946
R. Venkatesham, A. Manjula, and B. V. Rao
Vol 48
observed m/z (amu), 453.9562. IR (KBr, m, cmꢁ1) 2819, 1425,
1387, 1066, 778, 728, 673.
N-2-(Thiophen-2-yl)-(thiophen-2-ylmethylene)imidazo[1,2-a]
pyridin-3-amine. (Entry 10, Table 2), brown solid, m.p. 125–
128ꢀC. 1H NMR (DMSO-d6, 200 MHz) d (ppm) 9.1 (s, 1H),
8.32 (d, 1H, J ¼ 6.80 Hz), 7.54–7.50 (m, 3H), 7.35 (dd, 2H,
J ¼ 3.60 and 5.85 Hz), 7.19 (t, 1H, J ¼ 7.93 Hz), 7.13–7.06
N-(3-Chlorobenzylidene)-[2-(3-chlorophenyl)-imidazo[1,2-a]
pyridine-3-yl]amine. (Entry 3, Table 2), yellow solid, m.p. 93–
95ꢀC. 1H NMR (DMSO-d6, 200 MHz) d (ppm) 8.77 (s, 1H),
8.51 (d, 1H, J ¼ 6.80 Hz), 7.90 (d, 2H, J ¼ 5.30 Hz), 7.72 (t,
2H, J ¼ 8.70 Hz), 7.54 (d, 1H, J ¼ 9.06 Hz), 7.44 (d, 2H, J ¼
4.53 Hz), 7.38–7.26 (m, 3H), 6.95 (t, 1H, J ¼ 6.80 Hz). ESI
Mass (m/z) 366 (M þ 1). HRMS (QSTAR XL Hybrid MS/MS
system under ESI condition); Calculated m/z (amu);
(C20H13N3Cl2) 366.0564; observed m/z (amu), 366.0572. IR
(KBr, m, cmꢁ1): 2820, 2683, 1598, 1426, 1069, 779, 726, 674.
N-(2,4,6-Trimethoxybenzylidene)-[2-(2,4,6-trimethoxyphenyl)-
imidazo[1,2-a]pyridine-3-yl]amine. (Entry 8, Table 2), yellow
solid, m.p. 244–247ꢀC. 1H NMR (DMSO-d6, 200 MHz) d
(ppm) 8.77 (d, 1H, J ¼ 3.60 Hz), 8.39 (s, 1H), 7.53 (s,1H),
7.24 (s, 1H), 7.12 (dd, 4H, J ¼ 3.00 and 6.23 Hz), 6.91 (s,
1H), 3.93 (t, 6H, J ¼ 1.90 Hz), 3.87 (t, 3H, J ¼ 2.07 Hz),
3.85–3.81 (m, 9H). 13C NMR (CDCl3, 75 MHz, d) 158.90,
153.66, 142.64, 141.36, 132.69, 129.61, 125.56, 123.09,
117.18, 112.76, 105.17, 77.47, 77.07, 76.63, 60.98, 56.29,
56.12, 21.06. ESI Mass (m/z) 478 (M þ 1). HRMS (QSTAR
XL Hybrid MS/MS system under ESI condition); Calculated
m/z (amu); (C26H27N3O6), 478.1978; observed m/z (amu),
478.1990. IR (KBr, m, cmꢁ1) 2936, 2836, 1603, 1464, 1330,
1124, 1031, 813, 729.
(m, 2H), 6.83 (t, 1H, J ¼ 6.80 Hz). 13C NMR (CDCl3
þ
DMSO, 75 MHz, d) 149.38, 142.57, 132.48, 131.32, 130.32,
128.06, 127.39, 126.34, 125.24, 124.16, 116.71, 112.76. ESI
Mass (m/z) 310 (M þ 1). HRMS (QSTAR XL Hybrid MS/MS
system under ESI condition); Calculated m/z (amu);
(C16H11N3S2), 310.0472; observed m/z (amu), 310.0484. IR
(KBr, m, cmꢁ1) 3068, 1209, 689.
