Non-concerted nucleophilic [4+1] cycloaddition of (dimethylamino) methoxycarbene to arylazonicotinates in the synthesis of pyrazolo[3,4-c] pyridines and pyrazolo[4′,3′:4,5]pyrido[2,3-d]pyrimidines

Article abstract of DOI:10.1016/j.tet.2013.05.040

A novel reaction between 2-amino-5-arylazonicotinonitriles 3c-g and dimethylformamide dimethylacetal (DMF-DMA), leading to the formation of a new class of pyrazolo[3,4-c]-pyridine derivatives 8, has been developed. The process is believed to take place via a non-concerted [4+1] cycloaddition pathway involving nucleophilic addition of (dimethylamino)-methoxycarbene, generated from DMF-DMA, to the arylazonicotinates 3c-g. The pyridine derivatives 8 were observed to react with ammonia in refluxing acetic acid to yield novel pyrazolo[4′,3′:4,5]pyrido[2,3-d]pyrimidine derivatives 9. Other members of the pyrido[2,3-d]pyrimidine family 13 were synthesized by reactions between 2-amino-5-arylazonicotinate ethyl esters 3a,b and DMF-DMA, which produce amidine derivatives 10a,b that undergo cyclization to generate the corresponding pyrido[2,3-d]pyrimidines13a,b when treated with ammonia in refluxing acetic acid. Finally, the results of this effort revealed that pyrido[2,3-d]pyrimidines 13a,b also react with DMF-DMA to produce pentaazacyclopenta [a]naphthalene derivatives 14. The structures of all new substances prepared in this investigation were determined by using X-ray crystallographic analysis and spectroscopic methods.

Full text of DOI:10.1016/j.tet.2013.05.040

Accepted Manuscript
Non-concerted nucleophilic [4+1] cycloaddition of (dimethylamino)methoxycarbene
to arylazonicotinates in the synthesis of a pyrazolo[3,4-c]pyridines and
pyrazolo[4',3':4,5]pyrido[2,3-d]pyrimidines
Haider Behbehani, Hamada Mohamed Ibrahim, Mohamed H. Elnagdi
PII:
S0040-4020(13)00775-8
10.1016/j.tet.2013.05.040
TET 24378
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 22 February 2013
Revised Date: 1 May 2013
Accepted Date: 13 May 2013
Please cite this article as: Behbehani H, Ibrahim HM, Elnagdi MH, Non-concerted nucleophilic
[4+1] cycloaddition of (dimethylamino)methoxycarbene to arylazonicotinates in the synthesis of a
pyrazolo[3,4-c]pyridines and pyrazolo[4',3':4,5]pyrido[2,3-d]pyrimidines, Tetrahedron (2013), doi:
10.1016/j.tet.2013.05.040.
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ACCEPTED MANUSCRIPT
Non-concerted nucleophilic [4+1] cycloaddition of
(dimethylamino)methoxycarbene to arylazonicotinates in
the synthesis of a pyrazolo[3,4-c]pyridines and
pyrazolo[4',3':4,5]pyrido[2,3-d]pyrimidines
Haider Behbehani, Hamada Mohamed Ibrahim, Mohamed H. Elnagdi
NH2
N
N
N
NMe2
CN
CN
DMF-DMA
N
3
N
NH2
N
AcOH/AcONH4
NMe2
NMe2
N
N
N
N
N
N
X
X
X
Ar
Ar
Ar
9
8

ACCEPTED MANUSCRIPT
Non-concerted nucleophilic [4+1] cycloaddition of
(dimethylamino)methoxycarbene to arylazonicotinates in
the synthesis of a pyrazolo[3,4-c]pyridines and
pyrazolo[4',3':4,5]pyrido[2,3-d]pyrimidines
Haider Behbehani a, *, Hamada Mohamed Ibrahim b, Mohamed H. Elnagdi a
a Chemistry Department, Faculty of Science, Kuwait University, P.O. Box 5969, Safat 13060,
Kuwait.
b
Chemistry Department, Faculty of Science, Fayoum University, Fayoum 63514, A. R.,
Egypt; e-mail: hamadaaldeb@yahoo.com
Corresponding author. Tel.: +965-990-630-62; fax: +965-248-164-82; e-mail:
hidar@bahbahani.com
Abstract
A novel reaction between 2-amino-5-arylazonicotinonitriles 3c-g and dimethylformamide
dimethylacetal (DMF-DMA), leading to the formation of a new class of pyrazolo[3,4-c]-
pyridine derivatives 8, has been developed. The process is believed to take place via a non-
concerted [4+1] cycloaddition pathway involving nucleophilic addition of (dimethylamino)-
methoxycarbene, generated from DMF-DMA, to the arylazonicotinates 3c-g. The pyridine
derivatives 8 were observed to react with ammonia in refluxing acetic acid to yield novel
pyrazolo[4',3':4,5]pyrido[2,3-d]pyrimidine derivatives 9. Other members of the pyrido[2,3-
d]pyrimidine family 13 were synthesized by reactions between 2-amino-5-arylazonicotinate
ethyl esters 3a-b and DMF-DMA, which produce amidine derivatives 10a-b, that undergo
cyclization to generate the corresponding pyrido[2,3-d]pyrimidines13a-b when treated with
ammonia in refluxing acetic acid. Finally, the results of this effort revealed that pyrido[2,3-

ACCEPTED MANUSCRIPT
d]pyrimidines 13a-b also react with DMF-DMA to produce pentaazacyclopenta
[a]naphthalene derivatives 14. The structures of all new substances prepared in this
investigation were determined by using X-ray crystallographic analysis and spectroscopic
methods.
Keywords
nucleophilic [4+1] cycloaddition; nicotinonitrile; pyrazolo[3,4-c]pyridine; pyrido[2,3-
d]pyrimidine; pyrazolo[4',3':4,5]pyrido[2,3-d]pyrimidine
Introduction
Among the nitrogen-containing heterocyclic compounds, those possessing pyridine and fused
polycyclic pyridine structures are perhaps the most common. The biologically activities of
these substances have been used widely as antimicrobial,1 anti-inflammatory,2 anti-HIV,3
antiplasmodial,4 antitubercular,5 antibacterial,6 anticonvulsant,7 antimitotic,8 anticancer
agents,9,10 antinociceptive,11 as well as substances possessing insecticidal and fungicidal,12
and agrochemical importance.13 Also, pyridine ring containing compounds play an
exceptionally important role in biological redox chemistry, and a number of these substances
serve as substructures of therapeutically important natural products.14-21 In addition to their
biological importance, pyridines play important roles as starting materials, key intermediates
or reagents in preparative organic chemistry. One example is 4-dimethylaminopyridine
(DMAP), which is a widely used catalyst in acylation reactions, and also as an activator of α-
chiral carboxylic acids without accompanying racemisation.22 Moreover, their ability to form
complexes with metal ions makes pyridine derivatives highly sensitive reagents in analytical
sensor systems, luminescent agents and as building block in supramolecular chemistry.23,24
As a consequence of these fascinating properties and uses, pyridines and polycyclic fused
pyridines represent privileged structures and, thus, they have attracted the general and

ACCEPTED MANUSCRIPT
continuing interest of synthetic organic chemists. The study described below was aimed at the
development of novel methods to prepare representative members of a class of pyrazolo[3,4-
c]pyridines and pyrazolo[4',3':4,5]pyrido[2,3-d]pyrimidines, based on the use of the unique
chemistry of N,N-dimethylformamide dimethylacetal (DMF-DMA). To this effect, we have
developed a new process that utilizes this acetal to transform pyridyl-hydrazones to
pyrazolo[3,4-c]pyridine and pyrazolo[4',3':4,5]pyrido[2,3-d]pyrimidine derivatives in
moderate to high yields.
Results and Discussion
In recent studies, we have developed general methods for the efficient synthesis of
arylazonicotinates,25 and 2-amino-5-arylazo-6-aryl substituted nicotinates.26 We have
employed this process to prepare pyridyl-hydrazone substrates required to explore the unique
chemistry of DMF-DMA. Specifically, independent reactions of 3-oxo-2-arylhydrazono-
propanals 1 (Scheme 1) with ethyl cyanoacetate (2a) and malononitrile (2b) produced 2-
amino-5-arylazo nicotinic acid ethyl esters 3a-b and 2-amino-5-arylazonicotinonitriles 3c-g
respectively (Scheme 1 and Figure 1).
NH2
O
Y
N
CHO
NC
Y
N
AcOH/AcONH4
2a, Y=COOEt
NH
Ar
X
N
X
N
b, Y= CN
Ar
1
3
a
c
e
g
3
b
d
f
Cl
Cl
NO2
Ar
NO2
Cl
Br
NO2
NO2
Cl
NO2
Cl
Cl
Br
COOEt
Br
X
Y
Cl
COOEt
Cl
Cl
Cl
CN
CN
CN
CN
CN
Scheme 1: Synthesis of 2-amino-5-arylazonicotinic acid derivatives 3a-g.

