Ammonium acetate as a catalyst and/or reactant in the reaction of dimedone, aromatic aldehyde, and malononitrile: synthesis of tetrahydrobenzo[b]pyrans and hexahydroquinolines

Article abstract of DOI:10.1007/s00706-016-1683-0

Abstract: The reaction of aromatic aldehydes, dimedone, and malononitrile in the presence of ammonium acetate has afforded tetrahydrobenzo[b]pyrans instead of polyhydroquinolines under both grinding and reflux conditions; thus ammonium acetate acts as a c

Full text of DOI:10.1007/s00706-016-1683-0

Monatsh Chem
DOI 10.1007/s00706-016-1683-0
ORIGINAL PAPER
Ammonium acetate as a catalyst and/or reactant in the reaction
of dimedone, aromatic aldehyde, and malononitrile: synthesis
of tetrahydrobenzo[b]pyrans and hexahydroquinolines
Adeleh Moshtaghi Zonouz1 Somaieh Okhravi1 Davood Moghani1
•
•
Received: 28 September 2015 / Accepted: 27 January 2016
Ó Springer-Verlag Wien 2016
Abstract The reaction of aromatic aldehydes, dimedone,
and malononitrile in the presence of ammonium acetate has
afforded tetrahydrobenzo[b]pyrans instead of polyhydro-
quinolines under both grinding and reflux conditions; thus
ammonium acetate acts as a catalyst for this transformation
instead of a reactant. Polyhydroquinoline derivatives were
also synthesized via a one-pot condensation of aromatic
aldehydes, malononitrile and an enaminone, which was
prepared by the reaction of dimedone and ammonium
acetate, in refluxing ethanol in high yields.
syntheses are multicomponent reactions. Recently, the syn-
theses of 4H-chromene and quinoline derivatives have
attracted great interest due to biological and pharmacological
activities. The 4H-chromene derivatives show various phar-
macological properties such as spasmolytic, diuretic,
anticoagulant, anticancer, and antianaphylactic activities [8–
12]. Furthermore these compounds can be employed as pig-
ments, and also they constitute the structural unit of a series of
natural products [13, 14].
Quinoline derivatives are a class of important com-
pounds, which are widely recognized to have antitumor,
antibacterial, anticancer, and antimalarial activities [15–
18]. Tetrahydrobenzo[b]pyrans (4H-chromene derivatives)
are structurally similar to biologically active polyhydro-
quinolines. Due to this similarity, in ammonium acetate-
mediated reaction of aldehydes and active methylene
Graphical abstract
O
O
Ar
O
O
Ar
CN
NH4OAc
CN
+
O
ArCHO + CH2(CN)2
or
?
NH2
N
H
NH2
compounds
competitive
synthesis
of
tetrahy-
drobenzo[b]pyrans instead of polyhydroquinolines could
be achieved. Multi-component synthesis of polyhydro-
quinoline derivatives I from aldehydes, dimedone, ethyl
acetoacetate, and ammonium acetate have been reported
using TMSCl [19], ionic liquids [20, 21], polymers [22, 23]
and Yb(OTf)3 [24, 25], promotion of microwave [26],
CAN [27], solar thermal energy [28], potassium dode-
catungsto cobaltate trihydrate [29], Baker’s yeast [30],
organocatalyst [31, 32], K7[PW11CoO40] [33], montmor-
rilonite K10 [34], sulfamic acid [35], and FeF3 [36].
Synthesis of polyhydroquinolines I from aldehydes,
dimedone, ethyl acetoacetate, and ammonium acetate has
also been reported under aqueous media without any cat-
alyst [37].
Keywords Multi-component reactions Á
Tetrahydrobenzo[b]pyrans Á Polyhydroquinolines Á
Grinding Á Ammonium acetate
Introduction
Over the past decades, multi-component reactions (MCRs)
have proved to be very powerful and efficient bond-forming
tools in organic combinatorial and medicinal chemistry in the
contextofgreenchemistry[1–7]. Manyimportantheterocycle
& Adeleh Moshtaghi Zonouz
adeleh.moshtaghi@org.chemie.uni-giessen.de;
adelehmz@yahoo.com
Conflicting results have been obtained by replacing
ethyl acetoacetate with malononitrile. Synthesis of
2-amino-3-cyanopolyhydroquinolines II have been repor-
1
Chemistry Department, Faculty of Science, Azarbaijan
Shahid Madani University, Tabriz, Iran
ted via
a
multi-component reaction of aldehydes,
123

A. M. Zonouz et al.
Fig. 1 The general structures of
polyhydroquinolines I, II, and
tetrahydrobenzo[b]pyrans III
X
X
X
O
O
O
CN
Et
CO2
CH3
CN
N
H
NH2
N
H
NH2
O
I
II
III
1
dimedone, malononitrile, and ammonium acetate in
refluxing acetic acid [38], under solvent free conditions
and microwave irradiation [39], and under grinding [40].