N-(4-Methylbenzylidene)-2-p-tolylimidazo[1,2-a]pyridin-3-
amine. (Entry 11, Table 2), yellow solid, m.p. 95–98ꢀC. 1H
NMR (CDCl3, 200 MHz) d (ppm): 8.74 (s, 1H), 8.41 (d, 1H,
J ¼ 6.80 Hz), 7.68 (dd, 4H, J ¼ 4.53 and 7.55 Hz), 7.55
(d, 1H, J ¼ 9.06 Hz), 7.23–7.19 (m, 5H), 6.82 (t, 1H, J ¼
6.04 Hz), 2.41 (d, 6H, J ¼ 4.53 Hz). 13C NMR (CDCl3,
75MHz, d) 157.30, 142.64, 141.71, 137.43. 133.74, 133.50,
131.79, 129.34, 128.15, 128.00, 124.63, 123.63, 117.10,
112.03. ESI Mass (m/z) 326 (M þ 1). HRMS (QSTAR XL
Hybrid MS/MS system under ESI condition); Calculated m/z
(amu); (C22H19N3) 326.1657; observed m/z (amu), 326.1650.
IR (KBr, m, cmꢁ1) 3034, 2928, 1352, 821, 744.
N-(4-(Perchloropyridin-4-yloxy)benzylidene)-2-(4-(perchlor-
opyridin-4-yloxy)phenyl)imidazo[1,2-a]pyridin-3-amine. (Entry
12, Table 2), yellow solid, m.p. 205–207ꢀC. 1H NMR
(DMSO-d6, 200 MHz) d (ppm) 8.80 (s, 1H), 8.45 (d, 1H, J ¼
6.00 Hz), 7.88 (d, 6H, J ¼ 7.55 Hz), 7.51 (d, 1H, J ¼ 8.90
Hz), 7.25 (t, 1H, J ¼ 8.12 Hz), 7.03 (d, 2H, J ¼ 7.74 Hz),
6.97 (d, 1H, J ¼ 8.30 Hz). ESI Mass (m/z) 755 (Mþ)
(C30H13Cl8N5O2). IR (KBr, m, cmꢁ1) 2922, 1600, 1500, 1388,
1344, 1196.
N-(4-Fluoro-2-trifluoromethyl benylidene)-[2-(4-fluoro-2-
trifluoro methylphenyl)imidazo[1,2-a]pyridin-3-yl]amine. (Entry
1
6, Table 2), yellow solid, m.p. 105–108ꢀC. H NMR (DMSO-
d6, 200 MHz) d (ppm) 8.55 (d, 1H, J ¼ 6.80 Hz), 8.48 (t, 1H,
J ¼ 6.04 Hz), 8.30 (s,1H), 7.59 (t, 2H, J ¼ 9.82 Hz), 7.50 (t,
1H, J ¼ 5.30 Hz), 7.39–7.25 (m, 4H), 6.97 (t, 1H, J ¼ 6.80
Hz). ESI Mass (m/z) 469 (Mþ). HRMS (QSTAR XL Hybrid
MS/MS system under ESI condition): Calculated m/z (amu);
(C22H11N3F8), 470.0903; observed m/z (amu), 470.0919. IR
(KBr, m, cmꢁ1) 2852, 1501, 1428, 1321, 1172, 1125, 880, 838.
N-(4-Hydroxybenzylidene)-[2-(4-hydroxyphenyl)imidazo[1,2-a]
pyridin-3-yl]amine. (Entry15, Table 2), pale yellow solid, m.p.
278–281ꢀC. 1H NMR (DMSO-d6, 200 MHz) d (ppm) 9.14
(brs, 1H), 8.57 (brs, 1H), 8.03 (s, 1H), 7.73 (d, 1H, J ¼ 6.80
Hz), 7.02 (d, 2H, J ¼ 8.50 Hz), 6.94 (d, 2H, J ¼ 8.30 Hz)
6.80 (d, 1H, J ¼ 8.90 Hz), 6.53 (t, 1H, J ¼ 6.80 Hz), 6.18
N-(4-(3,5,6-Trichloropyridin-2-yloxy)benzylidene)-2-(4-(3,5,6-
tri chloropyridin-2-yloxy)phenyl)imidazo[1,2-a]pyridin-3-
1
amine. (Entry 13, Table 2), yellow solid, m.p. 173–175ꢀC. H
NMR (DMSO-d6, 200 MHz) d (ppm) 8.85 (s, 1H), 8.51 (d,
1H, J ¼ 6.80 Hz), 8.04 (dd, 2H, J ¼ 2.45 and 6.00 Hz), 7.93
(dd, 4H, J ¼ 8.50 and 14.35 Hz), 7.79 (t, 1H, J ¼ 3.40 Hz),
7.54 (d, 1H, J ¼ 8.90 Hz), 7.25 (dd, 4H, J ¼ 3.02 and 8.70
Hz), 6.94 (t, 1H, J ¼ 6.04 Hz). ESI Mass (m/z) 688 (M þ 1).
HRMS (QSTAR XL Hybrid MS/MS system under ESI condi-
tion); Calculated m/z (amu); (C30H15N5O2Cl6), 687.9435;
observed m/z (amu), 687.9426. IR (KBr, m, cmꢁ1) 2923, 1569,
1418, 1200.
(dd, 5H, J ¼ 8.30 and 10.95 Hz). 13C NMR (CDCl3
þ
DMSO, 75MHz, d) 161.31, 158.17, 157.50, 142,11, 130.82,
129.57, 128.38, 128.23, 125.64, 125.14, 123.99, 117.08,
116.30, 115.90, 112.89. ESI Mass (m/z) 330 (M þ 1)
(C20H15N3O2). IR (KBr, m, cmꢁ1) 3281, 2923, 2479, 1589,
1435, 1266.
5-Bromo-N-(4-chlorobenzylidene)-2-(4-chlorophenyl)imidazo
[1,2-a]pyridin-3-amine. (Entry 14, Table 2), yellow solid, m.p.
1
200–203ꢀC. H NMR (DMSO-d6, 200 MHz) d (ppm) 8.69 (s,
Cleavage of benzylidine derivative. To N-(4-chlorobenzyli-
1H), 8.48 (d, 1H, J ¼ 1.51 Hz), 7.77 (d, 2H, J ¼ 8.30 Hz),
7.71 (d, 2H, J ¼ 8.30 Hz), 7.47–7.38 (m, 5H), 7.30 (d, 1H,
J ¼ 2.26 Hz). ESI Mass (m/z) 443 (M þ 1) (C20H12BrCl2N3).
IR (KBr, m, cmꢁ1) 2924, 1402, 1087, 827, 796.
N-(3-Bromobenzylidene)-[2-(3-bromophenyl)-imidazo[1,2-a]
pyridine-3-yl]amine. (Entry 5, Table 2), yellow solid, m.p.
88–90ꢀC. 1H NMR (DMSO-d6, 200 MHz) d (ppm): 8.73 (s,
1H), 8.48 (d, 1H, J ¼ 6.80 Hz), 8.04 (d, 2H, J ¼ 1.70 Hz),
7.72 (dd, 2H, J ¼ 8.70 and 13.21 Hz), 7.56 (dd, 2H, J ¼ 7.93
and 13.03 Hz), 7.48 (d, 1H, J ¼ 8.12 Hz), 7.37–7.25 (m, 3H),
6.93 (t, 1H, J ¼ 6.80 Hz). ESI Mass (m/z) 456 (M þ 1).
HRMS (QSTAR XL Hybrid MS/MS system under ESI condi-
tion); Calculated m/z (amu); (C20H13N3Br2), 453.9554;
dene)-[2-(4-chloro
phenyl)imidazo[1,2-a]pyridin-3-yl]amine,
TFA in DCM (1:9 mL) was added dropwise and the resulting
reaction mixture was stirred at room temperature. The reaction
was monitored by TLC. The cleavage was complete by the
end of 15 h. The reaction mixture was then neutralized by sat-
urated sodium bicarbonate and extracted with DCM. The
organic layer was separated, dried over anhydrous sodium sul-
phate, filtered and solvent removed. The product 2-(4-chloro-
phenyl)imidazo[1,2-a]pyridin-3-amine was purified by column
chromatography (EtOAc and hexane).
2-(4-Chlorophenyl)imidazo[1,2-a]pyridin-3-amine. Brown solid,
m.p. 128–131ꢀC. 1H NMR (CDCl3, 200 MHz) d (ppm) 7.92
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet