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19. Chemicals were purchased from Fluka, Merck, Riedel-
dehaen AG, and Aldrich chemical companies. Yields refer
to isolated pure products. The oxidation products were
characterized by comparison of their spectral (IR, and 1H
NMR) and physical data with authentic samples. All
1,3,5-trisubstituted pyrazolines,22 4-substituted triazoline-
diones,15,21 2-imidazolines18 were synthesized according to
our previously reported procedure.
20. Typical procedure for oxidation of pyrazolines: a mixture
of 1,3,5-triphenylpyrazoline 2b (0.301 g, 1 mmol) and 4-(p-
chloro)phenyl-1,3,4-triazole-3,5-dione 1e (0.209 g, 1 mmol)
in CH2Cl2 (20 mL) was stirred vigorously at room
temperature for 15 min. The crude 1,3,5-trisubstituted
pyrazole 3 was obtained by simple filtration and evapo-
ration of the solvent. Highly pure pyrazole 3 could be
obtained simply by column chromatography (eluent
EtOAc–n-hexane, 2:8). The solvent was evaporated and
the pyrazole 3b was obtained as a yellow solid in 70%
yield, mp 133–134 °C [Lit.10 mp 138–139 °C]; IR (KBr):
3120, 3060, 1595, 1482 (cmÀ1); 1H NMR (CDCl3,
90 MHz): d 6.86 (1H, S, CH), 7.32 (10H, m, Ar), 7.96
(5H, m, Ar).
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