives have also
been recently reported [22-29].
Ionic liquids (ILs) have become popular as novel and
promising solvents for the organic synthesis due to their
inherent features. Along with their chemical and physical
properties which make a careful choice of cation/anion, they
have also been used as designer reaction media. Various ionic
liquids have been synthesized and used as novel reaction
media in organic synthesis, catalysis and preparation of
nanomaterials [1-3]. Covalently attaching functional group to
the cation or the anion or both, ILs have made it possible to
create task-specific ionic liquids (TSILs) which further
enhance the application of ILs in chemistry [4]. Wang et al.
have reported the palladium-catalyzed Heck reaction in the
presence of task-specific ionic liquid as base, ligand and
reaction medium [5]. Tajik and co-workers reported the
nitration of phenols using acidic ionic liquid under mild
conditions [6]. Pawar et al. synthesized the flavones in
[bmim]BF4 ionic liquid [7]. Hajipour and co-workers reported
a convenient method for the preparation of aldoximes in the
Microwave-assisted organic synthesis (MAOS) has been
known since 1986 [30]. This “non-conventional” synthetic
method has a wide range of applications and is a very efficient
way to accelerate the course of many organic reactions [31,
32]. In our previous works, we have reported on the results of
ionic liquids in the synthesis of coumarins [11,33]. We also
*Corresponding author. E-mail: h-valizadeh@azaruniv.edu

Valizadeh et al.
Synthesis of 4-Chlorobutyl Diphenylphosphinite
reported the facile synthesis of coumarins via TiCl4 catalyzed
Pechmann reaction [34]. Very recently, we prepared
A solution of chlorodiphenylphosphine (18 ml, 0.1 mol) in
CH2Cl2 (75 ml) was added slowly while stirring to a solution
of 4-chlorobutanol (10 ml, 0.1 mol) and K2CO3 (13.8 g, 0.1
mol) in CH2Cl2 (750 ml) at -5 °C for 5 h. After completion of
the reaction, dichloromethane was removed under reduced
pressure at room temperature and distilled cold water was
added to the residue and mixed thoroughly. The participating
4-chlorobutyl diphenylphosphinite was filtered off and
recrystallized from 85% ethanol to yield white crystals (95%).
1H NMR (400 MHz, CDCl3) δ 1.35 (2H, m, CH2), 1.41
(2H, m, CH2), 2.82 (2H, t, CH2-PPh2), 2.91 (2H, t, CH2-Cl),
7.27-7.35 (6H, m, Ar-H), 7.45-7.51 (4H, m, Ar-H). 13C NMR
(100 MHz, CDCl3) 19.75, 24.21, 36.63, 61.94, 123.10, 128.12,
130.52, 132.63.
benzocoumarins via
a
multicomponent reaction of
salicylaldehydes, malononitrile and ethylacetoacetate over
MgO under solvent-free conditions at room temperature [35].
Iranpoor and co-workers synthesized the phosphinite ionic
liquid, IL-OPPh2, and used it as TSIL in some organic
reactions [36-38]. We wish to report here the MW-assisted
facile synthesis of coumarin derivatives using IL-OPPh2 as a
reagent in a solventless system. The reaction of phenolic
compounds with di(methyl or ethyl) acetylenedicarboxylate in
the presence of TSIL (IL-OPPh2) afforded 4-substituted
coumarins in good yields (Scheme 1).
EXPERIMENTAL
Synthesis
of
1-(4-Diphenylphosphinitebutyl)-3-
General
methylimidazolium Chloride
All reagents were purchased from Merck Company and
used without further purification. Infrared spectra were
recorded in KBr and were determined on a Perkin Elmer FT-
Freshly prepared 4-chlorobutyl diphenylphosphinite (29.2
g, 0.1 mol) and N-methyl imidazole (8 ml, 0.1 mol) were
stirred in dichloromethane at 80 °C for 5 h. After completion
of the reaction, the unreacted materials were washed by
diethyl ether (3 × 8 ml). The diethyl ether was removed under
reduced pressure at room temperature, followed by heating
under high vacuum, to yield a colorless liquid that became
more viscous upon extensive drying, but did not solidify.
