M. Adib et al. / Tetrahedron Letters 48 (2007) 3217–3220
3219
removed and the solid residue was recrystallized from
EtOAc as red crystals, mp 145–147 °C, yield 0.65 g, 99%.
IR (KBr) (mmax/cmÀ1): 3430 (NH), 1639 (C@O), 1570,
1520, 1434, 1384, 1320, 1241, 1199, 1146, 1038, 982, 860,
740, 695. EI-MS, m/z (%): 328 (M+, 16), 299 (9), 251 (19),
223 (29), 207 (37), 121 (65), 105 (83), 78 (100), 57 (34).
Anal. Calcd for C21H16N2O2 (328.37): C, 76.81; H, 4.91;
N, 8.53. Found: C, 76.5; H, 5.0; N, 8.3. 1H NMR
(500.1 MHz, CDCl3): d 6.00 (1H, t, J = 6.7 Hz, CH), 6.58
(1H, d, J = 9.7 Hz, CH), 6.90 (1H, dd, J = 9.6 Hz and
J = 6.5 Hz, CH), 7.00 (1H, s, CH), 7.21 (1H, t, J = 7.2 Hz,
CH), 7.27 (2H, dd, J = 7.3 Hz and J = 7.7 Hz, 2CH),
7.30–7.34 (1H, d, J = 7.3 Hz, CH and 1H, br, NH), 7.43
(2H, t, J = 7.6 Hz, 2CH), 7.54 (1H, t, J = 6.4 Hz, CH),
7.55 (2H, d, J = 7.4 Hz, 2CH), 7.85 (2H, d, J = 7.6 Hz,
2CH). 13C NMR (125.8 MHz, CDCl3): d 99.89 (CHvinyl),
101.33, 108.04, 119.17, 124.95, 125.22, 127.92, 128.14,
128.21, 128.55 and 133.19 (10CH), 136.34 and 138.00
(2Cipso, PhCO), 140.43 (C–N), 154.71 (N–C@N), 165.09
and 190.58 (2C@O).
In conclusion, we have developed a simple and efficient
method for the preparation of imidazo[1,2-a]pyridin-
3(2H)-ones of potential synthetic and pharmacological
interest. This method carries the advantage that not only
is the reaction performed under neutral conditions, but
also the substances can be mixed without any modifica-
tion. The simplicity of this procedure makes it an inter-
esting alternative to other approaches.
Acknowledgement
This research was supported by the Research Council of
the University of Tehran as research project (6102036/1/
02).
References and notes
13. General procedure for the preparation of imidazo[1,2-
a]pyridines 8a–i exemplified by 2-(2-oxo-2-phenylethyl)-
2-phenylimidazo[1,2-a]pyridine-3(2H)-one 8a: A solution
of 7a (1 mmol) in toluene (20 mL) was refluxed for 6 h.
The solvent was removed, and the residue was crystallized
from EtOAc–n-hexane (2:1) to afford 8a as yellow crystals,
mp 151–152 °C, yield 0.32 g, 98%. IR (KBr) (mmax/cmÀ1):
1744 and 1680 (C@O), 1649, 1572, 1531, 1487, 1442, 1335,
1229, 1180, 996, 754, 694. EI-MS, m/z (%): 328 (M+, 6),
301 (2), 195 (14), 181 (16), 105 (100), 77 (27), 52 (21). Anal.
Calcd for C21H16N2O2 (328.37): C, 76.81; H, 4.91; N, 8.53.
Found: C, 76.6; H, 4.7; N, 8.2. 1H NMR (500.1 MHz,
CDCl3): d 3.87 and 4.22 (2H, 2d, AB system, 2J = 17.8 Hz,
CHAHB), 6.05 (1H, t, J = 6.7 Hz, CH), 6.73 (1H, d,
J = 9.6 Hz, CH), 7.02 (1H, dd, J = 9.6 Hz and J = 6.3 Hz,
CH), 7.34 (1H, t, J = 7.3 Hz, CH), 7.39 (2H, dd,
J = 7.8 Hz and J = 7.1 Hz, 2CH), 7.40 (2H, dd, J =
7.5 Hz and J = 7.8 Hz, 2CH), 7.44 (1H, d, J = 7.2 Hz,
CH), 7.53 (1H, t, J = 7.4 Hz, CH), 7.80 (2H, d,
J = 7.7 Hz, 2CH), 7.87 (2H, dd, J = 8.0 Hz and
J = 0.8 Hz, 2CH). 13C NMR (125.8 MHz, CDCl3): d
50.30 (CH2), 71.47 (C), 107.80 (CH-6), 119.09 (CH-8),
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125.08 (CH-5), 126.15 and 128.13 (2CH), 128.24 (CHpara
,
Ph), 128.52 and 128.72 (2CH), 133.44 (CHpara, PhCO),
135.77 (Cipso, Ph), 137.18 (CH-7), 138.10 (Cipso, PhCO),
157.32 (N–C@N), 181.35 (C@O, amide), 195.75 (C@O,
ketone).
8-Methyl-2-(2-oxo-2-phenylethyl)-2-phenylimi-
dazo[1,2-a]pyridine-3(2H)-one 8d: Yellow crystals, mp
160–162 °C, yield 0.33 g, 97%. IR (KBr) (mmax/cmÀ1): 1730
and 1672 (C@O), 1611, 1467, 1417, 1214, 1074, 755, 685.
EI-MS, m/z (%): 342 (M+, 6), 316 (2), 223 (29), 209 (38),
195 (29), 105 (100), 92 (66), 77 (79), 65 (22), 51 (17). Anal.
Calcd for C22H18N2O2 (342.40): C, 77.17; H, 5.30; N, 8.18.
Found: C, 77.2; H, 5.1; N, 8.2. 1H NMR (500.1 MHz,
CDCl3): d 2.20 (3H, s, CH3), 3.88 and 4.28 (2 H, 2d, AB
system, 2J = 17.8 Hz, CHAHB), 5.98 (1H, t, J = 6.7 Hz,
CH), 6.79 (1H, d, J = 5.7 Hz, CH), 7.30–7.34 (2H,
m,2CH), 7.38 (2H, t, J = 7.6 Hz, 2CH), 7.39 (2H, t,
J = 7.7 Hz, 2CH), 7.52 (1H, dd, J = 7.5 Hz and J =
7.2 Hz, CH), 7.83 (2H, d, J = 7.6 Hz, 2CH), 7.87 (2H, d,
J = 7.6 Hz, 2CH). 13C NMR (125.8 MHz, CDCl3): d
16.37 (CH3), 50.23 (CH2), 71.84 (C), 107.94 (CH-6),
122.69 (CH-5), 126.26 (CH3-C), 126.27 and 128.22 (2CH),
128.26 (CHpara, Ph), 128.58 and 128.74 (2CH), 133.43
(CHpara, PhCO), 133.62 (Cipso, Ph), 136.04 (CH-7), 138.64
(Cipso, PhCO), 158.33 (N–C@N), 182.09 (C@O, amide),
195.88 (C@O, ketone). 2-(2,5-Dimethylphenyl)-2-[2-(2,5-
dimethylphenyl)-2-oxoethyl]-8-methylimidazo-[1,2-a]pyri-
dine-3(2H)-one 8f: Yellow crystals, mp 142–144 °C, yield
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12. The procedure for the preparation of 1,4-diphenyl-2-(2-
pyridylamino)-2-butene-1,4-dione 7a is described. To a
magnetically stirred solution of 2-aminopyridine 5a
(0.188 g, 2 mmol) in dry CH2Cl2 (5 mL) was added
dropwise a solution of dibenzoylacetylene 6a (0.468 g,
2 mmol) in dry CH2Cl2 (2 mL) at 25 °C for 10 min. The
reaction mixture was stirred for 2 h. Then the solvent was