Regioselective three-component synthesis of novel indeno[1,2-b]-pyrazolo[4, 3-e]pyridines-fused derivatives of 4-azafluorenone alkaloid

Article abstract of DOI:10.1002/jhet.5570450116

(Chemical Equation Presented) New fused indeno[1,2-b]pyridine derivatives have been prepared in a multicomponent reaction from benzaldehydes, indanedione and the appropriate aminoheteroaryl compound. The simple methodology permitted the syntheses of a ser

Full text of DOI:10.1002/jhet.5570450116

Jan-Feb 2008
155
Regioselective Three-component Synthesis of Novel Indeno[1,2-b]-
pyrazolo[4,3-e]pyridines-Fused Derivatives of 4-Azafluorenone
Alkaloid
Jairo Quiroga,* Débora Cobo, Braulio Insuasty, Rodrigo Abonía
Grupo de Investigación de Compuestos Heterocíclicos, Department of Chemistry, Universidad del Valle, A. A. 25360, Cali, Colombia
Silvia Cruz
Department of Chemistry, Universidad de Nariño, A.A. 1175, Pasto-Colombia
Manuel Nogueras* and Justo Cobo
Department of Inorganic and Organic Chemistry, Universidad de Jaén, 23071 Jaén, Spain
Received April 24, 2007
Ar
O
CH3
O
O
CH3
N
N
+
+
ArCH=O
N
NH2
N
N
Ph
Ph
1
2
3
4a-i
New fused indeno[1,2-b]pyridine derivatives have been prepared in a multicomponent reaction from
benzaldehydes, indanedione and the appropriate aminoheteroaryl compound. The simple methodology
permitted the syntheses of a series of indeno[1,2-b]pyrazolo[4,3-e]pyridines 4 from 5-aminopyrazol 1 and
modulated by the corresponding benzaldehyde 2.
J. Heterocyclic Chem., 45, 155 (2008).
result, the development of simple and efficient procedures
to the synthesis of analogues of these alkaloids,
containing indenopyridine scaffold, has attracted
considerable attention [7].
INTRODUCTION
Multi-component reactions, an important class of
organic tandem reactions, are one-pot processes with at
least three components to form a single product, which
incorporates most or even all of atoms of the starting
materials [1]. During the past ten years, the huge
potential of such multi-component reactions has been
applied to develop large libraries of organic compounds
by combinatorial chemistry procedures in a facile and
benign fashion, because of both high efficiency and
convenience in comparison with multistage procedures.
Hence, most of the scientific efforts have been focus on
the development of multicomponent procedures to
prepare diverse heterocyclic compound libraries [1b].
On the other hand, six-membered nitrogen-containing
heterocycles are abundant in nature and exhibit diverse
and important biological properties [2]. The 4-azafluor-
enone alkaloids (indeno[1,2-b]pyridines) comprise a
small but biologically intriguing group of alkaloids. The
simplest member of this family, Onychine (Figure 1),
was first isolated from the Brazilian Annonaceae species
(onychopetalum amazonicum, Guatteria dielsiana) in
1976 and has shown to have anticandidal activity [3].
Recently, onychine derivatives were found to exhibit
adenosine A2, a receptor binding and phosphodiesterase
inhibiting activities for the treatment of neurodegenerative
disorders and inflammation related diseases [4]; and also
used as calcium antagonists [5] or herbicides [6]. As a
R
O
N
Figure 1. Onychine
Several approaches have been developed for the
synthesis of the indeno[1,2-b]pyridin-5-ones: oxidative
thermal rearrangement of 2-indanone oxime O-ally1
ethers [7]; direct cyclization of 2-aryl-3-methylpyridines
to give 5H-indeno[1,2-b]pyridines followed by oxidation
[7b]; cyclization of 2-aryl-3-nicotinic acids by the use of
polyphosphoric acid [7b,8], or by extrusion of organo-
phosphorus compounds [9]. However, even these methods
are still not satisfactory in view of using toxic catalyst,
narrow application scope of substrates, harsh reaction
conditions, scarce generality and operational complexity
due to the occurrence of several competitive side
reactions.
RESULTS AND DISCUSSION
Having in mind all the benefits of the multicomponent
cyclocondensation procedures [10] to build heterocyclic

156
J.Quiroga, D. Cobo, B. Insuasty, R. Abonía, S. Cruz, M. Nogueras, J. Cobo
Vol 45
scaffolds [11], we have planned a facile three-component
reaction for the construction of fused indeno[1,2-b]-
pyridines heterocycles using an aminoheteroaryl, a
carbonyl derivative and indanedione 3 (Scheme 1).
and a singlet at 2.11 ppm corresponding to CH3-group at
position 3 (see Table 2).
Table 2
1H-NMR Chemical Shifts (ꢀ) for compunds 4a-i.
Scheme 1
Comp.
CH3
Phenyl
Indene
Aryl C
R
O
R
O
4a
4b
4c
4d
4e
4f
1.98
2.09
2.11
2.08
2.03
2.02
2.02
8.28,
7.61,7.38
8.31, 7.53,
7.33
8.30, 7.53,
7.34
8.30, 7.54,
7.36
8.29, 7.55,
7.36
7.60, 7.54,
7.70, 7.96
7.60, 7.42,
7.56, 7.96
7.60, 7.43,
7.56, 7.94
7.60, 7.43,
7.59, 7.97
7.60, 7.43,
7.59, 7.97
760-7.52,
7.94
7.74-7.68,
7.48-7.45,
7.94
7.63, 7.43,
7.59, 7.99
7.60, 7.43,
7.58, 7.96
7.55, 7.56,
7.51
7.34, 7.54
O
O
Het
N
Het
NH2
7.05, 7.39
7.22, 7.45
7.58, 7.80
The use of 5-aminopyrazol 1, benzaldehydes 2 led as
predicted to a series of novel indeno[1,2-b]pyrazolo-
[4,3-e]pyridines 4. Accordingly, a mixture of equimolar
amounts of starting compounds such as amine, aldehydes
and indandione in DMF was refluxed during 6-8 hours to
render compounds 4 in acceptable yields (Scheme 2,
Table 1).
8.27, 7.60-
7.52, 7.38
8.27, 7.61-
7.50, 7.39
7.70,
760-7.52
7.74-7.68
4g
4h
4i
2.14
2.15
8.31, 7.55,
7.35
8.31, 7.54,
7.34
7.26,7.40,
7.31
6.98, 6.95,
6.90
Scheme 2
Ar
O
CH3
O
O
CH3
N
For 4b CH3 2.16 ppm; 4c CH3O 3.92 ppm; 4i –OCH2O- 6.09 ppm
+
NH2
ArCH=O
+
N
N
N
N
2
Ph
Ph
In the 13C (DEPT) all signals belonging to tertiary,
secondary and primary carbon atoms could be determined
for 4a-i compounds (Table 3).
4a-i
3
1
Table 1
We assume that the synthesis of 4 proceed by a Michael
type addition of the most nucleophilic ring carbon atom in
aminopyrazole 1 to the activated double bond of interme-
diate 5 (formed by Knovenagel condensation between
Synthesis of indeno[1,2-b]pyrazolo[4,3-e]pyridines
Yields (%)
Entry
Ar
Reaction Time (h)
benzaldehyde
2 and indandione 3) and posterior
4a
4b
4c
4d
4e
4f
C6H5
4-CH3C6H4
4-CH3OC6H4
4-FC6H4
6
6
58
52
47
54
51
49
69
58
68
cyclization of 6 with elimination of a hydrogen and water
molecules yield the indeno[1,2-b]pyrazolo[4,3-e]pyridines
4 (Scheme 3). Similar pathway was described in the
multicomponent reaction of indanedione with aldehydes,
acetophenones and ammonium acetate [12].
6
7
4-CF3C6H4
4-ClC6H4
8
5
4g
4h
4i
4-BrC6H4
7.5
8
A related behavior was observed when we studied the
similar three-component reaction between 6-aminopyrim-
idine 8, benzaldehydes 2 and indandione 3, which when
carried out lead to the formation of the corresponding
indeno[1,2:2,3]pyrido[2,3-d]pyrimidines 9 (Scheme 4). In
this reaction, the stable hydrated intermediate 10 was
isolated which suffered the aromatization by elimination
of a hydrogen and water molecules to render the final
product 9 [13].
2-FC6H4
3,4-OCH2OC6H3
8
The structures of all isolated compounds were assigned
by 1D and 2D NMR and mass spectrometries (Tables 2
and 3). Based on 1D and 2D NMR experiments such
HSQC, HMBC and NOESY techniques, it was possible to
assign all protons and carbon atoms of new products.
The NMR data are consistent with structures 4 (Table 2
1
Regarding to the mass spectra, all products 4 exhibit
similar pattern of fragmentation, showing the molecular
ion peak along with a typical loss of the substituents of
each aryl group.
and 3). For example compound 4c exhibits a H NMR
spectrum with two doublets at 7.97 and 8.29 ppm
corresponding to CH3O-phenyl group, multiplets
corresponding to N-phenyl group and indene fragment