1
IR spectrometer. H NMR spectra were recorded on a Bruker
Avance AC-400 MHz using DMSO-d6, acetone-d6 or CDCl3
as the deuterated solvents and TMS as the internal standard.
All melting points were measured in open glass-capillaries
using Stuart melting point apparatus. Elemental analyses were
carried out on a Perkin-Elmer 240C elemental analyzer and
are reported in percent atomic abundance. Microwave
experiments were conducted in a Milestone MicroSYNTH
apparatus.
1
Isolated yield was 91%. H NMR (400 MHz, CDCl3) δ 1.33
(2H, m, CH2); 1.39 (2H, m, CH2); 2.96 (3H, s, N-CH3); 3.68
(2H, t, N-CH2); 4.26 (2H, t, CH2-OPPh2); 7.76, 7.78 (2H, two
Cl-
OPPh2
+
N
IL-OPPh2 =
N
3
Me
CO2R2
CO2R2
OH
IL-OPPh2
Solvent-free
+
MWI, 2-5 min
R1
R1
O
O
CO2R2
2
1
4
Scheme 1. Solvent-free synthesis of coumarins using IL-OPPh2
863

Phosphinite Ionic Liquid (IL-OPPh2) as a Recyclable Reagent
singlets, C(4,5)-H); 8.99 (1H, s, C(2)-H). 13C NMR (100 MHz,
CDCl3) 19.05, 22.43, 32.13, 38.44, 61.56, 123.07, 123.16,
123.21, 124.09, 128.89, 131.04, 133.76.
122.36, 143.78, 148.96, 154.89, 160.05, 166.56. Anal. Calcd.
(%) for C11H8O5: C, 60.00; H, 3.66%. Found (%): C, 61.50; H,
3.75.
Ethyl-2-oxo-2H-pyrano[3,2-c]pyridine-4-carboxylate
(4d). FT-IR (KBr, cm-1): 1732 (C=O), 1438 (C=C), 1249
(CO). H NMR (400 MHz, DMSO-d6) δ (ppm): 1.35 (t, 3H,
MW-Assisted Synthesis of Coumarins Using IL-
OPPh2 General Procedure
1
Me), 4.16 (q, 2H, CH2), 6.95 (s, CH), 7.01 (dd, CH, J = 8.02
and 1.98 Hz), 7.11 (d, CH, J = 1.98 Hz), 7.46 (d, CH, J = 8.02
Hz). 13C NMR (100 MHz, DMSO-d6) δ (ppm): 22.21, 55.60,
111.24, 119.41, 131.21, 134.36, 153.14, 163.07, 165.52,
167.27, 175.98. Anal. Calcd. (%) for C11H9NO4: C, 60.27; H,
4.14; N, 6.39. Found (%): C, 60.31; H, 4.15; N, 6.35.
Ethyl-2-oxo-2H-pyrano[2,3-b]pyridine-4-carboxylate
(4e). FT-IR (KBr, cm-1): 1730 (C=O), 1464 (C=C), 1258 (C-
O). 1H NMR (400 MHz, DMSO-d6) δ (ppm): 1.30 (t, 3H, Me),
4.11 (q, 2H, CH2), 7.01 (s, CH), 7.11 (t, CH, J = 8.23 Hz),
7.57 (dd, CH, J = 8.21 and 3.28 Hz), 8.14 (dd, CH, J = 8.25
and 3.28 Hz). 13C NMR (100 MHz, DMSO-d6) δ (ppm):
31.30, 53.16, 114.24, 123.64, 126.12, 135.27, 143.41, 153.67,
160.54, 166.70, 169.02, 170.10. Anal. Calcd. (%) for
C11H9NO4: C, 60.27; H, 4.14; N, 6.39. Found (%): C, 61.11;
H, 4.16; N, 6.35.
