Catalyst free Michael addition of 3-methyl-2-pyrazolin-5-one to β-nitrostyrenes 'on water': A green protocol for facile synthesis of 4-(1-aryl-2-nitroethyl)-3-methyl-1H-pyrazol-5-ol

Article abstract of DOI:10.1016/j.tetlet.2013.08.042

A highly efficient and green protocol has been developed for the synthesis of 4-(1-aryl-2-nitroethyl)-3-methyl-1H-pyrazol-5-ol via Michael addition of 3-methyl-2-pyrazolin-5-one with β-nitrostyrenes under catalyst free conditions on aqueous medium. A series of 4-(1-aryl-2-nitroethyl)-3-methyl-1H- pyrazol-5-ols have been synthesized with good to excellent yield. C-alkylated product was observed exclusively with 3-methyl-2-pyrazolin-5-one without formation of N-alkylated product.

Full text of DOI:10.1016/j.tetlet.2013.08.042

Accepted Manuscript
Catalyst free Michael addition Of 3- methyl-2-pyrazolin-5-one to β-nitrostyr‐
enes “on water”: A green protocol for facile synthesis of 4-(1-aryl-2-nitroeth‐
yl)-3-methyl-1H-pyrazol-5-ol
H.M. Meshram, Nandigama Satish Kumar, Jagadeesh Babu Nanubolu, L.
Chandrasekhara Rao, N. Nageswara Rao
PII:
S0040-4039(13)01396-8
DOI:
http://dx.doi.org/10.1016/j.tetlet.2013.08.042
TETL 43405
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
13 June 2013
6 August 2013
8 August 2013
Please cite this article as: Meshram, H.M., Kumar, N.S., Nanubolu, J.B., Chandrasekhara Rao, L., Nageswara Rao,
N., Catalyst free Michael addition Of 3- methyl-2-pyrazolin-5-one to β-nitrostyrenes “on water”: A green protocol
for facile synthesis of 4-(1-aryl-2-nitroethyl)-3-methyl-1H-pyrazol-5-ol, Tetrahedron Letters (2013), doi: http://
dx.doi.org/10.1016/j.tetlet.2013.08.042
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Catalyst free Michael addition Of 3-methyl-2-
pyrazolin-5-one to β-nitrostyrenes “on water”
: A green protocol for facile synthesis of
4-(1-aryl-2-nitroethyl)-3-methyl-2-pyrazolin-5-ol
H. M. Meshrama,* Nandigama Satish Kumara, Jagadeesh Babu Nanubolub,
L. Chandrasekhara Raoa and N. Nageswara Raoa

Tetrahedron Letters
1
TETRAHEDRON
LETTERS
Pergamon
Catalyst free Michael addition Of 3- methyl-2-pyrazolin-5-one to β-nitrostyrenes
“on water”: A green protocol for facile synthesis of 4-(1-aryl-2-nitroethyl)-3-methyl-
1H-pyrazol-5-ol
H. M. Meshrama,* Nandigama Satish Kumara, Jagadeesh Babu Nanubolub,
L. Chandrasekhara Raoa and N. Nageswara Raoa
aMedicinal Chemistry and pharmacology division, bLaboratory of X-ray Crystallography,
CSIR - Indian Institute of Chemical Technology, Tarnaka, Hyderabad – 500607, India
Tel.: +91-40-27191640, Fax: +91-40-27193275, hmmeshram@yahoo.com
Abstract - A highly efficient and green protocol has been developed for the synthesis of 4-(1-aryl-2-nitroethyl)-3-methyl-1H-pyrazol-5-ol
via Michael addition of 3-Methyl-2-pyrazolin-5-one with β- nitrostyrenes under catalyst free conditions on aqueous medium. A series of 4-
(1-aryl-2-nitroethyl)-3-methyl-1H-pyrazol-5-ols have been synthesized with good to excellent yield. C-alkylated product was observed
exclusively with 3-methyl-2-pyrazolin-5-one without formation of N- alkylated product.
Keywords: β-nitrostyrene, pyrazole, 3-Methyl-2-Pyrazolin-5-one, Michael addition, Water.
The pyrazoles are well-known class of heterocyclic
compounds commonly found in numerous pharmaceutically
active compounds1 and showing wide range of biological
catalyst to aryl substituted unsaturated ketones, nitriles,and
esters in organic solvent and using catalysts.12 To the best of
our knowledge there is no report on the Michael addition of
properties
such
as
antileukemic,2
antitumor,3
and
3-methyl-2-pyrazolin-5-one
with
β-nitrostyrenes.
In
antiproliferative,4 GABA receptor antagonists
continuation of our work, in developing environmentally
benign reactions, the atom-economic catalytic processes, and
catalyst free reactions,13 we wish to report catalyst free
Michael addition of 3-methyl-2-pyrazolin-5-one to β-
nitrostyrenes using water as a solvent.
insecticides,5 anti-inflammatory and antimicrobial.6 In
particular, O-pyrozole glucopyranoside such as remoglifozin
etabonate is inhibitor of human sodium-glucose
cotransporters and antidiabetic agents.7a Recently, 4-benzyl-
5-methyl-1H-pyrazol-3-ols have been identified as potent and
selective inhibitors of rat L-2-hydroxy acid oxidase (Fig. 1).7b,
7c, 7d
In recent years an intense research effort has been
focused on developing clean and green protocols for the
synthesis of various heterocyclic compounds to avoid
hazardous organic solvents. Remarkably the replacement of
hazardous organic solvents with water is particularly
relevant.8 Organic reactions that occur „on water‟ have high
efficiency and important rate enhancements.9 Keeping the
biological importance of pyrazole derivatives in mind, we are
interested to develop a simple, efficient and green protocol for
the synthesis of 4-benzyl-5-methyl-1H-pyrazol-3-ols using
the Michael addition of 3-methyl-2-pyrazolin-5-one with β-
nitrostyrenes. Since the Michael addition is one of the most
important and useful reaction for carbon-carbon bond
formation in organic synthesis10 because the Michael adducts
can be readily transformed into different functionalities.11
Figure 1: Biologically important pyrazole derivatives
Initially, we have attempted the reaction of 3-methyl-2-
pyrazolin-5-one 1a with β-nitro styrene 2e without any
catalyst in water at room temperature, Michael addition
product 3e was obtained in 30% yield in 24 h. To optimize
the best reaction conditions, the experiments were carried out
at different temperatures and we found that reaction at 80 C
gives the desired C-alkylated product in 92% yield. N-
alkylation product was not observed during the course of the
o
Several results have been reported, on the Michael addition of
carbanion generated from 3-methyl-2-pyrazolin-5-one using

2
Tetrahedron Letters
reaction and it was confirmed by the analysis of crude
reaction mixture. The structure of the product was confirmed
by 1H NMR, 13C NMR, MS, IR spectral data and
unambiguously confirmed by single x-ray structure of
compound 3h (Fig. 2).
Further, we have screened various organic solvents like
acetonitrile, ethanol, and DMF. Polar solvents gave
satisfactory yield compare to non-polar solvent since the polar
solvents may enhance the enolization of pyrazole. Though the
reaction gave competitive yield in organic or aqueous
medium, we believe that water is the best solvent of choice
over organic solvents in terms of reaction time, yield and
environmental point of view.
Scheme 2. Michael addition of 3-methyl-2-pyrazolin-5-one to
the β-nitrostyrenes.
Table 2: Catalyst free Michael addition of 3-methyl-2-
pyrazolin-5-one (1a) with various β-nitrostyrenesa
Scheme 1. Michael addition of 3-methyl-2-pyrazolin-5-one to
the 1-chloro-4-(2-nitrovinyl)benzene.
Table 1: Solvent screening and optimization of the reaction
conditions for the Michael addition of 3-methyl-2-pyrazolin-
5-one (1a) to the 1-chloro-4-(2-nitrovinyl)benzene (2e)a
Having optimized reaction condition in hand, we were
interested to study the electronic effect of substitutions on
aromatic ring of β-nitrostyrenes. As we envisaged, β-
nitrostyrene bearing electron withdrawing groups such as
bromo, chloro and fluoro gave expected products in good
yield where as β-nitrostyrene bearing electron donating
groups such as methoxy, methyl required longer reaction time
to give corresponding Michael adducts with comparable
yield. In case of heterocyclic β-nitrostyrenes such as furan,
thiophene also gave corresponding Michael adducts in good
yield with extended reaction time (Table 2).

Tetrahedron Letters
Then we were curious to develop this green protocol in a
3
gram scale. So we have conducted the reaction of 3-methyl-2-
pyrazolin-5-one 1a (50 mmol) with 4-chloro-β-nitro styrene
2a (60 mmol) in 50 ml water with optimized condition. After
complete consumption of pyrazole 1a, the solid material was
filtered and washed with hot petroleum ether. The final
purification was accomplished by silica gel column
chromatography or by recrystallization in ethanol.
Further we extend this protocol to 3-methyl-1-phenyl-1H-
pyrazolin-5(4H)-one 1b, and the desired product was isolated
in good yield (Table 3).12f, 12g, 12h
Figure 2: X-ray crystal structure of 3h (ORTEP diagram).16
Scheme 3. 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one to the
β-nitrostyrenes
Mechanistically, enolization of pyrazole takes place on water
surface and then enol undergoes conjugated addition with the
β-nitrostyrene followed by the tautomerization to give the
desired product (Scheme4).14
Scheme 4. Plausible mechanism for the formation of 3.
In conclusion, we have developed an eco-efficient, effective
green and clean procedure for the expedient synthesis of a
series of pyrazole derivatives via Michael addition of 3-
methyl-2-pyrazolin-5-one with β-nitostyrenes “on water”. The
present protocol avoids the use of any basic, acidic or highly
toxic reagents and high boiling organic solvents like DMF or
DMSO. This approach shows the application of aqueous
medium for water insoluble organic compounds. Moreover
the aqueous medium and catalyst free condition supports the
environmental friendly nature of protocol and may be
transforming into economically viable procedure.
Table 3: Catalyst free Michael addition of 3-methyl-1-
phenyl-1H-pyrazolin-5(4H)-one with various β-nitrostyrenesa
Acknowledgement:
N. S. K, L. C. R and N. N. R thank the CSIR-UGC India for
award of a fellowship and Dr. A. Kamal, Outstanding
scientist and Head of MCP Division, for his support and
encouragement.
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126.8, 98.8, 77.8, 39.1, 9.8. ESI-MS: m/z: 248(M+H)+,
HRMS calcd for CHON: 248.10297, found:248.10239.
5-methyl-4-(2-nitro-1-p-tolylethyl)-1H-pyrazol-3-ol
(3b):
white solid; mp: 173-175. IR (KBr): √max 3395, 2924, 2574,
1606, 1547, 1519, 1375, 1219, 1150, 810, 650, 516, 429 cm-1
1
; H NMR (500 MHz, CDCl3+DMSO-d6) δ 2.02(s, 3H),
2.19(s, 3H), 4.43(t, J= 7.9 Hz, 1H), 4.87(dd, J= 7.9, 12.8 Hz,
1H), 5.01(dd, J= 7.9, 11.8 Hz, 1H), 6.98(d, J= 7.9 Hz, 2H),
7.16(d, J= 7.9 Hz, 2H), 7.56(s, 1H). 13C NMR (75 MHz,
CDCl3+DMSO-d6) δ 159.9, 143.7, 138.2, 127.1, 124.6,
99.2, 78.2, 34.2, 10.1. ESI-MS: m/z: 262(M+H)+, HRMS
calcd for CHON:262.11862, found: 262.11824.
4-(1-(4-methoxyphenyl)-2-nitroethyl)-5-methyl-1H-pyrazol-
3-ol (3c): Yellow solid; mp: 143-145. IR(KBr): √max 3430,
2919, 2847, 2632, 1609, 1546, 1514, 1248, 1022, 820, 552,
1
482 cm-1; H NMR (300 MHz, DMSO-d6) δ 2.09(s, 3H),
3.76(s, 3H), 4.53(t, J= 8.1 Hz, 1H), 4.97(dd, J= 12.6, 7.7 Hz,
1H), 5.11(dd, J= 12.6, 8.6 Hz, 1H), 6.82(d, J= 8.6 Hz, 2H),
7.33(d, J= 8.6 Hz, 2H), 7.50(s, 1H). 13C NMR (75 MHz,
CDCl3+DMSO-d6) δ 160.1, 158.2, 138.1, 132.0, 128.4,
113.7, 99.1, 78.0, 54.8, 38.4, 9.8. ESI-MS: m/z: 278(M+H)+,
HRMS calcd for CHON: 278.11353, found:278.11311.
4-(1-(4-fluorophenyl)-2-nitroethyl)-5-methyl-1H-pyrazol-3-
ol (3d): white solid; mp: 163-165. IR(KBr): √max 3424,
3390, 2924, 2571, 1605, 1537, 1512, 1224, 1155, 836, 535,
456 cm-1; 1H NMR (300 MHz, DMSO-d6) δ 2.10(s, 3H),
4.57(t, J= 8.1 Hz, 1H), 5.03(dd, J= 12.8, 7.9 Hz, 1H),
5.11(dd, J= 12.4, 8.4 Hz, 1H), 6.97(d, J= 8.4 Hz, 2H),
7.39(d, J= 5.2 Hz, 2H), 7.54(s, 1H). 13C NMR (75 MHz,
CDCl3+DMSO-d6) δ 159.0, 137.2, 135.2, 128.3, 128.2,
114.3, 114.0, 97.8, 76.5, 37.5, 8.9. ESI-MS: m/z:
266(M+H)+, HRMS calcd for CHONF:266.09355,
found:266.09322.
4-(1-(4-chlorophenyl)-2-nitroethyl)-5-methyl-1H-pyrazol-3-
ol (3e): white solid; mp: 148-150. IR(KBr): √max 3417, 2925,
2638, 1606, 1553, 1490, 1379, 1148, 1085, 1013, 815, 730,
646, 511, 453 cm-1; 1H NMR (500 MHz, DMSO-d6) δ
2.07(s, 3H), 4.54(t, J= 7.7 Hz, 1H), 5.01(dd, J= 13.3, 7.7 Hz,
1H), 5.09(dd, J= 13.3, 8.8 Hz, 1H), 7.22(d, J= 8.8 Hz, 2H),
7.34(d, J= 8.8 Hz, 2H). 13C NMR (75 MHz, CDCl3+DMSO-
d6) δ 159.7, 138.1, 137.9, 131.9, 128.4, 127.9, 98.0, 76.5,
38.0, 9.3. ESI-MS: m/z: 282(M+H)+, HRMS calcd for
CHONCl:282.06400, found:282.06370.
14. Xiao, z.; Lie, M.; Hu, L. Tetrahedron Lett. 2011, 52,
7099.
15. Typical experimental procedure: A mixture of 3-
methyl-1H-pyrazol-5(4H)-one (1) (1 mmol) and β-
nitrostyrene (2) (1.2 mmol) was suspended in 2mL of
water, and the reaction mixture was heated at 80 0C. The
progress of reaction was monitored by TLC. After
completion of the reaction, solid product obtained was
filtered, washed with water (2 × 10mL) and n-hexane (3
× 10 mL). Then the solid was dried under vacuum to
obtain the product (3). Further purification achieved by
column chromatography using EA/hexane as eluent.
16. CCDC number of the 3h is 925997. These data can be
obtained
free
of
charge
at
4-(1-(4-bromophenyl)-2-nitroethyl)-5-methyl-1H-pyrazol-3-
ol (3f): white solid; mp: 171-173. IR(KBr): √max 3417,
2925, 2637, 1606, 1552, 1487, 1378, 1148, 1073, 1008, 812,
www.ccdc.cam.ac.uk/conts/retrieving.html [or from the
Cambridge Crystallographic Data Centre (CCDC), 12
Union Road, Cambridge CB2 1EZ, UK; fax: +44(0)
1223 336 033; email: deposit@ccdc.cam.ac.uk].
1
726, 642, 512, 405 cm-1; H NMR (500 MHz, DMSO-d6) δ
1.99(s, 3H), 4.41(t, J= 8.8 Hz, 1H), 4.87(dd, J= 12.8, 7.91
Hz, 1H), 4.99(dd, J= 12.8, 7.9 Hz, 1H), 7.17(d, J= 7.9 Hz,
2H), 7.29(d, J= 7.9 Hz, 2H), 7.34(s, 1H). 13C NMR (75
MHz, CDCl3+DMSO-d6) δ 159.4, 138.9, 137.6, 130.8,
128.9, 120.0, 97.9, 76.9, 38.1, 9.3. ESI-MS: m/z:
326(M+H)+, HRMS calcd for CHONBr: 326.01348,
found:326.01351.
4-(1-(2-chlorophenyl)-2-nitroethyl)-5-methyl-1H-pyrazol-3-
ol (3g): brown solid; mp: 181-183. IR(KBr): √max 3384,
2926, 2573, 1608, 1548, 1435, 1379, 1222, 1148, 1035, 972,
859, 753, 604, 535, 453 cm-1; 1H NMR (300 MHz, DMSO-
Spectral data for new compound:
5-methyl-4-(2-nitro-1-phenylethyl)-1H-pyrazol-3-ol
(3a):
white solid; mp:167-169.IR(KBr): √max 3404, 2922, 2633,
1603, 1551, 1516, 1378, 1149, 705, 488 cm-1;1H NMR (300
MHz, DMSO-d6,) δ 2.10(s, 3H), 4.59(t, J= 8.1 Hz, 1H),
5.01(dd, J= 12.6, 7.5 Hz, 1H), 5.12(dd, J= 12.8, 8.6 Hz, 1H),
7.20-7.40(m, 5H), 7.53(s, 1H).13C NMR (125 MHz,
CDCl3+DMSO-d6) δ 160.3, 139.8, 138.2, 128.4, 127.3,

6
Tetrahedron Letters
d6) δ 2.14(s, 3H) , 4.90(dd, J= 11.8, 5.4 Hz, 1H), 5.09(m,
121.5, 109.0, 108.8, 101.8, 100.1, 78.9, 10.7. ESI-MS: m/z:
292(M+H)+.
2H), 7.16-7.25(m, 2H), 7.37(d, J= 9.0 Hz, 1H), 7.67(d, J=
9.0 Hz, 1H). 13C NMR (75 MHz, CDCl3+DMSO-d6) δ. ESI-
MS: m/z: 281(M+H)+, HRMS calcd for CHONCl:
282.06400, found: 282.06380.
4-(1-(4-methoxyphenyl)-2-nitroethyl)-3-methyl-1-phenyl-
1H-pyrazol-5-ol (4c): yellow solid; 1H NMR (CDCl3) δ
2.14(s, 3H), 3.76(s, 3H), 4.47(t, J= 7.4 Hz, 1H), 4.91(dd, J=
12.9, 6.7 Hz, 1H), 5.43(dd, J= 13.8, 7.9 Hz, 1H), 6.82(d, J=
8.8 Hz, 2H), 7.31(m, 5H), 7.53(d, J= 7.6 Hz, 2H). 13C NMR
(CDCl3) δ 158.8, 146.9, 135.6, 128.8, 128.7, 126.0, 120.7,
114.1, 76.9, 55.2, 38.9, 10.6. ESI-MS: m/z: 354(M+H)+,
HRMS calcd for CHON: 354.14474, found: 354.14483.
4-(1-(4-chlorophenyl)-2-nitroethyl)-3-methyl-1-phenyl-1H-
4-(1-(2-bromophenyl)-2-nitroethyl)-5-methyl-1H-pyrazol-3-
ol (3h): brown solid; mp: 201-203. IR(KBr): √max 3388,
3063, 2925, 2568, 1607, 1546, 1468, 1431, 1377, 1146,
1023, 969, 858, 752, 664, 568, 445, 423 cm-1; 1H NMR (500
MHz, DMSO-d6) δ 2.06(s, 3H), 4.72(dd, J= 12.2, 5.5 Hz,
1H), 5.02(dd, J= 10.0, 5.5 Hz, 1H), 5.12(t, J= 12.2 Hz, 1H),
7.01(t, J= 7.8 Hz, 1H), 7.17(t, J= 7.8 Hz, 1H), 7.37(s, 1H),
7.46(d, J= 7.8 Hz, 1H), 7.58(d, J= 7.8 Hz, 1H). 13C NMR (75
MHz, CDCl3+DMSO-d6) δ 159.7, 138.0, 136.6, 132.1,
129.0, 128.8, 127.7, 126.5, 97.1, 75.8, 34.8, 9.5. ESI-MS:
m/z: 326(M+H)+, HRMS calcd for CHONBr: 326.01348,
found: 326.01329.
1
pyrazol-5-ol (4e): white solid; H NMR (CDCl3) δ 2.15(s,
3H), 4.49(t, J= 6.4 Hz, 1H), 4.93(dd, J= 12.9, 7.0, Hz, 1H),
5.38(dd, J= 21.9, 9.9 Hz, 1H), 7.13-7.37(m, 5H), 7.41(d, J=
7.3 Hz, 2H), 7.52(d, J= 7.6 Hz, 2H). 13C NMR (CDCl3) δ
146.5, 137.6, 135.2, 133.2, 128.8, 128.7, 126.2, 120.9, 76.4,
38.9, 10.44. ESI-MS: m/z: 358(M+H)+, HRMS calcd for
CHON: 358.09515, found: 358.09530.
4-(1-(furan-2-yl)-2-nitroethyl)-5-methyl-1H-pyrazol-3-ol
(3i): brown solid; mp: 175-177. IR(KBr): √max 3428, 3128,
2925, 2646, 2570, 1738, 1611, 1549, 1526, 1425, 1381,
1
1143, 1074, 966, 830, 740, 659, 536, 479, 407 cm-1; H
NMR (400 MHz, DMSO-d6) δ 2.09(s, 3H), 4.68(t, J= 7.8
Hz, 1H), 4.92-5.03(m, 2H), 6.10(d, J= 2.6 Hz, 1H), 6.27(d,
J= 15.6 Hz, 1H), 7.35(s, H). 13C NMR (75 MHz,
CDCl3+DMSO-d6) δ 159.0, 151.5, 140.7, 137.4, 109.4,
105.5, 95.5, 75.1, 31.8, 9.0. ESI-MS: m/z: 238(M+H)+,
HRMS calcd for CHON: 238.08223, found: 238.08236.
5-mehtyl-4-(2-nitro-1-(thiophen-2-yl)ethyl)-1H-pyrazol-3-ol
(3j):brown solid; mp: 179-181. IR(KBr): √max 3413, 3120,
2922, 2571, 1733, 1608, 1563, 1519, 1429, 1377, 1150,
1
1040, 850, 712, 648, 593, 501 cm-1; H NMR (300 MHz,
DMSO-d6) δ 2.14(s, 3H), 4.86(t, J= 8.1 Hz, 1H), 5.00-
5.14(m, 2H), 6.90(t, J= 3.5 Hz, 1H), 6.96(d, J= 3.3 Hz, 1H),
7.16(d, J= 5.0 Hz, 1H), 7.70(s, 1H). 13C NMR (75 MHz,
CDCl3+DMSO-d6) δ 159.9, 143.7, 138.2, 127.1, 124.7,
124.6, 99.2, 78.2, 34.2, 10.1. ESI-MS: m/z: 254(M+H)+,
HRMS calcd for CHONS: 254.05939, found: 254.05921.
4-(1-(4-hydroxy-3-methoxyphenyl)-2-nitroethyl)-5-methyl-
1H-pyrazol-3-ol (3k): brown solid; mp: 71-73. IR(KBr): √max
3176, 2933, 1608, 1542, 1515, 1457, 1377, 1337, 1271,
1
1209, 1150, 1003, 874, 822, 745, 686, 652, 560 cm-1 ; H
NMR (300 MHz, DMSO-d6) δ 2.09(s, 3H), 3.79(s, 3H),
4.45(t, J= 7.9 Hz, 1H), 4.94(dd, J= 12.4, 7.7 Hz, 1H),
5.09(dd, J= 13.5, 9.0 Hz, 1H), 6.70-6.79(m, 2H), 6.98(s,
1H), 7.87(s, 1H). 13C NMR (75 MHz, CDCl3+DMSO-d6) δ
146.7, 144.6, 130.7, 119.3, 114.4, 110.5, 77.7, 55.1, 9.4.
ESI-MS: m/z: 294(M+H)+, HRMS calcd for CHON
:294.10845, found: 294.10843.
4-(1-(benzo[d][1,3]dioxol-5-yl)-2-nitroethyl)-5-methyl-1H-
pyrazol-3-ol (3l): brown solid; mp: 185-187. IR(KBr): √max
3407, 2920, 2640, 1724, 1605, 1554, 1501, 1443, 1383,
1
1241, 1037, 931, 823, 764, 651, 553, 512, 431, 405 cm-1; H
NMR (300 MHz, DMSO-d6) δ 2.10(s, 3H), 4.47(t, J= 8.1
Hz, 1H), 4.98(dd, J= 12.6, 7.9 Hz, 1H), 5.08(dd, J= 12.6, 8.4
Hz, 1H), 5.92(d, J= 2.0 Hz, 2H), 6.71(d, J= 7.9 Hz, 1H),
6.80(d, J= 7.9 Hz, 1H), 6.97(s, 1H). 13C NMR (75 MHz,
CDCl3+DMSO-d6) δ 160.0, 148.2, 146.9, 138.1, 135.5,

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Catalyst free Michael addition Of 3-methyl-2-
pyrazolin-5-one to β-nitrostyrenes “on water”:
A green protocol for facile synthesis of
4-(1-aryl-2-nitroethyl)-3-methyl-1H-pyrazol-5-ol
H. M. Meshrama,* Nandigama Satish Kumara, Jagadeesh Babu Nanubolub,
L. Chandrasekhara Raoa, N. Nageswara Raoa
R
O2N
R
N
+
Water
80 oC
O
N
H
NO2
HN
OH
N
R= 4-Me, 4-OMe, 4-F, 4-Cl, 4-Br,
2-Cl, 2-Br, 2-Furyl, 2-Thienyl