An efficient synthesis of 4H-chromene, 4H-pyran, and oxepine derivatives via one-pot three-component tandem reactions

Article abstract of DOI:10.1016/j.tetlet.2012.10.046

A new and efficient method has been developed for the synthesis of highly functionalized 2-amino-4H-pyran, 2-amino-4H-chromene, 2-amino-oxepine, and 2-hydroxy-oxepine derivatives through one-pot, three-component tandem reactions of structurally diverse 1,3-diketones, dialkyl acetylenedicarboxylates, and malononitrile or ethyl cyanoacetate in the presence of a catalytic amount of Na₂CO₃ in ethanol. This efficient technique has the advantages of giving products in good to high yields, in short reaction times, and with a simple isolation procedure.

Full text of DOI:10.1016/j.tetlet.2012.10.046

Tetrahedron Letters 53 (2012) 6977–6981
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
An efficient synthesis of 4H-chromene, 4H-pyran, and oxepine derivatives
via one-pot three-component tandem reactions
a
a,
⇑
a
a
b
Bagher Kazemi , Shahrzad Javanshir , Ali Maleki , Mostafa Safari , Hamid Reza Khavasi
a
Department of Chemistry, Iran University of Science and Technology, Tehran 1684613114, Iran
Department of Chemistry, Shahid Beheshti University, Tehran 1983963113, Iran
b
a r t i c l e i n f o
a b s t r a c t
Article history:
A new and efficient method has been developed for the synthesis of highly functionalized 2-amino-
H-pyran, 2-amino-4H-chromene, 2-amino-oxepine, and 2-hydroxy-oxepine derivatives through
one-pot, three-component tandem reactions of structurally diverse 1,3-diketones, dialkyl acetylenedi-
carboxylates, and malononitrile or ethyl cyanoacetate in the presence of a catalytic amount of Na CO
in ethanol. This efficient technique has the advantages of giving products in good to high yields, in short
reaction times, and with a simple isolation procedure.
Received 16 June 2012
Revised 27 September 2012
Accepted 11 October 2012
Available online 22 October 2012
4
2
3
Keywords:
Oxepine
Ó 2012 Elsevier Ltd. All rights reserved.
Pyran
Chromene
Multicomponent reaction
Dialkyl acetylenedicarboxylate
Malononitrile
The concept of privileged structures or scaffolds was first intro-
duced in 1988, and defined as ‘a single molecular framework able
involves tandem Michael addition and cyclization between struc-
turally diverse 1,3-diketones 3a–c, various dialkyl acetylenedicarb-
oxylates (DAADs) 2, and malononitrile (1a) or ethyl cyanoacetate
(1b) catalyzed by sodium carbonate (Scheme 1). To the best of our
knowledge, there are no such one-pot methods available for the syn-
thesis of 2-amino-oxepine and 2-hydroxy-oxepine derivatives. The
present study provides an insight into the manner by which differ-
ent types of substituted 1,3-diketones 3a–c undergo tandem
Michael addition and cyclization reactions with DAADs 2 and
malononitrile (1a) or ethyl cyanoacetate (1b).
1
to provide ligands for diverse receptors’. Since then, an increasing
number of structural frameworks have been described as privi-
leged structures including oxepine, 4H-pyran, and 4H-chromene
2
derivatives. These are important structural units found widely in
3
4
5
7
natural products such as anthraquinones, coumarins, flavonoids,
6
ricchiocarpin A and ricchiocarpin B, heliannuols B, C, and D,
lobatrienetriol, ciguatoxin,9 KW-3635,
8
10
janoxepin,
11
oxepina-
1
2
13
mides C, bauhiniastatin A, etc. (Fig. 1). Some of these natural
10
products originate from marine sources. The pharmacological
investigations reported for these structures showed that they have
various biological activities including antiplasmodial (for janoxe-
pine) and anticancer (for bauhiniastatin A). Due to their interesting
and important biological properties, the development of simple
and convenient methodologies for the synthesis of oxepine, 4H-
pyran, and 4H-chromene derivatives represents an attractive and
interesting endeavor in synthetic organic and medicinal chemistry
and, in fact, a number of strategies are reported in the literature for
the synthesis of these compounds.14–16
First, we attempted to optimize the conditions for the reaction
of malononitrile (1a), diethyl acetylenedicarboxylate (DEAD) (2b),
and dimedone (3a). When 1a (0.066 g, 1.0 mmol, 1.0 equiv), 2b
(0.170 g, 1.0 mmol, 1.0 equiv), and dimedone (3a) (0.140 g,
1.0 mmol, 1.0 equiv) were mixed together in ethanol without any
catalyst, only a trace of the expected product was detected, even
after 24 h. The catalytic effects of various Brønsted bases were then
studied (Table 1). Among the different catalysts, sodium carbonate
showed the best activity (entry 3, Table 1). In order to find the best
reaction medium, we utilized various solvents such as H
2
O, EtOH,
In continuation of our interest in multicomponent reactions
MeOH, EtOAc, CH Cl , and THF (5 ml) in the presence of sodium
2
2
1
7
(
MCRs), we report a versatile method for the synthesis of privi-
leged heterocyclic medicinal scaffolds incorporating 2-amino-
H-chromene 4a,b, 2-amino-4H-pyran 4c, 2-amino-oxepine 5a,b,
and 2-hydroxy-oxepine 6 annulated frameworks. The protocol
carbonate (0.021 g, 0.2 mmol, 0.2 equiv) under reflux conditions.
Ethanol proved to be the solvent of choice due to its safe nature
and because it provided higher yields. Solvent-free conditions gave
only moderate yields. The amount of catalyst required was opti-
mized in ethanol; the use of 20 mol % of sodium carbonate ap-
peared to be optimal.
4
⇑
Corresponding author. Tel.: +98 21 77240346; fax: +98 21 77491204.
E-mail address: shjavan@iust.ac.ir (S. Javanshir).
Having optimized the reaction conditions, the scope and limita-
tions of the method were studied. To this end, the reactions of
0
040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.10.046

6
978
B. Kazemi et al. / Tetrahedron Letters 53 (2012) 6977–6981
structurally diverse 1,3-diketones 3a–c with various DAADs 2 and
a or 1b were run under the optimized conditions. The results are
Table 1
a
Effect of the base on the preparation of 4b
1
Yieldb (%)
summarized in Table 2. With 3a and 3b, highly functionalized 2-
amino-4H-chromenes 4a,b and 2-amino-4H-pyran 4c were
synthesized respectively (entries 1–3, Table 2). Interestingly,
when the reaction was tested with 1,3-indandione (3c), novel 2-
amino-oxepine 5 and 2-hydroxy-oxepine 6 derivatives were char-
acterized as the exclusive products rather than the corresponding
pyrans 4 (entries 4–6). However, when a linear 1,3-diketone such
as acetylacetone (3d) was used, diethyl acetylenedicarboxylate
was not incorporated and the reaction did not proceed as expected
Entry
Base
1
2
3
4
5
—
KOH
—
87
89
82
79
Na
Et
NH
2
CO
N
3
3
4
OAc
a
The reactions were performed in 5 ml of solvent for 2.5 h in the presence of
0 mol % of base.
Isolated yield.
2
b
(
entries 7 and 8, Table 2) with 4,6-dimethyl-2-oxo-1,2-dihydropyr-
idine-3-carbonitrile (9) being obtained instead in a low yield
(
Scheme 2).
2 2 3
of the CH COOCH CH group, a multiplet at d = 4.01 assigned to
The structures of the products were supported by IR, 1H NMR,
two ester methylene groups, and
a
singlet at d = 7.26
and 1 C NMR spectra, and elemental analyses, and were further
confirmed by single-crystal X-ray diffraction studies performed
on compound 4b (Fig. 2).
3
corresponding to the amine group (NH ). In order to verify the
2
structure of 4b, a single crystal was obtained and analyzed by X-
1
8
ray crystallography (Fig. 2), which clearly indicated the forma-
tion of a 4H-chromene scaffold.
The IR spectrum of 4b showed the characteristic absorptions of
À1
a primary amine group (NH
group (C„N) at 2196 cm , and an ester carbonyl group (C@O)
at 1733 cm . The H NMR spectrum of 4b showed a singlet at
d = 1.04 attributed to the gem-methyl groups (CMe ), two triplet
signals at d = 1.09 (J = 7.1 Hz) and 1.11 (J = 7.1 Hz) representing
the two ester methyl groups, a singlet at d = 2.22 and two doublets
at d = 2.42 (J = 17.9) and 2.46 (J = 17.9 Hz) attributed to two cyclo-
hexane methylene groups, two doublets at d = 2.81 (J = 14.9 Hz)
and 2.93 (J = 14.9) due to the diastereotopic methylene protons
2
) at 3365 and 3325 cm , a cyanide
The IR spectrum of 5a showed absorptions at 3467, 3361, 2219,
À1
À1
1731, and 1703 cm indicating the presence of N–H, C„N, and
À1
1
1
two ester C@O groups, respectively. The H NMR spectrum of 5a
2
exhibited two single sharp peaks at d = 3.81 and 3.88 readily recog-
nized as two methoxy groups (MeO), multiplet signals at d = 7.60–
8.16 arising from the aromatic protons (ArH), and a singlet at
1
d = 8.18 assigned to the NH2 protons. However the H NMR spec-
trum revealed the absence of the diastereotopic methylene group
which appeared at d = 2.81 and d = 2.93 for compound 4b.
OH
OH
HO
OCH3
HO
O
O
OH
a flavonoid
OH
OH
bauhiniastatin A
N
N
O
COONa
O
O
.
H O
2
O
KW-3635
ricchiocarpin A
Figure 1. A few selected examples of compounds with embedded pyran, chromene, or oxepine cores.
RO C
2
CO R O
CO R O
2
CO R
2
O
O
RO C
2
RO C
2
RO C
2
2
NC
X
NC
Na CO (20 mol%)
ethanol, reflux
2
3
or
or NC
NC
O
CO R
2
O
H2N
O
O
H N
HO
2
X=CN, CO Et
2
R= Me, Et
1
2
3
4a-c
5a,b
6
Scheme 1. Synthesis of 2-amino-4H-chromenes 4a,b, 2-amino-4H-pyran 4c, 2-amino-oxepines 5a,b, and 2-hydroxy-oxepine 6.

B. Kazemi et al. / Tetrahedron Letters 53 (2012) 6977–6981
6979
Table 2
Synthesis of 2-amino-4H-chromenes 4a,b, 2-amino-4H-pyran 4c, 2-amino-oxepines 5a,b, and 2-hydroxy-oxepine 6 derivatives
a
Entry
X
R
1,3-Diketone
Product
MeO C
Time (h)
Yieldb (%)
O
2
O
MeO C
2
NC
1
CN
Me
2.5
81
O
H N
O
2
3
a
a
4
a
O
EtO C
2
EtO C
O
2
NC
2
CN
Et
O
2.5
89
H N
O
2
3
4
b
4
O
MeO C
2
MeO C
O
2
NC
3
4
CN
CN
Me
Me
4
4
54
63
O
O
H N
O
2
3
b
c
CO Me
2
O
MeO C
2
NC
O
O
O
H N
2
3
c
5a
CO Et
2
O
EtO C
2
NC
5
CN
Et
4
55
O
O
O
H N
2
3
c
c
5
b
CO Me
2
O
MeO C
2
NC
6
7
CO
2
Et
Me
Me
O
4.5
66
O
HO
3
6
CN
O
O
O
NC
O
N
H
3
d
d
6
30
O
8
CN
Et
9
3
a
2 3
All reactions were carried out with 1a or 1b (1 mmol), 2 (1 mmol), 3 (1 mmol), Na CO (20 mol %), reflux, EtOH (5 mL).
Isolated yield.
b
1
Examination of the IR and H NMR spectra of 6 suggested the pres-
malononitrile (1a) or ethyl cyanoacetate (1b) with DAADs 2 in
the presence of sodium carbonate may lead to the formation
of Michael adduct intermediates 7 which are in equilibrium
with the tautomeric form 8 (Scheme 3). The 2-amino-4H-pyrans
or 2-amino-4H-chromenes 4a–c may then be formed by nucle-
ophilic addition of the enolic form of the 1,3-diketones 3a,b to
the Michael adduct 8a followed by cyclization (Scheme 4). The
2-amino-oxepines 5a,b may be formed by nucleophilic addition
1
ence of an OH group which appeared in the H NMR spectrum as
part of the multiplet at d = 8.17. The 1H NMR spectrum of 6 also
revealed the absence of any diastereotopic methylene group or
ethoxy group. The C NMR spectra of 6 showed 17 distinct signals
that were consistent with the proposed structure.
According to our results, we propose the reaction mecha-
nisms shown in Schemes 3–5. The initial condensation of
1
3

6
980
B. Kazemi et al. / Tetrahedron Letters 53 (2012) 6977–6981
CO R
CO R
2
2
O
CO R
CO R
2
2
CN
O
O
NC
1
2
N
CO R
2
X
O
CN
N
O
NH2
O
N
H
7a
CO R
NC
2
3
d
9
O
RO2C
H
CO R
2
O
Scheme 2. Formation of 4,6-dimethyl-2-oxo-1,2-dihydropyridine-3-carbonitrile
9).
CN
(
O
O
CO2R
N
H
CO R
2
CN
CO R
O
2
C
CO R
O
2
HN
CN
O
NH2
[O]
CO R
2
O
CO R
2
O
CO R
CO R
2
2
CN
CN
O
a-c
NH2
O
5a,b
NH2
4
Scheme 4. The suggested mechanisms for the formation of 4a–c and 5a,b.
O RO C
CO R
2
2
CO R
CN
O
2
CO R
O
2
O-
Figure 2. ORTEP diagram of the crystal structure of 4b (CCDC = 902651).
OEt
CN
7
b
O
CO R
2
OH
O
H
CO R
2
6
air oxidation
CN
CO R
CO R
2
2
O
NC
NC
X
O
CO R
O
2
Na CO
2
3
EtO
CO R
2
CO R
X
CN
O
2
EtOH
-OEt
CO R
2
+
CO R
CO R
O
H
2
2
1
a X=CN
OH
H
O
CN
R=Me, Et
2
1b X=CO Et
2
O
Scheme 5. The proposed mechanism for the formation of 2-hydroxy-oxepine 6.
RO C
CO R
RO C
CO R
2
2
2
2
Spectral and analytical data for representative compounds
Ethyl 2-amino-3-cyano-4-(2-ethoxy-2-oxoethyl)-7,7-dimethyl-
NC
NC
X
X
8
8
a X=CN
7a X=CN
7b X=CO Et
5
-oxo-5,6,7,8-tetrahydro-4H-chromene-4-carboxylate (4b)
b X=CO Et
2
2
1
9
Yield: 89% (0.335 g); White solid (EtOH); mp 230–232 °C (Lit.
Scheme 3. The formation of Michael adducts from malononitrile (1a) or ethyl
cyanoacetate (1b) and DAADs 2.
À1
1
2
(
CH
38–239 °C); IR (KBr): 3365, 3325, 2196, 1733 cm
): d = 1.04 (6H, s, CH ), 1.09 (3H, t, J = 7.1 Hz,
), 1.11 (3H, t, J = 7.1 Hz, CH ), 2.22 (2H, s, CH ), 2.42 (1H, d,
), 2.46 (1H, d, J = 17.9, CH ), 2.81 (1H, d, J = 14.9,
), 2.93 (1H, d, J = 14.9, CH ), 4.01 (4H, m, CH ), 7.26 (2H,
); C NMR (125 MHz, DMSO-d ): d = 14.8, 14.9, 28.1, 28.2,
32.8, 39.7, 43.6, 50.9, 56.8, 60.7, 61.9, 111.7, 118.3, 160.2, 164.0,
170.5, 171.8, 200.0; Anal. Calcd for C19 (376.40): C,
; H NMR
500 MHz, DMSO-d
6
3
3
3
2
of the enolic form of 1,3-indanedione (3c) to the Michael ad-
duct 7a followed by cyclization and subsequent oxidation
Scheme 4).
J = 17.9, CH
CH
s, NH
a
H
b
a b
H
a
H
b
a
H
b
2
1
3
(
2
6
The 2-hydroxy-oxepine 6 may be formed by nucleophilic
addition of the enolic form of 1,3-indanedione (3c) to the Michael
adduct 7b followed by cyclization and subsequent elimination of
OEt and oxidation (Scheme 5). The driving force for the oxidation
may be due to the homoaromatic nature of the products.
In conclusion, we have described a new and efficient strategy for
the synthesis of highly functionalized 2-amino-4H-pyran, 2-amino-
24 2 6
H N O
60.63; H, 6.43; N, 7.44. Found: C, 60.91; H, 6.48; N, 7.26%.
Diethyl 2-amino-3-cyano-6-oxo-6H-indeno[1,2-b]oxepine-4,5-
dicarboxylate (5b)
4
H-chromene, 2-amino-oxepine, and 2-hydroxy-oxepine deriva-
Yield: 55% (0.210 g); Yellow crystals (EtOH); mp 197–199 °C; IR
À1
1
tives through tandem Michael addition–cyclization processes. The
products, which may have interesting biological and pharmacolog-
ical activities, are obtained in moderate to good yields.
(KBr): 3421, 3323, 2225, 1747, 1706 cm
DMSO-d ): d = 1.25 (3H, t, J = 7.0 Hz, CH ), 1.33 (3H, t, J = 7.0 Hz,
CH ), 4.26 (2H, q, J = 6.9 Hz, CH ), 4.35 (2H, q, J = 6.9 Hz, CH ),
; H NMR (500 MHz,
6
3
3
2
2

B. Kazemi et al. / Tetrahedron Letters 53 (2012) 6977–6981
6981
7
.57 (1H, t, J = 7.3 Hz, ArH), 7.64 (1H, d, J = 7.1 Hz, ArH), 7.71 (1H, t,
References and notes
1
3
J = 7.4 Hz, ArH), 8.10 (1H, d, J = 7.5 Hz, ArH), 8.18 (2H, s, NH
2
);
C
1.
Evans, B. E.; Rittle, K. E.; Bock, M. G.; Di Pardo, R. M.; Freidinger, R. M.; Whitter,
W. L.; Lundell, G. F.; Veber, D. F.; Anderson, P. S.; Chang, R. S. L.; Lotti, V. J.;
Cerino, D. J.; Chen, T. B.; Kling, P. J.; Kunkel, K. A.; Springer, J. P.; Hirshfield, J. J.
Med. Chem. 1988, 31, 2235–2246.
NMR (125 MHz, DMSO-d
6
): d = 14.4, 14.6, 62.3, 62.6, 91.9, 106.7,
15.4, 117.9, 123.4, 124.6, 133.2, 135.8, 136.0, 139.1, 139.4,
51.8, 156.9, 166.0, 166.1, 187.6; Anal. Calcd for C20
1
1
16 2 6
H N O
2
3
.
.
Poupaert, J.; Carato, P.; Colacino, E. Curr. Med. Chem. 2005, 12, 877–885.
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7
380.35): C, 63.16; H, 4.24; N, 7.37. Found: C, 63.34; H, 4.36; N,
.79.
6
8, 904–910.
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4
,5-dicarboxylate (6)
1241.
Yield: 66% (0.233 g); Orange crystals (EtOH); mp 291–293 °C; IR
7. Macias, F. A.; Molinillo, J. M. G.; Varela, R. M.; Torres, A.; Fronczek, F. R. J. Org.
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1
(
d
KBr): 3334, 2221, 1709, 1697 cm
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8.
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): d = 3.81 (3H, s, CH
3
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3
6
ArH), 7.68 (1H, d, J = 7.1, ArH), 7.78 (1H, t, J = 7.4, ArH), 8.17
9. Candenas, M. L.; Pinto, F. M.; Cintado, C. G.; Morales, E. Q.; Brouard, I.; Diaz, M.
T.; Rico, M.; Rodriquez, R.; Rodriguez, R. M.; Perez, R.; Perez, R. L.; Martin, J. D.
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2H, m, ArH and OH); 1 C NMR (100 MHz, DMSO-d
3
(
6
): d = 38.3,
5
1
C
2.6, 52.8, 91.2, 106.2, 114.6, 122.6, 123.9, 132.5, 135.2, 138.1,
38.6, 151.1, 155.9, 165.4, 165.7, 186.9; Anal. Calcd for
H11NO (353.28): C, 61.20; H, 3.14; N, 3.96. Found: C, 61.34;
18 7
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1
1. Sprogoe, K.; Manniche, S.; Larsen, T. O.; Christophersen, C. Tetrahedron 2005,
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1, 8718–8721.
H, 3.56; N, 3.79.
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1
1
4
,6-Dimethyl-2-oxo-1,2-dihydropyridine-3-carbonitrile (9)
9
320; (b) Hewitt, R. J.; Harvey, J. E. J. Org. Chem. 2010, 75, 955–958; (c) Li, D. Z.;
Yield: 30%; Cream crystals (EtOH); mp 277–279 °C; IR (KBr):
Tang, Y. B.; Kang, Z. Y.; Chen, R. Y.; Yu, D. Q. J. Asian Nat. Prod. Res. 2009, 11,
613–620; (d) Mao, S.; Probst, D.; Werner, S.; Chen, J.; Xie, X.; Brummond, K. M.
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Tetrahedron 2011, 67, 5717–5724; (c) Ding, D.; Zhao, C. G. Tetrahedron Lett.
À1
1
3
(
(
2
C
741, 3467, 3338, 2925, 2195, 1733,1701 cm
): d = 2.20 (3H, s, CH ), 2.28 (3H, s, CH
1H s, CH),12.3 (1H, NH); C NMR (100 MHz, DMSO-d
;
H
NMR
), 6.13
400 MHz, DMSO-d
6
3
3
13
6
): d = 19.7,
1.5, 99.9, 108.3, 116.9, 152.1161.3, 161.9. Anal. Calcd for
O (148.06): C, 64.85; H, 5.44; N, 18.91. Found: C, 64.99;
1
8
8 2
H N
2010, 51, 1322–1325; (d) Fotouhi, L.; Heravi, M. M.; Fatehi, A.; Bakhtiari, K.
H, 5.56; N, 19.07.
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