The condensation of (chlorocarbonyl)phenyl ketene with bisnucleophiles. synthesis of 4-hydroxy-5-phenylpyro-[2,3-c]pyrazol-6-ones and formation of pyrazolo[1,2-a]pyrazole-triones by hydrogen exchange in unstable mesoionic compounds

Article abstract of DOI:10.1071/CH09344

The addition of (chlorocarbonyl)phenyl ketene 2 to 5-alkylpyrazol-3(4H)- ones 1 led to the formation of 3-hydroxypyrazolo[1,2-a]pyrazole-dione/ pyrazolo[1,2-a]pyrazole-trione derivatives 3. This is ascribed to hydrogen exchange in initially formed unstabl

Full text of DOI:10.1071/CH09344

Full Paper
CSIRO PUBLISHING
Aust. J. Chem. 2010, 63, 92–95
www.publish.csiro.au/journals/ajc
The Condensation of (Chlorocarbonyl)phenyl Ketene with
Bisnucleophiles. Synthesis of 4-Hydroxy-5-phenylpyro-
[2,3-c]pyrazol-6-ones and Formation of Pyrazolo[1,2-a]
pyrazole-triones by Hydrogen Exchange in Unstable
Mesoionic Compounds
Mehdi Abaszadeh,A Hassan Sheibani,A,B and Kazem SaidiA
ADepartment of Chemistry, Shahid Bahonar University of Kerman, Kerman 76169, Iran.
BCorresponding author. Email: hsheibani@mail.uk.ac.ir
The addition of (chlorocarbonyl)phenyl ketene 2 to 5-alkylpyrazol-3(4H)-ones 1 led to the formation of 3-
hydroxypyrazolo[1,2-a]pyrazole-dione/pyrazolo[1,2-a]pyrazole-trione derivatives 3. This is ascribed to hydrogen
exchange in initially formed unstable, mesoionic pyrazolo[1,2-a]pyrazol-4-ium-5-olates. In contrast, condensation of the
same ketene with 3-alkyl-1-phenyl-2-pyrazolin-5-ones 4 afforded 4-hydroxy-3-alkyl-1,5-diphenylpyrano[2,3-c]pyrazol-
6-one derivatives 5. The latter reaction provides a new and rapid route to 4-hydroxy-2-pyrones fused to pyrazole rings, in
good to excellent yields.
Manuscript received: 18 June 2009.
Manuscript accepted: 29 July 2009.
Introduction
ketene 2 with 5-alkylpyrazol-3(4H)-ones was investigated. The
pyrazolones can in principle react as 1,2- or 1,3-bisnucleophiles
to form either pyrazolopyrone or pyrazolopyrazolone derivatives
(Scheme 1). In the reactions with N-unsubstituted pyrazolones,
specific 1,2-bisnucleophilic cycloaddition took place, and
pyrazolo[1,2-a]pyrazole-trione derivatives 3a–c were obtained
in good to excellent yields in short experimental procedures
(Scheme 1). They exist in two tautomeric forms I and II as
described below.
α-Oxoketenes are versatile bifunctional reagents for the synthe-
sis of numerous heterocyclic compounds. The reactions of bis-
nucleophiles with these ketenes leads to cyclic compounds,
as has been reported in several papers.[1–4] 5-Alkylpyrazol-
3(4H)-ones have been found to be very effective 1,2- and
1,3-bisnucleophilic reagents, which react with a wide vari-
ety of electrophiles under mild experimental conditions; they
have been used mainly for the synthesis of condensed poly-
functionally substituted pyrazolones.[5–7] These compounds
have four electron rich centres at the two nitrogens, oxy-
gen and C4, thus they can react with electrophiles.[8–10] In
this paper, we describe the preparation of 4-hydroxy-2-pyrones
fused to pyrazole rings by nucleophilic additions of pyra-
zolones 1 to (chlorocarbonyl)phenyl ketene 2. The 2-pyrone
moiety is an important structural motif present in many
molecules that show a broad range of biological activities such
as anti-HIV,[11] antimicrobial,[12] antifungal,[13] phytotoxic,[14]
anti-leukemic,[15] anti-Alzheimer,[16] and anti-inflammatory[11]
properties. 2-Pyrones are used in organic synthesis as building
blocks for more complex chemical structures because they may
participateinavarietyofcycloadditionreactionstoformbicyclic
lactones. For example, they readily undergo Diels–Alder reac-
tions with alkynes, producing substituted benzenes upon loss
of carbon dioxide.[17] 2-Pyrone also forms the core structure
of a variety of natural organic compounds. For example, the
coumarins are an important class of benzo-fused 2-pyrones.
5-Alkylpyrazol-3(4H)-ones exist in three tautomeric forms
due to their keto-enol or lactam-lactime tautomerism, and this
phenomenon is confirmed by spectral data (Scheme 2).[18,19]
Several high-level molecular orbital studies have been per-
formed on the tautomeric structures of the unsubstituted
pyrazolin-5-one ring in the gas phase and in solution.[20–22]
Hillier and coworkers[20] reported that the most stable form in
the gas phase is the CH tautomer, while Cao et al. and Luque
et al.[21] considered the OH tautomer the most stable. When
solvent effects were included, either the NH or CH tautomers
were found to be the most stable, depending on the method
used to simulate solvation. All three tautomeric forms have been
observed experimentally.[22] There are several reports in the lit-
erature on the condensation of (chlorocarbonyl)phenyl ketene
with pyrazoles, 1,2,3-triazoles, and 1,2,4-triazoles to gener-
ate mesoionic compounds.[23–25] When (chlorocarbonyl)phenyl
ketene 2 was added to a refluxing tetrahydrofuran solution
of the 5-alkylpyrazol-3(4H)-one derivative, the solution turned
red, thus suggesting the generation of an unstable mesoionic
compound (Scheme 3). The colours faded to yellow on contin-
ued heating. The short lifetimes of the red mesoionic pyrazolo
[1,2-a]pyrazol-4-ium-5-olates would be due to their tauto-
merizationto3-hydroxypyrazolo[1,2-a]pyrazole-dione/pyrazolo
Results and Discussion
In order to access analogues of 4-hydroxy-2-pyrones fused
to pyrazole rings, the condensation of (chlorocarbonyl)phenyl
© CSIRO 2010
10.1071/CH09344
0004-9425/10/010092

Condensation of (Chlorocarbonyl)phenyl Ketene with Bisnucleophiles
93
OH
O
O
O
R
R
Ph
O
Ph
O
N
N
N
H
N
H
Not formed
R
N
O
O
O
R
O
O
R
Ph
– HCl
N
N
N
ꢀ
C
C O
N
Cl
N
H
O
OH
O
Ph
Ph
1a–c
2
3I
3II
R
R
N
1a R ꢁ methyl
1b R ꢁ propyl
1c R ꢁ isopropyl
N
N
O
N
O
O
O
HO
O
Ph
Ph
Not formed
Scheme 1. Reaction of N-unsubstituted pyrazole-3(4H)-ones with (chlorocarbonyl)phenyl ketene.
R
R
OH
O
R
R
R
Ph
O
Dry THF
– HCl
Ph
N
N
N
N
H
O
N
H
OH
ꢀ
N
H
O
C
C O
H
N
Cl
N
N
O
N
O
Ph
Keto form
(CH)
Enol form
(OH)
Keto form
(NH)
Ph
4a–e
2
5a R ꢁ trifluoromethyl
5b R ꢁ methyl
5c R ꢁ ethyl
Scheme 2. Tautomerism in pyrazole-3(4H)-ones.
5d R ꢁ propyl
5e R ꢁ isopropyl
H
R
O
O
R
O
O
R
O
O
O
Scheme 4. Reaction of N-substituted pyrazole-3(4H)-ones with (chloro-
carbonyl)phenyl ketene.
N
N
ꢀN
N
N
N
OH
ꢂO
Ph
Ph
Ph
R
R
Ph
ꢀ
C
C O
Scheme 3. Tautomerization of mesoionic pyrazolo[1,2-a]pyrazol-4-ium-
5-olates to 3-hydroxypyrazolo[1,2-a]pyrazole-diones/pyrazolo [1,2-a]
pyrazole-triones 3.
N
Cl
N
N
OH
N
O
O
Ph
Ph
Oꢂ
O
H
R
C
O
R
Ph
O
Ph
[1,2-a]pyrazole-trione derivatives by intermolecular hydrogen
exchange (Scheme 3).
Product
N
N
N
N
O
O
ꢀ
The spectral data for the isolated compounds 3 demonstrate
that they exist as mixtures of the hydroxydione I and trione II
tautomers (Schemes 1 and 3).Thus, the IR spectra of compounds
3a–c revealed a strong absorption at 3150–2870 cm−1 attributed
to the OH group in the dione tautomer 3I (Scheme 1). In the 1H
NMR spectra, the OH proton appears at 13–12 ppm as a singlet.
