Synthesis of some ethyl 3-(aryldiazenyl)-7-oxo-dihydropyrido[2,3-f] quinoxaline-8-carboxylates

Article abstract of DOI:10.1515/znb-2007-0807

Ethyl 7,8-diamino-1-cyclopropyl-6-fluoro-4-oxo-1,4-dihydroquinoline-3- carboxylate (6) and its free acid 7 are prepared by chemical reduction of the respective 7-azido-8-nitroquinoline 5. Consecutive nucleophilic addition and cyclocondensation reactions o

Full text of DOI:10.1515/znb-2007-0807

Synthesis of Some Ethyl 3-(Aryldiazenyl)-7-oxo-dihydro-
pyrido[2,3-f]quinoxaline-8-carboxylates
Jalal A. Zahraa, Monther A. Khanfara, Mustafa M. El-Abadelaha, Bassam A. Abu Thaherb,
Naser S. El-Abadlac, and Wolfgang Voelterd
a Chemistry Department, Faculty of Science, The University of Jordan, Amman, Jordan
b Chemistry Department, Faculty of Science, Islamic University of Gaza, Gaza Strip
c Chemistry Department, Faculty of Science, Al-Aqsa University, Gaza Strip
d Interfakulta¨res Institut fu¨r Biochemie, Universita¨t Tu¨bingen, Hoppe-Seyler Str. 4,
D-72076 Tu¨bingen, Germany
Reprint requests to Prof. Dr. W. Voelter. E-mail: wolfgang.voelter@uni-tuebingen.de or
Dr. J. A. Zahra. E-mail: zahra@ju.edu.jo
Z. Naturforsch. 2007, 62b, 1045 – 1051; received February 15, 2007
Ethyl 7,8-diamino-1-cyclopropyl-6-fluoro-4-oxo-1,4-dihydroquinoline-3-carboxylate (6) and its
free acid 7 are prepared by chemical reduction of the respective 7-azido-8-nitroquinoline 5. Consec-
utive nucleophilic addition and cyclocondensation reactions of 6 with α-acetyl-N-arylhydrazonoyl
chlorides 8a – c in ethanol and triethylamine are site-selective and yield the corresponding 3-(aryldi-
azinyl)-2-methylpyrido[2,3- f ]quinoxalines 10a – c. Analytical and spectral (IR, MS, NMR) data of
6, 7, and 10a – c are in conformity with the assigned structures.
Key words: 7,8-Diamino-4-oxoquinoline-3-carboxylate, α-Acetyl-N-arylhydrazonoyl Chlorides,
Ethyl 7-Oxopyrido[2,3- f ]quinoxaline-8-carboxylates
Introduction
The quinoxaline system in its 2-quinoxalinylcarbon-
yl form is found appended to the cyclic peptide core of
quinomycins related to naturally occurring quinoxal-
ine-peptide antibiotics that also exhibit antitumor ac-
tivity [1, 2]. Numerous quinoxaline derivatives have at-
tracted attention owing to their biological importance
and have been synthesized by many research groups
[3 – 5]. Examples include species with antifungal [6],
anticancer [7] and antituberculosis [8] activities as well
as adenosine-binding [9] and benzodiazepine receptor
binding [10] properties. On the other hand, synthetic
second generation “floroquinolones” [11– 13], exem-
plified by ciprofloxacin 1 [13], represent a major class
of antibacterial agents with great therapeutic potential,
while some related derivatives, such as 2 [14], exhibit
antitumor activity [14, 15].
the structural features of both, fluoroquinolone (rings
A, B) and substituted quinoxaline (rings B, C) chemo-
types. Such hybrid heterocyclic systems might exhibit
interesting bioproperties. In this context, it is worth
mentioning that two 7-oxo-7,10-dihydropyrido[2,3-
f]quinoxaline-8-carboxylic acid derivatives (3a, 3b),
lacking an N-10 substituent, were once prepared
[16] by annulation of the pyridine moiety onto the
appropriate 5-aminoquinoxaline via the Gould-Jacobs
reaction (Scheme 1).