Although Kumar et al. [40] have reported the multi-
component reaction of aldehydes, dimedone, malononi-
trile, and ammonium acetate for the synthesis of
polyhydroquinolines II under grinding, Undale et al. [41]
after work-up and purification, the H NMR spectrum of
the obtained product revealed the formation of corre-
sponding tetrahydrobenzo[b]pyran derivative 1a instead of
polyhydroquinoline derivative 2a despite using an excess
amount of ammonium acetate. The reaction conditions
were then applied to a range of aldehyde substrates. The
results with different aldehydes are depicted in Table 1.
Aldehydes with both electron withdrawing and electron
donating substituents were well tolerated. It is evident that
ammonium acetate acts as a catalyst instead of a reactant
for the present transformation. Then we performed the
multi-component reaction of aldehydes, dimedone,
malononitrile, and ammonium acetate using ethanol as a
solvent both at room temperature and under reflux condi-
tions, and the same results were obtained. The reaction is
proposed to proceed through a mechanism shown in
Scheme 1. We also examined three-component reaction of
benzaldehyde, dimedone, and malononitrile, in the absence
of ammonium acetate, under grinding at room temperature.
No reaction was occurred. Furthermore, in using 20 mol%
of ammonium acetate, tetrahydrobenzo[b]pyran derivative
1a was obtained in 30 % yield and most of the reactants
remained unreacted.
have
obtained
the
corresponding
tetrahy-
drobenzo[b]pyrans III instead of polyhydroquinolines II
from the reaction of aldehydes, dimedone, malononitrile,
and ammonium acetate in ethanol (Fig. 1). Also Patil
et al. [42] have reported one-pot four-component
sequential synthesis of hexahydroquinoline derivatives in
aqueous media via enaminone intermediates. In continu-
ation of our interest in multi-component reactions [43–46]
and to combinatorial library synthesis of polyhydro-
quinoline derivatives II, we performed the multi-
component reaction of aromatic aldehydes, dimedone,
malononitrile, and ammonium acetate at room tempera-
ture under grinding, but unlike the Kumar’s report, we
obtained tetrahydrobenzo[b]pyran derivatives III instead
of polyhydroquinolines II. We also performed the
sequential reaction according the Patil et al. procedure
[42], but tetrahydrobenzo[b]pyran derivatives III were
obtained. Thus herein we wish to clarify the role of
ammonium acetate as a catalyst or a reactant and to report
the green synthesis of polyhydroquinoline derivatives II
by a sequential two-stage reaction of dimedone, ammo-
nium acetate, malononitrile, and arylaldehydes.
Therefore, the synthesis of polyhydroquinoline deriva-
tives 2a–g was performed using a two-stage process.