The spectrum of the trione tautomer 3II exhibited a singlet at
5.4–5.0 ppm, which is attributed to the malonyl-type proton at
C3.
In contrast to the reaction described in Schemes 1 and
3, the cycloaddition reactions described in Scheme 4 were
accomplished by mixing equimolar quantities of (chlorocar-
bonyl)phenyl ketene 2 and N-substituted pyrazolones 4 in
a dry solvent at ambient temperature. 4-Hydroxypyrano[2,3-
c]pyrazol-6-ones 5 were the only products.
Ph
Ph
Scheme 5. Proposed mechanism for the formation of pyranopyrazolones 5.
The structures of 5a–e were determined on the basis of their
elemental analyses, mass spectra, 1H- and 13C-NMR and IR
spectral data. Only one product was obtained in each case. The
1H NMR spectrum of 5a indicated two kinds of protons along
with one signal at low field (10.90 ppm) attributed to the OH
group. This assignment is consistent with literature precedents
for related compounds.[1,3,22]
Conclusions
The 2-phenylpyrazol-3(4H)-ones 4a–e can exist in either the
CH or OH tautomeric forms, as shown in Scheme 5. A plausible
mechanism for the formation of 5 therefore involves the reac-
tion of the ketene with the enol 5-alkyl-2-phenylpyrazol-3-ol
(Scheme 5).[26,27]
In summary, we have shown that the condensation of (chloro-
carbonyl)phenyl ketene 2 with 1,2- and 1,3-bisnucleophilic
pyrazol-3-one derivatives provides a convenient and rapid syn-
thesis of pharmacologically interesting compounds in high
yields. Furthermore, no cumbersome apparatus is needed; the

94
M. Abaszadeh, H. Sheibani, and K. Saidi
precipitate from the reaction mixtures, and their purification is
straightforward.
H 5.22, N 10.36%). νmax(KBr)/cm−1 3080 (broad, OH), 1762,
1742, 1685. δH (500 MHz, d6-DMSO) 11.83 (1H, s, OH), 8.02
(2H, d, 3JHH 6.78, ArH), 7.15 (2H, t, 3JHH 7.50, ArH), 6.87 (1H,
3
Experimental
t, JHH 6.79, ArH), 5.70 (1H, s, H6), 5.34 (1H, s, malonyl-H
on C2 keto), 3.37 (1H, m, CH), 1.20 (6H, d, 3JHH 6.78, 2CH3).
δC (125 MHz, d6-DMSO) 161.82, 161.46, 160.92, 158.09 (C=O
andC7), 135.99, 131.05, 130.05, 129.14, 126.05, 124.22, 123.30,
98.25 (C6), 88.57 (C2 enol), 67.87 (C2 keto), 26.82, 21.72. m/z
(ES-MS): 270 (100%, [M]+), 242 (10), 214 (8), 145 (38), 125
(10), 118 (98), 111 (12), 89 (37), 67 (10), 53 (12).
General Procedures
(Chlorocarbonyl)phenyl ketene 2 was prepared according to the
literature procedure.[28] The 5-alkyl-pyrazol-3(4H)-ones 1a–c
and 5-alkyl-2-phenylpyrazol-3-ones 4a–e were known and pre-
pared according to the reported procedure.[29] Solvents were
dried over sodium and distilled before use. Melting points were
determined on a Gallenkamp melting point apparatus and are
uncorrected. IR spectra were measured on a Mattson 1000 FT-IR
spectrophotometer. 1H NMR and 13C NMR spectra were deter-
mined on a Bruker DRX-500 AVANCE spectrometer at 500 and
125.77 MHz, respectively. Mass spectra were recorded on a Shi-
madzu QP 1100EX mass spectrometer operating at an ionization
potential of 70 eV. Elemental analyses were performed using a
Heracus CHN-O-Rapid analyzer.
General Procedure for Compounds 5
(Chlorocarbonyl)phenyl ketene (2 mmol) was added to 2-
phenyl-5-(trifluoromethyl)pyrazol-3(4H)-one (2 mmol) in dry
THF (20 mL) with stirring at ambient temperature over the
course of 20 min. The solid product was collected and recrystal-
lized from n-hexane/THF (2:3).
4-Hydroxy-1,5-diphenyl-3-(trifluoromethyl)pyrano
[2,3-c]pyrazol-6-one 5a
General Procedure for Compounds 3
Yield 0.37 g (82%), grey crystals, mp 214–216◦C (Found:
C 61.11, H 2.69, N 7.41%; C19H11F3N2O3 requires C 61.30,
H 2.98, N 7.52%). νmax(KBr)/cm−1 3204 (broad, OH), 1706,
1682, 1659. δH (500 MHz, d6-DMSO) 10.90 (1H, s, OH), 7.96–
7.31 (10H, m, ArH). δC (125 MHz, d6-DMSO) 161.44 (C=O),
132.20, 130.53, 129.58, 129.34, 128.68, 122.91, 121.26 (q, 1JC-F
267.75, CF3), 101.39, 97.97. m/z (ES-MS): 372 (100%, [M]+),
352 (13), 255 (21), 235 (25), 118 (90), 90 (20), 77 (42), 51 (13).
5-Methylpyrazol-3(4H)-one (2 mmol) was dissolved in boil-
ing anhydrous THF (20 mL), and a mixture of (chlorocar-
bonyl)phenyl ketene (2 mmol) in 5 mL dry THF was added drop
wise over 2 min, which caused the colour of the solution to
changetored.Thereactionmixturewasheatedatrefluxfor1/2 h,
during which time it turned yellow. The reaction mixture was
cooled, and the solid product was collected and recrystallized
from dry n-hexane/THF (2:3).
2
160.84, 151.41, 136.70, 135.45 (q, JC-F 39.25, C3), 135.28,
7-Methyl-2-phenyl-1H,5H-pyrazolo[1,2-a]pyrazolone 3a
4-Hydroxy-3-methyl-1,5-diphenylpyrano[2,3-c]pyrazol-
6-one 5b
Yield 0.17 g (87%), pale green crystals, mp 165–166◦C
(Found: C 64.32, H 3.83, N 11.46%; C13H10N2O3 requires C
64.46, H 4.16, N 11.56%). νmax(KBr)/cm−1 3105 (broad, OH),
1765, 1742, 1661, 1617. δH (500 MHz, d6-DMSO) 11.13 (1H,
Yield 0.33 g, (97%) white crystals, mp 232–234◦C (Found:
C 71.32, H 4.07, N 8.81%; C19H14N2O3 requires C 71.69, H
4.43, N 8.80%). νmax(KBr)/cm−1 3150 (broad, OH), 1710, 1682,
1659. δH (500 MHz, d6-DMSO) 11.63 (1H, s, OH), 7.78–7.29
(10H, m, ArH), 2.42 (3H, s, CH3). δC (125 MHz, d6-DMSO)
163.43 (C=O), 162.20, 150.87, 144.92, 137.61, 132.86, 132.34,
130.39, 129.20, 128.31, 127.96, 121.33, 99.39, 98.67, 14.81. m/z
(ES-MS): 318 (28%, [M]+), 200 (100), 132 (13), 118 (15), 91
(28), 77 (25), 67 (12), 51 (11).
3
3
s, OH), 8.03 (2H, d, JHH 7.04, ArH), 7.15 (2H, t, JHH 7.62,
ArH), 6.88 (1H, t, 3JHH 6.70, ArH), 6.06 (1H, s, H6), 5.31 (1H,
s, malonyl-H on C2 keto), 2.37 (3H, s, CH3). δC (125 MHz, d6-
DMSO) 170.57, 162.29, 161.40, 150.95 (C=O and C7), 136.22,
128.33, 124.07, 123.14, 101.40 (C6), 85.21 (C2 enol), 67.87 (C2
keto), 13.36. m/z (ES-MS): 242 (80%, [M]+), 186 (8), 145 (35),
118 (100), 89 (65), 77 (10), 63 (22), 51 (12).
3-Ethyl-4-hydroxy-1,5-diphenylpyrano[2,3-c]pyrazol-
6-one 5c
2-Phenyl-7-propyl-1H,5H-pyrazolo[1,2-a]pyrazolone 3b
Yield 0.20 g (80%), pale yellow crystals, mp 113–116◦C
(Found: C 66.32, H 5.46, N 10.65%; C15H14N2O3 requires C
66.66, H 5.22, N 10.36%). νmax(KBr)/cm−1 3050 (broad, OH),
1760, 1713, 1659, 1647. δH (500 MHz, d6-DMSO) 12.56 (1H,
Yield 0.35 g (94%), white crystals, mp 214–216◦C (Found:
C 72.08, H 4.62, N 8.26%; C20H16N2O3 requires C 72.28, H
4.85, N 8.43%). νmax(KBr)/cm−1 3100 (broad, OH), 1706, 1682,
1600. δH (500 MHz, d6-DMSO) 11.36 (1H, s, OH), 7.79–7.30
(10H, m, ArH), 2.82 (2H, q, 3JHH 7.42, CH2), 1.25 (3H, t, 3JHH
7.42, CH3). δC (125 MHz, d6-DMSO) 163.59 (C=O), 162.20,
150.93, 150.30, 137.68, 132.99, 132.35, 130.37, 129.18, 128.24,
127.93, 121.38, 99.24, 98.08, 22.35, 13.76. m/z (ES-MS): 332
(34%, [M]+), 214 (100), 146 (10), 118 (12), 91 (22), 77 (24),
51 (8).
3
s, OH), 8.05 (2H, d, JHH 6.77, ArH), 7.14 (2H, t, JHH 7.52,
ArH), 6.87 (1H, t, 3JHH 6.68, ArH), 5.72 (1H, s, H6), 5.30 (1H,
3
s, malonyl-H on C2 keto), 2.75 (2H, t, JHH 7.40, CH2), 1.62
(2H, m, CH2), 0.91 (3H, t, 3JHH 7.30 Hz, CH3). δC (125 MHz,
d6-DMSO) 162.13, 161.61, 158.16, 154.98 (C=O and C7),
136.30, 131.03, 129.07, 128.29, 127.99, 124.03, 123.05, 100.44
(C6), 90.24 (C2 enol), 67.87 (C2 keto), 28.88, 21.91, 14.40.
m/z (ES-MS): 270 (82%, [M]+), 145 (15), 118 (100), 98 (11),
90 (45), 89 (55).
4-Hydroxy-1,5-diphenyl-3-propylpyrano[2,3-c]pyrazol-
6-one 5d
Yield 0.36 g (90%), white crystals, mp 182–183◦C (Found:
C 72.58, H 5.03, N 8.05%; C21H18N2O3 requires C 72.82,
H 5.24, N 8.09%). νmax(KBr)/cm−1 3120 (broad, OH), 1729,
1682, 1612. δH (500 MHz, d6-DMSO) 11.45 (1H, s, OH), 7.79–
7.29 (10H, m, ArH), 2.78 (2H, t, 3JHH 7.30, CH2), 1.72 (2H, m,
7-Isopropyl-2-phenyl-1H,5H-pyrazolo
[1,2-a]pyrazolone 3c
Yield 0.21 g (84%), yellow crystals, mp 134–136◦C (Found:
C 66.28, H 5.49, N 10.47%; C15H14N2O3 requires C 66.66,

Condensation of (Chlorocarbonyl)phenyl Ketene with Bisnucleophiles
95
CH2), 0.93 (3H, t, 3JHH 7.28, CH3). δC (125 MHz, d6-DMSO)
163.38 (C=O), 162.14, 150.87, 149.01, 137.66, 132.83, 132.36,
130.36, 129.22, 128.33, 127.92, 121.36, 99.36, 98.17, 30.75,
22.34, 14.60. m/z(ES-MS): 346 (32%, [M]+), 318 (7), 228 (100),
200 (18), 118 (17), 91 (35), 77 (89), 65 (18), 51 (29).
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4-Hydroxy-3-isopropyl-1,5-diphenylpyrano
[2,3-c]pyrazol-6-one 5e
Yield 0.37 g (92%), white crystals, mp 171–172◦C (Found:
C 72.76, H 5.11, N 7.99%; C21H18N2O3 requires C 72.82,
H 5.24, N 8.09%). νmax(KBr)/cm−1 3157 (broad, OH), 1706,
1682, 1589. δH (500 MHz, d6-DMSO) 11.56 (1H, s, OH), 7.79–
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3
7.29 (10H, m, ArH), 3.31 (1H, m, CH), 1.31 (6H, d, JHH
6.76, 2CH3). δC (125 MHz, d6-DMSO) 163.33 (C=O), 162.06,
154.25, 150.96, 137.68, 132.85, 132.40, 130.36, 129.26, 129.16,
128.36, 127.96, 121.48, 99.33, 97.39, 28.71, 22.21. m/z(ES-
MS): 346 (30%, [M]+), 228 (100), 213 (10), 160 (5), 118 (7),
91 (16), 77 (22), 65 (5), 51 (7).
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Acknowledgements
The authors express appreciation to the Shahid Bahonar University of
Kerman Faculty Research Committee for its support of this investigation.
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