Thermal cyclization of 3-(1-naphthyl)-1-phenylpyrazole- 4-carboxylic acid in polyphosphoric acid [12]

Full text of DOI:10.1023/A:1021246424314

Chemistry of Heterocyclic Compounds, Vol. 38, No. 9, 2002
THERMAL CYCLIZATION OF
3-(1-NAPHTHYL)-1-PHENYLPYRAZOLE-
4-CARBOXYLIC ACID IN POLYPHOSPHORIC ACID
1
2
2
M. K. Bratenko , V. A. Chornous , and M. V. Vovk
Keywords: pyrazole-4-carboxylic acids, phenaleno[2,3-c]pyrazole, cyclization.
The thermal decarboxylation of pyrazole-4-carboxylic acids is used as a major method for the synthesis
of pyrazoles unsubstituted at C(4) [1-3]. In particular, 1,3-diphenylpyrazole is obtained by heating 1,3-diphenyl-
4
-carboxylic acid in quinoline at reflux in the presence of copper powder [4].
We have found that 1,3-disubstituted pyrazole-4-carboxylic acids 1a and 1b are converted upon heating
in polyphosphoric acid at 180°C to pyrazoles 2a and 2b. On the other hand, heating acid 1c, which contains an
α-naphthyl group at C(3) of the pyrazole ring, under analogous conditions leads not to decarboxylation, but
rather intramolecular acylation to give a new heterocyclic system, phenalenopyrazole 3, as the result of attack of
the carboxylic acid group at C(8) in the naphthalene ring.
Ar
–
CO2
N
N
COOH
N
Ph
Ar
2a,b
PPA
N
o
1
80 C
O
N
Ph
1
a–c
–
H O
2
N
3
Ph
1
, 2 a Ar = Ph, b Ar = 2-thienyl, 1c Ar = 1-C10
H
7
1
The H NMR spectra were taken on a Varian VXR-300 spectrometer at 300 MHz, DMSO-d
spectrum was taken on a UR-20 spectrometer in a KBr pellet.
6
. The IR
A sample of acid 1a-c (0.005 mol) was added to polyphosphoric acid (50 g) obtained by dissolving P
O
2 5
(
25 g) in 85% phosphoric acid (25 g). The suspension was heated to 180°C and maintained at this temperature
for 2 h, cooled, and poured onto 200 g of ice. The residue was filtered off, dried, and recrystallized.
,3-Diphenylpyrazole (2a) was obtained in 69% yield; mp 83-84°C (ethanol) (mp 84°C [4]). H NMR
spectrum, δ, ppm, J (Hz): 8.57 (1H, d, J = 2.4, 5-H); 7.96-7.92 (4H, m, o-Ph); 7.56-7.33 (6H, m, m-, p-Ph); 7.05
1
1
(
1H, d, J = 2.4, 4-H).
_
_________________________________________________________________________________________
1
Bukovina State Medical Academy, 58000 Chernovtsy, Ukraine; e-mail: chornous@chv.ukrpack.net.
2
Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 02094 Kiev, Ukraine; e-mail:
hetfos@ukrpack.net. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1311-1312,
September, 2002. Original article submitted September 19, 2000. Submitted after revision April 15, 2001.
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156
0009-3122/02/3809-1156$27.00©2002 Plenum Publishing Corporation

1
-Phenyl-3-(2-thienyl)pyrazole (2b) was obtained in 48% yield; mp 52-53°C (2:1 hexane–benzene).
H NMR spectrum, δ, ppm, J (Hz): 8.53 (1H, d, J = 2.7, 5-H); 7.87 (2H, d, J = 7.7, o-Ph); 7.60-7.43 (4H, m, m-,
p-Ph, H thienyl); 7.30 (1H, t, J = 6.8, H thienyl); 7.12 (1H, m, H thienyl). 6.92 (1H, d, J = 2.7, 4-H). Found, %:
C 69.29; H 4.42; N 12.24. C13 S. Calculated, %: C 69.00, H, 4.45; N 12.38.
-Oxo-2-phenylphenaleno[2,3-c]pyrazole (3) was obtained in 76% yield; mp 243-245°C (dioxane).
1
H
10
N
2
4
-1
1
IR spectrum, ν, cm : 1670 (C=O). H NMR spectrum, δ, ppm, J (Hz): 9.33 (1H, s, 3-H); 8.58 (1H, d, J = 7.8,
-H); 8.51 (1H, d, J = 7.8, 8-H); 8.38 (1H, d, J = 7.8, 5-H); 8.21 (1H, d, J = 7.8, 10-H); 8.11 (2H, d, J = 7.7,
7
o-HPh); 7.83 (1H, t, J = 7.8, 6-H); 7.78 (1H, t, J = 7.8, 9-H); 7.60 (2H, m, m-HPh); 7.45 (1H, t, J = 7.7, p-HPh).
Found, %: C 80.84; H 4.23; N 9.62. C20
H
12
N O. Calculated, %: C 81.07; H 4.08; N 9.45.
2
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