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Figure 1: ORTEP plot of the X-ray crystallographic data determined for 3c.27
Prior to initiating this effort, we envisaged that reaction of the nucleophilic carbene, produced
by methanol elimination from DMF-DMA, would undergo [4+1] cycloaddition reactions with
pyridyl-hydrazone derivatives like the 2-amino-5-arylazonicotinic acids 3, and that this
process would serve as a new approach for the preparation of pyrazolo[3,4-c]pyridines. To
test this proposal, reactions of the 2-amino-5-arylazo-nicotinonitriles 3c-g with excess DMF-
DMA in refluxing toluene were explored. Detailed spectroscopic and X-ray crystallographic
analyses (Figures 2 and 3, and Table 1) showed that the products 8c-g formed in these
reactions possess pyrazolo[3,4-c]pyridine amidine structures (Scheme 2). In addition, the
pyrazolo[3,4-c]pyridines 8 were found to react with ammonia in refluxing acetic acid to yield
the corresponding fused tricyclic pyrazolo[4',3':4,5]pyrido[2,3-d]pyrimidine derivatives 9
(Scheme 2). A plausible mechanism for the formation of the pyrazolo[3,4-c]pyridine amidines
8 begins with reaction of DMF-DMA with the amine moiety in 3 to afford the corresponding
amidine 4. Under the reaction conditions, DMF-DMA is expected to undergo methanol
elimination to produce (dimethylamino)methoxycarbene 5, in analogy to the reported
formation of (dimethylamino)ethoxycarbene upon heating dimethylformamide diethylacetal
(DMF-DEA).28 As a nucleophilic carbene, 5 then adds to the electron deficient C-4 center in
the pyridine ring of 4 to form adduct 6. Subsequent bond formation between the positively

ACCEPTED MANUSCRIPT
charged carbenium ion carbon and the negatively charged nitrogen in 6 then gives bicyclic
intermediate 7, which upon loss of methanol finally forms the pyrazolo[3,4-c]pyridine
derivative 8. The overall process transforming 4 to 8 can be visualized as a non-concerted
nucleophilic [4+1] cycloaddition reaction. Although similar cycloaddition reactions were
observed earlier by Seitz et. al.,28 as far as we are aware these are the first examples of such
reactions occurring between (dimethylamino)methoxycarbene and arylazonicotinates.
NMe2
NH2
N
CN
OMe
CN
N
N
Toluene
MeO CH NMe2
+
N
N
X
N
N
X
C
Ar
Ar
4
3c-g
OMe
OMe
NMe2
- MeOH
MeO CH NMe2
5
NMe2
NMe2
CN
NMe2
N
N
N
N
CN
H
CN
H
OMe
N
N
N
+
OMe
C
NMe2
NMe2
OMe
NMe2
N
N
N
X
N
X
N
X
Ar
4
5
7
6
Ar
Ar
- MeOH
NMe2
N
N
N
N
NH2
CN
N
AcOH/AcONH4
NMe2
NMe2
a
c
d
e
b
8,9
N
N
X
N
N
Ar
X
Cl
Ar
X
Ar
NO2
NO2
Br
Cl
8
9
Cl
Br
NO2
Cl
Cl
Cl
Cl
Scheme 2: Synthesis of pyrazolo[3,4-c]pyridines 8 and pyrazolo[4',3':4,5]pyrido[2,3-d]-
pyrimidines 9.

ACCEPTED MANUSCRIPT
Figure 2. ORTEP plot of the X-ray crystallographic data determined for 8a. Crystallographic
data have been deposited with the Cambridge Crystallographic Data Centre as supplementary
publication number CCDC 913248.29
Table 1: Selected bond lengths and bond angles in the crystal structure of 8a.
o
Bond
Bond length(Å)
1.316
Bond
Bond angle( )
N3-C3
N3-C4
C3-C2
C4-C5
C2-C6
N2-C2
N1-N2
N1-C1
N4-C1
C3-N3-C4
N3-C3-C2
N3-C4-C5
C2-C6-C5
N2-C2-C6
C1-C6-C5
N1-N2-C2
N1-C1-C6
N2-N1-C1
121.38
120.44(
122.35
118.99
112.47
136.13
102.51
104.72
115.40
1.373
1.436
1.399
1.419
1.352
1.356
1.363
1.400

ACCEPTED MANUSCRIPT
Figure 3. ORTEP plot of the X-ray crystallographic data determined for 8c. Crystallographic
data have been deposited with the Cambridge Crystallographic Data Centre as supplementary
publication number CCDC 925395.30
In order to develop an alternative route for the synthesis of the pyrazolo[4',3':4,5]pyrido[2,3-
d]pyrimidine derivatives 9, we explored reactions between 2-amino-5-arylazo nicotinic acid
ethyl esters 3a-b and dimethylformamide dimethylacetal (DMF-DMA). These processes
afford products which were shown to be the respective amidine derivatives 10a-b and not the
corresponding pyrazolo[3,4-c]pyridines 11a-b. The amidine derivatives 10a-b were reacted
with ammonia in refluxing acetic acid to yield the corresponding pyrido[2,3-d]pyrimidine
derivatives 13a-b. The pyrido[2,3-d]pyrimidines 13a-b were found to undergo nonconcerted
nucleophilic [4+1] cycloaddition reactions with DMF-DMA to produce the novel
pyrazolo[4',3':4,5]pyrido[2,3-d]pyrimidine derivative 14. The structures of these substances
were assigned based on their spectroscopic and mass spectrometric properties (Scheme 3).
From the previous findings we can conclude that the existence of the CN group at position 3
in the pyridine ring make the nucleophilic [4+1] cycloaddition between the

ACCEPTED MANUSCRIPT
(dimethylamino)methoxycarbene and arylazonicotinates easier since it make the C-4 center in
the pyridine ring more electron deficient in comparison with the COOEt group.
NH2
CO2Et
N
N
X
N
3a,b Ar
DMF-DMA
Toluene/
NMe2
NMe2
N
N
N
CO2Et
CO2Et
N
AcOH/AcONH4
N
NMe2
N
N
X
X
N
Ar
11
Ar
10
N
N
NH
N
N
NH2
DMF-DMA
Toluene/
CO2Et
N
O
_
EtOH
for 13b
Me
N
N
N
X
N
X
N
O
N
Ar
Ar
13
NMe2
12
a
b
N
10,13
Ar
N
X
Ar
Cl
14
NO2
NO2
Cl
Br
Ar =
X
Cl
NO2
Cl
Scheme 3: Synthesis of compounds 13a-b and pyrazolo[4',3':4,5]pyrido[2,3-d]pyrimidine 14.
In further studies, we observed that the 2-amino-5-arylazo nicotinates 3a-b readily react with
acetic anhydride to yield either the monoacylated derivatives 15a-b or the bis-acylated
derivatives 16a-b, depending upon the reaction time. Attempts to react 16a-b with DMF-
DMA were unsuccessful. Finally, the nicotinate 3d undergoes reaction with

ACCEPTED MANUSCRIPT
triethylorthoformate to yield the ethyl formimidate derivative 17, which does participate in
reaction with DMF-DMA to yield the pyrazolo[3,4-c]pyridine 8b (Scheme 4 and Figure 4).
O
HN
CH3
Y
DMF-DMA
Toluene/
N
Ac2O/
for 3a,b
,4h
No reaction
a
b
15
N
Cl
X
N
Ar
NO2
NO2
Cl
Ar
15
X
Y
NH2
Cl
Br
COOEt
COOEt
Y
N
O
O
CH3
N
CH3
Y
N
X
N
N
b
Ar
a
16
Ar
Ac2O/
for 3a,b
,12h
3a,b
Cl
NO2
Cl
NO2
N
X
N
X
Y
Cl
COOEt
Br
Ar
16
COOEt
NMe2
CN
OEt
N
N
CN
CH(OEt)3
N
N
DMF-DMA
Toluene/
for 3d
NMe2
N
N
N
X
N
X
Ar
Ar
17
8b
Ar
X
17,8b
Br
NO2
Cl
Scheme 4: Reaction of 2-aminonicotinates 3 with acetic anhydride and triethylorthoformate.

