R. Sakhuja, S. M. A. Shakoor, S. Kumari, and A. Kumar
Vol 000
δ = 176.00, 163.53, 157.09, 148.52, 143.13, 135.77, 132.19,
130.85, 128.49, 128.12, 118.27, 117.62, 116.29, 62.11,
21.61, 13.44. HRMS (TOF MS) calcd for C18H16ClN2O3+
3-(2-(4-Methoxyphenyl)imidazo[1,2-a]pyridin-3-yl)quinoxalin-2
(1H)-one 5b. Yield: 0.152 g (75%); yellow solid; mp 238–240°C.
1H NMR (DMSO-d6): δ = 12.64 (s, 1H), 8.57 (d, J= 6.9 Hz, 1H),
7.84 (d, J= 7.9 Hz, 1H), 7.68 (t, J= 8.2 Hz, 3H), 7.58 (d, J=8.0Hz,
1H), 7.44–7.32 (m, 3H), 6.93 (dd, J= 15.7, 7.8 Hz, 3H), 3.76
(s, 3H). 13C NMR (DMSO-d6 +CDCl3): δ = 159.57, 154.19,
150.34, 146.66, 145.43, 132.76, 132.63, 131.16, 129.70, 129.21,
127.73, 127.01, 126.55, 123.87, 116.91, 116.24, 115.89, 114.00,
112.73, 55.48. HRMS (TOF MS) calcd for C22H17N4O+2 369.1351,
found 369.1323 [M + H]+.
3-(2-(4-Methylphenyl)imidazo[1,2-a]pyridin-3-yl)quinoxalin-2
(1H)-one 5c. Yield: 0.148 g (70%); yellow solid; mp 174–175°C.
1H NMR (DMSO-d6): δ = 12.66 (s, 1H), 8.60 (d, J= 6.9 Hz, 1H),
7.85 (d, J= 7.3 Hz, 1H), 7.72 (d, J= 9.0 Hz, 1H), 7.60 (t, J=6.4Hz,
3H), 7.38 (dd, J= 18.3, 7.7 Hz, 3H), 7.15 (d, J= 8.0 Hz, 2H), 6.97
(t, J= 6.4 Hz, 1H), 2.30 (s, 3H). 13C NMR (DMSO-d6 +CDCl3):
δ = 154.20, 150.33, 146.78, 145.45, 137.59, 132.79, 132.63,
132.44, 131.28, 129.27, 129.22, 128.37, 127.12, 126.67, 123.92,
117.05, 116.67, 115.91, 112.89, 21.27. HRMS (TOF MS) calcd for
C22H17N4O+ 353.1402, found 353.1423 [M + H]+.
3-(2-(4-Chlorophenyl)imidazo[1,2-a]pyridin-3-yl)quinoxalin-2
(1H)-one 5d. Yield: 0.145 g (58%); yellow solid; mp >290°C. 1H
NMR (DMSO-d6): δ = 12.66 (s, 1H), 8.66 (d, J= 6.6 Hz, 1H), 7.85
(d, J= 7.8 Hz, 1H), 7.73 (t, J= 8.1 Hz, 3H), 7.62 (t, J=7.4Hz, 1H),
7.41 (d, J=7.5Hz, 5H), 7.01 (t, J=6.5Hz, 1H). 13C NMR
(DMSO-d6): δ = 154.14, 149.90, 145.57, 134.22, 132.97, 132.82,
132.62, 131.38, 130.15, 129.31, 128.66, 127.31, 127.12, 123.97,
117.19, 117.08, 115.92, 113.21. HRMS (TOF MS) calcd for
C21H14ClN4O+ 373.0856, found 373.0823 [M + H]+.
343.0849, found 343.0861 [M + H]+.
Ethyl 2-(2-(4-methoxyphenyl)-6-methylimidazo[1,2-a]pyridin-
3-yl)-2-oxoacetate 3h.
