Synthesis of 3-(Trifluoromethyl)pyrazoles and Polysubstituted Pyrazoles by a tBuOK-Mediated Intramolecular Cyclization

Article abstract of DOI:10.1002/ejoc.201500705

A highly efficient tBuOK-mediated synthesis of 3-(trifluoromethyl)pyrazoles and other polysubstituted pyrazoles by intramolecular cyclization of N-propargylhydrazones has been developed. This protocol provides an alternative route to 4-substituted 3-(trif

Full text of DOI:10.1002/ejoc.201500705

FULL PAPER
DOI: 10.1002/ejoc.201500705
Synthesis of 3-(Trifluoromethyl)pyrazoles and Polysubstituted Pyrazoles by a
tBuOK-Mediated Intramolecular Cyclization
Jia-Jie Wen,[a] Cheng-Ke Ding,[a] Zong-Cang Ding,[a] Ting Li,[a] and Zhuang-Ping Zhan*[a]
Keywords: Synthetic methods / Nitrogen heterocycles / Hydrazones / Cyclization
A highly efficient tBuOK-mediated synthesis of 3-(trifluoro-
methyl)pyrazoles and other polysubstituted pyrazoles by
intramolecular cyclization of N-propargylhydrazones has
been developed. This protocol provides an alternative route
to 4-substituted 3-(trifluoromethyl)pyrazoles with good
regioselectivity and shows good functional-group compati-
bility as well as high efficiency. Of note is the fact that the
reactions on the gram scale also gave excellent yields.
duction of a CF3 group at the 3-position of the pyrazole
ring[4] or the construction of pyrazoles bearing a 3-CF3
group.[5–7] Traditionally, 3-(trifluoromethyl)pyrazoles have
been constructed by the cyclocondensation of an appropri-
ate hydrazine with the corresponding 1,3-dielectrophilic
compound,[5] especially with 1,3-dicarbonyl compounds
(Scheme 1, method a). However, the drawback of this
method is obvious, namely its poor regioselectivity. An al-
ternative using a 1,3-dipolar cycloaddition strategy was re-
ported by Ma and co-workers[6a] (Scheme 1, method b), but
in this case 2 equiv. of Ag2O were required. Moreover, 4-
substituted pyrazoles cannot be synthesized by this reac-
tion. Intramolecular cyclization is also a good method for
the construction of 3-(trifluoromethyl)pyrazoles. The syn-
thesis of 3-(trifluoromethyl)pyrazoles by trifluoromethyl-
ation/cyclization of α,β-alkynic hydrazones with the Togni
reagent was reported by Wang and co-workers[7] (Scheme 1,
method c). However, this method was also inefficient for
the construction of 4-substituted 3-(trifluoromethyl)pyr-
azoles as only low to moderate yields were obtained.
Introduction
Compounds bearing CF3 groups are absent in nature,
but the introduction of trifluoromethyl groups into organic
molecules can lead to profound changes in their biological
properties.[1] Pyrazole bearing a 3-(trifluoromethyl) group is
a distinguished example, and has proven to be the core unit
of many commercial drugs and related candidates.[2,3] Rep-
resentative examples of successfully commercialized pyr-
azoles bearing a 3-CF3 group are shown in Figure 1. Cele-
coxib[2a] and Mavacoxib[2c] are selective COX-2 inhibitors,
and Penthiopyrad[2b] is a fungicide.
Figure 1. Selected examples of the polysubstituted pyrazole scaffold
in natural products and bioactive molecules.
In recent years, tremendous efforts have been directed
towards the development of efficient methods for the intro-
[a] Department of Chemistry, College of Chemistry and Chemical
Engineering, Xiamen University,
Xiamen 361005, Fujian, P. R. China
E-mail: zpzhan@xmu.edu.cn
http://chem-zzp.xmu.edu.cn/
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201500705.
Scheme 1. Synthesis of 3-trifluoromethylpyrazoles.
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© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2015, 5230–5235

3-(Trifluoromethyl)pyrazoles and Polysubstituted Pyrazoles
Continuing our research into the reactions of proparg- Table 1. Optimization of the reaction conditions for the synthesis
ylhydrazones,[8] we herein report the synthesis of 4-substi-
of pyrazole 2a.
tuted 3-(trifluoromethyl)pyrazoles in extremely high yields
from N-propargylhydrazones by a tBuOK-mediated intra-
molecular cyclization process under mild conditions
(Scheme 1, this method).