ACCEPTED MANUSCRIPT
Figure 4. ORTEP plot of the X-ray crystallographic data obtained for 15b. Crystallographic
data have been deposited with the Cambridge Crystallographic Data Centre as supplementary
publication number CCDC 917642.31
Conclusion
In this study, a novel route for the synthesis of pyrazolo[3,4-c]pyridines and
pyrazolo[4',3':4,5]pyrido[2,3-d]pyrimidines was developed. The methodology utilizes a
simple and efficient non-concerted nucleophilic [4+1] cycloaddition of (dimethylamino)-
methoxycarbene, generated from the DMF-DMA, to the arylazonicotinates.
Experimental
General:
Melting points were recorded on a Griffin melting point apparatus and are reported
uncorrected. IR spectra were recorded as KBr disks using a Perkin-Elmer System 2000 FT-IR
1
spectrophotometer. H-NMR (400 MHz) or (600 MHz) and 13C-NMR (100 MHz) or (150
MHz) spectra were recorded at 25 °C using CDCl3 or DMSO-d6 solutions with TMS as an
internal standard on a Bruker DPX 400 or 600 super-conducting NMR spectrometer.

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Chemical shifts are reported in ppm. Mass spectra and HRMS were measured using high
resolution GC-MS (DFS) thermo spectrometers with EI (70 EV). Reaction monitoring and
determination of the homogeneity of the prepared compounds were performed by using thin
layer chromatography (TLC). Crystal structures were determined by uaing a Rigaku R-AXIS
RAPID diffractometer and Bruker X8 Prospector. Microanalyses were performed on a LECO
CHNS-932 Elemental Analyzer.
General procedure for the preparation 2-amino-5-arylazo-6-aryl nicotinates 3a-g.
Independent mixtures of 1 (10 mmol), active methylenenitrile derivatives 2a-b (10 mmol),
and ammonium acetate (2 g) in acetic acid (20 mL) were stirred at reflux for 1-2 h. with
progress of the reactions monitored using TLC with 1:1 ethyl acetate-petroleum ether as
eluent. The mixtures were cooled and then poured into ice-water. The formed solids were
collected by filtration and crystallized from the indicated solvents to give 3 as pure products.
2-Amino-5-(2-chloro-5-nitrophenylazo)-6-(4-chlorophenyl)nicotinic acid ethyl ester (3a).
Recrystallized from DMF as deep orange crystals, yield: (89%), m.p. 266–268 °C; IR (KBr):
ꢀ/cm−1 3378, 3281 (NH2), 1709 (CO ester); 1H-NMR (DMSO-d6): δ = 1.35 (t, 3H, J = 7.2 Hz,
CH3CH2), 4.38 (q, 2H, J = 7.2 Hz, CH3CH2), 7.57 (d, J = 8.4 Hz, 2H, Ar-H), 7.85 (d, J = 8.4
13
Hz, 2H, Ar-H), 7.96-8.41 (m, 5H, 3Ar-H and NH2) and 8.63 ppm (s, 1H, pyridine H4); C-
NMR (DMSO-d6, at 100°C): δ = 13.95 (CH3CH2), 61.24 (CH3CH2), 106.27 (pyridine C3),
112.67, 124.64, 127.54, 128.12, 131.94, 132.63, 134.75, 135.81, 137.06, 139.12, 147.22,
148.64, 160.30, 161.67 and 165.88 ppm (Ar-C and CO); MS (EI): m/z (%) 460 (M++1,
71.22), 459 (M+, 100); HRMS (EI): m/z calcd. for C20H1535Cl2N5O4 (M+) 459.0495, found

ACCEPTED MANUSCRIPT
459.0493. Anal. calcd. for C20H15Cl2N5O4 (460.28): C, 52.19; H, 3.28; N, 15.22. Found: C,
52.23; H, 3.35; N, 15.19.
2-Amino-5-(4-chloro-3-nitrophenylazo)-6-(4-bromophenyl)nicotinic acid ethyl ester (3b).
Recrystallized from DMF as orange crystals, yield: (83%), m.p. 245–246 °C; IR (KBr):
ꢀ/cm−1 3388, 3278 (NH2), 1702 (CO ester); 1H-NMR (DMSO-d6): δ = 1.36 (t, 3H, J = 7.2 Hz,
CH3CH2), 4.37 (q, 2H, J = 7.2 Hz, CH3CH2), 7.72 (d, J = 8.4 Hz, 2H, Ar-H), 7.76 (d, J = 8.4
Hz, 2H, Ar-H), 7.94-7.96 (m, 3H, Ar-H ), 8.33 (br, 2H, NH2, D2O exchangeable), and 8.60
ppm (s, 1H, pyridine H4); 13C-NMR (DMSO-d6, at 100°C): δ = 14.01 (CH3CH2), 61.21
(CH3CH2), 106.05 (pyridine C3), 119.04, 123.36, 126.57, 127.78, 130.53, 131.95, 132.75,
132.84, 136.22, 136.66, 148.22, 151.37, 160.11, 161.16 and 165.97 ppm (Ar-C and CO); MS
(EI): m/z (%) 505 (M+ +2, 58.32), 504 (M+ +1, 100), 503 (M+, 43.30), 502 (66.67); HRMS
(EI): m/z calcd. for C20H1579Br35ClN5O4 (M+) 502.9990, found 502.9960. Anal. calcd. for
C20H15BrClN5O4 (504.73): C, 47.59; H, 3.00; N, 13.88. Found: C, 47.70; H, 2.94; N, 13.79.
2-Amino-5-(2-chloro-5-nitrophenylazo)-6-(4-chlorophenyl)nicotinonitrile (3c). Recrysta-
llized from DMSO as reddish brown crystals, yield: (77%), m.p. above 300 °C; IR (KBr):
ꢀ/cm−1 3489, 3379 (NH2), 2220 (CN), 1628(C=N); 1H-NMR (DMSO-d6): δ = 7.57 (d, J = 8.4
Hz, 2H, Ar-H), 7.81 (d, J = 8.4 Hz, 2H, Ar-H), 7.96 (d, J = 8.8 Hz, 1H, Ar-H), 8.10 (s, 1H,
Ar-H), 8.17 (br, 2H, NH2, D2O exchangeable), 8.27 (d, J = 8.8 Hz, 1H, Ar-H) and 8.36 ppm

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(s, 1H, pyridine H4); 13C-NMR (DMSO-d6): δ = 90.85 (pyridine C3), 112.58, 115.83, 125.24,
127.69, 131.14, 132.13, 132.81, 134.92, 135.42, 136.15, 139.71, 146.97, 148.04, 160.51 and
161.67 ppm (CN and Ar-C); MS (EI): m/z (%) 414 (M+ +2, 73.05), 413 (M+ +1, 61.45), 412
(M+, 100); HRMS (EI): m/z calcd. for C18H1035Cl2N6O2 (M+) 412.0236, found 412.0237.
Anal. calcd. for C18H10Cl2N6O2 (413.23): C, 52.32; H, 2.44; N, 20.34. Found: C, 52.25; H,
2.53; N, 20.40. Crystallographic Analysis for 3c. The crystals were mounted on a glass
fiber. All measurements were performed on a Rigaku R-AXIS RAPID diffractometer using
filtered Mo-kα radiation. The data were collected at a temperature of 20 ± 1 °C to a maximum
2θ value of 55.0° using the ω scanning technique. The structure was solved by the charge
flipping method and expanded using Fourier techniques. The non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were refined using the riding model. Crystal Data,
C18H10Cl2N6O2, M = 413.23, triclinic, a = 8.918(1) Å, b = 10.696(1) Å, c = 13.217(2) Å, V
=1132.2(2) Å3, α = 73.044(6)°, β = 81.609(6)°, γ = 70.078(5)°, space group: P-1, Z = 2, Dcalc
= 1.441 g cm−3 , No. of reflection measured 4609, 2 θ
= 52.7°, R1 = 0.047. Figure 1
max
illustrates the structure as determined. Full data can be obtained on request from the CCDC.27
2-Amino-5-(4-chloro-3-nitrophenylazo)-6-(4-bromophenyl)nicotinonitrile (3d). Recry-
stallized from DMF as reddish brown crystals, yield: (73%), m.p. above 300 °C; IR (KBr):
1
ꢀ/cm−1 3459, 3352 (NH2), 2225 (CN), 1639 (C=N); H-NMR (DMSO-d6): δ = 7.68-7.71 (m,
4H, Ar-H), 7.91-7.94 (m, 2H, Ar-H), 8.03 (br, 2H, NH2, D2O exchangeable), 8.29 (s, 1H, Ar-
13
H) and 8.37 ppm (s, 1H, pyridine H4); C-NMR (DMSO-d6, at 100°C): δ = 91.08 (pyridine
C3), 116.32, 120.01, 124.15, 126.85, 127.13, 131.14, 131.77, 133.42, 133.47, 136.28, 136.48,
148.56, 151.32, 160.76 and 161.40 ppm (CN and Ar-C); MS (EI): m/z (%) 458 (M+ +2,

ACCEPTED MANUSCRIPT
48.15), 457 (M+ +1, 100), 456 (M+, 65.79), 455(35.26); HRMS (EI): m/z calcd. for C18H1079Br
35ClN6O2 (M+) 455.9731, found 455.9732. Anal. calcd. for C18H10BrClN6O2 (457.68): C,
47.24; H, 2.20; N, 18.36. Found: C, 47.17; H, 2.28; N, 18.29.
2-Amino-6-(4-chlorophenyl)-5-(4-nitrophenylazo)nicotinonitrile (3e). Recrystallized from
EtOH/dioxane mixture (1:1) as pale brown crystals, yield: (71%), m.p. 219-220 °C; IR (KBr):
ꢀ/cm−1 3331, 3214 (NH2), 2225 (CN), 1654 (C=N); 1H-NMR (DMSO-d6): δ = 7.58 (d, J = 8.0
Hz, 2H, Ar-H), 7.79 (d, J = 8.0 Hz, 2H, Ar-H), 7.85 (d, J = 8.0 Hz, 2H, Ar-H), 8.06 (s, 2H,
NH2, D2O exchangeable), 8.36 (d, J = 8.0 Hz, 2H, Ar-H) and 8.42 ppm (s, 1H, pyridine H4);
13C-NMR (DMSO-d6): δ = 90.71 (pyridine C3), 115.96, 123.43, 125.21, 127.90, 131.26,
132.87, 134.92, 135.54, 136.54, 147.87, 155.46, 160.40 and 161.17 ppm (CN and Ar-C) MS
(EI): m/z (%) 379 (M+ +1, 41.22), 378 (M+, 100); HRMS (EI): m/z calcd. for C18H1135ClN6O2
(M+) 378.0626, found 378.0625. Anal. calcd. for C18H11ClN6O2 (378.78): C, 57.08; H, 2.93;
N, 22.19. Found: C, 57.17; H, 2.99; N, 22.26.
2-Amino-5-(3-bromophenylazo)-6-(4-chlorophenyl)nicotinonitrile (3f). Recrystallized
from dioxane as brown crystals, yield: (72%), m.p. above 300 °C; IR (KBr): ꢀ/cm−1 3424,
1
3317 (NH2), 2208(CN), 1639(C=N); H-NMR (DMSO-d6): δ = 7.56-7.63 (m, 5H, Ar-H),
7.77-7.91 (m, 3H, 1 Ar-H and NH2), 7.97 (d, J = 8.4 Hz, 2H, Ar-H) and 8.22 ppm (s, 1H,
pyridine H4); MS (EI): m/z (%) 413 (M++2, 100), 412 (M++1, 25.22), 411 (M+, 71.85);

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HRMS (EI): m/z calcd. for C18H1179Br35ClN5 (M+) 410.9880, found 410.9879. Anal. calcd. for
C18H11BrClN5 (412.68): C, 52.39; H, 2.69; N, 16.97. Found: C, 52.47; H, 2.75; N, 17.06.
2-Amino-5-(3-chlorophenylazo)-6-(4-chlorophenyl)nicotinonitrile (3g). Recrystallized
from dioxane as brown crystals, yield: (68%), m.p. 248-250 °C; IR (KBr): ꢀ/cm−1 3337, 3201
1
(NH2), 2217 (CN), 1656 (C=N); H-NMR (DMSO-d6): δ = 7.56-7.60 (m, 4H, Ar-H), 7.67-
7.71 (m, 2H, Ar-H), 7.80 (d, J = 7.6 Hz, 2H, Ar-H), 7.92 (brs, 2H, NH2, D2O exchangeable)
13
and 8.37 ppm (s, 1H, pyridine H4); C-NMR (DMSO-d6): δ = 90.36 (pyridine C3), 115.99,
121.65, 121.72, 127.70, 128.31, 130.32, 131.10, 131.28, 132.72, 134.05, 134.66, 135.63,
153.11, 160.08 and 160.37 ppm (CN and Ar-C); MS (EI): m/z (%) 369 (M++2, 72.50), 368
(M++1, 53.24), 367 (M+, 100); HRMS (EI): m/z calcd. for C18H1135Cl2N5 (M+) 367.0386,
found 367.0384. Anal. calcd. for C18H11Cl2N5 (368.23): C, 58.71; H, 3.01; N, 19.02. Found:
C, 58.59; H, 2.96; N, 19.10.
General procedure for the preparation of 8, 10 and 14.
Independent mixtures of the 5-arylazonicotinonitriles 3c-g, 2-amino-5-arylazonicotinates
ethyl ester 3a-b, pyrido[2,3-d]pyrimidine 13b (5 mmol) in dry toluene (20 mL), all containing
N,N-dimethylformamide dimethylacetal (DMF-DMA) (1.2 mL, 10 mmol), were stirred at
reflux under nitrogen for 6 h. The separated solid products obtained on standing at room
temperature were collected by filtration, washed with petroleum ether and crystallized from
the proper solvent.
(E)-N′-[2-(2-Chloro-5-nitrophenyl)-7-(4-chlorophenyl)-4-cyano-3-dimethylamino-2H-
pyrazolo[3,4-c]pyridin-5-yl]-N,N-dimethylformamidine (8a). Recrystallized from EtOH/

ACCEPTED MANUSCRIPT
dioxane (1:1) mixture as orange crystals, yield: (77%), m.p. 230-231 °C; IR (KBr): ͪ/cm−1
1
2211 (CN); H-NMR (DMSO-d6): δ = 2.85 (s, 6H, 2CH3), 3.15 (s, 3H, CH3), 3.24 (s, 3H,
CH3), 7.64 (d, J = 8.4 Hz, 2H, Ar-H), 8.11 (d, J = 8.8 Hz, 1H, Ar-H), 8.50 (d, J = 8.8 Hz, 1H,
Ar-H), 8.71 (d, J = 8.4 Hz, 2H, Ar-H), 8.80 (s, 1H, Ar-H) and 8.95 ppm (s, 1H, amidine H);
13C-NMR (DMSO-d6): δ = 34.85 (CH3), 40.93 (CH3), 43.98 (2CH3), 83.21, 120.12, 120.66,
125.25, 127.03, 129.06, 131.91, 135.03, 136.51, 137.91, 138.40, 140.90, 144.49, 147.07,
151.51, 156.75, 158.37 and 163.19 ppm (Ar-C and CN); MS (EI): m/z (%) 524 (M++2,
63.14), 523 (M++1, 26.10), 522 (M+, 100); HRMS (EI): m/z calcd. for C24H2035Cl2N8O2 (M+)
522.1080, found 522.1080. Anal. calcd. for C24H20Cl2N8O2 (523.39): C, 55.08; H, 3.85; N,
21.41. Found: C, 55.15; H, 3.89; N, 21.44. Crystallographic Analysis for 8a. The crystals
were mounted on a glass fiber. All measurements were performed on a Rigaku R-AXIS
RAPID diffractometer using filtered Mo-kα radiation. The data were collected at a
temperature of 20 ± 1 °C to a maximum 2θ value of 55.0° using the ω scanning technique.
The structure was solved by the charge flipping method and expanded using Fourier
techniques. The non-hydrogen atoms were refined anisotropically. Hydrogen atoms were
refined using the riding model. Crystal Data, C24H20Cl2N8O2, M = 523.38, triclinic, a =
10.688(2) Å, b = 11.032(2) (1) Å, c = 12.728(2) Å, V =1300.8(4) Å3, α = 82.587(6)°, β =
81.792(6)°, γ = 61.393(5)°, space group: P-1 (#2), Z = 2, Dcalc = 1.336 g cm−3 , No. of
reflection measured 5903, 2 θ max = 54.9 °, R1 = 0.0463. Figure 2 illustrates the structure as
determined. Full data can be obtained on request from the CCDC.29
(E)-N′-[2-(4-Chloro-3-nitrophenyl)-7-(4-bromophenyl)-4-cyano-3-dimethylamino-2H-
pyrazolo[3,4-c]pyridin-5-yl]-N,N-dimethylformamidine (8b). Recrystallized from EtOH as