Jan-Feb 2008
Synthesis of Indeno[1,2-b]pyrazolo[4,3-e]pyridines-Fused Derivatives
157
Table 3
13C-NMR Chemical Shifts (ꢀ) for compunds 4a-i.
4a
4b
4c
4d
4e
4f
4g
4h
4i
CH3
C3
13.4
15.3
15.2
15.0
14.9
13.6
13.6
15.3
15.3
144.8
114.7
141.2
119.2
188.0
136.3
163.8
151.9
144.9
146.3
115.7
142.4
120.1
189.9
137.4
165.1
152.8
146.0
146.1
115.8
142.4
120.1
190.0
137.4
165.2
152.8
145.9
145.7
115.6
142.4
120.1
189.9
137.3
165.1
152.8
144.8
145.5
115.1
142.4
119.9
189.7
137.2
165.0
152.8
143.7
144.6
114.4
141.1
119.2
188.0
136.3
163.8
151.9
143.4
144.6
114.3
141.1
119.1
188.0
136.3
163.8
151.9
143.4
145.7
115.6
142.5
120.7
189.7
137.4
164.9
152.9
134.6
145.8
115.7
142.4
120.2
189.9
137.4
165.1
152.8
145.6
C3a
C4
C4a
C5
C5a
C9a
C9b
C9c
Phenyl
Ci
Co
Cm
Cp
138.1
120.6
128.4
125.7
139.0
121.6
128.7
126.3
139.1
121.5
129.0
126.3
138.9
121.6
129.1
126.5
138.9
121.6
129.1
126.6
138.1
120.7
128.4
125.7
138.1
120.7
128.4
125.7
139.0
121.6
129.1
126.4
139.0
121.6
129.0
126.4
Aryl
Ci
122.4
131.1
134.4
120.5
123.4
131.4
134.6
121.4
123.4
131.4
134.6
121.4
123.5
131.6
134.8
121.5
123.6
131.7
135.0
121.5
122.5
131.2
134.5
120.5
122.5
131.3
134.5
120.6
123.6
131.6
134.8
121.5
123.4
131.4
134.7
121.4
Co
Cm
Cp
Aryl C
C1
C2
132.0
127.0
128.2
128.1
129.7
129.3
129.0
139.1
124.6
113.4
130.5
160.5
162.1
115.3
128.6
164.6
122.7
129.2
125.1
136.6
130.8
127.2
130.1
133.5
122.0
130.1
130.3
130.2
158.3
160.7
131.3
123.9
126.1
122.8
148.5
147.4
C3
C4
For 4b CH3 21.6 ppm; 4c CH3O 55.3 ppm; 4e CF3 125.4; 4i –OCH2O- 65.9 ppm
Scheme 3
O
Ar
O
CH3
O
O
Ar
1
N
ArCH=O
+
N
O
NH2
O
Ph
2
3
5
6
Ar
O
CH3
-H2O; -H2
N
4
N
N
H
OH
Ph
7
Scheme 4
O
N
Ar
O
N
Ar
O
ArCH=O
O
O
+
+
2
-H2O; -H2
HN
HN
MeO
HN
MeO
O
N
H
N
MeO
N
NH2
OH
8
9
10
O
3