Methyl-5-hydroxy-7-methyl-2-oxo-2H-chromene-4-
carboxylate (4f). FT-IR (KBr, cm-1): 1726 (C=O), 1460
(C=C), 1236 and 1251 (C-O). 1H NMR (400 MHz, DMSO-d6)
δ (ppm): 2.29 (s, 3H, Me), 3.89 (s, 3H, OMe), 6.71 (s, CH),
7.12 (d, CH, J = 3.02 Hz), 7.18 (d, CH, J = 3.02 Hz), 11.71 (s,
1H, OH). 13C NMR (100 MHz, DMSO-d6) δ (ppm): 20.51,
57.27, 102.16, 115.40, 116.19, 126.62, 129.45, 134.21,
157.43, 157.41, 168.30, 171.03. Anal. Calcd. for C12H10O5: C,
61.54; H, 4.30%. Found (%): C, 62.01; H, 4.33.
In a 10-ml glass microwave vessel, phenolic compound
(20 mmol), di(methyl or ethyl) acetylenedicarboxylate (20
mmol) and IL-OPPh2 (30 mmol) were mixed thoroughly. The
mixture was subjected to MW irradiation at 80W for a few
minutes (depending on the reactants, see Table 2). The
completion of the reaction was monitored by TLC using
(EtOAc/petroleum 2:5) as eluent. After completion of the
reaction (1.5-5 min) as indicated by TLC on silica gel F254
(EtOAc/petroleum 2:5), the residue was purified by column
chromatography to afford pure desired products 4a-h.
Spectral Data
Methyl-7,8-dihydroxy-2-oxo-2H-chromene-4-carboxy-
late (4a). FT-IR (KBr, cm-1): 3329 and 3220 (OH), 1724
(C=O), 1703 (C=O), 1581 (C=C), 1231 and 1249 (C-O).
1H NMR (400 MHz, CDCl3) δ (ppm): 3.92 (s, 3H, OMe), 6.61
(s, CH), 6.92 (d, CH, J = 8.85 Hz), 7.28 (d, CH, J = 8.85),
8.68 (br, 2OH). 13C NMR (100 MHz, CDCl3) δ (ppm): 56.60,
104.70, 118.14, 119.45, 124.12, 128.06, 145.53, 147.24,
158.00, 162.00, 170.17. Anal. Calcd. (%) for C11H8O6: C,
55.94; H, 3.41%. Found (%): C, 61.55; H, 3.43.
Methyl-5-hydroxy-2-oxo-2H-chromene-4-carboxylate
(4b). FT-IR (KBr, cm-1): 3418 (OH), 1720 (C=O), 1581
(C=C), 1231 and 1249 (C-O). 1H NMR (400 MHz, DMSO-d6)
δ (ppm): 3.91 (s, 3H, OMe), 5.13 (s, br, OH), 6.51 (s, CH),
6.53 (dd, CH, J = 7.22 and 3.21 Hz), 6.61 (dd, CH, J = 7.32
and 3.21 Hz), 7.18 (t, CH, J = 6.41 Hz). 13C NMR (100 MHz,
DMSO-d6) δ (ppm): 55.61, 102.90, 107.74, 117.45, 124.63,
128.85, 129.53, 130.74, 158.78, 159.20, 160.37. Anal. Calcd.
(%) for C11H8O5: C, 60.00; H, 3.66%. Found (%): C, 61.23; H,
3.69.
Methyl-6-chloro-8-methyl-2-oxo-2H-chromene-4-
carboxylate (4g). FT-IR (KBr, cm-1): 1769 and 1728 (C=O),
1461 (C=C), 1170 and 1190 (C-O). 1H NMR (400 MHz,
DMSO-d6) δ (ppm): 2.32 (s, 3H, Me), 3.78 (s, 3H, OMe), 6.88
(s, CH), 7.14 (d, CH, J = 3.15 Hz), 7.21 (d, CH, J = 3.15 Hz).
13C NMR (100 MHz, DMSO-d6) δ (ppm): 18.11, 33.14, 43.16,
55.04, 121.08, 123.46, 128.25, 130.29, 134.01, 150.32,
167.10, 172.63. Anal. Calcd. for C12H9ClO4: C, 57.05; H,
3.59. Found (%): C, 58.01; H, 3.61.
Methyl-6-hydroxy-2-oxo-2H-chromene-4-carboxylate
(4c). FT-IR (KBr, cm-1): 3222 (OH), 1728 (C=O), 1700
1
(C=O), 1578 (C=C), 1229 and 1241 (C-O). H NMR (400
Methyl-6-nitro-2-oxo-2H-chromene-4-carboxylate
MHz, DMSO-d6) δ (ppm): 4.01 (s, 3H, OMe), 6.79 (s, CH),
7.20 (dd, CH, J = 8.81 and 2.78 Hz), 7.31 (d, CH, J = 8.81),
7.65 (d, CH, J = 2.78), 8.56 (s, OH). 13C NMR (100 MHz,
DMSO-d6) δ (ppm): 53.65, 110.53, 117.36, 118.98, 120.85,
(4h). FT-IR (KBr, cm-1): 1732 (C=O), 1614, 1242 and 1279
1
(C-O), 1346 and 1522 (NO2). H NMR (400 MHz, CDCl3) δ
(ppm): 4.00 (3H, s, OCH3), 7.10 (1H, s, CH), 7.48 (1H, d, J =
864

Valizadeh et al.
9.5 Hz, CH), 8.40 (1H, dd, J = 9.5 and 2.7 Hz, CH), 9.27 (1H,
arom.), 6.60 (s, CH), 4.08 (s, OCH3); 13C NMR (100 MHz,
CDCl3) δ (ppm): 167, 158.5, 154, 145, 133.8, 130, 128.5,
127.3, 127, 125.2, 122.2, 116.4, 114.8, 109, 53.39.
d, J = 2.7 Hz, CH) ppm; 13C NMR (100 MHz, CDCl3) δ
(ppm): 53.60, 116.00, 118.26, 121.72, 123.47, 127.00, 14.70,
144.33, 157.59, 158.17, 163.18; Anal. Calcd. for C11H7O6N:
C, 53.02; H, 2.83; N, 5.62; O, 38.53. Found (%): C, 53.09; H,
2.88; N, 5.57; O, 38.50.
Methyl-2-oxo-2H-benzo[h]chromene-4-carboxylate
1
(4n). H NMR (400 MHz, CDCl3) δ (ppm): 7.4-8.5 (m, 4H,
arom.), 8.00 (d, J = 9.0 Hz, 1H, arom.), 7.50 (d, J = 9.0 Hz,
1H, arom.), 6.85 (s, CH), 3.93 (s, OCH3); 13C NMR (100
MHz, CDCl3) δ (ppm):165, 160.5, 152, 143.8, 135.7, 129.8,
128.2, 127.8, 125, 122.90, 122.55, 122, 118.6 , 111.9, 53.26.
Methyl-7-methoxy-2-oxo-2H-benzo[h]chromene-4-
Methyl-6,8-dinitro-2-oxo-2H-chromene-4-carboxylate
(4i). FT-IR (KBr, cm-1): 1762 (C=O), 17.24 (C=O), 1620,1540
and 1344 (NO2), 1264, 1210, 1174. 1H NMR (400 MHz,
CDCl3) δ (ppm): 4.13 (3H, s, OCH3), 7.35 (1H, s, CH), 9.00
(1H, d, J = 2.7 Hz), 9.70 (1H, d, J = 2.7 Hz); 13C NMR (100
MHz, CDCl3) δ (ppm): 54.16, 118.54, 122.60, 123.03, 126.94,
138.22, 139.95, 155.47, 158.90, 160.13, 162.70; Anal. Calcd.
for C11H6O8N2: C, 44.91; H, 2.06; N, 9.52; O, 43.51. Found
(%): C, 44.81; H, 2.12; N, 9.60; O, 43.44.
1
carboxylate (4o). H NMR (400 MHz, CDCl3) δ (ppm): 8.6
(1H, s), 7-8.4 (4H), 7.00 (1H, s, CH), 4.00 (s, OCH3); 13C
NMR (100 MHz, CDCl3) δ (ppm): 164.9, 159.3, 151.7, 144,
135, 129.3, 128, 128, 124.8, 123.6, 123.1, 122.1, 118.4, 111.6,
53.8.
