An efficient multi-component synthesis of 6-amino-3-methyl-4-aryl-2,4- Dihydropyrano[2,3-c]pyrazole-5-carbonitriles

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An Efficient Multi-component Synthesis
of 6-Amino-3-methyl-4-Aryl-2,4-
dihydropyrano[2,3-c]Pyrazole-5-
carbonitriles
G. Santhosh Kumar a , C. Kurumurthy a , B. Veeraswamy a , P.
Sambasiva Rao a , P. Shanthan Rao a & B. Narsaiah a
a Fluoroorganic Division , Indian Institute of Chemical Technology ,
Tarnaka , Hyderabad , 500607 , India
Published online: 16 Aug 2013.
To cite this article: G. Santhosh Kumar , C. Kurumurthy , B. Veeraswamy , P. Sambasiva
Rao , P. Shanthan Rao & B. Narsaiah (2013) An Efficient Multi-component Synthesis of 6-
Amino-3-methyl-4-Aryl-2,4- dihydropyrano[2,3-c]Pyrazole-5-carbonitriles, Organic Preparations
and Procedures International: The New Journal for Organic Synthesis, 45:5, 429-436, DOI:
10.1080/00304948.2013.816220
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Organic Preparations and Procedures International, 45:429–436, 2013
Copyright © Taylor & Francis Group, LLC
ISSN: 0030-4948 print / 1945-5453 online
DOI: 10.1080/00304948.2013.816220
OPPI BRIEF
An Efficient Multi-component Synthesis
of 6-Amino-3-methyl-4-Aryl-2,4-
dihydropyrano[2,3-c]Pyrazole-5-carbonitriles
G. Santhosh Kumar, C. Kurumurthy, B. Veeraswamy, P. Sambasiva
Rao, P. Shanthan Rao, and B. Narsaiah
Fluoroorganic Division, Indian Institute of Chemical Technology, Tarnaka,
Hyderabad-500607, India
Multi-component reactions are effective in building complex molecules in a single step in a
minimum amount of time and with facile isolation procedures; they have high economy1–7
and thus have become a powerful synthetic strategy in recent years.8–10 The multi-
component protocols are even more attractive when carried out in aqueous medium. Water
offers several benefits, including control over exothermicity, and the isolation of products
can be carried out by single phase separation technique. Pyranopyrazoles are a biologically
important class of heterocyclic compounds and in particular dihydropyrano[2,3-c]pyrazoles
play an essential role in promoting biological activity and represent an interesting template
in medicinal chemistry. Heterocyclic compounds bearing the 4-H pyran unit have re-
ceived much attention in recent years as they constitute important precursors for promising
drugs.11–13 Pyrano[2,3-c]pyrazoles exhibit analgesic,14 anti-cancer,15 anti-microbial and
anti-inflammatory16 activity. Furthermore dihydropyrano[2,3-c]pyrazoles show mollusci-
dal activity17,18 and are used in a screening kit for Chk 1 kinase inhibitor activity.19,20 They
also find applications as pharmaceutical ingredients and bio-degradable agrochemicals.21–29
Junek and Aigner30 first reported the synthesis of pyrano[2,3-c]pyrazole derivatives from
3-methyl-1-phenylpyrazolin-5-one and tetracyanoethylene in the presence of triethylamine.
Subsequently, a number of synthetic approaches such as the use of triethylamine,31
piperazine,32 piperidine,33 N-methylmorpholine in ethanol,34 microwave irradiation,35,36
solvent-free conditions,37–39 cyclodextrins (CDs),40 different bases in water,41 γ -alumina,42
and l-proline43 have been reported for the synthesis of 6-amino-4-alkyl/aryl-3-methyl-
2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles. Recently, tetraethylammonium bromide
(TEABr) has emerged as mild, water-tolerant, eco-friendly and inexpensive catalyst. To
the best of our knowledge, quaternary ammonium salts, more specifically TEABr, have not
Received March 8, 2013.
Address correspondence to B. Narsaiah, Fluoroorganic Division, Indian Institute of Chemical
Technology, Tarnaka, Hyderabad -500607, India. E-mail: narsaiahbanda84@gmail.com
429

430
Narsaiah et al.
been used as catalysts for the synthesis of pyrano[2,3-c]pyrazoles, and we decided to inves-
tigate the application of TEABr as a catalyst for the synthesis of a series of pyrazole-fused
pyran derivatives via multi-component reactions.
Initial reactions of ethyl acetoacetate (1, 2.0 mmol), 98% hydrazine hydrate (2,
2.5 mmol), benzaldehyde (3a, 2.0 mmol), and malononitrile (4, 2.0 mmol) (Scheme 1)
conducted in water without catalyst, led to no reaction.
Scheme 1
The same reaction was performed in water using TEABr. The product 2,4-
dihydropyrano[2,3-c]pyrazole (5a) was formed in 90% yield in water using TEABr as
catalyst presumably via initial formation of the pyrazolinone ring followed by condensation
with benzylidenemalononitrile (generated in situ from benzaldehyde and malononitrile).
The use of other catalysts such as 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), tetrabuty-
lammonium bromide (TBABr) and neat grinding of the components gave marginally low
Table 1
Preparation of 6-Amino-3-methyl-4-aryl-
2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles (5a–5p)
Cmpd
R
Time (min) Yield (%)
mp (◦C)
lit. mp (◦C)
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
5m
5n
5o
5p
C6H5
4-CH3C6H4
4-CH3OC6H4
4-BrC6H4
4-ClC6H5
3-FC6H4
4-CNC6H4
4-NO2C6H4
3-NO2C6H4
2,4-F2C6H3
3-CF3C6H4
2,5-(CH3)2C6H3
2-Furyl
15
10
20
10
10
10
15
25
30
15
20
25
30
30
30
15
90
88
82
88
90
89
91
80
76
85
84
88
78
75
70
68
244–245
208–209
211–213
178–180
234–236
181–184
196–198
192–194
250–252
178–179
188–190
202–204
175–177
189–190
180–182
162–164
244–24542
206–20742
210–21242
179–18042
234–23542
—
196–19839
193–19542
251–25342
176–17844
—
—
175–17740
190–19140
—
2-Thienyl
Styryl
n-Propyl
—

Aryl-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles
431
yields. The scope of present protocol was extended to variously substituted aldehydes and
2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile derivatives were obtained in high yields.
In summary, we have devised a simple, rapid, green method via a four-component reac-
tion for the synthesis of 6-amino-4-alkyl/aryl-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-
5-carbonitriles by using TEABr (10 mol%) as a catalyst and water as the solvent.
Experimental Section
IR spectra were recorded as KBr pellets on a Perkin-Elmer FT-IR 240-C spectrophotometer
using KBr optics. 1H NMR spectra were obtained on an Avance 300 MHz spectrometer in
CDCl3, DMSO-d6 and (D3C)2CO using TMS as an internal standard. Chemical ionization
mass spectra were acquired on VG-7070 H instrument at 70 ev. All reactions were monitored
by thin layer chromatography (TLC) on pre-coated silica gel 60 F254 (mesh) using n-hexane-
ethyl acetate. Spots were visualized with UV light. Merck silica gel (100–200 mesh) was
used for column chromatography.
Typical Procedure: A mixture of the aromatic aldehyde (2 mmol), malononitrile
(0.13 g, 2 mmol), ethyl acetoacetate (0.26 g, 2 mmol) 98% hydrazine hydrate (0.12 g,
2.5 mmol) and TEABr (10 mol%) was placed in 5 ml of water as a solvent in a round
bottom flask. The mixture was stirred and heated at reflux for 10–30 min. After completion
of the reaction, the content was allowed to cool to room temperature, and the precipitated
solid product was collected through filtration, washed with water followed by chloroform
(2 × 10 ml) and dried to afford products 5 as colorless solids. Compounds 5c, 5d, 5h, 5i,
5n were purified by column chromatography using n-hexane and ethyl acetate in 1:3 ratio
and other products were isolated in pure form without purification.
6-Amino-3-methyl-4-phenyl-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile (5a).
IR (cm−1): 3420 ( NH2), 3400 ( NH2), 2198 ( CN); 1H NMR (CD3)2CO, 300 MHz: δ
1.89 (s, 3H, CH3), 4.55 (s, 1H, CH = ), 6.25 (br, s, 2H, NH2), 7.17–7.44 (m, 5H, Ar-H);
MS (ESI): m/z [(M+H)+]: 253 [(M+Na)+]: 275.
Anal. Calcd for C14H12N4O: C, 66.65; H, 4.79; N, 22.21. Found: C, 66.32; H, 4.82;
N, 22.11.
6-Amino-4-(4-methoxyphenyl)-3-methyl-2,4-dihydro pyrano[2,3-c]pyrazole-5
carbonitrile (5b).
IR (cm−1): 3426 ( NH2), 3409 ( NH2), 2199 ( CN); 1H NMR (DMSO-d6, 300 MHz):
δ 1.85 (s, 3H, CH3), 3.79 (s, 3H, CH3), 4.50 (s, 1H, CH = ), 6.15 (br, s, 2H, NH2), 6.82
(d, J = 8.68 Hz, 2H, Ar-H), 7.09 (d, J = 8.68 Hz, 2H, Ar-H).
MS (ESI): m/z [(M+H)+]: 283 [(M+Na)+]: 305.
Anal. Calcd for C15H14N4O2: C, 63.82; H, 5.00; N, 19.85. Found: C, 63.62; H, 5.10;
N, 19.82.

432
Narsaiah et al.
6-Amino-4-(4-bromophenyl)-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile
(5c).
IR (cm−1): 3425 ( NH2), 3400 ( NH2), 2200 ( CN); 1H NMR ((CD3)2CO, 300 MHz):
δ 1.84 (s, 3H, CH3), 4.56 (s, 1H, CH= ), 6.02 (br, s, 2H, NH2), 7.11 (d, J = 7.96 Hz, 2H,
Ar-H), 7.43 (d, J = 7.96 Hz, 2H, Ar-H).
MS (ESI): m/z [(M+H)+]: 331.
Anal. Calcd for C15H14N4O2: C, 50.77; H, 3.35; N, 16.92. Found: C, 50.48; H, 3.48;
N, 16.79.
6-Amino-4-(4-chlorophenyl)-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile
(5d).
1
IR (cm−1): (cm−1): 3421 ( NH2), 3398 ( NH2), 2198 ( CN); H NMR ((CD3)2CO,
300 MHz): δ 1.83 (s, 3H, CH3), 4.55 (s, 1H, CH= ), 6.07 (br, s, 2H, NH2), 7.13 (d, J =
7.38 Hz, 2H, Ar-H), 7.83 (d, J = 7.38 Hz, 2H, Ar-H)
MS (ESI): m/z [(M+H)+]: 287.
Anal. Calcd for C14H11ClN4O: C, 58.65; H, 3.87; N, 19.54. Found: C, 58.48; H, 3.99;
N, 19.42.
6-Amino-3-methyl-4-(4-nitrophenyl)-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile
(5e).
IR (cm−1): 3424 ( NH2), 3405 ( NH2), 2199 ( CN); 1H NMR (DMSO-d6, 300 MHz): δ
1.84 (s, 3H, CH3), 4.54 (s, 1H, CH= ), 6.05 (br, s, 2H, NH2), 7.49 (d, J = 8.18 Hz, 2H,
Ar-H), 7.95 (d, J = 7.18 Hz, 2H, Ar-H).
MS (ESI): m/z [(M+H)+]: 298.
Anal. Calcd for C14H11N5O3: C, 56.56; H, 3.73; N, 23.56. Found: C, 56.35; H, 3.63;
N, 23.62.
6-Amino-4-(3-fluorophenyl)-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile
(5f).
IR (cm−1): 3418 ( NH2), 3398 ( NH2), 2201 ( CN); 1H NMR (DMSO-d6, 300 MHz): δ
1.83 (s, 3H, CH3), 4.55(s, 1H, CH= ), 6.07 (br, s, 2H, NH2), 7.05–7.12 (m, 3H, Ar-H),
8.52 (s, 1H, Ar-H).
MS (ESI): m/z [(M+H)+]: 271.
Anal. Calcd for C14H11FN4O: C, 62.22; H, 4.10; N, 20.73. Found: C, 62.56; H, 4.25;
N, 20.61.
6-Amino-4-(4-cyanophenyl)-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile
(5g).
IR (cm−1): 3424 ( NH2), 3399 ( NH2), 2198 ( CN); 1H NMR (DMSO-d6, 300 MHz): δ
1.83 (s, 3H, CH3), 4.54(s, 1H, CH= ), 6.07 (br, s, 2H, NH2), 7.32 (d, J = 8.12 Hz, 2H,
Ar-H), 7.54 (d, J = 8.12 Hz, 2H, Ar-H).
MS (ESI): m/z [(M+H)+]: 278.
Anal. Calcd for C15H11N5O: C, 64.97; H, 4.00; N, 25.26. Found: C, 64.65; H, 3.86; N,
25.13.

Aryl-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles
433
6-Amino-3-methyl-4-(p-tolyl)-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile (5h).
IR (cm−1): 3422 ( NH2), 3398 ( NH2), 2199 ( CN); 1H NMR (DMSO-d6, 300 MHz): δ
1.84 (s, 3H, CH3), 2.32 (s, 3H, CH3), 4.53 (s, 1H, CH= ), 5.66 (br, s, 2H, NH2), 6.85 (d,
J = 8.68 Hz, 2H, Ar-H), 7.10 (d, J = 8.68 Hz, 2H, Ar-H).
MS (ESI): m/z [(M+H)+]: 267 [(M+Na)+]: 299.
Anal. Calcd for C15H14N4O2: C, 67.65; H, 5.30; N, 21.04. Found: C, 67.79; H, 5.21;
N, 21.25.
6-Amino-3-methyl-4-(3-nitrophenyl)-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile
(5i).
IR (cm−1): 3419 ( NH2), 3399 ( NH2), 2200 ( CN); 1H NMR (DMSO-d6, 300 MHz): δ
1.84 (s, 3H, CH3), 4.56(s, 1H, CH= ), 6.07 (br, s, 2H, NH2), 7.05–7.12 (m, 3H, Ar-H),
8.52 (s, 1H, Ar-H).
MS (ESI): m/z [(M+H) +]: 298.
Anal. Calcd for C14H11N5O3: C, 56.56; H, 3.73; N, 23.56. Found: C, 56.38; H, 3.65;
N, 23.78.
6-Amino-4-(2,4-difluorophenyl)-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-5-
carbonitrile (5j).
IR (cm−1): 3422 ( NH2), 3401 ( NH2), 2198 ( CN); 1H NMR (DMSO-d6, 300 MHz): δ
1.89 (s, 3H, CH3), 4.94 (s, 1H, CH= ), 5.78 (br, s, 2H, NH2), 6.77–6.89 (m, 2H, Ar-H),
7.10–7.18 (m, 1H, Ar-H).
MS (ESI): m/z [(M+H)+]: 271.
Anal. Calcd for C14H10F2N4O: C, 58.33; H, 3.50; N, 19.44. Found: C, 58.10; H, 3.42;
N, 19.68.
6-Amino-3-methyl-4-(3-(trifluoromethyl)phenyl)-2,4-dihydropyrano[2,3-c]pyrazole-5-
carbonitrile (5k).
IR (cm−1): 3420 ( NH2), 3402 ( NH2), 2199 ( CN); 1H NMR (DMSO-d6, 300 MHz): δ
1.87 (s, 3H, CH3), 4.58(s, 1H, CH= ), 6.07 (br, s, 2H, NH2), 7.05–7.12 (m, 3H, Ar-H),
8.52 (s, 1H, Ar-H).
MS (ESI): m/z [(M+H) +]: 321.
Anal. Calcd for C15H11F3N4O: C, 56.25; H, 3.46; N, 17.49. Found: C, 56.01; H, 3.39;
N, 17.40.
6-Amino-4-(2,5-dimethylphenyl)-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-5-
carbonitrile (5l).
IR (cm−1): 3421 ( NH2), 3400 ( NH2), 2200 ( CN); 1H NMR (DMSO-d6, 300 MHz): δ
1.76 (s, 3H, CH3), 2.23 (s, 3H, CH3), 2.30 (s, 3H, CH3), 4.81 (s, 1H, CH= ), 5.93 (br, s,
2H, NH2), 6.82 (s, 1H, Ar-H), 6.90 (d, J = 7.55 Hz, 1H, Ar-H), 6.98 (d, J = 7.84 Hz, 1H,
Ar-H). MS (ESI): m/z [(M+H) +]: 281.

434
Narsaiah et al.
Anal. Calcd for C16H16N4O: C, 68.55; H, 5.75; N, 19.99. Found: C, 68.25; H, 5.62; N,
20.10.
6-Amino-4-(2-furyl)-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile (5m).
IR (cm−1): 3422 ( NH2), 3405 ( NH2), 2199 ( CN); 1H NMR ((CD3)2CO, 300 MHz): δ
1.87 (s, 3H, CH3), 4.57 (s, 1H, CH= ), 6.65 (br, s, 2H, NH2), 6.11–6.27 (m, 1H, Ar-H),
7.20 (d, 2H, Ar-H).
MS (ESI): m/z [(M+H)+]: 243.
Anal. Calcd for C14H12N4O: C, 59.50; H, 4.16; N, 23.13. Found: C, 59.21; H, 4.08; N,
23.02.
6-Amino-3-methyl-4-(2-thienyl)-2,4-dihydropyrano [2,3-c]pyrazole-5-carbonitrile (5n).
IR (cm−1): 3422 ( NH2), 3405 ( NH2), 2199 ( CN); 1H NMR ((CD3)2CO, 300 MHz): δ
1.87 (s, 3H, CH3), 4.57 (s, 1H, CH= ), 6.65 (br, s, 2H, NH2), 6.11–6.27 (m, 1H, Ar-H),
7.20 (d, 2H, Ar-H).
MS (ESI): m/z [(M+H)+]: 259.
Anal. Calcd for C12H10N4OS: C, 55.80; H, 3.90; N, 21.69. Found: C, 55.53; H, 3.82;
N, 21.81.
6-Amino-2,4-dihydro-3-methyl-4-styryl-2,4-dihydropyrano[2,3-c]pyrazole-5-
carbonitrile (5o).
IR (cm−1): 3415 ( NH2), 3400 ( NH2), 2199 ( CN); 1H NMR (DMSO-d6, 300 MHz): δ
2.01 (s, 3H, CH3), 4.68 (s, 1H, CH= ), 6.58 (br, s, 2H, NH2), 6.27–7.20 (m, 7H, Ar-H).
MS (ESI): m/z [(M+H)+]: 279.
Anal. Calcd for C16H14N4O: C, 69.05; H, 5.07; N, 20.13. Found: C, 69.31; H, 5.12;
N, 20.14.
6-Amino-3-methyl-4-(n-propyl)-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile (5p).
IR (cm−1): 3420 ( NH2), 3390 ( NH2), 2200 ( CN); 1H NMR (DMSO-d6, 300 MHz): δ
0.99(t, 3H, CH3),1.31–1.36 (m, 4H, CH2 CH2-), 1.80 (s, 3H, CH3), 3.56 (s, 1H, CH=),
6.55 (br, s, 2H, NH2).
MS (ESI): m/z [(M+H)+]: 219.
Anal. Calcd for C11H14N4O: C, 60.53; H, 6.47; N, 25.67. Found: C, 60.31; H, 6.82;
N, 25.53.
Acknowledgments
The authors are thankful to the Director, IICT for his constant encouragement and authors
G. S. Kumar, C. K. Murthy, B. V. Swamy and P. S. Rao are grateful to CSIR for providing
financial assistance in the form of Senior Research Fellowship.

Aryl-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles
435
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