Microwave promoted, sodium acetate catalyzed one pot synthesis of poly functionalized 4H-pyrans

Article abstract of DOI:10.1002/jccs.201100304

A clean and efficient one pot synthesis of 4H-pyran derivatives through condensation of aromatic aldehydes, malononitrile and dicarbonyl compounds under microwave irradiation in presence of Sodium acetate as a catalyst is described.

Full text of DOI:10.1002/jccs.201100304

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
Microwave Promoted, Sodium Acetate Catalyzed One Pot Synthesis of Poly
Functionalized 4H-Pyrans
Mahesh Shivaji Pandharpatte, Khudbudin Baban Mulani and
Nazeruddin Nasiruddin Gulam Mohammed*
Department of Chemistry (P.G. Centre), Poona College of Arts, Science & Commerce, Pune-411 001, India
(Received: May 24, 2011; Accepted: Aug. 30, 2011; Published Online: Mar. 6, 2012; DOI: 10.1002/jccs.201100304)
A clean and efficient one pot synthesis of 4H-pyran derivatives through condensation of aromatic alde-
hydes, malononitrile and dicarbonyl compounds under microwave irradiation in presence of Sodium ace-
tate as a catalyst is described.
Keywords: Multicomponent reaction; 4H-pyran derivatives; Microwave irradiation; Sodium ace-
tate.
1
2
INTRODUCTION
pyrimidines and pyridin-2-ones, with various other bio-
logical activities. The 4H-pyrans are synthesized mainly by
a three-components coupling reaction of aromatic alde-
hydes, malononitrile and b-diketones catalyzed by bases
Multi component reactions (MCRs) have emerged as
powerful tools in organic, combinatorial and medicinal
1
chemistry. The MCRs strategy offers significant advan-
1
3
14
15
tages over conventional multi step synthesis due to its flex-
2
ible, convergent, and atom economical nature. In a true
like Triethylamine, Piperidine, Rubidium fluoride,
16
Recently, Shestopalov and co-workers have developed a
one-pot electrochemical synthesis of title compounds cata-
lyzed by electro generated base with the yields ranged from
60 to 80%. However, many of these procedures suffer from
one or more disadvantages such as harsh reaction condi-
tions, prolonged time period, poor yields and use of hazard-
ous and expensive catalysts. Therefore, the development of
a clean, high-yielding and environmentally benign ap-
proach is still desirable. We wish to report a clean and effi-
cient method for the synthesis of 4H-pyran derivatives in
excellent yields through one-pot condensation of aromatic
aldehydes, malononitrile and dicarbonyl compounds us-
ing sodium acetate as catalysts in methanol as a solvent
under microwave irradiations. The reaction is depicted in
Scheme I.
sense, MCRs represent environmentally benign processes
by reducing the number of steps, energy consumption and
3
waste production. These features make MCRs well-suited
for the construction of diversified arrays of valuable het-
erocyclic scaffolds. Therefore, great efforts have been and
still are being made to find and develop new multi compo-
nent reactions. Usually, to drive the conversion of MCR,
one or two components are excessive and this always leads
to the trouble of separating and purifying the target prod-
ucts. Another drawback in MCRs is they can not be planed
perfectly in advance and majority of them are accidental.
After getting the product the logic and mechanism of the re-
action is proposed.
Polyfunctionalized 4H-pyrans constitute a structural
4
unit of a number of natural products and inherent reactiv-
5
ity of the pyran ring is versatile synthons. These 4H-py-
Scheme I Synthesis of 4H-pyran derivatives
6
rans are isosters of 1,4-dihydro pyridine with potential
pharmacological interest and active synthons that have
been extensively used in heterocyclic synthesis. In addi-
tion, polyfunctionalized 4H-pyrans are biologically inter-
esting compounds which possess various pharmacological
7
8
9
activities, e.g. antiallergic and antitumor activities. 4H-
pyrans are also useful intermediates for the synthesis of
1
various compounds, such as pyranopyridine derivatives
0
1
polyazanaphthalenes, pyrano[2,3-d]pyrazoles, pyrano
1
*
Corresponding author. E-mail: gmnazeruddin@yahoo.co.in
J. Chin. Chem. Soc. 2012, 59, 645-649
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645

Article
Pandharpatte et al.
RESULTS AND DISCUSSION
picted in Table 2.
4
H-pyran derivatives were obtained in excellent
We have also studied the effect of concentration of
catalyst (sodium acetate) under microwave irradiation at
280 W in methanol as a solvent. It was observed that 10
mol% of the catalyst was the optimum quantity to get the
desired product in excellent yield. The results are depicted
in Table 3. Different aldehydes containing electron-with-
drawing, electron releasing substituents and b-diketoesters
were used for universal applicability of the method for the
synthesis of pyrans. It was found that in all cases, the yields
were excellent.
yields and in shorter reaction time through the one-pot con-
densation of aromatic aldehydes (1 mmol), malononitrile
(
1 mmol) and dicarbonyl compounds (1.1 mmol) using so-
dium acetate (10 mol %) as catalysts in methanol as a sol-
vent under microwave irradiations (280 W).
The results are summarized in Table 1.
To investigate the reaction in detail a model reaction
was carried out by condensing Benzaldehydes, Malonitrile
and Ethyl acetoacetate in various solvents and catalyst (10
mol %) such as TBABr, CTAB, K
CH COONa, L-Proline (Table 2). The results showed that
when Sodium acetate was used as a catalyst its action was
more effective than L-Proline, K CO . In case entries 1, 2,
and 6, instead of desired product the intermediate al-
2
CO
3
, KH
2
PO
4
, NH
2
PO
4
,
Interestingly in the present study when sodium ace-
tate was used as catalyst in the reaction under microwave
irradiation the exclusive product obtained was pyran deriv-
3
1
7
2
3
atives. However, earlier Dewen Dong et al reported sub-
stituted pyridine derivatives. The possible mechanism is
depicted in Scheme II. Although the detailed mechanism of
the above reaction remains to be fully clarified, the forma-
5
kylidenemalononitrile with 90%, 85%, 60% and 80%
yields was obtained. The results of the reactions are de-
Table 1. Synthesis of products 4a-4k under MW (280 W), 10 mol % Sodium acetate as a catalyst
M.P
Entry
Product
Ar
R’
Time
Yield
Found
Lil.
[
[
[
[
[
21]
20]
20]
20]
20]
1
2
3
4
5
6
7
8
9
4a
4b
4c
4d
4e
4f
C H
6
OCH CH
2
4.0
3.5
5.5
3.5
4.0
6.0
4.5
3.5
4.0
3.5
3.5
178-179
171-172
132-133
175-176
179-181
142-144
181-183
163-165
172-173
158-159
170-172
178-179
90
93
82
85
91
80
88
83
87
89
86
5
3
3
3
3
3
3
3
3
4-Cl-C H
6
OCH CH
2
170-172
4
4-OMe-C H
6
OCH CH
2
136-138
4
4-NO -C H
2
OCH CH
2
176-178
6
4
2-Cl-C H
6
OCH CH
2
180-181
4
2-OMe-C H
6
OCH CH
2
-
4
4g
4h
4i
3,4,5-(OCH ) -C H OCH CH
2
-
3
3
6
3
2-NO -C H
2
OCH CH
2
-
6
4
C H
6
OCH3
OCH3
OCH3
-
161-162
-
5
[
18]
1
1
0
1
4j
2-Cl-C H
6 4
4k
4-NO -C H
2 6
4
Table 2. A model reaction by condensing Benzaldehydes, Malonitrile and Ethyl acetoacetate in
various solvents and catalyst (10 mol %) under microwave irradiation at 280 W
Yield % of Alkylide- Yield % of 4H
Entry
Catalyst
Solvent
Time (min)
nemalononitrile
Pyrane
1
2
3
4
5
6
7
8
9
TBABr
CTAB
K CO
Water
Water
8
8
8
8
8
8
4
8
4
4
90
85
-
-
-
Ethanol
10
50
-
2
3
TBABr+K CO
2
Water: Ethanol 30%
Water: Ethanol 10%
Water: Ethanol 10%
Ethanol
-
3
KH PO
2
60
80
-
4
4
NH PO
2
-
CH COONa
3
78
23
10
90
L-Proline
L-Proline
Ethanol
-
-
-
1
0
CH COONa
3
Methanol
-
646
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JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
One Pot Synthesis of Poly Functionalized 4H-Pyrans
Table 3. Effect of the concentration of the catalyst in methanol
under microwave irradiation at 280 W
to pyran ring.
Entry
Sodium acetate in mol %
Yield %
EXPERIMENTAL
1
2
3
4
5
5
7
59
68
80
90
87
All reagents were purchased from Merck and Loba
and used without further purification. Melting points were
measured in open capillary and are uncorrected. The prod-
8
10
12
1
13
ucts were characterized by IR spectra, H NMR, C NMR
and elemental analyses. IR spectra were recorded on
13
1
Perkin–Elmer FT-IR-1710 instrument. H NMR and
C
NMR was recorded on BrukerMSL-300 MHz and Bruker
MSL-200 MHz instruments using TMS as an internal stan-
dard. Elemental analyses were determined by an elemental
analyzer (CHNS-O, EA 1108-elemental analyzer, Carlo
Erba instruments). Microwave oven used was LG micro-
wave MOD-MG-1742WE, 2450 MHz and 700 W maxi-
mum output.
Scheme II Proposed mechanism for the formation of
H pyran
4
General procedure for the preparation of 4H-pyrans
(4a-4k)
A mixture of aromatic aldehyde (1.0 mmol), malono-
nitrile (1.0 mmol), active methylene compounds (1.1
mmol) and methanol 2 mL were taken in 50 mL beaker fol-
lowed by addition of sodium acetate (10 mol%). The
beaker was covered by watch glass and kept for microwave
irradiation at 280 W. Completion of the reaction was moni-
tored by TLC, after completion of the reaction, the reaction
mixture was cooled to room temperature and 5 mL of water
added and filtered. The residue was collected as a crude
product, washed with methanol and recrystallized by abso-
lute ethanol.
tion of compound 4 could be explained by a possible reac-
tion sequence presented in Scheme II. Compound 4 is ex-
pected to proceed via initial condensation of aromatic alde-
hydes with malononitrile to afford alkylidenemalononitrile
which further undergoes in situ Michael addition with ester
of active methylene carbonyl moiety to yield the intermedi-
ate 3a, followed by 3b and 3c, which is then cyclized to fur-
nished 4, a desired product. On other hand if 3b will pick
the proton form methanol (Solvent) then route of reaction
will be different, and finally the pyridine ring will be formed,
which is not possible here. This may be due to low basicity
of sodium aceate.
Ethyl 6-amino-5-cyano-2-methyl-4-phenyl-4H-pyran-
3
-carboxylate (4a)
o
White Solid, m.p. 178-179 C; IR (KBr): 927, 2727,
2
189, 1674, 1608, 1500, 1457, 1377, 1169, 1060, 965, 722;
1
H NMR (300 MHz, CDCl
brs, 2H, NH ), 4.3 (s, 1H, CH), 4.1 (q, 2H, J = 7.2 Hz,
CH ), 2.2 (s, 3H, CH ), 1.1 (t, 3H, J = 7.2 Hz, CH );
: Anal Calc. for C, 67.59; H, 5.67; N, 9.85;
3
): d 7.1-7.3 (m, 5H, Ar-H), 4.4
(
2
2
3
3
16 16 2 3
C H N O
Found: C, 67.64; H, 5.75; N, 9.82.
Ethyl 6-amino-4-(4-chlorophenyl)-5-cyano-2-methyl-
1
The Absolute configuration was further proved by H
4
H-pyran-3-carboxylate (4b)
o
White Solid, m.p. 171-172 C; IR (KBr): 3405, 3019,
1
3
NMR and C NMR. In Case of Pyridine derivative, there is
1
193, 1083, 1383, 1216, 1065, 925, 770, 669; H NMR
OCH group and should give singlet at about 3.5 ppm.
3
1
However in H NMR spectra of all the compounds this
2
(
3
300 MHz, CDCl ): d 7.1 (d, 2H, J = 8.1 Hz, Ar-H), 7.3 (d,
peak are absent so this is clear indication that there is no
2H, J = 8.1 Hz, Ar-H), 4.5 (brs, 2H, NH ), 4.4 (s, 1H, CH),
2
OCH
3
and ultimately it is pyran ring, not the pyridine ring.
3
4.0 (q, 2H, J = 6.9 Hz, CH ), 2.2 (s, 3H, CH ), 1.1 (t, 3H, J =
3
2
1
Further C NMR values for Carbon 2 and carbon 6 are 166
3 16 15 2 3
6.9 Hz, CH ); C H ClN O Anal. Calc. For C, 60.29; H,
ppm and 157 ppm clearly show that position 2 and 6 belong
4.74; N, 8.79; Found: C, 60.29; H, 4.79; N, 8.83.
J. Chin. Chem. Soc. 2012, 59, 645-649
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Article
Pandharpatte et al.
Ethyl 6-amino-5-cyano-4-(4-methoxyphenyl)-2-methyl-
9H, OCH
3
), 2.4 (s, 3H, CH
C NMR (CDCl ): d 13.98, 18.38, 56.08, 60.71, 62.26,
104.47, 107.86, 137.07, 139.40, 153.23, 156.0, 157.37,
165.88; C19 : Anal. Calc. for C, 60.95; H, 5.92; N,
3 3
), 1.1 (t, 3H, J = 7.2 Hz, CH );
1
3
4
H-pyran-3-carboxylate (4c)
o
White Solid, m.p. 132-133 C; IR (KBr): 2929, 2727,
3
1
456, 1377, 1303, 1154, 1076, 964, 722; H NMR (300
1
22 2 6
H N O
MHz, CDCl
3
): d 7.26 (d, 2H, J = 7.0 Hz, Ar-H), 7.14 (d,
H, J = 7.0 Hz, Ar-), 4.47 (brs, 2H, NH ), 4.39 (s, 1H, CH),
.0 (q, 2H, J = 7.2 Hz, CH ), 3.7 (s, 3H, OCH ), 2.3 (s, 3H,
), 1.14 (t, 3H, J= 7.2 Hz, CH : Anal.
7.48; Found:C, 60.98; H, 5.95; N, 7.50.
Ethyl 6-amino-5-cyano-2-methyl-4-(2-nitrophenyl)-4H-
pyran-3-carboxylate (4h)
2
4
2
2
3
o
Yellow Solid, m.p. 163-165 C; IR (KBr): 2924,
CH
3
3
); C17
H
18
N
2
O
4
Calc. For C, 64.96; H, 5.77; N, 8.91; Found: 64.92; H, 5.81;
N, 8.95.
2727, 2208, 1717, 1682, 1600, 1460, 1377, 1304, 1154,
1
1065, 965, 722, 446; H NMR (300 MHz, CDCl
3
): d
), 4.6 (s, 1H, CH),
), 2.4 (s, 3H, CH ), 1.1 (t, 3H, J =
); C NMR (CDCl ): d 13.63, 18.43, 32.89,
60.91, 107.24, 118.21, 124.0, 127.87, 130.58, 133.23,
139.09, 149.03, 158.0, 165.02; C16 : Anal. Calc. C,
Ethyl 6-amino-5-cyano-2-methyl-4-(4-nitrophenyl)-4H-
pyran-3-carboxylate (4d)
7.3-7.8 (m, 4H, Ar-H), 5.3 (brs, 2H, NH
2
4.0 (q, 2H, J = 7.2 Hz, CH
2
3
o
Yellow Solid, m.p. 175-176 C; IR (KBr): 3020,
13
7.2 Hz, CH
3
3
1
197, 1682, 1521, 1348, 1268, 1215, 1062, 760, 669; H
2
NMR (300 MHz, CDCl
.4 (d, 2H, J = 8.0 Hz, Ar-H), 4.7 (brs, 2H, NH
CH), 4.1 (q, 2H, J = 7.0 HzCH ), 2.1 (s, 3H, CH
: Anal. Calc. For C,
3
): d 8.2 (d, 2H, J = 8.0 Hz, Ar-H),
), 4.6 (s, 1H,
), 1.1 (t,
15 3 5
H N O
7
2
58.36; H, 4.59; N, 12.76; Found: C, 58.32; H, 4.65; N,
2
3
12.79.
3
5
1
H, J = 7.0 Hz, CH
3
); C16
H
15
N
3
O
5
Methyl 6-amino-5-cyano-2-methyl-4-phenyl-4H-pyran-
3-carboxylate (4i)
8.36; H, 4.59; N, 12.76; Found: C, 58.32; H, 4.61; N,
2.79.
o
White Solid, m.p. 172-173 C; IR (KBr): 3431, 3223,
Ethyl 6-amino-4-(2-chlorophenyl)-5-cyano-2-methyl-
2947, 2195, 1689, 1604, 1409, 1342, 1261, 1120, 1061,
1
951, 744, 583; H NMR (300 MHz, CDCl
4
H-pyran-3-carboxylate (4e)
o
White Solid, m.p. 179-181 C; IR (KBr): 3405, 3019,
3
): d 7.18-7.32
(m, 5H, Ar-H), 4.48 (brs, 2H, NH
(s, 3H, OCH ), 2.37 (s, 3H, CH
18.46, 38.50, 51.84, 62.08, 107.81, 118.92, 127.33,
128.59, 143.65, 157.60, 157.57, 166.36; C15
2
), 4.44 (s, 1H, CH), 3.58
1
400, 2193, 1677, 1590, 1215, 1068, 757, 669; H NMR
13
2
3
3 3
); C NMR (CDCl ): d
(
300MHz, CDCl
CH), 4.4 (brs, 2H, NH
s, 3H, CH ), 1.0 (t, 3H, J = 7.2 Hz, CH
3
): d 7.1-7.2 (m, 4H, Ar-H), 5.0 (s, 1H,
2
), 4.0 (q, 2H, J = 7.2 Hz, CH ), 2.2
2
14 2 3
H N O :
(
3
3
); C16
H
15ClN
2
O
3
:
Anal. Calc. C, 66.66; H, 5.22; N, 10.36; Found: C, 66.71;
H, 5.30; N, 10.45.
Anal. Calc. for C, 60.29; H, 4.74; N, 8.79; Found: C, 60.30;
H, 4.77; N, 8.84.
Methyl 6-amino-4-(2-chlorophenyl)-5-cyano-2-methyl-
4H-pyran-3-carboxylate (4j)
Ethyl 6-amino-5-cyano-4-(2-methoxyphenyl)-2-methyl-
o
White Solid, m.p. 158-159 C; IR (KBr): 3431, 2923,
1
2727, 2360, 2195, 1675, 1455, 377, 1157, 1063, 722; H
4
H-pyran-3-carboxylate (4f)
o
White Solid, m.p. 142-144 C; IR (KBr): 3309, 2900,
2
1
728, 2192, 1688, 1601, 1457, 1377, 1156, 1061, 772, 448;
NMR (300 MHz, CDCl
3
): d 7.1-7.4 (m, 4H, Ar-H), 5.0 (s,
), 3.6 (s, 3H, OCH ), 2.4 (s, 3H,
): d 18.40, 35.44, 51.67, 61.02,
106.76, 118.49, 127.28, 128.35, 129.85, 133.01, 140.88,
157.69, 166.11; C15 : C, 59.12; H, 4.30; N, 4.19;
H NMR (300 MHz, CDCl
brs, 2H, NH ), 4.4 (s, 1H, CH), 4.0 (q, 2H, J = 7.2 Hz,
CH ), 3.8 (s, 3H, OCH ), 2.4 (s, 3H, CH ), 1.1 (t, 3H, J =
); C NMR (CDCl ): d 13.86, 18.36, 38.63,
5.12, 60.61, 61.37, 107.72, 112.07, 113.50, 119.8, 129.85,
45.40, 156.81, 157.55, 159.64, 165.82; C17
3
): d 6.8-7.3 (m, 4H, Ar-H), 4.5
1H, CH), 4.6 (brs, 2H, NH
2
3
1
3
(
2
3 3
CH ); C NMR (CDCl
2
3
3
1
3
7
5
1
.2 Hz, CH
3
3
2 3
H13ClN O
Found: C, 59.21; H, 4.37; N, 9.15.
H
18
N
2
O
4
:
Methyl 6-amino-5-cyano-2-methyl-4-(4-nitrophenyl)-
4H-pyran-3-carboxylate (4k)
Anal. Calc. For C, 64.96; H, 5.77; N, 8.91; Found: C,
4.95; H, 5.79; N, 8.92.
o
Yellow Solid, m.p. 170-172 C; IR (KBr): 3402,
6
Ethyl 6-amino-5-cyano-4-(3,4,5-trimethoxyphenyl)-2-
methyl-4H-pyran-3-carboxylate (4g)
3330, 3202, 2955, 2201, 1689, 1605, 1520, 1345, 1065,
1
865, 731; H NMR (300 MHz, CDCl
3
): d 8.14-8.18 (d, 2H,
o
White Solid, m.p. 181-183 C; IR (KBr): 3341, 2980,
1
195, 1702, 1593, 1505, 1461, 1327, 1258, 1055, 434; H
J = 8.0 Hz, Ar-H), 7.34-7.38 (d, 2H, J = 8.0 Hz, Ar-H), 4.69
(brs, 2H, NH ), 4.54 (s, 1H, CH), 3.58 (s, 3H, OCH ), 2.39
): d 18.69, 13.69, 51.88,
60.72, 106.65, 118.27, 124.03, 128.30, 147.04, 160.95,
2
2
3
1
3
NMR (300 MHz, CDCl
3
): d 6.4 (s, 2H, Ar-H), 4.5 (brs, 2H,
), 3.8 (s,
3 3
(s, 3H, CH ); C NMR (CDCl
NH ), 4.4 (s, 1H, CH), 4.1 (q, 2H, J = 7.2 Hz, CH
2
2
648
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J. Chin. Chem. Soc. 2012, 59, 645-649

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
One Pot Synthesis of Poly Functionalized 4H-Pyrans
6
. Goldmann, S.; Stoltefuss, J. Angew. Chem., Int. Ed. Engl.
1
4
57.74, 165.77; C15
13 3 5
H N O : Anal. Calc. for C, 57.14; H,
1
991, 30, 1559.
. (a) Bloxham, J.; Dell, C. P.; Smith, C. W. Heterocycles 1994,
8, 399; (b) Zamocka, J.; Misikova, E.; Durinda J. Phar-
.16; N, 13.33; Found: C, 57.20; H, 4.10; N, 13.45.
7
3
CONCLUSION
An efficient and environmentally benign strategy for
mazie, 1991, 46, 610.
8
. Witte, E. C.; Neubert, P.; Roesoh, A. Ger Offen DE 3427985,
the synthesis of multi functional 4H pyran derivatives is
developed. The method offers several advantages includ-
ing high yield of products, short reaction time, easily avail-
ability of catalyst, ease of work-up and low-cost.
1
986; Chem. Abstr., 1986, 104, 224915f.
9. Wang, J. L.; Liu, D.; Zhang, Z. J.; Shan, S.; Han, X.;
Srinivasula, S. M.; Croce, C. M.; Alnemri, E. S.; Huang, Z.
Proc. Natl. Acad. Sci. USA 2000, 97, 7124.
1
0. Adbel-Fattah, A. H.; Hesien, M.; Metwally, S. A.; Elnagdi,
M. H. Liebigs Ann. Chem. 1989, 585.
ACKNOWLEDGMENT
1
1. Quintela, J. M.; Peinador, C.; Moreira, M. J. Tetrahedron
Authors are thankful to University Grants Commis-
sion, New Delhi, for financial Assistance under major re-
search project.
1
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2. Srivastava, S.; Batra, S.; Bhaduri, A. P.; Indian J. Chem.
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