1260
S. R. El-Gogary et al.
6.90–6.95 (2H, m, phenyl), 7.52 (1H, d, Ha), 7.53–7.57
(2H, m, phenyl), 7.80–7.88 (2H, m, H-6 and H-7), 8.50
(1H, d, Hb), 8.57–8.66 (2H, m, H-5 and H-8) ppm; 13C
NMR (CDCl3): d = 12.70, 14.18, 44.57, 63.63, 108.22,
111.45, 120.00, 120.27, 122.92, 130.05, 130.55, 132.58,
135.08, 137.67, 138.40, 142.12, 143.44, 160.42 ppm.
(0.27 g, 80%). M.p.: 162–164 °C; IR (KBr): ꢀm = 1743
1
(CO), 1589 (C=C), 1358 (N–O) cm-1; H NMR (CDCl3):
d = 1.47 (3H, t, J = 7.4 Hz, CH3), 3.34 (4H, t,
J = 5.4 Hz, CH2NCH2), 3.76 (4H, t, J = 5.3 Hz,
CH2OCH2), 4.57 (2H, t, J = 7.2 Hz, CH2CH3), 4.97 (1H,
d, J = 15.3 Hz, Hb), 7.60–7.86 (2H, m, H-6 and H-7),
8.46–8.50 (2H, m, H-5 and H-8), 9.49 (1H, d, J = 15.3 Hz,
Ha) ppm; 13C NMR (CDCl3): d = 14.45, 54.66, 63.22,
66.87, 85.62, 129.32, 121.34, 131.43, 131.72, 136.21,
136.47, 138.05, 138.55, 135.64, 150.89, 160.81 ppm; MS:
m/z (%) = 329 (M?–O, 3.8), 239 (C14H13N3O, 34.6), 129
(C8H5N2, 51.9).
(E)-2-(Ethoxycarbonyl)-3-[2-(2-hydroxy-4-nitro-
phenyl)ethenyl]quinoxaline 1,4-dioxide
(4e, C19H15N3O7)
Recystallization of the separated solid from aqueous
ethanol gave dark red crystals of compound 4e (0.25 g,
ꢀ
62%). M.p.: 190–191 °C; IR (KBr): m = 1743 (CO, ester),
1597 (C=C), 1350 (N–O) cm-1 1H NMR (CDCl3):
;
General procedure for synthesis of pyrido[3,4-b]-
quinoxaline 5,10-dioxides 8
d = 1.47 (3H, t, CH3, ester), 1.90 (1H, s, OH), 4.63 (2H,
q, CH2, ester), 6.90 (1H, m, phenyl), 7.42 (1H, d, Ha),
7.52–7.55 (2H, m, phenyl), 7.90–8.00 (2H, m, H-6 and
H-7), 8.20 (1H, d, Hb), 8.58–8.69 (2H, m, H-5 and H-8) ppm;
13C NMR (CDCl3): d = 14.71, 63.98, 114.21, 116.24,
125.69, 128.33, 131.09, 131.75, 131.77, 133.32 133.45,
137.10, 138.99, 145.98, 149.23, 150.21, 160.13, 168.54,
171.88 ppm.
A solution of enamine 5 (1 mmol) and an aliphatic amine
(1 mmol) in 10 cm3 chloroform and 10 cm3 isopropanol in
the presence of 0.12 g p-toluenesulfonic acid (1 mmol)
was refluxed for 4–8 h. The solvent was reduced to half of
its volume, and the precipitate was filtered off to give a
crude product. The filtrate was poured on cold water and
extracted with chloroform to afford a further amount of
product. The combined product was purified by column
chromatography using 2% ethanol/dichloromethane as
eluent.
