9924
D. S. Chekmarev et al. / Tetrahedron 62 (2006) 9919–9930
2923, 1627, 1576, 1492, 1452, 1432, 1247, 1148, 1072, 899,
774, 743, 688, 466 cmꢁ1. LC/MS: expected, 232.67; ob-
served, m/z: 233.0 [M+H]+. Anal. Calcd for C12H9ClN2O
(232.67): C, 61.95; H, 3.90; Cl, 15.24; N, 12.04. Found: C,
61.87; H, 3.77; Cl, 14.98; N, 12.03.
150.88, 151.18, 163.73. IR, nmax: 3431, 3071, 2924, 2853,
1626, 1490, 1439, 1378, 1256, 1152, 1077, 1019, 845,
793, 751, 696, 473 cmꢁ1. LC/MS: expected, 233.66; ob-
served, m/z: 234.0 [M+H]+. Anal. Calcd for C11H8ClN3O
(233.66): C, 56.55; H, 3.45; Cl, 15.17; N, 17.98. Found: C,
56.51; H, 3.37; Cl, 15.01; N, 17.94.
4.2.2. 2-(3-Chloropyrazin-2-yl)-1-phenylbutan-1-one, 3b
(Table 1, entries 2–4). The general procedure was followed.
1-Phenylbutan-1-one (326 mg, 2.20 mmol) was used. The
reaction was carried out at 60 ꢀC for 24 h. The yield was
4.2.5. 2-(3-Chloropyrazin-2-yl)-1-(2-furyl)ethanone, 3e
(Table 1, entry 8). The general procedure was followed.
1-(2-Furyl)ethanone (242 mg, 2.20 mmol) was used. The re-
action was carried out at room temperature for 24 h. The
product was isolated by column chromatography on silica
gel using 30% ethyl acetate in hexanes as ketone and enol
mixture. The yield was 225 mg (50%), yellow viscous oil.
1H NMR (DMSO-d6) for the keto form, d 4.60 (s, 2H),
6.78 (dd, J¼3.7, 1.7 Hz, 1H), 7.63 (dd, J¼3.7, 0.7 Hz,
1H), 8.06 (dd, J¼1.7, 0.7 Hz, 1H), 8.47 (d, J¼2.5 Hz, 1H),
8.64 (d, J¼2.5 Hz, 1H); for the enol form, d 6.36 (s, 1H),
6.68–6.71 (m, 1H), 7.04–7.06 (m, 1H), 7.90–7.91 (m, 1H),
8.20 (d, J¼2.7 Hz, 1H), 8.44 (d, J¼2.7 Hz, 1H), 13.84 (s,
1H). 13C NMR (DMSO-d6) for the keto form, d 44.89,
112.83, 119.67, 142.94, 143.04, 148.44, 148.84, 150.33,
151.30, 183.27. IR, nmax: 3341, 3132, 2926, 2854, 1677,
1636, 1570, 1466, 1385, 1331, 1276, 1215, 1150, 1085,
1010, 883, 856, 762, 594, 464 cmꢁ1. LC/MS: expected,
222.63; observed, m/z: 223.1 [M+H]+. Anal. Calcd for
C10H7ClN2O2 (222.63): C, 53.95; H, 3.17; Cl, 15.92; N,
12.58. Found: C, 54.15; H, 3.24; Cl, 15.74; N, 12.40.
1
500 mg (96%), yellow viscous oil. H NMR (DMSO-d6)
d 0.94 (t, J¼7.3 Hz, 3H), 1.96–2.16 (m, 2H), 5.21 (dd,
J¼7.7, 5.8 Hz, 1H), 7.48–7.54 (m, 2H), 7.58–7.63 (m,
1H), 7.91–7.95 (m, 2H), 8.41 (d, J¼2.4 Hz, 1H), 8.61 (d,
J¼2.4 Hz, 1H). 13C NMR (DMSO-d6) d 11.90, 23.46,
52.48, 128.07, 128.95, 133.36, 136.11, 142.78, 143.03,
148.35, 153.45, 197.45. IR, nmax: 3057, 2967, 2933, 2875,
1689, 1596, 1447, 1383, 1341, 1281, 1213, 1145, 1101,
1054, 988, 842, 744, 723, 692, 664, 470 cmꢁ1. LC/MS: ex-
pected, 260.73; observed, m/z: 261.1 [M+H]+. Anal. Calcd
for C14H13ClN2O (260.73): C, 64.50; H, 5.03; Cl, 13.60;
N, 10.74. Found: C, 64.69; H, 4.94; Cl, 13.49; N, 10.72.
4.2.3. 2-(3-Chloropyrazin-2-yl)-1-pyridin-4-ylethanone,
3c (Table 1, entries 5 and 6). The general procedure was
followed. 1-Pyridin-4-ylethanone (267 mg, 2.20 mmol)
was used. The reaction was carried out at 60 ꢀC for 24 h.
The product was isolated by column chromatography on sil-
ica gel using 30% hexanes in ethyl acetate as ketone and enol
mixture. The yield was 238 mg (51%), yellow solid, mp
123–125 ꢀC. 1H NMR (DMSO-d6) for the keto form,
d 4.87 (s, 2H), 7.91–7.94 (m, 2H), 8.49 (d, J¼2.6 Hz, 1H),
8.64 (d, J¼2.6 Hz, 1H), 8.85–8.87 (m, 2H); for the enol
form, d 6.71 (s, 1H), 7.81–7.84 (m, 2H), 8.35 (d,
J¼2.7 Hz, 1H), 8.56 (d, J¼2.7 Hz, 1H), 8.70–8.73 (m,
2H), 14.20 (s, 1H). 13C NMR (DMSO-d6) for the keto
form, d 45.69, 121.34, 141.84, 142.97, 143.13, 148.89,
150.40, 151.01, 195.81; for the enol form, d 92.06, 119.47,
138.97, 139.87, 141.66, 144.65, 150.38, 150.58, 162.64.
IR, nmax: 3428, 3028, 2922, 1623, 1593, 1554, 1491, 1435,
1410, 1254, 1149, 1074, 843, 814, 790, 751, 659,
448 cmꢁ1. LC/MS: expected, 233.66; observed, m/z: 234.0
[M+H]+. Anal. Calcd for C11H8ClN3O (233.66): C, 56.55;
H, 3.45; Cl, 15.17; N, 17.98. Found: C, 56.44; H, 3.39; Cl,
14.88; N, 17.93.
4.2.6. 2-(3-Chloropyrazin-2-yl)-1-(3-thienyl)ethanone, 3f
(Table 1, entry 9). The general procedure was followed.
1-(3-Thienyl)ethanone (277 mg, 2.20 mmol) was used.
The reaction was carried out at 60 ꢀC for 24 h. The product
was isolated by column chromatography on silica gel using
30% ethyl acetate in hexanes as ketone and enol mixture.
1
The yield was 290 mg (61%), yellow viscous oil. H NMR
(DMSO-d6) for the keto form, d 4.72 (s, 2H), 7.56–7.58
(m, 1H), 7.67–7.70 (m, 1H), 8.47 (d, J¼2.6 Hz, 1H), 8.64
(d, J¼2.6 Hz, 1H), 8.63–8.65 (m, 1H); for the enol form,
d 6.42 (s, 1H), 7.57–7.59 (m, 1H), 7.65–7.68 (m, 1H),
8.11–8.13 (m, 1H), 8.21 (d, J¼2.8 Hz, 1H), 8.47 (d,
J¼2.8 Hz, 1H), 14.06 (s, 1H); for the keto form, d 46.40,
126.55, 127.85, 134.85, 141.11, 142.92, 148.99, 150.76,
189.46; for the enol form, d 89.75, 125.23, 127.62, 131.61,
137.49, 138.18, 138.72, 148.11, 151.59, 162.34. IR, nmax
:
3336, 3104, 2922, 1675, 1618, 1509, 1491, 1413, 1383,
1317, 1260, 1229, 1175, 1148, 1085, 1061, 1010, 878,
790, 636, 464 cmꢁ1. LC/MS: expected, 238.70; observed,
m/z: 239.2 [M+H]+. Anal. Calcd for C10H7ClN2OS
(238.70): C, 50.32; H, 2.96; Cl, 14.85; N, 11.74; S, 13.43.
Found: C, 50.58; H, 2.91; Cl, 14.45; N, 11.49; S, 13.68.
4.2.4. 2-(3-Chloropyrazin-2-yl)-1-pyridin-3-ylethanone,
3d (Table 1, entry 7). The general procedure was followed.
1-Pyridin-3-ylethanone (267 mg, 2.20 mmol) was used. The
reaction was carried out at 60 ꢀC for 24 h. The product was
isolated by column chromatography on silica gel using 30%
hexanes in ethyl acetate as ketone and enol mixture. The
yield was 245 mg (53%), yellow solid, mp 126–128 ꢀC. 1H
NMR (DMSO-d6) for the keto form, d 4.88 (s, 2H), 7.58–
7.64 (m, 1H), 8.37–8.42 (m, 1H), 8.48 (d, J¼2.7 Hz, 1H),
8.64 (d, J¼2.7 Hz, 1H), 8.83–8.86 (m, 1H), 9.24–9.26 (m,
1H); for the enol form, d 6.59 (s, 1H), 7.49–7.54 (m, 1H),
8.24–8.27 (m, 1H), 8.28 (d, J¼2.7 Hz, 1H), 8.51 (d,
J¼2.7 Hz, 1H), 8.66–8.69 (m, 1H), 9.06–9.08 (m, 1H),
14.31 (s, 1H). 13C NMR (DMSO-d6) for the keto form,
d 45.69, 124.04, 131.35, 135.84, 142.95, 143.04, 148.98,
149.59, 150.62, 153.98, 195.03; for the enol form, d 90.74,
123.79, 130.36, 133.26, 138.62, 139.08, 144.30, 146.80,
4.2.7. 2-(3-Chloropyrazin-2-yl)-1-(2-thienyl)propan-1-
one, 3g (Table 1, entry 10). The general procedure was
followed. 1-(2-Thienyl)propan-1-one (308 mg, 2.20 mmol)
was used. The reaction was carried out at 60 ꢀC for 24 h.
The residue was purified by column chromatography on
silica gel using 30% ethyl acetate in hexanes. The yield
1
was 429 mg (85%), yellow solid, mp 70–71 ꢀC. H NMR
(DMSO-d6) d 1.55 (d, J¼6.9 Hz, 3H), 5.24 (q, J¼6.9 Hz,
1H), 7.22–7.26 (m, 1H), 7.91–7.94 (m, 1H), 7.99–8.03 (m,
1H), 8.45 (d, J¼2.5 Hz, 1H), 8.65 (d, J¼2.5 Hz, 1H). 13C
NMR (DMSO-d6) d 15.84, 47.21, 128.92, 133.42, 135.30,