Synthesis and anti-microbial activity of some new fluorinated 1H-pyrazoles

Article abstract of DOI:10.1016/j.jfluchem.2010.01.005

Several new trifluoromethyl-1H-pyrazoles were prepared by reaction of hydrazine monohydrate with 1,3-diketones. Their structures were confirmed by elemental analysis, IR, ¹H NMR and EI-MS spectroscopy. The anti-microbial activities of the newly synthesized compounds were examined by disc diffusion method against Escherichia coli, Staphylococcus aureus, Pyricularia oryzae and Rhizoctnia solani. All the trifluoromethyl-1H-pyrazoles exhibited a certain degree of anti-bacterial and anti-fungal activities.

Full text of DOI:10.1016/j.jfluchem.2010.01.005

Journal of Fluorine Chemistry 131 (2010) 584–586
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Synthesis and anti-microbial activity of some new fluorinated 1H-pyrazoles
*
Dun-Jia Wang , Ling Fan, Chun-Yang Zheng, Zheng-Dong Fang
Department of Chemistry and Environmental Engineering, Hubei Normal University, Huangshi 435002, PR China
A R T I C L E I N F O
A B S T R A C T
Article history:
Several new trifluoromethyl-1H-pyrazoles were prepared by reaction of hydrazine monohydrate with
1,3-diketones. Their structures were confirmed by elemental analysis, IR, 1H NMR and EI-MS
spectroscopy. The anti-microbial activities of the newly synthesized compounds were examined by disc
diffusion method against Escherichia coli, Staphylococcus aureus, Pyricularia oryzae and Rhizoctnia solani.
All the trifluoromethyl-1H-pyrazoles exhibited a certain degree of anti-bacterial and anti-fungal
activities.
Received 24 October 2009
Received in revised form 10 January 2010
Accepted 13 January 2010
Available online 22 January 2010
Keywords:
ß 2010 Elsevier B.V. All rights reserved.
Trifluoromethyl-1H-pyrazole
Synthesis
1,3-Diketones
Anti-microbial activity
1. Introduction
monohydrate with the 1,3-diketone precursors in hot ethanol led
to formation of the expected trifluoromethyl-1H-pyrazoles. As
Strategically positioned fluorine substituents, especially the
trifluoromethyl group, in heterocyclic compounds play important
roles in medicine and agrochemicals [1–4]. In particular, the
fluorinated pyrazoles have been shown to possess high biological
activities [5–7] as herbicides, fungicides, insecticides, analgesics,
antipyretics and anti-inflammatory agents. Accordingly, much
recent attention has been paid to the synthesis of trifluoromethyl
substituted pyrazoles [8–12]. Among the reported routes, the
reaction of hydrazine monohydrate with 1,3-diketones is still the
most frequently used and efficient method for the synthesis of
important pyrazole heterocycles [13,14]. Recently, we studied the
solid state structures of some new substituted pyrazoles [15]. As a
continuation of our work, herein we report the preparation of
several new fluorinated 1H-pyrazoles and their anti-microbial
activities against Escherichia coli, Staphylococcus aureus, Pyricularia
oryzae, Rhizoctnia solani.
shown in Table 1, the starting materials 1,3-diketones were
converted completely and the substituted 1H-pyrazoles were
obtained as major products accompanying minor unidentified
compounds. After recrystallization from dilute ethanol solution,
pure 1H-pyrazoles were isolated in moderate to good yields (54–
72%). And all products were characterized by element analysis,
FTIR, 1H NMR, and mass spectroscopy.
2.2. Spectral characterizations
The IR spectra of the title compounds showed broad bands in
the region of 3350–3150 cmꢀ1, due to N–H stretching vibrations.
Strong absorption bands in the ranges of 1616–1578 cmꢀ1 and
1519–1482 cmꢀ1 were assigned to the C55N stretching vibrations
and N–H bending vibrations, respectively. Several medium bands
corresponding to C55C stretching vibrations of the aromatic ring
were always found in the region of 1600–1450 cmꢀ1
. The
absorption of C–F stretching vibrations appeared as a very strong
band around 1246–1286 cmꢀ1. The absorption of N–N stretching
vibrations also exhibited a strong band in the range of 1058–
1071 cmꢀ1 [18,19].
2. Results and discussion
2.1. Synthesis of trifluoromethyl-1H-pyrazoles
The 1H NMR spectra of all trifluoromethyl-1H-pyrazoles in
CDCl3 showed a typical proton chemical shift of 3,5-disubstituted
Synthesis of the title compounds is outlined in Scheme 1.
