Pifa-mediated oxidative cyclization of 1-carbamoyl-1-oximylcycloalkanes: synthesis of spiro-fused pyrazolin-5-one N-oxides

Article abstract of DOI:10.1021/ol802952e

A convenient and efficient synthesis of spiro-fused pyrazolin-5-one N-oxides starting from readily available 1-carbamoyl-1-oximylcycloalkanes is developed. This general protocol features a novel and facile way for access to the five-membered azaheterocycl

Full text of DOI:10.1021/ol802952e

ORGANIC
LETTERS
2009
Vol. 11, No. 4
1015-1018
PIFA-Mediated Oxidative Cyclization of
1-Carbamoyl-1-oximylcycloalkanes:
Synthesis of Spiro-Fused
Pyrazolin-5-one N-Oxides
Kewei Wang,† Xiaolan Fu,† Jinying Liu,† Yongjiu Liang,‡ and Dewen Dong*,†,‡
Department of Chemistry, Northeast Normal UniVersity, Changchun, 130024, China,
and Changchun Institute of Applied Chemistry, Chinese Academy of Sciences,
Changchun, 130022, China
dongdw663@nenu.edu.cn
Received December 23, 2008
ABSTRACT
A convenient and efficient synthesis of spiro-fused pyrazolin-5-one N-oxides starting from readily available 1-carbamoyl-1-oximylcycloalkanes
is developed. This general protocol features a novel and facile way for access to the five-membered azaheterocycles by formation of a new
N-N single bond. The key cyclization step utilizes the formation of an N-oxonitrenium intermediate, mediated by the hypervalent iodine
reagent PIFA, and its subsequent intramolecular trapping by the amide moiety under rather mild experimental conditions.
The pyrazolin-5-one ring makes up the core structure of
numerous pharmaceutically active compounds, such as
edaravone.1,2 As an important class of aza-heterocycles,
pyrazolin-5-ones and their heterocyclic fused analogues have
found considerable utility as pharmaceutical agents,3 syn-
thetic scaffolds in combinatorial and medicinal chemistry,4
photographic couplers,5 chelating agents in coordination
chemistry,6 and agrochemical products.7 The therapeutic
importance of pyrazolin-5-one derivatives and their synthetic
versatility as intermediates in organic chemistry have directed
great research activity toward the construction of the skeleton
of this kind of heterocycle. The most notable method for
the synthesis of pyrazolin-5-ones involves the reactions
(3) (a) Yokoyama, N.; Ritter, B.; Neubert, A. D. J. Med. Chem. 1982,
25, 337–339. (b) Fryer, R. I.; Zhang, P.; Rios, R.; Gu, Z.-Q.; Basile, A. S.;
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P.; Nencini, C.; Pellerano, C.; Biggio, G.; Maciocco, A.; Tuligi, G.; Carrieri,
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X.; Huang, Q.; Yu, S.; Ma, C.; Mckerman, R.; Cook, J. M. Drug Des. Dis.
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E.; Mascia, M. P.; Pisu, M. G.; Biggio, G. Bioorg. Med. Chem. 2005, 13,
3531–3541. (f) Kimata, A.; Nakagawa, H.; Ohyama, R.; Fukuuchi, T.; Ohta,
S.; Suzuki, T.; Miyata, N. J. Med. Chem. 2007, 50, 5053–5056.
(4) (a) Attanasi, O. A.; Filippone, P.; Guidi, B.; Hippe, T.; Mantellini,
F.; Tietze, L. F. Tetrahedron Lett. 1999, 40, 9277–9280. (b) Lehmann, F.;
Holm, M.; Laufer, S. J. Comb. Chem. 2008, 10, 364–367.
† Northeast Normal University.
‡ Chinese Academy of Sciences.
(1) (a) Wiley, R. H.; Wiley, P. Pyrazolones, Pyrazolidones, and
DeriVatiVes; Weissberger, A., Ed.; Interscience: New York, 1964; Chapter
VIII, Vol. 20 of the series “The Chemistry of Heterocyclic Compounds”.
(b) Brune, K., Ed. Agents and Actions Supplements. 100 Years of
Pyrazolone Drugs. An Update; Birkhaeuser Verlag: Basil, Switzerland, 1986;
(5) (a) Yasuda, H.; Midorikawa, H. J. Org. Chem. 1966, 31, 1722–
1725. (b) Fleckenstein, L. J. The Theory of the Photographic Process, 4th
ed.; James, T. H., Ed.; Macmillan: New York, 1977; p 356.
Vol. 19, p 355
.
(6) (a) Rheingold, A. L.; King, W. Inorg. Chem. 1989, 28, 1715–1719.
(b) Caruso, F.; Rossi, M.; Tanski, J.; Sartori, R.; Sariego, R.; Moya, S.;
Diez, S.; Navarrete, E.; Cingolani, A.; Marchetti, F.; Pettinari, C. J. Med.
Chem. 2000, 43, 3665–3670. (c) Caruso, F.; Pettinari, C.; Marchetti, F.;
Natanti, P.; Phillips, C.; Tanski, J.; Rossi, M. Inorg. Chem. 2007, 46, 7553–
7560.
(2) For activities of edaravone, see: (a) Watanabe, T.; Yuki, S.; Egawa,
M.; Nishi, H. J. Pharmacol. Exp. Ther. 1994, 268, 1597–1604. (b) Kawai,
H.; Nakai, H.; Suga, M.; Yuki, S.; Watanabe, T.; Saito, K. I. J. Pharmacol.
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1996, 21, 1014–1016
.
10.1021/ol802952e CCC: $40.75
Published on Web 01/27/2009
2009 American Chemical Society

between ꢀ-oxo esters, or their derivatives, with hydrazines.8
Other methods are reported by air oxidation of 1,2-hydrazino-
hydrazones,9 palladium-catalyzed carbonylation of 1,2-diaza-
1,3-buta-dienes,10 or rearrangement of an oxadiazole derived
from a 2-cyanoacetanilide.11
1H-pyrazoles and isoxazoles from 1-carbamyl-1-oximylcy-
clopropanes, in the presence of POCl3/DMF (Vilsmeier
reagent) and POCl3/CH2Cl2, respectively.17 Thus, in con-
nection with these previous studies and following on from
our research on the synthesis of highly valuable heterocycles
through an oxidative processes, we have prepared a series
of 1-carbamoyl-1-oximyl cycloalkanes from ꢀ-oxo amide
derivatives and examined their reactivity toward the envi-
ronmentally friendly reagent PIFA. As a result of these
studies, we have developed a facile and efficient synthesis
of spiro-fused cycloalkano-(C4)-pyrazolin-5-one N-oxides via
PIFA-mediated intramolecular N-N bond formation.
The substrates, 1-carbamoyl-1-oximylcycloalkanes 1, were
prepared by the reaction of 1-acyl-1-carbamyl cycloalkanes
with hydroxylamine (NH2OH·HCl) in the presence of NaOAc
in ethanol at room temperature in high yields (up to 95%).18
We then selected cyclopropyl oxime 1a from a series of
substrates 1 (see Table 1) as the model compound to examine
On the other hand, hypervalent iodine reagents have been
extensively used as the oxidation reagents in synthetic
organic chemistry.12 One such reagent, phenyliodine(III)-
bis(trifluoroacetate) (PIFA) has attracted considerable atten-
tion of research due to its ready availability, low toxicity,
ease of handling, and reactivity similar to that of heavy metal
reagents.13 Its efficient utilization in metal-free transforma-
tions relies on both the extremely mild reaction conditions
required and its ability to oxidize chemoselectively a wide
range of functionalities such as phenols, amines, sulfides,
and carbonyl compounds. Recently, Tellitu and co-workers
developed novel metal-free approaches to the synthesis of
nitrogen-containing heterocycles using properly substituted
amides and amines as synthetic precursors via a PIFA-
mediated oxidization process.14
During the course of our studies on the synthesis of carbo-
and heterocycles based on ꢀ-oxo amide derivatives,15 we
successfully achieved efficient synthesis of substituted isothi-
azol-3(2H)-ones and pyrrolin-4-ones from readily available
1-carbamoyl ketene dithioacetals and enaminones, respec-
tively, in the presence of PIFA, in which an intramolecular
N-S or N-C bond is formed.16 Very recently, we have
reported a one-pot divergent synthesis of fully substituted
a
Table 1. Reactions of 1 with PIFA/TFA in CH2Cl2
entry
1
n
R1
R2
2
yieldb (%)
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1f
1g
1h
1i
1j
1k
1l
1m
1n
1o
1p
1
1
1
1
1
1
1
3
3
3
3
3
3
3
3
3
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
C6H5
Me
C6H5
2a
2b
2c
2d
2e
2f
2g
2h
2i
2j
2k
2l
2m
2n
2o
2p
80
73
71
68
75
81
72
89
84
85
83
91
94
88
92
87
(7) Tomlin, G., Ed. The Pesticide Manual, 10th ed.; British Crop
Protection Pub.: Surrey, 1991.
4-MeC6H4
4-MeOC6H4
4-ClC6H4
2-MeC6H4
2-MeOC6H4
2,4-Me2C6H3
C6H5
4-MeC6H4
4-MeOC6H4
4-ClC6H4
2-MeC6H4
2-MeOC6H4
2,4-Me2C6H3
C6H5
(8) (a) Ghosh, C. K.; Mukhopadhyay, K. K. Synthesis 1978, 779–781.
(b) Chantegrel, B.; Gelin, S. Synthesis 1985, 548–550. (c) Colotta, V.;
Cecchi, L.; MeLani, F.; Palazzino, G.; Filacchioni, G. Tetrahedron Lett.
1987, 28, 5165–5168. (d) Colotta, V.; Cecchi, L.; Melani, F.; Palazzino,
G.; Filacchioni, G.; Martini, C.; Giannaccini, G.; Lucacchini, A. J. Pharm.
Sci. 1989, 78, 239–242. (e) Abass, M.; Mostafa, B. B. Bioorg. Med. Chem.
2005, 13, 6133–6144.
(9) Attanasi, O. A.; Crescentini, L. D.; Filippone, P.; Foresti, E.;
Mantallini, F. J. Org. Chem. 2000, 65, 2820–2823.
9
10
11
12
13
14
15
16
(10) Boeckman, R. K., Jr.; Reed, J. E.; Ge, P. Org. Lett. 2001, 3, 3651–
3653.
(11) Kim, C.-K.; Zielinski, P. A.; Maggiulli, C. A. J. Org. Chem. 1984,
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(12) For recent reviews, see: (a) Zhdankin, V. V.; Stang, P. J. Chem.
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3008. (c) Wirth, T. Top. Curr. Chem. 2003, 224, 185–208. (d) Tohma, H.;
Kita, Y. AdV. Synth. Catal. 2004, 346, 111–124. (e) Moriarty, R. M. J.
Org. Chem. 2005, 70, 2893–2903. (f) Wirth, T. Angew. Chem., Int. Ed.
2005, 44, 3656–3665.
Me
a Reagents and conditions: 1 (1.0 mmol), PIFA (1.1 mmol), TFA (3.0
mmol), CH2Cl2 (11 mL), 0 °C, 1.5-4.5 h. b Isolated yield.
(13) (a) Kikugawa, Y.; Kawase, M. Chem. Lett. 1990, 581–582. (b)
Wardrop, D. J.; Basak, A. Org. Lett. 2001, 3, 1053–1056. (c) Wardrop,
D. J.; Burge, M. S. Chem. Commun. 2004, 1230–1231.
(14) (a) Serna, S.; Tellitu, I.; Dom´ınguez, E.; Moreno, I.; SanMart´ın,
R. Tetrahedron Lett. 2003, 44, 3483–3486. (b) Serna, S.; Tellitu, I.;
Dom´ınguez, E.; Moreno, I.; SanMart´ın, R. Tetrahedron 2004, 60, 6533–
6539. (c) Correa, A.; Tellitu, I.; Dom´ınguez, E.; Moreno, I.; SanMart´ın, R.
J. Org. Chem. 2005, 70, 2256–2264. (d) Correa, A.; Tellitu, I.; Dom´ınguez,
E.; SanMart´ın, R. J. Org. Chem. 2006, 71, 3501–3505. (e) Serna, S.; Tellitu,
I.; Dom´ınguez, E.; Moreno, I.; SanMart´ın, R. Org. Lett. 2005, 7, 3073–
3076. (f) Correa, A.; Tellitu, I.; Dom´ınguez, E.; SanMart´ın, R. J. Org. Chem.
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R. Org. Lett. 2006, 8, 4811–4813. (h) Tellitu, I.; Serna, S.; Herrero, M. T.;
Moreno, I.; Dom´ınguez, E.; SanMart´ın, R. J. Org. Chem. 2007, 72, 1526–
1529.
its reaction behavior in the presence of PIFA and trifluoro-
acetic acid (TFA).
Upon treatment of 1a with 1.5 equiv of PIFA and 3.0 equiv
of TFA in CH2Cl2 at room temperature for 1.5 h, the reaction
proceeded smoothly as indicated by TLC and furnished a
product after workup and purification by column chroma-
(16) (a) Huang, J.; Lu, Y.; Qiu, B.; Liang, Y.; Li, N.; Dong, D. Synthesis
2007, 2791–2796. (b) Huang, J.; Liang, Y.; Pan, W.; Yang, Y.; Dong, D.
Org. Lett. 2007, 9, 5345–5348.
(15) For our recent work, see: (a) Pan, W.; Dong, D.; Wang, K.; Zhang,
J.; Wu, R.; Xiang, D.; Liu, Q. Org. Lett. 2007, 9, 2421–2423. (b) Xiang,
D.; Wang, K.; Liang, Y.; Zhou, G.; Dong, D. Org. Lett. 2008, 10, 345–
348. (c) Zhang, R.; Liang, Y.; Zhou, G.; Wang, K.; Dong, D. J. Org. Chem.
2008, 73, 8089–8092.
(17) Wang, K.; Xiang, D.; Liu, J.; Pan, W.; Dong, D. Org. Lett. 2008,
10, 1691–1694.
(18) See Supporting Informationand ref 17.
1016
Org. Lett., Vol. 11, No. 4, 2009

tography. From the spectral and analytical data, the product
was characterized as 4-methyl-7-oxo-6-phenyl-5,6-diazaspiro-
[2.4]hept-4-ene 5-oxide 2a, a spiro-fused pyrazolin-5-one
N-oxide (Scheme 1).19 The reaction conditions, including
oximes 1 bearing variable amide and cycloalkyl groups.
Therefore, we provide a novel protocol for the synthesis of
spiro-fused cycloalkano-(C4)-pyrazolin-5-one N-oxides 2.
Actually, the reactions of oximes with hypervalent iodine
reagents have been investigated by some other researchers.
The deoximation reaction was observed when subjecting
ketoximes to hypervalent iodine reagents, such as (diacetoxy-
iodo)benzene (DAIB),20 (dichloroiodo)benzene (DCIB),21 and
[hydroxy(tosyloxy)iodo]benzene (HTIB).22In De’s work on the
reaction of oximes with HTIB, they obatined a new type of
product, 8,12-dioxa-13-azatricyclo [8.3.1.02,7tetradeca-
2(7),3,5,13-tetraen-14-ones] along with the deoximation
product.23 Aggarwal and co-workers achieved the synthesis
of quinoxaline N-oxides via a oxidative cyclization of benzil-
R-arylimino oximes mediated by iodobenzene diacetate
(IBD).24 The chemistry of heterocyclic N-oxides has raised
widespread interest due to the exceptionally high bioactivity
of these compounds.25 Unfortunately, to the best of our
knowledge, little is known regarding the synthesis and
properties of pyrazolin-5-one N-oxides except that Goromaru
and co-workers discovered two pyrazolin-5-one N-oxides
from the metabolites of isopropylantipyrine by means of GC-
MS.26 In the present work, we described the first X-ray
structure of one pyrazolin-5-one N-oxide.
It is well-known that nitrogen-containing compounds, such
as amides and amines, can be conveniently oxidized by PIFA
to the corresponding nitrenium ions, which are powerful
electrophiles that easily undergo intramolecular heterocy-
clization reactions.14d-h,27 However, synthetic applications
of these electrophilic intermediates remain limited except
when such nitrenium ions are stabilized by the electron-
donating effect of a suitable neighboring group (aryl, alkoxy,
or nitrogen-containing groups).28 In these cases, the “stabi-
lized” nitrenium ions can exhibit a long enough time to
Scheme 1. Reaction of 1a with PIFA/TFA
reaction temperature, the ratio of PIFA/TFA/1a, and the
concentration of PIFA, were then investigated. A series of
experiments revealed that 1.0 equiv of PIFA was sufficient
for the synthesis of 2a, and the optimal results were obtained
when the reaction of 1a was performed with PIFA (1.1 equiv,
0.1 M) and TFA (3.0 equiv) in CH2Cl2 at 0 °C for 2.0 h,
whereby the yield of 2a reached 80% (Table 1, entry 1).
Having established the optimal conditions for the cycliza-
tion process, we intended to determine its scope with respect
to the amide motif. Thus, a series of cyclopropyl oximes
1b-g were subjected to PIFA/TFA under conditions identical
to those for 2a in Table 1 (entry 1), and some of the results
are summarized in Table 1. It was observed that all the
reactions proceeded smoothly to afford the corresponding
spiro-fused cyclopropano-(C4)-pyrazolin-5-one N-oxides
2b-g in good yields (Table 1, entries 2-7).
We next extended the synthesis of spiro-fused pyrazolin-
5-one N-oxides by subjecting cyclopentyl oximes 1h-p to
the above cyclization conditions. The versatility of the
protocol proved to be suitable for 1h-o bearing variable
arylamide groups affording the corresponding spiro-fused
cyclopentano-(C4)-pyrazolin-5-one N-oxides 2h-o in high
yields (Table 1, entries 8-15). To our delight, cyclopentyl
oxime 1p bearing an alkylamide group also rendered
successfully the corresponding spiro-fused pyrazolin-5-one
N-oxide 2p in high yield (Table 1, entry 16). It is worth
mentioning that the structure of 2l was elucidated by means
of the X-ray single crystal analysis (Figure 1) and further
confirmed by NMR (1H, 13C) spectra.
(19) For the synthesis of spiro-fused pyrazolin-5-ones, see: (a) Magnien,
E.; Tom, W. J. Org. Chem. 1967, 32, 1229–1230. (b) Sammelson, R. E.;
Gurusinghe, C. D.; Kurth, J. M.; Olmstead, M. M.; Kurth, M. J. J. Org.
Chem. 2002, 67, 876–882. (c) Holzer, W.; Claramunt, R. M.; Perez-Torralba,
M.; Guggi, D.; Brehmer, T. H. J. Org. Chem. 2003, 68, 7943–7950.
(20) Moriarty, R. M.; Prakash, O.; Vavilikolanu, P. R. Synth. Commun.
1986, 16, 1247–1253.
(21) Radhbakrishna, A. S.; Augustine, B.; Sivaprakash, K.; Singh, B. B.
Synth. Commun. 1991, 21, 1473–1476.
(22) Pundeer, R.; Chaudhri, V.; Kinger, M.; Prakash, O. Indian J. Chem.,
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(23) De, S. K.; Mallik, A. K. Tetrahedron Lett. 1998, 39, 2389–2390.
(24) Aggarwal, R.; Sumran, G.; Saini, A.; Singh, S. P. Tetrahedron Lett.
2006, 47, 4969–4971.
(25) (a) Cerecetto, H.; Gonza´ez, M. Mini ReV. Med. Chem. 2001, 1,
219–231. (b) Cerecetto, H.; Porcal, W. Mini ReV. Med. Chem. 2005, 5,
57–71. (c) Boiani, M.; Gonza´ez, M. Mini ReV. Med. Chem. 2005, 5, 409–
424. (d) Cerecetto, H.; Gerpe, A.; Gonza´ez, M.; Aran, V. J.; Ochoa, C.
Mini ReV. Med. Chem. 2005, 5, 869–878.
(26) Goromaru, T.; Matsuura, H.; Furuta, T.; Baba, S. Chem. Pharm.
Bull. 1984, 32, 3179–3286.
(27) (a) Kikugawa, Y.; Kawase, M. Chem. Lett. 1990, 581–582. (b) Itoh,
N.; Sakamoto, T.; Miyazawa, E.; Kikugawa, Y. J. Org. Chem. 2002, 67,
7424–7428. (c) Miyazawa, E.; Sakamoto, T.; Kikugawa, Y. J. Org. Chem.
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Figure 1. ORTEP drawing of 2l.
5919–1922
.
(28) For nitrenium ions stabilized by electron-donating effect, see: (a)
Glover, S. A.; Goosen, A.; McClei, C. V.; Schoonraad, J. L. Tetrahedron
1987, 43, 2577–2592. (b) Kikugawa, Y.; Nagashima, A.; Sakamoto, T.;
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The results shown above demonstrated the efficiency and
synthetic value of the cyclization reaction with respect to
Org. Lett., Vol. 11, No. 4, 2009
1017

undergo further organic reactions.29 On the basis of the
obtained results and our previously reported work,16
plausible mechanism for the synthesis of pyrazolin-5-one
N-oxides 2 is presented in Scheme 2. Oximyl cycloalkane 1
In summary, a facile and efficient synthesis of spiro-fused
cycloalkano-(C4)-pyrazolin-5-one N-oxides 2 has been de-
veloped from readily available 1-carbamoyl-1-oximylcy-
cloalkanes 1, which involves the formation of a N-oxoni-
trenium intermediate, mediated by PIFA, and the succeeding
intramolecular trapping by the amide moiety to form a new
N-N single bond. This protocol is associated with readily
available starting materials, mild conditions, good to high
yields, and a broad range of synthetic potential of the
products. Further work on the utilization and extension of
the scope of the protocol and the examination of biological
activity of the novel products are currently under investiga-
tion in our laboratory.
a
Scheme 2
.
Plausible Mechanism for the Reaction of Cycloalkyl
Oximes 1 with PIFA/TFA
Acknowledgment. Financial support of this research by
theNationalNaturalScienceFoundationofChina(20711130229
and 20872136) is greatly acknowledged.
Supporting Information Available: Experimental details,
spectral data for compounds 1 and 2, and CIF data for 2l.
This material is available free of charge via the Internet at
http://pubs.acs.org.
initially reacts with PIFA to give intermediate A,24,30 which
is then transformed into N-oxonitrenium ion B via an
oxidative process,31 followed by an intramolecular cycliza-
tion reaction to yield pyrazolin-5-one N-oxide 2.
OL802952E
(30) (a) Kita, Y.; Takada, T.; Gyoten, M.; Tohma, H.; Zenk, M. H.;
Eichhorn, J. J. Org. Chem. 1996, 61, 5857–5864. (b) Kita, Y.; Yakura, T.;
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(29) For reviews on the chemistry of nitrenium ions, see: (a) Abramo-
vitch, R. A.; Jeyaraman, R. In Azides and Nitrenes: ReactiVity and Utility;
Scriven, E. F. V., Ed.; Academic Press: Orlando, 1984; pp 297-357. (b)
Falvey, D. E. In ReactiVe Intermediate Chemistry; Moss, R. A., Platz, M. S.,
Jones, M., Eds.; Wiley-Interscience: Hoboken, NJ, 2004; pp 594-650.
(31) The format ion of N-oxonitrenium ion B, instead of N-acylnitrenium
ion C, is based on the fact that the presented process can be extended to
certain alkyl amides (Table 1, entry 16), and the nitrenium ion in B can be
stabilized by its adjacent oxygen atom.
1018
Org. Lett., Vol. 11, No. 4, 2009