Eco-friendly and efficient synthesis of pyrano[2,3-d] pyrimidinone and tetrahydrobenzo[b]pyran derivatives in water

Article abstract of DOI:10.1080/15533171003629121

Tetrahydrobenzo[b]pyran and pyrano[2,3-d]pyrimidinone derivatives were synthesized efficiently in the presence of KAl(SO4)2.12H₂O (alum) in water. Green media, lack of toxicity, short reaction times, easy work-up and high yields are some advant

Full text of DOI:10.1080/15533171003629121

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Eco-friendly and Efficient Synthesis of Pyrano[2,3-
d] pyrimidinone and Tetrahydrobenzo[b]pyran
Derivatives in Water
Akbar Mobinikhaledi a , Naser Foroughifar a & Mohammad Ali Bodaghi Fard a
a Department of Chemistry, Faculty of Science, Arak University, Arak, Iran
Published online: 23 Mar 2010.
To cite this article: Akbar Mobinikhaledi , Naser Foroughifar & Mohammad Ali Bodaghi Fard (2010) Eco-friendly and
Efficient Synthesis of Pyrano[2,3-d] pyrimidinone and Tetrahydrobenzo[b]pyran Derivatives in Water, Synthesis and
Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 40:3, 179-185
To link to this article: http://dx.doi.org/10.1080/15533171003629121
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 40:179–185, 2010
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533171003629121
Eco-friendly and Efficient Synthesis of Pyrano[2,3-d]
pyrimidinone and Tetrahydrobenzo[b]pyran Derivatives
in Water
Akbar Mobinikhaledi, Naser Foroughifar, and Mohammad Ali Bodaghi Fard
Department of Chemistry, Faculty of Science, Arak University, Arak, Iran
diverse biological properties of pyranopyrimidinone derivatives,
there is wide spread interest for their synthesis. Compounds with
a uracil moiety have shown antitumor, antibacterial, antihyper-
tensive, hepatoprotective, vasodilator, antiallergic, antifungal,
antimalarial and herbicidal properties.[16−19] There are several
methods for the synthesis of pyranopyrimidinones under tradi-
tional thermal condition or microwave irradiation.[20−23] Each
of these reported methods has its own merits, with at least one
of the limitation of drastic condition, long reaction times, low
yields, and effluent pollution. KAl(SO4)2.12H2O (alum) with
mild acidity, involatility, and incorrositivity is insoluble in com-
mon organic solvents, and was used recently as an easily avail-
able acidic catalyst in different reactions.[24−28] As a continua-
tion of our research devoted to the development of green organic
chemistry and one-pot multicomponent reactions (MCRs) for
the synthesis of various heterocyclic compounds,[29−32] herein
we wish to report an efficient and green procedure for the prepa-
ration of 4H-benzo[b]pyrans and pyrano[2,3-d]pyrimidinones
via a domino Knoevenagel-cyclocondensation reaction using
KAl(SO4)2.12H2O (alum) as a catalyst in water.
Tetrahydrobenzo[b]pyran and pyrano[2,3-d]pyrimidinone
derivatives were synthesized efficiently in the presence of
KAl(SO4)2.12H2O (alum) in water. Green media, lack of toxicity,
short reaction times, easy work-up and high yields are some
advantages of this method.
Keywords alum, green synthesis, heterogeneous, water
INTRODUCTION
The development of environmentally benign and clean syn-
thetic procedures has become the goal of present day organic
synthesis. Water plays an essential role in life processes and
also as a medium for organic reactions.[1,2] The organic reac-
tions in aqueous media have attracted much attention in organic
synthesis, not only because water is one of the most abundant,
cheapest and environmentally friendly solvent, but also because
water exhibits unique reactivity and selectivity, which is dif-
ferent and, in most cases, higher than those in conventional
organic solvents.[3] Reactions in aqueous media are environ-
mentally safe, devoid of any carcinogenic effects, have a simple
work up and especially are important in industry. Thus, there
is a need for developing multicomponent reactions (MCRs) in
water and without the use of any harmful organic solvents and
catalysts. Tetrahydrobenzo[b]pyrans are an important class of
heterocyclic scaffolds in the field of drugs and pharmaceuti-
cal. These compounds are widely used as anticoagulant, di-
uretic, spasmolytic, anticancer and antianaphylactic agents.[4,5]
Numerous methods have been reported for the synthesis of
4H-benzo[b]pyrans.[6−15] However, some of these methods
have drawbacks such as long reaction times, use of expensive
reagents, low yields, harsh reaction conditions, effluent pollution
and tedious work-up procedures. On the other hand, due to the
EXPERIMENTAL
Melting points were measured by using capillary tubes
on an electro thermal digital apparatus and are uncorrected.
The progress of reactions was monitored by TLC using n-
hexane/EtOAc (2:1 v/v) as an eluent. IR spectra were recorded
as KBr disc on a galaxy series FT-IR 5030 spectrometer. NMR
spectra were recorded on a brucker spectrometer (300 MHz)
in DMSO-d6 with TMS as an internal standard. Microanalyses
were performed by the Elemental Analyzer (Elemental, Vario
EL III).
Typical Procedures
General Procedure for Synthesis of Tetrahydrobenzo[b]pyrans
A mixture of an aromatic aldehyde (1 mmol), malononi-
trile(1 mmol), dimedone (1 mmol) and alum (10% mol) in wa-
ter (5 ml) was heated at 80◦C with stirring for appropriate time
(see Table 1). After completion of the reaction confirmed by
TLC, water (10–15 ml) was added and the reaction mixture
Received 10 October 2009; accepted 17 January 2010.
The authors would like to acknowledge financial support from the
Research Council of Arak University.
Address correspondence to Prof. Akbar Mobinikhaledi, Chemistry
Dept., Arak University, Dr. Beheshti Ave., Arak 38156-879, Iran.
E-mail: akbar mobini@yahoo.com
179

180
A. MOBINIKHALEDI ET AL.
TABLE 1
Alum catalyzed synthesis of 4H-benzo[b]pyrans in water
M.P (◦C)
Product
Ar
Time (min)
Yield (%)a
Found
ReportedLit
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
C6H5
4-Br-C6H4
3-Cl-C6H4
4-Cl-C6H4
50
40
45
40
40
45
40
45
40
45
50
40
40
45
92
91
90
93
89
93
90
92
90
92
90
94
92
93
226–228
205–207
227–229
212–214
248–250
182–184
204–207
231–233
210–212
179–181
227–229
214–217
222–225
200–202
228–2306
203–2057
224–2259
209–2116
252–25414
180–18214
206–20813
236–23813
212–2149
177–1789
224–2269
223–22513
23012
2,3-Cl2-C6H3
2,4-Cl2-C6H3
4-OH-C6H4
3-OH-C6H4
3-NO2-C6H4
4-NO2-C6H4
2-NO2-C6H4
4-CH3-C6H4
4-N(Me)2-C6H4
4-OCH3-C6H4
203 12
aYields refer to isolated products.
cooled in a fridge to give the precipitate. The solid product was
filtered and washed with cold water (2 × 10 ml). The pure prod-
uct was obtained by recrystallization from ethanol:water (4:1).
Physical and Spectroscopic Data for Selected Compounds
(4a): IR (KBr) (νmax): 3393, 3317, 3185, 2958, 2196, 1687,
1652, 1367 cm−1. 1H NMR (DMSO–d6): δH: 0.94 (3H, s, Me),
1.04 (3H, s, Me), 2.08 (1H, d, J = 16.0 Hz, H-6), 2.23 (1H, d,
J = 16.0 Hz, H-6’), 2.50 (2H, m, CH2), 4.11 (1H, s, H-4), 7.06
(2H, br s, NH2), 7.19 (3H, m, H–Ar), 7.33 (2H, m, H–Ar). Anal.
calcd for C18H18N2O2: C, 73.45; H, 6.16; N, 9.52. Found: C,
73.97; H, 6.79; N, 9.42.
(4b): IR (KBr) (νmax): 3398, 3319, 3211, 2966, 2191, 1683,
1656, 1369 cm−1. 1H NMR (DMSO–d6): δH: 0.97 (3H, s, Me),
1.06 (3H, s, Me), 2.12 (1H, d, J = 16.0 Hz, H-6), 2.28 (1H, d,
J = 16.0 Hz, H-6’), 2.54 (2H, m, CH2), 4.21 (1H, s, H-4), 7.13
(2H, br s, NH2), 7.15 (2H, d, J = 8.5 Hz, H–Ar), 7.50 (2H, d,
J = 8.5 Hz, H–Ar). Anal. calcd for C18H17BrN2O2:
General Procedure for Synthesis of Pyrano[2,3-d]pyrimidi-
nones
A mixture of an aromatic aldehyde (1 mmol), malononitrile
(1 mmol), barbituric acid (1 mmol) and alum (10% mol) in water
(5 ml) was heated at 80◦C with stirring for appropriate time (see
Table 2). After completion of the reaction confirmed by TLC,
water (10–15 ml) was added and the mixure cooled in a fridge to
give the precipitate. The solid product was filtered and washed
with cold water (2 × 10 ml). The pure product was obtained by
recrystallization from ethanol:water (4:1).
TABLE 2
Alum catalyzed synthesis of pyrano[2,3-d]pyrimidinones in water
M.P (◦C)
Product
Ar
Time (min)
Yield (%)a
Found
Reported Lit
6a
6b
6c
6d
6e
6f
4-Br-C6H4
3-Cl-C6H4
30
35
40
30
35
40
35
45
85
80
88
90
87
81
80
88
222–234
243–245
239–240
243–246
161–163
271–273
236–238
251–253
230–231 22
240–24122
240–24222
241–24222
158–16022
268–27022
239–24022
254–25622
2,3-Cl2-C6H3
2,4-Cl2-C6H3
3-OH-C6H4
3-NO2-C6H4
4-NO2-C6H4
4-CN-C6H4
6g
6h
aYields refer to isolated products.

SYNTHESIS OF PYRANO[2,3-d] PYRIMIDINONE
181
O
O
HN
O
N
H
O
O
Ar
O
O
Ar
O
O
3
5
CN
CN
CN
HN
Alum (10% mol)
Alum (10% mol)
ArCHO
+
H2O, 80 0C
H2O, 80 0C
O
N
H
NH2
CN
NH2
4
2
6
1
SCH. 1. Alum efficiently catalyzed the synthesis of pyrano[2,3-d]pyrimidinones and 4H-benzo[b]pyrans.
C, 57.92; H, 4.59; N, 7.51. Found: C, 58.17; H, 4.71; N,
7.43.
(6d): IR (KBr) (νmax): 3389, 3305, 3184, 3078, 2193, 1718,
1676, 1410, 1282 cm−1. 1H NMR (DMSO–d6): δH: 4.75 (1H,
(4f): IR (KBr) (νmax): 3533, 3364, 3153, 2966, 2193, 1685, s, H-5), 7.25 (2H, br s, NH2), 7.38 (2H, s, H–Ar), 7.57 (1H,
1658, 1367 cm−1. 1H NMR (DMSO–d6): δH: 1.00 (3H, s, Me), s, H–Ar), 11.13 (1H, br s, NH), 12.17 (1H, br s, NH). Anal.
1.06 (3H, s, Me), 2.11 (1H, d, J = 16.0 Hz, H-6), 2.27 (1H, calcd for C14H8Cl2N4O3: C, 47.89; H, 2.30; N, 15.96. Found:
d, J = 16.0 Hz, H-6’), 2.47–2.61 (2H, m, CH2), 4.70 (1H, s, C, 47.72; H, 2.41; N, 15.85.
H-4), 7.15 (2H, br s, NH2), 7.25 (1H, d, J = 8.4 Hz, H–Ar), 7.39
(1H, d, J = 8.4 Hz, H–Ar), 7.56 (1H, s, H–Ar). Anal. calcd for
RESULTS AND DISCUSSION
C18H16Cl2N2O2: C, 59.52; H, 4.44; N, 7.71. Found: C, 59.91;
H, 4.63; N, 7.63.
To study the reaction in water, we tested the reaction of
(4j): IR (KBr) (νmax): 3394, 3323, 3213, 2970, 2193, 1683, dimedone, malononitrile and 4-chlorobenzaldehyde in the pres-
1655, 1523, 1365 cm−1. 1H NMR (DMSO–d6): δH: 0.99 (3H, ence of alum under different conditions. The best results were
s, Me), 1.06 (3H, s, Me), 2.14 (1H, d, J = 16.0 Hz, H-6), 2.30 obtained with 10 mol% of alum at 80◦C (93% yield). Encour-
(1H, d, J = 16.0 Hz, H-6’), 2.53–2.57 (2H, m, CH2), 4.39 (1H, aged by the above results, other 4H-benzo[b]pyran derivatives
s, H-4), 7.24 (2H, br s, NH2), 7.48 (2H, d, J = 8.4 Hz, H–Ar), were synthesized in high yields under the same conditions
8.21 (2H, d, J = 8.4 Hz, H–Ar). Anal. calcd for C18H17N3O4: (Scheme 1, Table 1).
C, 63.71; H, 5.05; N, 12.38. Found: C, 63.99; H, 5.17; N, 12.25.
4.4.5.
We have also tested the reaction of barbituric acid, mal-
ononitrile and aromatic aldehyds in the presence of alum and
(4m): IR (KBr) (νmax): 3381, 3321, 3209, 2962, 2191, 1682, observed that pyrano[2,3-d]pyrimidinone derivatives obtained
1656, 1367 cm−1. 1H NMR (DMSO–d6): δH: 0.97 (3H, s, Me), in good yields (Scheme 1, Table 2).
1.06 (3H, s, Me), 2.10 (1H, d, J = 16.0 Hz, H-6), 2.27 (1H,
The structure of products was confirmed by physical, spectro-
d, J = 16.0 Hz, H-6’), 2.47–2.55 (2H, m, CH2), 2.87 (6H, s, scopic (IR, 1H NMR) and elemental analysis data. For example,
-N(Me)2), 4.06 (1H, s, H-4), 6.66 (2H, d, J = 8.7 Hz, H–Ar), scheme 2 and 3 show the H- and 13C NMR spectra of 4f, re-
1
6.95 (2H, br s, NH2), 6.97 (2H, d, J =8.7 Hz, H–Ar). Anal. calcd spectively. In the 1H NMR spectrum of this compound (scheme
for C20H23N3O2: C, 71.19; H, 6.87; N, 12.45. Found: C, 71.49; 2) the broad singlet at δ= 7.15 ppm is assigned to the reso-
H, 6.71; N, 12.33.
nance of the NH2 group protons. The only proton of pyran ring
(6a): IR (KBr) (νmax): 3391, 3302, 3188, 3072, 2197, 1718, appeared at δ= 4.70 ppm. The signals related to the aromatic
1674, 1408, 1280 cm−1. 1H NMR (DMSO–d6): δH: 4.26 (1H, protons observed at δ= 7.23–7.56 ppm. The other signals res-
s, H-5), 7.20 (2H, br s, NH2), 7.22 (2H, d, J = 8.2 Hz, onated at the expected regions. The 13C NMR spectrum of 4f
H–Ar), 6.51 (2H, d, J = 8.2 Hz, H–Ar) 11.12 (1H, br s, (scheme 3) shows 18 signals, which is also expected for this
NH), 12.14 (1H, br s, NH). Anal. calcd for C14H9BrN4O3: C, structure. The work-up of the reaction is accomplished by sim-
46.56; H, 2.51; N, 15.51. Found: C, 47.11; H, 2.63; N, 15.39. ple filtration (after cooling of the reaction mixture to room
4.4.7.
temperature and then below 5◦C in a fridge), followed by

182
A. MOBINIKHALEDI ET AL.
SCH. 2. 1H NMR spectrum of 4f.
recrystalization from ethanol:water (4:1). These products are first step, the olefin 8 is produced by a Knoevenagel conden-
quite stable in aqueous media. sation between the aryl aldehyde 1 and malononitrile 2 pro-
Although we have not established the mechanism of the moted by alum. The barbituric acid in the presence of alum
reaction, a possible explanation is given in scheme 4. At the could be converted to its corresponding barbiturate 9 that could

SYNTHESIS OF PYRANO[2,3-d] PYRIMIDINONE
183
SCH. 3. 13C NMR spectrum of 4f.
easily react with olefin 8 to give the intermediate 10. The in- ter and proceeds efficiently in the presence of alum. This
termediate 10 converts to product 6 after proton transfer and one-pot reaction with regard to the reported observations[3]
tautomerization.
may take place at the interface of organic substrates with
The role of water as the reaction medium and its mech- water in a heterogeneous system. It is worthy to note
anism is not clear. Despite the low solubility of start- that vigorous stirring is required for the success of this
ing materials in water, the reaction is accelerated in wa- reaction.

184
A. MOBINIKHALEDI ET AL.
Alum
O
1
Ar
H
Ar
CN
CN
NC
NC
2
HO
Alum
Ar
CN
CN
H
8
Ar
O
H
Alum-O
O
CN
HN
9
HN
NH
10
O
N
H
O
N
O
1) Proton transfer
2) Tautomerization
O
O
Alum
Ar
O
HN
NH
CN
HN
5
O
6
O
NH2
N
O
H
SCH. 4. Proposed mechanism for one-pot synthesis of pyrano[2,3-d]pyrimidinones catalyzed by Alum in water.
CONCLUSION
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