Compounds 3a–h were synthesized from the corresponding
trifluoromethyl-1,3-diketones obtained according to the our
published procedures [16,17]. Nucleophilic attack of hydrazine
pyrazole (4-H) at
compounds 3a–3c, 3e, 3f appeared as an AA0BB0 system with
Jortho = 7.2–8.8 Hz at = 6.98–8.36 ppm, consistent with the
d = 6.47–6.97 ppm. The phenyl ring protons of
d
characteristic coupling pattern of p-disubstituted benzenes [20].
The naphthenyl ring protons of compounds 3d and 3h exhibited
* Corresponding author. Tel.: +86 714 6515602; fax: +86 714 6573832.
E-mail address: dunjiawang@163.com (D.-J. Wang).
multiple peaks at
d = 7.17–8.07 ppm and the pyridyl ring protons
0022-1139/$ – see front matter ß 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2010.01.005

D.-J. Wang et al. / Journal of Fluorine Chemistry 131 (2010) 584–586
585
omethyl-1,3-diketones with hydrazine in ethanol. Their structures
were confirmed by elemental analysis, IR, 1H NMR and EI-MS
spectroscopy. Their preliminary anti-microbial activities against E.
coli, S. aureus, P. oryzae and R. solani were tested in a concentration
of 50 mg/L by disc diffusion method. The results showed that
compounds 3b and 3g, in particular, exhibited significant anti-
bacterial and anti-fungal activities.
Scheme 1. Reaction of trifluoromethyl-1,3-diketones with hydrazine.
Table 1
Preparation of trifluoromethyl-1H-pyrazolesa.
4. Experimental
Yieldb (%)
4.1. Chemicals and methods
1H-Pyrazole
R1
mp (8C)
3a
3b
3c
3d
3e
3f
4-CH3OC6H4–
4-FC6H4–
139–141
117–118
155–156
190–192
163–165
136–137
151–152
162–163
65
57
70
72
67
54
62
58
Elemental analysis (C, H, N) was performed using a Perkin-
Elmer 2400 elemental analyzer. 1H NMR spectra were measured on
a Varian Mercury-Plus 400 NMR nuclear magnetic resonance
instrument in CDCl3 solution with TMS as internal standard.
Infrared spectra (4000–400 cmꢀ1) were recorded on a Nicolet FTIR
5700 spectrophotometer with KBr pellets. Mass spectra were
measured on a Finnigan Trace EI-MS 2000 spectrometer. Melting
points were determined by an X-4 digital melting point apparatus,
which are uncorrected. Reagents were of analytical grade and were
used without further purification.
4-NO2C6H4–
6-CH3O-2-naphthyl
4-C6H4CH2OC6H4–
4-C2H5OC6H4–
4-Pyridyl
3g
3h
2-Naphthyl
a
Standard rection conditions: 1,3-diketones (2.0 mmol), hydrazine monohydrate
(2.0 mmol), ethanol (10 mL), reflux, 4 h.
b
Recrystallized isolated yields. All starting materials reacted completely, and
there are some unidentified products in the mixture.
Table 2
4.2. General procedure for trifluoromethyl-1H-pyrazoles
Anti-microbial data of trifluoromethyl-1H-pyrazoles.
The corresponding trifluoromethyl-1,3-diketone (2.0 mmol)
was dissolved in hot ethanol (10 mL). To this solution hydrazine
monohydrate (2.0 mmol) in ethanol was added and the mixture
was refluxed under stirring for 4 h. After completion of the reaction
(detected by thin layer chromatography, TLC), the solvent was
removed by evaporation. The residual solid was recrystallized from
dilute ethanol solution to give the corresponding trifluoromethyl-
1H-pyrazole.
1H-Pyrazole
Anti-bacterial activity
zone of inhibition
in mm
Anti-fungal activity
zone of inhibition
in mm
E. coli
S. aureus
P. oryzae
R. solani
3a
15
18
10
11
12
14
16
12
32
–
13
20
9
12
19
11
11
11
11
17
13
–
13
16
10
12
12
13
19
12
–
3b
3c
3d
10
13
12
15
11
29
–
3e
3f
4.2.1. 5-(4-Methoxyphenyl)-3-(trifluoromethyl)-1H-pyrazole (3a)
White crystals, yield 65%, mp 139–141 8C; Rf = 0.40 (TLC, ethyl
3g
3h
Norfloxacin
Triadimefon
acetate/hexane = 1:3), IR (KBr):
n 3243 (b, s), 3046 (w), 2974 (m),
27
31
2836 (w), 1616 (s), 1518 (s), 1493 (vs), 1464 (s), 1282 (vs), 1248
(vs), 1163 (vs), 1130 (vs), 1058 (s), 983 (vs), 838 (s), 800 (s), 744
; d 3.87 (s, 3H, OCH3), 6.72 (s,
(s) cmꢀ1 1H NMR (400 MHz, CDCl3):
of compound 3g displayed a multiplet at
d
= 7.43–8.57 ppm.
However, the N–H resonance signals for the pyrazolyl ring of all
compounds were not observed in CDCl3 at room temperature, in
agreement with results in the literature [21].
1H, pyrazloyl C–H), 7.00 (d, 2H, Ar–H, J = 8.4 Hz), 7.52 (d, 2H, Ar–H,
J = 8.4 Hz) ppm, N–H not found; EI-MS (70 eV): m/z (%) 242.1 (M+,
100), 227.1 (54), 199.0 (73), 151.1 (67), 74.6 (50); Anal. Calcd. for
The EI mass spectra of compounds 3a–h were measured and
compared to confirm elemental compositions. The molecular ion
peaks (M+) for these compounds were observed in accordance with
the Nitrogen Rule.
C11H9N2OF3: C, 54.55; H, 3.74; N, 11.56; Found C, 54.82; H, 3.68; N,
11.69.
4.2.2. 5-(4-Fluorophenyl)-3-(trifluoromethyl)-1H-pyrazole (3b)
White crystals, yield 57%, mp 117–118 8C; Rf = 0.53 (TLC, ethyl
2.3. Anti-microbial activity
acetate/hexane = 1:3), IR (KBr): n 3242 (b,s), 3050 (m), 2937 (w),
1614 (s), 1515 (s), 1493 (vs), 1432 (s), 1279 (vs), 1250 (vs), 1163 (vs),
1125(vs), 1058(s), 984(vs), 840 (vs), 810 (vs), 745 (s) cmꢀ1; 1H NMR
Compounds 3a–h are screened in vitro for their anti-microbial
activity against E. coli, S. aureus, P. oryzae and R. solani. The zones of
inhibition formed for the compounds against bacteria and fungi
were presented in Table 2. All the title compounds showed certain
degree of anti-bacterial and anti-fungalactivities. Compound 3b and
3g exhibited slightly higher activities against E. coli, S. aureus, P.
oryzae and R. solani, compared with compounds 3a, 3c–f and 3h [22].
All test data in Table 2 were the average values from triplicate runs.
Although these compounds showed less anti-microbial activities
compared to their respective standards, additional compounds in
this series will be prepared to try to improve activity.
(400 MHz, CDCl3):
d 6.76 (s, 1H, pyrazloyl C–H), 7.18 (d, 2H, Ar–H,
J = 8.4 Hz), 7.57 (d, 2H, Ar–H, J = 8.8 Hz) ppm, N–H not found; EI-MS
(70 eV): m/z (%) 230.1 (M+, 63), 181.9 (52), 161.2 (60), 133.1 (100),
94.9 (64), 74.7(58), 68.9(42); Anal. Calcd. forC10H6N2F4: C, 52.19; H,
2.63; N, 12.17; Found C, 52.46; H, 2.59; N, 12.33.
4.2.3. 5-(4-Nitrophenyl)-3-(trifluoromethyl)-1H-pyrazole (3c) [7]
Colorless needles, yield 70%, mp 155–156 8C; Rf = 0.46 (TLC,
ethyl acetate/hexane = 1:3), IR (KBr):
n 3148 (m), 3060 (w), 3029
(w), 1610 (m), 1531 (s), 1519 (m), 1496 (m), 1344 (vs), 1286 (s),
1257 (vs), 1171 (s), 1133 (vs), 1071 (m), 989 (s), 854 (s), 833 (s),
; d 6.97 (s, 1H,
755 (m), 693 (m) cmꢀ1 1H NMR (400 MHz, CDCl3):
3. Conclusions
pyrazloyl C–H), 7.81 (d, 2H, Ar–H, J = 8.4 Hz), 8.36 (d, 2H, Ar–H,
J = 8.8 Hz) ppm, N–H not found; EI-MS (70 eV): m/z (%) 257.1 (M+,
100), 227.1 (41), 199.0 (40), 191.1 (44), 141.8 (43), 114.4 (41); Anal.
In this paper, several new 5-substituted-3-(trifluoromethyl)-
1H-pyrazoles were synthesized by the condensation of trifluor-

586
D.-J. Wang et al. / Journal of Fluorine Chemistry 131 (2010) 584–586
Calcd. for C10H6N3O2F3: C, 46.70; H, 2.35; N, 16.34; Found C, 46.55;
H, 2.30; N, 16.51.
(29), 62.7 (31); Anal. Calcd. for C14H9N2F3: C, 64.12; H, 3.46; N,
10.68; Found C, 64.37; H, 3.40; N, 10.76.
4.2.4. 5-(6-Methoxynaphthalen-2-yl)-3-(trifluoromethyl)-1H-
pyrazole (3d)
4.3. Procedure for anti-microbial activity
White crystals, yield 72%, mp 190–192 8C; Rf = 0.39 (TLC, ethyl
The preliminary anti-microbial activities of new trifluoro-
methyl-1H-pyrazoles were measured in a concentration of 50 mg/
L by disc diffusion method [25,26]. Two bacterial microorganisms
E. coli and S. aureus, and the two fungal microorganisms P. oryzae
and R. solani were used. DMSO was used as a solvent control and
the standard drugs used were Norfloxacin and Triadimefon. The
disc diffusion method was performed using Muller-Hinton agar
(Hi-Media) medium. The inhibition zones were measured in/mm
at the end of an incubation period of 24 h at 37 8C for bacteria and
72 h at 24 8C for fungi.
acetate/hexane = 1:3), IR (KBr):
1627 (s), 1606 (s), 1595 (m), 1485 (s), 1452 (s), 1337 (s), 1261 (s),
1206 (s), 1066 (s), 1034 (s), 915 (s), 887 (s), 806 (s), 713 (s) cmꢀ1
1H NMR (400 MHz, CDCl3):
3.95 (s, 3H, OCH3), 6.88 (s, 1H,
n 3312 (b,s), 3066 (m), 2962 (m),
;
d
pyrazloyl C–H), 7.17 (s, 1H, Ar–H), 7.22 (d, 1H, Ar–H, J = 9.2 Hz),
7.63 (d, 1H, Ar–H, J = 8.8 Hz), 7.80 (d, 1H, Ar–H, J = 8.8 Hz), 7.84 (d,
1H, Ar–H, J = 8.8 Hz), 7.99 (s, 1H, Ar–H) ppm, N–H not found; EI-MS
(70 eV): m/z (%) 292.2 (M+, 100), 249.1 (81), 201.0 (28), 152.3 (27);
Anal. Calcd. for C15H11N2OF3: C, 61.65; H, 3.79; N, 9.58; Found C,
61.47; H, 3.72; N, 9.74.
Acknowledgement
4.2.5. 5-(4-(Benzyloxy)phenyl)-3-(trifluoromethyl)-1H-pyrazole (3e)
Colorless needles, yield 67%, mp 163–165 8C; Rf = 0.26 (TLC,
This work was supported by the importantFoundation of
the Educational Commission of Hubei Province, PR China
(Q200822002).
ethyl acetate/hexane = 1:3), IR (KBr):
n 3329 (s), 3136 (b,s), 2958
(w), 1609 (s), 1518 (s), 1485 (m), 1421 (m), 1383 (m), 1340 (s),
1260 (s), 1188 (s), 1071 (s), 1032 (s), 905 (m), 852 (m), 740 (s), 698
; d 5.12 (s, 2H, OCH2), 6.70 (s,
(s) cmꢀ1 1H NMR (400 MHz, CDCl3):
References
1H, pyrazloyl C–H), 7.07 (d, 2H, Ar–H, J = 7.2 Hz), 7.40–7.52 (m, 7H,
Ar–H) ppm, N–H not found; EI-MS (70 eV): m/z (%) 318.2 (M+, 6),
227.8 (5), 90.7 (100), 65.1 (23); Anal. Calcd. for C17H13N2OF3: C,
64.15; H, 4.12; N, 8.80; Found C, 64.38; H, 4.06; N, 8.93.
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4.2.6. 5-(4-Ethoxyphenyl)-3-(trifluoromethyl)-1H-pyrazole (3f)
Colorless crystals, yield 54%, mp 136–137 8C; Rf = 0.44 (TLC,
ethyl acetate/hexane = 1:3), IR (KBr):
n 3262 (b, s), 3068 (w), 2985
(m), 2888 (w), 1615 (s), 1516 (s), 1493 (s), 1439 (m), 1389 (m),
1281 (s), 1246 (s), 1153 (s), 1116 (s), 1058 (s), 982 (s), 838 (s), 809
; d 1.85 (t, 3H, CH3,
(s), 746 (s) cmꢀ1 1H NMR (400 MHz, CDCl3):
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J = 7.2 Hz), 3.84 (q, 2H, OCH2, J = 7.2 Hz), 6.70 (s, 1H, pyrazloyl C–
H), 6.98 (d, 2H, Ar–H, J = 8.4 Hz), 7.49 (d, 2H, Ar–H, J = 8.4 Hz) ppm,
N–H not found; EI-MS (70 eV): m/z (%) 256.1 (M+, 40), 228.0 (100),
151.1 (30), 131.0 (23); Anal. Calcd. for C12H11N2OF3: C, 56.25; H,
4.33; N, 10.93; Found C, 55.98; H, 4.26; N, 11.15.
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4.2.7. 4-(3-(Trifluoromethyl)-1H-pyrazol-5-yl) pyridine (3g) [23]
Colorless crystals, yield 62%, mp 151–152 8C; Rf = 0.14 (TLC,
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ethyl acetate/hexane = 1:3), IR (KBr):
n 3308 (s), 3051 (m), 2862
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The procedure for the synthesis of the trifluoromethyl-1,3-diketones 1 is as
follows: the mixture of aryl methyl ketones (0.04 mol), ethyl trifluoracetate
(0.08 mol), CH3ONa (0.08 mol) and benzene (150 ml) was stirred at 50 8C for
8 h. The reaction mixture was cooled to room temperature, acidified with dilute
hydrochloric acid and then stirred until all solids dissolved. The benzene layer
was separated, washed with a saturated NaHCO3 solution, dried over anhydrous
MgSO4 and the solvent was removed by evaporation. The residual oil solidified on
standing and the solid was recrystallized from ethanol to obtain the trifluoro-
methyl-1,3-diketones.
(m), 2708 (m), 1606 (s), 1578 (s), 1496 (m), 1425 (s), 1364 (s), 1255
(s), 1179 (vs), 1150 (s), 1062 (s), 1016 (s), 969 (s), 903 (m), 818 (s),
683 (s) cmꢀ1; 1H NMR (400 MHz, CDCl3):
d 6.47 (s, 1H, pyrazloyl C–
H), 7.43 (d, 2H, Ar–H, J = 4.8 Hz), 8.57 (d, 2H, Ar–H, J = 5.2 Hz) ppm,
N–H not found; EI-MS (70 eV): m/z (%) 213.0 (M+, 74), 162.0 (100),
78.1 (81), 51.6 (59); Anal. Calcd. for C9H6N3F3: C, 50.71; H, 2.84; N,
19.71; Found C, 51.02; H, 2.83; N, 19.91.
4.2.8. 5-(Naphthalen-2-yl)-3-(trifluoromethyl)-1H-pyrazole (3h)
[24]
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White microcrystalline power, yield 58%, mp 162–163 8C;
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Rf = 0.36 (TLC, ethyl acetate/hexane = 1:3), IR (KBr):
n 3312 (s),
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1135–1142.
´
´
3058 (m), 2904 (m), 1600 (m), 1482 (m), 1447 (m), 1337 (s), 1255
(s), 1170 (s), 1118 (s), 1065 (s), 1032 (s), 904 (m), 864 (s), 833 (s),
791 (s), 754 (s), 704 (s) cmꢀ1; 1H NMR (400 MHz, CDCl3):
d 6.93 (s,
1H, pyrazloyl C–H), 7.55–7.57 (m, 2H, Ar–H), 7.67 (d, 1H, Ar–H,
J = 8.4 Hz), 7.87–7.91 (m, 2H, Ar–H), 7.95 (d, 1H, Ar–H, J = 8.4 Hz),
8.07 (s, 1H, Ar–H) ppm, N–H not found; EI-MS (70 eV): m/z (%)
262.2 (M+, 49), 211.1 (47), 164.9 (48), 151.4 (39), 126.9 (100), 105.6
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