(E)-2-[2-(Dimethylamino)ethenyl]-3-(ethoxycar-
bonyl)quinoxaline 1,4-dioxide (5, C15H17N3O4)
A mixture of 0.248 g 2-(ethoxycarbonyl)-3-methylquinox-
aline 1,4-dioxide (3, 0.01 mol) and 1.79 g DMF-DMA
(0.015 mol) in 20 cm3 benzene was refluxed for 24 h. The
solvent was removed under reduced pressure, and the red
precipitate was triturated with diethyl ether to give 5
1,2-Dihydro-2-methyl-1-oxopyrido[3,4-b]quinoxaline
5,10-dioxide (8a, C12H9N3O3)
Yield 0.16 g (67%); m.p.: 164–166 °C; IR (KBr):
ꢀ
m = 3097 (=CH), 1670 (CO), 1620 (C=C), 1346 (N–O)
cm-1; 1H NMR (CDCl3): d = 3.71 (3H, t, CH3), 7.27–7.38
(2H, m, H-6 and H-7), 7.83–7.86 (2H, m, H-5 and H-8),
8.44 (1H, d, J = 9.3 Hz, Hb), 8.62 (1H, d, J = 9.3 Hz, Ha)
ppm; 13C NMR (CDCl3): d = 32.49, 127.87, 128.99,
131.84, 132.69, 132.01, 134.39, 135.54, 137.31, 141.31,
145.00, 160.47 ppm; MS: m/z (%) = 227 (M?–O, 39.1),
211 (M?–2O, 8.3), 141 (C9H5N2, 7.5), 128 (C8H4N2, 2.3).
ꢀ
(2.36 g, 78%). M.p.: 158–160 °C; IR (KBr): m = 1739
1
(CO), 1593 (C=C), 1364 (N–O) cm-1; H NMR (CDCl3):
d = 1.47 (3H, t, J = 7.2 Hz, CH3CH2), 3.02 (6H, s,
N(CH3)2), 4.59 (2H, q, J = 7.2 Hz, CH2CH3), 4.76 (1H, d,
J = 15.5 Hz, Hb), 7.57–7.81 (2H, m, H-6 and H-7),
8.45–8.49 (2H, m, H-5 and H-8), 9.57 (1H, d,
J = 15.5 Hz, Ha) ppm; 13C NMR (CDCl3): d = 14.13,
63.22, 84.12, 119.37, 120.88, 132.40, 133.77, 136.21,
137.17, 137.95, 138.17, 136.55, 151.29, 160.95 ppm;
MS: m/z (%) = 303 (M?, 23.3), 304 (M??1, 10.0), 287
(M?–O, 8.3), 198 (C12H12N3, 46.7), 184 (C10H6N3O, 15.0),
168(C10H6N3, 16.7),128(C8H4N2, 41.7), 104(C6H4N2, 41.7).
1,2-Dihydro-1-oxo-2-(phenylmethyl)pyrido[3,4-b]-
quinoxaline 5,10-dioxide (8b, C18H13N3O3)
Yield 0.21 g (66%); m.p.: 206–207 °C; IR (KBr):
-1
;
1H
ꢀ
m = 1678 (CO), 1608 (C=C), 1340 (N–O) cm
NMR (CDCl3): d = 5.30 (2H, s, CH2Ph), 7.27–7.38 (5H,
m, Phenyl), 7.39–7.42 (2H, m, H-6 and H-7), 7.84–7.88
(2H, m, H-5 and H-8), 8.44 (1H, d, J = 9.3 Hz, Hb), 8.61
(1H, d, J = 9.3 Hz, Ha) ppm; 13C NMR (CDCl3):
d = 52.49, 96.51, 118.76, 128.60, 129.22, 131.50,
132.15, 132.51, 135.34, 135.66, 137.21, 140.32, 144.21,
160.77 ppm; MS: m/z (%) = 303 (M?-O, 12.4), 168
(C10H6N3, 2.2), 128 (C8H4N2, 3.4), 91 (C6H4CH3, 100).
(E)-2-(Ethoxycarbonyl)-3-[2-(4-morpholinyl)ethenyl]-
quinoxaline 1,4-dioxide (6, C17H19N3O5)
A mixture of 0.3 g enamine 5 (1 mmol) and 0.78 g
morpholine (1 mmol) in 10 cm3 chloroform and 10 cm3
isopropanol in presence of 0.12 g p-toluenesulfonic acid
(1 mmol) was refluxed for 6 h. The solvent was reduced to
half of its volume, and the formed precipitate was filtered
off. The filtrate was poured on cold water and extracted
with chloroform to get an additional amount of product 6.
The product was purified by column chromatography using
2% ethanol/dichloromethane as eluent to give compound 6
2-Butyl-1,2-dihydro-1-oxopyrido[3,4-b]quinoxaline
5,10-dioxide (8c, C15H15N3O3)
Yield 0.19 g (68%); m.p.: 225–226 °C; IR (KBr):
-1
;
1H
ꢀ
m = 1670 (CO), 1612 (C=C), 1340 (N–O) cm
123