In the present study, we wish to report on the syn-
thesis and properties of 4-oxopyridine-3-carboxylic
acid condensed with a substituted quinoxaline entity
(compounds 10a – c) as depicted in Scheme 3. This
tricyclic system, namely, ethyl 10-cyclopropyl-5-
fluoro-2-methyl-7-oxo-3-(aryldiazenyl)-7,10-dihydro-
Results and Discussion
Ethyl 7-chloro-1-cyclopropyl-6-fluoro-8-nitro-6-
pyrido[2,3-f]quinoxaline-8-carboxylate encompasses oxo-1,4-dihydroquinoline-3-carboxylate (4) [17, 18]
0932–0776 / 07 / 0800–1045 $ 06.00 © 2007 Verlag der Zeitschrift fu¨r Naturforschung, Tu¨bingen · http://znaturforsch.com
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J. A. Zahra et al. · Ethyl 3-(Aryldiazenyl)-7-oxo-dihydropyrido[2,3-f ]quinoxaline-8-carboxylates
Scheme 1.
Scheme 2.
Scheme 3.
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J. A. Zahra et al. · Ethyl 3-(Aryldiazenyl)-7-oxo-dihydropyrido[2,3-f ]quinoxaline-8-carboxylates
1047
Scheme 4.
was readily converted into the corresponding 7- the more nucleophilic 8-amino group in 6 with the
azido-8-nitroquinoline ester 5 following a reported electrophilic keto group in 9a – c. This step is fol-
procedure [19] (Scheme 2). Chemical reduction of 5 lowed by intramolecular 1,3-nucleophilic addition in-
with stannous chloride in boiling ethanol furnished the volving the 7-amino group and the electrophilic car-
corresponding 7,8-diaminoquinoline ester 6 together bon atom of the nitrile imine. Ultimately, these con-
with the 7,8-diaminoquinoline-3-carboxylic acid 7 secutive steps would lead to the initial formation
which was isolated in a separate step as detailed in of the respective 3-(N-arylhydrazono)-1,2,7,10-tetra-
the Experimental Section. Comparable results were hydropyrido[2,3-f]quinoxalines 12A which probably
obtained upon reduction of 5 with tin and 3N aqueous are in equilibrium with their 3-(N-arylhydrazono) tau-
hydrochloric acid under reflux conditions, wherein 7 is tomeric forms 12B (Scheme 4). However, no attempt
produced in higher proportion than 6 (Scheme 2). The was made to isolate the intermediate free bases 12A
formation of 7 is the result of partial hydrolysis of the which are expected to be unstable upon contact with
ester 6 as catalyzed by the prevailing acidic reduction air oxygen and easily undergo oxidation (via 12B) into
conditions under reflux.
the respective 3-arylazo derivatives 10a – c.
Direct interaction of the 7,8-diaminoquinoline es-
ter 6 with each of the α-acetyl-N-arylhydrazonoyl
chlorides 8a – c in ethanol and triethylamine under
reflux yielded the respective 3-arylazo-2-methylpyr-
ido[2,3-f]quinoxalines 10a – c regioselectively as the
main isolable end products (Scheme 3). The synthon 6
with its 7,8-diamino groups acts as a bis-nucleophile,
whilst the α-acetylnitrile imine 1,3-dipolar species
9a – c (generated in situ from the respective precursors
8a – c) act as bis-electrophiles. This reaction was mod-
eled after the recently described interaction between o-
diaminobenzene and α-acetylnitrile imine 1,3-dipolar
species [20]. Such one-pot cyclocondensation pro-
cesses are reminiscent of the known cyclization re-
actions of α-acetylnitrile imines towards various nu-
cleophilic compounds for which some recent reviews
were published [21, 22].
The IR, MS and NMR spectral data of 6, 7, and
10a – c, given in the Experimental Section, are in ac-
cordance with the suggested structures. Thus, their MS
spectra display the correct molecular ion peaks for
which the measured HRMS data are in good agreement
with the values calculated for the molecular formulae.
1
Assignments of the H and 13C signals to the differ-
ent respective protons and carbons are based on DEPT
and 2D (COSY, HMQC, HMBC) experiments which
showed correlations consistent with these assignments.
Thus, strong 1,3-correlation is observed between the
methyl protons of 2-Me at C-2 and C-3 which features
as a doublet due to coupling with the fluorine atom;
conversely, a much weaker 1,2-correlation is observed
with the singlet signal of C-2. Such correlations are
compatible with the structures 10a – c. Long-rangecor-
relations are also observed between 9-H and each of
It is noteworthy that none of the 3-arylazo-2-methyl CO2Et, C-7, C-10a and C-1ꢀ, as well as between 6-H
structural isomers 11a – c (Scheme 3) were isolated and each of C-7, C-4a and C-10a, and between 1ꢀ-H
in the process. The cyclization reaction thus ap- and each of C-9 and C-10a. In compounds 6 and 7, cor-
pears to be site-selective, at least under the condi- responding long-range correlations are also observed
tions employed, and to proceed via condensation of between 2-H, 5-H and their neighbor carbons.
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J. A. Zahra et al. · Ethyl 3-(Aryldiazenyl)-7-oxo-dihydropyrido[2,3-f ]quinoxaline-8-carboxylates
Experimental Section
hydrogen carbonate and extracted with ethyl acetate (2 ×
40 mL). The combined organic extracts were dried (MgSO4),
2,4-Dichloro-5-fluoro-3-nitrobenzoic acid, ethyl 3-(N,N-
dimethylamino)acrylate, cyclopropylamine and 3-chloro-
pentane-2,4-dione were purchased from Acros. Melting
points were determined on a Gallenkamp electrothermal
melting-temperature apparatus. 1H and 13C NMR spectra
were measured on a Bruker DPX-300 instrument with Me4Si
as internal reference. EIMS spectra were obtained using a
Finnigan MAT TSQ-70 spectrometer at 70 eV and an ion
the solvent was evaporated in vacuo and the residual solid
product recrystallized from chloroform / pet. ether (b. p. 40 –
60 ◦C) to deliver 0.37 g (37 %) of the diamino ester 6,
◦
m. p. 284 – 286 C (dec.). – IR (KBr): ν = 3462 (br), 3389,
3295, 3081, 2977, 1718, 1672, 1612, 1561, 1461, 1343,
1279, 1232, 1178, 1129, 1035 cm−1. – 1H NMR (300 MHz,
CDCl3): δ = 0.88 [(m, 2H) and 1.08 (m, 2H), 2ꢀ-H2
+
3ꢀ-H2)], 1.21 (t, J = 7.1 Hz, 3H, CH3CH2), 4.14 (q, J =
7.1 Hz, 2H, CH2Me), 4.30 (m, 1H, 1ꢀ-H), 5.05 (s, 2H, C8-
NH2), 5.43 (s, 2H, C7-NH2), 7.19 (d,3JH−F =11.2 Hz, 1H,
5-H), 8.39 (s, 1H, 2-H). – 13C NMR (75 MHz, CDCl3):
δ = 10.6 (C-2ꢀ + C-3ꢀ), 14.8 (CH3CH2), 38.5 (C-1ꢀ), 60.0
◦
source temperature of 200 C. IR spectra were recorded as
KBr discs on a Nicolet Impact-400 FT-IR spectrophotometer.
Microanalyses were performed at the Microanalytical Labo-
ratory of the Hashemite University, Zarqa, Jordan, and the
results agreed with the calculated values within experimental
error ( 0.4 %).
2
(CH2Me), 100.6 (d, JC−F = 21 Hz, C-5), 107.9 (C-3),
3
120.3 (d, 3JC−F = 7.2 Hz, C-4a), 125.7 (d, JC−F = 5.9 Hz,
2
C-8), 127.3 (C-8a), 129.3 (d, JC−F = 15.8 Hz, C-7), 149.8
1-(N-Arylhydrazono)-1-chloropropanones (8a – c)
1
(d, JC−F = 235 Hz, C-6), 151.2 (C-2), 165.1 (CO2Et),
4
172.6 (d, JC−F = 2.7 Hz, C-4). – C15H16FN3O3 (305.30):
These hydrazonoyl chlorides 8a [23, 24], 8b [23]
and 8c [23, 24] were previously characterized and were
prepared in this study via the Japp-Klingemann reac-
tion [25] which involves direct coupling of the appro-
priate arenediazonium chloride with 3-chloropentane-2,4-
dione in aqueous pyridine, following standard proce-
dures [23].
calcd. C 59.01, H 5.28, N 13.76; found C 58.79, H 5.33,
N 13.45.
The aqueous layer was acidified with 3N HCl and ex-
tracted with ethyl acetate (2 × 40 mL). The combined or-
ganic extracts were evaporated in vacuo, and the residual
solid product was recrystallized from chloroform / methanol
(1 : 1, v / v) and identified as the corresponding 3-carboxylic
acid 7. Yield: 0.36 g (36 %), m. p. 295 – 296 ◦C. – IR (KBr):
ν = 3421 (br), 3238, 3061, 2920, 2831, 1712, 1688, 1606,
1545, 1488, 1457, 1321, 1267, 1206, 1168, 1035 cm−1. –
1H NMR (300 MHz, CDCl3): δ = 0.99 [(m, 2H) and 1.15 (m,
2H), 2ꢀ-H2 + 3ꢀ-H2)], 4.46 (m, 1H, 1ꢀ-H), 5.23 (s, 2H, C8-
NH2), 5.83 (s, 2H, C7-NH2), 7.32 (d,3JH−F =10.9 Hz, 1H,
5-H), 8.59 (s, 1H, 2-H), 15.47 (s, 1H, CO2H). – 13C NMR
(75 MHz, CDCl3): δ = 10.7 (C-2ꢀ + C-3ꢀ), 39.8 (C-1ꢀ),
Ethyl 7-chloro-1-cyclopropyl-6-fluoro-8-nitro-4-oxo-1,4-di-
hydroquinoline-3-carboxylate (4)
This synthon was prepared from 2,4-dichloro-5-fluoro-3-
nitrobenzoic acid, ethyl 3-(N,N-dimethylamino)acrylate and
cyclopropylamine by adopting the stepwise synthetic proce-
dures reported [17] for the methyl ester analog; m.p. 175 –
176 ◦C (dec.) (ref. [18] 174 – 176 ◦C).
2
100.0 (d, JC−F = 21.2 Hz, C-5), 105.5 (C-3), 116.7 (d,
3
3JC−F = 8.6 Hz, C-4a), 125.8 (d, JC−F = 6.4 Hz, C-8),
Ethyl 7-azido-1-cyclopropyl-6-fluoro-8-nitro-4-oxo-1,4-di-
hydroquinoline-3-carboxylate (5)
2
128.1 (C-8a), 131.2 (d, JC−F = 15.6 Hz, C-7), 150.0
1
(d, JC−F = 238 Hz, C-6), 150.5 (C-2), 166.8 (CO2H),
This intermediate was prepared via interaction of sodium
azide and the corresponding 7-chloro-8-nitro-1,4-dihydro-
quinoline 4, in dimethylsulfoxide at ambient temperature, ac-
cording to a recently reported procedure [19].
4
177.2 (d, JC−F = 3.5 Hz, C-4). – C13H12FN3O3 (277.25):
calcd. C 56.32, H 4.36, N 15.16; found C 56.48, H 4.42,
N 15.02.
Method (ii): Tin granules (5.9 g, 0.05 gram atom) were
introduced into a stirred solution of 5 (1.28 g, 3.6 mmol) in
3N HCl. Thereafter, the resulting mixture was heated under
reflux and became turbid. Ethanol was added to the turbid re-
action mixture until a clear solution was obtained whilst heat-
ing under reflux was continued for 4 h. The resulting mixture
was then poured onto crushed ice (80 g) and worked up as
described in method (i) above for the diamino ester 6. Yield:
0.29 g (29 %).
Ethyl 7,8-diamino-1-cyclopropyl-6-fluoro-4-oxo-1,4-di-
hydroquinoline-3-carboxylate (6) and the corresponding
3-carboxylic acid (7)
Method (i): To a stirred solution of 5 (1.28 g, 3.6 mmol) in
absolute ethanol (100 mL) was added portionwise stannous
chloride dihydrate (6.6 g, 29.2 mmol). The reaction mixture
was stirred at r. t. for additional 30 – 40 min and then heated
under reflux for 6 h.
The aqueous layer was acidified with 3N HCl and worked
The resulting mixture was then poured onto crushed ice up as described in method (i) above for the isolation of the
(80 g), basified with a saturated aqueous solution of sodium 7,8-diamino acid 7. Yield: 0.41 g (41 %).
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J. A. Zahra et al. · Ethyl 3-(Aryldiazenyl)-7-oxo-dihydropyrido[2,3-f ]quinoxaline-8-carboxylates
1049
Ethyl 10-cyclopropyl-5-fluoro-2-methyl-7-oxo-3-(phenyldi-
azenyl)-7,10-dihydropyrido-[2,3-f]quinoxaline-8-carboxyl-
ate (10a)
(300 MHz, CDCl3): δ = 0.97 [(m, 2H) and 1.28 (m, 2H), 2ꢀ-
H2 + 3ꢀ-H2)], 1.42 (t, J = 7.1 Hz, 3H, CH3CH2), 2.47 (s, 3H,
C4ꢀꢀ-CH3), 2.98 (s, 3H, C2-CH3), 4.42 (q, J = 7.1 Hz, 2H,
CH2Me), 4.74 (m, 1H, 1ꢀ-H), 7.37 (d, J = 8.2, 2H, 3ꢀꢀ-H + 5ꢀꢀ-
A stirred mixture of 1-chloro-1-(N-phenylhydrazono)-
propanone (8a) (0.43 g, 2.2 mmol) and ethyl 7,8-diamino-
1-cyclopropyl-6-fluoro-4-oxo-1,4-dihydroquinoline-3-carb-
oxylate (6, 0.56 g, 2 mmol) in ethanol (40 mL) and chloro-
form (2 mL) was treated at r. t. with triethylamine (2 mL).
The resulting reaction mixture was then brought slowly to
gentle reflux◦for 3 – 4 h. Thereafter, the reaction mixture was
cooled (∼ 0 C), and the precipitated product was collected
and purified on preparative silica gel TLC plates, eluting with
chloroform plus◦methanol (98 : 2, v / v). Yield: 0.32 g (36 %),
m. p. 271 – 272 C (dec.). – IR (KBr): ν = 3433 (br), 3081,
2972, 2920, 2865, 1730, 1690, 1629, 1543, 1467, 1323,
1290, 1231, 1138, 1033 cm−1. – EIMS: m/z (%) = 445 (28)
[M]+, 417 (8), 416 (12), 373 (39), 372 (26), 356 (17), 345
(19), 328 (10), 284 (60), 283 (40), 253 (31), 214 (12), 184
(15), 149 (24), 105 (30), 93 (100), 77 (81). – HRMS: calcd.
445.1550; found 445.1501. – 1H NMR (300 MHz, CDCl3):
δ = 0.97 [(m, 2H) and 1.28 (m, 2H), 2ꢀ-H2 + 3ꢀ-H2)], 1.42
(t, J = 7.1 Hz, 3H, CH3CH2), 2.98 (s, 3H, C2-CH3), 4.42 (q,
J = 7.1 Hz, 2H, CH2Me), 4.74 (m, 1H, 1ꢀ-H), 7.59 (m, 3H,
3ꢀꢀ-H + 5ꢀꢀ-H and 4ꢀꢀ-H), 8.09 (dd, J = 8.0, 2.2 Hz, 2H, 2ꢀꢀ-
H + 6ꢀꢀ-H), 8.42 (d, 3JH−F = 10 Hz, 1H, 6-H), 8.82 (s, 1H,
9-H). – 13C NMR (75 MHz, CDCl3): δ = 11.1 (C-2ꢀ + C-3ꢀ),
14.5 (CH3CH2), 21.8 (C2-CH3), 42.5 (C-1ꢀ), 61.3 (CH2Me),
110.6 (d, 2JC−F = 20.5 Hz, C-6), 112.7 (C-8), 124.2 (C-2ꢀꢀ +
C-6ꢀꢀ), 129.4 (C-3ꢀꢀ + C-5ꢀꢀ), 130.0 (d, 3JC−F = 6.8 Hz, C-6a),
H), 8.01 (d, J = 8.2 Hz, 2H, 2ꢀꢀ-H + 6ꢀꢀ-H), 8.42 (d, 3JH−F
=
10 Hz, 1H, 6-H), 8.82 (s, 1H, 9-H). – 13C NMR (75 MHz,
CDCl3): δ = 11.0 (C-2ꢀ + C-3ꢀ), 14.5 (CH3CH2), 21.8 (C4ꢀꢀ-
CH3), 21.9 (C2-CH3), 42.4 (C-1ꢀ), 61.3 (CH2Me), 110.5 (d,
2JC−F = 20.5 Hz, C-6), 112.7 (C-8), 124.3 (C-2ꢀꢀ + C-6ꢀꢀ),
129.9 (d, 3JC−F = 6.8 Hz, C-6a), 130.1 (C-3ꢀꢀ + C-5ꢀꢀ), 134.4
(d, 4JC−F = 2.9 Hz, C-10a), 134.5 (d, 2JC−F = 14.1 Hz, C-4a),
136.4 (C-10b), 144.9 (C-4ꢀꢀ), 149.5 (C-2), 150.3 (C-9), 151.5
1
4
(C-1ꢀꢀ), 155.0 (d, JC−F = 260 Hz, C-5), 155.6 (d, JC−F
=
2 Hz, C-3), 165.4 (CO2Et), 172.4 (d, 4JC−F = 2.4 Hz, C-7). –
C25 H22 F N5 O3: calcd. C 65.35, H 4.83, N 15.24; found
C 65.12, H 4.74, N 15.06.
Ethyl 3-[(4-chlorophenyl)diazenyl]-10-cyclopropyl-5-fluoro-
2-methyl-7-oxo-7,10-dihydropyrido[2,3-f]quinoxaline-8-
carboxylate (10c)
This compound was prepared from 8c (0.51 g, 2.2 mmol)
and 6 (0.56 g, 2 mmol), following a similar procedure as
noted above for ◦the preparation of 10a. Yield: 0.41 g (43 %),
m. p. 267 – 268 C. – IR (KBr): ν = 3428 (br), 3074, 3002,
2967, 2849, 1719, 1622, 1524, 1465, 1290, 1161, 1135,
1085 cm−1. – EI MS: m/z (%) = 479 (12) [M]+, 450 (6),
407 (35), 378 (7), 356 (22), 328 (14), 311 (7), 284 (100), 256
(32), 253 (22), 213 (14), 186 (11), 139 (25), 127 (75), 111
(79). – HRMS: calcd. 479.1160; found 479.1102. – 1H NMR
(300 MHz, CDCl3): δ = 0.98 [(m, 2H) and 1.28 (m, 2H),
2ꢀ-H2 + 3ꢀ-H2)], 1.42 (t, J = 7.2 Hz, 3H, CH3CH2), 2.99
(s, 3H, C2-CH3), 4.41 (q, J = 7.2 Hz, 2H, CH2Me), 4.73
4
133.6 (C-4ꢀꢀ), 134.4 (d, JC−F = 2 Hz, C-10a), 134.5 (d,
2JC−F = 13.7 Hz, C-4a), 136.5 (C-10b), 149.4 (C-2), 150.4
1
(C-9), 153.1 (C-1ꢀꢀ), 155.0 (d, JC−F = 260 Hz, C-5), 155.5
(m, 1H, 1ꢀ-H), 7.55 (d, J = 8.7 Hz, 2H, 3ꢀꢀ-H + 5ꢀꢀ-H),
(d, 4JC−F = 1.5 Hz, C-3), 165.3 (CO2Et), 172.4 (d, 4JC−F
=
3
8.05 (d, J = 8.7 Hz, 2H, 2ꢀꢀ-H + 6ꢀꢀ-H), 8.42 (d, JH−F
=
1.6 Hz, C-7). – C24 H20 F N5 O3: calcd. C 64.71, H 4.53,
10 Hz, 1H, 6-H), 8.82 (s, 1H, 9-H). – 13C NMR (75 MHz,
N 5.72; found C 64.52, H 4.51, N 15.58.
CDCl3): δ = 11.1 (C-2ꢀ + C-3ꢀ), 14.5 (CH3CH2), 21.9
2
(C2-CH3), 42.5 (C-1ꢀ), 61.3 (CH2Me), 110.7 (d, JC−F
=
Ethyl 10-cyclopropyl-5-fluoro-2-methyl-3-[(4-methylphen-
yl)diazenyl]-7-oxo-7,10-dihydropyrido[2,3-f]quinoxaline-8-
carboxylate (10b)
20.8 Hz, C-6), 112.7 (C-8), 125.4 (C-2ꢀꢀ + C-6ꢀꢀ), 129.8
(C-3ꢀꢀ + C-5ꢀꢀ), 130.1 (d, JC−F = 6.8 Hz, C-6a), 134.4 (d,
3
4JC−F = 2.9 Hz, C-10a), 134.5 (d, JC−F = 14.1 Hz, C-4a),
2
136.7 (C-10b), 140.0 (C-4ꢀꢀ), 149.6 (C-2), 150.4 (C-9), 151.4
This compound was prepared from 8b (0.46 g, 2.2 mmol)
and 6 (0.56 g, 2 mmol), following a similar procedure as
noted above for ◦the preparation of 10a. Yield: 0.35 g (38 %),
m. p. 260 – 261 C (dec.). – IR (KBr): ν = 3447 (br), 3325,
3094, 2990, 2971, 2933, 2887, 1719, 1623, 1598, 1464,
1318, 1292, 1162, 1137, 1031 cm−1. – EIMS: m/z (%) =
459 (7) [M]+, 431 (3), 430 (3), 403 (6), 387 (13), 356 (24),
328 (14), 311 (6), 284 (64), 283 (39), 256 (25), 253 (19),
1
4
(C-1ꢀꢀ), 155.0 (d, JC−F = 260 Hz, C-5), 155.1 (d, JC−F
=
2 Hz, C-3), 165.3 (CO2Et), 172.4 (d, 4JC−F = 2.3 Hz, C-7). –
C24 H19 Cl F N5 O3 (479.89): calcd. C 60.07, H 3.99,
N 14.59; found C 59.88, H 3.86, N 14.45.
Acknowledgement
We thank the Deanship of Scientific Research of Jordan
209 (15), 188 (9), 132 (6), 119 (32), 107 (77), 106 (100), 91 University (Amman) and BMBF (Bonn, Germany) for finan-
(86). – HRMS: calcd. 459.1706; found 459.1675. – 1H NMR cial support.
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J. A. Zahra et al. · Ethyl 3-(Aryldiazenyl)-7-oxo-dihydropyrido[2,3-f ]quinoxaline-8-carboxylates
[1] a) M. J. Waring, K. R. Fox, Topics in Molecular and
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