ACCEPTED MANUSCRIPT
1
orange crystals, yield: (69%), m.p. 131-132 °C; IR (KBr): ͪ/cm−1 2207 (CN); H-NMR
(DMSO-d6): δ = 2.96 (s, 6H, 2CH3), 3.16 (s, 3H, CH3), 3.26 (s, 3H, CH3), 7.79 (d, J = 8.8 Hz,
2H, Ar-H), 8.07 (d, J = 8.8 Hz, 1H, Ar-H), 8.15 (d, J = 8.8 Hz, 1H, Ar-H), 8.55 (s, 1H, Ar-H),
8.69 (d, J = 8.8 Hz, 2H, Ar-H) and 8.94 ppm (s, 1H, amidine H); 13C-NMR (DMSO-d6): δ =
34.90 (CH3), 40.94 (CH3), 43.99 (2CH3), 83.38, 120.12, 122.20, 123.00, 125.55, 126.14,
130.91, 132.05, 132.23, 132.91, 135.52, 138.49, 140.37, 143.00, 147.93, 151.42, 156.70 and
158.31 ppm (Ar-C and CN); MS (EI): m/z (%) 568 (M++2, 100), 567 (M++1, 21.80), 566 (M+,
71.88), 538(44.96); HRMS (EI): m/z calcd. for C24H2079Br35ClN8O2 (M+) 566.0575, found
522.0574. Anal. calcd. for C24H20BrClN8O2 (567.84): C, 50.77; H, 3.55; N, 19.73. Found: C,
50.85; H, 3.48; N, 19.62.
(E)-N′-[7-(4-Chlorophenyl)-4-cyano-3-dimethylamino-2-(4-nitrophenyl)-2H-pyrazolo[3,4-
c]pyridin-5-yl]-N,N-dimethylformamidine (8c). Recrystallized from EtOH/dioxane (2:1)
mixture as deep orange powder and recrystallized from DMSO as orange crystals which were
used for the X-ray single crystal measurement, yield: (72%), m.p. 147–148 °C; IR (KBr):
1
ͪ/cm−1 2208 (CN); H-NMR (DMSO-d6): δ = 2.88 (s, 6H, 2CH3), 3.12 (s, 3H, CH3), 3.20 (s,
3H, CH3), 7.59 (d, J = 8.4 Hz, 2H, Ar-H), 8.04 (d, J = 8.8 Hz, 2H, Ar-H), 8.45 (d, J = 8.8 Hz,
2H, Ar-H), 8.72 (d, J = 8.4 Hz, 2H, Ar-H) and 8.87 ppm (s, 1H, amidine H); 13C-NMR
(DMSO-d6): δ = 34.64(CH3), 40.72(CH3), 43.72(2CH3), 82.91, 119.85, 121.97, 124.82,

ACCEPTED MANUSCRIPT
126.59, 128.80, 131.74, 134.86, 136.21, 140.29, 142.72, 143.81, 147.35, 151.01, 156.41 and
157.99 ppm (Ar-C and CN); MS (EI): m/z (%) 490 (M++2, 35.77), 489 (M++1, 29.94) 488
(M+, 100); HRMS (EI): m/z calcd. for C24H2135ClN8O2 (M+) 488.1470, found 488.1470. Anal.
calcd. for C24H21ClN8O2 (488.94): C, 58.96; H, 4.33; N, 22.92. Found: C, 58.88; H, 4.36; N,
22.84. Crystallographic Analysis for 8c. The crystals were mounted on a glass fiber. All
measurements were performed on a Rigaku R-AXIS RAPID diffractometer using filtered Mo-
kα radiation. The data were collected at a temperature of 20 ± 1 °C to a maximum 2θ value of
55.0° using the ω scanning technique. The structure was solved by the charge flipping method
and expanded using Fourier techniques. The non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were refined using the riding model. Crystal Data, C24H2135ClN8O2, M =
488.94, triclinic, a = 9.627(6) Å, b = 11.130(7) (1) Å, c = 13.467(8) Å, V =1410(2) Å3, α =
89.789(7)°, β = 83.98(1)°, γ = 79.452(9)°, space group: P-1 (#2), Z = 2, Dcalc = 1.335g cm−3 ,
No. of reflection measured 5903, 2 θ max = 48.6°, R1 = 4461. Figure 3 illustrates the structure
as determined. Full data can be obtained on request from the CCDC.30
(E)-N′-[2-(3-Bromophenyl)-7-(4-chlorophenyl)-4-cyano-3-dimethylamino-2H-pyrazolo-
[3,4-c]pyridin-5-yl]-N,N-dimethylformamidine (8d). Recrystallized from EtOH as pale
1
orange crystals, yield: (71%), m.p. 170–171 °C; IR (KBr): ͪ/cm−1 2207 (CN); H-NMR
(DMSO-d6): δ = 2.90 (s, 6H, 2CH3), 3.02 (s, 3H, CH3), 3.11 (s, 3H, CH3), 7.57-7.65 (m, 4H,
Ar-H), 7.78 (d, J = 8.0 Hz, 1H, Ar-H), 7.85 (d, J = 8.0 Hz, 1H, Ar-H), 7.95 (s, 1H, Ar-H),
8.40 (d, J = 8.4 Hz, 1H, Ar-H) and 8.85 ppm (s, 1H, amidine H); MS (EI): m/z (%) 523
(M++2, 100), 522 (M++1, 26.91), 521 (M+, 73.31); HRMS (EI): m/z calcd. for C24H2179Br

ACCEPTED MANUSCRIPT
35ClN7 (M+) 521.0724, found 521.0724. Anal. calcd. for C24H21BrClN7 (522.84): C, 55.14; H,
4.05; N, 18.75. Found: C, 55.22; H, 3.94; N, 18.79.
(E)-N′-[2-(3-Chlorophenyl)-7-(4-chlorophenyl)-4-cyano-3-dimethylamino-2H-pyrazolo-
[3,4-c]pyridin-5-yl]-N,N-dimethylformamidine (8e). Recrystallized from EtOH as orange
crystals, yield: (68%), m.p. 191–192 °C; IR (KBr): ͪ/cm−1 2205 (CN); 1H-NMR (DMSO-d6):
δ = 2.89 (s, 6H, 2CH3), 3.01 (s, 3H, CH3), 3.10 (s, 3H, CH3), 7.57-7.64 (m, 4H, Ar-H), 7.77
(d, J = 8.0 Hz, 1H, Ar-H), 7.90 (s, 1H, Ar-H), 8.16 (d, J = 8.4 Hz, 2H, Ar-H), and 8.89 ppm
(s, 1H, amidine H); MS (EI): m/z (%) 478 (M++1, 56.95), 477 (M+, 100); HRMS (EI): m/z
calcd. for C24H2135Cl2N7 (M+) 477.1230, found 477.1230. Anal. calcd. for C24H21Cl2N7
(478.39): C, 60.26; H, 4.42; N, 20.50. Found: C, 60.34; H, 4.51; N, 20.42.
(E)-5-(2-Chloro-5-nitrophenylazo)-6-(4-chlorophenyl)-2-(dimethylaminomethyleneamino)-
nicotinic acid ethyl ester (10a). Recrystallized from dioxane as red crystals, yield: (79%), m.p.
196–197 °C; IR (KBr): ꢀ/cm−1 1745 (CO ester); 1H-NMR (DMSO-d6): δ = 1.33 (t, 3H, J = 7.2
Hz, CH3CH2), 3.12 (s, 3H, CH3), 3.23 (s, 3H, CH3), 4.33 (q, 2H, J = 7.2 Hz, CH3CH2), 7.57
(d, J = 8.8 Hz, 2H, Ar-H), 7.91 (d, J = 8.8 Hz, 2H, Ar-H), 7.99 (d, J = 8.4 Hz, 1H, Ar-H), 8.16
(s, 1H, Ar-H), 8.23 (s, 1H, amidine H), 8.30 (d, J = 8.4 Hz, 1H, Ar-H) and 8.82 ppm (s, 1H,
pyridine H4); 13C-NMR (DMSO-d6): δ = 14.52 (CH3CH2), 35.29 (CH3), 40.84 (CH3), 61.23
(CH3CH2), 113.22, 122.14, 125.54, 125.92, 128.08, 132.50, 133.30, 134.95, 136.80, 139.98,

ACCEPTED MANUSCRIPT
140.08, 147.72, 149.14, 157.25, 158.55, 162.17 and 166.99 ppm (Ar-C and CO); MS (EI):
m/z (%) 516 (M++2, 69.24), 515 (M++1, 24.71), 514 (M+, 100); HRMS (EI): m/z calcd. for
C23H2035Cl2N6O4 (M+) 514.0917, found 514.0917. Anal. calcd. for C23H20Cl2N6O4 (515.36):
C, 53.60; H, 3.91; N, 16.31. Found: C, 53.57; H, 3.87; N, 16.24.
(E)-5-(4-Chloro-3-nitrophenylazo)-6-(4-bromophenyl)-2-(dimethylaminomethyleneamino)-
nicotinic acid ethyl ester (10b). Recrystallized from dioxane as orange crystals, yield: (77%),
m.p. 218–220 °C; IR (KBr): ꢀ/cm−1 1729 (CO ester); 1H-NMR (DMSO-d6): δ = 1.33 (t, 3H, J
= 7.2 Hz, CH3CH2), 3.10 (s, 3H, CH3), 3.22 (s, 3H, CH3), 4.32 (q, 2H, J = 7.2 Hz, CH3CH2),
7.70 (d, J = 8.4 Hz, 2H, Ar-H), 7.79(d, J = 8.4 Hz, 2H, Ar-H), 7.96-7.97 (m, 2H, Ar-H), 8.22
(s, 1H, amidine H), 8.34 (s, 1H, Ar-H) and 8.76 ppm (s, 1H, pyridine H4); 13C-NMR (DMSO-
d6): δ = 14.15 (CH3CH2), 34.61 (CH3), 42.08 (CH3), 60.83 (CH3CH2), 112.45, 121.26, 123.16,
125.29, 125.37, 125.92, 126.70, 128.18, 128.87, 130.52, 130.64, 133.08, 133.23, 137.32,
146.90, 156.70 and 166.48 ppm (Ar-C and CO); MS (EI): m/z (%) 560 (M++2, 100), 559
(M++1, 65.19), 558 (M+, 72.46), 529(89.23); HRMS (EI): m/z calcd. for C23H2079Br35ClN6O4
(M+) 558.0412, found 558.0412. Anal. calcd. for C23H20BrClN6O4 (559.81): C, 49.35; H,
3.60; N, 15.01. Found: C, 49.44; H, 3.66; N, 14.94.
4-(4-Bromophenyl)-2-(4-chloro-3-nitrophenyl)-1-dimethylamino-8-methyl-2,8-di-hydro-
pyrazolo[4',3':4,5]pyrido[2,3-d]pyrimidin-9-one (14). Recrystallized from EtOH/dioxane
(1:1) mixture as pale orange crystals, yield: (70%), m.p. 215–216 °C; IR (KBr): ꢀ/cm−1 1672

ACCEPTED MANUSCRIPT
1
(CO); H-NMR (DMSO-d6): δ = 2.91 (s, 6H, 2CH3), 3.62 (s, 3H, CH3), 7.83 (d, J = 8.4 Hz,
2H, Ar-H), 8.07 (d, J = 8.8 Hz, 1H, Ar-H), 8.16 (d, J = 8.8 Hz, 1H, Ar-H), 8.56 (s, 1H, Ar-H),
8.63 (d, J = 8.4 Hz, 2H, Ar-H) and 8.65 ppm (s, 1H, pyrimidine H7); 13C-NMR (DMSO-d6): δ
= 34.58 (CH3), 44.65 (2CH3), 108.50, 115.16, 123.24, 125.65, 126.17, 131.22, 132.00,
132.14, 132.38, 132.56, 132.83, 135.21, 142.24, 146.85, 149.89, 154.90, 155.66 and 160.06
ppm (Ar-C and CO); MS (EI): m/z (%) 555 (M++2, 100), 554 (M++1, 26.96), 553(M+,
76.39); HRMS (EI): m/z calcd. for C23H1779Br35ClN7O3 (M+) 553.0259, found 553.0253.
Anal. calcd. for C23H17BrClN7O3 (554.79): C, 49.79; H, 3.09; N, 17.67. Found: C, 49.87; H,
3.16; N, 17.64.
General Procedure for the Preparation of 9a-c and 13a-b.
Independent solutions of the pyrazolo[3,4-c]pyridine 8a-c, and amidines 10a-b (2.5 mmol) in
AcOH (10 mL) containing ammonium acetate (1.0 g) were stirred at reflux for 3 h. The
mixtures were cooled to room temperature and poured into ice cold water. The formed solids
were collected by filtration, washed with water and crystallized from the indicated solvents to
afford 9a-c and 13a-b as pure products.
2-(2-Chloro-5-nitrophenyl)-4-(4-chlorophenyl)-1-dimethylamino-2H-pyrazolo[4',3':4,5]-
pyrido[2,3-d]pyrimidine-9-amine (9a). Recrystallized from acetic acid as pale yellow
1
crystals, yield: (67%), m.p. 287-288 °C; IR (KBr): ꢀ /cm−1 3433, 3267 (NH2); H-NMR
(DMSO-d6): δ = 2.80 (s, 6H, 2CH3), 7.69 (d, J = 8.4 Hz, 2H, Ar-H), 8.19 (d, J = 8.8 Hz, 1H,
Ar-H), 8.58-8.65 (m, 4H, 3Ar-H and pyrimidine H7), 9.04 (s, 1H, Ar-H) and 7.99, 9.21 (2 br,
2H, NH2, D2O exchangeable); MS (EI): m/z (%) 496 (M+ +2, 60.67), 495 (M+ +1, 22.00), 494
(M+, 100); HRMS (EI): m/z calcd. for C22H1635Cl2N8O2 (M+) 494.0767, found 494.0767.

ACCEPTED MANUSCRIPT
Anal. calcd. for C22H16Cl2N8O2 (495.33): C, 53.35; H, 3.26; N, 22.62. Found: C, 53.23; H,
3.33; N, 22.55.
4-(4-Bromophenyl)-2-(4-chloro-3-nitrophenyl)-1-dimethylamino-2H-pyrazolo[4',3':4,5]-
pyrido[2,3-d]pyrimidine-9-amine (9b). Recrystallized from acetic acid as yellow crystals,
yield: (71%), m.p. 259-260 °C; IR (KBr): ꢀ /cm−1 3445, 3272 (NH2); 1H-NMR (DMSO-d6): δ
= 2.76 (s, 6H, 2CH3), 7.82 (d, J = 8.4 Hz, 2H, Ar-H), 8.15 (d, J = 8.8 Hz, 1H, Ar-H), 8.23 (d,
J = 8.8 Hz, 1H, Ar-H), 8.57(s, 1H, pyrimidine H7), 8.59 (d, J = 8.4 Hz, 2H, Ar-H), 8.70 (s,
1H, Ar-H) and 7.97, 9.13 (2 br, 2H, NH2, D2O exchangeable); MS (EI): m/z (%) 540 (M+ +2,
100), 539 (M+ +1, 21.66), 538 (M+, 77.59); HRMS (EI): m/z calcd. for C22H1679Br ClN8O2
(M+) 538.0262, found 538.0266. Anal. calcd. for C22H16BrClN8O2 (539.78): C, 48.95; H,
2.99; N, 20.76. Found: C, 48.88; H, 2.97; N, 20.69.
4-(4-Chlorophenyl)-2-(4-nitrophenyl)-1-dimethylamino-2H-pyrazolo[4',3':4,5]pyrido-
[2,3-d]pyrimidine-9-amine (9c). Recrystallized from acetic acid as pale orange crystals,
yield: (73 %), m.p. 265-266 °C; IR (KBr): ꢀ /cm−1 3437, 3263 (NH2); 1H-NMR (DMSO-d6): δ
= 2.75 (s, 6H, 2CH3), 7.68 (d, J = 8.8 Hz, 2H, Ar-H), 8.13 (d, J = 8.8 Hz, 2H, Ar-H), 8.54 (d,
J = 8.8 Hz, 2H, Ar-H), 8.57 (s, 1H, pyrimidine H7), 8.67 (d, J = 8.8 Hz, 2H, Ar-H) and 7.99,
13
9.11 (2 br, 2H, NH2, D2O exchangeable); C-NMR (DMSO-d6): δ = 44.01 (2CH3), 100.24,
114.27, 125.04, 125.35, 129.09, 129.35, 132.01, 135.22, 136.47, 141.71, 144.08, 145.57,

ACCEPTED MANUSCRIPT
148.95, 155.42, 157.04 and 162.14 ppm (Ar-C); MS (EI): m/z (%) 462 (M+ +2, 33.85), 461
(M+ +1, 27.05), 460 (M+, 100); HRMS (EI): m/z calcd. for C22H1735ClN8O2 (M+) 460.1157,
found 460.1156. Anal. calcd. for C22H17ClN8O2 (460.88): C, 57.33; H, 3.72; N, 24.31. Found:
C, 57.45; H, 3.58; N, 24.22.
6-(2-Chloro-5-nitrophenylazo)-7-(4-chlorophenyl)-3H-pyrido[2,3-d]pyrimidin-4-one (13a).
Recrystallized from DMF/dioxane mixture (1:1) as reddish brown crystals, yield: (74%), m.p.
above 300 °C; IR (KBr): ꢀ
/cm−1 3212 (NH), 1702 ( CO); 1H-NMR (DMSO-d6): δ = 7.62 (d, J
= 8.4 Hz, 2H, Ar-H), 7.87 (d, J = 8.4 Hz, 2H, Ar-H), 8.04 (d, J = 8.8 Hz, 1H, Ar-H), 8.16 (s,
1H, Ar-H), 8.37 (d, J = 8.8 Hz, 1H, Ar-H), 8.46 (s, 1H, pyrimidine H2), 8.66 (s, 1H, pyridine
13
H5) and 12.74 ppm (s, 1H, NH); C-NMR (DMSO-d6): δ = 112.84, 117.23, 123.10, 126.31,
127.88, 132.31, 133.12, 134.84, 135.78, 135.93, 140.48, 142.44, 146.98, 148.06, 154.98,
158.82 and 160.94 ppm (Ar-C and CO); MS (EI): m/z (%) 442 (M++2, 55.15), 441 (M++1,
21.67), 440 (M+, 100); HRMS (EI): m/z calcd. for C19H1035Cl2N6O3 (M+) 440.0185, found
440.0183. Anal. calcd. for C19H10Cl2N6O3 (441.24): C, 51.72; H, 2.28; N, 19.05. Found: C,
51.68; H, 2.34; N, 19.13.
7-(4-Bromophenyl)-6-(4-chloro-3-nitrophenylazo)-3H-pyrido[2,3-d]pyrimidin-4-one (13b).
Recrystallized from DMF/dioxane mixture (2:1) as pale orange crystals, yield: (75%), m.p.
above 300 °C; IR (KBr): ꢀ/cm−1 3218 (NH), 1713 ( CO); 1H-NMR (DMSO-d6): δ = 7.72-7.78

ACCEPTED MANUSCRIPT
(m, 4H, Ar-H), 8.00 (d, J = 8.4 Hz, 1H, Ar-H), 8.06 (d, J = 8.4 Hz, 1H, Ar-H), 8.46 (s, 1H,
pyrimidine H2), 8.48 (s, 1H, Ar-H), 8.64 (s, 1H, pyridine H5) and 12.79 ppm (s, 1H, NH);
13C-NMR (DMSO-d6): δ = 117.41, 117.47, 120.45, 123.24, 124.04, 127.02, 128.05, 130.99,
133.10, 133.31, 135.71, 142.90, 148.12, 150.55, 150.77, 160.00 and 160.72 ppm (Ar-C and
CO); MS (EI): m/z (%) 486 (M++2, 100), 485 (M++1, 83.28), 484 (M+, 75.53), 483(52.26);
HRMS (EI): m/z calcd. for C19H1079Br35ClN6O3 (M+) 483.9680, found 483.9680. Anal. calcd.
for C19H10BrClN6O3 (485.69): C, 46.99; H, 2.08; N, 17.30. Found: C, 46.87; H, 2.17; N,
17.23.
General procedure for the preparation 15a-b and 16a-b.
Independent solutions of the azonicotinates 3a-b (5 mmol) in acetic anhydride (10 mL) were
stirred at reflux for 4 h in the cases for 15a-b formation and in the case of 16a-b formation for
12 h. The mixtures were cooled to room temperature and the formed solids were collected by
filtration, washed with ethanol and rcrystallized from the indicated solvent.
2-Acetylamino-5-(2-chloro-5-nitrophenylazo)-6-(4-chlorophenyl)nicotinic acid ethyl
ester (15a). Recrystallized from EtOH/dioxane (2:1) mixture as reddish orange crystals, yield:
(83%), m.p. 257-258 °C; IR (KBr): ꢀ/cm−1 3231 (NH), 1719, 1673 (2 CO); 1H-NMR (DMSO-
d6): δ = 1.30 (t, 3H, J = 7.2 Hz, CH3CH2), 2.23 (s, 3H, COCH3), 4.29 (q, 2H, J = 7.2 Hz,
CH3CH2), 7.64 (d, J = 8.4 Hz, 2H, Ar-H), 7.91 (d, J = 8.4 Hz, 2H, Ar-H), 8.06 (d, J = 8.4 Hz,
1H, Ar-H), 8.20 (s, 1H, Ar-H), 8.39 (d, J = 8.4 Hz, 1H, Ar-H), 8.43 (s, 1H, pyridine H4) and
13
11.22 ppm (s, 1H, NH); C-NMR (DMSO-d6): δ = 14.49 (CH3), 24.38 (CH3), 61.78 (CH2),
113.36, 119.16, 126.98, 128.44, 129.16, 131.98, 132.11, 132.78, 133.57, 135.32, 135.57,
141.21, 147.48, 148.45, 158.16, 165.63 and 170.34 ppm (Ar-C and CO); MS (EI): m/z (%)

