A facile and efficient synthesis of tetrahydrobenzo[b]pyrans and dihydropyrano[4,3-b]pyrans derivatives using phosphate fertilizers MAP, DAP, and TSP as heterogeneous catalysts

Article abstract of DOI:10.1007/s13738-021-02223-x

A simple and efficient one-pot synthesis of tetrahydrobenzo[b]pyrans and dihydropyrano[4,3-b]pyrans derivatives was described. These reactions were realized through a three-component condensation of aromatic aldehyde, malononitrile, and 5,5-dimethyl-1,3-c

Full text of DOI:10.1007/s13738-021-02223-x

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-021-02223-x
ORIGINAL PAPER
A facile and efcient synthesis of tetrahydrobenzo[b]pyrans
and dihydropyrano[4,3‑b]pyrans derivatives using phosphate
fertilizers MAP, DAP, and TSP as heterogeneous catalysts
Soukaina Chehab1 · Youssef Merroun1 · Tourya Ghailane1 · Rachida Ghailane1 · Said Boukhris1 · Brahim Lakhrissi2 ·
Abdelaziz Souizi1
Received: 2 April 2020 / Accepted: 20 February 2021
© Iranian Chemical Society 2021
Abstract
A simple and efcient one-pot synthesis of tetrahydrobenzo[b]pyrans and dihydropyrano[4,3-b]pyrans derivatives was
described. These reactions were realized through a three-component condensation of aromatic aldehyde, malononitrile, and
5,5-dimethyl-1,3-cyclohexanedione or 4-hydroxy-6-methylpyran-2-one using phosphate fertilizers monoammonium phos-
phate, NH4(H2PO4)2, (MAP), diammonium phosphate, (NH4)2(HPO4), (DAP), and triple superphosphate, Ca(H2PO4)2.H2O,
(TSP) as heterogeneous catalysts. Under optimal reaction conditions, these fertilizers show an excellent catalytic activity.
Indeed, the tetrahydrobenzo[b]pyrans and dihydropyrano[4,3-b]pyrans derivatives were obtained with good yields in short
reaction times. Also, these fertilizers can be reused at least four times without signifcant loss of their catalytic activity.
Therefore, their application can be contributing to the development of green chemistry.
Keywords Tetrahydrobenzo[b]pyrans. Dihydropyrano[4,3-b]pyrans. Heterogeneous catalyst. MAP · DAP · TSP
Introduction
pharmacological domains, their synthesis in the presence
of diferent catalysts was received considerable attention
[5–8]. Indeed, the tetrahydrobenzo[b]pyrans derivatives
were synthesized via one-pot three-component condensa-
tion of aromatic aldehyde, malononitrile, and 5,5-dimethyl-
1,3-cyclohexanedione (dimedone) in the presence of difer-
ent catalysts such as piperazine [9], IRMOF-3 [10], silica gel
[11], synthetic diammonium hydrogen phosphate (DAHP)
[12], Na2CaP2O7 [13], polypyrrole/Fe3O4/CNT [14], RGO-
Pr-SH@AuNPs [15], Y2(CO3)3 [16], and H2PO4-Fe3O4
[17]. Moreover, the dihydropyrano[4,3-b]pyrans derivatives
were synthesized via one-pot three-component condensa-
tion of aromatic aldehyde, malononitrile, and 4-hydroxy-
6-methylpyran-2-on in the presence of various catalysts like
piperidine [18], 4-(succinimido)-1-butane sulfonic acid [19],
1H-imidazol-3-ium tricyanomethanide {[HIM]C(CN)3}[20],
sodium benzenesulfnates [21], succinimide-N-sulfonic acid
[22], [CH2O(CH2)2NH3]2(CF3COO)2 [23], RHPrBPCl [24],
and PS-TBD [25].
Recently, environmental protection has become one of the
most developed subjects. In this context, signifcant pro-
gress is being made in several research areas. Indeed, new
methodologies were developed, especially in the feld of
organic synthesis. They are based principally on the use of
environmentally benign chemicals and solvents as well as
renewable feedstocks. Thus, the use of catalysts in difer-
ent chemical reactions were considered an important route
that increases the product’s yield and environmental pro-
tection [1]. Synthesis of heterocyclic compounds via mul-
ticomponent reactions in the presence of diferent catalysts
was largely reported in some research studies [2–4]. Due to
the importance of the pyran derivatives in biological and
* Abdelaziz Souizi
souizi@yahoo.com
1
Faculty of Science, Laboratory of Organic, Organometallic
However, most of these reported methods present several
disadvantages: low yields, prolonged reaction time, harsh
reaction conditions, and excessive amounts of reagents or
expensive and non-recyclable catalysts.
and Theoretical Chemistry, University Ibn Tofail, Po
Box 133, 14000 Kenitra, Morocco
2
Faculty of Science, Laboratory of Agricultural Resources,
Polymer and Process Engineering, University Ibn Tofail, Po
Box 133, 14000 Kenitra, Morocco
Vol.:(0123456789)
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Journal of the Iranian Chemical Society
This work is a part of our attention in the valorization of
Moroccan phosphate and the development of highly ef-
cient, inexpensive, and environmentally benign methods for
organic synthesis [26–33]. It consists of the direct applica-
tion of three phosphate fertilizers prepared by OCP (Ofce
Cherifen des Phosphates) MAP (pH=5), DAP (pH=7.5),
and TSP (pH=3) [34, 35] as heterogeneous catalysts to show
their efectiveness in the synthesis of tetrahydrobenzo[b]
pyrans and dihydropyrano[4,3-b]pyrans derivatives via
three-component condensation of aromatic aldehyde,
malononitrile, and 5,5-dimethyl-1,3-cyclohexanedione or
4-hydroxy-6-methylpyran-2-on. These phosphate fertiliz-
ers are very inexpensive, nontoxic, and readily available.
From the chemical structure of these catalysts, we believe
that their surface has active acid sites. The presence of an
acidic proton gives them the possibility of reacting as Brøn-
sted acid with the oxygen carbonyl group of aldehyde.
We have noted in the literature only the use of
(NH4)2H2PO4 as a catalyst in organic synthesis [36, 37].
However, it is the frst time that phosphate fertilizers (MAP,
DAP, and TSP) were used directly as heterogeneous catalysts
in their commercial form of granules and without any pre-
liminary purifcation for the tetrahydrobenzo[b]pyrans and
dihydropyrano[4,3-b]pyrans derivatives synthesis.
Characterization of the synthetized products
2-Amino-4-(4-chlorophenyl)-3-cyano-7,7-dimethyl-5-oxo-
4H-5,6,7-tetrahydrobenzo[b]pyran
1
4a: Mp. 216–218 °C. H NMR (300 MHz, DMSO-d6,
δ ppm): 0.95 (3H, s, CH3), 1.04 (3H, s, CH3), 2.11 (1H,
d, CH2), 2.27 (1H, d, CH2), 2.54 (2H, s, CH2), 4.20 (1H,
s, CH), 7.07 (2H, s, NH2), 7.16 (2H, d, Ar–H), 7.35(2H,
d, Ar–H). 13C NMR (75 MHz, DMSO-d6, δ ppm): 27.18,
28.92, 32.24, 35.06, 50.41, 59.13, 112.30, 113.71, 119.21,
128.23, 129.59, 132.01, 143.51, 158.41, 162.39, 196.15.
2-Amino-3-cyano-7,7-dimethyl-5-oxo-4-phenyl-4H-
5,6,7,8-tetrahydrobenzo[b]pyran
1
4b: Mp. 234–236 °C. H NMR (300 MHz, DMSO-
d6, δ ppm): 0.96 (3H, s, CH3), 1.03 (3H, s, CH3), 2.09
(1H, d, CH2), 2.23 (1H, d, CH2), 2.49 (2H, s, CH2), 4.18
(1H, s, CH), 7.03–7.30 (7H, m, Ar–H and NH2). 13C NMR
(75 MHz, DMSO-d6, δ ppm): 27.12, 28.75, 32.17, 36.05,
50.13, 58.67, 113.18, 120.17, 127.04, 127.61, 128.54,
145.20, 158.85, 162.98, 196.15.
2-Amino-3-cyano-4-(4-methylphenyl)-7,7-dimethyl-5-
oxo-4H-5,6,7,8-tetrahydrobenzo[b] pyran
1
4c. Mp. 210–212 °C. H NMR (300 MHz, DMSO-d6,
δ ppm): 0.95 (3H, s, CH3), 1.04 (3H, s, CH3), 2.08 (1H,
d, CH2), 2.25 (3H, s, CH3), 2.26 (1H, d, CH2), 2.51(2H,
s, CH2), 4.12 (1H, s, CH), 6.99–7.10 (6H, m, Ar–H and
NH2). 13C NMR (75 MHz, DMSO-d6, δ ppm): 21.07,
27.21, 28.91, 32.28, 35.63, 50.44, 58.85, 113.31, 120.26,
127.55, 129.36, 136.10, 142.30, 158.89, 162.77, 196.14.
2-Amino-3-cyano-4-(4-nitrophenyl)-7,7-dimethyl-5-
oxo-4H-5,6,7,8-tetrahydrobenzo[b]pyran
Experimental
Chemical and apparatus
All chemical reagents used were purchased from Sigma-
Aldrich. The reactions were monitored by thin-layer chro-
matography (TLC). Melting points were measured on a
Kofer device. NMR 1H and 13C spectra were recorded with
a Brucker 300 MHz spectrometer in a DMSO-d6 (300 MHz
for 1H and 75 MHz for 13C).
1
4d. Mp. 180–182 °C. H NMR (300 MHz, DMSO-d6,
δ ppm): 0.96 (3H, s, CH3), 1.04 (3H, s, CH3), 2.11 (1H,
d, CH2), 2.26 (1H, d, CH2), 2.54 (2H, s, CH2), 4.37 (1H,
s, CH), 7.22 (2H, s, NH2), 7.44 (2H, d, Ar–H), 8.17 (2H,
d, Ar–H). 13C NMR (75 MHz, DMSO-d6, δ ppm): 27.39,
28.40, 32.31, 36.10, 50.30, 57.38, 112.17, 119.84, 124.17,
129.10, 146.71, 152.79, 159.03, 163.59, 196.21.
2-Amino-3-cyano-4-(4-dimethyaminophenyl)-7,7-dime-
thyl-5-oxo-4H-5,6,7,8-tetrahydrobenzo[b]pyran
General procedure for tetrahydrobenzo[b]pyrans
and dihydropyrano[4,3‑b]pyrans derivatives
synthesis
4e. Mp. 216–218 °C. 1H NMR (300 MHz, DMSO-d6,δ
ppm): 0.95 (3H, s, CH3), 1.03 (3H, s, CH3), 2.07 (1H, d,
CH2), 2.24 (1H, d, CH2), 2.49 (2H, s, CH2), 2.84 (6H,
s, N(CH3)2), 4.05 (1H, s, CH), 6.62–6.96 (6H, m, Ar–H
and NH2). 13C NMR (75 MHz, DMSO-d6, δ ppm): 27.19,
28.98, 32.25, 35.04, 39.39, 40.23, 50.51, 59.34, 112.29,
113.72, 120.46, 128.20, 133.01, 149.68, 158.80, 162.32,
196.16.
An equimolar mixture of an aromatic aldehyde (1 mmol),
malononitrile (1 mmol), 5,5-dimethyl-1,3-cyclohexanedi-
one (1 mmol) or 4-hydroxy-6-methylpyran-2-on and MAP
(8.5 mol%), DAP (7.6 mol%) or TSP (4.3 mol%) was dis-
solved in ethanol and stirred under refux conditions in the
appropriate times. The reaction completion was checked by
TLC (ethyl acetate: n-hexane (3:5)). Then, the mixture was
cooled at room temperature, and the obtained residue was
washed with dichloromethane. The fltrate was cooled to
give pure products. The synthesized products were charac-
terized by their spectral data 1H and 13C NMR and melting
points.
2-Amino-3-cyano-4-(4-hydroxy-3-methoxyphenyl)-7,7-
dimethyl-5-oxo-4H-5,6,7,8-tetrahydrobenzo[b]pyran
1
4f. Mp. 238–240 °C. H NMR (300 MHz, DMSO-d6,
δ ppm): 0.98 (s, 3H, CH3), 1.05 (s, 3H, CH3), 2.12 (d,
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Journal of the Iranian Chemical Society
1
1H, CH2), 2.26 (d, 1H, CH2), 2.50 (s, 2H, CH2), 3.73 (s,
3H, OCH3), 4.10 (s, 1H, CH), 6.53–6.70 (m, 3H, Ar–H),
6.81(s, 2H, NH2), 8.70 (s, 1H, OH). 13C NMR (75 MHz,
DMSO-d6, δ ppm): 27.18, 28.96, 32.18, 35.50, 50.61,
56.22, 59.48, 112.23, 113.64, 115.90, 119.96, 120.22,
136.30, 145.84, 147.80, 158.91, 162.56, 196.05.
6d. Mp. 250–252 °C. H NMR (300 MHz, DMSO-d6,
δ ppm): 2.22 (3H, s, CH3), 2.86 (6H, s, (N(CH3)2), 4.14
(1H, s, CH), 6.26 (1H, s, CH), 6.64–6.67 (2H, d, Ar–H),
6.97–7.00 (2H, d, Ar–H), 7.12 (2H, s, NH2).13C NMR
(75 MHz, DMSO-d6, δ ppm): 19.24, 35.30, 58.44, 97.88,
101.37, 111.79, 112.31, 119.49, 128.01, 131.24, 133.58,
149.50, 157.58, 157.93, 161.34, 162.44.
2-Amino-5,6,7,8-tetrahydro-4-(3,4,5-trimethoxyphe-
nyl)-7,7- dimethyl-5-oxo-4H-chromene-3-carbonitrile
2‐Amino‐7‐methyl‐5‐oxo‐4‐(4‐methoxyphenyl)‐
4H,5Hpyrano[4,3‐b]pyran‐3‐carbonitrile
1
4 g. Mp. 247–249 °C. H NMR (300 MHz, DMSO-d6,
1
δ ppm): 1.02 (s, 3H, CH3), 1.05 (s, 3H, CH3), 2.14 (d, 1H,
CH2), 2.29 (d, 1H, CH2), 2.53 (s, 2H, CH2), 3.63 (s, 3H,
OCH3), 3.72 (s, 6H, 2OCH3), 4.14 (s, 1H, CH), 6.38 (s, 2H,
NH2), 7.01 (s, 2H, Ar–H). 13C NMR (75 MHz, DMSO-d6, δ
ppm): 27.86, 28.88, 32.22, 36.07, 50.43, 56.22, 58.75, 60.38,
104.53, 112.78, 120.23, 136.51, 140.97, 153.22, 158.81,
163.28, 196.24.
6e. Mp. 205–207 °C. H NMR (300 MHz, DMSO-d6,
δppm): 2.22 (s, 3H, CH3), 3.68 (s, 3H, OCH3), 4.28 (s,
1H, CH), 6.29 (s, 1H, CH), 7.18–7.30 (m, 6H, Ar–H and
NH2).13C NMR (75 MHz, DMSO-d6, δppm): 19.24, 35.80,
56.62, 57.82, 97.95, 100.09, 119.27, 127.41, 128.95, 136.65,
143.28, 158.10, 161.33, 162.89.
2-Amino-7-methyl-4-(4-nitrophenyl)-5-oxo-4,5-
dihydropyrano[4,3-b]pyran-3-carbonitrile
2-Amino-5,6,7,8-tetrahydro-4-(2,3-dimethoxyphenyl)-
7,7-dimethyl-5-oxo-4H-chromene-3-carbonitrile
6f. Mp. 220–222 °C. 1H NMR (300 MHz, DMSO-d6, δ
ppm): 2.24 (3H, s, CH3), 4.52 (1H, s, CH), 6.33 (1H, s, CH),
7.39 (2H, s, NH2), 7.50–7.53 (2H, d, Ar–H), 8.18–8.21 (2H,
d, Ar–H).13C NMR (75 MHz, DMSO-d6, δ ppm): 19.30,
36.12, 56.65, 97.98, 99.53, 118.94, 123.65, 129.00, 146.51,
150.98, 158.15, 158.60, 161.30, 163.46.
1
4 h. Mp. 217–219 °C. H NMR (300 MHz, DMSO-d6,
δ ppm): 0.98 (s, 3H, CH3), 1.04 (s, 3H, CH3), 2.06 (d, 1H,
CH2), 2.24 (d,1H, CH2), 2.51 (s, 2H, CH2), 3.78 (s, 3H,
OCH3), 3.83 (s, 3H, OCH3), 4.55 (s, 1H, CH), 6.58 (d, 1H,
Ar–H), 6.85 (d, 1H, Ar–H), 6.93–6.99 (m, 3H, Ar–H et
NH2). 13C NMR (75 MHz, DMSO-d6, δ ppm): 27.29, 28.89,
29.81, 32.30, 50.50, 55.96, 58.36, 60.47, 111.39, 113.09,
120.35, 120.58, 124.16, 138.24, 146.46, 152.66, 159.17,
163.27, 196.14.
2‐Amino‐7‐methyl‐5‐oxo‐4‐(4‐bromophenyl)‐4H,5H‐
pyrano[4,3‐b]pyran‐3‐carbonitrile
6 g. Mp. 225–227 °C. 1H NMR (300 MHz, DMSO-d6,
δ ppm) 2.21 (3H, s, CH3), 4.30 (1H, s, CH), 6.29 (1H, s,
CH), 7.20–7.40 (4H, m, Ar–H), 7.50 (2H, s, NH2).13C NMR
(75 MHz, DMSO-d6, δ ppm): 19.27, 36.20, 57.12, 97.50,
99.98, 119.17, 126.96, 127.40, 128.37, 142.97, 158.05,
158.20, 161.30, 162.41.
2‐Amino‐7‐methyl‐5‐oxo‐4‐(4‐chlorophenyl)‐4H,5H‐
pyrano[4,3‐b]pyran‐3‐carbonitrile
1
6a. Mp. 228–230 °C. H NMR (300 MHz, DMSO-d6,
δ ppm): 2.23 (3H, s, CH3), 4.33 (1H, s, CH), 6.29 (1H, s,
CH), 7.22–7.27 (4H, m, Ar–H and NH2), 7.37–7.39 (2H,
d, Ar–H). 13C NMR (75 MHz, DMSO-d6, δ ppm): 19.27,
35.71, 57.41, 97.93, 100.21, 119.14, 128.33, 129.45, 131.53,
142.53, 158.05, 158.25, 161.30, 163.08.
Results and discussion
2 - A m i n o - 7 - m e h y l - 5 - o x o - 4 - p h e n y l - 4 , 5 -
dihydropyrano[4,3-b]pyran-3-carbonitrile
In order to evaluate the catalytic activity of MAP, DAP, and
TSP, the synthesis of tetrahydrobenzo[b]pyrans derivatives
via three-component condensation of 4-chlorobenzaldehyde,
malononitrile, and dimedone was chosen as a model reaction
(Scheme 1). At frst, the reaction was realized in the absence
and in the presence of MAP (8.5 mol%), DAP (7.6 mol%), or
TSP (4.3 mol%) under the same reaction conditions (ethanol
and refux) (Table 1).
1
6b. Mp. 236–238 °C. H NMR (300 MHz, DMSO-d6,
δ ppm): 2.23 (3H, s, CH3), 4.28 (1H, s, CH), 6.29 (1H, s,
CH), 7.18–7.33 (7H, m, Ar–H and NH2).13C NMR (75 MHz,
DMSO-d6, δ ppm): 19.27, 36.24, 57.90, 97.90, 100.71,
119.28, 126.96, 127.45, 128.39, 143.56, 158.05, 158.15,
161.33, 162.90.
2‐Amino‐7‐methyl‐5‐oxo‐4‐(4‐methylphenyl)‐4H,5H‐
pyrano[4,3‐b]pyran‐3‐carbonitrile
The catalytic test (Table 1) shows that in the absence of
catalysts, the reaction is kinetically prolonged. Indeed, the
reaction gives only traces of product even after 120 min,
while in the presence of MAP (pH=5), DAP (pH=7.5), or
TSP (pH=3), it allows access to the desired product rapidly
(30–50 min) with excellent yields (85–89%). The best results
are obtained in the presence of TSP characterized stronger
acidic character than the MAP and DAP. Therefore, we can
deduce that the rate of reaction increases with increasing of
the catalyst acidity.
1
6c. Mp. 223–225 °C. H NMR (300 MHz, DMSO-d6,
δ ppm): 2.22 (3H, s, CH3), 2.27 (3H, s, CH3), 4.23 (1H,
s, CH), 6.28 (1H, s, CH), 7.08–7.11 (4H, m, Ar–H), 7.19
(2H, s, NH2). 13C NMR (75 MHz, DMSO-d6, δ ppm): 19.26,
20.58, 35.85, 58.02, 97.89, 100.84, 119.31, 127.35, 128.93,
136.10, 140.63, 158.00, 161.31, 162.78.
2-Amino-7-mehyl-4-(4-Dimethylaminophényl)-5-oxo-
4,5-dihydropyrano[4,3-b]pyran-3-carbonitrile
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Journal of the Iranian Chemical Society
Scheme 1 Model reaction for
the tetrahydrobenzo[b]pyrans
derivatives synthesis
Cl
O
O
O
O
CN
CN
CN
MAP, DAP or TSP
Solvent, reflux
H
+
Cl
+
O
NH2
4a
2
1
3
Table 1 Catalytic test in tetrahydrobenzo[b]pyrans derivatives
Generally, the reaction conditions such as the reaction
synthesisa
time, the catalyst amount, and the solvent nature, and its
volume can be considered parameters that signifcantly
infuence the reaction yield. A study of the factors afect-
ing the reaction results was carried out to determine the
optimal conditions.
Entry
Catalyst
Time (min)
Yield (%)b
1
2
3
4
–
120
40
50
Trace
85
80
MAP
DAP
TSP
First, the model reaction was realized in diferent reac-
tion times, and the obtained yields are presented in Fig. 1.
From Fig. 1, it is noted that the product 4a yield
increases with the increase in the reaction time. Indeed,
the yields achieve 85% after 40 min as reaction time, 80%
after 50 min, and 89% after 30 min in the presence of
MAP, DAP, and TSP, respectively. After these reaction
times, it is shown that the yield remains practically con-
stant, proving the reaction completion.
30
89
a
Reaction conditions: 4-chlorobenzaldehyde (1 mmol), malononitrile
(1 mmol), dimedone (1 mmol), EtOH (3 mL), MAP (8.5 mol%), DAP
(7.6 mol%), and TSP (4.3 mol%), refux
b Isolated yields
MAP
DAP
TSP
100
90
80
70
60
50
40
30
20
10
0
The catalyst amount efect was also studied. For this,
the model reaction was carried out in the presence of dif-
ferent catalyst amount. Table 2 summarizes the obtained
results.
Table 2 shows that a mass of 3.3 mol% of MAP,
3.1 mol% of DAP, or 2.6 mol% of TSP is sufcient to syn-
thesize product 4a with excellent yields (90 to 96%). How-
ever, when these catalysts are used in excess, a decrease in
the yield is observed. This can be explained by the disper-
sion of the reagents on a sizeable catalytic surface, provok-
ing a reduction of interaction between reagents. The model
reaction was conducted in various solvents to determine
the appropriate one for the synthesis of product 4a. The
results are collected in Table 3.
0
10
20
30
40
50
60
Time (min)
Fig. 1 Reaction time efect on tetrahydrobenzo[b]pyrans derivatives
synthesis
Table 2 Infuence of the
catalyst amount on the
tetrahydrobenzo[b]pyrans
derivatives synthesisa
Entry
Catalyst
amount (mol
%)
Time (min)
Yield (%)b
MAP
DAP
TSP
MAP
DAP
TSP
MAP
DAP
TSP
1
2
3
4
5
1.7
3.3
5.2
6.9
8.5
1.5
3.1
4.6
6.1
7.6
0.8
1.7
2.6
3.4
4.3
40
40
40
40
40
50
50
50
50
50
30
30
30
30
30
91
94
91
89
85
89
90
88
85
80
86
90
96
93
89
a
Reaction conditions: 4-chlorobenzaldehyde (1 mmol), malononitrile (1 mmol), dimedone (1 mmol), (x
mol%) of MAP, DAP and TSP, EtOH (3 mL), refux
b Isolated yields
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Journal of the Iranian Chemical Society
Table 3 shows the facile synthesis of product 4a when the
ethanol was used as a solvent. This can be explained by the
vital role of the solvent polarity to facilitate the reagents’
condensation. Indeed, the reaction in the presence of ethanol
was shown the best yields of product 4a (90 to 96%). There-
fore, ethanol was considered as an appropriate solvent for
tetrahydrobenzo[b]pyrans derivatives synthesis.
Table 4 shows that 3 mL of ethanol is sufcient to syn-
thesize 4a with excellent yields (90–96%) and is considered
the optimal solvent volume for this reaction.
To confrm the heterogeneity of the used catalysts. A
mixture of ethanol (3 mL) and MAP (8.5 mol%), DAP
(7.6 mol%), or TSP (4.3 mol%) was stirred under refux for
60 min. Then, fltered to remove the catalyst and the fl-
trate was used as a reaction medium for the condensation of
4-chlorobenzaldehyde (1 mmol), malononitrile (1 mmol),
and dimedone (1 mmol) at reflux for 120 min (Fig. 2),
which led to the product traces. These results are the same
as those obtained for the reaction in the absence of cata-
lysts (Table 1), indicating no trace of catalysts to activate the
It should be noted that the solvent volume is also an
important parameter, which infuences the yield of the reac-
tion products. For this, the synthesis of product 4a was car-
ried out under the operating conditions previously deter-
mined (reaction time, catalyst amount, and solvent) in the
presence of diferent solvent volume (1 to 5 mL) (Table 4).
Table 3 Solvent efect on the
tetrahydrobenzo[b]pyrans
derivatives synthesisa
Entry
Solvent
Time (min)
Yield (%)b
DAP
MAP
TSP
MAP
DAP
TSP
1
2
3
4
5
6
EtOH
40
40
40
40
40
40
50
50
50
50
50
50
30
30
30
30
30
30
94
82
84
79
78
80
90
80
79
76
75
77
96
87
85
80
80
83
MeOH
CH3CN
THF
Dioxane
Chloroform
a
Reaction conditions: 4-chlorobenzaldehyde (1 mmol), malononitrile (1 mmol), dimedone (1 mmol),
3.3 mol% of MAP, 3.1 mol% of DAP and 2.6 mol% of TSP, ethanol (3 mL), refux
b Isolated yield
Table 4 Infuence of the
solvent volume on the
tetrahydrobenzo[b]pyrans
derivatives synthesisa
Entry
Volume of
Time (min)
MAP
Yield (%)b
DAP
ethanol
TSP
MAP
DAP
TSP
1
2
3
1 ml
3 ml
5 ml
40
40
40
50
50
50
30
30
30
90
94
87
87
90
85
92
96
80
a
Reaction conditions: 4-chlorobenzaldehyde (1 mmol), malononitrile (1 mmol), dimedone (1 mmol),
3.3 mol% of MAP, 3.1 mol% of DAP, and 2.6 mol% of TSP, ethanol, refux
b Isolated yields
Fig. 2 Heterogeneity test
1 3

Journal of the Iranian Chemical Society
fltrate. Therefore, we can conclude that the used catalysts
are heterogeneous and insoluble in the reaction medium.
The excellent catalyst durability is an important criterion,
which proves their efciency. It corresponds to its capacity
for reuse several times without signifcant loss of its cata-
lytic activity. In order to study the reusability of MAP, DAP,
and TSP, the model reaction was realized under the optimal
conditions previously determined. After completing the
reaction, the catalyst was recovered, washed with dichlo-
romethane, and dried at 100 °C for 1 h. Then, the catalyst
was reused for the next reaction. The obtained yields are
presented in Fig. 3.
The determination of the optimal reaction conditions was
realized by studying the efect of diferent reaction param-
eters (reaction time, catalyst amount, solvent nature, and
volume) on the yield of 6a. Figure 4 and Table 5 present
the results.
Figure 4 shows an increase in the yields of the product
6a; indeed, 82, 85, and 81% were obtained after 70, 60, and
40 min in the presence of MAP, DAP, and TSP respectively.
The experimental results (Table 5) show that the excel-
lent yields (93, 92, and 91%) were obtained for the reaction
at refux (40–70 min) in 1 mL of ethanol in the presence of
MAP (3.3 mol%), DAP (4.6 mol%), and TSP (2.6 mol%),
respectively.
Figure 3 shows that the yields remain the best even after
four cycles of reuse. Indeed, the three used catalysts keep
their catalytic efciency even after their reuse.
The reusability of the catalysts used in the synthesis of
product 6a was also studied. The results show that the yields
remain practically unchanged even after fve reuse cycles,
proving that the MAP, DAP, and TSP have a high reuse
capacity (Fig. 5).
To extend the application of MAP, DAP, and TSP fer-
tilizer phosphates in organic reactions, the synthesis of
dihydropyrano[4,3-b]pyrans derivatives was realized as a
second reaction to test the catalytic efciency of the cata-
lysts. First, the condensation of 4-chlorobenzaldehyde, malo-
nonitrile, and 4-hydroxy-6-methylpyran-2-on was chosen as
a model reaction (Product 6a) (Scheme 2).
For the generalization study of tetrahydrobenzo[b]pyrans
and dihydropyrano[4,3-b]pyrans derivatives synthesis, the
reactions were realized in the presence of MAP, DAP,
and TSP under optimal conditions using various aromatic
aldehydes with different groups (donors and attractors)
(Scheme 3). The obtained results are collected in Table 6.
The results show that the condensation of aldehyde,
malononitrile, and dimedone give products with good
to excellent yields. Indeed, the aromatic aldehydes with
The catalytic test results show that only traces of the
product were obtained in the absence of catalysts, even after
180 min. While in the presence of MAP, DAP, or TSP, the
product 6a was obtained after only 40 min with good yields
(70–81%).
MAP
DAP
TSP
MAP
94
DAP
94
TSP
92
90
80
70
60
50
40
30
20
10
0
96
94
94
100
80
60
40
20
0
90
90
89
89
88
86
1
Cycle 1
2
3
4
Cycle 2
Cycle 3
Cycle 4
0
10
20
30
40
50
60
70
8 0
90
Time (min)
Number of cycle
Fig. 3 Reusability of the MAP, DAP, and TSP catalysts in the model
Fig. 4 Optimization of the reaction time of dihydropyrano[4,3-b]
reaction
pyrans derivatives synthesis
Scheme 2 The model reaction
NH2
CN
for dihydropyrano[4,3-b]pyrans
O
OH
O
O
O
derivatives synthesis
MAP, DAP or TSP
Solvent, reflux
CN
CN
+
+
Cl
H3C
O
H3C
O
Cl
2
1
5
6a
1 3

Journal of the Iranian Chemical Society
MAP
DAP
92
TSP
90
Table 5 Optimization of the catalyst amount, solvent nature, and vol-
ume of the dihydropyrano[4,3-b]pyrans derivatives synthesisa
93
93
92
92
91
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
90
90
89
88
87
87
84
85
Catalyst Catalyst
amount
Solvent
Time (min) Yieldb (%)
(mol%)
MAP
DAP
TSP
8.5
6.9
5.2
3.3
1.7
3.3
3.3
3.3
3.3
3.3
3.3
3.3
3.3
3.3
10/7.6
6.1
4.6
3.1
1.5
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.3
3.4
2.6
1.7
0.8
2.6
2.6
2.6
2.6
2.6
2.6
2.6
2.6
2.6
EtOH
EtOH
EtOH
EtOH
70
70
70
70
70
70
90
120
120
120
120
82
85
88
90
86
93
75
70
67
60
72
93
90
87
85
89
91
87
83
90
79
73
69
63
70
92
91
89
81
83
89
87
82
85
74
69
65
57
68
91
89
84
EtOH
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
MeOH
CH3CN
Dioxane
CH2Cl2
Toluene
THF
EtOH (1 mL) 70
EtOH (3 mL) 70
EtOH (5 mL) 70
EtOH
EtOH
EtOH
EtOH
Number of cycle
Fig. 5 Reusability of MAP, DAP, and TSP in the dihydropyrano [4,3-
b] pyrans derivatives synthesis at optimum reaction conditions
electron-donating groups (4-CH3, 4-N(CH3)2, 4,3-OH,
OCH3, 4-OCH3, 2,3-OCH3, 3,4,5-OCH3) give desired prod-
ucts with good yields with 77 to 93% yields in short reac-
tion times varying between 30–50 min. When the aromatic
aldehyde with an electron-withdrawing group (4-NO2) is
used, the reaction gives the achieved products with high
yields (85 to 91%) after 30 and 50 min. The aldehyde with
halogen functionality (4-Cl) shows a rapid reactivity to
provide the corresponding product 4a with excellent yields
90–96% in short reaction times (30–50 min). Thus, electron-
donating groups improved the reaction rate and furnished
tetrahydrobenzo[b]pyrans derivatives in excellent yields.
When replacing dimedone in the reaction with 4-hydroxy-
6-methyl pyran-2-one, we notice that all the desired prod-
ucts (6a–6 g) were obtained at prolonged reaction times
(40–80 min) with good to excellent yields (87–93%). The
catalytic activity of MAP, DAP, and TSP has not signif-
cantly afected the nature of the aromatic aldehyde.
60
60
60
60
60
60
80
120
120
120
120
EtOH
MeOH
CH3CN
Dioxane
CH2Cl2
Toluene
THF
EtOH (1 mL) 60
EtOH (3 mL) 60
EtOH (5 mL) 60
EtOH
EtOH
EtOH
EtOH
40
40
40
40
40
40
60
90
90
90
90
To understand the catalyst behavior in the reagent acti-
vation that facilitate their interaction for leading to the
product, Scheme 4 presents the proposed mechanism based
on previous reports [41, 42] for tetrahydrobenzo[b]pyrans
dihydropyrano[4,3-b]pyrans derivatives synthesis in the
presence of MAP. The same mechanism may occur in the
presence of DAP or TSP.
EtOH
MeOH
CH3CN
Dioxane
CH2Cl2
Toluene
THF
EtOH (1 mL) 40
EtOH (3 mL) 40
EtOH (5 mL) 40
In the frst step, the proton acid of the catalyst activated
malononitrile. Next, the proton from NH4H2PO4 increased
the electrophilicity of the carbonyl group of aldehyde. The
Knoevenagel condensation of activated malononitrile (2)
with an activated aldehyde (3) generates intermediate
(4) that with dehydration, give 2-benzylidenemalononi-
trile intermediate (I). In the second step, the dimedone
(4) was converted to the enolizable dimedone (II) in the
presence of NH4H2PO4. Subsequently, Michael’s addition
a
Reaction conditions: 4-chlorobenzaldehyde (1 mmol), malononitrile
(1 mmol), 4-hydroxy-6-methylpyran-2-on (1 mmol), refux
b Isolated yields
1 3

Journal of the Iranian Chemical Society
Scheme 3 Tetrahydrobenzo[b]
pyrans and dihydropyrano[4,3-
b]pyrans derivatives synthesis
Cl
O
3
O
O
CN
O
NH2
O
4a-4h
MAP, DAP or TSP
EtOH, reflux
CN
CN
+
R
NH2
2
1
CN
O
OH
H3C
O
O
Cl
6a-6g
H3C
O
5
O
of the enolizable dimedone (II) to 2-benzylidene malon-
onitrile intermediate (I), leading to the intermediate (III),
followed by intramolecular cyclization to give the inter-
mediate (IV). Finally, tautomerization afords the desired
product (VII). A similar mechanism may be proposed for
the formation of dihydropyrano[4,3-b]pyrans derivatives.
To estimate the efciency of three used catalysts (MAP,
DAP, and TSP) in the tetrahydrobenzo[b]pyrans and
dihydropyrano[4,3-b]pyrans derivatives synthesis, a com-
parative study was carried out between MAP, DAP, and
TSP and other catalysts reported in the literature (Table 7).
The results (Table 7) show that the MAP, DAP, and
TSP possess an exciting catalytic activity. They can be
considered efficient, nontoxic, and inexpensive cata-
lysts than others reported in the literature to synthesize
tetrahydrobenzo[b]pyrans dihydropyrano[4,3-b]pyrans
derivatives.
Conclusion
Based on the work results, a green, efcient, and simple
method were developed for the tetrahydrobenzo[b]pyrans
and dihydropyrano[4,3-b]pyrans derivatives synthesis via
three-component reaction using phosphate fertilizers MAP,
DAP, and TSP as heterogeneous catalysts.
To evaluate the catalyst’s efciency, the optimization of
the reaction condition, namely the reaction time, the catalyst
amount, the nature, and the volume of the solvent, was car-
ried out to achieve good yields of product in short reaction
times. The process proposed consists of the use of MAP,
DAP, and TSP as nontoxic, inexpensive, and recyclable
catalysts that contribute to the valorization of Moroccan
phosphate and the environment protection as the economy
of the energy cost.
1 3

Journal of the Iranian Chemical Society
Table 6 Yields, reaction times, and melting points for the tetrahydrobenzo[b]pyrans and dihydropyrano[4,3-b]pyrans derivatives synthesisa
Entry
4a
Structure
Catalyst
MAP
Time (min)
40
Yieldb (%)
Mp (°C) found
Mp (°C) reported
216–218[38]
Cl
O
94
216–218
O
CN
NH2
DAP
TSP
MAP
50
30
40
90
96
90
4b
4c
234–236
210–212
234–236[38]
208–210[11]
O
O
O
CN
O
NH2
DAP
TSP
MAP
50
30
40
86
92
80
CH3
CN
O
NH2
DAP
TSP
MAP
50
30
40
82
86
91
4d
4e
4f
NO2
180–182
216–218
238–240
179–182[10]
214–218[10]
240–242[38]
CN
O
NH2
DAP
TSP
MAP
50
30
40
89
85
84
N(CH3)2
O
CN
O
NH2
DAP
TSP
MAP
50
30
40
93
87
83
OH
OCH3
O
CN
O
NH2
DAP
TSP
50
30
79
85
1 3

Journal of the Iranian Chemical Society
Table 6 (continued)
Entry
4 g
Structure
Catalyst
MAP
Time (min)
40
Yieldb (%)
90
Mp (°C) found
Mp (°C) reported
247–249[11]
247–249
OCH3
OCH3
H3CO
O
CN
O
NH2
DAP
50
88
TSP
MAP
30
40
89
84
4 h
217–219
216–218[39]
OCH3
O
OCH3
CN
O
NH2
DAP
TSP
MAP
50
30
70
77
87
93
6a
6b
6c
6d
228–230
236–238
223–225
250–252
228–230[19]
236 [19]
224–225[40]
–
NH2
CN
O
H3C
O
O
Cl
DAP
TSP
MAP
60
40
70
92
91
91
NH2
CN
CN
O
H3C
O
O
DAP
TSP
MAP
60
40
80
90
90
90
NH2
O
O
H3C
O
CH3
DAP
TSP
MAP
70
50
80
87
88
89
DAP
TSP
65
45
90
88
1 3

Journal of the Iranian Chemical Society
Table 6 (continued)
Entry
6e
Structure
Catalyst
MAP
Time (min)
80
Yieldb (%)
88
Mp (°C) found
Mp (°C) reported
202–205[40]
205–207
NH2
CN
O
H3C
O
O
OCH3
DAP
70
86
TSP
MAP
60
75
87
90
6f
220–222
225–227
220–222[19]
226–227[40]
NH2
CN
O
O
H3C
O
NO2
DAP
TSP
MAP
65
45
70
91
90
93
6 g
NH2
CN
O
O
H3C
O
Br
DAP
TSP
60
40
92
90
a
Reaction conditions (4a-4 h): 4-chlorobenzaldehyde (1 mmol), malononitrile (1 mmol), dimedone (1 mmol), 3.3 mol% of MAP, 3.1 mol% of
3.1 mol% DAP and 2.6 mol% of TSP, ethanol (3 mL), refux
Reaction conditions (6a-6 g): 4-chlorobenzaldehyde (1 mmol), malononitrile (1 mmol), 4-hydroxy-6-methylpyran-2-on (1 mmol), 3.3 mol% of
a
MAP, 4.6 mol% of DAP and 2.6 mol% of TSP, EtOH (1 mL), refux
b Isolated yields
1 3

Journal of the Iranian Chemical Society
R
H
CN
CN
HO
CN
CN
H
CN
CN
+
-H2O
C N
O
C N
1
3
2
4
H
H
H
H
I
O
O
O
O
O
P
P
R
R
O
O
O
NH4
NH4
R
H
CN
CN
H3C
CH3
O
H3C
O
CH3
I
O
+
H
O
CN
CN
H
O
H
II
H3C
5
R
O
H
O
H
H
O
CH3
III
O
O
P
P
H
H
O
O
O
O
NH4
NH4
O
O
P
O
O
NH4
R
R
O
H
O
CN
NH
CN
CN
H3C
H3C
O
CH3
OH
V
CH3
IV
H
H
H
H
O
O
O
O
O
O
P
P
O
NH4
O
NH4
R
O
CN
H3C
O
NH2
CH3
Product (VI)
Scheme 4 The suggested mechanism for the tetrahydrobenzo[b]pyrans derivatives synthesis using MAP as a catalyst
1 3

Journal of the Iranian Chemical Society
Table 7 Comparison of the
catalytic efciency of MAP,
DAP, and TSP and other
catalysts reported in the
literature for the synthesis
of tetrahydrobenzo[b]
Entry
Catalyst
Reaction conditions
Time (min)
Yield (%)
Ref
1
2
3
4
5
6
7
8
MAP
DAP
TSP
EtOH/refux
EtOH/refux
EtOH/refux
Mw at 140 W
H2O:EtOH/80 °C
H2O:EtOH /40 °C
EtOH/80 °C
H2O:EtOH/refux
60 °C
H2O/70 °C
EtOH/refux
80 °C
MeOH/refux
H2O:EtOH/ t.a
r.t
40–70
50–60
30–40
5
30
80
120
60
300
90
18
180
60
93–94
90–92
91–96
92
89
78
94
95
90
92
94
85
79
81
This work
This work
This work
[43]
[44]
[45]
[46]
[47]
[10]
[11]
[48]
[49]
[18]
[50]
pyrans (Entry 4–10) and
dihydropyrano[4,3-b]pyrans
derivatives (Entry 11–16)
[Et3NH] [HSO4]
FSM-16/AEPC-SO3H
Fructose
NH4Al(SO4)2 12H2O
Fe3-xTixO4
IRMOF-3
9
10
11
12
13
14
15
Silica gel
Nanocell-OBF2
[bmim][BF4]
Piperidine
Urée
180
30
1,4-piperazinediethane-
94
[51]
sulfonic acid
16
H6P2W18O62.18H2O
H2O/refux
60
94
[40]
22. N.G. Khaligh, S.B.A. Hamid, S.J.J. Titinchi, Polycycl. Aromat.
Comp. 37, 31 (2017)
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