7720
J. S. Yadav et al. / Tetrahedron Letters 48 (2007) 7717–7720
12. Doyle, M. P.; McKervey, M. A.; Ye, T. Modern Catalytic
Methods for Organic Synthesis with Diazo Compounds
from Cyclopropanes to Ylides; Wiley-Inter-Science: New
York, 1998.
13. (a) Ye, T.; McKervey, M. A. Chem. Rev. 1994, 94, 1091–
1160; (b) Padwa, A.; Hornbuckle, S. A. Chem. Rev. 1991,
91, 263–309; (c) Doyle, M. P. Chem. Rev. 1986, 86, 919–
939.
14. (a) Regitz, M.; Mass, G. Diazo Compounds—Properties
and Synthesis; Academic Press: New York, 1986, p 90; (b)
Jones, K.; Toutounji, T. Tetrahedron 2001, 57, 2427–
2431.
Brown semi-solid, IR (KBr): m 3415, 3112, 2925, 2854,
1645, 1523, 1452, 1342, 1274, 1149, 1019, 759, 712, 622,
;
436 cmÀ1 1H NMR (300 MHz, CDCl3): d 8.24 (d,
J = 6.4 Hz, 1H), 7.75 (br s, 1H), 7.51 (d, J = 8.5 Hz,
1H), 7.19 (dt, J = 1.4, 7.1 Hz, 1H), 7.69 (t, J = 7.1 Hz,
1H), 4.74 (s, 2H); 13C NMR (proton decoupled, 75 MHz,
CDCl3): d 145.1, 130.9, 127.9, 122.5, 121.7, 110.4, 108.1,
41.3; ESIMS: m/z: (M++H): 167; HRMS calcd for
C8H8N2Cl (M++H): 167.0376; found, 167.0375. Com-
pound 3n: Brown solid, mp 64–65 ꢁC; IR (KBr): m 2917,
2849, 1699, 1524, 1464, 1299, 1177, 939, 761, 721 cmÀ1; 1H
NMR (300 MHz, CDCl3): d 7.90 (d, J = 6.4 Hz, 1H), 7.27
(br s, 1H), 6.45 (d, J = 8.5 Hz, 1H), 6.15 (t, J = 8.5 Hz,
1H), 2.73 (t, J = 7.1 Hz, 2H), 1.60 (s, 3H, CH3), 1.65–1.67
(m, 2H), 1.45–1.10 (m, 24H), 0.83 (t, J = 8.5 Hz, 3H); 13C
NMR (proton decoupled, 75 MHz, CDCl3): d 145.6,
137.9, 129.2, 128.7, 122.9, 110.2, 108.0, 32.5, 30.1, 30.0,
29.7, 29.6, 29.5, 29.4, 29.2, 29.1, 29.0, 27.3, 25.7, 24.1, 19.3,
16.7, 13.3; ESIMS: m/z: (M++H): 343; HRMS calcd for
C23H39N2 (M++H): 343.3113; found: 343.3124. Com-
pound 3p: Colorless solid, mp 134–135 ꢁC, IR (KBr): m
3188, 3079, 2965, 1685, 1652, 1583, 1535, 1437, 1298, 1144,
1055, 951, 774 cmÀ1; 1H NMR (300 MHz, CDCl3): d 9.10
(br s, 1H); 8.23 (dd, J = 0.7, 1.9 Hz, 1H), 8.21 (dd, J = 0.7,
1.9 Hz, 1H), 7.69 (dt, J = 1.9, 6.8, Hz, 1H), 7.14 (dd,
J = 0.9, 9.4 Hz, 1H), 7.01 (ddd, J = 1.1, 2.4, 4.9 Hz, 1H),
2.19 (dt, J = 0.7, 8.4 Hz, 1H), 1.86 (d, J = 8.4 Hz, 1H),
1.38 (s, 3H), 1.31 (s, 3H); 13C NMR (proton decoupled,
75 MHz, CDCl3): d 168.2, 151.7, 147.3, 138.6, 130.3,
119.6, 114.7, 35.5, 31.1, 28.7, 28.5, 14.7; ESIMS: m/z:
(M++H): 315; HRMS calcd for C15H15N2F3Cl (M++H):
315.0875, found, 315.0882.
15. General procedure: A mixture of a-diazoketone (1 mmol),
2-aminopyridine (1 mmol) and Cu(OTf)2 (0.1 mmol) in
dichloroethane (10 mL) was stirred at 80 ꢁC for the
appropriate time (Table 1). After completion of the
reaction, as indicated by TLC, the reaction mixture was
quenched with water and extracted with ethyl acetate
(2 · 15 mL). Evaporation of the solvent followed by
purification on silica gel (Merck, 100–200 mesh, ethyl
acetate–hexane, 2–8) afforded the pure imidazo[1,2-a]pyr-
idine. Compound 3a: Gray solid, mp 131–133 ꢁC; IR
(KBr): m 2924, 2854, 1740, 1629, 1500, 1471, 1366, 1269,
1
1200, 1140, 1073, 1024, 915, 740, 692, 498, 426 cmÀ1; H
NMR (300 MHz, CDCl3): d 8.09 (d, J = 6.7 Hz, 1H), 7.91
(d, J = 7.5 Hz, 2H), 7.82 (s, 1H), 7.63 (d, J = 9.0 Hz, 1H),
7.40 (t, J = 7.5 Hz, 2H), 7.30 (d, J = 7.5 Hz, 1H), 7.14 (dd,
J = 6.7, 9.0 Hz, 1H), 6.74 (t, J = 6.7 Hz, 1H); 13C NMR
(proton decoupled, 75 MHz, CDCl3): d 145.6, 131.9,
128.7, 127.9, 126.0, 125.5, 124.7, 117.4, 116.2, 108.1;
ESIMS: m/z: (M++H): 195; HRMS calcd for C13H11N2
(M++H): 195.0922; found, 195.0921. Compound 3i: