Mono- and bis-2-amino-4h-pyrans: Alum catalyzed three - or pseudo five-component reaction of 4-hydroxycoumarin, malononitrile and aldehydes

Article abstract of DOI:10.2174/157017811794697421

An efficient method for the three- Or pseudo five-component synthesis of mono- and bis-2-amino-4H-pyrans in excellent yields using Alum (KAl(SO ₄)₂.12H₂O) as recyclable catalyst is described. The present methodology offers

Full text of DOI:10.2174/157017811794697421

150
Letters in Organic Chemistry, 2011, 8, 150-154
Mono- and Bis-2-amino-4H-pyrans: Alum Catalyzed Three- or Pseudo
Five-Component Reaction of 4-Hydroxycoumarin, Malononitrile and
Aldehydes
Ali Reza Karimi* and Cyrus Eslami
Department of Chemistry, Arak University, Arak 38156, Iran
Received May 09, 2010: Revised July 10, 2010: Accepted December 10, 2010
Abstracts: An efficient method for the three- or pseudo five-component synthesis of mono- and bis-2-amino-4H-pyrans
in excellent yields using Alum (KAl(SO4)2.12H2O) as recyclable catalyst is described. The present methodology offers
several advantages such as excellent yields, simple procedures, shorter reaction times, milder conditions and the catalysts
exhibited remarkable reusable activity.
Keywords: Alum (KAl(SO4)2.12H2O), 2-Amino-4H-pyrans, 4-Hydroxycoumarin.
INTRODUCTION
further studies are still necessary for the essence of facile,
environmental and economical multicomponent metho-
dology. Due to the biological activity of 4H-pyrans and our
interest in the synthesis of heterocyclic compounds [27],
herein, we report a simple and efficient method for the
preparation of mono- and bis-2-amino-4H-pyran derivatives
using Alum as the catalyst in the multi-component reaction
of 4-hydroxycoumarin, malononitrile and aldehydes.
4H-pyran is a privileged heterocyclic ring system
because many of its derivatives possess useful pharmaco-
logical activities [1]. 2-Amino-4H-pyran derivatives
represent an important class of compounds. They are often
used in cosmetics and pigments, and utilized as potentially
biodegradable agrochemicals [2]. Polyfunctionalized 4H-
pyrans also constitute a structural unit of many natural
products [3] and biologically interesting compounds which
possess various pharmacological activities [1], such as
antiallergic [3], antitumor [1] antibacterial [4]. 4H-Pyran
derivatives are also potential calcium channel antagonists [5]
which are structurally similar to biologically active 1,4-
dihydropyridines.
RESULTS AND DISCUSSION
Alum is an inexpensive, water-soluble, non-toxic and
commercially available compound that can be used in the
laboratory without special precautions. Alum, well known
for its traditional role in water treatments (coagulation and
clarification) has recently been reported as a reusable, cheap
and excellent catalyst for the preparation of organic
compounds, for example, in the transesterification of palm
oil [28], synthesis of ꢁ-aminophosphonates [29], 2,3-
dihydroquinazolin-4(1H)-ones [30], 1,3,4-Oxadiazoles [31],
di-hydropyrimidinones [32], cis-isoquinolonic acids [33],
pyrroles [34] and coumarins [35]. Thus, continuing our
research on new one-pot reactions, we considered Alum to
be ideal for affecting the synthesis of mono- and bis-2-
amino-4H-pyrans via a three- or pseudo five-component
reaction of 4-hydroxycoumarin, malononitrile and aldehydes
in ethanol/water media at room temperature.
Recently, 2-amino-4H-pyrans were synthesized by three-
component condensation reaction of aldehyde, malononitrile
or ethyl 2-cyanoacetate and ꢀ-dicarbonyl compounds such as
dimedone, barbituric acid or hydroxycoumarin in the
presence of base such as piperidine [6], morpholine, pyridine
[7] triethylamine [8], sodium methoxide [9] or 1,1,3,3-
tetramethylguanidine [10]. Recently, it was found that
chemical bases could be replaced with an electrogenerated
base to promote reactions [11]. Also this condensation has
been catalyzed by variety of reagents such as: HMTAB [12],
TEBA [13], RE(PFO)3 [14], NaBr [15], (S)-proline [16], the
use of microwave irradiation [17], KF-basic alumina under
ultrasound irradiation [18], DAHP [19], Na2SeO4 [20],
Mg/La mixed oxide catalyst [21], TMG-[bmim][X] and [2-
aemim][PF6] [22], morpholine [23], CTACl (cetyltrimethyl-
ammonium chloride) [24], TBAB [25] and aminoalcohol
[26].
The synthesis of mono-2-amino-4H-pyran derivatives 4a-
i were achieved by the three-component condensation of
aldehydes 1a-i, malononitrile 2 and 4-hydroxycoumarin 3 in
the presence of 10 or 15 mol % catalyst. The reaction was
carried out in aqueous ethanol using Alum as catalyst at
room temperature to give products 4a–i in good to high
yields (Scheme 1). Bis-2-amino-4H-pyran derivatives 4j-k
were obtained by pseudo five-component reaction of
isophthalaldehyde 1j or terephthalaldehyde 1k (1 mmol),
malononitrile 2 (2.2 mmol) and 4-hydroxycoumarin 3 (2
mmol).
Thus, each of the known procedures for the synthesis of
corresponding 2-amino-4H-pyrans has its merits; however,
*Address correspondence to this author at the Department of Chemistry,
Arak University, Arak 38156, Iran; Tel: +98 861 4173400; Fax: +98 861
4173406; E-mail: ar_karimi55@yahoo.com
Firstly, 3-chlorobenzaldehyde 1a, 4-nitrobenzaldehyde
1b and propionaldehyde 1i were chosen as models for the
1570-1786/11 $58.00+.00
© 2011 Bentham Science Publishers Ltd.

Mono- and Bis-2-amino-4H-pyrans
Letters in Organic Chemistry, 2011, Vol. 8, No. 2
151
O
R1
OH
O
O
CN
Alum
R1-CHO
+
+
NC
O
CN
O
H2N
1a-i
2
3
4a-i
H2N
O
O
CN
O
OHC
2.2 mmol (2 + 3)
CHO
O
Alum
O
O
NC
NH2
1j-k
4j-k
Scheme 1. Three or pseudo five-component synthesis of mono- and bis-2-amino-4H-pyrans 4a-k.
Table 1. Optimization of Reaction
Entry
Aldehyde
Catalysta
Solvent
Yielda
1
2
3-chlorobenzaldehyde 1ab
3-chlorobenzaldehyde 1ab
3-chlorobenzaldehyde 1ab
3-chlorobenzaldehyde 1ab
3-nitrobenzaldehyde 1bb
3-nitrobenzaldehyde 1bb
3-nitrobenzaldehyde 1bb
propionaldehyde 1ic
Alum 5%
Alum 10%
Alum 15%
-
EtOH:H2O (4:1)
EtOH:H2O (4:1)
EtOH:H2O (4:1)
EtOH:H2O (4:1)
EtOH:H2O (4:1)
EtOH:H2O (4:1)
EtOH:H2O (4:1)
EtOH:H2O (4:1)
EtOH:H2O (4:1)
EtOH:H2O (4:1)
EtOH
68%
81%
90%
30%
73%
86%
95%
73%
80%
70%
83%
55%
40%
31%
20%
10%
3
4
5
Alum 5%
Alum 10%
Alum 15%
Alum 5%
Alum 10%
Alum 15%
Alum 15%
Alum 15%
Alum 15%
Alum 15%
Alum 15%
Alum 15%
6
7
8
9
propionaldehyde 1ic
10
11
12
13
14
15
16
propionaldehyde 1ic
3-chlorobenzaldehyde 1ab
3-chlorobenzaldehyde 1ab
3-chlorobenzaldehyde 1ab
3-chlorobenzaldehyde 1ab
3-chlorobenzaldehyde 1ab
3-chlorobenzaldehyde 1ab
CH3CN:H20 (4:1)
THF
CH3CN
CH2Cl2
Toluene
ayields refer to isolated products (25 ºC). breaction time: 4h. creaction time: 9h.
reaction with malononitrile 2 and 4-hydroxycoumarin 3. Our
investigation began with the evaluation of amounts of Alum
as a catalyst in the reaction of 3-chlorobenzaldehyde 1a or 4-
nitrobenzaldehyde 1b (1 equiv), malononitrile 2 and 4-
hydroxycoumarin 3 (1 equiv) at 25 ºC. After 4 h with 5, 10
and 15 mol% of Alum, yields of 68%, 81% and 90%,
respectively for 1a, and 73%, 86% and 95%, respectively for
1b were obtained (Table 1, entries 1-3 and 5-7). However,
the results indicated that the yield was decreased using 15
mol% of Alum by comparison with 10 mol% loading on the
formation of 4i (Table 1, entries 9 and 10). In the absence of
Alum there were low yield of the products (Table 1, entry 4).
CH3CN, THF, CH3CN:H2O (4:1) and CH2Cl2 as solvents
furnished poor yields (Table 1, entries 12-15). Side products
were obtained when CH3CN:H2O (4:1) and CH2Cl2 was used
as solvent. The results indicated that the yield gradually
decreased as we moved from highly polar to less polar
solvents. Other solvents, such as toluene were ineffective for
this transformation (Table 1, entry 16). Hence, the conditions
of entries 3 and 9, shown in Table 1, were the optimized
reaction conditions for aromatic and aliphatic aldehydes,
respectively. We next examined a wide variety of aldehydes
(both aromatic and aliphatic) and dialdehydes to establish the
scope of this catalytic transformation (Table 2).
The choice of reaction solvent was crucial. Changing the
solvent from EtOH/H2O to ethanol was not beneficial as the
yield was reduced to 83% (Table 1, entry 11). The use of
Although we have not yet established the mechanism, a
possible explanation is given in Scheme 2. Aldehyde 1 first
condenses with malononitrile
2
to afford arylidene

152 Letters in Organic Chemistry, 2011, Vol. 8, No. 2
Karimi and Eslami
Table 2. Synthesis of 4a-k Catalyzed by Alum
4a-k
Aldehyde
Yield
Time
M.p. (°C)
Lit. M.p. (°C)
4a
4b
4c
4d
4e
4f
3-chlorobenzaldehyde
4-nitrobenzaldehyde
2,4-dichlorobenzaldehyde
3-nitrobenzaldehyde
benzaldehyde
90%a
95%a
92%a
87%a
82%a
81%a
85%a
79%b
80%b
78%c
79%c
4h
2h
253-256
278-280
311-313
264-266
254-256
256-258
211-215
229-232
249-251
307 dec.
296 dec.
-
258-260 [19]
257-259 [19]
262-264 [19]
256-258 [19]
-
4h
4h
4h
4-fluorobenzaldehyde
cinnamaldehyde
4h
4g
4h
4i
6h
acetaldehyde
9h
-
propionaldehyde
9h
-
-
4j
terphthalaldehyde
isoterphthalaldehyde
2.5h
2.5h
-
4k
aYields refer to isolated products (reaction temperature: 25 ºC); Alum: 15 mol%.
b25 ºC; Alum: 10 mol%. c(0.5h : 25 ºC and then 2h : 70 ºC); Alum: 15 mol%.
malononitrile 5 in the presence of Alum. This step was
regarded as a fast Knoevenagel condensation. Then, 5 is
attacked via Michael addition of 4-hydroxycoumarin 3 to
give the intermediate 6 followed by the cycloaddition of
hydroxyl group to the cyano moiety to form the desired
product 4 (Scheme 2).
ethanol to give the desired products. The crude products
were recrystallized from EtOH or EtOH:H2O to yield mono-
and bis-2-amino-4H-pyrans 4a-i and 4j-k.
The products 4a-g are known compounds and their
structures were deduced by comparison of their physical and
spectroscopic data (IR and 1H NMR) with those of
previously reported. The new products 4h-k were
characterized on the basis of their elemental analysis and IR,
1H NMR and 13C NMR spectra.
We found that the catalyst showed high catalytic activity
and could be recovered and recycled several times without
significant loss of activity.
Spectral Data
EXPERIMENTAL
2-Amino-4-(3-chlorophenyl)-5-oxo-4,5-dihydropyrano[3,2-
c]chromene-3-carbonitrile (4a)
Mps were measured on an Electrothermal 9100
apparatus. IR spectra were measured on a Unicom Galaxy
1
Series FTIR 5000 Spectrophotometer. H NMR and 13C
White solid. IR (KBr) (vmax, cm-1): 3383, 3325, 3196,
2928, 2206, 1697, 1668, 1608, 1383, 760. 1H NMR (DMSO-
d6, 300 MHz) ꢀ: 4.51(1H , s, CH), 7.23–7.35 (4H, m, Harom),
7.48 (2H, bs, NH2), 7.46–7.53 (2H, m, Harom), 7.72 (1H, dt,
J=8.1 and 1.6 Hz, Harom), 7.90 (1H, dd, J=7.9 and 1.4 Hz,
Harom) ppm.
NMR spectra were determined on a Bruker Avance 300
MHz spectrometer. Elemental analyses were performed
using a Vario EL III elemental analyzer.
General Procedure for Preparation of 6a-f, 7a-c and 8a-d
2-Amino-4-(4-nitrophenyl)-5-oxo-4,5-dihydropyrano[3,2-
c]chromene-3-carbonitrile (4b)
A mixture of aldehyde 1a-i or 1j-k (1 mmol),
malononitrile 2 (1 mmol for 1a-i or 2.2 mmol for 1j-k), 4-
hydroxycoumarin (1 mmol for 1a-i or 2.2 mmol for 1j-k),
and Alum (15 mol% for aromatic aldehydes or 10 mol% for
aliphatic aldehydes) in 5 mL EtOH:H2O (4:1) was stirred at
room temperature or 70 ºC for several hours (Table 2). Upon
completion, monitored by TLC (n-hexane/ethyl acetate: 2/1),
the solid was filtered off and washed with water and cool
Pale yellow solid. IR (KBr) (vmax, cm-1): 3481, 3433,
3369, 3200, 2195, 1716, 1672, 1606, 1506, 1373, 1346, 765.
1H NMR (DMSO-d6, 300 MHz) ꢀ: 4.67 (1H, s, CH), 7.46–
7.61 (4H, m, Harom), 7.58 (2H, bs, NH2), 7.73 (1H, t, J= 8.0
Hz, Harom), 7.91 (1H, d, J=7.8 Hz, Harom), 8.18 (2H, d, J= 8.4
Hz, Harom) ppm.
Alum
Alum
HN
Alum
NH
O
H
O
O
Alum
R
O
NC
R
CNH
O
CN
C
C
NC
Product
+
NC
O
R
H
O
H
H
R
O
H
O
N
Alum
O
1
2
5
3
6
4
Scheme 2. Plausible mechanism of the Alum-catalyzed synthesis of 2-amino-4H-pyrans.

Mono- and Bis-2-amino-4H-pyrans
Letters in Organic Chemistry, 2011, Vol. 8, No. 2
153
2-Amino-4-(2,4-dichlorophenyl)-5-oxo-4,5-
dihydropyrano[3,2-c]chromene-3-carbonitrile (4c)
Hz, Harom), 7.80 (1H, d, J=7.9 Hz, Harom) ppm. 13C NMR
(DMSO-d6, 75 MHz) ꢀ: 8.99, 26.47, 32.21, 54.89, 103.97,
113.31, 116.95, 120.04, 122.55, 125.00, 133.16, 152.48,
154.77, 159.98, 160.35 ppm. Anal. Calcd for C15H12N2O3: C,
67.16; H, 4.51; N, 10.44. Found: C, 66.97; H, 4.70; N, 10.62.
White solid. IR (KBr) (vmax, cm-1): 3416, 3279, 3173,
1
2200, 1707, 1672, 1599, 1379, 758. H NMR (DMSO-d6,
300 MHz) ꢀ: 5.53 (1H, s, Harom), 7.29–7.39 (3H, m, Harom),
7.46–7.52 (2H, m, Harom), 7.54 (2H, s, NH2), 7.72 (1H, t,
J=8.1 Hz, Harom), 7.88 (1H, d, J=7.8 Hz, Harom) ppm.
4,4’-(1,4-phenylene)-bis-(2-amino-5-oxo-4,5-
dihydropyrano[3,2-c]chromene-3-carbonitrile) (4j)
2-Amino-4-(3-nitrophenyl)-5-oxo-4,5-dihydropyrano[3,2-
c]chromene-3-carbonitrile (4d)
White solid. IR (KBr) (vmax, cm-1): 34.68, 3393, 3325,
3192, 2198, 1709, 1674, 1606, 1379, 760. 1H NMR (DMSO-
d6, 300 MHz) ꢀ: 4.43 (1H, s, CH), 7.20–7.50 (12H, m, NH2
and Harom), 7.69 (2H, m, Harom), 7.87–7.90 (2H, m, Harom).
13C NMR (DMSO-d6, 75 MHz) ꢀ: 37.00, 58.32, 104.42,
113.35, 115.88, 116.99, 119.75, 122.90, 125.10, 128.21,
131.38, 133.37, 142.55, 152.54, 153.92, 158.58, 160.05 ppm.
Anal. Calcd for C32H18N4O6: C, 69.31; H, 3.27; N, 10.10.
Found: C, 69.88; H, 3.34; N, 10.27.
White solid. IR (KBr) (vmax, cm-1): 3398, 3323, 3211,
3088, 2876, 2195, 1699, 1674, 1602, 1531, 1456, 1379,
1
1062. H NMR (DMSO-d6, 300 MHz) ꢀ: 4.73 (1H, s, CH),
7.45–7.65 (3H, m, Harom), 7.56 (2H, bs, NH2), 7.70– 7.82
(2H, m, Harom), 7.91 (1H, dd, J=7.9 and 1.4 Hz, Harom), 8.10–
8.14 (2H, m, Harom) ppm.
2-Amino-5-oxo-4-phenyl-4,5-dihydropyrano[3,2-
c]chromene-3-carbonitrile (4e)
4,4’-(1,3-phenylene)-bis-(2-amino-5-oxo-4,5-
dihydropyrano[3,2-c]chromene-3-carbonitrile) (4k)
White solid. IR (KBr) (vmax, cm-1): 3373, 3284, 3180,
White solid. IR (KBr) (vmax, cm-1): 3408, 3321, 3192,
1
2198, 1709, 1674, 1604. H NMR (DMSO-d6, 300 MHz) ꢀ:
1
2193, 1714, 1672, 1606, 1379, 760. H NMR (DMSO-d6,
4.44 (1H, s, Harom), 7.26 (2H, d, J=7.6, Harom), 7.28-7.34 (3H,
m, Harom), 7.41 (2H, bs, NH2), 7.45-7.50 (2H, m, Harom), 7.72
(1H, t, J=7.6, Harom), 7.92 (1H, d, J=7.8, Harom) ppm.
300 MHz) ꢀ: 4.43 (1H, s, CH), 7.10–7.13 (1H, m, Harom),
7.18–7.27 (1H, m, Harom), 7.39–7.49 (5H, m, NH2 and Harom),
7.70 (1H, m, Harom), 7.86 (1H, t, J=7.6 Hz, Harom) ppm. 13C
NMR (DMSO-d6, 75 MHz) ꢀ: 37.13, 57.96, 58.32, 104.16,
104.55, 113.33, 117.03, 119.66, 122.87, 125.15, 126.39,
126.72, 127.40, 129.36, 133.36, 143.67, 143.88, 152.55,
153.80, 154.11, 158.40, 158.77, 159.87 ppm. Anal. Calcd for
C32H18N4O6: C, 69.31; H, 3.27; N, 10.10. Found: C, 69.93;
H, 3.21; N, 10.21.
2-Amino-4-(4-fluorophenyl)-5-oxo-4,5-dihydropyrano[3,2-
c]chromene-3-carbonitrile (4f)
White solid. IR (KBr) (vmax, cm-1): 3379, 3310, 3192,
3074, 2195, 1716, 1676, 1604, 1560, 1506, 765. H NMR
(DMSO-d6, 300 MHz) ꢀ: 4.54 (1H, s, CH), 7.34–7.60 (4H,
m, Harom), 7.50 (2H, bs, NH2), 7.71 (2H, t, J= 7.9 Hz, Harom),
7.89-8.07 (2H, m, Harom) ppm. Anal. Calcd for C19H11FN2O3:
C, 68.26; H, 3.32; N, 8.38. Found: C, 68.45; H, 3.28; N,
8.55.
1
CONCLUSION
In conclusion, we have described an efficient, one-pot,
and three- or pseudo five-component method for the
synthesis of mono- and bis-2-amino-4H-pyrans catalyzed by
Alum. Short reaction times, high yields and easy workup are
the advantages of this protocol.
2-Amino-5-oxo-4-styryl-4,5-dihydropyrano[3,2-
c]chromene-3-carbonitrile (4g)
Pale Yellow solid. IR (KBr) (vmax, cm-1): 3383, 3323,
1
3200, 2191, 1716, 1674, 1606, 1377. H NMR (DMSO-d6,
300 MHz) ꢀ: 4.04 (1H, d, J=7.9 Hz, CH), 6.23 (1H, dd,
J=15.7 and 7.9 Hz, Halkene), 6.54 (1H, d, J=15.7, Halkene),
7.20–7.33 (3H, m, Harom), 7.37–7.49 (6H, m, NH2 and Harom),
ACKNOWLEGMENT
7.70 (1H, t, J=7.2 Hz, Harom), 7.85 (1H, d, J=7.9 Hz, Harom
ppm.
)
We gratefully acknowledge the financial support from
the Research Council of Arak University.
2-Amino-4-methyl-5-oxo-4,5-dihydropyrano[3,2-
c]chromene-3-carbonitrile (4h)
White solid. IR (KBr) (vmax, cm-1): 3394, 3317, 3211,
2962, 2195, 1707, 1672, 1608, 1456, 1386, 761. H NMR
(DMSO-d6, 300 MHz) ꢀ: 1.29 (3H, d, J= 6.5 Hz, CH3), 3.37
(1H, q, J=6.5 Hz, CH), 7.28 (2H, bs, NH2), 7.43–7.48 (2H,
m, Harom), 7.70 (1H, t, J=7.8 Hz, Harom), 7.80 (1H, d, J=7.9
Hz, Harom) ppm. Anal. Calcd for C14H10N2O3: C, 66.14; H,
3.96; N, 11.02. Found: C, 65.95; H, 3.88; N, 10.92.
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