Yield: 0.570 g (84%); brown solid; mp
117–118°C. 1H NMR (CDCl3): δ = 9.45 (s, 1H), 7.81 (d, J=9.0Hz,
1H), 7.57 (d, J= 8.7 Hz, 2H), 7.51 (d, J= 9.1 Hz, 1H), 7.01
(d, J= 8.7 Hz, 2H), 3.86 (s, 3H), 3.77 (q, J= 7.2 Hz, 2H), 2.45
(s, 3H), 1.05 (t, J= 7.2 Hz, 3H). 13C NMR (CDCl3): δ = 177.43,
164.23, 161.30, 160.67, 160.14, 157.38, 146.87, 134.68, 131.43,
127.71, 126.78, 125.75, 117.99, 116.52, 114.70, 62.12, 55.15,
18.11, 13.06. HRMS (TOF MS) calcd for C19H19N2O+4 339.1344,
found 339.1327 [M + H]+.
Ethyl 2-(2-(4-methoxyphenyl)-7-methylimidazo[1,2-a]pyridin-
3-yl)-2-oxoacetate 3i. Yield: 0.530 g (79%); brown solid; mp
131–132°C. 1H NMR (CDCl3): δ = 9.52 (d, J = 7.0 Hz, 1H),
7.62 (s, 1H), 7.57 (d, J = 8.6 Hz, 2H), 7.01 (t, J = 6.2 Hz, 3H),
3.86 (s, 3H), 3.77 (q, J = 7.2 Hz, 2H), 2.52 (s, 3H), 1.05
(t, J = 7.2 Hz, 3H). 13C NMR (CDCl3): δ = 176.49, 163.73,
161.46, 160.98, 158.04, 148.30, 143.33, 131.28, 128.24,
125.55, 118.17, 117.46, 116.02, 113.92, 62.12, 55.40, 21.69,
13.48. HRMS (TOF MS) calcd for C19H19N2O+4 339.1344,
found 339.1368 [M + H]+.
2-Phenylimidazo[1,2-a]pyridylquinoxalin-2-ones 5a–j: general
procedure. Method A. A mixture of substituted 2-phenylimidazo
[1,2-a]pyridylglyoxalate (3a–i, 0.6 mmol) and o-phenylenediamine
(4a–b, 0.72 mmol) were dissolved in CH2Cl2 (10 mL).
Montmorillonite K-10 (300 mg) was added to the mixture, and the
solvent was evaporated in vacuo. The dry mixture was then
transferred to a microwave reaction tube and irradiated in focused
microwave oven (CEM) at temperatures 90–100°C at an 80-W
power for the specified time mentioned in Table 3. The reaction
was monitored via TLC. After the completion of the reaction, the
reaction mixture was diluted with CH2Cl2 (3 × 50 mL), and
the organic layer was separated from the catalyst by filtration. The
crude product obtained by evaporating the solvent in vacuo was
purified by either flash chromatography purification (5a, 5c, 5e–g,
5j) or recrystallization with MeOH/CH2Cl2 (5b, 5d, 5h, 5i) to yield
3-(2-(4-Nitrophenyl)imidazo[1,2-a]pyridin-3-yl)quinoxalin-
2(1H)-one 5e.
Yield: 0.046 g (20%); pale yellow solid; mp
240–242°C. 1H NMR (CDCl3): δ = 8.77 (d, J = 7.0 Hz, 1H),
8.24 (d, J = 8.4 Hz, 2H), 7.90 (dd, J = 16.7, 8.2 Hz, 3H), 7.77
(d, J = 9.0 Hz, 1H), 7.60 (t, J = 7.7 Hz, 1H), 7.43 (t,
J = 7.8 Hz, 2H), 7.13–6.94 (m, 2H). HRMS (TOF MS) calcd
for C21H14N5O+3 384.1096, found 384.1125 [M + H]+.
3-(6-Methyl-2-phenylimidazo[1,2-a]pyridin-3-yl)quinoxalin-
2(1H)-one 5f. Yield: 0.126 g (60%); yellow solid; mp >290°
1
C. H NMR (DMSO-d6): δ = 12.65 (s, 1H), 8.39 (s, 1H), 7.86
pure quinoxaline-2-ones 5a–j.
Method B. A mixture of substituted 2-phenylimidazo[1,2-a]
(d, J = 7.9 Hz, 1H), 7.74–7.58 (m, 4H), 7.44–7.23 (m, 6H), 2.29
(s, 3H). 13C NMR (DMSO-d6 + CDCl3): δ = 154.27, 150.48,
146.06, 144.42, 135.26, 132.86, 132.69, 131.37, 129.57,
129.38, 128.61, 128.25, 128.10, 124.53, 123.93, 122.23,
116.72, 116.54, 115.91, 18.18. HRMS (TOF MS) calcd for
C22H17N4O+ 353.1402, found 353.1378 [M + H]+.
3-(2-(4-Chlorophenyl)-7-methylimidazo[1,2-a]pyridin-3-yl)
quinoxalin-2(1H)-one 5g. Yield: 0.134 g (58%); yellow solid;
mp >290°C. 1H NMR (CDCl3 + CD3OD): δ = 8.61 (d, J = 7.1 Hz,
1H), 7.90 (dd, J = 8.1, 1.4 Hz, 1H), 7.64–7.53 (m, 3H), 7.48 (dt,
J = 2.0, 1.1 Hz, 1H), 7.41 (ddd, J = 8.3, 7.3, 1.3 Hz, 1H), 7.35–
7.30 (m, 2H), 7.26 (dd, J = 8.2, 1.4 Hz, 1H), 6.80 (dd, J = 7.2,
1.7 Hz, 1H), 2.48 (d, J = 1.2 Hz, 3H). 13C NMR
(CDCl3 + CD3OD): δ = 154.24, 148.56, 147.38, 146.67, 138.57,
134.04, 133.63, 132.69, 130.86, 129.55, 128.82, 128.22,
125.06, 124.35, 115.86, 115.50, 115.31, 21.41. HRMS (TOF
MS) calcd for C22H16ClN4O+ 387.1012, found 387.1049
[M + H]+.
pyridylglyoxalate (3a–i, 0.6 mmol), o-phenylenediamine (4a–b,
0.72 mmol), and Yb(OTf)3 (0.06 mmol) were dissolved in THF
(3mL) in a microwave reaction tube. The reaction tube was irradi-
ated in focused microwave oven (CEM) at temperatures 80–90°C
at an 80-W power for a specified time (1.5–3 h). The reaction
was monitored via TLC. After the completion of the reaction,
THF was evaporated, and the reaction mixture was diluted with
water and extracted with ethyl acetate (3× 50mL), and the organic
layer was separated. The crude product obtained by evaporating the
organic solvent in vacuo was purified by flash chromatography to
yield pure quinoxaline-2-ones 5a–d and 5f–j.
3-(2-Phenylimidazo[1,2-a]pyridin-3-yl)quinoxalin-2(1H)-
one 5a.
Yield: 0.146g (72%); brownish yellow solid; mp 273–
1
274°C. H NMR (CDCl3 + CD3OD): δ = 8.75 (d, J = 7.0 Hz, 1H),
7.90 (d, J = 6.9Hz, 1H), 7.73 (dd, J = 11.4, 8.7 Hz, 3H), 7.51 (t,
J = 8.4 Hz, 1H), 7.42–7.25 (m, 5H), 7.02 (d, J = 9.0 Hz, 1H), 6.94
(t, J = 7.5Hz, 1H). 13C NMR (CDCl3 + CD3OD): δ = 154.60,
148.87, 148.71, 146.30, 135.10, 132.72, 131.07, 130.87, 128.78,
128.37, 128.23, 128.10, 126.93, 125.70, 124.47, 117.02, 115.81,
113.19. HRMS (TOF MS) calcd for C21H15N4O+ 339.1245,
found 339.1223 [M+ H]+.
3-(2-(4-Methoxyphenyl)-6-methylimidazo[1,2-a]pyridin-3-yl)
quinoxalin-2(1H)-one 5h.
Yield: 0.142 g (62%); yellow
solid; mp 285–287°C. 1H NMR (DMSO-d6): δ = 12.64
(s, 1H), 8.34 (s, 1H), 7.90–7.82 (m, 1H), 7.68–7.55 (m, 4H),
7.45–7.33 (m, 2H), 7.24 (dd, J = 9.1, 1.7 Hz, 1H), 6.94–6.85
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet