An efficient synthesis of 1-H-pyrazole-4-carboxylic acid esters with Vilsmeier reagent under neat conditions

Article abstract of DOI:10.1002/jhet.5570410316

A convenient, solvent-free Vilsmeier reagent is experimented under neat condition (both thermal and microwave conditions). An efficient method for the synthesis of various substituted 1H-pyrazole-4-carboxylic acid esters is reported.

Full text of DOI:10.1002/jhet.5570410316

May-Jun 2004
405
An Efficient Synthesis of 1-H-Pyrazole-4-Carboxylic Acid Esters With
Vilsmeier Reagent Under Neat Conditions
R. Sridhar, G. Sivaprasad and P. T. Perumal*
Organic Chemistry Division, Central Leather Research Institute,
Adyar, Chennai-600 020, INDIA
Received July 22, 2003
A convenient, solvent-free Vilsmeier reagent is experimented under neat condition (both thermal and
microwave conditions). An efficient method for the synthesis of various substituted 1H-pyrazole-4-car-
boxylic acid esters is reported.
J. Heterocyclic Chem., 41, 405 (2004).
Scheme 1
Introduction.
Aldehyde synthesis employing a formylating agent
derived from a formamide, most commonly DMF and
POCl3 has come to be known as 'the Vilsmeier aldehyde
synthesis' or 'the Vilsmeier-Haack formylation' [1,2]. It is a
versatile method both in the introduction of a formyl group
[3] and in the synthesis of various cyclised products [4] by
the addition of chloromethyleneiminium salt. Solvents
used [5] in Vilsmeier reaction include CHCl3, CH2Cl2,
benzene, toluene, o-dichlorobenzene, dioxane and THF. In
case of liquid amides like DMF, dimethyl acetamide, N-
methyl pyrrolidone, an excess of the amide is employed to
act as solvent. Excess POCl3 is also employed as solvent in
cases where the amide taken is in quantitative amounts.
Recently solvent-free solid supported Vilsmeier reaction
using microwaves has been reported [6,7]. However, it is
observed that the Vilsmeier reaction under neat condition
has not been attempted so far.
Scheme 2
In continuation of our work on the synthesis of pyra-
zoles [7] through the application of Vilsmeier reagent on
solid support we herein report a novel solvent-free applica-
tion of Vilsmeier reagent under neat conditions. Though
solid supported Vilsmeier reactions are novel, the recycla-
bility and disposability of the solid support in these reac-
tions are questionable. Aforementioned novel neat reac-
tion method overcomes these difficulties in using the solid
support.
The acidity of the active methylene protons in the hydra-
zones or semicarbazones of β-keto esters eases the cycliza-
tion and thereby facilitating the formation of pyrazoles
after adding to the Vilsmeier reagent.
In order to study the effect of an electronegative chlorine
atom on the acidity of the active methylene proton and to
substitute the 5-position of the pyrazole moiety, the hydra-
zone of ethyl 2-chloroacetoacetate was subjected to similar
reaction conditions. 5-Substituted 1H-pyrazole was
obtained after cyclisation followed by the loss of one HCl
molecule (Scheme 3).
Results and Discussion.
Kira et al have reported the synthesis of 1H-pyrazoles
from hydrazones [8a], and semicarbazones [8b] of ace-
tophenone upon treatment with POCl3 and DMF. Herein
we report the reaction of hydrazones of β-keto esters with
six equivalents of the chloromethylenedimethylammo-
nium chloride under neat conditions to target pyrazoles in
excellent yield (Scheme 1). Also we have made a compar-
ison between the above-mentioned neat method and the
reaction of hydrazones of β-keto esters with DMF and
POCl3.
Various substituted 1H-pyrazole-4-carboxylic acid
esters have been prepared and characterized (Table 1).
Scheme 3
When semicarbazones of β-keto esters were reacted
with Vilsmeier reagent, 1H-pyrazole-4-carboxylates
unsubstituted at 1-position were obtained (Scheme 2).

406
R. Sridhar, G. Sivaprasad and P. T. Perumal
Vol. 41
Table 1
Synthesis of 1H-Pyrazole-4-carboxylic Acid Esters: Comparison Between Conventional Heating and Microwave-assisted
Methods Under Neat Condition
Entry
R
R
R
3
Mp
Conventional
Microwave-
1
2
(°C) [b]
heating method
assisted method
Time
Yield [a]
Time
(min)
Yield [a]
%
(hrs) % [c] % [d]
2a
2b
2c
2d
2e
2f
2g
2h
2i
CH
CH
CH
CH
CH
C H (NO )
2 2
C H (NO )
6 3 2 2
114
122
140
125
96
133
138
169
128
80
6
6
6
6
6
6
6
6
6
6
6
6
84
82
88
85
88
84
85
90
85
86
82
87
78
80
84
81
84
79
83
88
84
81
75
78
5
5
5
5
5
5
5
5
5
5
5
5
86
85
88
87
87
86
86
92
87
89
84
88
3
3
3
3
3
6
3
C H
2
5
CH C H
C H (NO )
2
6
5
6 3 2 2
C(CH )
C H (NO )
6 3 2 2
C H (NO )
6 3 2 2
3 3
C H
ClCH
2
5
2
CH
n-C H
C H (NO )
2 2
3
3
7
6
3
C H
C H
C H (NO )
6 3 2 2
2
5
5
5
5
6
5
C H
p-Cl C H
C H (NO )
2
6
4
6 3 2 2
C H
o-F C H
C H (NO )
6 3 2 2
2
6
4
2j
2k
4l
C H
CH
H
H
2
3
CH
n-C H
3 7
97
107
3
C H
CH
C H (NO )
2 2
2
5
3
6
3
1
13
[a] Isolated yields after column chromatography; [b] All the products were characterised by H and C NMR, Mass spectral
and elemental analysis data; [c] Yield obtained in the neat method; [d] Yield obtained in the method with solvent (DMF).
Appliances Ltd.; Bangalore, India was used in the present stud-
ies. The overall dimensions of the domestic oven are 525(W) x
419 (D) x 281 (H) mm with a chamber of 350 (W) x 370 (D) x
208 (H) mm. The microwave frequency is 50 Hz and the oven
capacity is 26 liters. Analytical TLC was performed on pre-
coated plastic sheets of silica gel G/UV-254 of 0.2 mm thickness
(Macherey-Nagel, Germany) using 15 % ethyl acetate:petroleum
ether solvent system. IR spectra (KBr pellet) were obtained on a
Substrate to reagent ratio needs to be 1:6 for obtaining
maximum yield. For attaining homogeneity of the reaction
mixture, the reagent dissolved in CH2Cl2 was added to the
substrate at 0-5 °C. After 15 min vacuum was applied to
this mixture to remove the solvent. Then the reaction ves-
sel is maintained at 50 °C in an oil bath and again con-
nected to vacuum for 20 min to remove traces of DMF pre-
sent in reagent itself. After drying the reaction mixture the
content was maintained at 70-80 °C for about 6h.
The effect of microwave on the reaction yield was also
studied by the application of microwave on the reaction
mixture after drying the solvent (Table 1). There was no
appreciable increase in the yield using microwaves, but
there was a considerable reduction in the reaction time.
The neat method is not only convenient for the synthesis of
1H-pyrazole-4-carboxylates but also the yields obtained
through the neat are better in comparison with the usual
solution phase method (Table 1).
1
Perkin Elmer Spectrum RX I FT-IR. H NMR spectra were
obtained on a JEOL instrument at 500 MHz or on a Brucker
13
instrument at 300 MHz in CDCl and C NMR spectra were
3
recorded at 125 MHz or at 75 MHz in CDCl using TMS as inter-
3
nal standard. Mass spectra were recorded using JEOL DX-303 in
EI ionization mode at 70 eV. Commercially available
chloromethylenedimethylammonium chloride (Aldrich) was
used as such for the synthesis of title compound.
General Procedure for the Synthesis of 1H-Pyrazole-4-car-
boxylic Acid Esters Under Neat Condition.
To chloromethylenedimethylammonium chloride (6 mmol,
Aldrich) dissolved in 10 mL of dichloromethane, substrate (1
mmol) was added at 0 °C. The mixture was stirred for 15 min.
Conclusion.
Then CH Cl was removed by applying vacuum at room tem-
2
2
In summary a convenient, solvent-free Vilsmeier reagent
under neat condition is reported (both in thermal and
microwave conditions) to synthesis various substituted 1H-
pyrazole-4-carboxylates in comparatively better yields.
Proven antibacterial activity [9] of 1H-pyrazole-4-car-
boxylic acids and carboxylates prompted us to synthesize
the title compounds through this novel methodology.
perature. Afterwards the residue was heated to 50 °C and again
evaporated. This mixture was then kept in an oil bath at 70-80
°C for 6 h or irradiated in microwave for 5 min with a pulse
rate of 20 sec. and 40% of power. Then the content was added
to cold saturated NaOAc and stirred. Finally the product was
extracted with CHCl and separated through column chro-
3
matography with ethyl acetate: hexane 15:85. All the products
1
13
were characterized by H and C NMR, Mass spectral and
elemental analysis data.
EXPERIMENTAL
Methyl 1-(2,4-Dinitrophenyl)-3-methyl-1H-pyrazole-4-carboxy-
late (Entry 2a).
The microwave reactions were carried out in a domestic
microwave oven. A BPL microwave cooking system, Model
B M O - 7 0 0 T, manufactured by BPL-SANYO Utilities and
This compound was obtained as pale yellow crystals (15%
1
ethyl acetate:petroleum ether); mp. 114 °C; H NMR (300 MHz,

May-Jun 2004
An Efficient Synthesis of 1-H-Pyrazole-4-Carboxylic Acid Esters
407
Methyl 1(2,4-Dinitrophenyl)-3-propyl-1H-pyrazole-4-carboxy-
late (Entry 2f).
CDCl ): δ 8.73 (d, J = 2.4 Hz, 1H), 8.55 (dd, J = 2.4 Hz, J = 8.7
3
Hz, 1H), 8.21 (s, 1H), 7.85 (d, J = 8.7 Hz, 1H), 3.87 (s, 3H), 2.52
13
(s, 3H); C NMR (75 MHz, CDCl ): δ 162, 154, 146, 143, 137,
3
134, 128, 126, 121, 115, 52, 13; IR (KBr): cm 3090, 1725,
This compound was obtained as pale yellow crystals (15%
-1
1
ethyl acetate:petroleum ether); mp. 133 °C; H NMR (500 MHz,
CDCl ) δ: 8.70-8.70 (d, J=2.3 Hz, 1H), 8.51-8.53 (d, J=2.3, 8.6
+
1690, 1546, 1353, 1267; MS: (m/z) 306 (M ).
3
Hz, 1H), 8.23 (s, 1H, pyrazole -CH), 7.80-7.82 (d, J=8.6 Hz, 1H),
3.85 (s, 3H), 2.86-2.89 (d, J=7.5 Hz, 2H), 1.67-1.74 (sextet,
A n a l. Calcd. for C
H N O : C, 47.06; H, 3.27; N, 18.30.
12 10 4 6
Found: C, 47.45; H, 3.36; N, 18.51.
13
J=7.5 Hz, 2H), 0.95-0.98 (t, J=7.5 Hz, 3H); C NMR (125
Ethyl 1-(2,4-Dinitrophenyl)-3-methyl-1H-pyrazole-4-carboxy-
late (Entry 2b).
MHz, CDCl ppm): δ 163, 159, 146, 144, 137, 134, 128, 126,
-1
3,
121, 116, 52, 29, 22, 14; IR (KBr): cm 3326, 3106, 1716, 1699,
This compound was obtained as pale yellow crystals (15%
+
1620, 1535, 1340, 1280, 742; MS: (m/z) 334 (M ).
1
ethyl acetate:petroleum ether); mp. 122 °C; H NMR (300 MHz,
CDCl ): δ 8.70 (d, J = 2.4 Hz, 1H), 8.50 (dd, J = 2.4 Hz, J = 8.7
A n a l. Calcd. for C
H N O : C, 50.29; H, 4.22; N, 16.77.
14 14 4 6
Found: C, 50.35; H, 4.29; N, 16.68.
3
Hz, 1H), 8.20 (s, 1H), 7.83 (d, J = 8.7 Hz, 1H), 4.35 (q, J = 7.1
13
Hz, 2H), 2.49 (s, 3H), 1.37 (t, J = 7.1 Hz, 3H); C NMR (75
Ethyl 1-(2,4-Dinitrophenyl)-3-phenyl-1H -pyrazole-4-carboxy-
late (Entry 2g).
MHz, CDCl ): δ 163, 155, 147, 144, 137, 135, 128, 126, 122,
-1
3
117, 61, 15, 14; IR (KBr): cm 3074, 1722, 1693, 1550, 1349,
This compound was obtained as orange crystals (15% ethyl
+
1276; MS: (m/z) 320 (M ).
1
acetate:petroleum ether); mp. 138 °C; H NMR (200 MHz,
CDCl , ppm): δ 8.72-8.73 (d, J=2.2 Hz, 1H), 8.46-8.52 (dd,
A n a l. Calcd. for C
H N O : C, 48.75; H, 3.75; N, 17.50.
13 12 4 6
Found: C, 48.82; H, 3.81; N, 17.46.
3
J=2.2, 8.9 Hz, 1H), 8.37 (s, 1H, pyrazole -CH), 7.79 -7.84 (d,
Benzyl 1-(2,4-Dinitrophenyl)-3-methyl-1H-pyrazole-4-carboxy-
late (Entry 2c).
J=8.9 Hz, 1H), 7.72-7.77 (m, 2H), 7.40-7.44 (m, 3H), 4.26-4.37
13
(q, J=7.0, 7.2 Hz, 2H), 1.29-1.36 (t, J=7.0, 7.2 Hz, 3H);
NMR (50 MHz, CDCl ppm): δ 162, 156, 146, 144, 137, 135,
C
3,
131, 129, 128, 127, 126, 121, 116, 61, 14; IR (KBr): cm 3137,
3098, 2911, 1728, 1606, 1537, 1448, 1280, 832; MS: (m/z) 382
This compound was obtained as pale yellow crystals (15%
-1
1
ethyl acetate:petroleum ether); mp. 140 °C; H NMR (500 MHz,
CDCl ): δ 8.70-8.70 (d, J=2.9 Hz, 1H), 8.49-8.52 (d, J=2.9, 8.6
3
Hz, 1H), 8.25 (s, 1H, pyrazole -CH), 7.78-7.80 (d, J=8.6 Hz, 1H),
+
(M ).
A n a l. Calcd. for C
H N O : C, 56.53; H, 3.69; N, 14.66.
13
7.33-7.42 (m, 5H), 5.30 (s, 2H), 2.50 (s, 3H); C NMR (125
18 14 4 6
Found: C, 56.47; H, 3.66; N, 14.59.
MHz, CDCl ppm): δ 162, 155, 146, 143, 137, 136, 134, 129,
-1
3,
129, 128, 128, 126, 121, 116, 67, 14; IR (KBr): cm 3363, 3088,
2947, 2891, 1691, 1608, 1547, 1510, 1352, 1278, 1121, 745; MS:
Ethyl 1-(2,4-Dinitrophenyl)-3(4-chlorophenyl)-1H-pyrazole-4-
carboxylate (Entry 2h).
+
(m/z) 382 (M ).
A n a l. Calcd. for C
This compound was obtained as yellow crystals (15% ethyl
1
acetate:petroleum ether); mp. 169 °C; H NMR (500 MHz,
CDCl , ppm): δ 8.77-8.77 (d, J=2.3 Hz, 1H), 8.55-8.57 (d, J=2.3,
3
H N O : C, 56.55; H, 3.69; N, 14.65.
18 14 4 6
Found: C, 56.42; H, 3.76; N, 14.51.
t-Butyl 1(2,4-Dinitrophenyl)-3-methyl-1H-pyrazole-4-carboxy-
late (Entry 2d).
8.9 Hz, 1H), 8.39 (s, 1H,pyrazole -CH), 7.88 -7. 90 (d, J=8.9 Hz,
1H), 7.74 -7.76 (d, J=8.0 Hz, 2H, p-chlorophenyl), 7.39 -7.41 (d,
J=8.0 Hz, 2H, p-chlorophenyl), 4.30-4.34 (q, J=6.9, 7.4 Hz, 2H),
This compound was obtained as pale yellow crystals (15%
13
1.32-1.35 (t, J=6.9, 7.4 Hz, 3H); C NMR (125 MHz, CDCl
ppm): δ 162, 155, 146, 144, 137, 136, 135, 131, 129, 128, 128,
1
ethyl acetate:petroleum ether); mp. 125 °C; H NMR (500 MHz,
CDCl , ppm): δ 8.83-8.83 (d, J=2.3 Hz, 1H), 8.59-8.61 (dd, J=2. 3,
3,
3
9.2 Hz, 1H), 8.21 (s, 1H, pyrazole -CH), 8.15-8.17 (d, J=9.2 Hz,
-1
126, 121, 116, 61, 14; IR (KBr): cm 3136, 3091, 2926, 1691,
+
1603, 1536, 1349, 1285, 848, 774, 741; MS: (m/z) 417 (M ).
13
1H), 3.79 (s, 9H, t-Butyl), 2.36 (s, 3H); C NMR (125 MHz,
Anal. Calcd. for C
Found: C, 51.72; H, 3.10; N, 13.51.
H ClN O : C, 51.87; H, 3.14; N, 13.44.
18 13 4 6
CDCl ppm): δ 163, 153, 146, 143, 136, 135, 128, 127, 121, 115,
-1
3,
51, 30, 13; IR (KBr): cm 3100, 3091, 2984, 2900, 1715, 1608,
+
1548, 1349, 1264, 1106, 836, 780, 739; MS: (m / z) 348 (M ).
Ethyl 1-(2,4-Dinitrophenyl)-3(2-fluorophenyl)-1H-pyrazole-4-
carboxylate (Entry 2i).
A n a l. Calcd. for C
H N O : C, 51.73; H, 4.63; N, 16.09.
15 16 4 6
Found: C, 51.72; H, 4.70; N, 16.18.
This compound was obtained as yellow crystals (15% ethyl
1
acetate:petroleum ether); mp. 128 °C; H NMR (500 MHz,
CDCl , ppm): δ 8.74-8.74 (d, J=2.3 Hz, 1H), 8.51-8.54 (dd,
3
Ethyl 1(2,4-Dinitrophenyl)-3-chloromethyl-1H-pyrazole-4-car-
boxylate (Entry 2e).
J=2.3, 9.2 Hz, 1H), 8.40 (s, 1H,pyrazole -CH), 7.86-7.88 (d,
J=9.2 Hz, 1H), 7.45-7.48 (t, J=7.45 Hz, 1H, o-fluorophenyl),
7.39-7.43 (m, 1H, o-fluorophenyl), 7.18-7.22 (t, J=7.45 Hz, 1H,
This compound was obtained as pale yellow crystals (15% ethyl
1
acetate:petroleum ether); mp. 96 °C; H NMR (500 MHz, CDCl ,
3
ppm): δ 8.75-8.76 (d, J=2.3 Hz, 1H), 8.55-8.58 (dd, J=2.3, 8.6 Hz,
1H), 8.29 (s, 1H, pyrazole -CH), 7.87-7.89 (d, J=8.6 Hz, 1H), 4.83
(s, 2H, chloromethyl), 4.34-4.38 (q, J=6.9, 7.5 Hz, 2H), 1.37-1.39
o-fluorophenyl), 7.10-7.13 (m, 1H, o-fluorophenyl), 4.21-4.26
13
(q, J=6.85, 7.45 Hz, 2H), 1.20-1.22 (t, J=6.85, 7.45 Hz, 3H);
NMR (125 MHz, CDCl ppm): δ 162, 160, 151, 146, 144, 137,
C
13
(t, J=6.9, 7.5 Hz, 3H); C NMR (125 MHz, CDCl ppm): δ 162,
3,
153, 147, 144, 137, 135, 128, 127, 121, 116, 61, 37, 14; IR (KBr):
3,
134, 131, 131, 128, 126, 124, 121, 118, 116, 115, 61, 14; IR
-1
(KBr): cm 3143, 3090, 2992, 2775, 1721, 1608, 1548, 1350,
+
1294, 1132, 837, 767, 741; MS: (m/z) 400 (M ).
Anal. Calcd. for C H FN O : C, 54.01; H, 3.27; N, 14.00.
18 13 4 6
Found: C, 53.89; H, 3.29; N, 13.88.
-1
cm 3100, 3091, 2984, 2900, 1715, 1608, 1548, 1349, 1264, 1106,
+
836, 780, 739; MS: (m / z) 355 (M ).
Anal. Calcd. for C H ClN O : C, 44.02; H, 3.13; N, 15.80.
13 11
Found: C, 44.15; H, 3.18; N, 15.69.
4 6

408
R. Sridhar, G. Sivaprasad and P. T. Perumal
Vol. 41
Ethyl 3-Methyl-1H-pyrazole-4-carboxylate (Entry 2j).
Acknowledgement.
This compound was obtained as yellow solid (15% ethyl
Authors R. S. and G. S. are thankful to CSIR, New Delhi for
the award of Fellowship.
1
acetate:petroleum ether); mp. 80 °C; H NMR (500 MHz,
CDCl , ppm): δ 8.89 (bs, 1H, pyrazole -NH), 7.95 (s, 1H, pyra-
3
zole -CH), 4.25-4.35 (q, J=6.9, 7.4 Hz, 2H), 2.57 (s, 3H), 1.35-
REFERENCES AND NOTES
13
1.37 (t, J=6.9, 7.4 Hz, 3H); C NMR (125 MHz, CDCl ppm):
3,
+
δ 164, 146, 141, 111, 60, 14, 12; MS: (m/z) 154 (M ).
A n a l. Calcd. for C H N O : C, 54.54; H, 6.54; N, 18.17.
*
E-mail: ptperumal@hotmail.com; Fax No. 91-044-2491 1589.
7
Found: C, 54.47; H, 6.62; N, 18.05.
10 2 2
[1] For reviews on the Vi l s m e i e r-Haack reaction, [a]C. Jutz,
Advances in Organic Chemistry, Vol. 9, Iminium salts in Organic
Chemistry, part 1, Taylor, E. C. (ed.), John Wiley, New York, 225-342
(1976); [b]S. Seshadri, J. Sci. Ind. Res., 32, 128 (1973); [c]C. M. Marson,
Tetrahedron 48, 3659 (1992); [d]O. Meth-cohn and S. P. Stanforth,
Comprehensive Organic Chemistry, Pergamon Press, 777-794 (1991).
[2] A. Vilsmeier and A. Haack, Ber. Dtsch. Chem. Ges., 60, 119
(1927).
Methyl 3-Propyl-1H-pyrazole-4-carboxylate (Entry 2k).
This compound was obtained as yellow solid (15% ethyl
1
acetate:petroleum ether); mp. 97 °C; H NMR (500 MHz,
CDCl ): δ 9.8 (bs, 1H), 8.01 (s, 1H,pyrazole -CH), 3.6 (s, 3H),
3
2.87-2.88 (d, J= 7.5 Hz, 2H), 2.07-2.09 (m, 2H), 1.24-1.26 (t, J=
13
7.5 Hz, 3H); C NMR (125 MHz, CDCl ppm): δ 163, 148,
3,
[3a] C. Jutz and W. Muller, Chem. Ber., 100, 1536 (1967); [b]G.
Dauphin, Synthesis, 799 (1979).
+
135, 128, 62, 38, 30, 14; MS: (m/z) 168 (M ).
A n a l. Calcd. for C H N O : C, 57.13; H, 7.19; N, 16.66.
[4a] M. Mittelbach and H. Junek, J. Heterocyclic Chem., 19, 1021
(1982); [b]M. A. Kira and K. Z. Gadalla, Egypt. J. Chem., 21, 395 (1978).
[5a] O. Meth-cohn and B. Tarnowski, Adv. Heterocycl. Chem. 31,
207 (1982); [b]I. Cristea, Heterocyclic Commun. 2, 549 (1996); [c]O.
Meth-cohn, B. Narine and B. Tarnowski, J. Chem. Soc. Perkin Trans-I
1531 (1981).
[6] S. Paul, M. Gupta and R. Gupta, Synlett, 8, 1115 (2000).
[7a] R. Sridhar and P. T. Perumal, Synth Commun. , 33, 1483
(2003); [b]S. Selvi, S and P. T. Perumal, J. Heterocyclic Chem. 39, 1129
(2002).
[8a] M. A. Kira, M. O. Abdel-Raeman and K. Z. Gadalla,
Tetrahedron Lett., 109 (1969); [b]M. A. Kira, M. N. Aboul-Enein and M.
I. Korkor J. Heterocyclic Chem. 7, 25 (1970).
[9a] L. Cecchi, F. Melani, G. Palazzino, G. Filacchioni and G. C.
Porretta, Formaco, 3 9, 888 (1984) (Eng); [b]L. Cecchi, F. Melani, G.
Palazzino and G. Filacchioni, Formaco, 39, 953 (1984) (Eng).
8
Found: C, 57.25; H, 7.29; N, 16.78.
12 2 2
Ethyl 1-(2,4-Dinitrophenyl)-3-methyl-5(N,N-dimethyl)-1H-pyra-
zole-4-carboxylate (Entry 4l).
This compound was obtained as pale yellow crystals (15%
1
ethyl acetate:petroleum ether); mp. 107 °C; H NMR (500 MHz,
CDCl ): δ 8.78-8.78 (d, J = 2.9 Hz, 1H), 8.53-8.55 (dd, J = 2.9 Hz,
3
J = 8.6 Hz, 1H), 7.85-7.87 (d, J = 8.6 Hz, 1H), 4.31-4.35 (q, J =
6.9, 7.5 Hz, 2H), 2.59 (s, 6H), 2,45 (s, 3H), 1.37-1.40 (t, J = 6.9,
13
7.5 Hz, 3H); C NMR (125 MHz, CDCl ): δ 163, 155, 154, 146,
3
144, 136, 129, 128, 121, 107, 60, 41, 15, 15; IR (KBr): cm 3098,
2931, 1703, 1609, 1540, 1347, 1262, 1101, 834; MS: (m/z) 363
-1
+
(M ).
A n a l. Calcd. for C
H N O : C, 49.59; H, 4.72; N, 19.28.
15 17 5 6
Found: C, 49.72; H, 4.81; N, 19.26.