Treatment of dimedone (2 mmol) and ammonium acetate
˚
(3 mmol) in dry toluene in the presence of 4 A molecular
sieves under reflux for 2 h furnished 3-amino-5,5-dime-
thyl-2-cyclohexen-1-one (3) in 90 % yield. Then the
mixture of 3-amino-5,5-dimethyl-2-cyclohexen-1-one
(1 mmol), benzaldehyde (1 mmol), and malononitrile
(1 mmol) in 5 cm3 ethanol was refluxed until completion
of reaction as indicated by TLC (22 h). After recrystal-
lization of the precipitated solid from ethanol, 2-amino-7,7-
dimethyl-5-oxo-4-phenyl-1,4,5,6,7,8-hexahydroquinoline-
3-carbonitrile (2a) was obtained in 75 % yield. The reac-
tion was also performed in the presence of ammonium
acetate and imidazole as catalysts. Addition of ammonium
acetate or imidazole caused the acceleration of reaction and
Results and discussion
We initially examined the one-pot reaction of benzalde-
hyde (1 equiv.), dimedone (1 equiv.), malononitrile (1
equiv.), and ammonium acetate (1.5 equiv.) under solvent-
free conditions at room temperature under grinding. All
reactants were taken in a mortar, mixed thoroughly, and
ground well at room temperature for 15 min. However,
123

Ammonium acetate as a catalyst and/or reactant in the reaction of dimedone, aromatic aldehyde…
Table 1 Ammonium acetate-mediated reaction of aromatic aldehydes, dimedone, and malononitrile at room temperature under grinding
Entry
Ar
Product
Yield/%
M.p./°C
1
C6H5
1a
1b
1c
1d
1e
1f
90
78
92
94
81
92
94
80
98
85
85
91
88
228–230 (228–230 [47])
230–232 (233–234 [8])
211–212 (210–211 [47])
179–180 (176–178 [47])
199–201
2
2-O2NC6H4
3-O2NC6H4
4-O2NC6H4
2-MeOC6H4
3-MeOC6H4
2-ClC6H4
3-ClC6H4
2-BrC6H4
4-BrC6H4
2-MeC6H4
3-MeC6H4
4-MeC6H4
3
4
5
6
199–201 (207–209 [49])
211–213 (208–210 [47])
222–224 (222–224 [48])
154–156
7
1g
1h
1i
8
9
10
11
12
13
1j
216–218 (206–208 [49])
205–207
1k
1l
202–204
1m
218–220 (218–220 [48])
Scheme 1
CN
CN
O
CN
CN
NH4OAc
+
Ar
H
Ar
CN
CN
O
O
Ar
O
O
Ar
O
O
H
H
CN
N
CN
NH
Ar
O
OH
O
Ar
CN
NH2
O
-
1a 1m
the reduction of reaction time to 14 h and 45 min,
respectively. So, the optimized conditions (refluxing in
ethanol in the presence of 20 mol% imidazole) were then
applied to a series of aldehyde substrates (Scheme 2;
Table 2).
Conclusion
Based on the obtained experimental results, in the multi-
component reaction of aromatic aldehydes, dimedone,
malononitrile, and ammonium acetate under both grinding
123

A. M. Zonouz et al.
Scheme 2
Table 2 The two-stage synthesis of polyhydroquinoline derivatives 2a–2g in refluxing ethanol in the presence of catalytic amount of imidazole
Entry
Ar
Product
Time/min
Yield/%
M.p./°C
1
2
3
4
5
6
7
C6H5
2a
2b
2c
2d
2e
2f
45
45
90
60
90
75
65
75
87
89
70
90
80
88
288–290 (280–281 [39])
281–282 (282–283 [39])
288–289 (288–289 [39])
275–276
3-O2NC6H4
4-MeOC6H4
2-BrC6H4
4-BrC6H4
2-MeC6H4
4-MeC6H4
292–294 (295–296 [39])
276–279
2g
[300 ([300 [39])
1
1494 (s), 1371 (s), 1251 (s), 1212 (s), 1037 (s) cm-1; H
NMR (400 MHz, CDCl3): d = 1.07 (s, 3H, CH3), 1.14 (s,
3H, CH3), 2.18–2.29 (m, 2H, CH2), 2.46 (s, 2H, CH2), 3.85
(s, 3H, OCH3), 4.48 (s, 2H, NH2), 4.73 (s, 1H, C(4)-H),
6.87–6.91 (m, 2H, ArH), 7.11 (d, J = 8.0 Hz, 1H, ArH),
7.20 (t, J = 8.0 Hz, 1H, ArH) ppm; 13C NMR (100 MHz,
CDCl3): d = 26.67, 29.35, 32.52, 32.61, 50.67, 55.58,
61.81, 111.25, 112.45, 119.10, 120.45, 128.26, 128.62,
131.63, 157.17, 157.53, 157.74, 194.47 ppm.
and reflux conditions, ammonium acetate acts as an effi-
cient catalyst instead of reactant and led to the formation of
tetrahydrobenzo[b]pyrans instead of polyhydroquinolines.
Experimental
General procedure for the synthesis
of tetrahydrobenzo[b]pyrans 1a–1m
2-Amino-4-(2-bromophenyl)-5,6,7,8-tetrahydro-7,7-dime-
thyl-5-oxo-4H-chromene-3-carbonitrile
A mixture of 1.1 cm3 benzaldehyde (10 mmol), 0.66 g
malononitrile (10 mmol), 1.4 g dimedone (10 mmol), and
1.15 g ammonium acetate (15 mmol) was thoroughly
mixed in a mortar by grinding until the completion of
reaction as indicated by TLC (15 min). The precipitate
was filtered, washed with water, and recrystallized from
ethanol gave compound 1a as white crystals (2.21 g,
90 %).
(1i, C18H17BrN2O2)
M.p.: 154–156 °C; IR (KBr): vꢀ = 3465 (m), 3327 (m),
3196 (m), 2958 (m), 2872 (m), 2197 (s), 1676 (s), 1603 (s),
1
1366 (s), 1213 (s), 1038 (s) cm-1; H NMR (400 MHz,
CDCl3): d = 1.09 (s, 3H, CH3), 1.13 (s, 3H, CH3), 2.18-
2.28 (m, 2H, CH2), 2.48 (s, 2H, CH2), 4.70 (s, 2H, NH2),
4.92 (s, 1H, C(4)-H), 7.07 (dt, J = 8.0, 2.0 Hz, 1H, ArH),
7.18 (d, J = 8.0 Hz, 1H, ArH), 7.26 (dt, J = 8.0, 2.0 Hz,
1H, ArH), 7.54 (d, J = 8.0 Hz, 1H, ArH) ppm; 13C NMR
(100 MHz, CDCl3): d = 26.92, 29.56, 32.42, 36.60, 50.67,
60.27, 111.92, 117.38, 122.45, 126.96, 127.62, 128.73,
132.03, 141.89, 156.53, 156.74, 194.67 ppm.
2-Amino-5,6,7,8-tetrahydro-4-(2-methoxyphenyl)-7,7-
dimethyl-5-oxo-4H-chromene-3-carbonitrile
(1e, C19H20N2O3)
M.p.: 199–201 °C; IR (KBr): vꢀ = 3395 (m), 3330 (m),
3220 (m), 2964 (m), 2189 (s), 1685 (s), 1654 (s), 1606 (s),
123

Ammonium acetate as a catalyst and/or reactant in the reaction of dimedone, aromatic aldehyde…
2-Amino-5,6,7,8-tetrahydro-7,7-dimethyl-4-(2-methylphe-
nyl)-5-oxo-4H-chromene-3-carbonitrile
3-amino-5,5-dimethyl-2-cyclohexen-1-one (3, 1 mmol),
and 10 mg imidazole (0.2 mmol) in 5 cm3 ethanol was
performed as above method. The reaction was completed in
45 min and 2b obtained as yellow crystals (290 mg, 87 %).
(1k, C19H20N2O2)
M.p.: 205–207 °C; IR (KBr): vꢀ = 3374 (m), 3142 (m),
2958 (m), 2187 (s), 1684 (s), 1668 (s), 1608 (m), 1364 (s),
1216 (s), 1039 (s) cm-1; 1H NMR (400 MHz, CDCl3):
d = 1.08 (s, 3H, CH3), 1.14 (s, 3H, CH3), 2.20–2.25 (AB
quartet, J = 20.0 Hz, 2H, CH2), 2.49 (s, 2H, CH2), 2.60 (s,
3H, CH3), 4.57 (s, 2H, NH2), 4.70 (s, 1H, C(4)-H), 6.97-
7.15 (m, 4H, ArH) ppm; 13C NMR (100 MHz, CDCl3):
d = 19.27, 26.84, 29.46, 32.54, 32.70, 50.76, 61.68,
112.52, 119.12, 126.50, 126.86, 127.85, 130.37, 135.32,
142.48, 156.62, 157.44, 194.74 ppm.
2-Amino-7,7-dimethyl-5-oxo-4-(2-bromophenyl)-
1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile
(2d, C18H18BrN3O)
M.p.: 275–276 °C; IR (KBr): vꢀ = 3442 (m), 3324 (m),
3215 (m), 2955 (m), 2184 (s), 1662 (s), 1630 (s), 1496 (s),
1
1370 (s), 1270 (s) cm-1; H NMR (400 MHz, DMSO-d6):
d = 0.96 (s, 3H, CH3), 1.03 (s, 3H, CH3), 1.96 (d,
J = 16 Hz, 1H, CH2), 2.17 (d, J = 16 Hz, 1H, CH2),
2.38, 2.50 (AB quartet, J = 14 Hz, 2H, CH2), 4.86 (s, 1H,
C(4)-H), 5.74 (s, 2H, NH2), 7.07 (t, J = 8.0 Hz, 1H, ArH),
7.14 (d, J = 8.0 Hz, 1H, ArH), 7.28 (t, J = 8.0 Hz, 1H,
ArH), 7.49 (d, J = 8.0 Hz, 1H, ArH), 8.93 (s, 1H, NH)
ppm; 13C NMR (100 MHz, CDCl3): d = 26.89, 29.52,
33.02, 36.36, 50.43, 60.43, 112.57, 117.25, 122.45, 127.06,
127.67, 128.68, 132.13, 141.64, 149.53, 158.27,
194.07 ppm.
2-Amino-5,6,7,8-tetrahydro-7,7-dimethyl-4-(3-methylphe-
nyl)-5-oxo-4H-chromene-3-carbonitrile
(1l, C19H20N2O2)
M.p.: 202–204 °C; IR (KBr): vꢀ = 3349 (m), 3177 (s), 2964
(m), 2191 (s), 1683 (s), 1656 (s), 1604 (s), 1371 (s), 1214
(s), 1036 (s), cm-1; 1H NMR (400 MHz, CDCl3): d = 1.08
(s, 3H, CH3), 1.14 (s, 3H, CH3), 2.29 (s, 2H, CH2), 2.34 (s,
3H, CH3), 2.48 (s, 2H, CH2), 4.38 (s, 1H, C(4)-H), 4.55 (s,
2H, NH2), 7.02-7.04 (m, 3H, ArH), 7.17–7.21 (m, 1H,
ArH) ppm; 13C NMR (100 MHz, CDCl3): d = 21.45,
26.74, 29.61, 32.63, 36.33, 49.96, 62.52, 113.12, 118.82,
124.62, 127.46, 128.25, 128.37, 138.05, 143.64, 156.62,
157.05, 194.67 ppm.
2-Amino-7,7-dimethyl-4-(2-methylphenyl)-5-oxo-
1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile
(2f, C19H21N3O)
M.p.: 276–279 °C; IR (KBr): vꢀ = 3441 (m), 2961 (m),
2180 (s), 1664 (s), 1620 (s), 1497 (s), 1368 (s), 1271
(s) cm-1; 1H NMR (400 MHz, DMSO-d6): d = 0.93 (s,
3H, CH3), 1.03 (s, 3H, CH3), 1.95 (d, J = 16.0 Hz, 1H,
CH2), 2.16 (d, J = 16.0 Hz, 1H, CH2), 2.30 (d,
J = 16.8 Hz, 1H, CH2), 2.41 (d, J = 16.8 Hz, 1H,
CH2), 2.47 (s, 3H, CH3), 4.60 (s, 1H, C(4)-H), 5.68 (s,
2H, NH2), 6.96–7.10 (m, 4H, ArH), 8.84 (s, 1H,NH) ppm;
13C NMR (100 MHz, CDCl3): d = 19.84, 26.76, 29.53,
32.54, 32.73, 50.82, 60.98, 112.57, 118.82, 126.59,
126.87, 127.63, 129.87, 135.21, 142.28, 149.89, 159.24,
194.45 ppm.
3-Amino-5,5-dimethyl-2-cyclohexen-1-one (3)
A mixture of 0.28 g dimedone (2 mmol) and 0.23 g
ammonium acetate (3 mmol) in 5 cm3 dry toluene in the
˚
presence of 4 A molecular sieves was refluxed for 2 h.
After completion of the reaction as indicated by TLC, the
reaction mixture was cooled to room temperature and the
precipitate was filtered and then purified by recrystalliza-
tion from dry toluene. 3-Amino-5,5-dimethyl-2-
cyclohexen-1-one (3) was obtained as needles (0.25 g,
90 %). M.p.: 163–165 °C (Ref. [50] 163.5–164 °C).
Acknowledgments The authors sincerely acknowledge the Research
Office of Azarbaijan Shahid Madani University for financial support.
General procedure for the synthesis
of polyhydroquinolines 2a–2g
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