Facile Conversion of Pyrazolines to Pyrazole
J. Chin. Chem. Soc., Vol. 51, No. 6, 2004 1375
tions.12,13 Of course, this reaction was examined with SiO2 in
the absence of N-bromosulfonamide, and the progress of the
reaction was not observed.
267-270d °C, was 90%. The reagent was identified by NMR,
IR spectroscopies. IR spectrum (KBr pellets): 3070, 1620,
1
1310, 1130 cm-1. H NMR (acetone-d6): d 7.9 (t, 1H), 8 (d,
In conclusion, the presented method is an efficient and
selective protocol for aromatization of 1,3,5-trisubstituted
pyrazolines to pyrazoles. Thus, microwave irradiation could
be used for the oxidation of a wide variety of pyrazoline de-
rivatives with BNBTS and TBBDA in the presence of a cata-
lytic amount of SiO2. Also, the results show that the mole of
SiO2 in TBBDA is approximately 50% that of in BNBTS.
2H), 8.3 (s, 1H). 13C NMR spectrum (acetone): d 123.4,
128.7, 127.9, 122.3.
General procedure for oxidation of 1,3,5-trisubstituted
pyrazoline with TBBDA or BNBTS
A mixture of 1,3,5-trisubstituted pyrazoline 3 (1
mmol), BNBTS or TBBDA (1 mmol) and SiO2 (0.014-0.02
mmol) was introduced in a flask and was irradiated in a mi-
crowave oven at a power output of 1000 W for the appropri-
ate time as indicated in Tables 1 and 2. After irradiation and
monitoring on TLC (hexan:aceton, 10:1), the product is ex-
tracted with carbon tetrachloride; K2CO3 (0.5 g) was added
and stirred for 0.5 h, and the insoluble sulfonamide 1 or 2 was
removed by filtration and washed with cold carbon tetrachlo-
ride (10 mL). Removal of the solvent under reduced pressure
gave the crude product. The pure product 4 was obtained by
recrystalization with methanol/H2O (10:1).
EXPERIMENTAL
IR and NMR spectra were recorded using a Shimadzu
435-U-04 spectrophotometer (KBr pellets) and a 90 MHz
Jeol FT-NMR spectrometer, respectively. A Butane Indus-
trial Co. microwave (220 v, 1000 w) was used for the micro-
wave irradiations.
Procedure for preparation of benzene-1,3-disulfonyl-
amide
To benzene-1,3-disulfonyl acid sodium salt (0.016 mol)
was added PCl5 (0.0165 mol) as chlorination agent. For start-
ing the reaction, the vessel should be heated (40-50 °C), then
the reaction completes spontaneously. After complete con-
version (2 h), crushed ice (100 g) was added; the product was
separated from inorganic materials by chloroform. Then to
the solution was added NH3 (l) (400 mL); the reaction mix-
ture was stirred with a mechanical stirrer. After complete ad-
dition, removal of the solvent under reduced pressure gave
the crude product. The pure product (90%, m.p. 228-230 °C)
was obtained by crystallization with ethanol. IR spectrum
(KBr pellets): 3320, 3090, 1600, 1320, 1130 cm-1. 1H NMR
(acetone-d6): d 6.7 (s, 4H), 7.7 (t, 1H), 8.1 (d, 2H), 8.3 (s, 1H).
13C NMR: 124.2, 130.6, 129.8, 124.2.
Received February 24, 2004.
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Procedure for preparation of N,N,N¢,N¢-Tetrabromo-
benzene-1,3-disulfonylamide [TBBDA]
N,N,N¢,N¢-Tetrabromo-benzene-1,3-disulfonylamide
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sodium hydroxide solution (3 M) at room temperature and
was the solution transferred to a beaker. Then bromine
(0.0584 mol) was added to the solution with vigorous stir-
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