A facile one pot synthesis of pyrano[2,3-c]pyrazole derivatives under microwave irradiation

Article abstract of DOI:10.1081/SCC-120014044

A series of substituted pyrano[2,3-c]pyrazole derivatives were synthesized by the one pot reaction of aromatic aldehydes, malononitrile and 3-methyl-1-phenyl-2-pyrazolin-5-one under microwave irradiation in good yields.

Full text of DOI:10.1081/SCC-120014044

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A FACILE ONE POT SYNTHESIS OF PYRANO[2,3-
c]PYRAZOLE DERIVATIVES UNDER MICROWAVE
IRRADIATION
Jian-Feng Zhou a , Shu-Jiang Tu b , Hui-Qin Zhu a & San-Jun Zhi a
a Department of Chemistry, Huaiyin Normal College, Huaian, 223001, P.R. China
b Department of Chemistry, Xuzhou Normal University, Xuzhou, 221009, P.R. China
Published online: 16 Aug 2006.
To cite this article: Jian-Feng Zhou , Shu-Jiang Tu , Hui-Qin Zhu & San-Jun Zhi (2002) A FACILE ONE POT SYNTHESIS OF
PYRANO[2,3-c]PYRAZOLE DERIVATIVES UNDER MICROWAVE IRRADIATION, Synthetic Communications: An International Journal
for Rapid Communication of Synthetic Organic Chemistry, 32:21, 3363-3366, DOI: 10.1081/SCC-120014044
To link to this article: http://dx.doi.org/10.1081/SCC-120014044
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SYNTHETIC COMMUNICATIONS
Vol. 32, No. 21, pp. 3363–3366, 2002
A FACILE ONE POT SYNTHESIS OF
PYRANO[2,3-c]PYRAZOLE DERIVATIVES
UNDER MICROWAVE IRRADIATION
1,
2
Shu-JiangTu, Hui-Qin Zhu,1
*
Jian-FengZhou,
and San-Jun Zhi1
1Department of Chemistry, Huaiyin Normal College,
Huaian 223001, P.R. China
2Department of Chemistry, Xuzhou Normal University,
Xuzhou, 221009, P.R. China
ABSTRACT
A series of substituted pyrano[2,3-c]pyrazole derivatives were
synthesized by the one pot reaction of aromatic aldehydes,
malononitrile and 3-methyl-1-phenyl-2-pyrazolin-5-one under
microwave irradiation in good yields.
Polyfunctionalized 4H-pyrans are a common structural unit in a
number of natural products,[1] 4H-pyrans ring can be transformed to pyridine
systems related to pharmacologically important calcium antagonists of the
DHP type.[2–4] Substituted pyrazoles and condensed pyrazoles are important
*Corresponding author. E-mail: jfzhou@xinhuanet.com
3363
DOI: 10.1081/SCC-120014044
Copyright & 2002 by Marcel Dekker, Inc.
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3364
ZHOU ET AL.
as pharmaceuticals[5,6] and biodegradable agrochemicals.[7,8] However, the
synthesis of variety of substituted condensed pyrano[2,3-c]pyrazole deriva-
tives were carried out by traditional heating with long time.[9,10]
Recently, the rate enhancement and wide applicability of microwave
heating organic synthesis has been reviewed.[11,12] In our laboratory, we have
researchered a facile synthesis of arylidenecyclo-alka[b]2-amino-4-aryl-3-
cyano-4H-pyrans by the one pot reaction of malononitrile with 2,4-bisaryli-
denecyclopentanone or 2,6-bisarylidenecyclohexanone using piperidine as
catalyst under microwave irradiation.[13] In this paper, we would like to report
the synthesis of substituted condensed pyrano[2,3-c]pyrazole derivatives by
the one pot reaction of aromatic aldehydes, malononitrile and 3-methyl-1-
phenyl-2-pyrazolin-5-one under microwave irradiation. The reactions were
generally finished in 2–8 min with good yields and easy work-up (Table 1).
The synthetic route is shown as following (Sch. 1):
All of title compounds were characterized on the base of spectral data
and elemental analysis. Also the product of 4d were further confirmed by
MS spectra.
Table 1. The Reaction Times and Yields of Compounds 4a–f
Reaction
Time (min)
Compounds
Ar
Yield (%)*
4a
4b
4c
4d
4e
4f
C6H5
4-ClC6H4
4-BrC6H4
4-O2NC6H4
3-O2NC6H4
4-CH3OC6H4
8
5
5
3
3
2
61
91
80
75
73
66
*Yields of the isolated products.
Scheme 1.

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PYRANO[2,3-c]PYRAZOLE DERIVATIVES
EXPERIMENTAL
3365
Melting points were determined in open capillaries and uncorrected.
1
IR spectra were recorded on a Nicolet FT-IR 5DX instrument. H NMR
were measured on a Bruker 300 MHz spectrometer in CDCl3 with TMS as
internal standard. MS spectra were recorded on a VGZAB-HS (FAB).
Elemental analyzer were determined using Perkin-Elmer 240 C elemental
analyzer. The reactions were carried out with a modified commercial micro-
wave oven (Sanle WP650D 650 w) under atmospheric pressure.
General Procedure for Pyrano[2,3-c]pyrazole Derivatives
Into an Erlenmeyer flask (25 mL) equipped with reflux condenser were
introduced the aromatic aldehyde 1 (1 mmol), malononitrile 2 (1 mmol),
3-methyl-2-phenyl-2-pyrazolin-5-one 3 (1 mmol), dry ethanol (3 mL), and
piperidine (0.05 mL). After irradiation with microwaves for 2–8 min
(monitored by TLC), the reaction mixture was cooled. The precipitate
was collected by suction filtration and washed with cold ethanol. The crude
product was recrystallized from ethanol to give a pure sample. Specific
details on each product are as follows:
4a: White solid, m.p. 168–170ꢀC (167–168ꢀC).[10] 1H NMR (CD3Cl) ꢀ:
1.94 (s, 3H, CH3), 4.69 (s, 1H, 4-H), 4.74 (br, s, 2H, NH2), 7.75–7.31
(m, 10H, ArH). IR (KBr): 3450, 3320, 2200, 1660, 1590 cmꢁ1. Anal. calcd.
for C20H16N4O (%): C, 60.98; H, 4.88; N, 17.07. Found: C, 60.70; H, 4.84;
N, 16.95.
4b: White solid, m.p. 174–175ꢀC (186–187ꢀC).[10] 1H NMR (CD3Cl)
ꢀ: 1.95 (s, 3H, CH3), 4.68 (s, 1H, 4-H), 4.75 (br, s, 2H, NH2), 7.78–7.33
(m, 9H, ArH). IR (KBr): 3420, 3360, 2200, 1680, 1600 cmꢁ1. Anal. calcd. for
C20H15ClN4O (%): C, 55.17; H, 4.14; N, 15.45. Found: C, 54.95; H, 4.10;
N, 15.35.
4c: White solid, m.p. 183–184ꢀC (184–185ꢀC).[10] 1H NMR (CD3Cl)
ꢀ: 1.94 (s, 3H, CH3), 4.70 (s, 1H, 4-H), 4.78 (br, s, 2H, NH2), 7.71–7.30
(m, 9H, ArH). IR (KBr): 3420, 3360, 2200, 1680, 1600 cmꢁ1. Anal. calcd. for
C20H15BrN4O (%): C, 58.68; H, 3.67; N, 13.69. Found: C, 58.45; H, 3.61;
N, 15.23.
4d: White solid, m.p. 194–196ꢀC. H NMR (CD3Cl) ꢀ: 1.93 (s, 3H,
1
CH3), 4.77 (s, 1H, 4-H), 4.84 (br, s, 2H, NH2), 8.20–7.35 (m, 9H, ArH).
IR (KBr): 3420, 3330, 2200, 1680, 1600 cmꢁ1. Ms m/e: 373 (m þ 1). Anal.
calcd. for C20H15N5O3 (%): C, 64.34; H, 4.02; N, 18.77. Found: C, 64.02;
H, 3.95; N, 18.66.

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3366
ZHOU ET AL.
4e: White solid, m.p. 188–190ꢀC (178–179ꢀC).[10] 1H NMR (CD3Cl)
ꢀ: 1.93 (s, 3H, CH3), 4.76 (s, 1H, 4-H), 4.88 (br, s, 2H, NH2), 8.20–7.34
(m, 9H, ArH). IR (KBr): 3420, 3330, 2200, 1680, 1600 cmꢁ1. Anal. calcd. for
C20H15N5O3 (%): C, 64.34; H, 4.02; N, 18.77. Found: C, 64.01; H, 3.95;
N, 18.64.
4f: White solid, m.p. 170–172ꢀC (177–178ꢀC).[10] 1H NMR (CD3Cl)
ꢀ: 1.92 (s, 3H, CH3), 4.68 (s, 1H, 4-H), 4.76 (br, s, 2H, NH2), 7.63–7.28
(m, 9H, ArH). IR (KBr): 3450, 3320, 2200, 1660, 1600 cmꢁ1. Anal. calcd. for
C20H18N4O2 (%): C, 70.39; H, 5.03; N, 18.87. Found: C, 70.02; H, 4.99;
N, 18.62.
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Received in Japan June 1, 2001