158
J.Quiroga, D. Cobo, B. Insuasty, R. Abonía, S. Cruz, M. Nogueras, J. Cobo
Vol 45
.
OCH3 ). Anal. Calcd for C27H19N3O2.1/2H2O: C, 76.04; H, 4.73;
N, 9.85. Found: C, 75.82; H, 4.70; N, 10.03
Finally, the isolation of single crystals of compound 4d
permitted the X-ray diffraction analysis that was used to
corroborate unambiguously the postulated structures [14].
In summary, we have developed a multi-component
condensation to obtain fused indeno[1,2-b]pyridine
heterocycles, which was applied to prepare a series of
poly-substituted indeno[1,2-b]pyrazolo[4,3-e]pyridines
from 5-aminopyrazole, 1,3-indanedione and aromatic
aldehydes in a easy fashion. The application of a similar
procedure with 6-aminopyrimidine rendered the related
indeno[1,2:2,3]pyrido[2,3-d]pyrimidine. In light of its
operational simplicity, simple purification procedure,
good yields, and reduced environmental impact as well as
increased safety for small-scale high-speed synthesis, this
protocol is superior to the existing methods or the
indenopyridine synthesis.
4-(4-Fluorophenyl)-3-methyl-1-phenylindeno[1,2-b]pyra-
zolo[4,3-e]pyridin-5(1H)-one (4d). This compound was
obtained according to general procedure as pale yellow crystals.
Mp 255-257 °C, yield 54%. MS (70eV) m/z (%): 406 (36), 405
.
(100, M+), 404 (41), 390 (15, M+-CH3 ). Anal. Calcd for
C26H16FN3O.1/3H2O: C, 75.90; H, 4.08; N, 10.21. Found: C,
76.11; H, 3.86; N, 9.87.
4-(4-Trifluoromethylphenyl)-3-methylphenyl-1H-indeno-
[1,2-b]pyrazolo[4,3-e]pyridin-5(1H)-one (4e). This compound
was obtained according to general procedure as pale yellow
crystals. Pf 280-281 °C, 51% de rendimiento. MS (70eV) m/z
(%): 456 (29), 455 (100, M+), 454 (18), 440 (4, M+-CH3 ), 386
.
.
(3, M+-CF3 ). Anal. Calcd for C27H16F3N3O.1/3H2O: C, 70.28; H,
3.64; N, 9.11. Found: C, 70.36; H, 3.32; N, 9.09
4-(4-Chlorophenyl)-3-methyl-1-phenylindeno[1,2-b]pyra-
zolo[4,3-e]pyridin-5(1H)-one (4f). This compound was
obtained according to general procedure as pale yellow crystals.
Mp 269-270 °C, yield 49%. MS (70eV) m/z (%): 423 (36), 422
.
(29), 421 (100, M+), 420 (22), 406 (5, M+-CH3 ), 386 (10, M+-
EXPERIMENTAL
Cl.). Anal. Calcd for C26H16ClN3O.1/3H2O: C, 72.98; H, 3.93; N,
9.82. Found: C, 72.77; H, 4.04; N, 9.91.
Melting points were determined in a Buchi Melting Point
1
4-(4-Bromophenyl)-3-methyl-1-phenylindeno[1,2-b]pyra-
zolo[4,3-e]pyridin-5(1H)-one (4g). This compound was
obtained according to general procedure as pale yellow crystals.
Mp 274-276 °C, yield 69%. MS (70eV) m/z (%): 468 (23), 466
(100), 468 (42), 465 (77, M+), 386 (24, M+-Br.), 385 (13). Anal.
Calcd for C26H16BrN3O.1/2 H2O: C, 65.70; H, 3.60; N, 8.84.
Found: C, 65.83; H, 3.24; N, 9.02.
4-(2-Fluorophenyl)-3-methyl-1-phenylindeno[1,2-b]pyra-
zolo[4,3-e]pyridin-5(1H)-one (4h). This compound was
obtained according to general procedure as pale yellow crystals.
Mp 247-249 °C, yield 58%. MS (70eV) m/z (%): 406 (23), 405
(97, M+), 385 (23), 357 (14), 77 (100), 51 (10). HRMS (EI):
C26H16FN3O requires: 405.1277; found: 405.1277.
3-Methyl-4-(3,4-methylendioxyphenyl)-1-phenylindeno[1,2-
b]pyrazolo[4,3-e]pyridin-5(1H)-one (4i). This compound was
obtained according to general procedure as pale yellow crystals.
Mp 223-224 °C, yield 68%. MS (70eV) m/z (%): 432 (30), 431
(100, M+), 401 (10), 91 (11), 77 (100), 51 (10). HRMS (EI):
C27H17N3O3 requires: 431.1264; found: 431.1270.
Apparatus and are uncorrected. The H- and 13C NMR spectra
were run on a Bruker DPX 400 spectrometer operating at 400
MHz and 100 MHz respectively, using dimethyl sulfoxide-d6 as
solvent and tetramethylsilane as internal standard. The mass-
spectra were scanned on a Hewlett Packard HP Engine-5989
spectrometer (equipped with a direct inlet probe) operating at 70
eV. High Resolution Mass Spectra (HRMS) were recorded in a
Waters Micromass AutoSpec NT spectrometer (STIUJA). The
elemental analyses have been obtained using a LECO CHNS-
900 and a Thermo Finnigan FlashEA1112 CHNS-O (STIUJA)
elemental analyzers.
General procedure for the synthesis of indeno[1,2-b]-
pyrazolo[4,3-e]pyridines (4a-i).
A solution of 5-amino-3-
methyl-1-phenylpyrazole 1 (1 mmol), benzaldehyde 2 (1 mmol)
and 1,3-indandione 3 (1 mmol) in dimethylformamide (10 mL)
containing a catalytic amount of triethylamine was heated under
reflux for 6-8 h. The resulting solid product was collected by
filtration, washed with ethanol, dried and finally recrystallized
from dimethylformamide.
Acknowledgement. Authors are grateful to COLCIENCIAS,
to Universidad del Valle, to the Spanish "Consejeria de
Innovacion, Ciencia y Empresa, Junta de Andalucia" and
Servicios Tecnicos de la Universidad de Jaen (STIUJA). SC
thanks to Universidad de Nariño for fellowship.
3-Methyl-1,4-diphenylindeno[1,2-b]pyrazolo[4,3-e]pyridin-
5(1H)-one (4a). This compound was obtained according to
general procedure as pale yellow crystals. Mp 220-221 °C, yield
58 %. MS (70eV) m/z (%): 388 (26), 387 (100, M+), 372 (6, M+
.
- CH3 ), 77 (7). HRMS (EI): C26H17N3O requires: 387.1382;
found: 387.1372.
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