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502 (M++1, 72.45), 501 (M+, 100),. HRMS (EI): m/z calcd. for C22H1735Cl2N5O5 (M+)
501.0601, found 501.0602. Anal. calcd. for C22H17Cl2N5O5 (502.32): C, 52.61; H, 3.41; N,
13.94. Found: C, 52.64; H, 3.37; N, 13.88.
2-Acetylamino-5-(4-chloro-3-nitrophenylazo)-6-(4-bromophenyl)nicotinic acid ethyl ester
(15b). Recrystallized from EtOH/dioxane (2:1) mixture as reddish orange crystals, yield:
(85%), m.p. 207-208 °C; IR (KBr): ꢀ/cm−1 3265 (NH), 1713, 1668 (2 CO); 1H-NMR (DMSO-
d6): δ = 1.30 (t, 3H, J = 7.2 Hz, CH3CH2), 2.22 (s, 3H, COCH3), 4.28 (q, 2H, J = 7.2 Hz,
CH3CH2), 7.74-7.81 (m, 4H, Ar-H), 8.00 (d, J = 8.8 Hz, 1H, Ar-H), 8.07 (d, J = 8.8 Hz, 1H,
13
Ar-H), 8.41 (s, 1H, pyridine H4), 8.47 (s, 1H, Ar-H) and 11.17 ppm (s, 1H, NH); C-NMR
(DMSO-d6): δ = 14.06 (CH3), 23.93(CH3), 61.31(CH2), 118.55, 120.40, 123.91, 126.86,
127.06, 127.64, 130.98, 133.06, 133.26, 135.21, 140.51, 148.18, 150.62, 150.73, 157.14,
165.19 and 169.81 ppm (Ar-C and CO); MS (EI): m/z (%) 547 (M++2, 100), 546 (M++1,
80.16), 545 (M+, 75.53), 544(47.46); HRMS (EI): m/z calcd. for C22H1779Br35ClN5O5 (M+)
545.0096, found 545.0096. Anal. calcd. for C22H17BrClN5O5 (546.77): C, 48.33; H, 3.13; N,
12.81. Found: C, 48.39; H, 3.21; N, 12.77. Crystallographic Analysis for 15b. The crystals
were mounted on a glass fiber. All measurements were performed on Bruker X8 Prospector.
The data were collected at a temperature of 20 ± 1 °C to a maximum θ value of 66.61° using
the ω scanning technique. The structure was solved by the direct method using SHELXS-97
(Sheldrick, 2008) and refined by Full-matrix least-squares on F2. The non-hydrogen atoms
were refined anisotropically. Data were corrected for absorption effects using the multi-scan
method (SADABS). Crystal Data, C22H17BrClN5O5, M = 546.76, monoclinic, a = 9.6837(2)
Å, b = 22.9877(4) Å, c = 20.6329(4) Å, V = 4574.66(15) Å3, α = γ = 90.00°, β =

ACCEPTED MANUSCRIPT
95.1230(10)°, space group: P 1 21/c 1, Z = 4, Dcalc = 1.588 g cm−3 , No. of reflection measured
8056, 2 θ max = 66.68°, R1 = 0.064. Figure 4 illustrates the structure as determined. Full data
can be obtained on request from the CCDC.31
5-(2-Chloro-5-nitrophenylazo)-6-(4-chlorophenyl)-2-diacetylaminonicotinic acid ethyl
ester (16a). Recrystallized from EtOH as red crystals, yield: (89%), m.p. 229-230 °C; IR
(KBr): ꢀ/cm−1 3231 (NH), 1720, 1705, 1681 (3 CO); 1H-NMR (DMSO-d6): δ = 1.31 (t, 3H, J
= 7.2 Hz, CH3CH2), 2.31 (s, 6H, 2COCH3), 4.36 (q, 2H, J = 7.2 Hz, CH3CH2), 7.64 (d, J = 8.4
Hz, 2H, Ar-H), 7.91 (d, J = 8.4 Hz, 2H, Ar-H), 8.10 (d, J = 8.4 Hz, 1H, Ar-H), 8.23 (s, 1H,
Ar-H), 8.45 (d, J = 8.4 Hz, 1H, Ar-H) and 8.64 ppm (s, 1H, pyridine H4); 13C-NMR (DMSO-
d6): δ = 14.34 (CH3), 26.75 (CH3), 62.67 (CH2), 113.56, 124.98, 127.68, 128.44, 128.73,
129.79, 132.93, 133.57, 133.76, 134.51, 136.14, 141.32, 144.73, 147.51, 148.43, 152.96,
158.34, 163.37 and 172.37 ppm (Ar-C and CO); MS (EI): m/z (%) 544 (M++1, 2.95), 543
(M+, 8.55); HRMS (EI): m/z calcd. for C24H1935Cl2N5O6 (M+) 543.0706, found 543.0709.
Anal. calcd. for C24H19Cl2N5O6 (544.35): C, 52.96; H, 3.52; N, 12.87. Found: C, 53.02; H,
3.45; N, 12.94.
6-(4-Bromophenyl)-5-(4-chloro-3-nitrophenylazo)-2-diacetylaminonicotinic acid ethyl
ester (16b). Recrystallized from EtOH as orange crystals, yield: (89%), m.p. 180-181 °C; IR
1
(KBr): ꢀ/cm−1 1720, 1696, 1672 (3 CO); H-NMR (DMSO-d6): δ = 1.31 (t, 3H, J = 7.2 Hz,

ACCEPTED MANUSCRIPT
CH3CH2), 2.30 (s, 6H, 2COCH3), 4.35 (q, 2H, J = 7.2 Hz, CH3CH2), 7.76-7.82 (m, 4H, Ar-H),
8.07 (d, J = 8.8 Hz, 1H, Ar-H), 8.14 (d, J = 8.8 Hz, 1H, Ar-H), 8.60 (s, 1H, Ar-H) and 8.65
ppm (s, 1H, pyridine H4); 13C-NMR (DMSO-d6): δ = 13.93 (CH3), 26.31(2CH3), 62.18(CH2),
121.00, 124.39, 124.53, 126.96, 128.52, 129.22, 131.27, 133.18, 133.44, 134.42, 144.17,
148.30, 150.55, 152.26, 157.49, 162.97 (Ar-C) and 171.92 ppm (2 CO); MS (EI): m/z (%)
589 (M++2, 100), 588 (M++1, 24.27), 587 (M+, 75.54), 586(4.03); HRMS (EI): m/z calcd. for
C24H1979Br35ClN5O6 (M+) 587.0201, found 587.0201. Anal. calcd. for C24H19BrClN5O6
(588.81): C, 48.96; H, 3.25; N, 11.89. Found: C, 48.88; H, 3.28; N, 11.97.
(E)-N-[6-(4-Bromophenyl)-5-(4-chloro-3-nitrophenylazo)-3-cyanopyridin-2-yl]form-
imidic acid ethyl ester (17). A mixture of 5-arylazonicotinonitrile 3d (1.14 g, 5 mmol) and
triethylorthoformate (1.2 mL, 10 mmol) in dry toluene (20 mL) was stirred at reflux under
nitrogen for 12 h. The separated solid product obtained upon standing at room temperature
was collected by filtration, washed with petroleum ether and crystallized from EtOH/dioxane
(1:1) mixture as orange crystals. yield: (74 %), m.p. 208-209 °C; IR (KBr): ꢀ/cm−1 2232
(CN), 1621 (C=N); 1H-NMR (DMSO-d6): δ = 1.40 (t, 3H, J = 7.2 Hz, CH3CH2), 4.47 (q, 2H,
J = 7.2 Hz, CH3CH2), 7.74 (d, J = 8.4 Hz, 2H, Ar-H), 7.82 (d, J = 8.4 Hz, 2H, Ar-H), 8.02-
8.08 (m, 2H, Ar-H ), 8.46 (s, 1H, Ar-H), 8.58 (s, 1H, amidine H) and 8.82 ppm (s, 1H,
13
pyridine H4); C-NMR (DMSO-d6): δ = 14.40 (CH3), 64.85 (CH2), 103.34, 116.10, 120.86,
124.82, 127.53, 128.49, 131.51, 131.82, 133.66, 133.92, 135.67, 141.96, 148.61, 150.92,
158.51, 161.87 and 163.50 ppm (Ar-C and CN), MS (EI): m/z (%) 514 (M+ +2, 85.15), 513
(M+ +1, 100), 512 (M+, 65.77), 511 (70.10); HRMS (EI): m/z calcd. for C21H1479Br35ClN6O3

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(M+) 511.9993, found 511.9993. Anal. calcd. for C21H14BrClN6O3 (513.74): C, 49.10; H,
2.75; N, 16.36. Found: C, 49.14; H, 2.69; N, 16.29.
Acknowledgements
Financial support for this study was provided by the University of Kuwait through a research
grant (SC03/11). The facilities of Analab/SAF supported by research grants GS01/01,
GS01/05, GS01/03 and GS03/08 are gratefully acknowledged. We are also grateful to Prof.
Herbert Meier from Mainz University, Germany for providing a key reference and suggesting
[4+1] cycloaddition mechanism.
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