Methyl-8-methyl-2-oxo-2H-chromene-4-carboxylate
(4j). FT-IR (KBr, cm-1): 1730 (C=O), 1591, 1270, 1240, 1160.
1H NMR (400 MHz, CDCl3) δ (ppm): 2.49 (3H, s,CH3), 4.02
(1H, s, OCH3), 6.94 (1H, s, CH), 7.24 (1H, t, J = 8 Hz,
CH),7.46 (1H, dd, J = 8 and 2 Hz, CH), 8.10 (1H, dd, J = 8
and 2 Hz, CH) ppm; 13C NMR (100 MHz, CDCl3) δ (ppm):
15.75, 53.14, 115.65,118.90, 124.27, 124.56, 126.64, 133.80,
143.05, 152.70, 160.10, 164.55; Anal. Calcd. for C12H10O4: C,
66.05; H, 4.62; O, 29.33. Found C, 66.10; H, 4.58; O, 30.03.
Methyl-6-tert-butyl-2-oxo-2H-chromene-4-carboxy-
RESULTS AND DISCUSSION
The IL-OPPh2 was prepared from the two-steps reaction of
4-chlorobutanol, chlorodiphenylphosphine and 3-methyl-
imidazole in 91% yield (Scheme 2). In a typical experiment,
1:1:1 ratio of hydroquinone, dimethyl acetylenedicarboxylate
(DMAD) and IL-OPPh2 were charged into a 10-ml glass
microwave vessel and was subjected to MW irradiation at
80W. 6-Hydroxy-4-carbethoxycoumarin 4c was prepared. The
whole reaction was monitored by a MAT-90 GC/MS. The
concentration of the reactant phenolic compound and the
product was directly affected by the GC/MS ChemStation
system according to the area of each chromatograph peak.
Then we investigated the result of the process with different
molar ratios of the reactants and TSIL. We also examined the
reaction under higher power of the microwave. The results are
summarized in Table 1. It can be seen that IL-OPPh2 is of very
1
late (4k). H NMR (400 MHz, CDCl3) δ (ppm): 1.35 (9H, s,
3CH3), 4.00 (3H, s, OCH3), 6.90 (1H, s, CH), 7.27 (1H, d, J =
9 Hz), 7.59 (1H, dd, J = 9 and 2.4 Hz), 8.25 (1H, d, J = 2.4
Hz); 13C NMR (100 MHz, CDCl3) δ (ppm): 31.27, 34.69,
52.98, 115.24, 116.62, 119.19, 123.10, 129.98, 142.48,
147.81, 152.29, 160.19, 164.35; Anal. Calcd. for C15H16O4: C,
69.22; H, 6.20; O, 24.59. Found C, 69.40; H, 6.35; O, 24.45.
Ethyl-3-oxo-3H-benzo[f]chromene-1-carboxylate (4l).
1H NMR (400 MHz, CDCl3) δ (ppm): 1.41 (3H, t, J = 7.1 Hz,
CH3); 4.50 (2 H, q, J = 7.1 Hz, OCH2); 6.56 (1H, s, CH), 7.45
(1H, d, J = 9.0 Hz, arom.), 7.3-7.5 (2H, m, 2CH, arom.), 7.80
(1H, d, J = 8.4 Hz, arom.), 7.88 (1H, d, J = 7.8 Hz, arom.),
8.00 (1H, d, J = 9.0 Hz). 13C NMR (100 MHz, CDCl3) δ
(ppm): 13.96; 63.06; 115.48, 117.37, 123.56, 126.10, 128.00,
129.42, 134.52, 110.11, 128.02, 130.91, 146.33, 154.91,
159.58, 167.34.
high
activity
for
this
reaction.
6-Hydroxy-4-
carbethoxycoumarin 4c was prepared in high yield at 80W and
increasing the power of microwave did not prove to be of any
advantage (Table 1, entries 12-14). It was found that the best
results were obtained using 1.5:1:1 molar ratio of IL-
OPPh2/DMAD/hydroquinone at 80W in this experiment
(Table 1, entry 7).
Reducing the molar ratio of TSIL/reactants to 0 resulted in
the decrease of the yield of the product to 0% (Table 1, entry
1). Increasing the molar ratio of TSIL/reactants to 1.5 resulted
in the increase of the yield of product to 91% (Table 1, entry
Methyl-3-oxo-3H-benzo[f]chromene-1-carboxylate
1
(4m). H NMR (400 MHz, CDCl3) δ (ppm): 7.3-8.0 (m, 4H,
arom.), 8.05 (d, J = 9.0 Hz, 1H arom.), 7.52 (d, J = 9.0 Hz, 1H,
865

Phosphinite Ionic Liquid (IL-OPPh2) as a Recyclable Reagent
CH2Cl2 , K2CO3
-5oC , 5h
95%
Cl
Cl
Cl
PPh2
+
Ph2PO
HO
7
5
6
CH2Cl2
80 oC, 5h
91%
N
Me
N
Cl-
+
N
OPPh2
N
3 = IL-OPPh2
Me
Scheme 2. Synthesis of IL-OPPh2.
Table 1. Different Conditions for the MW-Assisted Synthesis of Coumarin 4c Using IL-OPPh2
Entry
The ratio of IL-OPPh2/DMAD/
Hydroquinone (mol/mol/mol)
MW (W)
Time
(min)
5.0
4.0
4.0
3.5
3.0
3.5
3.0
3.5
3.5
3.0
3.5
3.0
3.0
3.0
Yield
(%)a
0
1
2
3
4
5
6
7
8
0/1/1
1/1/1
80
80
80
80
80
80
80
80
80
80
80
90
100
110
82
83
83
85
86
91
91
91
90
91
87
85
85
1.1 /1/1
1.2/1/1
1.3/1/1
1.4/1/1
1.5/1/1
1.6/1/1
1.7/1/1
1.8/1/1
1.9/1/1
1.5/1/1
1.5/1/1
1.5/1/1
9
10
11
12
13
14
aThe concentration of the reactant and the product was directly given by the system of GC/MS
chemstation according to the area of each chromatograph peak.
7). This indicated that TSIL is an effective reagent and catalyst
were prepared smoothly after 1.5-5 min with good yields.
Thermal conditions were also used for the synthesis of
coumarins 4a, 4d and 4g in the presence of IL-OPPh2. These
products were prepared in 58%, 55% and 61% yield,
respectively over 3.5 h at 80 °C under these conditions.
for this reaction. In order to investigate the scope and
limitation of IL-OPPh2 for the reaction of various phenols,
other phenol derivatives were also tested. The results are
summarized in Table 2. In each case, the related coumarins
866

Valizadeh et al.
Table 2. MW-Assisted Synthesis of Coumarins Using IL-OPPh2 as a Reagent in Solventless System
Entry
Substrate
Product
Product Time Yield
number (min) (%)a
M.P. (°C)
Reprted [Ref.]
Found
OH
CO Me
2
HO
OH
1
2
2.5
1.5
77
76
214-217
215-217 [39]
115-116 [40]
4a
4b
HO
O
O
OH
OH
OH
CO Me
2
114-116
OH
O
O
CO Me
2
OH
HO
3
4
5
3.5
5
77
71
72
203-206
100-102
105-108
205-207 [39]
100-101 [40]
105-106 [40]
4c
4d
4e
O
O
OH
OH
CO Et
2
N
N
O
O
OH
CO Et
2
N
5
N
O
O
OH
CO Me
2
OH
6
7
2.5
5
77
72
112-122
92-95
119-120 [40]
94-96 [40]
4f
Me
O
O
Me
Cl
OH
OH
CO Me
2
Cl
4g
Me
O
O
Me
867

Phosphinite Ionic Liquid (IL-OPPh2) as a Recyclable Reagent
Table 2. Continued
8
3.5
75
128-130
129-130 [41]
4h
9
2.0
3.0
76
76
130-132
108-109
130-131 [41]
109-110 [41]
4i
4j
10
11
12
13
2.5
5
74
65
69
118-120
135-138
137-139
119 [41]
135.9-136.4 [42]
138 [42]
4k
4l
5
4m
O
OH
O
14
5
5
72
80
159-160.5
225-226.5
162 [43]
4n
4o
CO2Me
OCH3
15
225-227 [43]
aIsolated yield.
868

Valizadeh et al.
Phenol-containing electron-withdrawing group (entry 7)
acetate and the ionic liquid was recycled in the next run. The
results showed that, TSIL could be recycled three times
without loss of its activity for the synthesis of coumarins from
the reaction of the related phenolic compounds with di(methyl
or ethyl) acetylenedicarboxylate (Table 3).
and (2 or 4)-hydroxypyridine (entries 4 and 5) produced
minimum yields in a longer period of time. Phenol-containing
electron-withdrawing groups such as 4-nitrophenol and 2-
nitrophenol did not react under these conditions.
As proposed in Scheme 3, initially, Michael addition of IL-
OPPh2 to DMAD produced anion 8. The reaction of this anion
Several studies have been reported on the synthesis of 4-
substituted coumarins via the reaction of di(methyl or ethyl)
acetylenedicarboxylate with phenolic compounds using
triphenylphosphine as the reagent [39-43]. The yields of
coumarin derivatives reported in these studies are compared
with those obtained through our methodology in Table 4.
In conclusion, diphenylphosphine-functionalized ionic
liquid is an effective reagent and catalyst for the synthesis of
coumarins via the reaction of phenolic compounds with
di(methyl or ethyl) acetylenedicarboxylate under MWI
conditions. The diphenylphosphine group in ionic liquid can
greatly accelerate the reactions. The advantages of the present
protocol are shorter reaction times, mild reaction conditions,
with hydroquinone afforded the intermediate
9
and
hydroquinone monoanion (HQ-). HQ- was added to
intermediate 9 to produce intermediate 10 which, in turn,
produced intermediate 11 by aromatization and subsequent
cyclization. Finally, ß-elimination was done by 11 to produce
IL-OPPh2 and the related coumarin 4c. ꢀ
The recyclability of ionic liquid IL-OPPh2 was also
examined. For this purpose, the reactions for the synthesis of
coumarin 4a, 4d and 4f were selected as the typical
experiments. The product and other unreacted materials were
isolated from the reaction mixture by extraction with ethyl
CO2R2
Ph2
OH
HO
IL
P
+
O
..
-
IL-OPPh2
CO2R2
CO2R2
Ph2
8
R2O2C
O
P
IL
+
O
Ph2
IL
P
CO2R2
+
CO2R2
O
-
H
OH
O
+
R2O2C
H
9
OH
10
O
CO2R2
Ph2
P
IL
+
O
O
HO
CO2R2
IL-OPPh2
+
H
O
O
11
OH
Scheme 3. Suggested mechanism for the synthesis of 4-substituted coumarins in the presence of IL-OPPh2
869

Phosphinite Ionic Liquid (IL-OPPh2) as a Recyclable Reagent
Table 3. The Comparison of Efficiency of IL-OPPh2 in MW-Assisted
Synthesis of Coumarins 4a, 4d and 4f after three Times
Yield a(%) in IL-OPPh2
Run
4a
77
76
77
4d
71
69
70
4f
77
76
75
1
2
3
aYields of isolated product.
Table 4. Comparison of the Yields of the Coumarin Derivatives Using
IL-OPPh2 and PPh3
Yield (%)
Product
PPh3 [ref.]
73 [41]
70 [41]
84 [41]
56 [43]
60 [42]
75 [43]
83 [43]
IL-OPPh2
76
76
72
69
65
80
72
4i
4j
4g
4m
4l
4n
4o
aYields of isolated product.
good yields and recyclability of the ionic liquid. This
convenient technique is the most effective aompared with the
existing methods for the synthesis of 4-substituted coumarins.
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ACKNOWLEDGMENTS
The partial financial assistance from the Vice-Chancellor
for Research of Azarbaijan University of Tarbiat Moallem is
gratefully acknowledged.
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