1130
S. Selvi and P. T. Perumal
Vol. 39
1-(2, 4-Dinitrophenyl)-4-ethyl-3-phenylpyrazole (2b).
products. Therefore a hydroxyl group at the 2-position is
not essential and the presence of electron withdrawing
does not affect the reaction. The use of microwave irradia-
tion has drastically reduced the reaction time from several
hours to a few seconds with good yields.
This compound was obtained as a pale yellow solid; 1H NMR
(300 MHz, CDC13): d 8.63 (s, 1H), 8.45 (d, J = 9.0 Hz, 1H), 7.83
(d, J = 9.0 Hz, 1H), 7.64 (t, J= 7.2 Hz), 7.62 (s, 1H) 7.34-7.44
(m, 3H), 2.73 (q, J = 7.4 Hz, 2H), 1.27 (t, J = 7.4 Hz, 3H); 13
C
NMR (75 MHz, CDC13) 157.36, 154.39, 144,59, 137.11, 132.25,
128.56, 127.75, 127.19, 126.48, 124.28 121.15, 18.19, 14.13;
IR(KBr) 3091, 3065, 1605, 1547; MS m/z 338 (M+).
Anal. Calcd. for C17H14N4O4: C, 60.35; H, 4.17; N, 16.56;
Found: C, 60.44; H, 3.98; N, 16.32.
In conclusion, we have disclosed a one-pot efficient
microwave assisted synthesis of 4-alkyl-1,3-diarylpyra-
zoles in moderate to good yields from a -alkylacetophe-
none phenylhydrazones via Vilsmeier cyclization. In this
method, the reaction time has been brought down from
hours to seconds compared to conventional heating
method. Its broad scope as well as the easy access to the
starting materials and short reaction time under microwave
irradiation should make this methodology widely applica-
ble in organic synthesis.
4-Methyl-1-(4-Nitrophenyl)-3-phenylpyrazole (2c).
This compound was obtained as a pale yellow solid; 1H NMR
(300 MHz,CDC13): d 8.29 (d, J = 8.7 Hz, 2H), 7.87 (d, J = 8.7
Hz, 2H), 7.85 (s, 1H), 7.77 (d, J = 7.1 Hz, 2H) 7.36-7.48 (m,
3H), 2.32 (s, 3H); 13C NMR (75 MHz, CDC13): d 154.51,
144.86, 144.27, 132.82, 128.55 128.24, 127.59, 127.02, 125.32,
118.33, 117.73, 10.26; IR (KBr) 1596, 1509, 1330, 1308; MS m/z
279 (M+).
EXPERIMENTAL
Anal. Calcd. for C16H13N3O2: C, 68.81; H, 4.69, N, 15.04.
Found: C, 68.37; H, 4.54; N, 15.31.
Melting points were uncorrected. Infrared spectra were
recorded as KBr pellets on a Nicolet Impact 400 spectrometer.
1H NMR and 13C NMR spectra were recorded on a Bruker spec-
trometer operating at 300 MHzand at 75 MHz respectively, using
CDC13 solvent with TMS as the internal standard. Mass spectra
were obtained on a Hewlett Packard 5890 Series II with an HP
5971A mass selective detector.
4-Ethyl-1-(4-nitrophenyl)-3-phenylpyrazole (2d).
This compound was obtained as a yellow solid; 1H NMR (300
MHz, CDC13): d 8.30 (d, J = 8.9Hz, 2H) 7.88 (d, J = 8.9Hz, 2H)
7.86 (s.1H) 7.73 (d, J = 7.4 Hz, 2H) 7.88 (d, J = 8.9 Hz, 2H),
7.86 (s.1H), 7.73 (d, J = 7.4 Hz, 2H), 7.36-7.47 (m, 3H) 2.33 (q,
J = 7.4 Hz, 2H) 1.28 (t, J = 7.4 Hz, 3H); 13 C NMR (75 MHz,
CDC13) 153.15, 144.37, 144.24, 132.99, 128.56, 128.29, 127.79,
125.75, 125.57, 125.33, 117.78, 18, 17, 14.38; IR (KBr) 3063,
2964, 2926, 1593, 1512; MS m/z 293 (M+).
General Procedure for the Preparation of 4-Alkyl-1,3-diarylpyra-
zoles (2) Under Conventional Heating Method.
a -Alkylacetophenone phenylhydrazones 1a-h (0.005 mol) was
dissolved in 8 mL DMF, cooled to 0 °C and 1.4 mL of POC13,
was added dropwise over 10 min. The reaction mixture was then
heated at 90 °C for 4-5 h. The contents of the flask were poured
into crushed ice and left in the refrigerator overnight. The prod-
uct obtained was collected by filtration, washed with water and
dried. This crude material was purified by column chromatogra-
phy using 60 - 120 silica gel and petroleum ether-ethyl acetate
(80:20) solvent system as eluent to afford 2a-h. In the case of 2i,
the reaction mixture was stirred at room temperature for 5 h.
Anal. Calcd for C17H15N3O2: C, 69.61; H, 5.15; N, 14.32.
Found: C, 69.87; H, 5.04; N, 14.12.
1-(2,4-Dinitrophenyl)-4-methyl-3-(4-methylphenyl)pyrazole (2e).
This compound was obtained as a pale yellow crystalline solid;
1H NMR (300 MHz, CDC13): d 9.00 (s, 1H), 8.44 (d, J = 9.0 Hz,
1H), 7.82 (d, J=9.0 Hz, 1H), 7.60(s, 1H), 7.52 (d, J = 7.9 Hz,
2H), 7.36 (d, J = 7.9Hz 2H), 2.37 (s, 3H), 2.29(s, 3H); 13C NMR
(75 MHz, CDC13: d 161.59, 154.75, 138.41, 136.88,
129.60,129.38, 128.45, 126.42, 126.84, 126.28, 124.11, 114.10,
104.47, 21.13, 10.16; IR (KBr) 1602, 1552, 1523, 1359, 1245;
MS m/z 338 (M+).
General Procedure for the Preparation of 4-Alkyl-1,3-diarylpyra-
zoles (2) Under Microwave Irradiation Method.
Anal. Calcd. for C17H14N4O4: C, 60.35; H, 4.17; N, 16.56.
Found: C, 60.12; H, 4.31; N, 16.72.
a -Alkylacetophenone phenylhydrazones 1a-h (0.005 mol) was
dissolved in 8 mL DMF, cooled to 0 °C and 1.4 mL of POC13,
was added drop wise over 10 min. Then the reaction mixture was
subjected to microwave irradiation for 30 - 50 sec at 30% power
(210 W). After the usual work-up, the crude product was purified
by column chromatography.
1-(2,4-Dinitrophenyl)-4-ethyl-3-(4-methylphenyl)pyrazole (2f).
This compound was obtained as a pale yellow solid; 1H NMR
(300 MHz, CDC13): d 8.62 (s, 1H), 8.43 (d, J = 9.0 Hz 1H), 7.83
,
(d, J = 9.0 Hz, 1H) 7.59 (s, 1H), 7.54 (d, J = 8.1 Hz, 2H), 7.22
(d, J = 8.1 Hz, 2H), 2.71 (q, J = 7.4 Hz, 2H), 2.37(s, 3H), 1.26
(t, J = 7.4 Hz, 3H); 13C NMR (75 MHz, CDC13): d 154.48,
144.48, 138.59, 137.16, 129.40, 129.30, 127.69, 127.62, 127.19,
126.46, 124.20, 121, 19, 21.31, 18.26, 14.13; IR (KBr) 3054,
2942, 1531; MS m/z 352 (M+).
1-(2,4-Dinitrophenyl)-4-methyl-3-phenylpyrazole (2a).
This compound was obtained as a pale yellow solid; 1H NMR
(300 MHz, CDC13): d 8.61 (s, 1H), 8.43 (d, J = 9.3 Hz 1H), 7.80
,
(d, J = 9.3 Hz, 1H), 7.68 (d, J = 8.2 Hz, 2H), 7.61 (s, 1H), 7.36 -
7.45 (m, 3H) 2.31 (s, 3H); 13C NMR (75 MHz CDC13): d 154.80,
144.58, 142.26, 136.98, 132.11, 129.08, 128.45, 127.63, 127.23,
124.26, 121.13, 119.29, 10.29; IR (KBr) 1603, 1553, 1520, 1336;
MS m/z 324 (M+).
Anal. Calcd. for C18H16N4O4: C, 61.36; H, 4.58; N, 15.90.
Found: C, 61.12; H, 4.74; N, 16.15.
4-Methyl-3-(4-methylphenyl)-1-(4-nitrophenyl)pyrazole (2g).
This compound was obtained as a pale yellow solid; 1H NMR
(300 MHz, CDC13): d 8.32 (d, J = 8.4 Hz, 2H), 7.68 (d, J = 8.4
Anal. Calcd. for C16H12N4O4: C, 60.35; H, 4.17; N, 16.56.
Found: C, 60,44; H, 3.98; N, 16.32.