Results and Discussion
Substrate 1a was chosen as the model substrate for our
study, and some of the results are listed in Table 1. Initially,
substrate 1a was treated with a catalytic amount of
DMAP[8b] [4-(dimethylamino)pyridine; 5 mol-%] in
CH3CN at room temperature (room temp.); however, this
gave no product at all. The reaction performed at a higher
temperature (80 °C) or with a high catalyst loading did not
work (Table 1, Entries 1 and 2). Changing the solvent to
DMF also led to no reaction (Table 1, Entry 3). We specu-
lated that a stronger base may promote the reaction. With
this in mind, we then tested a range of other bases, includ-
ing K2CO3, Cs2CO3, and tBuOK, and found that the treat-
ment of 1a with Cs2CO3 did furnish the pyrazole 2a in 91%
yield within 3 h (Table 1, Entry 5). The structure of 2a was
unambiguously determined by a single-crystal X-ray struc-
ture analysis (Figure 2).[9] Further studies revealed that
tBuOK was the best base for this transformation; it not
only improved the yield of 2a to 92%, but also dramatically
shortened the reaction time (10 min; Table 1, Entry 6).
Solvent screening revealed that the solvents DMSO,
PhCH3, CH3NO2, DCE, and 1,4-dioxane did not lead to
any detectable product formation or decreased the yield
(Table 1, Entries 7–11). In contrast, the use of CH3CN as
solvent increased the yield to 96% (Table 1, Entry 12).
Moreover, it was found that the reaction mediated by
1.0 equiv. of tBuOK also gave a high yield (Table 1, en-
try 13). Hence, the optimal reaction conditions for this
cyclization were determined to comprise 1 equiv. of tBuOK
as base, CH3CN as the solvent, and room temperature for
10 min.
Entry[a]
Base
Solvent
Time
Yield[b] [%]
1[c]
2[c]
3
4
5
6
7
8
9
10
11
12
13
DMAP (5 mol-%)
DMAP (1.5 equiv.)
DMAP (1.5 equiv.)
K2CO3 (1.5 equiv.)
Cs2CO3 (1.5 equiv.)
tBuOK (1.5 equiv.)
tBuOK (1.5 equiv.)
tBuOK (1.5 equiv.)
tBuOK (1.5 equiv.)
tBuOK (1.5 equiv.)
CH3CN
CH3CN
DMF
DMF
DMF
5 h
5 h
5 h
5 h
3 h
10 min
10 min
5 h
5 h
5 h
n.r.
n.r.
n.r.
n.r.
91
92
67
n.r.
n.r.
n.r.
n.r.
96
DMF
DMSO
PhCH3
CH3NO2
DCE
tBuOK (1.5 equiv.) 1,4-dioxane
tBuOK (1.5 equiv.)
tBuOK (1.0 equiv.)
5 h
10 min
10 min
CH3CN
CH3CN
99
[a] Reaction conditions: 1a (0.2 mmol), solvent (3 mL). [b] Isolated
yield. n.r. = no reaction. [c] Reaction temperature was in the range
from room temp. to 80 °C.
3-(Trifluoromethyl)pyrazoles are the core structures of
many bioactive molecules;[2,3] thus, we set out to synthesize
these compounds by using the optimized reaction condi-
tions (Scheme 2). The starting substrate bearing a phenyl
group at the alkynyl position was first examined, and the
targeted product 2b was formed in good to excellent yields,
although a longer reaction time (5 h) was required. Simi-
larly, a substrate bearing the 2-naphthyl group at the alk-
ynyl position also reacted smoothly to give 2c in 93% yield.
Figure 2. X-ray crystal structure of product 2a (ellipsoids are drawn
at the 30% probability level).
The pyrazoles 2d and 2e were also obtained in good yields. R2, R3, R4) at various positions of the N-propargylhydraz-
Pleasingly, the substrate bearing thiophene at the alkynyl one 1 (Table 2). The alkynyl position R2 was found to toler-
position was also tolerated, and the corresponding pyrazole ate phenyl groups substituted with an electron-donating
2f was obtained in 95% yield. In addition, an excellent yield group (OMe; Table 2, Entry 2) as well as alkyl and het-
was obtained with R2 as an alkyl group (Scheme 2, product eroaryl substituents, for example butyl and 2-thienyl
2g). Moreover, a terminal alkyne also reacted smoothly to (Table 2, Entries 4 and 7). However, a phenyl group substi-
give the desired pyrazole in 93% yield (Scheme 2, product tuted with an electron-withdrawing group (NO2) seemed to
2h).
completely prevent the formation of pyrazole and led to a
We next evaluated the scope of the reaction under the complex mixture (Table 2, Entry 3). Of note is the fact that
optimal conditions by placing different substituents (R1, a terminal alkyne also reacted to give the desired pyrazole
Eur. J. Org. Chem. 2015, 5230–5235
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J.-J. Wen, C.-K. Ding, Z.-C. Ding, T. Li, Z.-P. Zhan
Table 2. Synthesis of polysubstituted pyrazoles.
FULL PAPER
Scheme 2. Synthesis of 4-substituted 3-(trifluoromethyl)pyrazoles.
Reaction conditions: 1 (0.2 mmol), CH3CN (3 mL), in Schlenk
tube; isolated yields.
in 94% yield (Table 2, Entry 5). The introduction of the tri-
methylsilyl (TMS) group led to the formation of a product
resulting from TMS extrusion (Table 2, Entry 6).
[a] Reaction conditions: 1 (0.2 mmol), CH3CN (3 mL), in Schlenk
tube. [b] Isolated yields.
Hydrazones derived from heteroaryl (including 2-thienyl
and 2-furyl) aldehydes were also found to be suitable sub-
strates for this transformation (Table 2, products 2o, 2p, and
2t). With R3 as 1-naphthyl and styrenyl, the corresponding
pyrazoles were formed in yields of 94 and 99%, respectively
(Table 2, Entries 10 and 12). Moreover, a hydrazone derived
from an alkyl aldehyde also gave an excellent yield (Table 2,
Entry 11). Meanwhile, branching at the propargylic posi-
tion was also tolerated (R1 = n-pentyl) and the desired pyr-
azole was obtained in 97% yield (Table 2, Entry 14). Ad-
ditionally, replacing the R4 phenyl group by a cyclohexyl
ring also gave the desired product in 94% yield (Table 2,
Entry 15).
We previously reported the conversion of N-Ts-proparg-
ylhydrazones into allenic hydrazones.[8b] Based on the above
results and those of our previous investigations, the path-
way for the formation of 2 is considered to proceed as illus-
trated in Scheme 3. The reaction possibly starts with the
isomerization of the propargylhydrazone 1 to the allenic
compound A mediated by tBuOK. The subsequent cycliza-
tion of A is expected to provide intermediate B, which un-
dergoes auto-isomerization to give the desired product 2.
Scheme 3. Plausible reaction mechanism for the formation of 2.
To illustrate the practicability of this method, two reac- the same substrate in Scheme 2, which reveals that this is a
tions were carried out on the gram scale (Scheme 4). Sub- highly efficient preparative method. Moreover, propargylic
strate 1b bearing a CF3 group at the 3-position was exam- hydrazone 1l could also be converted into the correspond-
ined, and the desired product 2b was formed in 91% yield ing pyrazole 2l in 91% yield on the gram scale [Scheme 4
[Scheme 4 (a)]. This is a yield similar to that obtained with (b)].
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Eur. J. Org. Chem. 2015, 5230–5235

3-(Trifluoromethyl)pyrazoles and Polysubstituted Pyrazoles
4-Benzyl-3-(4-bromophenyl)-1-phenyl-1H-pyrazole (2a): White solid
(49.4 mg; m.p. 140–142 °C). 1H NMR (400 MHz, CDCl3): δ = 4.00
(s, 2 H), 7.18–7.26 (m, 4 H), 7.27–7.33 (m, 2 H), 7.36–7.43 (m, 2
H), 7.48–7.54 (m, 2 H), 7.56–7.59 (m, 2 H), 7.59–7.62 (m, 1 H),
7.64–7.67 (m, 1 H), 7.67–7.70 (m, 1 H) ppm. 13C NMR (100 MHz,
CDCl3): δ = 31.0, 118.8, 120.4, 122.0, 126.3, 126.4, 127.8, 128.6,
128.7, 129.4, 131.7, 132.5, 140.0, 140.2, 150.4 ppm. IR (film): ν =
˜
3060, 2920, 1600, 1502, 756 cm–1. HRMS (ESI): calcd. for
+
C22H18BrN2 [M + H]+ 389.0648, 391.0628; found 389.0642,
391.0621.
4-Benzyl-1-phenyl-3-(trifluoromethyl)-1H-pyrazole (2b): Light-yel-
1
low liquid (46.7 mg). H NMR (400 MHz, CDCl3): δ = 4.00 (s, 2
H), 7.26–7.32 (m, 3 H), 7.32–7.40 (m, 3 H), 7.41–7.48 (m, 2 H), 7.54
(s, 1 H), 7.60–7.66 (m, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ
= 29.6, 119.5, 121.77 (q, J = 268.0 Hz), 121.80, 126.6, 127.4, 128.0,
128.6, 128.7, 129.4, 139.2, 139.3, 141.3 (q, J = 36.4 Hz) ppm. 19F
NMR (376 MHz, CDCl ): δ = –60.91 ppm. IR (film): ν = 3064,
˜
3
2925, 1601, 1493, 757.4 cm–1. HRMS (ESI): calcd. for
C17H14F3N2 [M + H]+ 303.1104; found 303.1101.
+
Scheme 4. Two reactions carried out on the gram scale.
4-(1-Naphthylmethyl)-1-phenyl-3-(trifluoromethyl)-1H-pyrazole (2c):
Viscous liquid (46.7 mg). 1H NMR (400 MHz, CDCl3): δ = 4.38 (s,
2 H), 7.15–7.23 (m, 2 H), 7.25–7.32 (m, 2 H), 7.33–7.38 (m,1 H),
7.39–7.50 (m, 5 H), 7.75–7.82 (m, 1 H), 7.83–7.89 (m, 1 H), 7.89–
7.97 (m, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 27.2, 119.4,
121.5, 121.9 (q, J = 267.6 Hz), 123.9, 125.6, 125.8, 126.3, 127.0,
127.3, 127.7, 128.1, 128.8, 129.3, 131.6, 134.0, 134.9, 139.2, 141.1
Conclusions
We have reported a highly efficient method for the syn-
thesis of 4-substituted 3-(trifluoromethyl)pyrazoles and
(q,
J = δ =
35.8 Hz) ppm. 19F NMR (376 MHz, CDCl3):
other 4-substituted pyrazoles from N-propargylhydrazones –60.92 ppm. IR (film): ν = 3063, 2951, 1600, 1498, 781 cm–1.
˜
HRMS (ESI): calcd. for C21H16F3N2 [M + H]+ 353.1261; found
+
by a tBuOK-mediated intramolecular cyclization process.
The method is applicable to a wide range of substrates, thus
353.1260.
providing a convenient access to a variety of highly func- 4-(4-Methoxybenzyl)-1-phenyl-3-(trifluoromethyl)-1H-pyrazole (2d):
Light-yellow liquid (49.5 mg). 1H NMR (400 MHz, CDCl3): δ =
tionalized pyrazoles. Of note is the fact that the reactions
3.82 (s, 3 H), 3.93 (s, 2 H), 6.87–6.92 (m, 2 H), 7.15–7.21 (m, 2 H),
also gave excellent yields on the gram scale.
7.29–7.35 (m, 1 H), 7.40–7.46 (m, 2 H), 7.50–7.53 (m, 1 H), 7.60–
7.65 (m, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 28.7, 55.2,
114.1, 119.5, 121.8 (q, J = 214.4 Hz), 122.4, 127.4, 127.9, 129.4,
129.6, 131.3, 139.3, 141.2 (q, J = 29.2 Hz), 158.3 ppm. 19F NMR
Experimental Section
(376 MHz, CDCl ): δ = –60.94 ppm. IR (film): ν = 3053, 2934,
˜
3
General: All the solvents were freshly distilled prior to use. All reac-
tion mixtures were stirred with a magnetic bar in flame-dried glass-
ware. Column chromatography on silica gel (300–400 mesh) or
Al2O3 (200–300 mesh) was carried out by using technical-grade pe-
troleum ether (boiling range 60–90 °C) (distilled prior to use) and
2837, 1600, 1505, 756 cm–1. HRMS (ESI): calcd. for
C18H16F3N2O+ [M + H]+ 333.1209; found 333.1214.
4-{[1-Phenyl-3-(trifluoromethyl)-1H-pyrazol-4-yl]methyl}benzonit-
1
rile (2e): Light-yellow solid (47.8 mg; m.p. 94–95 °C). H NMR
1
analytical-grade EtOAc (without further purification). H and 13C
(400 MHz, CDCl3): δ = 4.05 (s, 2 H), 7.31–7.37 (m, 3 H), 7.42–
7.48 (m, 2 H), 7.58–7.61 (m, 1 H), 7.61–7.64 (m, 3 H), 7.64–7.67
(m, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 29.7, 110.7,
118.7, 119.6, 119.7, 121.6 (q, J = 268.1 Hz), 127.8, 128.0, 129.4,
129.6, 132.5, 139.2, 141.5 (q, J = 6.6 Hz), 144.8 ppm. 19F NMR
NMR spectra were recorded with a Bruker Avance 400/100/
376 MHz or 500/125 MHz spectrometer by using CDCl3 or (CD3)2-
SO as solvent and TMS as internal standard. 19F NMR spectra
were recorded with a Bruker Avance 376 MHz spectrometer by
using CDCl3 as solvent and TMS as internal standard. Chemical
shifts are reported in ppm. IR spectra were recorded with a Nicolet
Avatar 360 FT-IR spectrometer as thin films on KBr wafers. Mass
spectra were recorded with an En Apex Ultra 7.0 FT-MS high-
resolution mass spectrometer. Melting point were recorded with a
Yanaco MP-500 melting point apparatus.
(376 MHz, CDCl ): δ = –60.87 ppm. IR (film): ν = 3068, 2954,
˜
3
1602, 1498 cm–1. HRMS (ESI): calcd. for C18H13F3N3 [M + H]+
+
328.1057; found 328.1061.
1-Phenyl-4-(thiophen-2-ylmethyl)-3-(trifluoromethyl)-1H-pyrazole
(2f): Light-yellow liquid (47.6 mg). 1H NMR (400 MHz, CDCl3):
δ = 4.20 (s, 2 H), 6.90–6.95 (m, 1 H), 6.96–7.01 (m, 1 H), 7.18–7.24
(m, 1 H), 7.30–7.38 (m, 1 H), 7.41–7.50 (m, 2 H), 7.62–7.69 (m, 2
H), 7.71 (s, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 24.0,
119.6, 121.3, 121.7 (q, J = 268.0 Hz), 124.2, 125.6, 127.0, 127.6,
128.1, 129.5, 139.3, 141.1 (q, J = 36.8 Hz), 141.7 ppm. 19F NMR
General Experimental Procedures for the Preparation of Polysubsti-
tuted Pyrazoles 2: The corresponding propargylhydrazone
1
(50 mg) and tBuOK (1.0 equiv.) were placed in a 10 mL Schlenk
tube followed by the addition of CH3CN (3 mL). The reaction mix-
ture was then stirred at room temp. under N2. Upon completion of
the reaction (monitored by TLC), the solvent was removed under
vacuum, and the crude residue was purified by silica gel column
chromatography to afford the corresponding pyrazoles 2 (eluent:
petroleum ether/EtOAc, 100:1).
(376 MHz, CDCl ): δ = –60.92 ppm. IR (film): ν = 3072, 2925,
˜
3
1600, 1493, 758 cm–1. HRMS (ESI): calcd. for C15H12F3N2S+ [M
+ H]+ 309.0668; found 309.0667.
4-Pentyl-1-phenyl-3-(trifluoromethyl)-1H-pyrazole (2g): Light-yel-
1
low liquid (49.1 mg). H NMR (400 MHz, CDCl3): δ = 0.93 (t, J
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J.-J. Wen, C.-K. Ding, Z.-C. Ding, T. Li, Z.-P. Zhan
FULL PAPER
= 6.9 Hz, 3 H), 1.33–1.44 (m, 4 H), 1.60–1.70 (m, 2 H), 2.62 (t, J
4-Benzyl-3-(furan-2-yl)-1-phenyl-1H-pyrazole (2p): Yellow solid
= 7.7 Hz, 2 H), 7.27–7.37 (m, 1 H), 7.40–7.50 (m, 2 H), 7.63–7.71 (48.6 mg; m.p. 45–47 °C). 1H NMR (500 MHz, CDCl3): δ = 4.08
(m, 2 H), 7.75 (s, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
13.9, 22.4, 23.2, 29.9, 31.4, 119.4, 121.9 (q, J = 268.0 Hz), 122.7,
(s, 2 H), 6.46 (dd, J = 3.4, 1.8 Hz, 1 H), 6.65 (d, J = 3.2 Hz, 1 H),
7.20–7.28 (m, 4 H), 7.28–7.33 (m, 2 H), 7.36–7.41 (m, 2 H), 7.47–
126.9, 127.3, 129.5, 139.5, 141.5 (q, J = 36.3 Hz) ppm. 19F NMR 7.57 (m, 2 H), 7.63–7.68 (m, 2 H) ppm. 13C NMR (125 MHz,
(376 MHz, CDCl ): δ = –61.05 ppm. IR (film): ν = 3053, 2932,
CDCl3): δ = 30.7, 107.5, 111.2, 118.9, 120.4, 126.2, 126.3, 127.2,
˜
3
1602, 1492, 757 cm–1. HRMS (ESI): calcd. for C15H18F3N2 [M +
128.5, 128.6, 129.2, 139.8, 140.0, 142.1, 143.3, 148.4 ppm. IR (film):
+
H]+ 283.1417; found 283.1410.
ν = 3061, 2923, 1599, 1503, 756 cm–1. HRMS (ESI): calcd. for
˜
C20H17N2O+ [M + H]+ 301.1336; found 301.1334.
4-Methyl-1-phenyl-3-(trifluoromethyl)-1H-pyrazole (2h): Light-yel-
1
low liquid (46.4 mg). H NMR (400 MHz, CDCl3): δ = 2.24 (s, 3
4-Benzyl-3-(1-naphthyl)-1-phenyl-1H-pyrazole (2q): Yellow liquid
(47.1 mg). 1H NMR (400 MHz, CDCl3): δ = 3.74 (s, 2 H), 7.05–
7.18 (m, 3 H), 7.18–7.27 (m, 3 H), 7.37–7.44 (m, 2 H), 7.45–7.57
(m, 4 H), 7.70–7.78 (m, 3 H), 7.86–7.94 (m, 2 H), 7.98–8.08 (m, 1
H) ppm. 13C NMR (100 MHz, CDCl3): δ = 30.6, 118.7, 122.7,
125.2, 125.8, 126.0, 126.1(8), 126.2(3), 126.3, 128.1, 128.2, 128.4,
128.5, 128.6, 129.3, 130.7, 132.4, 133.8, 140.1, 140.6, 151.5 ppm.
H), 7.28–7.37 (m, 1 H), 7.40–7.50 (m, 2 H), 7.60–7.70 (m, 2 H),
7.72 (s, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 8.1, 117.1,
119.4, 121.9 (q, J = 214.0 Hz), 127.3, 127.6, 129.5, 139.4, 142.1 (q,
J = 29.0 Hz) ppm. 19F NMR (376 MHz, CDCl3): δ = –61.51 ppm.
IR (film): ν = 3053, 2963, 1601, 1495, 1392 cm–1. HRMS (ESI):
˜
+
calcd. for C11H10F3N2 [M + H]+ 227.0791; found 227.0795.
IR (film): ν = 3052, 2923, 1600, 1504, 756 cm–1. HRMS (ESI):
˜
3-(4-Bromophenyl)-4-(4-methoxybenzyl)-1-phenyl-1H-pyrazole (2i):
Light-yellow solid (48.6 mg; m.p. 104–106 °C). 1H NMR
(400 MHz, CDCl3): δ = 3.81 (s, 3 H), 3.98 (s, 2 H), 6.84–6.92 (m,
2 H), 7.12–7.20 (m, 2 H), 7.24–7.30 (m, 1 H), 7.40–7.48 (m, 2 H),
7.52–7.58 (m, 2 H), 7.58–7.66 (m, 3 H), 7.68–7.74 (m, 2 H) ppm.
13C NMR (100 MHz, CDCl3): δ = 30.2, 55.3, 114.1, 118.8. 121.0,
122.0, 126.3, 127.7, 129.38, 129.41, 129.5, 131.6, 132.2, 132.5,
+
calcd. for C26H21N2 [M + H]+ 361.1700; found 361.1694.
4-Benzyl-3-pentyl-1-phenyl-1H-pyrazole (2r): Light-yellow liquid
1
(47.4 mg). H NMR (400 MHz, CDCl3): δ = 0.88 (t, J = 7 Hz, 3
H), 1.28–1.38 (m, 4 H), 1.58–1.68 (m, 2 H), 2.60 (t, J = 7.8 Hz, 2
H), 3.83 (s, 2 H), 7.15–7.25 (m, 4 H), 7.26–7.33 (m, 2 H), 7.34–7.41
(m, 2 H), 7.51 (s, 1 H), 7.56–7.63 (m, 2 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 14.0, 22.5, 26.8, 28.9, 30.1, 31.8, 118.4,
120.3, 125.5, 126.1, 128.4, 128.5, 129.2, 140.2, 140.5, 153.5 ppm.
140.0, 150.2, 158.2 ppm. IR (film): ν = 3051, 2928, 2834, 1600,
˜
1503, 755 cm–1. HRMS (ESI): calcd. for C23H20BrN2O+ [M + H]+
419.0754, 421.0734; found 419.0751, 421.0730.
IR (film): ν = 3027, 2928, 1600, 1504, 754 cm–1. HRMS (ESI):
˜
+
calcd. for C21H25N2 [M + H]+ 305.2013; found 305.2011.
3-(4-Bromophenyl)-4-pentyl-1-phenyl-1H-pyrazole (2k): Light-yel-
1
low solid (45.1 mg; m.p. 74–76 °C). H NMR (400 MHz, CDCl3):
(E)-4-Benzyl-1-phenyl-3-styryl-1H-pyrazole (2s): Light-yellow solid
(47.8 mg; m.p. 111–113 °C). 1H NMR (400 MHz, CDCl3): δ = 3.93
(s, 2 H), 7.98–7.05 (m, 1 H), 7.10–7.21 (m, 5 H), 7.21–7.29 (m, 5
H), 7.29–7.36 (m, 2 H), 7.36–7.42 (m, 2 H), 7.46 (s, 1 H), 7.55–7.63
(m, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 30.5, 118.7,
121.3, 126.1, 126.3, 126.5, 127.0, 127.6, 128.5, 128.58, 128.61,
δ = 0.92 (s, 3 H), 1.33–1.43 (m, 4 H), 1.60–1.72 (m, 2 H), 2.66 (t,
J = 7.6 Hz, 2 H), 7.23–7.32 (m, 1 H), 7.40–7.50 (m, 2 H), 7.54–
7.62 (m, 2 H), 7.62–7.70 (m, 2 H), 7.70–7.77 (m, 2 H), 7.78 (s, 1
H) ppm. 13C NMR (100 MHz, CDCl3): δ = 14.1, 22.5, 24.8, 29.7,
29.9, 31.7, 118.7, 121.7, 122.0, 126.1, 126.3, 129.37, 129.40, 131.6,
132.9, 140.1, 150.2 ppm. IR (film): ν = 3051, 2928, 2857, 1600,
˜
129.3, 130.6, 137.3, 139.9(4), 139.9(8), 149.2 ppm. IR (film): ν =
˜
+
1502, 755 cm–1. HRMS (ESI): calcd. for C20H22BrN2 [M + H]+
3025, 2923, 1599, 1503, 754 cm–1. HRMS (ESI): calcd. for
369.0961, 371.0941; found 369.0968, 371.0947.
+
C24H21N2 [M + H]+ 337.1700; found 337.1696.
3-(4-Bromophenyl)-4-methyl-1-phenyl-1H-pyrazole (2l): Light-yel-
3-(Furan-2-yl)-4-methyl-1-phenyl-1H-pyrazole (2t): Light-yellow so-
lid (44.8 mg; m.p. 70–71 °C). 1H NMR (500 MHz, CDCl3): δ =
2.29 (s, 3 H), 6.48–6.51 (m, 1 H), 6.68–6.71 (m, 1 H), 7.21–7.26 (m,
1 H), 7.37–7.44 (m, 2 H), 7.50–7.53 (m, 1 H), 7.66–7.72 (m, 3 H)
ppm. 13C NMR (125 MHz, CDCl3): δ = 9.7, 107.2, 111.1, 116.0,
118.8, 126.0, 126.7, 129.2, 139.9, 141.9, 143.8, 148.7 ppm. IR (film):
1
low solid (47.2 mg; m.p. 79–80 °C). H NMR (400 MHz, CDCl3):
δ = 2.30 (s, 3 H), 7.24–7.30 (m, 1 H), 7.40–7.48 (m, 2 H), 7.55–7.61
(m, 2 H), 7.66–7.74 (m, 4 H), 7.75–7.79 (m, 1 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 10.3, 116.2, 118.7, 121.6, 126.1, 127.2,
129.0, 129.4, 131.5, 132.7, 140.0, 150.4 ppm. IR (film): ν = 3051,
˜
2925, 1599, 1503, 755 cm–1. HRMS (ESI): calcd. for C16H14BrN2
+
ν = 3058, 2921, 1601, 1497, 773 cm–1. HRMS (ESI): calcd. for
˜
[M + H]+ 313.0335, 315.0315; found 313.0333, 315.0312.
C14H13N2O+ [M + H]+ 225.1023; found 225.1021.
3-(4-Bromophenyl)-1-phenyl-4-(thiophen-2-ylmethyl)-1H-pyrazole
(2n): Llight-yellow solid (49.6 mg; m.p. 133–134 °C). 1H NMR
[400 MHz, (CD3)2SO]: δ = 4.24 (s, 2 H), 6.84–6.88 (m, 1 H), 6.90–
6.95 (m, 1 H), 7.27–7.35 (m, 2 H), 7.46–7.53 (m, 2 H), 7.57–7.63
(m, 2 H), 7.63–7.69 (m, 2 H), 7.84–7.90 (m, 2 H), 8.46 (s, 1 H)
ppm. 13C NMR [100 MHz, (CD3)2SO]: δ = 25.0, 118.6, 120.1,
121.7, 124.7, 125.5, 126.8, 127.5, 129.3, 129.7, 130.0, 132.0, 132.6,
4-Benzyl-3-(4-bromophenyl)-5-pentyl-1-phenyl-1H-pyrazole
(2u):
1
Yellow liquid (48.4 mg). H NMR (400 MHz, CDCl3): δ = 0.75 (t,
J = 6.8 Hz, 3 H), 1.08–1.16 (m, 4 H), 1.28–1.36 (m, 2 H), 2.60 (t,
J = 8.0 Hz, 2 H), 4.04 (s, 2 H), 7.16–7.25 (m, 3 H), 7.27–7.33 (m,
2 H), 7.40–7.48 (m, 3 H), 7.49–7.57 (m, 6 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 13.7, 21.9, 24.6, 28.4, 29.6, 31.3, 114.5,
121.6, 125.7, 126.0, 127.96, 128.03, 128.4, 129.1, 129.4, 131.4,
139.8, 144.0, 149.5 ppm. IR (film): ν = 3068, 2922, 1600, 1502,
˜
755 cm–1. HRMS (ESI): calcd. for C20H16BrN2S+ [M + H]+
395.0213, 397.0192; found 395.0210, 397.0190.
132.7, 140.1, 140.5, 143.3, 150.1 ppm. IR (film): ν = 3061, 2955,
˜
2927, 1598, 1500, 1365, 729 cm–1. HRMS (ESI): calcd. for
+
C27H28BrN2 [M + H]+ 459.1431, 461.1410; found 459.1428,
4-Benzyl-1-phenyl-3-(thiophen-2-yl)-1H-pyrazole (2o): Light-yellow
461.1405.
1
solid (47.8 mg; m.p. 112–113 °C). H NMR (400 MHz, CDCl3): δ
= 4.11 (s, 2 H), 7.05–7.13 (m, 1 H), 7.24–7.39 (m, 8 H), 7.40–7.47
4-Benzyl-1-cyclohexyl-3-phenyl-1H-pyrazole (2v): Light-yellow solid
(m, 2 H), 7.56 (s, 1 H), 7.66–7.75 (m, 2 H) ppm. 13C NMR (47.1 mg; m.p. 109–111 °C). 1H NMR (500 MHz, CDCl3): δ =
(100 MHz, CDCl3): δ = 30.9, 118.6, 120.0, 125.00, 125.03, 126.1, 1.20–1.33 (m, 2 H), 1.38–1.49 (m, 2 H), 1.68–1.78 (m, 2 H), 1.86–
126.3, 127.4, 127.5, 128.6, 129.3, 135.8, 139.7, 146.2 ppm. IR (film): 1.94 (m, 2 H), 2.17–2.24 (m, 2 H), 4.0 (s, 2 H), 4.11 (tt, J = 11.8,
ν = 3061, 2920, 1599, 1503, 756 cm–1. HRMS (ESI): calcd. for
3.8 Hz, 1 H), 7.11 (s, 1 H), 7.19–7.25 (m, 3 H), 7.28–7.34 (m, 3 H),
˜
C20H17N2S+ [M + H]+ 317.1107; found 317.1111.
7.37–7.42 (m, 2 H), 7.62–7.68 (m, 2 H) ppm. 13C NMR (125 MHz,
5234
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© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2015, 5230–5235

3-(Trifluoromethyl)pyrazoles and Polysubstituted Pyrazoles
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127.7, 128.3, 128.4, 128.5, 134.2, 141.1, 148.8 ppm. IR (film): ν =
˜
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Experimental Procedures for the Preparation of Polysubstituted Pyr-
azole 2l on the Gram Scale: The corresponding hydrazone (2.0 g,
7.27 mmol) and Cs2CO3 (8.84 g, 8.72 mmol) were placed in an
oven-dried round-bottomed flask, and then DMF (35 mL) was
added. Finally, the corresponding propargyl bromide (1.04 g,
8.72 mmol) was added under N2, and the reaction mixture was
stirred at room temperature. Upon completion (monitored by
TLC), the mixture was diluted with water (150 mL), and the aque-
ous phase was extracted with EtOAc (3ϫ 40 mL). The combined
organic layers were dried with Na2SO4. The solvent was removed
under vacuum, and the crude residue was purified by recrystalli-
zation (hexane/MeOH, 100:1) to afford the corresponding the
propargylhydrazone 1l (1.48 g, 65% yield). tBuOK (358 mg,
3.2 mmol) was placed in a 150 mL three-necked bottle followed by
the addition of CH3CN (70 mL) and substrate 1l (1 g, 3.2 mmol),
dissolved in CH3CN (15 mL) under N2. The reaction mixture was
stirred at room temp. Upon completion (monitored by TLC), the
solvent was removed under vacuum and the crude residue purified
by flash column chromatography on silica gel (petroleum ether/
EtOAc, 100:1) to afford the corresponding pyrazole 2l (0.908 g,
91% yield).
Acknowledgments
We are grateful to the National Natural Science Foundation of
China (No. 21272190) and the Program for Changjiang Scholars
and Innovative Research Team (PCSIRT) in University.
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Received: May 31, 2015
Published Online: July 14, 2015
Eur. J. Org. Chem. 2015, 5230–5235
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5235